CN110662339B

CN110662339B - Plasma source, excitation system for exciting plasma and optical monitoring system

Info

Publication number: CN110662339B
Application number: CN201910160394.XA
Authority: CN
Inventors: 马克·A·梅洛尼
Original assignee: Verity Instruments Inc
Current assignee: Verity Instruments Inc
Priority date: 2018-06-28
Filing date: 2019-03-04
Publication date: 2022-07-01
Anticipated expiration: 2039-03-04
Also published as: KR102159932B1; JP6739566B2; CN110662339A; TWI721373B; TW202002723A; JP2020004701A; KR20200001970A

Abstract

The invention provides a plasma source and an excitation system for exciting a plasma, and an optical monitoring system. In one embodiment, the plasma source comprises: (1) a coaxial resonator body having an inner length and including a first end, a second end, an inner electrode, and an outer electrode, (2) a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed position along the inner length and configured to provide a radio frequency signal to the coaxial resonator body, (3) a window positioned at the first end of the coaxial resonator body, and (4) a mounting flange positioned proximate the window at the first end of the coaxial resonator body and defining a plasma cavity, wherein the window forms one side of the plasma cavity and isolates the coaxial resonator body from a plasma in the plasma cavity.

Description

Plasma source, excitation system for exciting plasma and optical monitoring system

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of united states patent application No. 16/022,389 entitled "MICROWAVE PLASMA SOURCE" filed by Mark a.meloni at 28.6.2018, which in turn claims the right of united states provisional application No. 62/530,589 entitled "MICROWAVE PLASMA SOURCE" filed by Mark a.meloni at 10.7.7.2017, both commonly assigned with the present application and the entire contents of which are incorporated herein by reference.

Technical Field

The present application relates generally to monitoring semiconductor processes and, more particularly, to optically monitoring processes via microwave excitation of process gases and observation of resulting optical signals.

Background

In the field of semiconductor processing, it is well known to selectively remove or deposit material from a semiconductor wafer to form integrated circuit structures thereon. Removal of material from a semiconductor wafer is typically accomplished by employing an etching process, such as reactive ion etching or plasma etching. Deposition of materials onto wafers may involve processes such as chemical and physical vapor deposition and molecular beam epitaxy. Other removal and deposition processes are also known. Such processes are precisely controlled and performed in a regulated process chamber.

Because precise amounts of material must be deposited on or removed from a semiconductor wafer, the process must be continuously and accurately monitored to accurately determine the state of the particular process and related wafers. Optical monitoring of a process is a very useful tool for determining the status of an ongoing process. For example, the excited gas within the interior of the process chamber may be optically monitored and examined for specific known compounds by spectroscopic analysis of predetermined wavelengths of light emitted from the plasma formed by the excited gas. Conventional optical monitoring methods include Optical Emission Spectroscopy (OES), absorption spectroscopy, and reflectometry.

One conventional method of monitoring optical emissions (light) from within a semiconductor plasma processing chamber is to use an optical monitoring system consisting of an array-based optical spectrometer and an optical coupling system that transmits light from the plasma in the interior of the chamber to the spectrometer. The optical emission spectrum is typically recorded as a series of light intensity measurements and repeatedly resampled at specific time intervals. The series of light intensity measurements may be recorded by a photodiode detector with a bandpass filter in a set of narrow spectral bands or by a spectrometer over a broad spectrum.

Disclosure of Invention

In one aspect, the invention provides a plasma source for exciting a plasma from one or more gases and monitoring optical emissions therefrom. In one embodiment, the plasma source comprises: (1) a coaxial resonator body having an inner length and including a first end, a second end, an inner electrode, and an outer electrode, (2) a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed position along the inner length and configured to provide a radio frequency signal to the coaxial resonator body, (3) a window positioned at the first end of the coaxial resonator body, and (4) a mounting flange positioned proximate the window at the first end of the coaxial resonator body and defining a plasma cavity, wherein the window forms one side of the plasma cavity and isolates the coaxial resonator body from a plasma in the plasma cavity.

In another aspect, the present invention provides an ignition system for igniting a plasma. In one embodiment, the excitation system comprises: (1) a coaxial resonant cavity body having an inner length and including a first end, a second end, an inner electrode, and an outer electrode, (2) a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed location along the inner length and configured to provide a radio frequency signal to the coaxial resonant cavity body, and (3) a source controller configured to provide a radio frequency signal to the radio frequency signal interface.

In yet another aspect, the present invention provides an optical monitoring system. In one embodiment, the optical monitoring system includes: (1) a plasma source configured to ignite, excite a plasma within a plasma cavity in gaseous communication with a process chamber and generate optical emissions from the plasma, (2) a source controller configured to provide a radio frequency signal to a radio frequency signal interface of the plasma source to generate an electromagnetic field in the plasma cavity for ignition and excitation of the plasma, (3) an optical coupling system configured to deliver an optical signal observed from the excitation of the plasma, and (4) a spectrometer configured to receive the optical signal and convert the optical signal to an electrical signal.

Drawings

The invention may be understood by reference to the following detailed description taken in conjunction with the accompanying drawings, which are briefly described below.

FIG. 1 illustrates a block diagram of an example process control system that employs a plasma source for excitation and optical monitoring of a plasma to determine the status of a process within a process tool;

FIG. 2A illustrates a three-dimensional view of an embodiment of an 3/4 wave plasma source constructed in accordance with the principles of the present invention;

FIG. 2B illustrates an exploded view of the plasma source of FIG. 2A;

FIG. 3A illustrates a three-dimensional view of an embodiment of an 1/4 wave plasma source constructed in accordance with the principles of the present invention;

FIG. 3B illustrates an exploded view of the plasma source of FIG. 3A;

FIG. 4A illustrates a three-dimensional cross-sectional view of an embodiment of a plasma source constructed in accordance with the principles of the present invention;

FIG. 4B illustrates an end view of the plasma source illustrated in FIG. 4A;

FIGS. 5A through 5D illustrate three-dimensional views of embodiments of other plasma sources constructed in accordance with the principles of the present invention;

FIGS. 6A through 6D illustrate different views of a modular inner electrode constructed in accordance with the principles of the present invention;

FIG. 7A illustrates a plot of electric field strength along an axis of a plasma source constructed in accordance with the principles of the present invention;

FIG. 7B illustrates plots of ignition and sustaining power levels for a plasma source constructed in accordance with the principles of the present invention;

FIG. 8 illustrates a plot of an example spectrum provided by a plasma source constructed in accordance with the principles of the present invention;

FIGS. 9A and 9B illustrate three-dimensional and cross-sectional views of a mounting flange of a plasma source constructed in accordance with the principles of the present invention;

FIG. 10A illustrates a three-dimensional view of an embodiment of a plasma source system having an external RF match/tuner and mounting flange constructed in accordance with the principles of the present invention;

FIG. 10B illustrates a three-dimensional view of the plasma source system of FIG. 10A including a neodymium ring magnet surrounding the mounting flange;

FIG. 11 illustrates a three-dimensional view of an embodiment of another plasma source system having an external RF match/tuner and a bypass flow mounting arrangement constructed in accordance with the principles of the present invention;

FIG. 12 illustrates a plot of an example resonant behavior of a plasma source constructed in accordance with the principles of the present invention;

FIG. 13 illustrates a block diagram of a source controller for a plasma source constructed in accordance with the principles of the present invention; and

fig. 14 illustrates a flow chart of a process for operating a plasma source or a portion thereof constructed in accordance with the principles of the present invention.

