CN116411251A

CN116411251A - Quick annealing equipment

Info

Publication number: CN116411251A
Application number: CN202111656034.2A
Authority: CN
Inventors: 寇崇善
Original assignee: Mingyuan Precision Technology Co ltd; Highlight Technology Corp
Current assignee: Mingyuan Precision Technology Co ltd; Highlight Technology Corp
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2023-07-11

Abstract

The invention provides a rapid annealing device which is applicable to tempering treatment of silicon carbide wafers. The rapid annealing equipment comprises a variable-frequency microwave power source system, a resonant cavity heating system and a measurement and control system. Variable frequency microwave power source systems use solid state power amplifiers and have the flexibility of rapid frequency sweep during heat treatment to compensate for loading effects caused by temperature variations in the material to be annealedThe resulting resonant frequency changes. To improve energy use efficiency and provide sufficient microwave energy uniformity region, TM is used ₀₁₀ The resonant cavity structure of (2) can be used for annealing 4-8 inch silicon carbide wafers. The measurement and control system combines software and hardware to form an automatic system with instant feedback, and further flexibility, stability and reliability are provided for the whole equipment.

Description

Quick annealing equipment

Technical Field

The present invention relates to semiconductor devices, and more particularly to a rapid annealing device.

Background

Silicon carbide (SiC) has a wide band gap, a high breakdown electric field, high thermal conductivity, and excellent chemical inertness, making it an important semiconductor material for manufacturing high temperature, high power, and high frequency devices. Ion implantation is an indispensable technique for manufacturing SiC semiconductor elements. While annealing (annealing) is a necessary step to remove lattice damage and activate implanted ions after ion implantation. For silicon carbide, it is necessary to perform ion implantation post-annealing at a temperature greater than 1,500 ℃ to achieve the process effect.

Conventional annealing is typically performed in a ceramic furnace, either resistive heating or low frequency induction heating. However, the heating/cooling rate of the ceramic furnace is slow (20 ℃ C./min), which makes it difficult to perform silicon carbide annealing at temperatures above 1,500 ℃ C. This limits the maximum annealing temperature because if silicon carbide is exposed to temperatures exceeding 1,400 ℃ for a long period of time, constituent species on the substrate surface sublimate and redeposit (commonly known as step bunching) causing an increase in silicon carbide wafer surface roughness. Such a limitation on the annealing temperature may result in insufficient activation of the implanted ions, resulting in higher contact and channel region resistance. While excessive surface roughness can negatively impact the performance of the silicon carbide element, one of which is the reduced inversion layer mobility (inversion layer mobility), resulting in a silicon carbide MOSFET having a higher on-resistance. Recently, although several capping techniques (capping technology) have been proposed to suppress the above-mentioned problems. However, these techniques still have their highest temperature limitations and require complex processing steps. In addition, prolonged exposure of silicon carbide to high temperatures can result in the formation of a carbon-rich surface and ultimately a graphite surface. Another adverse effect of conventional annealing is that the implanted boron ions undergo both out-diffusion and in-diffusion.

Conventional annealing has drawbacks in operation, in addition to the above-mentioned problems, a first problem being thermal efficiency. The heat dissipation of the furnace body is mainly radiation, and the radiation quantity is increased in proportion to the fourth power of the temperature. Therefore, if the area to be heated is wide, the energy efficiency required for heating is significantly reduced. For the resistance heating furnace, a double tube structure is generally adopted to avoid heater contamination. Thus, the area to be heated becomes wider. In addition, since the presence of the double tube makes the heated material far from the heat source, it is necessary to set the heater to be higher than the temperature of the heated material, which also becomes a factor greatly reducing the efficiency. Therefore, the heat capacity of the heating system becomes very large, and a long time is required for heating up or cooling down. This is a factor that reduces throughput and aggravates the surface roughness of the heated material.

A second problem with conventional annealing relates to waste of material from the furnace. Since materials capable of withstanding temperatures above 1,500 ℃ and used as heating furnaces are limited, high purity materials with high melting points are required. Materials that can be conventionally used in silicon carbide annealing furnaces are graphite and silicon carbide sintered bodies. However, these materials are expensive and if the furnace is large, replacement requires considerable costs. Meanwhile, the higher the temperature is, the shorter the service life of the furnace body is, and the replacement cost is far higher than that of a common silicon wafer annealing process.

Therefore, in order to avoid the problem of surface degradation of the silicon carbide wafer caused by too slow heating speed in the conventional annealing technology, the development of the rapid annealing technology is critical. Although halogen lamp and laser technology can achieve rapid thermal processing, there are problems such as the highest achievable annealing temperatures, surface melting, high residual defect densities, and implant redistribution. In contrast, microwave heating becomes an effective method for rapid annealing of silicon carbide.

