Abstract:
A substrate support, such as an edge ring, includes an inner portion, and an outer portion contiguous with the inner portion and extending radially outward therefrom. The inner portion has a raised annular extension forming a ridge for supporting a substrate.

Description:
BACKGROUND 
     This invention relates to a substrate support for a thermal processing chamber. 
     In many semiconductor device manufacturing processes, the required high levels of device performance, yield, and process repeatability can only be achieved if the temperature of the substrate (e.g., a semiconductor wafer) is tightly monitored and controlled during processing of the substrate. 
     Rapid thermal processing (RTP), for example, is used for several different fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), rapid thermal nitridation (RTN), and rapid thermal silicidation (RTS). The temperature in an RTP chamber may exceed 1100° C. and is subject to rapid change, thereby making precise control of the substrate temperature more complicated and more difficult. 
     Additionally, although it is desirable to provide a substantially uniform temperature throughout the substrate during many manufacturing processes, the support on which the substrate rests can affect the manufacturing system&#39;s ability to achieve such uniformity. In susceptorless systems, for example, the substrate is usually only supported around its perimeter with an edge ring. In some situations, however, the edge ring acts as a thermal load which removes heat from the edge of the substrate, thereby making it difficult to provide a uniform temperature across the substrate and interfering with the temperature measurements. 
     SUMMARY 
     In general, in one aspect, a substrate support includes an inner portion, and an outer portion contiguous with the inner portion and extending radially outward therefrom. The inner portion includes a raised annular extension for supporting a substrate. In one implementation, the substrate support is an edge ring. 
     In another aspect, a method of processing a substrate in a thermal process chamber includes supporting the substrate on an edge ring within the chamber. The edge ring includes an inner portion and an outer portion contiguous with the inner portion and extending radially outward therefrom. The inner portion includes an annular ridge for supporting the substrate. 
     Various implementations include one or more of the following features. The inner portion can include a substantially flat surface formed in a first plane and the outer portion can include a substantially flat surface formed in a second plane. The annuler extension can extend from the first plane toward the second plane. 
     The inner portion can be annular-shaped with an inner radius and an outer radius larger than the inner radius. The raised extension can form a ridge along the inner radius. 
     An upstanding structure can connect the inner and outer portions to retain the substrate on the ridge. The ridge can have a height less than the height of the upstanding structure, and the height of the upstanding structure can be at least as great as the combined height of the ridge and a nominal thickness of the substrate. 
     The ridge can be substantially parallel to the upstanding structure and can be located at an inner diameter less than the diameter of the substrate. In some implementations, the ridge has a radial width equal to or less than approximately 0.015 inches and a height of at least approximately 0.020 inches above an upper surface of the inner portion. The foregoing dimensions are suitable for use with 8-inch (200 mm) substrates in certain processing chambers, such as the RTP Centura™ or the RTP Centura XE™, manufactured by Applied Materials, Inc. Other dimensions may be suitable for wafers of different sizes, for example, a 6-inch (150 mm) or a 12-inch (300 mm) semiconductor wafer, or for different wafer processing systems. 
     The substrate support can include silicon or silicon carbide and can be disposed in a thermal processing chamber. A process gas can be provided in the chamber. Additionally, the chamber can be heated, and the substrate support and the substrate can be spun about a central axis during heating. 
     Various implementations include one or more of the following advantages. A substrate support with the raised extension or ridge provides a substantially uniform contact area with the semiconductor substrate regardless of the precise position of the substrate on the support. Moreover, since a constant contact area can be formed near substantially the entire perimeter of the substrate, the difference in temperature from one radial slice of the substrate to another is reduced. Thus, a more uniform temperature can be obtained across the substrate surface. As a result, better control over thermal processing of substrates can be provided and the likelihood of substrate breakage due to thermal gradients across the substrate can be reduced. 
     The substrate support also can provide the capability of transferring heat to and from the entire substrate in a repeatable fashion, thereby resulting in less variation in the processing of one substrate to the next. The configuration of the substrate support still allows the substrate to remain within the inner portion of the substrate support when the support is rotated during substrate processing. 
     The distance between the substrate and a reflector beneath the substrate can be kept constant with respect to edge rings in existing systems by providing the new edge ring with a relatively deep pocket for retaining the substrate. In this manner, the edge ring can be used in existing systems without requiring significant adjustment of other system components to compensate for the presence of the new raised edge. 
