US20110089166A1 - Temperature measurement and control of wafer support in thermal processing chamber - Google Patents

Abstract

The present invention provides apparatus and methods for achieving uniform heating to a substrate during a rapid thermal process. More particularly, the present invention provides apparatus and methods for controlling the temperature of an edge ring supporting a substrate during a rapid thermal process to improve temperature uniformity across the substrate.

Description

CROSS REFERENCE TO RELATED PATENT APPLICATIONS
• Field of the Invention
• This application is a divisional application of co-pending U.S. patent application Ser. No. 11/623,238, filed Jan. 15, 2007, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention generally relates to the field of semiconductor processing. More particularly, the present invention relates to methods and apparatus for thermally processing a semiconductor substrate.
• 2. Description of the Related Art
• Rapid thermal processing (RTP) is a process for annealing substrates during semiconductor processing. During RTP, thermal radiation is generally used to rapidly heat a substrate in a controlled environment to a maximum temperature of up to about 1350° C. This maximum temperature is maintained for a specific amount of time ranging from less than one second to several minutes depending on the process. The substrate is then cooled to room temperature for further processing. High intensity tungsten halogen lamps are commonly used as the source of heat radiation. The substrate may be provided additional heat by a heated susceptor conductively coupled to the substrate.
• The semiconductor fabrication process has several applications of RTP. Such applications include thermal oxidation, high temperature soak anneal, low temperature soak anneal, and spike anneal. In thermal oxidation, a substrate is heated in oxygen, ozone, or a combination of oxygen and hydrogen which causes silicon substrate to oxidize to form silicon oxide. In high temperature soak anneal, a substrate is exposed to different gas mixtures such as nitrogen, ammonia, or oxygen. Low temperature soak anneal is generally used to anneal substrate deposited with metal. Spike anneal is used when the substrate needs to be exposed to high temperature for a very short time. During a spike anneal, the substrate is rapidly heated to a maximum temperature sufficient to activate dopant and cooled rapidly to end the activation process prior to substantial diffusion of the dopant.
• RTP usually requires a substantially uniform temperature profile across the substrate. In the state of the art process, the temperature uniformity may be improved by controlling heat sources, such as a laser, an array of lamps, configured to heat the substrate on the front side while a reflective surface on the back side reflects heat back to the substrate. Emissivity measurement and compensation methodology have been used to improve the temperature gradient across the substrate.
• As the semiconductor industry develops, the requirement for temperature uniformity during a RTP also increases. In some processes, it is important to have substantially small temperature gradient from about 2 mm inside the edge of the substrate. Particularly, it may be necessary to heat a substrate at a temperature between about 200° C. to about 1350° C. with a temperature deviation of about 1° C. to 1.5° C. The state of the art RTP systems have difficulties to reach this kind of uniformity, especially near the edge of the substrate. In a RTP system, an edge ring is usually used to support a substrate near the periphery. The edge ring and the substrate overlap producing a complicated heating situation near the edge of the substrate. In one aspect, the substrate may have different thermal properties near the edge. This is mostly pronounced for a patterned substrate, or for a silicon-on isulator—(SOI) substrate. In another aspect, the substrate and the edge ring overlap near the edge, it is difficult to achieve uniform temperature profile near the edge by measuring and adjusting the temperature of the substrate alone. Depending on the edge ring's thermal properties relative to the substrate's thermal and optical properties, the temperature profile of a substrate is generally either edge high or edge low.
• FIG. 1 schematically illustrates two types of common temperature profiles of a substrate processed in a RTP chamber. The vertical axis denotes measured temperatures on a substrate. The horizontal axis denotes the distance from the edge of the substrate.Profile1 is an edge high profile where the edge of the substrate has the highest temperature measurement.Profile1 is an edge low profile where the edge of the substrate has the lowest temperature measurement. It is difficult to remove temperature deviation near the edge of the substrate in the state of the art RTP systems.
• Therefore, there is a need for apparatus and methods used in RTP for improved temperature uniformity.
SUMMARY OF THE INVENTION
• The present invention generally provides apparatus and methods for achieving uniform heating to a substrate during a rapid thermal process.
• One embodiment of the present invention provides a chamber for processing a substrate comprising a chamber enclosure defining a processing volume, a substrate support disposed in the processing volume, an edge ring disposed on the substrate support, the edge ring is configured to support the substrate on a periphery of the substrate, a first heat source configured to heat the substrate, and a second heat source configured to heat the edge ring, wherein the second heat source is independently controllable from the first heat source.
