APPARATUS AND METHODS FOR MANAGING THE TEMPERATURE QF A SUBSTRATE IN A HIGH VACUUM PROCESSING SYSTEM

Field of the Invention

[0001] The invention relates generally to high vacuum processing systems and methods and, in particular, to apparatus and methods for controlling a temperature of a supported member, such as a substrate or one or more substrates supported on a pallet, during ion beam processing in a high vacuum processing system.

Background of the Invention

[0002] Substrates are supported in vacuum chambers of high vacuum processing systems for treatment by processes such as ion beam etching, reactive ion etching, and plasma etching that remove a material layer from the substrates, processes such as ion beam deposition, physical vapor deposition, and chemical vapor deposition that deposit a material layer on the substrates, and other processes that modify a substrate surface property. In such surface treatment processes, the substrate rests on, or is secured to, a substrate support fixture, such as a platen, a chuck, or an electrode. During processing, a large amount of thermal energy is being transferred to the processed substrate, particularly in ion beam etch systems. At the same time, the processed substrate must be kept at, or below certain temperature levels. Therefore, the thermal energy must be transported from the substrate support fixture and dumped outside of the system. Therefore, the overall product throughput of the system is significantly limited by the cooling capacity of the support fixture. Beam-induced heating restricts the maximum etch rate that can be obtained for temperature-sensitive substrate materials, such as substrates fabricated from a polymer or organic resists coating a substrate.

[0003] The fabrication of thin film magnetic heads for magnetic storage devices requires high rate, high precision ion beam etching processes. Other processes, such as reactive ion etching, for forming thin film magnetic heads are tolerant of considerably higher etch rates than ion beam etching, but lack the precision of ion beam etching processes. Although the development of ion beam etching systems with higher achievable etch rates may have significant

commercial importance, substrate cooling must be improved to accommodate the higher etching rates.

[0004] Heat conduction between a substrate and a conventional substrate holding fixture using backside heat transfer gas cooling is relatively inefficient in a near vacuum or other low pressure environment quite difficult because heat does not transfer well at these pressures. For example, the conduction of heat between coextensive surfaces of a substrate fixture and the substrate is slow and inefficient because actual contact on an atomic scale between the surfaces is limited to a small fraction of the coextensive contacting areas. Gaps that separate the remaining surface areas prohibit conduction.

[0005] In addition to adequate heat transfer, the substrate holding fixture must also easily clamp and release the substrate without damaging or contaminating the substrate and a high vacuum seal must be maintained between a sealing media and the vacuum chamber while the substrate is clamped to restrict escape of the heat transfer gas. The lack of heat transfer efficiency can be compensated by reducing the temperature of the substrate holding fixture to a much lower value than required at the substrate. Substrate holding fixtures may be cooled by circulating a chilled thermally conductive liquid, such as pure chilled water introduced at a temperature just above the liquid's freezing point, through narrow flow passages in the substrate fixture.

[0006] Despite the cooperation of these cooling techniques, conventional substrate fixtures cannot prevent substrate temperatures from being significantly elevated during a high power ion beam etching process. Many temperature-sensitive materials may be damaged at temperatures exceeding about 70 ⁰ C. Consequently, the current of the impinging ion beam may be limited by the ability to cool the substrate when executing an ion beam etching process. Lower substrate temperatures may be obtained by adding a common freezing-point additive, such as ethylene glycol or propylene glycol, to the thermally conductive liquid. However, use of these freezing-point additives greatly increases the viscosity of the circulated liquid, which decreases the ability to flow the thermally conductive liquid through the narrow flow passages in the substrate fixture.

[0007] A different, but related, substrate temperature control problem is that the etch rate of certain materials, such as gallium nitride, is very temperature sensitive. As a result, the

substrate temperature must be carefully controlled during ion beam etching processes for controlling the etch rate. In particular, the substrate temperature should be controlled to within a few degrees Celsius during the etch process and between different runs processing different substrates or groups of substrates. This level of temperature control is difficult to achieve using gas-assisted cooling because the substrate temperature cannot be precisely raised or lowered in correlation with variations in the process.