Detailed Description

In some applications, it may be difficult to measure plasma optical emission within the chamber while the plasma reacts with the semiconductor wafer. For example, when the process gas within the chamber is excited remotely from the wafer, and the excited reactant requires a significant amount of time to interact with the wafer surface, the amount of plasma optical emission associated with the wafer may be limited or non-existent. For example, the amount of plasma optical emission is limited when it results in a signal that lacks detail, has a low signal-to-noise ratio, or lacks the desired data. In these so-called "dark plasma" applications, measurement of the optical emission of the plasma (if available) may not provide an accurate representation of the process acting on the semiconductor wafer, since the optical emission of the plasma may not include the optical emission characteristics of the reactions occurring on the wafer surface. Similarly, some semiconductor processes do not utilize plasma and no optical emission is observed.

It is recognized herein that it is often desirable to excite a process gas or gases in proximity to the wafer or in a process chamber or other relevant or convenient location associated therewith to generate light to optically monitor a particular known emission line or broad spectral signature emitted from a reaction in the chamber. The present invention provides a solution for plasma excitation and monitoring of optical emissions caused by the excitation. Generally, the present invention provides a plasma source designed to receive a Radio Frequency (RF) signal and provide an Electromagnetic (EM) field as an excitation source for a process gas.

The plasma source includes a coaxial resonant cavity body including a cavity having a length denoted herein as an inner length L1 extending from an open end to a shortened end of the cavity. The open end is positioned proximate to a process end of the coaxial resonant cavity body, and the shortened end is positioned at an opposite end of the coaxial resonant cavity body. The RF signal interface is coupled to the coaxial resonant cavity body at a location along an inner length, denoted herein as a coupling point distance L2. The coupling point distance L2 extends from the open end of the coaxial resonant cavity body to a centerline of the center conductor of the RF signal interface that extends into the coaxial resonant cavity body.

The values of the inner length L1 and the coupling point distance L2 are based on maximization of an Electromagnetic (EM) field established at or near a surface of a process environment at a process end using RF signals received via an RF signal interface. The inner length L1 of the coaxial resonant cavity body and the coupling point distance L2 depend on the actual operating frequency and the associated free space wavelength of the RF wave provided via the RF signal interface. Additional discussion of inner length L1 and coupling point distance L2 is discussed below (e.g., with respect to fig. 4A). Fig. 4A illustrates dimensions L1 and L2 for an embodiment of the plasma source 400.

The discussion and examples herein relate to plasma-based processes and plasma process chambers, but those skilled in the art will appreciate that the various principles and features of the invention may be used with any type of system in which excitation of process gases and monitoring of optical excitation may be performed. In addition to processes that directly involve semiconductor wafers, processes such as chamber cleaning may also be optically monitored by applying the plasma sources described herein. The described plasma source may also be used in non-semiconductor applications where gas monitoring is of interest. For example, the plasma source may be used for emission monitoring associated with industrial chimneys, chemical plants, and the like.

Fig. 1 illustrates a block diagram of an embodiment of a process control system 100, the process control system 100 employing a plasma source for plasma excitation and monitoring to determine the status of a process within a process tool. In the process system 100, the process gases within the process chamber 110 are remotely energized from the wafer 120. By the time the excited reactant interacts with the surface of the wafer 120, the amount of optical emission may be limited or absent, as discussed above. Thus, measurement of optical emissions from plasma 130 may not provide an accurate characterization of the etching process of semiconductor wafer 120, as optical emissions from plasma 130 may not include emissions from reactions occurring on the surface of wafer 120.

Thus, the process system 100 advantageously employs the plasma sources 150 and 150' to provide optical signals for viewing. The plasma source 150 is attached directly to the process chamber 110 via an appropriate port near the wafer 120, and the plasma source 150' is positioned on the exhaust line of the system 100. In general, the plasma sources disclosed herein may be positioned at any one or more locations that provide for interaction with process gases. The plasma source 150 may include optical elements positioned within the plasma source 150, which are or part of a fiber optic cable assembly 152, that direct collected light transmitted through a window of the plasma source 150 to the spectrometer 160. Similarly, the fiber optic cable assembly 152 'directs the light provided by the plasma source 150' to the spectrometer 160. For example, the fiber optic cable assemblies 152 and 152' may be fiber optic bundles or may include other optical elements, such as lenses or filters. As illustrated in fig. 1, multiple plasma sources 150 and 150' may be used simultaneously in different locations of the process system 100 to provide independent monitoring. In such implementations, each plasma source 150 and 150' has a corresponding input port of the spectrometer 160 for delivering the generated optical signal for measurement. Although a shared spectrometer 160 is shown in fig. 1, a separate spectrometer or other light measurement system (e.g., photodiode sensor) may be used for each plasma source.

In addition to the plasma sources 150 and 150', the optical interface 140, which may include a collimator or other optical elements, may be oriented to collect optical emissions from the plasma 130. As shown in fig. 1, the optical interface 140 directly observes the light emitted from the plasma 130. However, if the optical signal provided by plasma 130 is insufficient, then a plasma source similar to plasma sources 150 and 150' may be used in place of optical interface 140.

In addition to spectrometer 160 and computer 170, process system 100 also includes chamber controller 175 and source controller 177. A chamber controller 175, typically of the industrial computer type, may be configured to direct the operation of the process chamber 110 by receiving monitoring data and control signals from the computer 170 or spectrometer 160. The source controller 177 may communicate with the chamber controller 175 to receive information (e.g., process settings, gas type, gas pressure, etc.) and plasma source control parameters for at least RF power level, phase, and frequency. Source controller 177 may be or be similar to the source controller described in association with fig. 13. Source controller 177 may also be configured to provide RF signals having defined power levels, phases, and frequencies to plasma sources 150 and 150'. Source controller 177 may provide RF signals to plasma sources 150 and 150' (via RF interfaces on each source) via

coaxial cables

178 and 179. For example, source controller 177 may provide an RF signal having a nominal frequency of 2.45GHz within the 2.4 to 2.5GHz ISM band. Other examples of RF signal frequencies include: a 915MHz nominal frequency within the 902 to 928MHz ISM band, a 5.8GHz nominal frequency within the 5.725 to 5.875GHz ISM band, or a 24.125GHz nominal frequency within the 24 to 24.25GHz ISM band. Typically, the frequency is constant or varies less in continuous or discrete steps. The amount of RF power supplied may be controlled manually or automatically. Source controller 177 may also vary the RF power used to ignite or respond to external commands as described herein. As such, source controller 177 may be coupled to spectrometer 160, computer 170, and/or chamber controller 175 to vary the power level of the RF signal delivered to plasma sources 150 and 150'. Source controller 177 may also be used to automatically control the amount of power or center frequency of the RF signal supplied to the coaxial RF resonators of plasma sources 150 and 150'. Source controller 177 may comprise necessary logic, software, a combination of circuits and software, etc. to control the RF signals.

For clarity, not all connections between elements of FIG. 1 are described or enumerated. In general, it should be understood that source controller 177 may interact directly with the plasma sources 150 and 150' and directly or indirectly with the chamber controller 175, spectrometer 160, and computer 170. For example, spectrometer 160 may send a signal to source controller 177 to increase or decrease the RF signal level to change the measured optical signal level in response to a predetermined value of the signal level. Similarly, because it may be advantageous to continuously maintain plasma excitation of the plasma source, the chamber controller 175 and/or computer 170 may send signals to the source controller 177 to set the RF signal level regardless of any optical signals measured by the spectrometer 160. This activity may be performed to maintain the temperature of the plasma source to improve stability or accommodate variations during the multi-step process performed in the chamber 110.

The purpose of the optical monitoring may vary based on the location of the plasma source. For example, if the plasma source is positioned prior to the process gas interacting with the wafer, optical monitoring can be used to characterize the proper decomposition or presence of particular reactants. If positioned close to the wafer, optical monitoring can be used to characterize the compositional changes of the process gas caused by the interaction of the process gas and the wafer. Optical monitoring can also be used to characterize changes in process gas composition or to understand reaction product formation if located after interaction with the wafer. Examples of the positions before, near, and after correspond to the positions of the optical interface 140, the plasma source 150, and the plasma source 150', respectively, as illustrated in fig. 1.

