RAPID THERMAL PROCESSING APPARATUS AND METHOD

Abstract: An apparatus and method for rapidly and uniformly heating a workpiece (12) includes a plurality of walls defining a first chamber (20), a first source of radiation (44) for producing incident radiation on a first energy transfer surface of the workpiece (19), a holder for holding the workpiece in a workpiece plane in the chamber and a radiation absorbing surface on at least one wall of the chamber (22, 24, 26). The holder has an energy transfer surface, the energy surfaces of the holder and of the workpiece reflecting and emitting radiation in the chamber and the radiation absorbing surface absorbing non-incident radiation reflected and emitted from the energy transfer surfaces.

Description: RAPID THERMAL PROCESSING APPARATUS AND METHOD BACKGROUND OF THE INVENTION This invention relates to rapid thermal processing of a workpiece and more particularly relates to thermal processing of semiconductor wafers. Rapid thermal processing reactors are commonly used to anneal semiconductor wafers. The operating parameters for these reactors are becoming more demanding as device spacing on semiconductor wafers is reduced. For example high temperature rapid thermal processing for devices with 0.25μm spacings requires a temperature uniformity in the device of +1-3 degrees celsius and for devices with 0.18μm spacings a temperature uniformity of +/-1 degree celsius is required. Various others have attempted to uniformly irradiate a semiconductor wafer for using devices as described in United States Patent No. 4,649,264 issued March 10, 1987, to Sheets, United States Patent No. 5,279,973 issued January 18, 1994, to Suizu, United States Patent No. 4,482,393 issued November 13, 1984, to Nishiyama et al., United States Patent No. 5,155,336 issued October 13, 1992, to Gronet et al., United States Patent No. 4,981,851 issued January 1, 1991, to Kakoschke and United States Patent No. 4,958,061 issued September 18, 1990, to Wakabayashi et al. Generally, each of the references above discloses at least one light source and various reflector arrangements for directing at the semiconductor wafer light produced by the light source. Using conventional light sources, often a plurality of light sources are required and efficient use must be made of reflectors in order to achieve required radiation pattern on the wafter to achieve a desired thermal pattern in the wafer. The design of such reflectors and, in general, irradiating systems of the type described in the patents, normally are required to compensate for reflection, emission and absorption effects of the wafer itself. This is because the wafer can reflect and emit radiation which is reflected from various reflecting surfaces in the chamber back at the wafer, thereby creating local hot spots in the wafer. Furthermore, differences in geometry and thermal properties of various areas on the wafer can complicate the emissive, absorptive and reflective effects further contributing to localized hot spots in the wafer. What would be desirable, therefore, is a system which uniformly irradiates the wafer and reduces the effects of radiation absorbed and reflected by the wafer. By reducing these effects, the required temperature uniformity for devices with spacings less than lμm can be achieved. SUMMARY OF THE INVENTION In accordance with one aspect of the invention, there is provided an apparatus for rapidly and uniformly heating a workpiece includes a plurality of walls defining a first chamber, a first source of radiation for producing incident radiation on a first energy transfer surface of the workpiece, a holder for holding the workpiece in a workpiece plane in the chamber and a radiation absorbing surface on at least one wall of the chamber. The holder has an energy transfer surface, the energy transfer surfaces of the holder and of the workpiece reflecting and emitting radiation in the chamber and die radiation absorbing surface absorbing non-incident radiation reflected and emitted from the energy transfer surfaces. The radiation absorbing surface may include anodized stainless steel, anodized aluminum, black nickel coating, a paint containing graphite or other absorbing material. Preferably, the apparatus includes a first controller for controlling the first source of radiation to achieve a desired thermal pattern in the workpiece by controlling the radiation to achieve a desired radiation pattern incident on the workpiece. The first controller may include a first reflector disposed behind the first source of radiation such that the first source of radiation is disposed between the first reflector and the workpiece. Preferably, radiation from the first source is directed at the first surface of the workpiece at an angle of incidence less than 80 degrees to the first surface. Preferably, at least one of the walls has a first opening for admitting radiation into the chamber, the first opening having a cross-sectional area of less than or equal to the area of the radiation absorbing surface. Preferably, the first source of radiation includes a first high power inert gas arc such as a water wall arc having an arc axis disposed generally parallel to the energy absorbing surface. Preferably, the first source of radiation produces radiation having at least 60% of its energy at wavelengths less than 1.2μm and is operable to produce a radiation flux of at least 40W/cm 2 at the first surface with a response time of less man lOmSec. Preferably, the apparatus includes a window covering the opening, the window having a partially reflecting surface disposed at an angle to the first surface, the window being disposed between the first source and the holder such that the incident radiation passes through the window and such that the partially reflecting surface of the window is operable to direct the non-incident radiation impinging upon the reflecting surface toward at least one of the radiation absorbing surfaces. The apparatus may include a cooler for cooling the window ϋ rough contact with a fluid coolant. Optionally, at least one of the radiation absorbing surfaces may be disposed