[0008] What is needed, therefore, are apparatus and methods improving the control of substrate temperature in high vacuum processing systems, such as ion beam etch (IBE) systems, that overcome these and other disadvantages of conventional thermally-controlled substrate fixtures used in high vacuum processing equipment and conventional methods for controlling the temperature of substrate fixtures.

Summary of the Invention

[0009] The present invention is directed generally to apparatus and methods for improving the control of the temperature of a supported member, such as a substrate or a pallet carrying one or more substrates, in high vacuum processing systems, such as ion beam etch (IBE) systems. In accordance with an embodiment of the invention, an apparatus is provided for controlling the temperature of a supported member exposed to a treatment that heats the substrate. The apparatus comprises a first member having a surface configured to support the supported member and a second member coupled with the first member. The first member receives heat from the supported member transferred to the surface and the second member includes a channel configured for a flow of a temperature control liquid. A supply passageway extends through the first and second members to communicate with a heat transfer gas space defined between the surface of the first member and the supported member. Thermoelectric devices are disposed between the first and second members. Each of the thermoelectric devices has a first side contacting the first member proximate to the surface and a second side contacting the second member proximate to the liquid-carrying channel. The thermoelectric devices transfer heat between the first and second sides to regulate the temperature of the first member and, thereby, the temperature of the supported member.

[0010] In accordance with another embodiment of the invention, a method for controlling the temperature of a supported member comprises exposing the supported member to an ion beam that heats the supported member, transferring heat from the supported member with a backside gas in a heat transfer gas space between a backside of the substrate and a surface of a support member. The method further comprises cooling the support surface with a plurality of thermoelectric devices that transfer the heat from the support member to a heat transfer member and cooling the heat transfer member with a flow of a thermally conductive liquid.

Brief Description of the Drawings

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0012] FIG. 1 is a cross-sectional view of a portion of a high vacuum processing system incorporating a substrate fixture in accordance with an embodiment of the invention. [0013] FIG. 2 is a top perspective view of a cap plate and a heat exchange plate of the substrate fixture of FIG. 1 shown disassembled for clarity.

[0014] FIG. 3 is a bottom perspective view of the cap plate and heat exchange plate of the substrate fixture of FIG. 1 shown disassembled for clarity.

[0015] FIG. 4 is a bottom view of the heat exchange plate of FIGS. 2 and 3 shown with the thermoelectric coolers present.

[0016] FIG. 5 is a bottom view of the cap plate of FIGS. 2 and 3.

[0017] FIG. 6 is a top perspective view of the substrate fixture of Fig. 1.

[0018] FIG. 7 is a top view of the substrate fixture of FIG. 6 in which the substrate- supporting pallet is omitted for clarity.

[0019] FIG. 8 is a cross-sectional view taken generally along line 8-8 in FIG. 7 and in which the substrate-supporting pallet is positioned on the substrate fixture. [0020] FIG. 9 is a cross-sectional view taken generally along line 9-9 in FIG. 7 and in which the substrate-supporting pallet is positioned on the substrate fixture.

[0021] FIG. 10 is a cross-sectional view taken generally along line 10-10 in FIG. 7 and in which the substrate-supporting pallet is positioned on the substrate fixture.

Detailed Description

[0022] With reference to FIG. 1, a high vacuum processing system 10 in the form of an ion beam etch system includes a vacuum chamber or vessel 12 having a vacuum-tight chamber wall 13, which is only partially shown, that encloses an evacuated processing space 15. A port 14 with a lumen extending through the chamber wall 13 places the processing space 15 in communication with a vacuum pump 16. The vacuum pump 16 includes suitable components with a pumping capacity effective for evacuating the processing space 15 of the vacuum vessel 12 to a vacuum pressure suitable for processing one or more substrates 20 with an ion beam 18 of charged particles. The charged particles in the ion beam 18 may be positive ions generated by an ion source (not shown) from an ionizable working gas and accelerated toward the substrates 20. Bombardment of the substrates 20 by the ion beam 18 processes the substrates 20 to achieve an intended beneficial result. Among other beneficial results, the ion beam 18 may be used to remove material from the surfac ^* e of the substrates 20 by an etching process. The substrates 20, which are secured in fixed spatial relationship with a pallet 22 by cooperating clamp members (not shown), are positioned spatially inside the processing space 15 at a location exposed to the ion beam 18.