     Additional features and advantages will be readily apparent from the following detailed description, drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevated partial cross-sectional view of an RTP system according to the present invention. 
     FIG. 2 is a cross-sectional side view of the RTP system according to the present invention. 
     FIG. 3 is a plan view of an exemplary edge ring, not drawn to scale, according to the present invention. 
     FIG. 4 is a cross-sectional side view of the edge ring of FIG. 3, not drawn to scale, along line  4 — 4 . 
     FIG. 5 is a cross-sectional side view of the edge ring of FIG. 3, not drawn to scale, showing various dimensions of the edge ring. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 illustrate a rapid thermal processing (RTP) system including a processing chamber  100  for processing a disk-shaped silicon substrate  106 . Various features of the RTP system are described in further detail in co-pending U.S. patent application Ser. No. 08/641,477, entitled “Method and Apparatus for Measuring Substrate Temperatures”, filed on May 1, 1996, which is incorporated herein by reference. 
     The substrate  106  is mounted inside the chamber on a substrate support structure  108  and is heated by a heating element  110  located directly above the substrate. The heating element  110 , which can include tungsten (W) halogen lamps  111 , generates radiation  112  which enters the processing chamber  100  through a water-cooled quartz window assembly  114  disposed above the substrate. The lamps  111  can be arranged in multiple zones which are grouped together in several control groups. A temperature control algorithm is used to control lamps and thereby to control the temperature. Beneath substrate  106  is a reflector  102  which is mounted on a water-cooled, stainless steel base  116 . The reflector  102  can be made of aluminum and has a highly reflective surface coating. The underside of substrate  106  and the top of reflector  102  form a reflecting cavity  118  for enhancing the effective emissivity of the substrate, thereby improving the accuracy of temperature measurement. 
     The temperatures at localized regions  109  of the substrate  106  are measured by a plurality of temperature probes  126  and pyrometers  128 . The temperature probes  126 , which can include fiber-optic probes, are distributed at varying distances from the center of the substrate  106 . 
     During thermal processing, the support structure  108  is rotated, for example, at about 90 revolutions per minute. Thus, each probe samples the temperature profile of a corresponding annular ring area on the substrate. The support structure which rotates the substrate includes an edge ring  134  which contacts the substrate around the substrate&#39;s outer perimeter, thereby leaving all of the underside of the substrate exposed except for a small annular region near the substrate&#39;s edge. To minimize the thermal discontinuities that may occur at the edge of the substrate  106  during processing, the edge ring  134  can be made of the same, or similar, material as the substrate, for example, silicon or silicon carbide coated with silicon or an oxide of silicon. 
     The edge ring  134  rests on a rotatable tubular quartz cylinder  136  that is coated with silicon to render it opaque in the frequency range of pyrometers  128 . The silicon coating on the quartz cylinder acts as a baffle to block out radiation from external sources that might disturb the temperature measurements. The bottom of the quartz cylinder is held by an annular upper bearing race  142  which rests on a plurality of ball bearings  138  that are, in turn, held within a stationary, annular, lower bearing race  140 . 
     During processing, a process gas is introduced into the space between the substrate  106  and the water-cooled quartz window assembly  114  through an inlet port  101 . Gases are exhausted through an exhaust port  105  coupled to a vacuum pump (not shown). 
     An optional purge ring  107  is fitted into the chamber body and surrounds the quartz cylinder  136 . The purge ring  107  has an internal annular cavity which opens to a region above the upper bearing race  142 . The internal cavity is connected to a regulated purge gas supply through a passageway  103 . During process steps that include providing a process gas into the upper portion of the chamber  100 , a flow of purge gas enters the chamber through the purge ring  107 . 
     Referring to FIGS. 3-5, the edge ring  134 , which is supported by the quartz cylinder  136 , has an inner portion forming a substantially flat ledge with a raised extension  164  on its upper surface adapted to support a substrate  106 . The raised extension  164  forms a ridge along the inner radius of the inner portion  150 . The ridge  164  extends a height h 1  above the upper surface of the inner portion  150 . In the illustrated implementation, which is suitable for use with 200 mm substrates, h 1  is approximately 0.020 inches (0.508 mm). However, when used in other processing systems, greater heights may be appropriate. Similarly, the dimensions discussed above can be scaled appropriately for use with larger or smaller substrates, such as 300 mm substrates. 
