Abstract:
Disclosed are method and apparatus for treating a substrate. The apparatus is a dual-function process chamber that may perform both a material process and a thermal process on a substrate. The chamber has an annular radiant source disposed between a processing location and a transportation location of the chamber. Lift pins have length sufficient to maintain the substrate at the processing location while the substrate support is lowered below the radiant source plane to afford radiant heating of the substrate. One or more lift pins has a light pipe disposed therein to collect radiation emitted or transmitted by the substrate when the lift pin contacts the substrate surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a division of U.S. patent application Ser. No. 14/189,664, filed Feb. 25, 2014, which claims benefit of U.S. Provisional Patent Application Ser. No. 61/789,185, filed Mar. 15, 2013, which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    Embodiments disclosed herein relate to semiconductor processing. More specifically, embodiments disclosed herein relate to apparatus and methods for measuring temperature during thermal processing. 
       BACKGROUND 
       [0003]    Thermal processing is common in semiconductor manufacturing. Semiconductor substrates are often subjected to thermal treatment following a material process such as deposition, implantation, or etching. Temperature of a substrate undergoing a thermal process is often measured. In some such processes, heat sources in the chamber produce a large amount of thermal energy that can overwhelm thermal energy being emitted by the substrate. Thus, there is a continuing need for methods and apparatus for measuring temperature of a substrate during thermal processing. 
       SUMMARY 
       [0004]    Disclosed are method and apparatus for treating a substrate. The apparatus is a dual-function process chamber that may perform both a material process and a thermal process on a substrate. The chamber has an annular radiant source disposed between a processing location and a transportation location of the chamber. Lift pins have length sufficient to maintain the substrate at the processing location while the substrate support is lowered below the radiant source plane to afford radiant heating of the substrate. One or more lift pins has a light pipe disposed therein to collect radiation emitted or transmitted by the substrate when the lift pin contacts the substrate surface. 
         [0005]    The light pipe is shielded from thermal noise in the chamber by a tip that contacts a surface of the substrate. The light pipe may be coupled to a thermal sensor by a conduit, such as a fiber optic. 
         [0006]    A method of using such a light pipe to detect thermal state of a substrate in a noisy environment may include sensing a radiation wavelength that is transmitted at varying intensities as thermal state of the substrate changes, and sensing a radiation wavelength that is transmitted at intensities independent of thermal state of the substrate and comparing the two signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0008]      FIG. 1  is a schematic cross-sectional view of a chamber according to one embodiment. 
           [0009]      FIG. 2A  is a cross-sectional view of a light pipe according to another embodiment. 
           [0010]      FIG. 2B  is a close-up view of the light pipe of  FIG. 2A . 
           [0011]      FIG. 3  is a cross-sectional view of a light pipe according to another embodiment. 
       
    
    
       [0012]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0013]    A chamber is configured for deposition of material on a first side of a substrate and irradiation on a second side of the substrate opposite the first side of the substrate. Such a chamber is a dual-function chamber capable of performing both a material process and a thermal process on a substrate without removing the substrate from the chamber, thus eliminating the time needed to transport the substrate from a deposition chamber to an anneal chamber. The chamber has a radiant energy assembly positioned at a peripheral region of the chamber and defining a radiant source plane between a processing location and a transportation location of the chamber, a reflector disposed around the radiant energy assembly, and a gas source disposed above the processing location.  FIG. 1  is a schematic cross-sectional view of a chamber  100  according to one embodiment. The chamber  100  has a wall  104  and a lid portion  102  that enclose an interior volume  138  thereof. A substrate support  106  separates the interior volume  138  into an upper volume  136  and a lower volume  134 . Process gases are admitted to the upper volume  136  of the chamber through an inlet  108  formed in the lid portion  102 , and a substrate disposed on a substrate receiving surface  116  of the substrate support  106  is exposed to the process gases at a processing location  160  of the chamber  100 . Processing gases flow across the substrate receiving surface  116  of the substrate support  106 , around a peripheral portion thereof, and exit the chamber  100  through a pumping portal  110 . 
         [0014]    A shaft  132  of the substrate support  106  penetrates a lower wall  140  of the chamber, and includes a conduit  130  that provides fluid communication between a source of cooling gas (not shown) and a substrate receiving surface  116 . The substrate support  106  is actuated vertically to move a substrate disposed on the substrate receiving surface  116  of the substrate support  106  between the processing location  160  and a transportation location  124  of the chamber. The transportation location  124  defines a location of the substrate at which a substrate handling apparatus (not shown) may manipulate a substrate through a portal  122 . 