[0023] A substrate chuck or fixture 24 supports the pallet 22 and the substrates 20 carried on the pallet 22 in the processing space 15 inside the vacuum vessel 12. The substrate fixture 24 is mounted to a tubular access column 26 extending through a sealed opening 28 in an end region 29 of the chamber wall 13. An upper end of the access column 26 has a sealed engagement with the substrate fixture 24. The access column 26 encloses a lumen through which electrical and fluid utilities are routed to the substrate fixture 24.

[0024] The substrate fixture 24 is biased by biasing elements having the form of compression springs 30 that are compressed between the substrate fixture 24 and a support plate 32 inside the processing space 15. The support plate 32 is mounted to the access column 26. The compression springs 30 exert a force biasing the substrate fixture 24 in a direction away from the end region 29 of the chamber wall 13. Each of a plurality of actuators (not shown),

which may comprise bi-directional pneumatic cylinders, includes a piston moving a rod 34 mechanically coupled with the substrate fixture 24. Motion of the rods 34 moves the substrate fixture 24 relative to the pallet 22 and against the biasing force of the compression springs 30 to provide a clearance between the pallet 22 and substrate fixture 24. A transfer mechanism (not shown) is inserted into the clearance between the pallet 22 and substrate fixture 24 to lift or otherwise remove the pallet 22 during exchanges of processed and unprocessed substrates 20. [0025] The substrate fixture 24 is located inside the inner perimeter of a frame 36.

Spanning between the frame 36 and support plate 32 are stanchions 38 that space the support frame 36 from support plate 32. Frame 36 includes stationary lift arms (not shown) disposed at the notched or scalloped corners of the substrate fixture 24, which are best visible in FIG. 6, and projecting inwardly from the inner perimeter of the frame 36. When the substrate fixture 24 is lowered toward the support plate 32, the corners of the pallet 22 contact the lift arms so that the pallet 22 is lifted from the support fixture 24 to provide the necessary clearance between the pallet 22 and substrate fixture 24.

[0026] With reference to FIGS. 2-10, the substrate fixture 24 includes a base member or base plate 40, a support member or cap plate 42, and a heat exchange member or heat exchange plate 44 disposed between the base plate 40 and the cap plate 42. The base plate 40 and heat exchange plate 44 are secured together as an assembly by fasteners 45 (FIG. 9) coupled with threaded openings 41 (FIG. 9) in base plate 40 and extending through clearance openings 43 in heat exchange plate 44. An O-ring 46 (FIGS. 8-10) is seated in an O-ring groove 48 (FIG. 2) extending peripherally about the perimeter of the cap plate 42 and circumscribes a recessed upper surface or side 50 of the heat exchange plate 44. The O-ring 46 sits in the O-ring groove 48 such that the O-ring 46 is partially raised above an upper surface or side 52 of the cap plate 42. The pallet 22 contacts the O-ring 46 to peripherally seal and define a heat transfer gas space 54 (FIGS. 8-10) as a gap between the underside of the pallet 22 and the upper side 52 of the cap plate 42. The invention contemplates that a single substrate (not shown) may be processed without the assistance of pallet 22 as the intermediate supported member supported by the cap plate 42. In the absence of pallet 22, the supported member supported by the cap plate 42 may be a single substrate that directly contacts the O-ring 46 to peripherally seal and define the heat transfer gas space 54.