Fig. 2A illustrates a three-dimensional view of an embodiment of an 3/4 wave plasma source 200 constructed in accordance with the principles of the present invention. Fig. 2B illustrates a three-dimensional exploded view of the plasma source 200, indicating the major components of the plasma source 200 and facilitating disassembly for repair and/or maintenance. The plasma source 200 may be the plasma source 150 and/or 150' of fig. 1. The plasma source 200 reduces the complexity of existing techniques and may be conveniently assembled from a mounting flange 210, an o-ring 220, a window 230, a coaxial resonant cavity body 240, and an RF signal interface 250 joined by mechanical fasteners such as bolts or screws (collectively represented as elements 260 in fig. 2A and 2B). A fiber entrance 270 is shown at the end of the coaxial resonator body 240.

The opto-mechanical and RF configurations of the plasma source 200 decouple the process volume of the plasma source 200 from the operating conditions. The coaxial resonator body 240 of the plasma source 200 is separated from the process volume by the window 230 and thus reduces the effects from process gas species, pressure loading and other interactions compared to existing designs. The window 230 has a process side 234 and an ambient side 238. In general, the RF resonance condition of the coaxial resonant cavity body 240 is stable regardless of process volume variations of the surface of the process side 234 of the contact window 230.

The plasma source 200 projects a high intensity electromagnetic field out of the coaxial resonator body 240, across the window 230, and into any process gases contained in the plasma chamber within the mounting flange 210 that are in gas communication with the process chamber. Fig. 4 illustrates the plasma chamber 460 relative to the mounting flange. One advantage of the design of the plasma source 200 is that interaction with the process space is minimized. For example, most components of the plasma source 200 are isolated from the process environment such that only the mounting flange 210, o-ring 220, and window 230 may contact the process space, associated process gases, and any energized plasma.

Reducing the mechanical and material complexity of the plasma source 200 reduces potential contamination, material incompatibility, and poor interaction with processes performed in the chamber. The mounting flange 210 may be formed from an aluminum alloy as is common for process chambers and internally coated as needed. The window 230 is preferably 1 to 5mm thick c-axis oriented sapphire, which is highly resistant to process gas and plasma attack. The o-ring 220 may be formed of a perfluorinated rubber compound that is resistant to the process gas and plasma environment. The coaxial resonator body 240 may also be constructed from an aluminum alloy or other metal.

The plasma source 200 may operate in a wide pressure range, is suitable for a variety of process types, and may operate in various monitoring locations, including the process chambers and foreline operations indicated by the plasma sources 150 and 150' of fig. 1. Although the actual pressure may vary, the operating pressure range of the plasma source 200 may vary from about 0.1 millitorr or less when directly connected to the process chamber to over 10 torr when attached to the foreline of the chamber.

To facilitate placement at various locations, the plasma source 200 may advantageously have a compact form factor. For example, the 3/4 wave plasma source 200 may have dimensions (excluding cables and electronics) of about 100mm x35mm x35mm (L x W x H). As shown in fig. 2A, the plasma source 200 is conveniently designed for mounting to a Klein Flange (KF) interface, such as a conventional KF40 interface. As detailed below, the plasma source 200 may also be configured to mate to other conventional or even proprietary interface designs, such as other KF interfaces, ASA interfaces, conflett (ConFlat) or CF interfaces, or other vacuum flange types.

Fig. 3A illustrates a three-dimensional view of an embodiment of an 1/4 wave plasma source 300 constructed in accordance with the principles of the present invention. Fig. 3B illustrates a three-dimensional exploded view of the plasma source 300, indicating the major components of the plasma source 300 and facilitating disassembly for repair and/or maintenance. Similar to the plasma source 200, the plasma source 300 may be conveniently assembled from a mounting flange 310, an o-ring 320, a window 330, a coaxial resonant cavity body 340, and an RF signal interface 350. The components of the plasma source 300 may be connected and held together using mechanical fasteners and the mechanical fasteners are generally represented in fig. 3A and 3B as elements 360. Mechanical fasteners 360 may pass through clearance openings 365 to engage threaded holes 367 in mounting flange 310. Mechanical fasteners may similarly be used with clearance openings and threaded holes in other plasma sources disclosed herein.

A fiber entrance 370 is shown at the end of the coaxial resonator body 340. The 1/4 wave plasma source 300 may have dimensions of about 40mm x40mm x40 mm. The components of the plasma source 300 may be constructed from the materials used to construct the plasma source 200. Each of the coaxial resonator bodies of

plasma sources

200 and 300 has a fixed internal length, nominally based on an odd multiple of a quarter length of the RF excitation wavelength provided via RF signal interfaces 250, 350. The nominal internal lengths of the coaxial resonant cavity bodies (including the longer 5/4 wave or 7/4 wave plasma sources) cooperate to optimize the Electromagnetic (EM) field at the window.

Fig. 4A illustrates a three-dimensional cross-sectional view of an embodiment of a plasma source 400 constructed in accordance with the principles of the present invention. Fig. 4B illustrates an end view of the plasma source 400. The plasma source 400 includes a coaxial resonant cavity body 410, an RF signal interface 420, a mounting flange 430, a window 440, an isolation screen 450 (shown only in fig. 4B), and a plasma chamber 460. In some embodiments, the values of the inner length L1 and the coupling point distance L2 of the coaxial resonant cavity body 410 are based on maximization of an Electromagnetic (EM) field established at or near the process environment surface of the window 440 using an RF signal received via the RF signal interface 420. Maximization of the EM field at the window 440 may cause the resulting plasma to wet the window 440, thereby assisting the window 440 in self-cleaning by the action of striking the plasma by maintaining an increased window temperature. Thus, the plasma source 400 maintains the optical transmission properties of the window 440 consistent due to the reduction in contamination. Other dimensions of the coaxial resonator body 410 are defined by the wavelength characteristics at the operating frequency of interest. Due to international standardization of usage and interference, the operating frequency may be, but is not required to be, within the industrial, scientific, and medical (ISM) frequency band (e.g., 2.4 to 2.5GHz, 5.725 to 5.875GHz, etc.).

In some 3/4-wave embodiments, the plasma source 400 may have an overall length of about 100mm, and the inner length of the coaxial resonant cavity body 410 (indicated by dimension L1) may be about 70-95 mm, and the coupling point distance L2 may be about 10-80 mm. The overall length of the plasma source 400 extends from the interface 432 of the mounting flange 430 to the opening of the fiber entrance 490 positioned at the end of the plasma source 400 opposite the mounting flange 430. The end of the plasma source 400 opposite the mounting flange is also a second end of the coaxial resonator body 410 opposite the process end. The particular or fixed inner length of coaxial resonant cavity body 410 depends on the actual operating frequency and the associated free-space wavelength of the RF waves. For example, for the 2.4 to 2.5GHz ISM band, the wavelength range is 125 to 120mm, and the length of the 3/4 wave resonator is about 90mm, i.e., an inner length of 90 mm. Similarly, for the 2.4 to 2.5GHz ISM band with a wavelength range of 125 to 120mm, the length of the 1/4 wave resonator is about 30mm, i.e. an inner length of 30 mm. The values of the inner length L1 of the coaxial resonant cavity body 410 and the coupling point distance L2 may be modified based on the RF properties (complex dielectric constant, etc.) of the window 440.