• Another embodiment of the present invention provides a rapid thermal processing chamber comprising a chamber body defining a chamber volume, a temperature controlled edge ring disposed in the chamber volume, wherein the temperature controlled edge ring is configured to thermally coupled with a substrate being processed near a periphery of the substrate, a first heat source configured for primarily heating a surface of the substrate, and a second heat source configured for primarily heating the temperature controlled edge ring.
• Yet another embodiment of the present invention provides a method for uniformly heating a substrate to a target temperature comprising positioning the substrate in a processing chamber connected with a first heat source, thermally coupling a periphery of the substrate to an edge ring, heating a surface of the substrate with the first heat source, and maintaining the edge ring at a ring temperature differs from the target temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
• So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
• FIG. 1 schematically illustrates two types of common temperature profiles of a substrate processed in a RTP chamber.
• FIG. 2 schematically illustrates a sectional view of a rapid thermal processing system in accordance with one embodiment of the present invention.
• FIG. 3 schematically illustrates a sectional view of a rapid thermal processing system in accordance with another embodiment of the present invention.
• FIG. 4 schematically illustrates a sectional view of an edge ring in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION
• The present invention provides apparatus and methods for achieving uniform heating to a substrate during a rapid thermal process. More particularly, the present invention provides apparatus and methods for controlling the temperature of an edge ring supporting a substrate during a rapid thermal process to improve temperature uniformity across the substrate.
• FIG. 2 schematically illustrates a sectional view of a rapidthermal processing system10 in accordance with one embodiment of the present invention. The rapidthermal processing system10 comprises achamber body35 defining aprocessing volume14 configured for annealing a disk-shaped substrate12 therein. Thechamber body35 may be made of stainless steel and may be lined with quartz. Theprocessing volume14 is configured to be radiantly heated by aheating assembly16 disposed on aquartz window18 of the rapidthermal processing system10. In one embodiment, thequartz window18 may be water cooled.
• Aslit valve30 may be formed on a side of thechamber body35 providing a passage for thesubstrate12 to theprocessing volume14. Agas inlet44 may be connected to agas source45 to provide processing gases, purge gases and/or cleaning gases to theprocessing volume14. Avacuum pump55 may be fluidly connected to theprocessing volume14 through anoutlet54 for pumping out theprocessing volume14.
• Acircular channel22 is formed near the bottom of thechamber body35. Amagnetic rotor21 is disposed in thecircular channel22. Atubular riser39 rests on or otherwise coupled to themagnetic rotor21. Thesubstrate12 is supported by a peripheral edge by anedge ring20 disposed on thetubular riser39. Amagnetic stator23 is located externally of themagnetic rotor21 and is magnetically coupled through thechamber body35 to induce rotation of themagnetic rotor21 and hence of theedge ring20 and thesubstrate12 supported thereon. Themagnetic stator23 may be also configured to adjust the elevations of themagnetic rotor21, thus lifting thesubstrate12 being processed. Additional magnetic rotation and levitation information is available in the U.S. Pat. No. 6,800,833, which is hereby incorporated by reference.
• Thechamber body35 may include areflector plate27 near the back side of thesubstrate12. Thereflector plate27 has an opticalreflective surface28 facing the back side of thesubstrate12 to enhance the emissivity of thesubstrate12. In one embodiment, thereflector plate27 may be water cooled. Thereflective surface28 and the back side of thesubstrate12 define areflective cavity15. In one embodiment, thereflector plate27 has a diameter slightly larger than the diameter of thesubstrate12 being processed. For example, if the rapidthermal processing system10 is configured to process 12 inch substrates, the diameter of thereflector plate27 may be about 13 inches.
• A purge gas may be provided to thereflector plate27 through apurge gas inlet48 connected to apurge gas source46. The purge gas ejected to thereflector plate27 helps cooling of thereflector plate27 especially near theapertures25 where heat is not reflected back to thesubstrate12.
• In one embodiment, anouter ring19 may be coupled between thechamber body35 and theedge ring20 to separate thereflective cavity15 from theprocessing volume14. Thereflective cavity15 and theprocessing volume14 may have different environments.
• Theheating assembly16 may comprise an array ofheating elements37. The array ofheating elements37 may be UV lamps, halogen lamps, laser diodes, resistive heaters, microwave powered heaters, light emitting diodes (LEDs), or any other suitable heating elements both singly or in combination. The array ofheating elements37 may be disposed in vertical holes formed in areflector body53. In one embodiment, theheating elements37 may be arranged in a hexagon pattern. A coolingchannel40 may be formed in thereflector body53. A coolant, such as water, may enter thereflector body53 from aninlet41, travel adjacent the vertical holes cooling the array ofheating elements37, and exit the reflector body from anexit42.
