WO1998058098A1

WO1998058098A1 - Magnetic parts and method for using same

Info

Publication number: WO1998058098A1
Application number: PCT/US1998/012576
Authority: WO
Inventors: Donald M. Mintz; Jianming Fu
Original assignee: Applied Materials, Inc.
Priority date: 1997-06-18
Filing date: 1998-06-15
Publication date: 1998-12-23

Abstract

A method for allowing process kits made of magnetic materials to be used for processes that are normally adversely effected by magnetic materials is disclosed. A magnetic part (23) is heated to a temperature near or above the part's Curie temperature prior to beginning processing, and is maintained at a temperature near or above the part's Curie temperature during processing. Preferably the magnetic material is a material that has a low coefficient of thermal expansion at temperatures near or less than the Curie temperature and has a Curie temperature near the operating temperature of the process.

Description

MAGNETIC PARTS AND METHOD FOR USING SAME

FIELD OF THE INVENTION

The present invention relates to the use of magnetic parts in processes which may be adversely affected by undesirable magnetic fields. More particularly the present invention relates to the use of ferromagnetic nickel-iron alloys as process kit parts for use in the fabrication of semiconductor devices.

BACKGROUND OF THE INVENTION

A semiconductor device is formed by layering various materials on a wafer in a prescribed pattern. Popular methods for depositing semiconductor layers include physical vapor deposition and chemical vapor deposition. While these processes are effective for film layering, material that deposits on surfaces within the deposition chamber other than those of the substrate may tend to flake or crumble from chamber surfaces as the chamber thermally cycles, particularly when a significant amount of material has accumulated. Such flaking or crumbling may cause wafer contamination. Accordingly, in order to reduce this type of contamination, chamber surfaces must be periodically cleaned or replaced. The semiconductor device market is extremely price competitive. Companies continually strive to reduce their cost per article processed. In order to reduce cost per article processed, part replacement must be minimized and cleaning procedures simplified. One technique for ^• simplifying chamber cleaning is to use process kits (i.e., shields, pedestals, shutters, collimators and clamp rings which may be easily removed from the chamber for cleaning or replacement) . A process kit part for use in a PVD process should exhibit the following characteristics: 1) an absence of properties (e.g., magnetic field) which adversely affect the process; 2) desirable coefficient of thermal expansion (i.e., a coefficient of thermal expansion similar to that of the materials with which the process kit part will interface - e.g., similar to the coefficient of the deposited material and/or the substrate); and 3) desirable etch properties. Presently the choice of process kit part materials for use in semiconductor fabrication is severely limited, many otherwise desirable materials exhibiting potentially deleterious magnetic properties. Among those materials that do not exhibit deleterious magnetic properties, few exhibit desirable etch properties. Those that do often require elaborate cleaning procedures .

Consider, these characteristics against the background of a conventional sputtering apparatus. First with reference to the absence of deleterious magnetic properties, to deposit a film of material within a sputtering chamber of such an apparatus, a target of material to be deposited and a wafer on which target material is to be deposited are mounted within the chamber. A gas is flowed into the chamber and a negative voltage is applied to the target with respect to the chamber walls so as to excite the gas into a plasma state. As ions from the plasma bombard the target, energy is transferred from the energetic ions to the target, causing target particles to leave the target and travel in linear trajectories.