such that the included angle between the workpiece plane and the radiation absorbing surface, inside the first chamber, is greater than 90 degrees. Optionally, the included angle between the radiation absorbing surface and an adjacent wall of the first chamber is less than 90 degrees. Optionally, the radiation absorbing surface includes a plurality of facets forming a generally sawtooth pattern in the surface, respective adjacent facets being disposed at less than 90 degrees to each other. Optionally, the chamber may have at least one reflecting wall perpendicular to the arc axis. A secondary source of radiation such as a xenon arc lamp may be provided in the first chamber for producing further incident radiation for producing a desired radiation pattern on the workpiece. A second chamber, may also be included in the apparatus, the first chamber being disposed on a first side of the workpiece plane and the second chamber being disposed on a second side of the workpiece plane, the second side being opposite the first side. The second chamber will have a plurality of walls, each wall having a reflecting surface for reflecting back to the workpiece radiation emitted by die workpiece. At least one second side reflector may be disposed opposite the second side, for reflecting back to the second surface radiation emitted by the second surface. The at least one reflector can be shaped to distribute reflected radiation onto the second side such that a substantially uniform temperature distribution is maintained over the second side. In addition the apparatus may include at least one edge reflector disposed adjacent edge portions of the workpiece, the edge reflector being operable to reflect back to the edge portions radiation emitted by the edge portions. The second side reflector and the edge reflector cooperate to distribute reflected radiation onto the second side and the edges such that a substantially uniform temperature distribution is maintained over the second side and the edges of the workpiece. T e apparatus may include a second source of radiation such as at least one short xenon arc lamp for irradiating a second surface of the workpiece, the second surface being on a side of the workpiece, opposite the first surface. Preferably, the second source of radiation is located in the second chamber and a second controller for controlling the second source of radiation is provided to achieve a desired thermal pattern in the workpiece by maintaining a desired radiation pattern on the second surface. Preferably, the second controller includes a second reflector disposed behind the second source of radiation such that the second source is disposed between the second reflector and the workpiece. Alternatively the second source may includes at least one tungsten lamp. In accordance with another aspect of me invention, there is provided a method of rapidly and uniformly heating a workpiece, the method comprising the steps of: a) directing radiation from a first radiation source at a first surface of the workpiece to produce incident radiation on the first surface; and b) absorbing non-incident radiation reflected and emitted from energy transfer surfaces including the first surface and surfaces in the vicinity of the first surface so that the first surface is exposed primarily only to incident radiation emitted directly from the radiation source. The method may further include the steps of: a) holding the workpiece in a first chamber; b) admitting ϋ e radiation into the first chamber; and c) absorbing the non-incident radiation at radiation absorbing surfaces of at least one wall forming the first chamber. In accordance with another aspect of the invention, there is provided a mediod of rapidly and uniformly heating a workpiece, the method comprising the steps of: a) directing radiation from a first radiation source at a first surface of the workpiece to produce incident radiation on the first surface; b) directing radiation from a second radiation source at a second surface of the workpiece to produce incident radiation on the second surface, the first and second surfaces being disposed on opposite sides of the workpiece; and, c) absorbing non-incident radiation reflected and emitted from energy transfer surfaces, including the first and second surfaces and surfaces, in the vicinity of the workpiece. The method may further include the steps of: a) holding the workpiece in a chamber having a plurality of walls, at least one wall having a radiation absorbing surface; b) admitting the radiation from the first and second sources into the chamber; and c) absorbing the non-incident radiation at the radiation absorbing surface of the at least one wall. The above described apparatus reduces the effects of wafer reflectivity and non-uniformity by absorbing virtually all of the wafer radiation before it can return to the wafer. The position of the source relative to e radiation absorbing surfaces and the radiation source causes radiation reflected from the wafer along with most of the thermal radiation from the wafer to reach the radiation absorbing surfaces of me walls of the chamber. By using a gas arc, a reliable and reproducible radiation source is obtained. In addition, the arc described herein has a spectral distribution in which over 90% of the arc's radiation is below the 1.2 micron band gap absorption of cold silicon. Thus, virtually all of the arc radiation is strongly absorbed by silicon at all temperatures and very little passes through the wafer. In addition, an arc of the type described herein has a 1 mSec time response which provides improved control of heating profiles and facilitates easy, accurate temperature measurement. The spectral distribution of the arc causes most of the incident radiation impinging upon the wafer to be absorbed on the exposed surface of the wafer. At these wavelengths, power will not reach the wafer's second side (device side) by passing through the wafer. Minimizing the transfer of power through the wafer, minimizes pattern effects of the wafer and reduces any thermal gradient perpendicular to the surface of the wafer, which reduces