• The array ofheating elements37 are connected to acontroller52 which are capable of adjusting heating effects of the array ofheating elements37. In one embodiment, the array ofheating elements37 may be divided into a plurality of heating groups to heat thesubstrate12 by multiple concentric zones. Each heating group may be controlled independently to provide desired temperature profile across a radius of thesubstrate12. Detailed descriptions of theheating assembly16 may be found in U.S. Pat. No. 6,350,964 and No. 6,927,169, which are hereby incorporated by reference.
• In one embodiment, an edgering heating assembly38 configured primarily to heat theedge ring20 may be disposed outside the array ofheating elements37. The edgering heating assembly38 is connected to thecontroller52 which may adjust the heating power of the edgering heating assembly38. The edgering heating assembly38 is independently controllable from the array ofheating elements37, hence controlling the temperature of theedge ring20 independently from the temperature of thesubstrate12. In one embodiment, the edgering heating assembly38 may be one of the heating groups of the array ofheating elements37.
• The rapidthermal processing system10 further comprise a plurality ofthermal probes24 configured to measure thermal properties of thesubstrate12 at different radial locations. In one embodiment, the plurality ofthermal probes24 may be a plurality of pyrometers optically coupled to and disposed in a plurality ofapertures25 formed in thereflector plate27 to detect a temperature or other thermal properties of a different radial portion of thesubstrate12. Detailed description of similar temperature probes may be found in the U.S. Pat. No. 5,755,511, which is hereby incorporated by reference. The plurality of temperature probes24 is connected with thecontroller52 which may conduct a closed loop control to adjust the power supplies to the array ofheating elements37 to provide a tailored radial thermal profile across thesubstrate12.
• The rapidthermal processing system10 further comprises an edge ringthermal probe31 coupled to and disposed in anaperture32 on thereflector plate27 near theedge ring20. The edge ringthermal probe31 may be a pyrometer configured to measure a temperature or other thermal properties of theedge ring20. The edge ringthermal probe31 is connected with thecontroller52 which is connected to the edgering heating assembly38. Thecontroller52 may conduct a closed loop control to the edgering heating assembly38 using the measurement from the edge ringthermal probe31. In one embodiment, theedge ring20 may be heated to a desired temperature independently from thesubstrate12 during a thermal process.
• Agas jet47 may be disposed near theedge ring20 for cooling theedge ring20. In one embodiment, thegas jet47 may share the samepurge gas source46 with thepurge gas inlet48. Thegas jet47 may be directed to theedge ring20 and ejecting a cooling gas, such as helium, to cool theedge ring20. Thegas jet47 may be connected to thegas source46 through avalve49 which may be controlled by thecontroller52. Thecontroller52, therefore, may include the cooling effect of thegas jet47 in the closed looped temperature control of theedge ring20.
• Theedge ring20 may be designed to have thermal properties, such as thermal mass, emissivity and absorptivity, according to the thermal properties of thesubstrate12 being processed to improve substrate temperature profile. The thermal properties of theedge ring20 may be altered by choosing different materials, different thicknesses and different coatings. A detailed description of edge ring design may be found in the U.S. Pat. No. 7,127,367 (Attorney Docket No. 008504), which is hereby incorporated by reference. In one embodiment, theedge ring20 may be made from silicon with a nickel coating.
• During a rapid thermal process, thesubstrate12 may be transferred to theprocessing volume14 through theslit valve30 and supported by theedge ring20. Themagnetic rotor21 may rotate thesubstrate12 and position thesubstrate12 in a desired elevation. During most processes, the objective is to rapidly heat thesubstrate12 uniformly to a target temperature. In one embodiment of the present invention, heat transfer to thesubstrate12 mainly comes from radiation of the array ofheating elements37 and conduction and/or radiation from theedge ring20 which is heated in a desired temperature. A uniform temperature profile across thesubstrate12 may be achieved by controlling the array ofheating elements37 and by keeping theedge ring20 at the desired temperature which is usually different than the target temperature for thesubstrate12.
• Controlling the array ofheating element37 may be conducted by measuring the temperature of thesubstrate12 across a radius using the plurality ofthermal probes24. In one embodiment, the plurality ofthermal probes24 may be evenly distributed across thereflector plate27 corresponding to a radius of thesubstrate12. The measured temperatures from the plurality ofthermal probes24 are sampled by thecontroller52. Thecontroller52 may used the measured temperatures to adjust the array ofheating elements37 so that the temperature across a radius of thesubstrate12 becoming uniform. In one embodiment, thecontroller52 may adjust the array ofheating elements37 by a plurality of concentric zones. Detailed descriptions of controlling heating elements by multiple zones may be found in U.S. Pat. No. 5,755,511 and U.S. patent application Ser. No. 11/195,395, published as U.S. Patent Application Publication No. 2006/0066193 (Attorney Docket No. 009150), which are hereby incorporated by reference.
