Patent Publication Number: US-2011052159-A1

Title: Apparatus for uniform thermal processing

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for a uniform thermal processing and particularly for uniformly heating wafers. 
     2. Description of the Prior Art 
     Along with the advances of science and technology and the steady enhancement of living quality plus the continuously growing of computers and the peripheral industries thereof, the IC (integrated circuit) application fields are wider and wider. As to the IC devices in current applications, the silicon wafers are used as the base material for the most IC substrates. On a wafer, a number of semiconductor processes, such as layer deposition, lithographing, etching, removing the photoresist, and followed by packaging and testing, etc. are performed to accomplish the IC device fabrication. 
     In the above-mentioned semiconductor processes, especially in thermal annealing and thermal oxidizing processes, “temperature” is one of the most important production parameters. A lately developed “rapid thermal processing” (RTP) provides an effective and efficient thermal processing for the wafers. In this thermal processing technology, however, one of the critical issues is how to reach a uniform temperature distribution within a wafer as well as from wafer to wafer. 
       FIG. 1A  is a simplified cross-sectional view, schematically showing a conventional thermal processing apparatus.  FIG. 1B  is a plan view, schematically showing a set of heating lamps in  FIG. 1A . Referring to  FIG. 1A  and  FIG. 1B , a conventional thermal processing apparatus  100  mainly comprises a chamber  110 , a supporter  120  and a set of heating lamps  130 . Wherein, the supporter  120  and the set of heating lamps  130  are disposed inside the chamber  110  and are separated by a thermally transparent plate  140 , such as a quartz plate. The set of heating lamps  130  locates above the supporter  120  and comprises a plurality of heating lamps  132  and reflectors  134 . A wafer  10  is placed on the supporter  120 . The set of heating lamps  130  is used for heating the wafer  10 . 
     Prior to heating the wafer  10 , an individual heating lamp  132  and the appropriate reflector  134  thereof must be adjusted to get a certain heat flux distribution on the wafer  10  to meet the requirements of the conventional thermal processing process. In general, by controlling the distance between the heating lamp  132  and the wafer  10 , the shape of the reflector  134  and the heating power applied to the heating lamp  132 , a desired contribution by an individual heating lamp  132  on the overall heat flux distribution of the wafer  10  will be obtained. In this way, the individual heating lamp adjustment is completed. 
     Next, according to the heat flux distribution on the wafer  10  by an individual heating lamp  132 , the overall heat flux distribution on the wafer  10  by a set of heating lamps  130  is thus estimated. Since the wafer  10  is in a disk shape, these heating lamps  132  are arranged in an axi-symmetric array to form a set of heating lamps  130  as shown in  FIG. 1B . Remarkably, the local area of the wafer  10  right under the heating lamp  132  receives a local maximum heat flux due to the relatively shortest distance between the heat source and the heated spot. On the other hand, the area of the wafer  10  farther away from the heating lamp  132  therefore receives a lower heat flux. Accordingly, it is very hard to meet a uniform requirement of the heat flux distribution on the wafer  10 . 
     To make the heat flux distribution on the wafer  10  uniform, a rotatable design of a supporter  120  with a proper velocity was developed. Thus, the heat flux distribution on wafer  10  along a circumferential direction is relatively uniform.  FIG. 2  illustrates the heat flux distribution on a wafer with the rotating supporter in a conventional thermal processing apparatus. In  FIG. 2 , the chart of heat flux distribution on the wafer  10 , the abscissa represents radial positions on the wafer  10  (in unit of cm), the ordinate represents the heat fluxes received on the wafer  10  (in unit of W/cm 2 ), and the zero value of abscissa represents the center of the wafer  10 . 
     Referring to  FIG. 1B  and  FIG. 2 , the local area, on the upper surface of wafer  10  and between two adjacent rings of heating lamps  132 , is a non-perpendicular incidence zone and the heat flux thereon is relatively lower. Even if the wafer  10  rotates, the accumulated heat density on this non-perpendicular incidence zone is still lower than that on the zone right under the heating lamp  132 . The wafer  10  with a proper rotating velocity may get a relatively uniform heat flux distribution along a circumferential direction (P-direction shown in  FIG. 1B ). Along the radial direction of the wafer  10  (R-direction shown in  FIG. 1B ), however, the heat flux distribution thereon still has a big fluctuation. As shown in  FIG. 2 , the fluctuating amplitude is about ±5%. The so-called “fluctuating amplitude” herein means (peak value−average value)/average value. 