The coaxial resonant cavity body 410 is mechanically robust and designed to minimize the emission of RF signals received via the RF interface 420 (except for being directed through the window 440 and into the plasma chamber 460 within the mounting flange 430). The coaxial resonator body 410 includes an inner electrode 470 and an outer electrode 480. The RF signal interface 420 is electrically coupled to the inner electrode 470 and the outer electrode 480 to provide excitation of the plasma source 400 via the received RF signal. The relative dimensions of the inner electrode 470 and the outer electrode 480 are selected to approximate the 50 ohm nominal impedance of the coaxial resonator body 410 when connected via the RF signal interface 420. The relative sizes of the inner electrode 470 and the outer electrode 480 may vary to correspond to the impedances of the RF signal interface 420 and external RF components. In other examples, the dimensions of the inner electrode 470 and the outer electrode 480 may be selected to approximate a 75 ohm nominal impedance. As shown in fig. 4A, the coaxial resonant cavity body 410 is inductively coupled to the RF signal interface 420 because the center conductor 422 of the RF signal interface 420 is in direct electrical connection with the inner electrode 470. In other embodiments, the coaxial resonant cavity body 410 may be capacitively coupled by extending the center conductor 422 of the RF signal interface 420 into the region between the outer electrode 480 and the inner electrode 470 without contacting the inner electrode 470. The RF signal interface 420 directly contacts the outer electrode 480.

One or more tuning stubs 425 may be used to perform impedance matching with respect to the RF signal interface and/or frequency adjustment of the plasma source 400. The tuning stub 425 may be a metal or non-metal screw or other adjustable protrusion into the space between the outer electrode 480 and the inner electrode 470. The amount of tuning stub 425 entering the space can be adjusted to alter the impedance and/or frequency. The number and placement of tuning stubs 425 along the coaxial resonant cavity body 410 may be based on experience, test data, and electromagnetic modeling. The location of the tuning stubs 425 and their number may also vary depending on the type or size of the plasma source. For example, the number and location of tuning stubs may vary depending on whether the plasma source is an 1/4 wave plasma source or a 3/4 wave plasma source. Fig. 4A shows an example of example locations and numbers of tuning stubs.

The RF signal may be provided via a source controller (e.g., source controller 177 of fig. 1). As mentioned above, the RF signal may have a nominal frequency of 2.45GHz within the 2.4-2.5 GHz ISM band. RF signal interface 420 is designed to match the impedance of the cable/source that delivers the RF signal (e.g.,

cables

178 and 179 in fig. 1, and the RF power supply of source controller 177). RF signal interface 420 may be a 50 ohm RF connector, such as an N-type connector, a subminiature version a connector, or another type of RF connector.

The mounting flange 430 is mechanically coupled to the coaxial resonant cavity body 410 with the window 440 and the o-ring 435 positioned therebetween, and the o-ring 435 is positioned between the window 440 and the mounting flange 430. Advantageously, the coaxial resonant cavity body 410 and the mounting flange 430 are removably coupled together. The ability to easily disassemble and reassemble these components allows for maintenance of the window 440 and o-ring 435. A screw 437 or another type of mechanical fastener may be used for removable mechanical coupling of the coaxial resonant cavity body 410 and the mounting flange 430. Coupling the coaxial resonant cavity body 410 to the mounting flange 430 also provides an electrical connection through the mating surfaces of the coaxial resonant cavity body 410 and the mounting flange 430 for a low resistance conductive path for RF shielding and grounding.

The interface 432 of the mounting flange 430 is configured to connect to an interface that communicates with a gas or gases from the process chamber. The interface 432 of the mounting flange 430 may be, for example, a KF40 type connector. The interface 432 may vary depending on the type of interface connected. In addition, as illustrated, for example, in fig. 9A and 9B, the plasma chamber of the mounting flange used with the coaxial resonant cavity body 410 can change and still provide decoupling between the coaxial resonant cavity body 410 and the process volume with limited impact on the operating characteristics of the plasma source 400. The o-ring 435 may be constructed of a material such as Kalrez perfluororubber, which is commonly used in the industry to withstand process gases, pressure, and heat.

The mounting flange 430 mechanically supports the coaxial resonator body 410 of the plasma source 400, in addition to an interface suitable for mounting. The mounting flange 430 may also support the screen 450 (if used). The isolation screen 450 includes openings or apertures to regulate the outflow of process gases between a plasma chamber 460 defined by the inner surface of the mounting flange 430 and a process volume, such as in a process chamber. In addition, the isolation screen 450 can inhibit migration of plasma excited proximate the window 440 into a substantial portion of the attached process volume. The isolation screen 450 may be used in some applications where contamination considerations are desired (e.g., when coupled to a process chamber indicated by the plasma source 150 of fig. 1), and the isolation screen 450 may not be used in some applications where contamination considerations are not desired (e.g., in a foreline position indicated by the plasma source 150' of fig. 1).

The isolator screen 450 may be attached to the mounting flange 430 and positioned coincident with the interface 432 or at other locations within the plasma chamber 460. The isolation screen 450 may be made of the same material as the mounting flange 430. For example, the isolation screen 450 may be constructed of aluminum. The isolation screen 450 may be removably attached to the mounting flange 430 (e.g., via a clamp or threaded connection) or may be permanently attached, e.g., via welding. The isolation screen 450 may also be a non-integrated part of the plasma source 400, and an appropriately designed shielded centering ring may be used for the KF-type interface. The inner surfaces of the plasma chamber 460 that may be contacted by the plasma and/or process gases may be coated with zirconia, yttria, refractory oxide, or another similar product to reduce contamination and damage due to the process gases. The window 440 may also be constructed of conventional materials for resisting contamination due to process gases. For example, the window 440 may be a sapphire or fused silica window.

In addition to isolating a large portion of the plasma source 400 from the process volume, the window 440 also provides transmission of RF energy into the plasma chamber 460 and transmission of optical emissions generated by excitation of the plasma 465 in the plasma chamber 460. As stated above, one side of the window 440 (the process side 444) is in contact with the process volume of ambient gas, and the other side of the window 440 (the ambient side 448) is optionally at ambient conditions.

An optical fiber assembly (not shown) may be placed within the inner electrode 470 via a fiber inlet 490 positioned at an end of the plasma source 400 opposite the mounting flange 430. The fiber optic assembly can provide an optical signal to a spectrometer (e.g., spectrometer 160 in fig. 1). The aperture 495 is located near the window 440 to allow the fiber assembly to directly access and strongly couple to the optical emission provided by the plasma 465. The aperture 495 is designed to limit the impact on the EM field and the generation and location of the resulting plasma. The aperture 495 is an optical signal aperture that is typically small (about 1mm diameter) compared to the RF excitation wavelength, and is positioned to provide a field of view of the plasma that is accessible by the fiber optic cable assembly. The fiber optic assembly (not shown in fig. 4A) may have a cylindrical cross-section and be held in the fiber inlet 490 by a set screw or other fastener.

In some applications, magnets may be used to provide magnetic confinement around the plasma chamber 460 of the plasma source 400 to support electron cyclotron resonance and assist in igniting and sustaining the plasma 465 at lower RF power or over a wider pressure range. The magnet or magnets may be placed around the mounting flange 430 or embedded within the mounting flange 430. Fig. 9B illustrates a cylindrical magnet embedded in the mounting flange, and fig. 10B illustrates a neodymium ring magnet placed around the mounting flange. For a nominal operating condition of 2.45GHz excitation, an electron cyclotron resonance can be supported using a 875 gauss field; other magnetic field strengths may be used.

As stated above, the positioning of the aperture 495 and the optical fiber is coordinated with the plasma excitation. To further assist in defining the location of plasma ignition within the plasma chamber 460, the end of the inner electrode at the window 440 (referred to as the window end 497) may be shaped. The position of the aperture 495 may also vary to correspond to the shape of the inner electrode 470 at the window end 497. Thus, the fiber entry can be changed to conform to the aperture 495. Fig. 5A-5D illustrate three-dimensional views of embodiments of a coaxial resonator body of a plasma source constructed with various shapes of windowed ends of inner electrodes, according to the principles of the present invention.