Ideally, magnetic fields within the chamber will either be so low as to allow sputtering to proceed unaffectedly or will be tailored (e.g., via inclusion of a magnet behind the sputtering target) to promote favorable deposition characteristics such as selected target erosion to result in uniform layer deposition. Accordingly, process kit parts introduced to the chamber must not adversely affect the processes performed therein by undesirably altering the magnetic fields. For this reason, process kit parts are purposely fabricated from non-magnetic materials (i.e., materials that do not exhibit a magnetic field at ambient temperatures) to avoid the deleterious effects caused by magnetic materials during sputtering processes (e.g., shunting magnetic fields from the sputtering target magnets, thereby altering the erosion profile of the sputtering target, and/or altering the plasma distribution adjacent the wafer and/or altering electron bombardment of the target or the wafer due to residual magnetic fields within the magnetic materials) . Second, with regard to desirable coefficient of thermal expansion, as a sputtering chamber thermally cycles, the process kit parts and chamber walls (collectively referred to herein as chamber surfaces), any deposited material and any wafer contained within the chamber will heat and cool, each expanding and contracting according to its respective coefficient of thermal expansion. This expansion and contraction causes particles of deposited material to flake off of chamber surfaces when the deposited material and the chamber surfaces expand and contract at different rates. Thus, periodic cleaning or replacement of chamber surfaces is required. Particles also may be generated by the rubbing of surfaces whose coefficients of thermal expansion differ. Accordingly the deposition chamber and process kit parts should be configured so as to minimize the amount of interfacing between parts having different coefficients of thermal expansion.

Third, regarding desirable etch properties, a particularly problematic interface occurs between the clamp ring (typically a metal) and the substrate (typically silicon) . Most metals have higher thermal expansion coefficients than silicon and other substrate materials which possess extremely low thermal expansion coefficients. Thus, a significant amount of surface rubbing occurs at the clamp ring/substrate interface. In order to reduce the particles generated thereby, titanium clamp rings are used because titanium has a low coefficient of thermal expansion and is able to withstand the high process temperatures required for sputtering deposition (i.e., wafer temperatures) . Although titanium clamp rings help reduce particle generation at the clamp ring/substrate interface, they cannot be economically recycled when used in titanium deposition processes because deposited titanium cannot be selectively etched from a titanium part (titanium being used prevalently by the semiconductor industry) . Further complicating chamber cleaning is the fact that titanium-nitride layers are popular for forming metal interconnects in semiconductor devices. However, titanium- nitride is brittle and when deposited alone promotes particle flaking that may contaminate underlying wafers. To prevent flaking, a layer of titanium is deposited over the titanium-nitride layer. The titanium layer is more tightly bonded than is the titanium-nitride layer, thereby effectively gluing the titanium-nitride layer in place. Such titanium layers are referred to as pasting layers, and are periodically deposited on chamber surfaces to prevent the deposited titanium-nitride film from flaking therefrom.

The current process for removing such titanium- nitride/titanium layers from titanium process kit parts is time consuming and therefore adversely affects the cost per article processed and thus the overall cost of equipment ownership. Specifically, a titanium-nitride layer is removed via a wet chemical etch and a titanium layer is physically removed via bead blasting. This chemical etch/bead blast sequence must be repeated for each pair of titanium-nitride/titanium layers because neither process can satisfactorily remove both deposited layers. In most applications it is common to repeat the titanium-nitride /titanium layering 20-40 times before the process kit is cleaned. To repeat the chemical etch/bead blast sequence 20-40 times for each process kit part is simply too time consuming (and thus too expensive) for most semiconductor processing applications. Furthermore, due to the high cost of titanium, disposal of titanium parts is not an economical solution. Accordingly, a need exists for process kit parts that can be easily cleaned and that will not adversely affect the deposition process.

SUMMARY OF THE INVENTION In order to satisfy the need for an improved process kit, the present invention provides a method that enables the use of process kit parts having a desirable coefficient of thermal expansion, and desirable etch properties, but having potentially deleterious magnetic properties. The method of the present invention ameliorates the process kit parts potentially deleterious magnetic properties by heating the process kit part to a temperature near of above the parts Curie temperature (i.e., the temperature at which the part no longer exhibits the potentially deleterious magnetic property) prior to production processing (i.e., processing of parts for eventual use or sale) , thereby eliminating or attenuating the magnetic property and expanding the universe of useable process kit materials. Preferably the process kit part is selected such that its Curie temperature is below the operating temperature of the process. Thus, assuming efficient process kit part heating, the process kit part is heated to a temperature at which its potentially deleterious magnetic property disappears or is sufficiently ameliorated so as not to adversely affect the process. The process kit part is preferably heated to and maintained at a temperature substantially near the Curie temperature because desirably low coefficients of thermal expansion are exhibited at temperatures near and below the Curie temperature. Thus, in order to achieve both low coefficient of thermal expansion (exhibited at temperatures near and below the Curie temperature) and sufficient amelioration of magnetic field (achieved at temperatures near and above the Curie temperature) , the process kit part is preferably maintained at a temperature near the Curie temperature during production processing.