         [0015]    A radiant source assembly  112  is disposed at a periphery  142  of the chamber  100  and defines a radiant source plane  126  that is between the processing location  160  and the transportation location  124 . A plurality of lift pins  114  are disposed through the substrate receiving surface  116  of the substrate support  106  and are actuated to maintain a substrate near the processing location  160  while the substrate support  106  retracts below the radiant source plane  126 . The substrate is thereby exposed to radiation from the radiant source assembly  112 . In one aspect, the substrate may be positioned at a thermal processing location  128  different from the processing location  160 , which may be a material processing location, by actuating the lift pins. 
         [0016]    The radiant source assembly  112  typically surrounds the substrate support  106 . An inner extent  144  of the radiant source assembly  112  is located a radial distance “d” from an outer extent  146  of the substrate support  106 . The distance “d” is chosen to produce a selected irradiance of a substrate located at or near the processing location  160 . By varying the distance “d” between the radiant source assembly  112  and the outer extent  146  of the substrate support  106 , amount and intensity of radiation affecting the substrate may be adjusted. The distance “d” is typically substantially constant at all points of the radiant source assembly  112 , and is between about 0.001 cm (i.e. 10 μm) and about 5 cm, for example between about 1 cm and about 3 cm, for a chamber configured to process 300 mm wafers. The distance “d” may also be different at different locations in the chamber  100 , according to any desired design. For example, the distance “d” may be different at different points around the extent of the radiant energy assembly  112 . 
         [0017]    A shield ring  118 , which may be metal or ceramic, is disposed around an edge  148  of the substrate receiving surface  116 . The shield ring  118  substantially covers an outer extent  146  of the substrate support  106  to prevent deposition thereon. The shield ring  118  rests on a ledge  150  formed in the outer extent  146  of the substrate receiving surface  116 . In most cases, a substrate disposed on the substrate receiving surface  116  contacts the shield ring  118 . In alternate embodiments, the substrate may have an outer radius less than an inner radius of the shield ring  118 , such that the substrate does not contact the shield ring  118 . 
         [0018]    In operation, the substrate support  106  moves vertically within the chamber  100 , extending and retracting to various positions at different stages of processing. Fully retracted to a transportation location, the substrate receiving surface  116  is positioned near the transportation location  124  to allow a substrate handling mechanism (not shown) to deposit and retrieve substrates. The lift pins  114  are extended by actuator  162  to lift the substrate above the substrate receiving surface  116 . Actuator  162  moves independently of substrate support  106  by virtue of a motor (not shown) coupled to the actuator  162 . As the substrate support  106  rises from the transportation position, the lift pins  114  are retracted, so the substrate receiving surface  116  engages the substrate. 
         [0019]    The substrate receiving surface  116  may incorporate an electrostatic chuck, which is typically a conductor  158  disposed in an insulating substrate receiving surface  116 . The conductor  158  may be a plate, a wire mesh, or a single-path wire circuitously routed through the substrate receiving surface  116 . Power is typically coupled to the conductor  158  through a conduit  156  disposed through the shaft  132  of the substrate support. As the substrate receiving surface  116  engages the substrate, the electrostatic chuck may be energized to immobilize the substrate on the substrate support  106 . Cooling gas may also be established through the conduit  130  at that time. 
         [0020]    The substrate support  106 , with the substrate positioned thereon, moves the substrate toward the processing locations  128  and  160 . The substrate support  106 , with the shield ring  118  resting on the ledge  150 , passes by the radiant source assembly  112  as the substrate support  106  rises toward the processing location  160 . When the substrate receiving surface  116  reaches the processing location  160 , the substrate may be subjected to a material process, such as deposition, implant, or etch. The shield ring  118  may have a notch  164  for engaging a cover ring  166 , which may be metal or ceramic, extending outward from the shield ring  118  toward the lid portion  102 . The cover ring  166  and notch  164  improve the function of the shield ring  118  by controlling gas flow from the upper volume  136  past the cover ring  166  into the lower volume  134 . The notch  164  and barrier  166  are optional. As the substrate support  106  moves toward the processing locations  160  and  128 , the shield ring  118  engages the cover ring  166 . As the substrate support  106  moves toward the processing location  128  from the processing location  160 , the cover ring moves with the shield ring  118  and the substrate support  106   
         [0021]    In some embodiments, an edge support may be provided that extends inward from the sidewall  104  at a point between the radiant source assembly  112  and the transportation location  124 . The edge support (not shown) may be configured to engage the shield ring  118  as the substrate support  106  moves toward the transportation location  124 . In such an embodiment, the ledge  150  has an outer radius less than an outer radius of the shield ring  118 , such that a portion of the shield ring  118  extends beyond the outer extent  146  of the substrate support  106 . Such a configuration enables removing the shield ring  118  from the substrate support  106  to improve access to the substrate receiving surface  116  at the transportation location  124 . 