     An outer portion  152  of the edge ring  134  is supported from underneath by the cylinder  136 . The transition between the inner portion  150  and the outer portion  152  forms an inward facing, upstanding surface  154  that keeps the substrate  106  contained in the pocket of the edge ring  134  during processing. A 200 mm substrate  106  has a diameter of approximately 7.874 inches (200 mm), plus or minus 0.040 inches (1.0 mm), and a thickness of approximately 0.03 inches (0.775 mm), plus or minus 0.001 inch (0.025 mm). Such a substrate is sometimes referred to as an 8-inch substrate. The upstanding surface  154  is designed to be at least as high as the combined height of the ridge  164  and the thickness of a substrate  106  to make sure that the substrate  106  does not slip off the edge ring  134  when the support structure  108  and substrate spin. To allow for fabrication tolerances and variations in the thicknesses of different substrates, the illustrated implementation has an upstanding surface  154  that is about 0.005 inches (0.127 mm) taller than the nominal combined height of the ridge  164  and substrate  106 . The outer portion  152  of the edge ring  134  in the illustrated implementation has a substantially flat upper surface  156  that is at the same elevation as the top of the upstanding surface  154  to allow smooth flow of process gases across the surface. In the illustrated implementation, the outer diameter d 2  of the outer portion  152  is approximately 9.257 inches (235 mm). 
     The relative heights of the ridge  164  and the upstanding surface  154 , as well as the thickness of the inner portion  150 , can be selected so that the distance from the bottom of the substrate  106  to the reflector  102  beneath the substrate remains substantially constant with respect to existing RTP systems. Forming the edge ring  134  with such dimensions allows the edge ring to be used in the existing systems without requiring numerous adjustments to other components of the system. In the illustrated implementation, for example, the thickness h 2  of the inner portion  150  is approximately 0.015 inches (0.381 mm), and the thickness h 3  of the outer portion  152  is approximately 0.017 inches (0.432 mm). The upstanding surface  154  extends a height h 4  above the top of the ridge  164 . In the illustrated implementation, the height h 4  is approximately 0.035 inches (0.9 mm). 
     The inner portion  150  should be sufficiently broad so that the raised extension  164  supports the substrate  106  around or near its entire perimeter to provide a light seal. In the illustrated implementation, the outer diameter d 1  of the inner portion  150  is approximately 7.987 inches (203 mm). The radial width w 1  of the inner portion  150 , excluding the radial width of the ridge  164 , is approximately 0.162 inches (4.115 mm). The ridge  164  has a radial width w 2  of approximately 0.015 inches (0.381 mm), and the ridge is located at an inner diameter less than the diameter of the substrate  106 . Radial widths greater or less than 0.015 inches (0.381 mm) also can be used for the ridge. However, the dimensions should be selected to ensure that if a substrate  106  is positioned off-center on the ridge  164 , a gap will not be formed between the ridge  164  and one side of the substrate. Such a gap could allow light to leak into the cavity  118 . 
     The support structure  108  also is designed to create a light seal between the edge ring  134  and the quartz cylinder  136 . The bottom of the edge ring  134 , near its outer edge  160 , forms an annular-shaped shoulder  162  which has an inside diameter that is slightly larger than the outside diameter of the quartz cylinder  136 , so that it fits over the cylinder forming a light seal. In the illustrated implementation, the height h 5  of the shoulder  162  is approximately 0.087 inches (2.21 mm). 
     The illustrated implementation of FIGS. 3-5 is formed by grinding a disk of chemical vapor deposited (CVD) silicon carbide with a diamond grinding head. Exterior corners are fully rounded and interior corners are rounded to a radius of at least approximately 0.01 inches (0.25 mm) to reduce mechanical stresses in the edge ring  134 . The entire edge ring  134  can be coated with approximately 0.004 inches (0.1 mm) of silicon on each side. In various implementations, layers of different or additional materials also can be added to the edge ring. 
     Other implementations are within the scope of the following claims. Thus, for example, although the invention has been described in the context of an edge ring support, it also can be used for other wafer support or platform designs. Similarly, the foregoing dimensions are suitable for use of the edge ring  134  in certain processing chambers, such as the RTP Centura™ or the RTP Centura XE™, manufactured by Applied Materials, Inc. Other dimensions may be suitable for wafers of different sizes, for example, a 6-inch (150 mm) or a 12-inch (300 mm) semiconductor wafer, or for wafer processing systems different from the RTP system described above.