thermal stress. This is particularly important for devices that involve insulating layers such as silicon on oxide. BRIEF DESCRIPTION OF THE DRAWINGS In drawings which illustrate embodiments of the invention, Figure 1 is a cross-sectional view of an apparatus according to a first embodiment of die invention; Figure 2 is a cross-sectional view of the apparatus of Figure 1 taken along lines 2-2 of Figure 1; Figure 3 is a cross-sectional view of an apparatus according to a second embodiment of the invention; Figure 4 is a cross-sectional view of an apparatus according to a third embodiment of the invention; Figure 5 is a cross-sectional view of an apparatus according to a fourth embodiment of the invention; Figure 6 is a cross-sectional view of an apparatus according to a fifth embodiment of the invention; and Figure 7 is a cross-sectional view of an apparatus according to a sixth embodiment of the invention. Figure 8 is a cross-sectional view of an apparatus according to a seventh embodiment of the invention; DETAILED DESCRIPTION Referring to Figure 1, an apparatus for rapidly and uniformly heating a workpiece is shown generally at 10. In this embodiment, the workpiece is a silicon wafer 12 having a first surface 14, a second surface 16 disposed opposite the first surface and a circular edge portion 18 defining a circular perimeter of the wafer and surrounding a central portion 19 of the wafer 12. The first surface 14 is generally a substrate side while the second surface 16 is generally a device side. It will be appreciated that the first side generally has a uniform heat coefficient while the second side has areas of different heat coefficients. It will further be appreciated that the first and second sides of the wafer act as energy transfer surfaces which are operable to absorb radiation, resulting in thermal heating of the wafer, are operable to reflect a portion of radiation impinging thereupon and are operable to emit heat radiation, depending upon me temperature of the wafer 12. The apparatus 10 includes a plurality of walls defining a first chamber 20. In diis embodiment, there are first, second and iird walls 22, 24 and 26 which extend at right angles to the plane of the drawing, each disposed at right angles to each odier, and fourth and fifth walls extending parallel to the plane of the drawing. Referring to Figure 2, die fourth wall is shown at 28 and me fifth wall is shown at 29. Referring back to Figure 1, d e first wall 22 generally has no discontinuities, the second wall 24 has a first opening 30 U erein and die third wall has an access opening 32 generally for robotic access. When robotic access is not in progress, d e access opening 32 is closed by a removable cover 34. Referring to Figure 2, the fourth and fifth walls 28 and 29 generally have no discontinuities. Referring to Figure 1, in ϋ is embodiment, walls 22, 24, and 26 and die access opening cover 34 (seen in Figure 1) are formed from anodized stainless steel such tiiat least one inner facing surface of each wall is black in colour and radiation absorptive. Hence walls 22, 24 and 26 have respective radiation absorbing surfaces 36, 38, and 40, each having a surface area operable to absorb radiation impinging ti ereon. from inside t_he enclosure. Each of the walls 22, 24, 26 may be water cooled using conventional methods. Referring to Figure 2, die remaining walls 28 and 29 are coated with a highly reflective surface coating such as aluminum and have respective reflecting surfaces 31 and 33. Referring back to Figure 1, preferably, die first opening 30 in the second wall 24 has a cross-sectional area of less dian or equal to the area of the total radiation absorbing surface area in the first chamber and provides an aperture through which radiation is admitted into die first chamber 20. The total radiation surface area is the sum of die surface area of each of the radiation absorbing surfaces in the first chamber. Generally, it is desirable to maximize die radiation absorbing surface area while minimizing the cross-sectional area of die first opening 30 to enable die radiation absorbing surfaces to absorb as much radiation as possible from die interior of the first chamber 20. A first high power inert gas arc 44 having an arc axis 45, is secured about die first opening 30 such mat die arc axis is parallel to die radiation absorbing surfaces 36, 38 and 40 and perpendicular to d e reflecting surfaces 28 and 29. The high power arc acts as a first source of radiation for producing incident radiation on die first energy transfer surface 14 of die wafer 12. The high power inert gas arc is preferably a water wall arc, of the type described in United States Patent No. 4,027,185, issued May 31, 1977 to Nodwell et al., United States Patent No. 4,700,102 issued Oct 13, 1987 to Camm et al., and United States Patent No. 4,937,490 issued Jun 26, 1990 to Camm et al., the disclosures of which are incorporated herein by reference. Generally, for processing silicon wafers it is preferred that the gas arc 55 be capable of producing radiation having at least 95% of its energy content at wavelengths less dian 1.2 x 10 " * meters and be capable of producing a radiation flux in the range of 30- 100W/cm 2 and preferably 50W/cm 2 at die first surface 14. This level of radiation flux is sufficient to provide enough radiant energy in die first chamber 20 to heat d e wafer 12 while radiation reflected from die wafer 12 is absorbed by die radiation absorbing surfaces 36, 38 and 40 or is reflected onto tiiese surfaces by die reflecting surfaces 31 and 33 of walls 28 and 29 shown in Figure 2. In odier words, die apparatus does not rely on any reflected radiation from die wafer to heat die wafer, rather die entire heating effect is due primarily to the incident radiation directly from die first source of radiation. Referring back to Figure 1, die gas arc 44 should also be capable of achieving an on/off response time of less dian lOmSec and preferably 1 mSec which is much less time man die mermal time constant of die wafer. This allows the radiation to be momentarily deactivated to permit temperature measurements