Fig. 5A illustrates a coaxial resonator body 510 having a window end 512 for an inner electrode, the window end 512 being cross-shaped and having 4 asymmetric arms. This configuration of the windowed end 512 positions plasma ignition near the location of the longest arm 514. Thus, the position of the fiber entrance 516 is repositioned. In this embodiment, the optical fiber is no longer axially oriented within the inner electrode, but rather is positioned through the fiber entrance 516 and aligned with the gap between the longest arm 514 and the inner diameter of the outer electrode of the coaxial resonator body 510. A set screw may be used in the opening 519 to hold the fiber in place. Fig. 5B illustrates a coaxial resonator body 520 having a window end 522 of an inner electrode, the window end 522 in a shape having a single point 524, the point 524 being opposite an adjustable keyway 526 for altering a distance from the point 524 to an inner surface of an outer electrode of the coaxial resonator body 520. An optical fiber may be inserted into the fiber entrance 528 and aligned with the gap between the point 524 and the adjustable keyway 526. Fig. 5C illustrates a coaxial resonant cavity body 530 having a windowed end 532 of the inner electrode, the windowed end 532 being cross-shaped and having symmetrical circular arms. The aperture 534 is positioned in the center of the window end 532. In this embodiment, the optical fiber may be axially oriented within the inner electrode of the coaxial resonant cavity body 530. Fig. 5D illustrates a coaxial resonant cavity body 540 including a window end 542 of an inner electrode in the shape of a frustum of a cone. Aperture 544 is positioned in the center of the frustum of cone of window end 542. The coaxial resonant cavity body 540 further includes a recess 548 configured to receive a mounting bracket (e.g., mounting bracket 1040 of fig. 10A). In this embodiment as with the coaxial resonant cavity body 530, the optical fiber may be axially oriented within the inner electrode of the coaxial resonant cavity body 540. The coaxial resonant cavity bodies of fig. 5A-5D can be connected to a mounting flange or other mounting surface via mechanical fasteners placed through the

openings

511, 521, 531 and 541.

To support configurability of the plasma source, various different window ends are removably mechanically attached to the adaptable inner electrode. Fig. 6A illustrates a cross-sectional view of a coaxial resonator body 600 assembled from the adaptable

inner electrode assemblies

610 and 620 illustrated in fig. 6B-6D. The inner electrode body 610 includes a female threaded portion designed to receive the male threaded portion of the window end 620. When assembled together, the inner electrode body 610 and the window 620 provide an inner electrode 630 of the coaxial resonator body 600. Coaxial resonator body 600 also includes outer electrode 640, through-hole 650 for a fastener, and aperture 660. The assembled inner electrode 630 corresponds to the inner electrode of fig. 5C. The coaxial resonant cavity body 600 also includes a hole 670 and a flat portion 675 configured for mounting an RF signal interface, such as the interface 250 of fig. 2A.

The coordination of the design of the inner electrodes, windows, and apertures attempts to provide optimal RF power delivery for plasma excitation and plasma positioning to conveniently and efficiently collect the optical emission signals. Thus, the tuning of the design involves providing a plasma near the window surface and at the viewpoint of the fiber. The location of the plasma may be correlated to the concentration of the electric field provided by the RF source and shaped by the coaxial resonant cavity. Fig. 7A illustrates an electric field strength plot 700 indicating strong localization of the field at the window of the plasma source. Graph 700 includes a curve 705 showing that the magnitude or strength of the electric field in volts/meter decreases as the distance from the window increases. Plot 700 is generated from a model of an 3/4 wave design, such as the plasma sources disclosed herein, prior to ignition of a plasma. The plasma source for plot 700 includes window end 542 shown in figure 5D. Fig. 7B illustrates the power performance results from graph 700.

Fig. 7B illustrates a graph 710 showing the power of an RF signal source versus the pressure within the plasma chamber of a plasma source constructed in accordance with the principles of the present invention. Plot 710 illustrates the ignition and sustaining power performance of an 3/4 wave plasma source having an inner electrode with window end 542 shown in figure 5D. The dashed curve 720 is the ignition or firing power level and the solid curve 730 is the sustain power level. Specifically, such a plasma source may be ignited at a power level of less than 200mW (dashed curve 720) and may be maintained at a power level of less than 100mW (solid curve 730). As expected according to Paschen's law, the power versus pressure curve shows that the required power level is generally higher as the pressure decreases. For certain operating scenarios, the plasma source may be ignited at a higher pressure and associated lower power condition, and maintained at the same or different power condition when the pressure is reduced to a lower level.

FIG. 8 illustrates a plot 800 of an example spectrum 810 provided by a plasma source having an electric field strength such as that represented in FIG. 7A and a power performance such as that represented in FIG. 7B. The spectrum may be provided by a spectrometer, such as spectrometer 160 in fig. 1. The location, low power operation, and efficient optical coupling of the plasma provide a large optical signal as shown in spectrum 810. For spectrum 810, a plasma of mixed nitrogen and oxygen was ignited and sustained with about 200 millitorr pressure and 300mW applied RF power at 2.410GHz excitation. Low power operation of the plasma source (e.g., at 300mW) results in reduced disassociation of the excited gas, allowing the expression of atomic and molecular spectral features, which can be used for process analysis of polyatomic species and the determination of chemical compounds.

The adjustability of the plasma source described herein allows the coaxial resonator body disclosed herein to be connected to multiple interfaces and locations. Fig. 9A and 9B illustrate views of a mounting flange of a plasma source constructed in accordance with the principles of the present invention. Different chamber interfaces and different requirements for airflow may affect the design of the mounting flange. In general, a mounting flange with a minimum volume advantageously mitigates slow response due to gas transport. However, this advantage needs to be balanced with the mechanical requirements of the installation.

Certain mounting flange features (e.g., flange inner diameter) aid in the localization of the EM field and resulting plasma. In this connection, it is advantageous to suppress plasma from directly contacting the metal portion of the mounting flange due to erosion and particle formation. Due to the exposure of the plasma, the inner diameter of the mounting flange may be coated for protection. Fig. 9A and 9B illustrate two examples of mounting flanges having different plasma cavity shapes and volumes.

The mounting flange 910 shown in fig. 9A has a cylindrical inner bore forming a plasma chamber 920 that allows easy gas flow, and a large open area near the window that tends to unseat the plasma. The mounting flange 910 includes a window recess 980 and an o-ring groove 930 for receiving a window and an o-ring. The mounting flange 910 also includes openings 940 for receiving fasteners for connecting the coaxial resonant cavity body to the mounting flange 910.

The mounting flange 950 shown in FIG. 9B has a shortened and tapered internal bore as compared to the mounting flange 910 of FIG. 9A. The tapered bore forms a plasma chamber 960. A smaller open area near the window results in a higher positioning of the plasma. The smaller open area of the plasma chamber 960 may inhibit gas flow. In some embodiments, the suppression of gas flow may be partially mitigated by increasing the process side diameter of the plasma chamber 960 and shortening the overall length of the mounting flange 950. The mounting flange 950 includes a window recess 982 and an o-ring groove 932 for receiving the window and o-ring. The mounting flange 950 also includes openings 942 for receiving fasteners for connecting the coaxial resonant cavity body to the mounting flange 950. The mounting flange 950 further includes magnets 990, which are shown embedded but may protrude from the mounting flange 950. The cross-sectional view of the mounting flange 950 shown in fig. 9B indicates how the tapered bore of the mounting flange 950 supports embedding the magnet 990 in the mounting flange 950. The magnet 990 in this configuration may be polarized to provide a magnetic field that is perpendicular to the electrical component of the EM field (i.e., radially polarized relative to the cylindrical axis of the plasma source).

The rapid attenuation of the EM field away from the window reduces the coupling of the flange to the design of the coaxial resonator body and the window. Thus, the coaxial resonator body may be considered "universal" and other mounting arrangements may be readily adapted to meet the requirements of mounting the plasma source. In particular embodiments, a separate mounting flange may not be used and appropriate design features for the o-ring and window may be constructed directly on the chamber, foreline, or other mounting location. Thus, mechanical fasteners (e.g., screws 437 in fig. 4) may be used to connect the coaxial resonator body to the interface without the use of a mounting flange.