Silicon carbide can effectively absorb microwave energy (300 MHz-300 GHz), and microwaves can provide very fast heating and cooling rates of silicon carbide wafers and good control of annealing time with a properly designed annealing system. Microwaves have the characteristic of selective heating, because the microwaves are only absorbed by the semiconductor wafer, but not by the surrounding environment, and the annealing heating rate is very fast. Meanwhile, in the rapid annealing process, the temperature of the environment around the silicon carbide wafer is limited to be raised, and the cooling rate of the silicon carbide wafer can be high after the microwave source is turned off. When compared to conventional annealing techniques, the silicon carbide is annealed using microwaves, which shows that the heating rate can exceed 600 c/s and the temperature can be as high as 2,000 c. The surface roughness produced by the microwave annealing at 1,850 ℃ for 35 seconds was 2nm; compared to a conventional annealing technique at 1,500℃for 15 minutes, the surface roughness is 6nm. Meanwhile, the microwave annealing shows excellent performance in terms of sheet resistance and depth of redistribution of implanted elements (SIDDARTH G. SUNDARESAN, etc.; journal of ELECTRONIC MATERIALS, vol.36, no.4,2007).

Resonant cavity coupling is the most widely used method in microwave heating. Microwave ovens are typically constructed in the form of a single-mode resonant cavity or a multi-mode resonant cavity operating at a fixed frequency. Single mode resonators can generate much higher electromagnetic field strengths than multimode resonators and are therefore more suitable for rapid heating processes. Heating rates as high as 10 deg.c/sec-100 deg.c/sec can be achieved using a single mode cavity, while the heating rates in a multimode cavity are relatively low. However, there are technical difficulties in the prior art when the heating rate is further increased to a level well above 100 ℃/sec. First, when the physical properties of the heated material change with temperature during the heat treatment, the resonant frequency of the resonant cavity changes. A mismatch with the resonant cavity can result if a fixed frequency rf/microwave source is used. Thus, the reflection of the input electromagnetic wave can be greatly increased, and the heating efficiency is seriously affected. Second, even though the resonant frequency of the resonant cavity may be mechanically tuned, it reacts slowly to changes, which results in a slower heating rate.

Disclosure of Invention

In order to overcome the limitations of the prior art, the invention discloses a technology and equipment for rapid and selective heating by using a variable frequency microwave source, which can meet the requirements of rapid heating speed and high heating temperature in the annealing process of silicon carbide wafers.

The invention uses frequency-variable solid electronic components instead of fixed frequency magnetrons as a microwave power source. The variable frequency power source allows for the selection of the optimal operating microwave frequency and has the flexibility to scan the frequency during the heat treatment to compensate for the resonance frequency changes caused by temperature variations of the material to be annealed to achieve optimal energy efficiency. Compared with a Traveling Wave Tube (TWT) variable frequency source used in the existing commercial system, the solid-state microwave power source adopted by the invention is cheaper to manufacture, smaller in size, free from a high-voltage system and easier to electronically control.

The invention introduces a directional coupler and a power meter in the measurement and control system to monitor the forward wave and the reflected wave, and is additionally connected with an infrared ray high Wen Jiju and a computer for monitoring, tuning and controlling the whole microwave heating process. Because the rapid heat treatment is required to be completed in a short time, the manual adjustment and control process is difficult, the measurement and control system provided by the invention combines software and hardware to form an automatic system with instant feedback, and further flexibility, stability and reliability are provided for the whole equipment.

In detail, the invention provides a rapid annealing device comprising a variable frequency microwave power source system, a resonant cavity heating system and a measurement and control system. The variable frequency microwave power source system provides a microwave with a first frequency by utilizing a solid variable frequency microwave power source. The resonant cavity heating system comprises a resonant cavity with a wafer bearing base and an antenna, wherein a material to be annealed is placed on the wafer bearing base, and microwaves provided by the variable-frequency microwave power source system are input into the resonant cavity through the antenna, and a resonant mode is excited in the resonant cavity so as to carry out annealing treatment on the material to be annealed. The measuring and controlling system comprises a directional coupler, a power meter, an optical temperature measuring device, an air pressure control system and a computer, wherein the air pressure control system monitors and controls an air pressure value of the resonant cavity, the directional coupler detects a forward signal of microwaves provided by the variable-frequency microwave power source system and a reflected signal from the resonant cavity heating system, the power meter obtains a power change according to the forward signal and the reflected signal, the optical temperature measuring device monitors a temperature value of the material to be annealed, the computer correspondingly generates an adjustment command according to the temperature value and the power change, and the variable-frequency microwave power source system carries out a sweep frequency mode according to the adjustment command so as to select the best working microwave frequency of the lowest microwave reflection to replace the first frequency, so that the resonant frequency change of the microwave resonant cavity caused by the temperature change of the material to be annealed is compensated.

The variable frequency microwave power source system comprises the solid variable frequency microwave power source and an impedance matcher, wherein the impedance matcher is connected with the antenna, the solid variable frequency microwave power source comprises a microwave signal generator and a solid power amplifier, and the microwave signal generator generates a low-power microwave signal and sends the low-power microwave signal to the solid power amplifier. The solid state power amplifier amplifies the low power microwave signal to generate high power microwaves.

The solid state variable frequency microwave power source and the impedance matcher form a frequency modulation quick matching mechanism to quickly reduce the reflection of the microwave, improve the energy utilization efficiency and maintain the safety of the microwave power source, wherein the impedance matcher has a fixed impedance, and the solid state variable frequency microwave power source enters the sweep frequency mode according to the adjustment instruction of the measurement and control system so as to select the optimal working microwave frequency of the lowest microwave reflection as a second frequency of the microwave, so that the resonance frequency change of the microwave resonant cavity caused by the temperature change of the material to be annealed is compensated.