or diermal images to be taken widiout the influence of source radiation and allows die radiation to be quickly reactivated to resume and maintain the temperature of die wafer 12. It also allows very accurate temperature profiles of the wafer 12 to be acquired, using conventional temperature and thermal imaging equipment. One possible application of die arc's fast time constant is to compare wafer radiation widi die arc on and off to measure both reflective and thermal radiation. These real time measurements of reflectivity can be used to calculate emissivity and when combined with diermal radiation measurements give temperature. The absorbing chamber eliminates the cavity effect that would be created by a reflecting chamber so true wafer emissivity can be measured. An estimate of die hemispherical reflectivity can be obtained by careful positioning of an imaging detector diat resolves die wafer in two dimensions and using die know spatial and angular distribution of irradiance on die wafer. During heating of die wafer 12, different areas of d e wafer 12 will generally emit radiation at different rates. Therefore a first reflector 46 is disposed behind die gas arc 44, parallel to d e axis of die gas arc such mat d e gas arc 44 is disposed between die first reflector 46 and die wafer 12, to control die radiation flux distribution from the gas arc 44 to achieve a desired radiation pattern incident on die wafer 12. The reflecting walls 28 and 29 also assist in forming this desired radiation pattern, die pattern being a generally uniform flux distribution over die entire first surface 14 of the wafer 12. This is achieved by forming die reflector 46 with first and second angled portions 48 and 50 such diat portions of radiation directly emanating from the gas arc 44 are reflected by die first and second angled portions 48 and 50 which concentrate and direct portions of this radiation at die edge portion 18 of die wafer 12. The reflecting surfaces 31 and 33 also reflect some of die radiation emitted by die first source onto die wafer 12. These surfaces produce respective images of die gas arc which causes die arc to appear longer dian it really is which helps produce a uniform radiation pattern past the end portions of the arc. Hence, die first reflector 46 and die reflecting walls 28 and 30 effectively control the first source of radiation to achieve a desired radiation pattern on die first surface 14. The effect of this uniform radiation pattern is to create a generally uniform temperature distribution across d e first surface 14. It will be appreciated that using conventional reflector design techniques, a suitable first reflector can be designed to create most practical radiation patterns. A window 56 is disposed over die first opening 30 and separates the gas arc 44 from die first chamber 20, while permitting radiation from the gas arc 44 and first reflector 46 to pass into die chamber 20 through d e first opening 30. Generally, d e window is of conventional quartz design and permits most of die radiation incident on first and second surfaces diereof to pass d erethrough however, some radiation is reflected. Hence die window may be considered to have first and second partially reflecting surfaces 58 and 60. It will be appreciated d at die wafer 12 reflects and emits radiation in all directions, some of which intersect the radiation absorbing surfaces 36, 38 and 40 of die walls and some of which intersect the first partially reflecting surface 58 of the window 56. This reflected and emitted radiation which impinges on die walls 22, 24 and 26 of the chamber 20 is absorbed by die radiation absorbing surfaces 36, 38 and 40. Some of the reflected and emitted radiation which impinges upon the window 56 passes dirough the window and is reflected back into die chamber 20 by the first reflector 46 while some of this radiation is reflected by die window 56 back into die chamber 20. To avoid excessive reflection of diis radiation by e first reflector 46, it is desirable to keep die first opening 30 and hence die window 56 as small as possible while still permitting enough radiation from die gas arc 44 to enter the chamber 20 to irradiate die first surface 14 of die wafer 12 with the above mentioned 50W/cm 2 radiation flux. Use of die high powered gas arc 44 makes this possible as it is so powerful d at it produces sufficient radiation dirough die relatively small first opening 30 to irradiate die wafer widi die required flux intensity. The first, diird, fourth and fifth (not shown) walls 22, 26 and 28 have respective outer side edges only two of which are shown at 62 and 64 which lie in a workpiece plane 66. To diese edges is connected a second chamber 68 having similar walls, only three of which are shown at 70, 72 and 74. The first chamber 20 is dius disposed on a first side 76 of die workpiece plane 66 while the second chamber 68 is disposed on a second side 78 of the workpiece plane 66, d e second side 78 being opposite the first side 76. The second chamber 68 also has a bottom portion 80 connecting each of the walls 70, 72, 74 togedier such diat when the second chamber 68 is connected to die first chamber 20 the enclosed space is completely enclosed. The walls 70, 72 and 74 of die second chamber 68 and d e bottom portion 80 of e second chamber 68 are each coated with a highly reflecting surface coating 82 such as aluminum for reflecting back to die wafer 12 radiation emitted by die wafer. The walls 70, 72, 74 of die second chamber 68 are terminated in an inwardly directed flange portion 84 to which is connected an annular workpiece holder 86. The workpiece holder has first and second main energy transfer surfaces 88 and 90, each of which is operable to reflect and emit radiation into eidier die first or second chambers 20, 68. It will be appreciated d at energy reflected or emitted by diese surfaces 88 and 90, which enters the first chamber 20 can be expected to be readily absorbed by the radiation absorbing surfaces 36, 38, 40, 42 of the walls 22, 24, 26 in die first chamber 20 while energy which enters me second chamber 68 will be reflected by die highly