The present invention provides the semiconductor fabrication field a wider range of materials for use as process kit parts. This wider range of materials includes materials with more favorable etch properties than those previously available for use in semiconductor device fabrication. Accordingly the present invention enables the use of simplified cleaning procedures, therefore increasing productivity and reducing the cost per article processed. Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and IB are diagrammatic illustrations, in section, of the pertinent portions of a sputtering chamber for employing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a diagrammatic illustration, in section, of the pertinent portions of an exemplary sputtering chamber 11 for employing the present invention. The sputtering chamber 11 generally includes a vacuum chamber enclosure wall 13 having at least one gas inlet 15 and an exhaust outlet 17 connected to an exhaust pump (not shown) . A substrate support substrate support 19 is disposed at the lower end of the sputtering chamber 11, and a sputtering target 21 is mounted to the upper end of the sputtering chamber 11. A clamp ring 23 is operatively coupled to the substrate support 19 so as to press a substrate 25 (see FIG. IB) uniformly against the substrate support 19. A shutter assembly (not shown) is rotatably mounted within the sputtering chamber 11 for selectively positioning a shutter disk 27 between the target 21 and the remainder of the sputtering chamber 11 (i.e., placing the shutter disk 27 in a closed position). Thus when positioned in the closed position deposition material is prevented from depositing on surfaces beneath the shutter disk 27. Preferably the shutter disk 27 is positioned so as to be between the clamp ring 23 and the substrate support 19 when the shutter disk 27 is in the closed position (as shown in FIG. 1A) . A shield 29 is coupled along the edge of the target 21 and extends to the substrate support 19 for limiting the travel of deposition materials. The target 21 is electrically isolated from enclosure wall 13. Enclosure wall 13 is preferably grounded so that a negative voltage may be maintained on the target 21 with respect to grounded enclosure wall 13. FIG. IB shows the sputtering chamber 11 of FIG. 1A with the shutter disk 27 in the open position, and with the clamp ring 23 pressing the substrate 25 against the substrate support 19.

For convenience, as indicated above, the shutter disk 27, the shield 29, the substrate support 19, a collimator (not shown) and the clamp ring 23 are referred to herein collectively as the process kit parts. In operation, the substrate 25 is positioned on the substrate support 19 and a gas (typically a non-reactive species such as Argon) is flowed into the sputtering chamber 11 through the gas inlet 15 and is pumped from the sputtering chamber 11 (at a selected flow rate) through the exhaust outlet 17. The pressure within sputtering chamber 11 is controlled by a flow controller coupled to the gas inlet 15 which controls the rate at which gases are flowed into the sputtering chamber 11. A D.C. power supply (not shown) applies a negative voltage to the target 21 with respect to enclosure wall 13 so as to excite the chamber gas into a plasma state. A conventional magnetron sputtering apparatus employs a magnet (not shown) above the target 21 to increase the concentration of plasma ions adjacent to the sputtering surface of the target 21. Ions from the plasma bombard the target 21 and sputter atoms and larger particles of target material from the target 21. The sputtered particles travel along linear trajectories, and a portion of the particles collide with, and deposit on, substrate 25 and on process kit surfaces, as well as on surfaces of the sputtering chamber 11. Thus, a deposited layer is formed on the surface of the substrate 25, on the surfaces of the process kit parts and on the exposed surfaces of the sputtering chamber 11.