The air pressure control system comprises a pressure detection unit arranged on the resonant cavity and used for monitoring the air pressure value of the resonant cavity, and further comprises an exhaust unit and an air input unit which are respectively connected with the resonant cavity, so that the air pressure value of the resonant cavity is kept at a preset air pressure.

Wherein, a monitor is electrically connected with the computer to display the monitoring result of the measurement and control system in real time.

Before the high-power annealing process is performed, the impedance element of the impedance matcher is adjusted so that the reflected microwaves are small, and the matching condition is achieved. When the high-power annealing process is performed, the physical characteristics of the material to be annealed are changed due to the temperature rise, so that the resonant frequency of the microwave resonant cavity is changed, and the microwave reflection is improved. At this time, the measurement and control system sends out an adjustment instruction to the solid-state variable-frequency microwave power source to adjust to a rapid sweep frequency mode so as to obtain the minimum reflection operating frequency and achieve impedance matching with the resonant cavity heating system.

The resonant cavity of the resonant cavity heating system comprises a cavity body formed by an upper disc, a hollow cylinder and a lower disc, wherein the upper disc and the lower disc are respectively arranged at two sides of the hollow cylinder. The resonant cavity heating system also includes the wafer carrier pedestal.

The antenna of the resonant cavity consists of a metal ball connected with a metal rod, and the metal rod is arranged on the upper disc and connected with the impedance matcher of the variable-frequency microwave power source system, so that microwaves are input into the resonant cavity through the antenna.

Wherein the upper disc and the lower disc are parabolic discs respectively.

Wherein, the inner side surfaces of the upper disc and the lower disc are respectively coated with an infrared reflection layer.

The wafer bearing base is positioned in the center of the microwave resonant cavity and is the area with the strongest microwave energy.

The wafer bearing base is rotatably arranged in the resonant cavity so as to increase the annealing uniformity of the material to be annealed.

The wafer bearing base comprises a base and an upper cover, and the material to be annealed is placed in a chamber surrounded by the base and the upper cover.

Wherein the wafer carrier absorbs a portion of the microwaves to generate heat for conductively heating the material to be annealed, and the wafer carrier allows another portion of the microwaves to penetrate to directly heat the material to be annealed in the chamber of the wafer carrier.

Wherein the wafer carrying pedestal of the resonant cavity is composed of a microwave absorbing material and allows more than 50% of the microwaves to penetrate to heat the material to be annealed.

Wherein the microwave absorbing material is porous partially sintered silicon carbide with a porosity of between 20% and 30%, or graphite.

Wherein the first frequency of the microwave is 433.05-434.79MHz or 902-928MHz, preferably 434MHz, the sweep frequency range of the sweep mode is + -10 MHz, the commonThe vibrating cavity is a single TM ₀₁₀ The quality factor (Q) of the cavity of the resonant cavity exceeds 6,000.

Wherein the material to be annealed is silicon carbide.

Wherein the material to be annealed is a silicon carbide wafer.

In view of the above, the rapid annealing apparatus of the present invention has the following advantages and features:

(1) The 434MHz microwave resonant cavity is used for carrying out the rapid annealing reaction of the silicon carbide wafer, and a single resonance TM is adopted ₀₁₀ The mode may provide sufficient electromagnetic field uniformity for processing 4-8 inch wafers. The cylindrical resonant cavity comprises upper and lower inner surfaces formed by parabolic curves, so that the problem of great radiation loss of the silicon carbide wafer at high temperature can be solved, and the requirement of heating the silicon carbide wafer to a temperature of more than 1,500 ℃ to 2,000 ℃ can be met.

(2) The use of a variable frequency solid state electronic component as a microwave power source instead of a fixed frequency magnetron, with the flexibility of scanning the frequency during heat treatment, allows the selection of the optimum operating microwave frequency to compensate for the change in resonant frequency of the microwave resonant cavity caused by temperature variations of the material to be annealed. Meanwhile, the rapid matching mode is formed by the rapid annealing device and the impedance matcher, so that the requirement of rapid annealing can be met.

(3) The wafer bearing base of the resonant cavity can absorb part of heat generated by microwaves and uniformly conduct the heat to the silicon carbide wafer besides fixing the silicon carbide wafer, so that the silicon carbide wafer is prevented from being broken due to internal thermal stress. While allowing most microwaves to penetrate to heat the silicon carbide wafer and also preventing overheating of the silicon carbide wafer edge.

(4) The measurement and control system combines software and hardware to form an automatic system with instant feedback, and further flexibility, stability and reliability are provided for the whole equipment.

In order to further understand and appreciate the technical features and effects of the present invention, a preferred embodiment and a detailed description are provided.

Drawings

Fig. 1 is a schematic view of a rapid annealing apparatus of the present invention. .

Fig. 2 is a schematic circuit block diagram of the rapid annealing apparatus of the present invention.