reflecting surface coating 82 on the walls 70, 72 and 74 and bottom portion 80 of die second chamber 68. Alternatives Alternatively, the walls of the first chamber 20 may be made from anodized aluminum, in which case die radiation absorbing surface includes anodized aluminum, or the walls may be made from virtually any other metal or thermal conductive material and coated widi a black nickel coating or a black paint coating containing graphite, where either of these two coatings acts as the radiation absorbing surface. Referring to Figure 3, an apparatus according to a second embedment of d e invention is shown generally at 100. The apparatus is similar to the apparatus shown in Figure 1, widi exception diat an integrated second reflector 102 including a second side reflector portion 104 and an edge reflector portion 106 is located in die second chamber 68, opposite die second surface 16 of die wafer 12, for reflecting back to die second surface 16 and edge portion 18 of die wafer 12 radiation emitted by die second surface 16 and edge portion 18. The second reflector 102 cooperates to distribute reflected radiation on die second surface 16 and edge portion 18 such diat die greater amount of radiation emitted by die edge portion 18 compared to the central portion 19 of die wafer 12 is concentrated and reflected back at die edge portions 18 such diat a substantially uniform temperature distribution is maintained over die second surface 16 and edge portion 18 of die wafer 12. Referring to Figure 4, an apparatus according to a diird embodiment of die invention is shown generally at 110. The apparatus is similar to the apparatus shown in Figure 2, widi die exception diat a second source of radiation, including first and second xenon arc lamps 112 and 114 is provided in die second chamber 68, between die wafer 12 and die second reflector 102, for irradiating d e second surface 16 of the wafer. The second reflector 102 is operable to reflect back at the second surface 16 radiation emitted by die xenon arc lamps 112 and 114 and radiation emitted and reflected by die second surface 16 to achieve a desired radiation pattern on die second surface 16 to maintain a desired uniform temperature distribution across the second surface 16. Use of die second source of radiation is contemplated where very accurate control of die temperature distribution of the second surface 16 is required. Alternatively, in diis embodiment die second source of radiation may be provided by at least one tungsten lamp (not shown). Alternately, a ring-like temperature security member of die type described in US Patent No. 4,958,061, incorporated herein by reference, may be employed to balance the absorption and emission of radiation from the edge portion 18. As a further alternative, a hemispherically-shaped screen of die type described in US Patent No. 4,981,815 to Kakoschke on January 1, 1991, incorporated herein by reference, may be employed around die edge portion. Or an annular light source and a reflector surrounding die light source, of die type described in US Patent no. 4,981,815 may be employed around the edge portion. The apparatus according to die first embodiment, shown in Figures 1 and 2, may introduce a irradiance non-uniformity of a few percent of the wafer radiation due to d e position of die window. In addition, d e window adds to diermal memory of the chamber. During processing the window will be heated by radiation from the source as well as by diermal radiation from die wafer. The window is transparent to most of die lamp radiation but absorbs most infrared radiation from die wafer. Since die points on die window opposite die wafer centre receive more radiation dian points near die edge, a radial temperature gradient will be created in die window centred on die wafer. Subsequent wafers will be exposed to die non-uniform window depending upon die number of wafers processed, on window cooling, on diermal properties of die window and on d e process cycle. The effects of die window are reduced by repositioning it and making some modifications as shown in Figure 5. Referring to Figure 5, an apparatus according to a fourth embodiment of die invention is shown generally at 120. The apparatus includes a first chamber 20 formed by first 22, fourth 28 and fifth (not shown) walls and a second chamber 68, similar to corresponding components of the embodiment shown in Figure 1, however, d e apparatus has second and third walls 122 and 124 which are different from corresponding walls of the embodiment shown in Figure 1. The second and diird walls 122 and 124 do, however, have respective radiation absorbing surfaces 123 and 125. In particular, die second wall 122 extends from die first wall 22 only approximately 3/4 of die distance to die diird wall 124. Also, the diird wall 124 extends only approximately 1/3 of die distance to die second wall 122, leaving a first opening 126 between die second and diird walls 122 and 124. A first asymmetrical reflector 128 having a reflector mourn portion 130 is connected between die second and diird walls 122 and 124 to form a corner portion 132 of d e first chamber 20. A high power gas arc 134 of the type described in connection wid Figure 1 is disposed widiin the reflector 128. A window 136 having a partially reflecting surface 138 as described above extends between d e second and third walls 122 and 124 to lie at a first obtuse angle 140 relative to the second wall 122 and at a second obtuse angle 142 relative to the diird wall 124, hence d e window 136 is disposed at an angle 146 to die first surface 14 of the wafer 12. The window 136 covers the mouth opening 130 of the reflector 128 such diat die window 136 is disposed between the gas arc 134 and the holder 86 such d at incident radiation passes through the window 136 and such that the partially reflecting surface 138 is operable to direct radiation emitted and reflected by energy transfer surfaces such as 14 and 90 in die first chamber 20 toward at least one of the radiation absorbing surfaces 36, 123, 125 of the walls 22, 122, 124 of the first chamber 20. The reflector is asymmetrical in at it