         [0022]    After processing at the processing location  160  is complete, the substrate support  106  may be positioned for back-side thermal processing of the substrate. Any chucking of the substrate is disengaged by interrupting power to the conductor  158  (or vacuum to the substrate receiving surface in a vacuum chuck embodiment), the substrate support  106  retracts, and the lift pins  114  are actuated into an extended position. This disengages the substrate from the substrate receiving surface  116 , and maintains the substrate at the processing location  160  as the substrate support  106  retracts to the thermal processing position below the radiant source plane  126 . The substrate back side is thereby exposed to radiation from the radiant source assembly  112 . If desired, the substrate may be moved to a thermal processing location  128  different from the processing location  160  by actuating the lift pins. In such embodiments, the processing location  160  may be a material processing location. It should be noted that a thermal processing location may be above or below the material processing location, as desired depending on the energy exposure needs of specific embodiments. A substrate  168  is shown in  FIG. 1  in a thermal processing position. 
         [0023]    During thermal processing, the radiant source assembly  112  is powered, and energy radiates from the radiant source assembly  112  toward the substrate  168 . The “back side” of the substrate  168 , meaning the substrate surface  172  opposite the surface  170  on which a material process was performed, is irradiated in this fashion. Besides providing an integrated material and thermal processing chamber, irradiating the back side  172  of the substrate  168  in this fashion may improve energy efficiency of the thermal process by irradiating a less reflective surface of the substrate  168 . In some embodiments, the material process performed on the substrate  168  forms a reflective layer or partial layer on the surface  170  that reduces energy absorption. Irradiating the back side  172  avoids the increased reflectivity. Moreover, the reflectivity of the surface  170  may reflect radiation from the radiant source assembly  112  that travels through the substrate  168  back through the substrate  168  for further efficiency improvement. 
         [0024]    In some embodiments, position of the substrate  168  during thermal processing may be modulated to improve uniformity of radiation on the substrate  168 . The substrate  168  may be moved further up or down from the thermal processing location  128  cyclically by actuating the lift pins  114  to move any non-uniformities in the radiation pattern to various locations on the back side  172 , thus reducing the impact of the non-uniformity and/or substrate bending on substrate processing. Maximum deviation of the back side  172  from the thermal processing location  128  may be expressed as a ratio to substrate thickness. The elevation ratio may vary between about 0.1 and about 100 substrate thicknesses. 
         [0025]    When the substrate support  106  is at a thermal processing location, as shown in  FIG. 1 , a thermal sensor  120  senses a thermal condition of the substrate  168 , positioned above the substrate receiving surface  116  on extended lift pins  114 , by line-of-sight through a gap  154  between the radiant source assembly  112  and the shield ring  118 . In embodiments omitting the shield ring  118 , the gap  154  will be between the radiant source assembly  112  and the outer extent  146  of the substrate support  106 . The thermal processing location may therefore be defined by the desired gap  154  between the radiant source assembly  112  and the shield ring  118  or the outer extent  146  of the substrate support  106  and the inner extent  144  of the radiant source assembly  112 . 
         [0026]    After thermal processing is complete, the substrate is typically re-engaged with the substrate receiving surface  116  by retracting the lift pins  114 . Chucking may be re-applied, and cooling gas re-established to cool the substrate. The substrate support  106  may then be moved into position for further processing, if desired, or back to the transportation location for retrieval of the substrate. When the substrate support  106  is positioned at the transportation location, access to the substrate is provided by extending the lift pins  114  so that a robot blade may be inserted between the substrate and the substrate receiving surface  116 . 
         [0027]    The substrate receiving surface  116  may be reflective. A dielectric mirror surface is provided in one embodiment. In other embodiments, a reflective metal, such as silver, is applied over a ceramic material, or under a transparent material. The reflective material may be extended into the fluid flow recesses in a conformal fashion. For example a reflective liner may be applied to the fluid flow recesses, if desired. Any known conformal process may be used to form a conformal reflective surface, if desired. In another embodiment, the reflective material may be applied only to the fluid flow recesses, for example by depositing the reflective material conformally and removing the reflective material from the flat surfaces between the recesses, either by physical means such as polishing or by chemical means such as etching. 