In accordance with the present invention one or more of the process kit parts is magnetic, exhibiting a magnetic field at temperatures below the Curie temperature. Preferably the process kit parts also exhibit low coefficients of thermal expansion at temperatures near and less than the Curie temperature; and/or a Curie temperature near the operating temperature of the process. It is understood that the transition from a low coefficient of thermal expansion to a high coefficient of thermal expansion and the transition from magnetic to non-magnetic occurs gradually over a range of temperatures. Likewise it is understood that a process may operate effectively over a range of temperatures. Accordingly as used herein a value described as near another value means within the range of ^' possible values which achieve the desired characteristics (e.g., low thermal coefficient of expansion, low magnetic field levels, desired process performance - conformal deposition layers) .

Generally for sputtering processes, ferromagnetic materials exhibit these desired characteristics. For conventional sputtering deposition of titanium and titanium- nitride, the percentages of alloy components can be controlled to achieve the desired Curie temperature and the desired coefficient of thermal expansion. For example, the Curie temperature and the coefficient of thermal expansion for a nickel-iron alloy increases as the nickel content increases above 36% and the magnetic properties of a nickel- iron alloy increase as the nickel content decreases below 32%. Thus, the preferred nickel content for a nickel-iron alloy is between 32% and 36%.

The alloys listed in the chart below, all manufactured by the Carpenter Steel Division of Carpenter Technology Corporation, are examples of alloys that are well suited for use in sputtering deposition when deposition is performed in accordance with the present invention. The linear coefficients of expansion over a given temperature range, and the Curie temperatures exemplify the range of values available, and the ability to select a material having a coefficient of expansion and a Curie temperature that corresponds to the process requirements.

According to the present invention one or more magnetic process kit parts are provided for use within a process that, in the absence of the present invention, would be adversely affected by the process kit parts' magnetic properties. Each process kit part is heated to a temperature near or greater than the process kit part's Curie temperature prior to production processing, and is maintained at a temperature near or greater than the process kit part's Curie temperature during processing. A temperature near the process kit part' s Curie temperature is preferred in order to maintain a low coefficient of thermal expansion .

Consider, for example, the sputtering chamber 11 of FIG. 1 configured for titanium-nitride/titanium deposition at 435°C, wherein the clamp ring 23 is comprised of KOVAR™, a ferromagnetic material having a Curie temperature of 435°C and a low coefficient of thermal expansion at temperatures near and below the Curie temperature. Further, KOVAR' s™ coefficient of thermal expansion is very similar to those of titanium-nitride and titanium. Accordingly, and the KOVAR™ clamp ring and the titanium-nitride/titanium deposited on the KOVAR™ clamp ring will expand and contract at similar rates and less particle generation will occur. When the sputtering chamber 11 idles, the sputtering chamber 11 and the KOVAR™ clamp ring 11 cool to a temperature below the 435°C process temperature. At temperatures below the 435°C Curie temperature (in this example also the desired process temperature) the KOVAR™ clamp ring 23 exhibits magnetic properties. As the temperature of the KOVAR™ clamp ring 11 decreases below the Curie temperature, the magnetic properties exhibited by the KOVAR™ clamp ring 11 increase. Accordingly it is preferred that the KOVAR™ clamp ring 23 be heated to within 50-100°C of the Curie temperature, and preferably to 435°C (in this example both the Curie temperature and the process temperature) before deposition of production parts begins. Preferably, to heat the clamp ring 23 to 435°C a pasting layer of titanium is deposited on the shutter disk 27. Specifically, the shutter disk 27 is rotated to the closed position, a voltage is applied between the enclosure wall 13 and the target 21, and a gas is flowed into the sputtering chamber 11 where it is ionized under the influence of an electric field formed between the enclosure wall 13 and the target 21. The electric field further causes the gas ions to impact the surface of the target 21. As the ions impact the target 21, kinetic energy from the ions is transferred to the target 21, heating the target 21 and causing target material to sputter. The sputtered target material deposits on the closed shutter disk 27 and on other chamber surfaces located above the shutter disk 27, including the KOVAR™ clamp ring 23. Heat is conducted from the deposited target material to the surfaces on which it deposits. A combination of conductive and radiative heating causes the surfaces within the sputtering chamber 11, including the surfaces of the KOVAR™ clamp ring 23, to heat to 435°C. Additionally, heat may be provided to the KOVAR™ clamp ring 23 via conventional methods such as through a heated pedestal or through infrared lamps or the like.