has first and second side portions 148, 150 of different lengdis. The first side portion 148 is adjacent the second wall 122 and is relatively short compared to die second side portion 150, which is disposed adjacent e diird wall 124. The first side portion 148 is operable to reflect radiation generally upwardly toward die entire surface of die wafer, aldiough die right hand side edge portion 18.1 of die wafer 12, which is relatively near to the gas arc 134 receives more radiation. The second side portion 150 is operable to reflect radiation preferentially upwardly toward die left hand side edge portion 18.2 of die wafer 12, which is relatively distant from die gas arc 134. The larger size of die second side portion 150 acts to direct more radiation to d e farther edge portion 18.2 to compensate for the generally non-uniform radiation pattern produced by die smaller second side portion to obtain a relatively uniform distribution of radiation on die first surface 14. This achieves a relatively uniform temperature distribution over the first surface 14. In this embodiment, diermal memory is reduced because the window receives less radiation and dierefore stays cooler. The window's small size and large distance from die wafer reduces radiation transfer back to die wafer and makes die contribution more uniform. The wafer image in the window is not a major concern because radiation from die wafer diat is reflected by the window is directed to die highly absorbing chamber walls and does not return to the wafer. The small solid angle subtended by die window, die larger distance and angle of die window needed to direct reflected light away from the wafer is possible because of die relatively small reflector and large distance to die wafer made possible by die extremely high power and small volume of die gas arc. Optionally, die window may be cooled by a cooling system as described in 0 Published Canadian Patent Application No. 2,113,772, published July 22, 1994, incorporated herein by reference, which transfers heat from die window dirough contact with a fluid coolant. Referring to Figure 6, an apparatus according to a fifth embodiment of the invention is shown generally at 160. Generally, die fifth embodiment is similar to die 5 embodiment described in Figure 4, with die exception diat die first and second walls 22 and 122 are disposed such diat an included angle 162 between d e workpiece plane 66 and die radiation absorbing surface 36 on die first wall, inside die first chamber 20, is greater dian 90 degrees and such diat die included angle 164 between die radiation absorbing surface 36 on the first wall 22 and die radiation absorbing surface 123 on the second wall 122 is less O dian 90 degrees. This wall orientation tends be more effective at absorbing radiation reflected and emitted by die energy transfer surfaces dian previously described embodiments. Referring to Figure 7, an apparatus according to a sixth embodiment of die invention is shown generally at 170. The apparatus according the sixth embodiment essentially eliminates die first and second walls shown in Figures 1-5 and replaces these walls 5 widi a single wall 172 having a plurality of facets 174 forming a generally sawtooth pattern. Respective adjacent facets are disposed at angles 176 less dian 90 degrees to each odier and are covered widi a radiation absorbing coating 178 including black graphite. The facets 174 are disposed relative to die workpiece plane such diat radiation reflected and emitted from the second surface strikes die facets 174 at a relatively low angle of incidence which reduces any reflective effects of die facets 174 and enhances die absorption of die first chamber 20. This embodiment provides efficient absorption of emitted and reflected radiation from the first surface 14. Referring to Figure 8, an apparatus according to a sevend embodiment of d e invention is shown generally at 180. The apparatus according to die sevendi embodiment is essentially identical to die apparatus described with respect to Figures 1 and 2 widi the exception diat it includes a secondary source of radiation 180 in die first chamber 20 for producing further incident radiation to provide more control over the desired radiation pattern on die workpiece. In this embodiment die secondary source of radiation includes first and second xenon arc lamps 184 and 186 disposed on opposite sides of the first window 30. This arrangement could, for example, produce a radially varying intensity pattern on die first side 14 of the wafer 12. While a plurality of embodiments have been described, each has its own strengths and weaknesses. For example, the embodiment shown in Figures 1 and 2 relates to a basic design which provides good temperature uniformity in the wafer. The embodiment shown in Figure 3 provides improved uniformity over diat of Figure 1 but at greater cost. The embodiment shown in Figure 4 provides greater compensation for the effects created by patterned wafers. The embodiment shown in Figure 5 provides better temperature uniformity man in d e previous embodiments. The embodiments shown in Figures 6 and 7 more reliably produces a suitable radiation pattern on the wafer and provides high temperature uniformity in die wafer. The embodiment shown in Figure 8 provides the best performance but is considerably more complicated dian die previous embodiments. The above apparatus provides improved temperature uniformity independent from wafer properties. The apparatus balances energy losses through the device side of die wafer and edge while heating and cooling entirely through the substrate side of the wafer. The first chamber is operable to absorb radiation reflected and emitted from the wafer thus removing any dependency on wafer properties to create the desired radiation pattern. The source and reflector constitute a small portion of the first chamber thus providing easy access to die wafer for diagnostic and temperature measurement purposes. While specific embodiments of die invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting die invention as construed in accordance widi die accompanying claims.