[0027] A lower surface or side 56 of the cap plate 42, which is disposed opposite to upper side 52, includes a grid of ribs comprising a plurality of narrow spacers or ribs 58 and a thin spacer or rib 60 having a discontinuity near the center of cap plate 42. Ribs 58 are arranged in a plurality of rows and a thin rib 60 is arranged to bisect the rows of ribs 58. Projecting from the lower side 56 of cap plate 42 is a rim 64 that extends about the periphery of the cap plate 42 and encircles a recess 65. The ribs 58, 60 lend structural support to the cap plate 42. [0028] Posts 66 project from the upper side 50 of the heat exchange plate 44 toward the lower side 56 of cap plate 42. The ribs 58, 60 and posts 66 cooperate with rim 64 to define a grid of partitions that compartmentalize recess 65 into a plurality of, for example, sixteen individual compartments 68. Each of the individual compartments 68 is dimensioned to receive a corresponding one of a plurality of thermoelectric devices 70 (FIG. 4), although the invention does not require that each compartment 68 be filled with a thermoelectric device 70. Centrally- located ribs 58 may be bifurcated into closely-spaced parallel upright members and the ribs 58 are segmented by grooves to provide wireways for routing wires 115 (FIG. 8) to the thermoelectric devices 70. Threaded openings 72 in posts 66 are registered with countersunk clearance openings 74 in the cap plate 42. Additional registered pairs of countersunk clearance openings 76 and threaded openings 78 are provided in the cap plate 42 and heat exchange plate 44, respectively. Small fasteners 80 extending through registered openings 72, 74 and registered openings 76, 78 operate to secure the assembled cap plate 42 and heat exchange plate 44 together.

[0029] The upper side 52 of the cap plate 42 is generally planar so that the heat transfer gas space 54 (FIGS. 8-10) has a substantially uniform height inside the perimeter circumscribed by Oring 46 (FIGS. 8-10). The compartments 68 are arranged such that the thermoelectric devices 70 are disposed in a plane substantially parallel to the upper side 52 of the cap plate 42. [0030] A lower surface or side 81 of the heat exchange plate 44, which is disposed opposite to upper side 50, includes a central liquid region 82, a peripheral liquid region 84 near the perimeter of the heat exchange plate 44, a liquid channel 86 coupling the liquid regions 82, 84, and a rim 85 that circumscribes the liquid regions 82, 84 and liquid channel 86. The liquid channel 86 is defined by a thin-walled partition 88 carried by the lower side 81 of heat exchange plate 44. The partition 88 contacts the base plate 40 so that the liquid channel 86 is partially

closed by an upper surface or side 99 of the base plate 40. An O-ring 90 (FIGS. 8-10), which is stationed in an O-ring groove 92 extending about the rim 64 of the heat exchange plate 44 and is compressed between the upper side 99 of base plate 40 and the heat exchange plate 44, seals with the rim 85 of the base plate 40.

[0031] A liquid passageway 94 in the base plate 40 couples a liquid inlet 96, which is defined by a fitting, with a liquid outlet 98. The liquid outlet 98 emerges from the upper side 99 of the base plate 40 to communicate with the peripheral liquid region 84 of the heat exchange plate 44. Liquid channel 86 winds helically about the central liquid region 82 for directing a coolant or thermally conductive liquid 95 of a pre-selected temperature between the base plate 40 and the heat exchange plate 44. The liquid inlet 96 is coupled by a conduit 101 with an external coolant source 100. Another liquid passageway (not shown) in the base plate 40 communicates with the peripheral liquid region 84 and is coupled by a drain passage 102 with a conduit 103 extending to a coolant drain 104. The coolant drain 104 either disposes of the elevated- temperature thermally liquid 95 heated by flow through liquid channel 86 or cools the elevated- temperature thermally liquid 95 for recirculation. Alternatively, the thermally conductive liquid 95 may be circulated in the opposite direction from the central liquid region 82 to the peripheral liquid region 84. The thermally conductive liquid 95 flowing through the liquid channel 86 may be chilled pure water at 5°C to 10 ⁰ C supplied from a chiller unit integrated into coolant source 100, although the invention is not so limited.

[0032] Extending through the base plate 40, cap plate 42, and heat exchange plate 44 is a central inlet gas passageway 106 (FIG. 9), which emerges on the upper side 52 of cap plate 42. An external gas source 108 is coupled by a conduit 107 with the inlet gas passageway 106 with the heat transfer gas space 54 defined between the pallet 22 and the cap plate 42. Pressurized backside gas, such as helium, is transferred through the inlet gas passageway 106 and exhausted from the inlet gas passageway 106 to the heat transfer gas space 54. The gas flow is regulated by a flow control device 109. A central outlet gas passageway 110 (FIG. 9) extends through the cap plate 42 and heat exchange plate 44 for coupling the heat transfer gas space 54 with an exhaust conduit (not shown). The backside heat transfer gas in space 54 facilitates the transfer of heat between the pallet 22 and the cap plate 42 by mechanisms understood by a person having ordinary skill in the art.