In some applications without a mounting flange, mechanical fasteners may be used to attach the coaxial resonant cavity body to the interface and secure the o-ring and window therebetween. Although the mounting

flanges

910 and 950 indicate that mechanical fasteners are used to join the mounting flanges and the coaxial resonator body, the joining may be performed via other methods, such as by providing the coaxial resonator body with a male threaded portion that is engageable with a female threaded portion of the mounting flange (or vice versa). Further, window recesses such as 980 and 982 may be formed in whole or in part in a portion of the coaxial resonator body other than the mounting flange.

Fig. 10A illustrates a three-dimensional view of an embodiment of a plasma source system 1000 in which an external RF match/tuner 1020 is connected to a plasma source 1030 via a mounting bracket 1040. The plasma source 1030 includes a coaxial resonator body 1050 and a mounting flange 1060 constructed in accordance with the principles of the present invention. The coaxial resonator body 1050 includes an axially oriented fiber entrance 1055. Impedance matching is often required due to variations in the manufacture and performance of RF components. An external tuner, such as RF match/tuner 1020, may be used for impedance matching. Tuner 1020 may include a tuning circuit based on an array of "tuning pads" connected in series between an RF supply (e.g., RF source controller 177 of fig. 1) and a plasma source (e.g., source 200 of fig. 2A) via an RF connection 1022. Tuner 1020 is also connected to an RF signal interface mounted to coaxial resonator body 1050 via elbow connector 1024. The RF signal enters the RF connection 1022, passes through a circuit board inside the RF match/tuner 1020, enters the RF elbow connector 1024 and then connects to the RF signal interface 1026 (not shown in fig. 10A) mounted to the coaxial resonant cavity body 1050.

Fig. 10B illustrates a three-dimensional view of the plasma source system 1000 of fig. 10A including a neodymium ring magnet 1070 surrounding a mounting flange 1060. The magnets in this configuration may be axially polarized to provide a magnetic field that is parallel or anti-parallel with respect to the electrical component of the EM field (i.e., axially polarized with respect to the cylindrical axis of the plasma source 1030). Fig. 10B also illustrates an RF signal interface 1026 that is not shown in fig. 10A.

In particular embodiments, it may be useful to allow the gas to sweep through an excitation region near the window. Fig. 11 illustrates a three-dimensional view of another embodiment of a plasma source system 1100 in which a coaxial resonant cavity body 1110 is connected to an external RF match/tuner 1120 through a mounting bracket 1130. The coaxial resonant cavity body 1110 includes an axially oriented fiber entrance 1155. The tuner 1120 includes an RF connection 1122 and also connects to an RF signal connector 1126 of the coaxial resonant cavity body 1110 via an RF elbow connector 1124. The "side-by-side" mechanical positioning of the tuner 1120 and coaxial resonant cavity body 1110 can vary, and for example, the RF elbow connector 1124 can be removed and the tuner 1120 can be positioned "parallel" to the tube assembly 1160. In this side-stream arrangement, a "generic" coaxial resonant cavity body 1110 is attached to the side of an appropriately designed tube assembly 1160. This configuration may be used, for example, in the foreline, indicated by the plasma source 150' of fig. 1, and in differentially pumped applications where response time is critical. In another embodiment, the tube assembly 1160 may not be used and the coaxial resonant cavity body 1110 may be mounted to a flat surface (e.g., an outer wall of a chamber), such as indicated by the position of the plasma source 150 in FIG. 1.

The resonant cavity plasma sources described herein are designed to reduce the impact of various operating conditions provided by the process environment, such as the pressure load of the cavity, the cavity Q, reflected power, voltage standing wave ratio (VWSR), etc., which results in a change in the resonant frequency. However, these effects require some accommodation. Fig. 12 illustrates a curve 1200 of an example resonant behavior change for a plasma source such as shown in fig. 10B. The solid curve 1210 indicates the resonance condition before plasma ignition, and the dashed curve 1220 indicates the resonance condition when the plasma source is excited and provides sustained optical emission. The resonance before plasma ignition, indicated by the solid curve 1210, is compared to the resonance of the dashed curve 1220 when the plasma source is excited, indicating that the resonance frequency is shifted by about 1MHz and that S11 (input return loss) increases from about-25 dB to-15 dB. In essence, the plasma acts as a load coupled to the coaxial cavity resonator. Plasma loading results in inefficient power delivery and changes in the excitation of the plasma, further driving changes in the optical emission signal from the excited plasma. The resulting optical emission signal instability is not required for process control and may need to be compensated. Instability can manifest itself as a change in the amplitude of the optical emission signal or a change in the spectral characteristics.

For these purposes, a source controller may be used. Fig. 13 illustrates a block diagram of a source controller 1300 for a plasma source constructed in accordance with the principles of the present invention. The source controller 1300 is configured to provide an RF signal to an RF signal interface of the plasma source and to control the amount of power, phase, and frequency of the RF signal. If the RF signal is pulsed, then the source controller 1300 may also adjust the periodicity and duty cycle of any pulsed RF waveform. The RF signal provided to the plasma source is used to generate an EM field that is delivered to ignite and sustain a plasma (e.g., in a plasma chamber of the plasma source). The source controller 1300 may be stand-alone or may be integrated with other control devices (e.g., the spectrometer 160, the computer 170, and the chamber controller 175 of fig. 1).

The source controller 1300 includes components that define and control RF signals. A number of configurations of suitable RF signal chains for defining and controlling the RF signals are envisaged. The configurations defined herein provide at least the desired frequency, signal level and signal stability, and signal level measurement capabilities that facilitate operation of the plasma source. The source controller 1300 includes a synthesizer 1310, an attenuator 1320 (which may be analog, digital, or integrated with bias control of an amplifier), an amplifier 1330 (which may include one or more amplifiers or preamplifiers), an isolator 1350, a bi-directional coupler 1360, and a power sensor 1370. Matching network 1380 (e.g., tuner 1020 of fig. 10A) may be external to (or integrated with) the source controller, which in turn is connected to plasma source 1390. The source controller 1300 may or may not include all of these components in each application. For example, the bi-directional coupler 1360 and the power sensor 1370 may not be included, e.g., when monitoring of forward/reflected RF power is not required. Additionally, the isolator 1350 may be eliminated for a particular RF amplifier configuration, e.g., without regard to feedback.

Synthesizer 1310 is configured to generate an RF signal including setting the frequency, phase, and power of the RF signal. The synthesizer 1310 receives DC power from a DC power supply for generating an RF signal. Synthesizer 1310 also receives instructions from a user or an external controller to establish frequency, phase, and power. The synthesizer 1310 may also receive instructions from the spectrometer or another optical monitoring device coupled to the plasma source and employ the instructions to alter the power or frequency. For example, feedback from the spectrometer may indicate ignition of the plasma within a plasma chamber of the plasma source and allow the synthesizer 1310 to reduce the power used to sustain the plasma ignition. One suitable RF synthesizer is the model ADF4355 available from Analog Devices of Norwood, MA, USA, Mass. The DC power source may be a conventional DC source and the synthesizer 1310 may receive DC power via conventional power connections and interfaces.

The attenuator 1320 receives the RF signal from the synthesizer 1310 and attenuates the RF signal to a desired level. One suitable attenuator is a model F1956 digital step attenuator available from the IDT of San Jose, Calif., USA. The amplifier 1330 receives the attenuated RF signal from the attenuator 1320 and enhances the attenuated RF signal with a fixed or variable gain factor. Amplifier 1330 may be a single or multiple amplifiers or preamplifiers as needed to provide the desired gain. Suitable amplifiers may be designed around the CGH27030 HEMT from Kerui corporation of Dalham, N.C., Cree of Durham, USA. Isolator 1350 is configured to protect the components of source controller 1300 from reflected power. Suitable isolators are available from Skyworks of Woburn, MA, USA, Mass.