• In one embodiment, heat exchange between theedge ring20 and a periphery of thesubstrate12 is used to adjust the temperature profile near the edge of thesubstrate12. Heat exchange may be achieved by conduction and/or radiation between thesubstrate12 and theedge ring20. In one embodiment, heat exchange may be conducted by heating theedge ring20 to a temperature different from the target temperature of thesubstrate12.
• In one embodiment, a desired temperature may be predetermined for theedge ring20 according to process requirements and thermal properties of both theedge ring20 and thesubstrate12. In one embodiment, the predetermined desired temperature of theedge ring20 may be about 10° C. to about 15° C. different from the target temperature of thesubstrate12. In one embodiment, the predetermined desired temperature of theedge ring20 may be higher than the target temperature of thesubstrate12. In another embodiment, the predetermined desired temperature of theedge ring20 may be lower than the target temperature of thesubstrate12. The desired edge ring temperature may be determined from either heat transfer modeling (conductive, radiative, convective) or from experimental results. In either case, the optical properties of the substrate and/or the edge ring are varied and the temperature uniformity of the wafer is measured. the results of these experiments lead to prediction of the desired temperature profile for the edge ring to achieve the best uniformity on the substrate.
• In another embodiment, the desired temperature for theedge ring20 may be dynamic and adjustable according to the in-situ thermal measurements of thesubstrate12 and theedge ring20.
• Heating theedge ring20 may be achieved primarily by using the edgering heating assembly38. A closed loop control may be achieved by thecontroller52 by adjusting the temperature of theedge ring20 from the measurement of the edge ringthermal probe31. Adjustment of the temperature of theedge ring20 may be achieved by adjusting the power supply of the edgering heating assembly38 and/or flow rate of the cooling gas from thegas jet47. In one embodiment, theedge ring20 may be over heated and then cooled down to a desired temperature with cooling gas from thegas jet47.
• In one embodiment of the present invention, the cooling gas for thegas jet47 may be used to cool theedge ring20 to between about 100° C. and about 200° C. after processing one substrate and prior to the entry of the next substrate.
• The method of the present invention can provide less than 2° C., 3 sigma temperature uniformity for spike annealing. The method of the present invention provide less than 1° C., 3 sigma temperature uniformity for high temperature soak annealing up to 1350° C. In one embodiment, the method of the present invention can heat a substrate at a temperature between about 200° C. to about 1350° C. with a temperature deviation of about 1° C. to about 1.5° C.
• The edgering heating element38 of the rapidthermal processing system10 is illustrated as a plurality of heating lamps. Other suitable heating device, such as for example solid state heaters (i.e., LEDs), laser heaters, inductive heaters, and microwave heaters, electrical heaters (e.g., resistive heating) can be used in the rapid thermal processing systems of the present invention.
• Additionally, the edge ring heating element may be positioned in other suitable locations, such as underneath the edge ring, on a side of the edge ring.FIG. 3 schematically illustrates a sectional view of a rapidthermal processing system100 having an edgering heating element51 positioned below theedge ring20.
• In another embodiment, a substrate may be heated from a backside during thermal processing. An exemplary backside heating chamber may comprise an edge ring for supporting the substrate by a periphery with a frontside (the production side) facing up. An array of heating elements, similar to theheating elements37, may be positioned underneath the edge ring so that the substrate can be heated from the backside. A plurality of probes may be positioned across the radius of the substrate above the edge ring to measure a temperature profile of the substrate during thermal processing. An edge ring heater dedicated to independently heat the edge ring may be positioned near the edge ring, underneath the edge ring, above the edge ring, or on a side of the edge ring. An edge ring probe may be positioned adjacent the edge ring configured to measure the temperature of the edge ring. A controller may be connected to the edge ring heater, the edge ring probe, the array of heating elements and the plurality of probes to control the temperature profile of the substrate and the temperature of the edge ring in-situ.
• FIG. 4 schematically illustrates a sectional view of anedge ring110 in accordance with one embodiment of the present invention. Theedge ring110 has aslant lip111 configured to support thesubstrate12. Theedge ring110 is designed to reduce the contact area with thesubstrate12. By reducing the contact area between thesubstrate12 and theedge ring110, the heating condition near the edge of thesubstrate12 may be simplified and edge high/low effect may be reduced. Additionally, reducing contact area also reduces particle contamination in the processing chamber.
• Although the above discussion is focused on achieving uniform temperature profile across a substrate, a non-uniform temperature profile could also be achieved using the apparatus and methods of the present invention.
• While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims (20)