Claims: What is claimed is: 1. An apparatus for rapidly and uniformly heating a workpiece, die apparatus comprising: a) a plurality of walls defining a first chamber; b) a first source of radiation for producing incident radiation on a first energy transfer surface of said workpiece; c) a holder for holding die workpiece in a workpiece plane in said chamber, said holder having an energy transfer surface, die energy transfer surfaces of d e holder and of die workpiece reflecting and emitting radiation in said chamber; d) a radiation absorbing surface on at least one wall of said chamber for absorbing non-incident radiation reflected and emitted from said energy transfer surfaces. 2. An apparatus as claimed in claim 1 wherein said radiation absorbing surface includes anodized stainless steel. 3. An apparatus as claimed in claim 1 wherein said radiation absorbing surface includes anodized aluminum. 4. An apparatus as claimed in claim 1 wherein said radiation absorbing surface includes black nickel coating. 5. An apparatus as claimed in claim 1 wherein said radiation absorbing surface includes paint containing graphite. 6. An apparatus as claimed in claim 1 further including a first controller for controlling the first source of radiation to achieve a desired diermal pattern in the workpiece. 7. An apparatus as claimed in claim 6 wherein the first controller is operable to control the radiation from the first source of radiation to achieve a desired radiation pattern incident on die workpiece. 8. An apparatus as claimed in claim 7 further including a secondary source of radiation in die first chamber for producing further incident radiation for producing a desired radiation pattern on the workpiece. 9. An apparatus as claimed in claim 8 wherein said secondary source of radiation includes a xenon arc lamp. 10. An apparatus as claimed in claim 7 wherein said first controller includes a first reflector disposed behind die first source of radiation such that the first source of radiation is disposed between die first reflector and said workpiece. 11. An apparatus as claimed in claim 1 wherein radiation from die first source is directed at die first surface of die workpiece at an angle of incidence less dian 80 degrees to die first surface. 12. An apparatus as claimed in claim 1 wherein at least one of said walls has a first opening for admitting radiation into die chamber, die first opening having a cross- sectional area of less dian or equal to d e area of said radiation absorbing surface. 13. An apparatus as claimed in claim 1 wherein said first source of radiation includes a first high power inert gas arc having an arc axis. 14. An apparatus as claimed in claim 13 wherein said energy absorbing surface is disposed generally parallel to the arc axis. 15. An apparatus as claimed in claim 13 wherein said chamber has at least one reflecting wall perpendicular to the arc axis. 16. An apparatus as claimed in claim 13 wherein said first high power inert gas arc includes a water wall arc. 17. An apparatus as claimed in claim 1 wherein said first source of radiation produces radiation having at least 95% of its energy at waveleng is less d an 1.2 x 10* meters. 18. An apparatus as claimed in claim 1 wherein said first radiation source is operable to produce a radiation flux of at least 40 W/cm 1 at said first surface. 19. An apparatus as claimed in claim 1 wherein said first radiation source has a response time of less dian lOmSec. 20. An apparatus as claimed in claim 1 further including a second chamber, the first chamber being disposed on a first side of said workpiece plane and die second chamber being disposed on a second side of said workpiece plane, said second side being opposite said first side. 21. An apparatus as claimed in claim 20 wherein said second chamber has a plurality of walls, each wall having a reflecting surface for reflecting back to the workpiece radiation emitted by said workpiece. 22. An apparatus as claimed in claim 21 further including at least one second side reflector disposed opposite said second side, for reflecting back to said second surface radiation emitted by said second surface. 23. An apparatus as claimed in claim 22 wherein said at least one reflector is shaped to distribute reflected radiation onto said second side such that a substantially uniform temperature distribution is maintained over said second side. 24. An apparatus as claimed in claim 23 further including at least one edge reflector disposed adjacent edge portions of said workpiece, said edge reflector being operable to reflect back to said edge portions radiation emitted by said edge portions. 25. An apparatus as claimed in claim 24 further including: a) at least one second side reflector disposed opposite said second side, for reflecting back to said second surface radiation emitted by said second surface; b) at least one edge reflector disposed adjacent edge portions of said workpiece, said edge reflector being operable to reflect back to said edge portions radiation emitted by said edge portions, said second side reflector and said edge reflector cooperating to distribute reflected radiation onto said second side and said edges such diat a substantially uniform temperature distribution is maintained over said second side and said edges of said workpiece. 26. An apparatus as claimed in claim 25 further including a second source of radiation for irradiating a second surface of the workpiece, the second surface being on a side of die workpiece, opposite the first surface. 27. An apparatus as claimed in claim 26 wherein the second source of radiation is located in die second chamber. 28. An apparatus as claimed in claim 27 further including a second controller for controlling die second source of radiation to achieve a desired thermal pattern in the workpiece. 29. An apparatus as claimed in claim 28 wherein die second controller is operable to maintain a desired radiation pattern on said second surface. 30. An apparatus as claimed in claim 29 wherein said second controller includes a second reflector disposed behind die second source of radiation such that said second source is disposed between die second reflector and said workpiece. 