The bi-directional coupler 1360 is configured to tap the amplified RF signal and provide a tapped signal to a power sensor 1370. The power sensor 1370 detects the gain and phase (or forward/reflected RMS power) of the amplified RF signal. The output from power sensor 1370 may be used to adjust the RF power level provided by source controller 1300 or to adjust matching network 1380. The values from the power sensor 1370 may also be communicated to an external system (e.g., the spectrometer 160 of fig. 1), and accounting for the relationship between RF signal level and optical signal level may be used to normalize the optical signal level for improved optical signal analysis. Bi-directional couplers are available from a number of suppliers, such as pasirelnac (pasernak). The matching network 1380 is configured to provide impedance matching for delivering the amplified RF signal to the plasma source 1390.

The source controller 1300 may include a communication module 1307 for providing communication to an external system (e.g., the computer 170 or spectrometer 160 of FIG. 1). The source controller 1300 may use USB, ethernet, or other communication protocols. For example, the synthesizer 1310 may receive instructions via the communication module 1307. Since synthesizer 1310 and other elements of source controller 1300 may be a Serial Peripheral Interface (SPI) or built-in integrated circuit (I2C) bus device; the microcontroller 1305 may be used to control the internal components of the source controller 1300. The power module 1303 may receive external 24VDC power and convert to the necessary 3.3 or 5VDC voltage for use with internal components. The components of the source controller 1300 may be suitably integrated into an RF shielded enclosure or box to limit RF signal emissions and provide external coaxial RF connections. The source controller 1300 may provide a variable nominal output level of 0.01 to 40 watts over a frequency range (e.g., 2.4 to 2.5 GHz). The signal level and frequency adjustment may be continuous or discrete. For example, a 10 milliwatt stepped signal level adjustment and a 1MHz stepped frequency adjustment may be used. In order to maintain the ignition of the plasma during the regulation, the source controller 1300 should not terminate the RF signal during the transition.

Semiconductor processing typically involves multiple process steps in the same chamber, where different treatments are applied to the wafer. The plasma sources, plasma source systems, or portions thereof disclosed herein may be used for one or more of these process steps. Since stability of process control is critical to producing the necessary changes to the wafer, it is also critical for the plasma source to monitor the stability of any process. In view of the fact that the plasma source excites the process gas and generates heat, the plasma source has a stability time constant that should be considered. In addition, maintaining an elevated temperature of the window of the plasma source can inhibit contaminant build-up on the window. In view of this, FIG. 14 illustrates a flow chart of a process 1400 for operating a plasma source or a portion thereof constructed in accordance with the principles of the present invention during a multi-step semiconductor process.

The method 1400 may employ one of the plasma sources disclosed herein and begins at a preparation step 1410. Preparation may include checks of duration, pressure, and gases for each process to define the effective readiness state of the plasma source. In step 1420, the readiness state may be set by a source controller of the plasma source. The readiness state may include setting a predetermined RF signal level and frequency of the plasma source. For example, the RF signal level may be set at a high level (e.g., 10 watts) to support rapid temperature increases of the plasma source and its components. Step 1420 may be performed sufficiently before any first process step to monitor to ensure that sufficient warm-up time is provided. Following step 1420, operating parameters of the plasma source during the next process step may be received at the source controller in step 1430. The operating parameters may include a predetermined RF signal level and frequency selected to provide the plasma source with the optical signal level required to monitor the next process step. For example, the RF signal level may be set to a value of 100mW based on the gas and pressure of the process step to avoid excessive optical signal collection at the spectrometer.

After receiving the operating parameters, the parameters may be applied to the plasma source to adjust its operating state in step 1440. Once the appropriate operating conditions have been achieved, the plasma source may be allowed to operate for the duration of the current process step during step 1450. The method 1400 then continues to step 1455, where it is determined whether additional process steps are to be monitored. If additional process steps exist, the process 1400 returns to step 1420 and the readiness of the plasma source is re-established for the additional process steps. If no additional process steps are performed or monitoring is not required, the method 1400 continues to step 1460 where the plasma source may be set to an idle state. The idle state may have the same conditions as the ready state, the operational state, or may "turn off" the plasma source. For example, the idle state may reduce the RF signal to an off state to support operation of the plasma source (e.g., during an exhaust cycle) to remove wafers from the chamber when the semiconductor chamber will experience operating conditions at pressures outside of a range. The process 1400 ends at step 1470 and at this point, the plasma source may be turned off or prepared for a new monitoring period.

The apparatus, system or method described above, or at least a portion thereof, may be embodied in or performed by various processors (e.g., the controller and computer of fig. 1), such as a digital data processor or computer, wherein the processor is programmed or stores executable programs or sequences of software instructions to perform one or more steps of a method or function of the apparatus or system. The software instructions of such programs may represent algorithms and be encoded in machine-executable form on non-transitory digital data storage media, such as magnetic or optical disks, Random Access Memory (RAM), magnetic hard disks, flash memory, and/or Read Only Memory (ROM), to enable various types of digital data processors or computers to perform one, more, or all of the steps of one or more of the above-described methods or functions of the systems described herein.

Certain embodiments disclosed herein may further relate to or include a computer storage product with a non-transitory computer-readable medium having program code thereon for performing various computer-implemented operations embodying at least a portion of an apparatus, system, or performing or directing at least some steps of a method set forth herein. Non-transitory medium as used herein refers to all computer-readable media except transitory propagating signals. Examples of non-transitory computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media, such as CD-ROM disks; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and execute program code, such as ROM and RAM devices. Examples of program code include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter.

Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.

Various aspects of the disclosure may be claimed, including the apparatus, systems, and methods disclosed herein. Aspects disclosed herein include:

A. a plasma source for exciting a plasma from one or more gases and optical monitoring thereof, the plasma source comprising: (1) a coaxial resonator body having an inner length and including a first end, a second end, an inner electrode, and an outer electrode, (2) a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed position along the inner length and configured to provide a radio frequency signal to the coaxial resonator body, (3) a window positioned at the first end of the coaxial resonator body, and (4) a mounting flange positioned proximate the window at the first end of the coaxial resonator body and defining a plasma cavity, wherein the window forms one side of the plasma cavity and isolates the coaxial resonator body from a plasma in the plasma cavity.

B. An excitation system for exciting a plasma, comprising: (1) a coaxial resonant cavity body having an inner length and including a first end, a second end, an inner electrode, and an outer electrode, (2) a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed location along the inner length and configured to provide a radio frequency signal to the coaxial resonant cavity body, and (3) a source controller configured to provide a radio frequency signal to the radio frequency signal interface.

C. An optical monitoring system, comprising: (1) a plasma source configured to ignite, excite a plasma within a plasma cavity in gaseous communication with a process chamber and generate optical emissions from the plasma, (2) a source controller configured to provide a radio frequency signal to a radio frequency signal interface of the plasma source to generate an electromagnetic field in the plasma cavity for ignition and excitation of the plasma, (3) an optical coupling system configured to deliver an optical signal observed from the excitation of the plasma, and (4) a spectrometer configured to receive the optical signal and convert the optical signal to an electrical signal.