     Thus, excessive fluctuating amplitude of heat flux distribution on a wafer will produce a thermal stress. It may cause dislocation and crossover, i.e. bare wire connection in the IC. In addition, it may also cause a discrepant chemical-reaction rate on the wafer or from wafer to wafer. All those will reduce the production yield of wafers in company with an increased production cost. Along with the tendency of larger-size wafer and tinier-size IC, the problems due to excessive temperature non-uniformity in a wafer would become more serious and worse. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to provide a thermal processing apparatus suitable for uniformly heating wafers to increase the production yield of wafers with reduced production cost. 
     The present invention provides a thermal processing apparatus suitable for heating an object. The thermal processing apparatus comprises a chamber, a rotatable supporter and a set of beating lamps. Wherein, the rotatable supporter is disposed inside the chamber, the heated object is placed on the rotatable supporter and the set of heating lamps is disposed inside the chamber and over the rotatable supporter. The set of heating lamps comprise a plurality of heating lamps, which are arranged as an axi-symmetric array of a plurality of concentric rings. The above-mentioned concentric rings are arranged with appropriate intervals. The rotation center of the heated object is shifted from the concentric rings&#39; center by an offset, a determined vector, so that the object center is at the position with local mean heat flux from lamps between the most inner lamp subset and its adjacent lamp subset. In other words, the center of the rings of heating lamps and the rotation center of heated object are not at the same position. Adjusting the offset, the local areas of the heated object may pass through the position right under the ring of lamps with local maximum irradiance, and then pass through the position between two adjacent rings of lamps with local minimum irradiance, and eventually will be back to its original position. This phenomenon should occur at least once per revolution. The improvement of uniform irradiance on the heated object can thus be achieved. 
     The present invention further provides another thermal processing apparatus suitable for heating a heated object. The thermal processing apparatus comprises a chamber, a supporter and a rotatable set of heating lamps. Wherein, the supporter is disposed inside the chamber, the heated object is placed on the supporter and the rotatable set of heating lamps is disposed inside the chamber and above the supporter. The rotatable set of heating lamps comprises a plurality of heating lamps, which are arranged as an axi-symmetric array of a plurality of concentric rings. The above-mentioned concentric rings are arranged with an appropriate interval between adjacent two concentric rings. The rotatable set of heating lamps has an array center. The center of heated object is shifted from the center of concentric rings by an offset, which is a determined vector. For heating the object, the set of heating lamps rotates not about its own centers but about the center of the heated object. Adjusting the offset, the local areas of the heated object may pass through the position right under the ring of lamps with local maximum irradiance, and then pass through the position between two adjacent rings of lamps with local minimum irradiance, and eventually will be back to its original position. This phenomenon should occur at least once per revolution. The improvement of uniform irradiance on the heated object can thus be achieved. In general, the rotary one may be the set of lamps or the heated body or the both as well. 
     According to the thermal processing apparatus in an embodiment of the present invention, the heated object is, for example, a disk-like object such as a wafer, and the heating lamps are, for example, arranged in several concentric rings. Besides, the number of the concentric rings is preferable 6, wherein the first one is a single heating lamp at the center. The intervals between each two adjacent concentric rings from inner to outer are preferably in an interval ratio of 4/3:1.5:2:2:2. If the offset distance is denoted by e, then, the distance between the first ring and the second ring is L 1 =4e/3. The distance between the second ring and the third ring is L 2 =1.5e. The distance between the third ring and the fourth ring is L 3 =2e. The distance between the fourth ring and the fifth ring is L 4 =2e. The distance between the fifth ring and the sixth ring is L 5 =2e. If the diameter of the heated object is D, the offset distance e can be calculated by a formula, 
     