Reference numerals illustrate:

10: variable frequency microwave power source system 36c: lower disc

12: solid state variable frequency microwave power source 37: infrared reflecting layer

14: microwave signal generator 38: air pressure control system

16: solid state power amplifier 40: exhaust unit

18: impedance matcher 41: pressure control unit

30: resonant cavity heating system 42: gas input unit

32: wafer carrier 46: pressure detection unit

32a: base 50: measurement and control system

32b: upper cover 52: directional coupler

33: chamber 54: power meter

34: antenna 56: computer with a computer program

34a: metal bar 58: optical temperature measuring device

34b: metal balls 60: monitor

35: the rotating shaft 100: rapid annealing equipment

36: resonant cavity 200: material to be annealed

36a: upper disk 36b: hollow cylinder

Detailed Description

For the purpose of facilitating understanding of the technical features, contents and advantages of the present invention and the effects achieved thereby, the present invention will be described in detail herein with reference to the accompanying drawings and in the form of examples, but the gist of the accompanying drawings used herein is for illustration and assistance of the description, and not necessarily for the true proportion and precise configuration of the present invention after implementation, so that the proportion and configuration of the accompanying drawings should not be interpreted to limit the scope of the present invention in terms of the claims actually implemented. In addition, for ease of understanding, like elements in the following embodiments are denoted by like reference numerals.

Furthermore, the terms used throughout the specification and claims, unless otherwise indicated, shall have the ordinary meaning and be given to each term used in this field, in the context of the disclosure and in the special context. Certain words used to describe the present composition will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in the description of the present composition.

The use of "first," "second," "third," and the like herein does not specifically refer to order or sequence, nor is it intended to limit the present disclosure to only distinguish between components or operations that may be described in the same technical term.

Second, the words "comprising," "including," "having," "containing," and the like, as used herein, are open-ended terms, meaning including, but not limited to.

The invention discloses a rapid annealing device using microwaves, which can rapidly and selectively heat a material to be annealed to a very high temperature, and can meet the requirements of high heating speed and high heating temperature in the annealing process of silicon carbide wafers. The rapid annealing apparatus of the present invention can be divided into three main parts: (1) a variable frequency microwave power source system, (2) a resonant cavity heating system, and (3) a measurement and control system (i.e., a monitoring and control system). Microwaves are generated by a solid-state variable-frequency microwave power source and are coupled to a resonant cavity heating system through an impedance matcher to heat a target object (namely a material to be annealed). The measurement and control system is used for tuning, monitoring and controlling the microwave heating process.

Referring to fig. 1 and 2, fig. 1 is a schematic structural diagram of a rapid annealing apparatus according to the present invention, and fig. 2 is a schematic circuit block diagram of the rapid annealing apparatus according to the present invention. The rapid annealing apparatus 100 of the present invention comprises: variable frequency microwave power source system 10, resonant cavity heating system 30, and measurement and control system 50. The variable frequency microwave power source system 10 of the present invention utilizes a solid state variable frequency microwave power source 12 to provide microwaves having a first frequency. The microwave frequency (i.e., the first frequency) used in the present invention is exemplified by 434MHz, but is not limited thereto.

The resonant cavity heating system 30 comprises a resonant cavity 36 having a wafer carrying pedestal 32 and an antenna 34, wherein a material 200 to be annealed is placed in a chamber 33 of the wafer carrying pedestal 32 of the resonant cavity 36. Microwaves provided by the variable frequency microwave power source system 10 are introduced into the resonant cavity 36 via the antenna 34 of the resonant cavity heating system 30 and excite a resonant mode in the resonant cavity 36 to anneal the material 200 to be annealed. The material 200 to be annealed is, for example, silicon carbide, and is, for example, a silicon carbide wafer. However, although the material to be annealed is exemplified as a silicon carbide material, and is specifically exemplified as a silicon carbide wafer, the present invention is not limited thereto, and any material that can be annealed, whether or not it requires rapid heating, may be applied to the present invention.

The measurement and control system 50 detects a forward signal of the microwave provided by the variable frequency microwave power source system 10 and a reflected signal from the resonant cavity heating system 30, so as to generate an adjustment command in real time according to the changes of the forward signal and the reflected signal, so that the variable frequency microwave power source system 10 enters the sweep mode according to the adjustment command to find the optimal working microwave frequency of the lowest microwave reflection, and selects the optimal working microwave frequency of the lowest microwave reflection as the second frequency to replace the original first frequency in real time, thereby compensating the resonance frequency change generated by the material 200 to be annealed and achieving the condition of minimum reflected wave.

In detail, in the rapid annealing apparatus 100 of the present invention, the variable frequency microwave power source system 10 comprises a solid state variable frequency microwave power source 12 and an impedance matcher (Match Box) 18, the impedance matcher 18 is connected to the antenna 34 (i.e. coupled antenna), wherein the solid state variable frequency microwave power source 12 comprises a microwave Signal Generator (Signal Generator) 14 and a solid state power amplifier (Solid State Power Amplifier; SSPA) 16. The microwave signal generator 14 is configured to generate a low-power microwave signal, and the solid-state power amplifier 16 amplifies the low-power microwave signal to generate high-power microwave, wherein the variable-frequency microwave power source system 10 performs impedance matching by the impedance matcher 18 to reduce reflection of the microwave, improve energy utilization efficiency and maintain safety of the microwave power source. The invention belongs to industrial applications, and the available frequencies belong to the ISM frequency band (Industrial Scientific Medical Band). The radio regulations of the international electrounion, which are defined in the microwave range, include: 433.05-434.79MHz, 902-928MHz, 2400-2483.5MHz …, etc. Because the higher the microwave frequency, the smaller the cavity size and the smaller the energy uniformity region. The present invention is aimed at processing 8 inch wafers, so that TM is used ₀₁₀ Single mode resonance, which has a resonant cavity diameter of about 500mm. At this size, microwaves having frequencies above 2400MHz will have difficulty providing an annealing treatment region of sufficient uniformity and will readily excite other resonant modes, not only losing the advantages of single mode operation, but also the microwave energy distribution will be less likely to maintain the desired uniformity. Therefore, the microwave center frequency used in the present invention is preferably in the range of about 433.05-434.79MHz or 902-928MHz, preferably 434MHz. The sweep frequency range of the sweep frequency mode is about + -10 MHz, that is, the sweep frequency range is, for example, the first frequency of the original microwave is increased or decreased by 10MHz, wherein the sweep frequency range is only an example, and the value of the sweep frequency range can be increased or decreased according to the actual requirement. The output power applicable to the present invention can be changed according to the process requirements and is not limited to a specific range.