[0033] The invention contemplates that the atmosphere of heat transfer gas in space 54 may be static while the substrates 20 are being treated by ion beam 18 or may dynamically flow through the heat transfer gas space 54. Exemplary dynamic flow devices are described in U.S. Patent No. 4,949,783, which is hereby incorporated by reference herein in its entirety, and are commercially available in high vacuum processing systems under the Flowcool™ trade name from Veeco Instruments Inc. (Woodbury, New York).

[0034] As best shown in FIGS. 4, 8, and 10, each of the thermoelectric devices 70 includes a lower support plate 112, an upper support plate 114, and multiple thermoelectric elements 116 extending between the lower and upper support plates 112, 114. The thermoelectric elements 116 consist of an array of up to several hundred dissimilar n-type and p- type semiconductors, which may be formed from p-doped and n-doped bismuth-telluride, thermally joined in parallel and electrically joined in series at both ends to form couples. The lower and upper support plates 112, 114 may be thin ceramic wafers with a relatively high thermal conductivity that add rigidity and electrically insulate the thermoelectric elements 116. One or both of the support plates 112, 114 includes metallization, which is dispoed on a surface that does not confront the cap plate 42 or heat transfer plate 44, or another circuit interface used to electrically couple the thermoelectric elements 116 with the terminals of a power supply 118. Typically, these electrical connections are coupled with the power supply 118 by the conductors of insulated wires 115, which constitute the positive and negative leads to the thermoelectric elements 116. The power supplied by the power supply 118 over wires 115 is normally direct current (DC) power. The wires 115 are routed through the lumen of access column 26 and an electrical feedthrough (not shown) filling a passage 117 extending through the base plate 40 and heat transfer plate 42.

[0035] The thickness of the thermoelectric devices 70 is selected relative to the vertical dimension of the ribs 58, 60 and rim 64 such that, when the cap plate 42 and the heat exchange plate 44 are fastened together, the ribs 58, 60 and rim 64 fail to contact the upper side 50 of the heat exchange plate 44 and the posts 66 fail to contact the lower side 56 of the cap plate 42. The thermoelectric devices 70 are clamped between the cap plate 42 and heat exchange plate 44, which constrains lateral movement of the thermoelectric devices 70 within the compartments 68. The lower side 56 of the cap plate 42 and the upper side 50 of the heat exchange plate 44 are

separated by a gap defined predominantly by recess 65 (FIG. 3) and partially by thin gaps, which are considerably smaller and not visible in the drawings, where ribs 58, 60 and rim 64 confront the upper side 50 of heat exchange plate 44 and where posts 66 confront the lower side 56 of cap plate 42. These gaps interrupt potential heat transfer paths between the cap plate 42 and heat exchange plate 44 so that these members are substantially thermally isolated from each other. The fasteners 80, which have a relatively small cross-sectional area that limit their ability to transfer heat, supply the only conductive paths between the cap plate 42 and heat exchange plate 44. In an alternative embodiment of the invention, the fasteners 80 may be formed from a non- metal or thermal insulator characterized by a low thermal conductivity to further reduce heat transfer between the cap plate 42 and heat exchange plate 44, An annular gap, as best shown in FIGS. 6 and 7, is also present between the perimeter of the rim 64 of cap plate 42 and the confronting inner edge of the rim 85 of heat transfer plate 44 for further disrupting heat flow between these members.