Each of aspects A, B and C may have, in combination, one or more of the following additional elements:

element 1: wherein the inner length of the coaxial resonant cavity body is nominally an odd multiple of a quarter wavelength of the provided radio frequency signal. And (2) element: wherein the fixed position is at a distance from the first end coupling point along the inner length, and the values of the coupling point distance and the inner length cooperate to enhance and locate an electromagnetic field proximate the window derived from the provided radio frequency signal. Element 3: wherein the window is made of a material selected from the group consisting of sapphire and fused silica and has a thickness of three millimeters or less. Element 4: wherein the radio frequency signal interface is inductively electrically coupled to the inner and outer electrodes. Element 5: wherein the radio frequency signal interface is electrically coupled to the inner and outer electrodes via a capacitance. Element 6: it further comprises one or more tuning stubs adjustable within the volume between the outer and inner electrodes. Element 7: wherein the coaxial resonant cavity body, the mounting flange, and the window are removably connected. Element 8: wherein at the first end, the inner electrode has a window end having a shape that defines a location of the plasma within the plasma cavity. Element 9: wherein the shape is selected from the group consisting of a cross with symmetrical circular arms, a cross with truncated arms, an asymmetrical cross, a single point, and a frustum of a cone. Element 10: wherein the window end of the inner electrode is removable. Element 11: it further comprises a barrier screen. Element 12: it further includes an optical signal aperture proximate the window and coincident with the location of the plasma. Element 13: wherein the location of the optical signal aperture corresponds to the shape of the inner electrode at the first end. Element 14: it further includes a fiber entrance port coincident with the optical signal aperture. Element 15: wherein the fiber entrance extends along a length of the coaxial resonant cavity body between the first end and the second end. Element 16: wherein the coaxial resonant cavity body has an impedance that matches an impedance of a source of the radio frequency signal. Element 17: further comprising a magnet providing a magnetic field that interacts with the plasma within the plasma cavity to assist ignition of the plasma and sustain the plasma after the ignition. Element 18: wherein the magnet is coupled to the mounting flange. Element 19: wherein the source controller controls a power level, a frequency, a phase, and a duty cycle of the radio frequency signal. Element 20: wherein the source controller automatically controls an amount of power based on forward and reflected power measured between the source controller and the plasma source. Element 21: wherein the source controller includes a radio frequency synthesizer defining a frequency of the radio frequency signal, and a variable gain radio frequency signal path setting an amount of power. Element 22: wherein the source controller automatically controls the frequency of the RF signal based on RF signal gain and phase information measured between the source controller and the plasma source. Element 23: wherein the source controller is positioned at a distal end of the coaxial resonant cavity body. Element 24: it further comprises: a window positioned at the first end of the coaxial resonant cavity body; and a mounting flange positioned proximate to the window at the first end of the coaxial resonant cavity body and defining a plasma chamber, wherein the window forms one side of the plasma chamber and isolates the coaxial resonant cavity body from a plasma in the plasma chamber. Element 25: wherein the source controller automatically controls the amount of power of the radio frequency signal based on forward and reflected power measured between the source controller and the plasma source.

Claims

1. A plasma source for exciting a plasma from one or more gases and monitoring optical emissions therefrom, the plasma source comprising:

a coaxial resonator body having an inner length and comprising a first end, a second end, an inner electrode, and an outer electrode;

a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed location along the inner length and configured to provide a radio frequency signal to the coaxial resonant cavity body;

a window positioned at the first end of the coaxial resonant cavity body; and

a mounting flange positioned proximate to the window at the first end of the coaxial resonant cavity body and defining a plasma chamber, wherein the window forms one side of the plasma chamber and isolates the coaxial resonant cavity body from a plasma in the plasma chamber,

wherein the fixed position is at a distance along the inner length from the first end coupling point, and the values of the coupling point distance and the inner length cooperate to enhance and locate an electromagnetic field derived from the provided radio frequency signal proximate to the window.

2. The plasma source of claim 1, wherein the inner length of the coaxial resonant cavity body is nominally an odd multiple of a quarter wavelength of the provided radio frequency signal.

3. The plasma source of claim 1, wherein the window is made of a material selected from sapphire and fused silica and has a thickness of three millimeters or less.

4. The plasma source of claim 1, wherein the radio frequency signal interface is inductively electrically coupled to the inner electrode and the outer electrode.

5. The plasma source of claim 1, wherein the radio frequency signal interface is capacitively electrically coupled to the inner electrode and the outer electrode.

6. The plasma source of claim 1, further comprising one or more tuning stubs adjustable within a volume between the outer and inner electrodes.

7. The plasma source of claim 1, wherein the coaxial resonant cavity body, the mounting flange, and the window are removably connected.

8. The plasma source of claim 1, wherein at the first end, the inner electrode has a window end having a shape that defines a location of the plasma within the plasma cavity.

9. The plasma source of claim 8, wherein the shape is selected from the group consisting of a cross with a symmetrical circular arm, a cross with a truncated arm, an asymmetrical cross, a single point, and a frustum of a cone.

10. The plasma source of claim 8, wherein the window end of the inner electrode is removable.

11. The plasma source of claim 1, further comprising an isolation shield.

12. The plasma source of claim 1, further comprising an optical signal aperture proximate the window and coincident with a location of the plasma.

13. The plasma source of claim 12, wherein a location of the optical signal aperture corresponds to a shape of the inner electrode at the first end.

14. The plasma source of claim 12, further comprising a fiber entrance coincident with the optical signal aperture.

15. The plasma source of claim 14, wherein the fiber inlet extends along a length of the coaxial resonant cavity body between the first end and the second end.

16. The plasma source of claim 1, wherein the coaxial resonant cavity body has an impedance that matches an impedance of a source of the radio frequency signal.

17. The plasma source of claim 1, further comprising a magnet providing a magnetic field that interacts with the plasma within the plasma cavity to assist ignition of the plasma and sustain the plasma after the ignition.

18. The plasma source of claim 17, wherein the magnet is coupled to the mounting flange.

19. An excitation system for exciting a plasma, comprising:

a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed location along the inner length and configured to provide a radio frequency signal to the coaxial resonant cavity body; and;

a source controller configured to provide a radio frequency signal to the radio frequency signal interface,

wherein the fixed position is at a distance along the inner length from the first end coupling point, and the values of the coupling point distance and the inner length cooperate to enhance and locate an electromagnetic field derived from the provided radio frequency signal.

20. The excitation system of claim 19, wherein the source controller controls a power level, frequency, phase, and duty cycle of the radio frequency signal.

21. The excitation system of claim 20, wherein the source controller automatically controls the amount of power based on forward and reflected power measured between the source controller and a plasma source comprising the coaxial resonant cavity body.

22. Excitation system according to claim 20, wherein the source controller comprises a radio frequency synthesizer defining the frequency of the radio frequency signal, and a variable gain radio frequency signal path setting an amount of power.

23. The excitation system of claim 22, wherein the source controller automatically controls the frequency of the radio frequency signal based on radio frequency signal gain and phase information measured between the source controller and the plasma source.

24. The excitation system of claim 19, wherein the source controller is positioned at a distal end of the coaxial resonant cavity body.

25. The excitation system of claim 19, further comprising: a window positioned at the first end of the coaxial resonant cavity body; and a mounting flange positioned proximate to the window at the first end of the coaxial resonant cavity body and defining a plasma chamber, wherein the window forms one side of the plasma chamber and isolates the coaxial resonant cavity body from a plasma in the plasma chamber.

26. The excitation system of claim 25, wherein values of the coupling point distance and the inner length cooperate to enhance and locate an electromagnetic field derived from the provided radio frequency signal proximate to the window.

27. An optical monitoring system, comprising:

a plasma source configured to ignite, excite a plasma within a plasma cavity in gaseous communication with a process chamber, and generate optical emissions from the plasma, the plasma source comprising:

a radio frequency signal interface electrically coupled to the inner electrode and the outer electrode at a fixed location along the inner length and configured to provide a radio frequency signal to the coaxial resonant cavity body, wherein the fixed location is at a coupling point distance along the inner length from the first end and the values of the coupling point distance and the inner length cooperate to enhance and locate an electromagnetic field derived from the provided radio frequency signal;

a source controller configured to provide a radio frequency signal to a radio frequency signal interface of the plasma source to generate an electromagnetic field in the plasma chamber for ignition and excitation of the plasma;

an optical coupling system configured to pass an optical signal observed from the excitation of the plasma; and

a spectrometer configured to receive the optical signal and convert the optical signal to an electrical signal.

28. The optical monitoring system of claim 27, wherein the source controller automatically controls the amount of power of the radio frequency signal based on forward and reflected power measured between the source controller and the plasma source.