However, the microwave frequency (i.e., the first frequency) to which the present invention is applicable is not limited to the above range, and for example, the present invention may be applied to a microwave frequency of about 2400-2483.5MHz, even to a frequency not specified by the international electrotechnical radio rule, such as 500MHz or other frequencies for which use permission is required. The resonant cavity design and the dimensions of the processable wafer will preferably be changed correspondingly, and will not be described in detail since a person of ordinary skill in the art will know how to change them according to the disclosure of the present invention.

Impedance matching is important for realizing rapid heating, and the material 200 to be annealed changes the resonant frequency of the resonant cavity due to the change of physical characteristics caused by temperature rise, so that microwave reflection is reduced, and the original heating efficiency is maintained by the rapid response reduction of microwave reflection. The present invention employs a fast matching (fast matching) mechanism consisting of a solid state variable frequency microwave power source 12 and an impedance matcher 18 to achieve the above-described requirements. That is, the resonant frequency and impedance change of the resonant cavity 36 in the recording process are measured and recorded, and the range of the capacitor (C) and the inductor (L) corresponding to the impedance matching is selected, so that the impedance of the capacitor (C) and the inductor (L) is fixed without changing. During the annealing process, when the resonant frequency and impedance of the resonant cavity 36 are changed, the present invention can change the operating frequency of the solid-state variable frequency microwave power source 12, and can achieve a fast matching reaction by matching with the above-mentioned fixed impedance matching circuit. That is, the impedance matcher 18 has a fixed impedance, and the solid-state variable-frequency microwave power source 12 sweeps the microwave signal according to the adjustment command generated by the measurement and control system 50 according to the microwave reflection, so as to achieve the goal of reducing the microwave reflection by finding the optimal microwave frequency. In other words, before the high-power annealing process is not performed, the impedance elements of the impedance matcher 18 are adjusted so that the reflected microwaves are small, and the matching condition is achieved. When a high power annealing process is performed, the physical properties of the material 200 to be annealed are changed due to the temperature rise, and thus the resonant frequency of the resonant cavity 36 is changed to increase the microwave reflection. At this point, the measurement and control system 50 sends an adjustment command to the solid-state variable frequency microwave power source 12 to adjust to the fast sweep mode to obtain the minimum reflected operating frequency for impedance matching with the resonant cavity heating system 30. It should be clear to a person having ordinary skill in the art from the disclosure of the present invention how to monitor the load impedance variation range and how to use the corresponding fixed matching circuit, so that the description is omitted.

In the resonant cavity heating system 30 of the rapid annealing apparatus 100 of the present invention, the resonant cavity 36 of the resonant cavity heating system 30 includes a cavity composed of an upper disk 36a, a hollow cylinder 36b, and a lower disk 36c, which is composed of stainless steel. The upper and lower disks 36a and 36c are, for example, parabolic disks, so as to effectively reflect infrared rays radiated from the high temperature silicon carbide wafer onto the material 200 to be annealed. The upper disk 36a and the lower disk 36c are respectively disposed on both sides of the hollow cylinder 36 b. The antenna 34 of the resonant cavity 36 is composed of, for example, a metal ball 34b having a diameter of about 20mm connected to a metal rod 34a having a diameter of about 10mm, the metal rod 34a being provided on the top center of the upper disk 36a and connected to the impedance matcher 18 of the variable frequency microwave power source system 10, whereby microwaves are introduced into the resonant cavity 36 via the antenna 34 and the above-mentioned resonant modes are excited in the resonant cavity 36. Wherein, for inserting or extracting the material 200 to be annealed, one of the upper and lower disks 36a and 36c of the resonant cavity 36 is, for example, detachably connected to the hollow cylinder 36b so as to remove or place the material 200 to be annealed from above or from below. However, the invention is not limited thereto, and in another possible design, the invention may be modified to add an outlet to the hollow cylinder 36b to remove or place the material 200 to be annealed from the sides. In other words, although the present invention is illustrated above, any technical means for removing or placing the material 200 to be annealed is within the scope of the present invention.