         [0028]    A reflective substrate receiving surface  116  may be configured to selectively reflect radiation likely to be absorbed by the substrate  168 . For example, in one embodiment, a dielectric mirror configured to reflect radiation having a wavelength between about 0.2 μm and about 1.0 μm may be useful. Such a dielectric mirror may be fashioned by forming alternating layers having different refractive indices on the substrate receiving surface  116 . 
         [0029]    It should be noted that the substrate need not be positioned at the same location for material (i.e. deposition or implant) and thermal processing. In the foregoing description, it is suggested that the processing location  160  is the same during material and thermal processing, but it is not required to be so. For example, a thermal processing location may be different from a material processing location. The substrate may be raised or lowered from a material processing location to a thermal processing location. The location of the thermal processing location with respect to the material processing location generally depends on design of the radiant source and the needs of the material process. 
         [0030]    The chamber  100  may be a PVD chamber in one embodiment. In such an embodiment, the lid portion  102  of the chamber  100  will include a sputtering target, magnetron, and gas feed system as is known in the art. In an alternate embodiment, the chamber  100  may be a CVD chamber, PECVD chamber, or etch chamber, with a showerhead or showerhead electrode disposed in the lid portion  102  as is known in the art. In another embodiment, the chamber  100  may be a P3i chamber with an inductive plasma source disposed in, or coupled to, the lid portion  102 , as is known in the art. A radiant source assembly such as the radiant source assembly  112  may be used in any processing chamber desirous of integrated thermal processing. 
         [0031]    The chamber  100  described above in connection with  FIGS. 1-2B  is a dual-function chamber that performs a material process and a thermal process on a substrate in a single chamber. Such a dual-function chamber is useful for processes that feature a material process followed by a thermal process. Such processes include, but are not limited to, metal deposition and reflow, silicidation, deposition (CVD, ALD, PECVD, epitaxy) and anneal, implant and anneal, and plasma nitridation and reoxidation. Such processes may be performed in a single chamber by coupling a peripheral radiation source, substantially as described above, to a chamber that performs the material process. 
         [0032]    Measurement of substrate temperature is accomplished through non-contact means by disposing a light pipe in one lift pin and coupling the light pipe to a thermal radiation sensor, such as a pyrometer.  FIG. 2A  is a detailed view of a lift pin  114 , so configured. The lift pin  114  has a body  202  with a tip  204  and a base  206 . A light pipe  208  is disposed within the body  202  of the lift pin  114 . The base  206  may have a threaded coupling  210  that couples to a threaded mount  212 . The threaded mount  212  may be attached to the actuator  162  of  FIG. 1 . The light pipe has a base end  216  that extends into the base  206  of the lift pin  114  and into the mount  212 . A face seal  214  is disposed about the base end  216  of the light pipe and abutting a shoulder  218  of an opening  220  in the mount  212 . A conduit  222 , such as a fiber optic cable, for example a 200 μm fiber bundle, couples to the light pipe  208  at the base end  216  thereof through the opening  220 . A crush seal  224  is positioned about the base end  216  of the light pipe  208  adjacent to the face seal  214 . The crush seal  224  is positioned to be compressed by the base  206  as the lift pin  114  is attached to the mount  212 . Compression of the crush seal  224  applies force on the face seal  214 , urging the face seal  214  against the shoulder  218  to seal the opening  220 . Compression of the crush seal  224  also urges the crush seal  224  against the light pipe  208  to provide a radial seal around the light pipe  208 . The face seal  214  may be a dual seal with two seal members between the crush seal  224  and the shoulder  218 . 
         [0033]    The tip  204  of the lift pin  114  has a swivel coupling  226  disposed between the tip  204  of the lift pin  114  and the light pipe  208 .  FIG. 2B  is a detailed view of the swivel coupling  226  disposed inside the tip  204 . The swivel coupling  226  extends beyond the tip  204  and the light pipe  208  to prevent contact between a substrate and either the tip  204  or the light pipe  208 . The swivel coupling  226  is free to rotate within the tip  204  so that a contact surface  228  of the swivel coupling  226  may remain in full contact with the substrate surface along the entire extent of the contact surface  228  in the event the substrate surface rotates or bows. The contact surface  228  prevents environmental thermal radiation present in the chamber from entering the light pipe  208 , so that substantially the only radiation received by the light pipe  208  is radiation emitted by the substrate. 