       
         
           
             
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     In general, the value of X is 0.3 cm and it is the design tolerance because of no chip fabricated at the outer edge of a wafer. 
     According to the thermal processing apparatus in an embodiment of the present invention, the offset angle is 15° as shown in  FIG. 3C . When D=30 cm, the powers for the first set of heating lamps through the sixth set are in the ratio of 31:36:57:71:65:99, respectively. 
     According to the thermal processing apparatus in an embodiment of the present invention, the supporter is a wafer supporter. 
     In the above-described apparatus for thermal processing of the present invention, the following novel measures are applied. At first, the heat flux distribution generated by an individual heating lamp is obtained by, for example, measurement. Selecting a proper arrangement of the set of heating lamps, the appropriate intervals between two concentric rings of heating lamps are subsequently determined. Finally the offset between the center of the heated object and the center of the set of heating lamps, and the heating powers for the rings of the heating lamps are adjusted and controlled. Due to relative eccentric rotation of the set of heating lamps with respect to the center of heated object and, an improvement in uniformity for the heat flux distribution on the surface of the heated object can be effectively achieved. 
     The objective of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve for explaining the principles of the invention. 
         FIG. 1A  is a schematic cross-sectional view of a conventional thermal processing apparatus. 
         FIG. 1B  is a schematic plan view of the set of heating lamps in  FIG. 1A . 
         FIG. 2  schematically illustrates a heat flux distribution on a wafer after the rotating process in a conventional thermal processing apparatus. 
         FIG. 3A  is a schematic cross-sectional view, schematically illustrating a thermal processing apparatus according to the first embodiment of the present invention. 
         FIG. 3B  is a drawing, schematically showing a partial plan view of the set of heating lamps in  FIG. 3A . 
         FIG. 3C  is a drawing, schematically showing a partial plan view of the relative position between the set of heating lamps and the heated object with offset in  FIG. 3A . 
         FIG. 3D  is a drawing, schematically showing a partial plan view of the set of heating lamps with intervals between two adjacent rings of heating lamps in  FIG. 3A . 
         FIG. 4  is a cross-sectional view, schematically illustrating a thermal processing apparatus according to a second embodiment of the present invention. 
         FIG. 5  is a cross-sectional view, schematically illustrating a thermal processing apparatus according to a third embodiment of the present invention. 
         FIG. 6  illustrates a heat flux distribution of a rotating wafer with offset in a thermal processing apparatus of the first embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The First Embodiment 
       FIG. 3A  is a schematic cross-sectional view of a thermal processing apparatus in the first embodiment of the present invention.  FIG. 3B  is a drawing, schematically showing a partial plan view of the set of heating lamps in  FIG. 3A . Referring to FIGS.  3 A and  3 B, a thermal processing apparatus  200  of the present invention comprises, for example, a chamber  210 , a rotatable supporter  220 , a set of heating lamps  230 , a gas intake  240  and an exhaust outlet  250 . Wherein, the rotatable supporter  220 , such as a wafer supporter, and the set of heating lamps  230  are disposed inside the chamber  210 , and the set of heating lamps  230  is located over the rotatable supporter  220 . 
     The centerline A 2  of object  20  is parallel to the array centerline Al of the set of heating lamps  230 . The set of heating lamps  230  comprises a plurality of heating lamps  232  and reflectors  234 , and the heating lamps  232  are, for example, infrared halogen lamps. A heated object  20  is placed on the rotatable supporter  220  and heated by the set of heating lamps  230 . In the embodiment, the heated object  20  is, for example, a disk-like wafer. 
     For conveniently controlling the set of heating lamps  230  that formed by a plurality of the heating lamps  232  and the reflectors  234  to generate a desired heat flux distribution on the heated object  20 , the heating lamps  232  are installed in, for example, a cone-shaped reflectors  234 , and the set of heating lamps  230  is, for example, disk-like (or short cylinder-like). The gas intake  240  and the exhaust outlet  250  are disposed at both sides of the chamber  210 , respectively. Wherein, the gas intake  240  is used for inputting a reaction gas needed in a semiconductor process, and the exhaust outlet  250  is used for exhausting out the reacted gas. 
     Referring to  FIGS. 3A and 3B , an adjusting technology for the present invention comprises, for example, several steps as follows. Adjusting the individual heating lamp  232  together with the reflector  234  thereof, the heat flux distribution on the heated object  20  generated by an individual heating lamp is obtained by measurement. 
     To get the required overall heat flux distribution on the heated object  20  generated by a plurality of individual heating lamps  232  together with the reflectors  234  thereof a numerical analysis by superposition method is performed. Wherein, the calculation step is conducted with experimentation. 
     Next, the heated object  20  is placed in the above-described thermal processing apparatus  200 . Wherein, the set of heating lamps  230  is formed by a plurality of the individual heating lamps  232 . The heated object  20  is, for example, a disk-like wafer. For 30 cm φ  heated object and 1.58 cm φ  heating lamps, a set of heating lamps  232  is axi-symmetrically arranged, for example, as six concentric rings, C 1 , C 2 , C 3 , C 4 , C 5  and C 6 . The C 1  is usually formed from a single lamp as a center. The intervals between two adjacent concentric rings are in a ratio of, for example, 4/3:1.5:2:2:2 from the inner to the outer. In the embodiment, the ring C 1  is the center of the set of heating lamps  230 . The radial lines R 1  and R 2  are the diameter extension lines of the set of heating lamps. 
     Furthermore, as shown in  FIG. 3A , the thermal processing apparatus  200  of the present invention further includes temperature sensors  222  and a power member  224 . The temperature sensors  222  can be used to measure the local temperatures of the heated object  20  where the irradiance primarily from one subset of the heating lamps. The power member  224  is used for applying heating powers to the subsets of the heating lamps according to the temperature feedback of the heated object  20 . 
       FIG. 3C  is a drawing, schematically showing a partial plan view of the set of heating lamps  230  with the relative position of the heated object in  FIG. 3A . Referring to  FIGS. 3A and 3C  and the above-described steps, the disposition of the set of heating lamps  230  and the heated object  20  are adjusted so that a desired horizontal offset, represented by a vector V, between the array centerline A 1  of the set of heating lamps  230  (i.e. the center of the ring C 1 ) and the centerline A 2  of the rotatable object  20  is obtained. Wherein, the offset V is with a directional angle θ, for example 15°, and an offset distance e. 
       FIG. 3D  is a drawing, schematically showing a partial plan view of the set of heating lamps with intervals between two adjacent rings of heating lamps in  FIG. 3A . Referring to  FIGS. 3A and 3D , since the offset distance is denoted by c, then the distance between the ring C 1  and the ring C 2  is L 1 =4e/3, the distance between the ring C 2  and the ring C 3  is L 2 =1.5 Se, the distance between the ring C 3  and the ring C 4  is L 3 =2e, the distance between the ring C 4  and the ring C 5  is L 4 =2e and the distance between the ring C 5  and the ring C 6  is L 5 =2e. If the diameter of the heated object  20  is D, the offset distance e can be calculated by a formula, 
     