31. An apparatus as claimed in claim 26 wherein said second source includes at least one short xenon arc lamp. 32. An apparatus as claimed in claim 26 wherein said second source includes at least one tungsten lamp. 33. An apparatus as claimed in claim 12 further including a window covering said opening, said window having a partially reflecting surface disposed at an angle to die first surface, said window being disposed between said first source and said holder such diat said incident radiation passes through said window and such that said partially reflecting surface of said window is operable to direct die non-incident radiation impinging upon die reflecting surface toward at least one of die radiation absorbing surfaces. 34. An apparatus as claimed in claim 33 further including a cooler for cooling said window dirough contact widi a fluid coolant. 35. An apparatus as claimed in claim 1 wherein said at least one of said radiation absorbing surfaces is disposed such diat die included angle between die workpiece plane and said at least one radiation absorbing surface, inside die first chamber, is greater than 90 degrees. 36. An apparatus as claimed in claim 1 wherein the included angle between said at least one radiation absorbing surface and an adjacent wall of the first chamber is less than 90 degrees. 37. An apparatus as claimed in claim 1 wherein said at least one radiation absorbing surface includes a plurality of facets forming a generally sawtoo i pattern in said surface, respective adjacent facets being disposed at less d an 90 degrees to each odier. 38. A meϋ od of rapidly and uniformly heating a workpiece, die method comprising die steps of: a) directing radiation from a first radiation source at a first surface of said workpiece to produce incident radiation on said first surface; and, b) absorbing non-incident radiation reflected and emitted from energy transfer surfaces including d e first surface and surfaces in d e vicinity of said first surface so diat die first surface is exposed primarily only to incident radiation emitted directly from die radiation source. 39. A mediod as claimed in claim 38 further including d e steps of: a) holding said workpiece in a first chamber; b) admitting said radiation into said first chamber; and c) absorbing said non-incident radiation at radiation absorbing surfaces of at least one wall forming said first chamber. 40. A mediod as claimed in claim 39 further including die step of controlling said first source of radiation to achieve a desired diermal pattern in said workpiece. 41. A method as claimed in claim 40 further including the step of controlling die radiation from said first radiation source to achieve a desired radiation pattern incident on said workpiece. 42. A method as claimed in claim 38 further including die step of directing said radiation at said first surface at an angle of incidence less dian 80 degrees to said first surface. 43. A mediod as claimed in claim 42 further including die step of directing said radiation dirough a window having a partially reflecting surface disposed at an angle to said first surface for directing said non-incident radiation impinging upon said partially reflecting surface toward at least one of said radiation absorbing surfaces. 44. A mediod as claimed in claim 43 further including die step of cooling said window dirough contact with a cooling fluid. 45. A mediod as claimed in claim 38 further including die step of reflecting back to a second surface of said workpiece substantially all of the radiation emitted by said second surface to reduce the effects of differences in heat coefficients in different areas of said workpiece, said second surface of said workpiece being disposed on a side opposite said first side, die step of reflecting employing a second reflecting surface disposed opposite die second surface. 46. A mediod as claimed in claim 38 further including die step of reflecting back to a second surface and edges of said workpiece substantially all of the radiation emitted by said second surface and edges of said workpiece. 47. A mediod as claimed in claim 46 wherein die step of reflecting back includes the step of reflecting radiation emitted from said second surface and said edges with a shaped reflector disposed opposite said second surface and said edges, said reflector being shaped to distribute reflected radiation back to said second surface and said edges such diat a generally uniform temperature distribution is maintained over said second surface and said edges. 48. A mediod as claimed in claim 38 further including d e step of irradiating a second surface of said workpiece, widi a second source of radiation, said second surface being on a side of said workpiece, opposite said first surface. 49. A method as claimed in claim 48 further including the step of controlling said second source of radiation to achieve a desired radiation pattern on said workpiece. 50. A mediod as claimed in claim 49 further including the step of controlling said second source of radiation to achieve a desired diermal pattern in said workpiece. 51. A mediod of rapidly and uniformly heating a workpiece, the method comprising the steps of: a) directing radiation from a first radiation source at a first surface of said workpiece to produce incident radiation on said first surface; b) directing radiation from a second radiation source at a second surface of said workpiece to produce incident radiation on said second surface, said first and second surfaces being disposed on opposite sides of said workpiece; and, c) absorbing non-incident radiation reflected and emitted from energy transfer surfaces, including die first and second surfaces and surfaces, in die vicinity of said workpiece. 52. A method as claimed in claim 51 further including d e steps of: a) holding said workpiece in a chamber having a plurality of walls, at least one wall having a radiation absorbing surface; b) admitting said radiation from said first and second sources into said chamber; and c) absorbing said non-incident radiation at die radiation absorbing surface of said at least one wall. 53. A mediod as claimed in claim 52 further including the step of controlling die radiation from said first and second radiation sources to achieve a desired radiation pattern incident on said workpiece. 54. A mediod as claimed in claim 53 further including d e step of reflecting radiation from said first source from a first reflector disposed behind said first source and reflecting radiation from said second source from a second reflector disposed behind said second source.

Inventors: CAMM DAVID MALCOLM, CAMM, DAVID, MALCOLM
Applicants: CAMM DAVID MALCOLM, VORTEK IND LTD, CAMM, DAVID, MALCOLM, VORTEK INDUSTRIES LTD.
Application year: 1995
Main classification: F27B17
IPC codes: C23C16, F27B17, H01L21