Wherein, to improve energy efficiency and proper microwave energy uniformity, the present invention preferably employs a 434MHz microwave source to generate microwaves, and resonant cavity 36 preferably generates a single TM ₀₁₀ The quality factor (Q) of the cavity of the resonant cavity 36 exceeds 6,000 due to the structure of the resonant mode, and thus the microwave intensity is high. Taking the material 200 to be annealed as a silicon carbide wafer, for example, the diameter of the resonant cavity 36 is approximately 500mm, and silicon carbide wafers of various sizes (4 inches, 6 inches, and 8 inches) may be annealed. The silicon carbide wafer is placed in the wafer carrier pedestal 32 in the center of the resonant cavity 36 and is located in the region of highest microwave intensity. The wafer carrier 32 is rotatably disposed in the resonant cavity 36, for example, to increase the uniformity of heating of the material 200 to be annealed, wherein the wafer carrier 32 is disposed on a spindle 35, for example, and the spindle 35 is rotated by a motor (not shown). However, it should be understood that the wafer carrier 32 of the present invention may be rotated by any known technique and is not limited to the above examples. Furthermore, although the resonant cavity 36 with a diameter of 500mm is taken as an example of the present invention, the present invention is not limited thereto, and the resonant cavity 36 of the present invention may have other suitable diameter and length according to practical requirements.

Silicon carbide wafers are in extremely high temperature conditions, where radiative heat dissipation dominates (proportional to the temperature 4 times). Meanwhile, because the wafer is of a planar structure and has a large radiation area, radiation loss must be greatly reduced to improve heating efficiency so as to reach heating temperature. In the present embodiment, the upper and lower surfaces of the resonant cavity 36 are formed with optically polished parabolic structures (upper and lower disks 36a and 36 c), and are respectively coated with an infrared reflecting layer 37 to increase the reflectivity of infrared rays as a mirror to minimize radiation loss. The infrared reflection layer 37 is made of a high-reflectivity material such as gold. In addition, the inner surface of the hollow cylinder 36b of the resonant cavity 36 may be selectively coated or uncoated with the infrared reflection layer 37. The silicon carbide wafer to be heated is positioned within the resonant cavity 36 and is preferably placed within a wafer carrier pedestal 32 made of a suitable microwave absorbing material. The wafer carrier pedestal 32 is preferably disposed in a central location of the resonant cavity 36, which is the region of greatest microwave energy.

The wafer carrier 32 functions to uniformly distribute heat generated by absorbing microwaves to the silicon carbide wafer (i.e., the material 200 to be annealed) in addition to fixing the silicon carbide wafer, thereby preventing the silicon carbide wafer from being broken due to internal thermal stress. For example, the wafer carrier 32 of the resonant cavity 36 includes a base 32a and a top cover 32b, wherein the top cover 32b is detachably covered on the base 32a, so as to surround the chamber 33, and the material 200 to be annealed is detachably positioned in the chamber 33 surrounded by the base 32a and the top cover 32 b. In addition, the base 32a and/or the chamber 33 of the wafer carrier 32 of the present invention are not limited to a specific shape. For example, if the material 200 to be annealed is a wafer, the projected shape of the base 32a of the wafer carrier pedestal 32 and/or the chamber 33 may be, for example, circular. In addition, although the upper cover 32b preferably completely covers the chamber 33 of the base 32a, thereby completely covering the material 200 to be annealed in the chamber 33, the invention is not limited thereto, i.e. the upper cover 32b may also be a part of the chamber 33 covering the base 32a, and expose the surface of the rest of the material 200 to be annealed.

In the present invention, the wafer carrier 32 of the resonant cavity 36 generates heat, for example, to absorb a portion of the microwaves to conductively heat the material 200 to be annealed, and the wafer carrier 32 simultaneously allows another portion of the microwaves to penetrate directly to perform a heating reaction with the silicon carbide wafer placed in the chamber 33 of the wafer carrier 32. The wafer carrier 32 of the resonant cavity 36 is preferably constructed of a microwave absorbing material and preferably allows more than 50% microwave penetration to heat the silicon carbide wafer. The porous, sintered silicon carbide with a porosity of 20% to 30% is a suitable wafer carrier base material, mainly because 434MHz microwaves can be absorbed by silicon carbide but the penetration depth of the microwaves can exceed 20mm, and the porous silicon carbide manufactured by sintering can achieve the function of the wafer carrier base 32, and can be heated and cooled for many times without cracking, so that the service life is long. Graphite may also be used as the material for the wafer carrier 32.

In addition, silicon carbide wafers are very thin in thickness, and if exposed directly to microwaves, the edges thereof are prone to produce a high electric field intensity distribution, which can cause overheating and even tip discharge. The wafer carrier 32 preferably wraps around the edge of the silicon carbide wafer to be annealed to prevent overheating of the edge of the silicon carbide wafer.

In the present invention, the measurement and control system 50 further comprises a gas pressure control system 38 disposed on the resonant cavity heating system 30 for monitoring and controlling the pressure of the resonant cavity 36 and the flow rate of the input gas, so that the gas pressure of the resonant cavity 36 is maintained at a predetermined gas pressure, for example, wherein the predetermined gas pressure is between about 0.1 atm and 10 atm, which is set according to the process. The air pressure control system 38 includes a pressure detecting unit 46 disposed on the resonant cavity 36 for monitoring the air pressure of the resonant cavity 36, and the pressure detecting unit 46 is, for example, a Vacuum gauge (Vacuum gauge). The air pressure control system 38 further comprises an air discharging unit 40, a pressure control unit 41 and a gas input unit 42, wherein the air discharging unit 40 and the gas input unit 42 are respectively connected to the resonant cavity 36. The pressure control unit 41 is a controller for receiving the air pressure value monitored by the pressure detecting unit 46, and controlling the operation of the air exhausting unit 40 and/or the air inputting unit 42 so that the air pressure value of the resonant cavity 36 is maintained at the predetermined air pressure.