       
         
           
             
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     In general, the value of X is 0.3 cm and it is the design tolerance because of no chip fabricated at the outer edge of a wafer. 
     Referring to  FIGS. 3A and 3B , after the above-described steps, by adjusting the heating powers, the rings C 1 , C 2 , C 3 , C 4 , C 5  and C 6  of heating lamps  232  are with various power ratios respectively. Wherein, if D=30 cm the power ratios are 31:36:57:71:65:99. Moreover, the powers for the rings C 1 , C 2 , C 3 , C 4 , C 5  and C 6  can be controlled by, for example, PID (proportional integration differentiation) mode. Then, the heated object  20  rotates around the centerline thereof. This is equivalent to that the set of heating lamps  230  eccentrically rotates relatively to the heated object  20  due to the effect from the offset V. Referring to  FIG. 3C , by adjusting the offset V, the local areas of the heated object  20  can preferably pass regions of local maximum irradiance (shown as the position b in  FIG. 3C ) and local minimum irradiance (shown as the position a in  FIG. 3C ) during rotation. In comparison with the conventional thermal processing apparatus  100 , in the thermal processing apparatus  200  of the present invention, the heated object  20  rotates with an offset in a constant velocity. Besides, the ratios of intervals between adjacent concentric rings and the heating powers of the rings of heating lamps  232  are adjusted. In this way, the heated object  20  in the thermal processing apparatus of the present invention is able to receive uniform heat fluxes from the set of heating lamps  230 . 
     The Second Embodiment 
       FIG. 4  is a cross-sectional view, schematically illustrating a thermal processing apparatus according to a second embodiment of the present invention. Unlike the above-described thermal processing apparatus  200  in the first embodiment, the set of heating lamps of the thermal processing apparatus  300  in the second embodiment is rotatable, and the supporter  320  of the thermal processing apparatus  300  is not rotated. Remarkably, the offset V is also arranged. The set of heating lamps  330  rotates eccentrically around the centerline B 2  of the heated object. This is equivalent to that the heated object  20  rotates about the centerline B 2  thereof and with an offset as shown in the first Embodiment. As to the other components and the relative positions thereof of the thermal processing apparatus  300  are the same as those in the first embodiment, so descriptions for the other components are omitted for simplicity. In the same way as the first embodiment of the present invention, the heated object  20  receives a uniform heat flux from the rotating set of heating lamps  330  by adjusting the ratio of interval between rings, the offset distance e, the offset angle θ and the heating powers of the rings of heating lamps  332 . 
     The Third Embodiment 
       FIG. 5  is a schematic section view of a thermal processing apparatus in the third embodiment of the present invention. Unlike the above-described thermal processing apparatus  200  in the first embodiment, the set of heating lamps of the thermal processing apparatus  400  in the third embodiment is also rotatable. In other words, both the set of heating lamps  430  and the heated objected  20  are all in rotation. One possibility is that the heated object  20  rotates about the centerline B 2  thereof and the set of heating lamps  430  rotates eccentrically about the centerline B 2  of heated object  20  as well. As a result, a relative eccentric rotation of the heated objected  20  with respect to the set of heating lamps  430  is achieved. As to the other components and the relative positions thereof of the thermal processing apparatus  400  are the same as those in the first embodiment, so the descriptions of the other components are omitted for simplicity. In the same way as the first embodiment of the present invention, the heated object  20  receives a uniform heat flux from the relatively rotating set of heating lamps  430  by adjusting the ratio of interval between concentric rings, the offset distance e, the offset angle θ and the heating powers of the rings of heating lamps  432 . 
     A heat flux distribution under the eccentric rotation according to the present invention is shown in  FIG. 6 . It schematically illustrates the heat flux distribution on a wafer after the eccentrically rotating in a thermal processing apparatus of the first embodiment. In  FIG. 6 , the abscissa represents radial position on a wafer (in unit of cm), the ordinate represents the received heat flux on the wafer (in unit of W/cm 2 ), and the zero value of the abscissa represents the center position of the heated object  20  (for example, the wafer). 
     Referring to  FIGS. 3A and 6 , the heated object  20  is a disk-like wafer with a diameter of, for example, 30 cm and each heating lamp  232  has a diameter of 1.58 cm. The heating lamps are located at six concentric rings, C 1 , C 2 , C 3 , C 4 , C 5  and C 6 , to form the set of heating lamps  230  with six subsets. The subsets are the rings of heating lamps and with the intervals of L 1 =4e/3, L 2 =1.5e, L 3 =2e, L 4 =2e and L 5 =2e. Taking the offset angle θ=15°, the offset distance e can be calculated from the formula 
     