         [0034]    The contact surface  228  of the swivel coupling  226  is contoured to provide a light trap. A groove  230  formed in the contact surface  228  reduces parallelism between the contact surface  228  of the swivel coupling  226  and the substrate surface, which reduces reflective transmission of light through the interface between the contact surface  228  and the substrate surface. The groove  230  provides a non-parallel portion of the contact surface  228  to disturb reflective propagation of light through the interface, reducing intrusion of radiation around the swivel coupling  226  and into the light pipe  208 . 
         [0035]    The lift pin  202  may be a thermally conductive material to provide a heat shield for the light pipe  208  disposed inside. A metal, such as copper, may be used. 
         [0036]      FIG. 3  is a cross-sectional view of a tip  300  of a lift pin  302  for use in the chamber  100  according to another embodiment. The lift pin  302  has the light pipe  208  disposed within. The tip  300  is a “blind” tip because the end of the light pipe  208  is covered by a cover  308  that reduces thermal noise around the light pipe  208 . The cover  308  has a ledge  312  that protrudes radially outward from the light pipe  208  and engages an inward extension  314  of a threaded clamp  306 . The threads of the threaded clamp  306  in turn engage a threaded end  304  of the lift pin  302 . A compression ring  316  may be used between the ledge  312  and the extension  314 . An insulator  310  is disposed around a portion  318  of the light pipe  208  that protrudes above the end of the lift pin  302 . The insulator may be a material that has low thermal conductivity, such as quartz, to prevent intrusion of thermal noise into the light pipe through the side. The cover  308  is typically a thermally conductive material, for example a metal like tungsten, to facilitate the light pipe  208  absorbing thermal energy from a substrate in contact with the cover  308 . The lift pin  302  generally has the same base construction as the lift pin of  FIG. 2A , where the light pipe  208  is optically coupled to the conduit  222  for transmission of a signal to a thermal sensor. 
         [0037]    A chamber such as the chamber  100 , with a lift pin  114  configured to sense thermal emissions from a substrate may be used to sense a substrate temperature in an environment with high levels of thermal noise. A first signal may be ascertained that contains information about the thermal state of the substrate and thermal noise from the environment. A second signal may also be ascertained that contains only, or substantially, thermal noise from the environment. Comparing the first signal and the second signal reveals a composite signal that contains information about the thermal state of the substrate with very little noise. In some embodiments, the first signal is a transmissivity signal that varies inversely with temperature. In embodiments that feature relatively opaque substrates where little radiation is transmitted by the substrate into the light pipe, thermal noise from the chamber is relatively low, and direct substrate emissions may be used to sense substrate temperatures at low levels such as 200° C. Where the substrate is more transparent, thermal noise from the chamber is transmitted by the substrate into the light pipe and direct substrate emissions, which are at similar wavelengths, may be overwhelmed. In such embodiments, wavelengths that are only emitted by the chamber, and not by the substrate, may be used as a measure of environmental thermal noise. It is known that transmissivity of materials such as silicon declines at some wavelengths, particularly longer wavelengths, as temperature rises, so transmissivity of the substrate may be monitored using one wavelength while thermal noise is monitored at a second wavelength at which the substrate is transparent at all temperatures, such as a shorter wavelength, and the two signals may be compared to determine temperature of the substrate. 
         [0038]    In one embodiment, a lift pin configured with a light pipe as described herein, is used to collect thermal radiation at two different wavelengths, one wavelength selected based on a change in transmissivity of the substrate with temperature at that wavelength, and another wavelength characteristic of thermal noise in the chamber that is transmitted at all temperatures of interest. The first wavelength may be a long wavelength, such as a wavelength above about 1200 nm, for example about 1280 nm or 1550 nm, and the second wavelength may be a shorter wavelength, such as less than about 1100 nm, for example about 920 nm. In such an embodiment, the substrate is transparent to the second wavelength at all temperatures of interest while transmission of the first wavelength varies with temperature. The intensity of radiation detected at the second wavelength is used as an indicator of radiation levels in the chamber, and is subtracted from the intensity of radiation detected at the first wavelength using known emission characteristics of the radiation source. The resulting signal indicates radiation transmitted by the substrate. The transmitted intensity may be correlated to substrate temperature, so that as the transmitted intensity changes, temperature may be determined. In such an embodiment, the temperature will be inversely related to the intensity of the radiation signal. 
         [0039]    While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.