In detail, in the present embodiment, a gas such as nitrogen or argon is inputted into the resonance chamber 36 through the gas input unit 42 at a set gas supply flow rate, and is discharged through the gas discharge port connection exhaust unit 40 of the resonance chamber 36. Before the gas is input into the resonant cavity 36 through the gas input unit 42, the resonant cavity 36 may be evacuated by the exhaust unit 40, and then the gas such as nitrogen or argon is input into the resonant cavity 36 through the gas input unit 42 until the resonant cavity 36 reaches the predetermined pressure, thereby enabling the resonant cavity 36 to reach the set pure gas atmosphere. The gas input unit 42 is, for example, a gas source of the above-mentioned gas, and the gas source is, for example, connected to the resonant cavity 36 by a first control valve (not numbered). The exhaust unit 40 is, for example, a vacuum pump, and the vacuum pump is, for example, connected to the resonant cavity 36 by a second control valve (not numbered).

The present invention can input the gas such as nitrogen or argon into the resonant cavity 36 through the gas input unit 42 at the above-mentioned gas supply flow rate, and can be combined with the gas discharge unit 40, and the gas in the resonant cavity 36 is discharged through the gas discharge unit 40 at a gas discharge flow rate corresponding to the gas supply flow rate, so that the gas pressure value of the resonant cavity 36 is kept at the above-mentioned predetermined gas pressure. However, it should be understood that although the above-described means for maintaining the air pressure value is exemplified, the present invention is not limited thereto, and any means may be applied to the present invention as long as the air pressure value of the resonant cavity 36 can be maintained at the predetermined air pressure. For example, the present invention may also omit the pressure control unit 41, and directly receive the air pressure value monitored by the pressure detection unit 46 by the computer 56, which will be described later, and control the air supply flow of the air input unit 42 and the air exhaust flow of the air exhaust unit 40.

In the rapid annealing apparatus 100 of the present invention, the measurement and control system 50 further comprises a directional coupler (Directional Coupler) 52 and a Power Meter (Power Meter) 54, wherein the directional coupler 52 is used for detecting the input and reflected microwave signals, and the detected signals are sent to the Power Meter 54 for monitoring the coupling of the microwaves with the resonant cavity 36 and the material 200 to be annealed. In particular, a directional coupler 52 is provided between the solid state power amplifier 16 and the impedance matcher 18 for detecting the input and reflected microwave signals, i.e. the directional coupler 52 may be used to detect the forward signal of the microwaves provided by the variable frequency microwave power source system 10 and the reflected signal from the resonant cavity heating system 30. The directional coupler 52 then sends these detected signals to the power meter 54 for immediate monitoring of the changes in the coupling of microwaves to the resonant cavity 36 and the material 200 to be annealed (e.g., power changes). The computer 56 can receive the power variation data and generate an adjustment command in real time according to the power variation, so as to control the operation of the variable frequency microwave power source system 10.

The measurement and control system 50 further includes an optical temperature measuring device (Optical Pyrometer) 58 for monitoring a temperature value of the material 200 to be annealed in real time, wherein the optical temperature measuring device 58 is, for example, an infrared pyrometer. The computer 56 is further electrically connected to the optical temperature measuring device 58, so as to correspondingly generate an adjustment command to control the energy input by the microwave according to the temperature value monitored by the optical temperature measuring device 58 and the power variation, thereby achieving the required heating or cooling temperature control. The Emissivity (Emissivity) of the silicon carbide material measured by the present invention using a blackbody radiation source is 0.74, and this Emissivity value is input into the optical temperature measuring device 58 for all temperature measurements in the disclosed technique. In addition, the measurement and control system 50 further includes a monitor 60 electrically connected to the computer 56 for displaying the monitoring results of the various components of the measurement and control system 50 in real time, for example, all microwave and temperature data can be input to the computer for recording and processing and displayed on the monitor 60 immediately.

In summary, the rapid annealing equipment of the invention has the following advantages and features:

(1) The 434MHz microwave resonant cavity is used for carrying out the rapid annealing reaction of the silicon carbide wafer, and single resonance TM is adopted ₀₁₀ The mode may provide sufficient electromagnetic field uniformity for processing 4-8 inch wafers. The cylindrical resonant cavity comprises upper and lower inner surfaces formed by parabolic curves, so that the problem of great radiation loss of the silicon carbide wafer at high temperature can be solved, and the requirement of heating the silicon carbide wafer to a temperature of more than 1,500 ℃ to 2,000 ℃ can be met.

(2) The use of a variable frequency solid state microwave source as a microwave power source instead of a fixed frequency magnetron, having the flexibility to sweep the frequency during heat treatment, allows the optimum operating microwave frequency to be selected to compensate for the change in resonant frequency of the microwave resonant cavity caused by temperature variations in the material to be annealed. Meanwhile, the rapid matching mode is formed by the rapid annealing device and the impedance matcher, so that the requirement of rapid annealing can be met.

The foregoing is by way of example only and is not intended as limiting. Any equivalent modifications or variations to the present invention without departing from the spirit and scope of the present invention are intended to be included in the following claims.