After the KOVAR™ clamp ring 23 reaches 435°C the flow of gas ceases, the shutter disk 27 is rotated to the ^■ open position, the flow of gas resumes and alternating layers of titanium and titanium-nitride are deposited on the substrate 25, and on other surfaces within the sputtering chamber 11. When a sufficient layer of material has been deposited on the substrate 25, the gas flow is stopped, the chamber is pumped down to a sufficient vacuum level, and the substrate 25 is extracted. A subsequent substrate 25a (not shown) is mounted on the substrate support 19 and clamped by the KOVAR™ clamp ring 23. Typically, between sequential depositions the temperature of the KOVAR™ clamp ring 23 will remain sufficiently near its Curie temperature so as not to exhibit magnetic properties that will interfere with the deposition process. If so, deposition may proceed without again depositing layers on the shutter disk 27.

In the event that a given magnetic part would cause irregular target erosion or other deleterious effects during sputter deposition on the shutter disk 27, the magnetic process kit part can be heated to its Curie temperature in the absence of sputtering, via alternative heating mechanisms either internal or external to the process chamber.

Prior to the present invention, parts made of magnetic materials could not be used in sputtering deposition chambers because the magnetic properties exhibited by such parts would adversely affect the deposition process, interfering with the transportation of plasma ions to the target and interfering with the transportation of target material to the substrate. Semiconductor fabrication applications were limited to the use of non-magnetic materials having low coefficients of thermal expansion. A significant disadvantage of these nonmagnetic parts is the elaborate cleaning processes they often require. The wider range of material made available by the present invention enables a material to be specifically chosen so as to provide favorable etch ^• properties with respect to the deposition material and to provide sufficient correlation between the material's Curie temperature and the process temperature.

For example, deposited titanium-nitride/titanium layers may be easily cleaned from the KOVAR™ clamp ring 23 by the following simple process: 1. Soaking the KOVAR™ parts in a solution of potassium hydroxide, hydrogen peroxide and water at a ratio of 1:10:20 by weight and ensuring that the solution stays below 27°C (80°F); 2. Adding to the solution a mixture of hydrogen peroxide, ammonium hydroxide, and deionized (>2 Mohm-cm) water in the ratio of 7:1:8; 3. Immersing the part in the solution until all Titanium-containing deposits are gone; 4. If some residue from the sputter-deposition metal remains after the etch, dipping the part in cold tap water and then removing the residue using an abrasive pad;

5. Rinsing with cold deionized (>8 Mohm-cm) water for 1 minute;

6. Rinsing in hot (40°C/104°F) deionized (>2 Mohm-cm) water for 2-3 minutes;

7. Blow-drying the part with 0.1-micron filtered dry nitrogen; and, if the part is streaked, repeating steps 5 and 6.

Accordingly the present invention allows a material to be selected for use in a given process, based on the material's etch properties. Process kit parts therefore may undergo significantly simplified cleaning procedures as exemplified by the process described above.

The foregoing description discloses only the preferred- embodiments of the invention, modifications which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, although as described above, the process kit parts of the present invention are preferably made of a magnetic material, the invention is not limited thereto. In accordance with the principles of the present invention, any portion of a processing apparatus may be made of a magnetic material, provided the magnetic material is heated to a temperature near or greater than its Curie temperature before processing begins, and is maintained at a temperature near or greater than its Curie temperature during processing. The methods of heating the part to its Curie temperature are not limited to sputtering deposition on the shield of the process chamber, but may alternatively include sputter depositing on a number of dummy (i.e., non- production) substrates (e.g. when the shutter disk is omitted or is in the open position as shown in FIG. IB.) . It should be noted in some configurations, the material of the process kit parts may heat considerably more efficiently than does the wafer. In such configurations a process kit part material should be chosen that has a correspondingly higher Curie temperature.