[0036] The thermoelectric devices 70, which operate by the Peltier effect as understood by a person having ordinary skill in the art, convert electrical energy from the power supply 118 to heat pumping energy. In particular, direct current power applied between the lower and upper support plates 112, 114 induces pumped heat flow from the cap plate 42 through the thermoelectric elements 116 to the heat exchange plate 44 as the thermoelectric elements 116 convert electrical energy to heat pumping energy. Heat is conducted through the thermoelectric elements 116 and between the support plates 112, 114 by charge carriers. As heat is continuously absorbed from the upper support plate 114 and transferred by the thermoelectric elements 116 to the lower support plate 112, the upper support plate 114 defines a cold side of each thermoelectric device 70 that absorbs heat and the lower support plate 112 defines a hot side that rejects the heat.

[0037] The upper support plate 114 of each thermoelectric device 70 is in physical and thermal contact with the lower side 56 of cap plate 42 to establish a thermal interface for the absorption of thermal energy or heat from the cap plate 42 across the shared areas of thermal contact. The upper support plates 114 contact a majority of the surface area of the lower side 56 of cap plate 42 for absorbing heat from the cap plate 42. The contacting surface area may extend across approximately 90% of the surface area of the lower side 56 of cap plate 42. The lower

support plate 112 of each thermoelectric device 70 is in physical and thermal contact with the upper side 50 of heat exchange plate 44 to establish another thermal interface for the flow of the rejected heat from the thermoelectric devices 70 to the heat exchange plate 44 across the shared areas of contact. A thermally conductive medium (not shown), such as a thermal grease or graphite pads, may be placed between the lower support plate 112 of each thermoelectric device 70 and the thermal transfer plate 44 and between the upper support plate 114 of the thermoelectric devices 70 and the cap plate 42 to act as a conductive interface and, thereby, potentially improve the thermal contact.

[0038] The properties and number of thermoelectric devices 70 may be tailored to provide a targeted reduction in the temperature of the cap plate 42. The thermoelectric devices 70 may be selected from among the XLT series of thermoelectric coolers commercially available from Marlow Industries Inc. (Dallas, Texas), which exhibit a durability adequate to survive a high number of continuous cycles over a broad temperature range. Although the invention is not so limited, a specific thermoelectric device 70 suitable for use in the invention is the model XLT2385 thermoelectric cooler commercially available from Marlow Industries Inc. (Dallas, Texas), which is capable of providing a maximum temperature drop for an unloaded state of 56.5°C-dry N ₂ from the cold side to the hot side with the hot side at a temperature of 27°C and a maximum temperature drop for an unloaded state of 64.0°C-dry N ₂ from the cold side to the hot side with the hot side at a temperature of 50 ⁰ C. The thermoelectric devices 70 may comprise single stage thermoelectric devices or, alternatively, may comprise stacked or cascaded thermoelectric devices.

[0039] In use and with reference to FIGS. 1-10, heat transfer gas is supplied to heat transfer gas space 54 and the thermally conductive liquid 95 is flowed through the liquid channel 86. The cooling effect of the flowing thermally conductive liquid 95 in liquid channel 86 reduces the temperature of the heat exchange plate 44 and the cap plate 42. The temperature reduction from the flowing thermally conductive liquid 95 is further communicated by the heat exchange plate 44 to the cap plate 42. The thermoelectric devices 70 are energized by the power supply 118, which causes heat transfer or heat flow in a direction from the cap plate 42 to the upper support plate 114 of each thermoelectric device 70 and through the thermoelectric elements 116 to the lower support plate 112. The heat transfer through the thermoelectric

devices 70 reduces the temperature of the upper support plate 114. A temperature differential exists between the lower and upper support plates 112, 114 that increases in a direction from the upper support plate 114 to the lower support plate 112.

[0040] The incident ion beam 18 on the pallet 22 and the substrates 20 carried on the pallet 22 represents a heat load in that a fraction of the ion kinetic energy of each incident ion is converted to heat. The backside heat transfer gas in the heat transfer gas space 54 transfers heat away from the substrates 20 and pallet 22 to the cap plate 42. A significant portion of the generated heat is subsequently transferred from the cap plate 42 to the upper support plate 114 of each thermoelectric device 70, which cools the cap plate 42. The thermoelectric devices 70 operate as temperature-modifying elements for corresponding portions of the pallet 22 to extract heat from portions of the substrates 20 to which each is closest. A portion of the heat is transferred by thermal conduction between contacting portions of the cap plate 42 and heat exchange plate 44, The heat is subsequently transferred from the lower support plate 112 of each thermoelectric device 70 to the heat exchange plate 44 and to the thermally conductive liquid 95 flowing through the liquid channel 86. A temperature gradient exists because of heat flow from the heated substrates 20 to the heat exchange plate 44. The thermally conductive liquid 95, which is warmed from its inflow temperature by the transferred heat, removes the heat from the substrate fixture 24 for external dissipation.