Claims

1. A rapid annealing apparatus comprising:

a variable frequency microwave power source system for providing a microwave having a first frequency using a solid state variable frequency microwave power source;

the resonant cavity heating system comprises a resonant cavity with a wafer bearing base and an antenna, wherein a material to be annealed is placed on the wafer bearing base, microwaves provided by the variable-frequency microwave power source system are input into the resonant cavity through the antenna, and a resonant mode is excited in the resonant cavity so as to carry out annealing treatment on the material to be annealed; and

the system comprises a directional coupler, a power meter, an optical temperature measuring device, an air pressure control system and a computer, wherein the air pressure control system monitors and controls an air pressure value of the resonant cavity, the directional coupler detects a forward signal of microwaves provided by the variable-frequency microwave power source system and a reflected signal from the resonant cavity heating system, the power meter obtains a power change according to the forward signal and the reflected signal, the optical temperature measuring device monitors a temperature value of a material to be annealed, the computer correspondingly generates an adjustment command according to the temperature value and the power change, the variable-frequency microwave power source system carries out a sweep frequency mode according to the adjustment command, and therefore the optimal working microwave frequency of the lowest microwave reflection is selected to replace the first frequency, so that the resonant frequency change of the resonant cavity caused by the temperature change of the material to be annealed is compensated.

2. The rapid annealing apparatus of claim 1, wherein the variable frequency microwave power source system comprises the solid state variable frequency microwave power source and an impedance matcher, the impedance matcher being connected to the antenna, wherein the solid state variable frequency microwave power source comprises a microwave signal generator and a solid state power amplifier, the microwave signal generator generating a low power microwave signal which is fed into the solid state power amplifier to generate the high power microwave.

3. The rapid annealing apparatus of claim 2, wherein the solid state variable frequency microwave power source and the impedance matcher form a frequency modulation rapid matching mechanism to rapidly reduce reflection of the microwave, wherein the impedance matcher has a fixed impedance, the solid state variable frequency microwave power source enters the sweep mode according to the adjustment command of the measurement and control system, thereby selecting the optimum operating microwave frequency of the lowest microwave reflection as a second frequency of the microwave so as to compensate for a change of the resonant frequency of the resonant cavity caused by a temperature change of the material to be annealed.

4. The rapid annealing apparatus of claim 1, wherein the gas pressure control system comprises a pressure detection unit disposed on the resonant cavity for monitoring the gas pressure value of the resonant cavity, and further comprises a gas exhaust unit and a gas input unit respectively connected to the resonant cavity, so as to maintain the gas pressure value of the resonant cavity at a predetermined gas pressure.

5. The rapid annealing apparatus of claim 1, further comprising a monitor electrically connected to the computer for displaying the monitoring result of the measurement and control system in real time.

6. The rapid annealing apparatus of claim 1, wherein the resonant cavity of the resonant cavity heating system comprises a cavity composed of an upper disk, a hollow cylinder and a lower disk, wherein the upper disk and the lower disk are disposed on both sides of the hollow cylinder, respectively.

7. The rapid annealing apparatus of claim 6, wherein the antenna of the resonant cavity is composed of a metal ball connected with a metal rod, the metal rod is disposed on the upper disk and connected with an impedance matcher of the variable frequency microwave power source system, so that the microwaves are input into the resonant cavity through the antenna.

8. The rapid annealing apparatus of claim 7, wherein the upper disk and the lower disk are parabolic disks, respectively.

9. The rapid annealing apparatus of claim 7, wherein inner side surfaces of the upper and lower disks are coated with an infrared reflection layer, respectively.

10. The rapid annealing apparatus of claim 1, wherein the wafer carrier pedestal is located at a center of the resonant cavity, the center being a region of strongest microwave energy.

11. The rapid annealing apparatus of claim 1, wherein the wafer carrier pedestal is rotatably disposed in the resonant chamber to increase the annealing uniformity of the material to be annealed.

12. The rapid annealing apparatus of claim 11, wherein the wafer carrier comprises a base and a lid, and the material to be annealed is disposed in a chamber formed by the base and the lid.

13. The rapid annealing apparatus of claim 1, wherein the wafer carrier absorbs a portion of the microwaves to generate a heat to conductively heat the material to be annealed, and the wafer carrier allows another portion of the microwaves to penetrate to directly heat the material to be annealed in the chamber of the wafer carrier.

14. The rapid annealing apparatus of claim 13, wherein the wafer carrier of the resonant chamber is comprised of a microwave absorbing material and allows more than 50% of the microwaves to penetrate to heat the material to be annealed.

15. The rapid annealing apparatus of claim 14, wherein the microwave absorbing material is porous sintered silicon carbide with a porosity of between 20% and 30%, or graphite.

16. The rapid annealing apparatus according to claim 1, wherein the first frequency of the microwave is 433.05-434.79MHz or 902-928MHz, the sweep frequency range of the sweep mode is + -10 MHz, and the resonant cavity is a single TM ₀₁₀ The quality factor (Q) of the cavity of the resonant cavity exceeds 6,000.

17. The rapid annealing apparatus of claim 1, wherein the first frequency of the microwave is 434MHz and the diameter of the resonant cavity is 500mm.

18. The rapid annealing apparatus of claim 1, wherein the first frequency of the microwave is 500MHz.

19. The rapid annealing apparatus of claim 1, wherein the material to be annealed is silicon carbide.

20. The rapid annealing apparatus of claim 1, wherein the material to be annealed is a silicon carbide wafer.