The invention applies equally to apparatuses that are not composed entirely of a magnetic material such as apparatuses made of composite materials which include magnetic materials or apparatuses coated with magnetic materials, provided the net effect is to produce deleterious magnetic properties only at temperatures less than the Curie temperature .

Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.

Claims

The Invention Claimed Is:

1. A method for treating an apparatus having a magnetic property for use in a first process adversely affected by said magnetic property, said method comprising: providing an apparatus comprised of a first material having said magnetic property; heating the apparatus to within a temperature range in which the magnetic property is sufficiently diminished so as not to adversely affect the first process; and maintaining the apparatus within said temperature range during the first process.

2. The method of claim 1 wherein heating the apparatus further comprises heating the apparatus to a Curie temperature of the apparatus .

3. The method of claim 1 wherein a processing temperature of the first process is near said temperature range.

4. The method of claim 1 wherein heating the apparatus further comprises placing the apparatus within a chamber for performing the first process and performing the first process on an object other than the apparatus until the apparatus is heated to within said temperature range.

5. The method of claim 1 wherein heating the apparatus further comprises placing the apparatus within a chamber for performing the first process and performing the first ' process on dummy substrates until the apparatus is heated to within said temperature range.

6. The method of claim 1 wherein heating the apparatus further comprises placing the apparatus within a chamber for performing the first process and performing the first process on a shield until the apparatus is heated to within said temperature range.

7. The method of claim 5 wherein performing the first process on the dummy substrates comprises depositing alternating layers of titanium-nitride and titanium.

8. The method of claim 6 wherein performing the first process on the shield comprises depositing alternating layers of titanium-nitride and titanium.

9. The method of claim 1 wherein the apparatus has a low coefficient of thermal expansion at temperatures near said temperature range and less than said temperature range.

10. The method of claim 1 further comprising: performing the first process; and etching the apparatus after performing the first process to selectively remove a material deposited on the apparatus during the first process.

11. The method of claim 1 wherein the apparatus is ferromagnetic .

12. The method of claim 10 wherein the apparatus comprises "KOVAR."

13. The method of claim 10 wherein the apparatus comprises "INVAR." ^'

14. The method of claim 12 wherein etching the apparatus further comprises removing titanium from the apparatus.

15. The method of claim 1 wherein the apparatus has a Curie temperature near an operating temperature of the first process and has a low coefficient of thermal expansion at temperatures near the Curie temperature.

16. A process for depositing layers on an object comprising: providing a magnetic process kit part; heating the magnetic process kit part to within a temperature range in which the magnetic property is sufficiently diminished so as not to adversely affect the depositing process; maintaining the magnetic process kit part within the temperature range during the depositing process; and depositing layers on the object.

17. The process of claim 16 wherein heating the magnetic process kit part comprises placing the magnetic process kit part within a chamber for depositing layers on the object and depositing layers on a dummy object until the magnetic process kit part is heated to within said temperature range.

18. The process of claim 16 wherein heating the magnetic process kit part comprises placing the magnetic process kit part within a chamber for depositing layers on the object and depositing layers on a shield of the chamber until the magnetic process kit part is heated to within said temperature range.

19. The process of claim 16 wherein heating the magnetic process kit part comprises placing the magnetic process kit ' part within a chamber for depositing layers on the object and depositing layers on the magnetic process kit part until the magnetic process kit part is heated to within said temperature range .

20. The process of claim 16 wherein the magnetic process kit part has a low coefficient of thermal expansion at temperatures near the temperature range and at temperatures below the temperature range.

21. The process of claim 16 wherein the magnetic process kit part has a Curie temperature near a depositing temperature at which the layers are deposited, and has a low coefficient of thermal expansion at temperatures near the Curie temperature and below the Curie temperature.

22. The process of claim 16 further comprising etching the magnetic process kit part to selectively remove a material deposited on the process kit part during said depositing layers on the object.

23. An object having layers deposited thereon in accordance with the process of claim 16.

24. A process kit for use in a semiconductor device fabrication process having a process temperature, comprising : at least one magnetic part having a Curie temperature in the range of temperatures equal to and below the process temperature.