1. A rapid thermal processing chamber, comprising:

a chamber body defining a chamber volume;

an edge ring to thermally couple to a substrate to be processed in the chamber, wherein the edge ring is disposed in the chamber volume;

a first heat source to heat a surface of the substrate; and

a second heat source to heat the edge ring.

2. The rapid thermal processing chamber ofclaim 1, further comprising a thermal probe to measure at least one thermal property of the edge ring.

3. The rapid thermal processing chamber ofclaim 2, further comprising a cooling device to reduce the temperature of the edge ring.

4. The rapid thermal processing chamber ofclaim 1, wherein the first and second heat sources together comprise a lamp assembly to radiantly heat the chamber volume, and the lamp assembly has independently temperature controllable zones.

5. The rapid thermal processing chamber ofclaim 1, wherein the first heat source and second heat source are disposed on opposite sides of the edge ring.

6. The rapid thermal processing chamber ofclaim 1, wherein the second heat source is one of a radiant heater, a conductive heat source, a resistive heater, an inductive heater, and a microwave heater.

7. A method for uniformly heating a substrate to a target temperature, comprising:

positioning the substrate in a processing chamber, wherein the processing chamber is connected with a first heat source;

thermally coupling a periphery of the substrate to an edge ring;

heating a surface of the substrate with the first heat source; and

maintaining the edge ring at a first temperature, wherein the first temperature differs from the target temperature.

8. The method ofclaim 7, further wherein maintaining the edge ring at the first temperature comprising heating the edge ring with a second heat source, wherein the first and second heat sources are independently controllable.

9. The method ofclaim 8, wherein the first and second heat sources together comprise a lamp assembly having independently controllable zones.

10. The method ofclaim 8, further comprising cooling the edge ring using a purge gas.

11. The method ofclaim 8, further comprising:

measuring a temperature of the edge ring using a thermal probe to determine a measured temperature; and

adjusting the second heat source according to the measured temperature.

12. The method ofclaim 7, wherein the first temperature differs from the target temperature for about 10° C. to about 15° C.

13. The method ofclaim 7, wherein the first temperature is higher than the target temperature.

14. The method ofclaim 7, wherein the first temperature is lower than the target temperature.

15. A rapid thermal processing chamber, comprising:

a chamber body defining a processing volume;

a substrate support mechanism disposed in the processing volume;

an edge ring disposed on the substrate support mechanism, wherein the edge ring supports a substrate being processed by a peripheral edge of the substrate, and heat exchange between the edge ring and the peripheral edge of the substrate adjusts a temperature profile of the substrate near the peripheral edge;

a first heat source to rapidly heat the substrate disposed on the edge ring; and

a second heat source to heat the edge ring at a temperature different from a temperature of the substrate.

16. The rapid thermal processing chamber ofclaim 15, wherein the first heat source comprises an array of heating elements.

17. The rapid thermal processing chamber ofclaim 16, wherein the first heat source and the second heat source are disposed on opposite sides of the substrate.

18. The rapid thermal processing chamber ofclaim 17, wherein the second heat source comprises one or more laser heaters.

19. The rapid thermal processing chamber ofclaim 16, wherein the array of heating elements are lamps disposed outside the chamber body and configured to provide thermal energy through a quartz window of the chamber body, and the second heat source comprises a plurality of lamps disposed radially outwards of the first heat source.

20. The rapid thermal processing chamber ofclaim 15, further comprising:

a cooling device to reduce to temperature of the edge ring.

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