       
         
           
             
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     (in unit of cm) to get e=1.953 cm. After setting the offset distance e, the heating powers are also adjusted subsequently. The heating power applied to each heating lamp at the same concentric ring is basically the same. For D=30 cm, and six concentric rings, the heating powers applied to the individual concentric ring are in a ratio of 31:36:57:71:65:99, respectively. In the process with the above-described adjustments, a generated heat flux distribution is obtained in  FIG. 6 . It indicates that the adjusting technology and the apparatus for thermal processing of the present invention are very effectively to obtain a uniform heat flux distribution on a heated object  20  (for example, a wafer). As shown in  FIG. 6 , the fluctuating amplitude of heat flux distribution on the heated object  20  is reduced from ±5% to only about ±0.5%. The so-called “fluctuating amplitude” herein means (peak value−average value)/average value. 
     Since the relative rotation between the heated object  200  and the set of heating lamps  330  in 2 nd  embodiment and the 3 rd  embodiment are similar to that in the 1 st  embodiment, the efficiencies similar to that in the first embodiment are verified for the thermal processing apparatus  300  in the second embodiment and the thermal processing apparatus  400  in the third embodiment. That is, the fluctuating amplitude of heat flux distribution on the heated object  20  may be reduced quite much as well. 
     Remarkably, the object shape to be heated in the apparatus for thermal processing of the present invention is not limited to a disk-like shape; it can have other shapes. Further, the heated object is not limited to a wafer; it can be other suitable material to be heated. Therefore, the apparatus for thermal processing of the present invention are not limited to the semiconductor processes; they are suitable for thermal processes of other material as well. In addition, the number of the rings of heating lamps is determined by the diameter of heating lamps and the size of the heated object. Thus, the number of the rings of heating lamps is not limited to “six” only, it can be other numbers (for example, a number larger or smaller than six). The ratio of ring interval corresponding to the heating lamps accordingly is 4/3:1.5:2:2:2:2 . . . 2, wherein “ . . . ” represents “2”. Besides, the set of heating lamps in the apparatus for thermal processing of the present invention is not limited to be disposed at one side of a heated object only; it can be two sets and disposed at both sides of a heated object, respectively. All these alternatives still belong to the scope protected by the present invention. 
     To sum up, the apparatus for thermal processing of the present invention is distinguished from the conventional thermal processing apparatuses by the following features. Firstly, the heat flux distribution generated by an individual heating lamp is obtained by, for example, measurement. Secondly, a proper arrangement of the set of heating lamps is selected and adjusted. Thirdly, the offset between the center of the heated object and the center of the set of heating lamps is adjusted. Due to this offset, the heated object and the set of heating lamps are relatively moved in a way of eccentric rotation. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.