[0041] The temperature of the processed substrates 20 reflects the temperature of the cap plate 42. The presence of the thermoelectric devices 70 increases the net drop in temperature across the cap plate 42 and the heat exchange plate 44 of substrate fixture 24 so that the substrates 20 are maintained at a lower temperature while exposed to the ion beam 18. As a result, heat is more efficiently transferred away from the substrates 20. Because of the additional incremental temperature reduction provided by the thermoelectric devices 70, the current of the ion beam 18 in the high vacuum processing system 10 used to process the substrates 20 may be increased to increase the etching rate and system throughput, Certain temperature-sensitive materials, such as gallium nitride, may be processed in the high vacuum processing system 10 without damaging the substrates 20. The temperature reduction of the substrate fixture 24 is achieved without adding common freezing-point additives, such as ethylene glycol or propylene glycol, to the thermally conductive liquid 95 flowing through the liquid channel 86.

[0042] In an alternative embodiment of the invention, a drive mechanism (not shown) may be coupled with the substrate fixture 24 for rotating and/or tilting all, or part, of the substrate fixture 24 and, therefore, the substrates 20 carried on the pallet 22 relative to the ion beam 18 and chamber wall 13. Electrical connections for the drive mechanism may be routed through the access column 26 to a drive mechanism inside the vacuum vessel 12 or the access column 26 may actively participate in the rotation and/or tilting. The electrical interface electrically coupling the thermoelectric devices 70 with the power supply 118 may comprise a slip ring (not shown) often used to provide a signal transmission path when transmitting electrical signals between a stationary structure and a structure that rotates with respect to the stationary structure. Generally, slip rings typically include conductive brushes that contact conductive bands to pass electrical current from the stationary structure to the rotating structure. [0043] In certain embodiments of the invention, the substrate fixture 24 may include at least one temperature sensor 120 (FIG. 8) that detects or measures the temperature of the cap plate 42 of the substrate fixture 24. The temperature sensor 120 supplies the measured temperature as feedback signals on a continuing or intermittent basis to a temperature controller 122 (FIG. 8) interfaced with the power supply 118 to define a temperature control unit. Alternatively, the temperature feedback signals may be supplied to another controller (not shown) associated with the high vacuum processing system 10 and interfaced with the power supply 118. The temperature sensor 120 may be embedded in the cap plate 42, as depicted in FIG. 8, or may be otherwise thermally coupled with the substrate fixture 24. Multiple temperature sensors 120 may be disposed at different locations in the substrate fixture 24 to provide distributed temperature information to the power supply 118 for ensuring temperature uniformity across the cap plate 42. Suitable temperature sensors 120 include resistance temperature detectors, thermocouples, thermistors, and infrared devices, although the invention is not so limited. In one embodiment of the invention, the temperature sensor 120 may be a thermocouple thermally coupled with rib 60 of the cap plate 42.

[0044] A temperature controller 122 receives the temperature information as input from the temperature sensor 120 across an insulated conductor or wire 119 that establishes a communications path. The temperature controller 112 may utilize the temperature feedback information to regulate the operating power delivered from the power supply 118 to the

thermoelectric devices 70 so as to improve the ability to precisely control the temperature of the substrates 20. The temperature controller 122 may include a programmable system, such as a microprocessor, capable of being programmed to execute instructions effective to control the temperature of the cap plate 42 of the substrate fixture 24 and the substrates 20 at one uniform temperature. In particular, the temperature controller 122 calculates control signals for the thermoelectric devices 70 and sends the calculated control signals to the power supply 118. The power supply 118 responds to the control signals by changing the electrical current supplied to the thermoelectric devices 70. The electrical current through the thermoelectric devices 70 is increased or decreased by the power supply 118, as required, in relation to a difference between the measured temperature and a temperature set point established in a comparative control circuit or by a software control residing in the temperature controller 122. Maintaining the cap plate 42 of the substrate fixture 24 at, or near, a measured temperature operates to maintain the substrates 20 below a certain temperature.

[0045] The program executed by the temperature controller 122 may provide for varying the temperature as a function of time and may include cycling the cap plate 42 of the substrate fixture 24 and the substrates 20 through ranges of temperatures during processing. The temperature controller 122 may be a proportional, a proportional-derivative (PD), a proportional- integral (PI), or a proportional-integral-derivative (PID) controller that uses feedback information from the temperature sensor 120 to control the substrate temperature based upon deviations of the measured temperature from the temperature set point. In this manner, the sensor 120 and temperature controller 122 cooperate to provide a closed loop control system. [0046] The temperature controller 122 may also calculate and send additional control signals to the coolant source 100 to control the flow of the thermally conductive liquid 95 to liquid inlet 96 and, ultimately, liquid channel 86. The temperature controller 122 may also control the temperature of the thermally conductive liquid 95.

[0047] For expanded temperature control, the temperature controller 122 may be configured to switch the thermoelectric devices 70 between heating and cooling by reversing the current delivered from the power supply 118 to the support plates 112, 114. In this switched condition in which the temperature controller 122 is configured for bipolar operation, the thermoelectric devices 70 may be used to heat the substrate fixture 24, for example, before

venting the vacuum vessel 12 of the high vacuum processing system 10 to atmosphere. The temperature controller 122 may include a relay that permits bipolar operation. [0048] The thermoelectric devices 70 are shown wired or otherwise electrically connected in series with the power supply 118. Alternatively, the thermoelectric devices 70 may be wired or otherwise electrically connected in parallel with the power supply 118. In an alternative embodiment of the invention, some of the thermoelectric devices 70 may be serially coupled to the power supply 118 for cooling the substrate fixture 24 and the remainder of the thermoelectric devices 70 may be serially coupled for heating the substrate fixture 24. The ability to heat and cool the substrate fixture 24 improves the precision of temperature regulation. The power supply 118 is operated under the control of temperature controller 122 to regulate the currents through the thermoelectric devices 70 to maintain a desired substrate temperature for the nearest substrate 20 (or substrate portion) by heating or cooling the portion of the pallet 22 carrying the substrate 20. The thermoelectric devices 70 may be used to establish a controlled substrate temperature above ambient temperature in some processes to volatilize etch products from the ion beam process and, thereby, increase the reactive etching rate. [0049] Further details and embodiments of the invention will be described in the following example.

[0050] Example and Comparative Example

[0051] A substrate fixture, substantially similar to substrate fixture 24, was equipped with an array of sixteen thermoelectric devices arranged as shown in FIGS. 1-10. The thermoelectric devices were model XLT2385 thermoelectric coolers manufactured by Marlow Industries Inc. (Dallas, Texas). The thermoelectric coolers were operated at a one-quarter of their rated power to cool the cap plate of the substrate fixture. The temperature of the cap plate 42 was monitored using a thermocouple. An ion beam having a beam voltage of 800 volts (V) and a beam current of 1200 milliamps (rnA) was directed onto a substrate supported on the cap plate. The ion beam, which delivered a beam power of 960 watts, is characterized by an etch rate of about 55 nm/min. While exposed to the ion beam, the temperature of the cap plate measured by the thermocouple was less than 50 ⁰ C.

[0052] Under the same conditions and for purposes of comparison, a substrate supported by the cap plate of a substrate fixture lacking thermoelectric devices was exposed to an ion beam

- - having a beam voltage of 700 volts and a beam current of 1100 milliamps. This ion beam, which delivered a beam power of 770 watts, is characterized by an etch rate of about 45 nm/min. While exposed to the ion beam, the observed temperature of the cap plate was approximately 70 ⁰ C. [0053] While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept.