WO2025166093A1 - Pvt system with improved hot zone alignment - Google Patents

Abstract

A physical vapor transport system with improved hot zone package alignment includes a first video pyrometer to view a center of a first hot zone at a first end of the hot zone package to measure a first temperature of the hot zone package and provide a first video feed showing instantaneous positions of the hot zone package as it is rotated. A second video pyrometer views a second hot zone viewport at a second end of the hot zone package to measure a second temperature of the center of the hot zone package and provide a second video feed showing instantaneous positions of the hot zone package as it is rotated. A controller processes the temperature measurements and video feeds and adjusts the system components or settings to correct for mis-alignment of the hot zone package. Such adjustments can be made prior to or during a process run while PVT growth of SiC bulk material is occurring.

Description

PVT SYSTEM WITH IMPROVED HOT ZONE ALIGNMENT

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] The present application claims the benefit of, and priority to U.S. Provisional Patent Application No. 63/548,949 filed on February 2, 2024, and U.S. Provisional Patent Application No. 63/695,423 filed on September 17, 2024, the entire contents of each of which are hereby incorporated herein by reference.

TECHNICAL FIELD

[002] The present disclosure generally relates physical vapor transport (PVT) systems and to novel methods of hot zone package alignment, temperature measurement, and process control of the system.

BACKGROUND

[003] Unless otherwise indicated herein, the materials described in this section are not prior art to this application and are not admitted being prior art by inclusion in this section.

[004] Physical vapor transport (PVT) systems are currently used for growth of single crystal bulk SiC, AIN, ZnSe, ZnSeTe, CdTe, CdS, and ZnTe materials.

[005] Alignment of the hot zone package, that includes the support structure (typically quartz vessel for inductively heated systems), heat insulation (typically graphite foam and graphite felt), and a graphite crucible for PVT growth of SiC bulk material, allows for reproducible growth. The hot zone package for inductively heating the PVT reactor is loaded manually, semi-manually or automatically into the system and is supported by an insulating pedestal, which is, in turn, supported by a metal base that is coupled to a ferrofluidic feedthrough and rotation motor to provide rotation of the hot zone package. Graphite foam parts are normally used as a cushion between the quartz pedestal and the quartz support vessel. Graphite felt is typically used as heat insulation around the crucible containing SiC seed and source material. The graphite crucible and insulation are designed to provide one or more viewports to measure crucible temperature with one or more infrared pyrometers and to create a desired vertical and radial temperature gradients inside of the crucible for sublimation growth.

[006] For accurate measurements of the crucible temperature, the hot zone package is installed aligned with the axis of rotation such that the center of the viewport is always aligned with the pyrometer field of view. Accuracy of the hot zone package placement is typically determined by the accuracy of the assembly of the hot zone package (e.g., wrapping of insulation around the crucible), the placement of the hot zone package within the vacuum chamber, and tolerances in machined components. Verification of alignment of the hot zone package in the chamber and of the pyrometer is typically done at the beginning growth process when crucible temperature is above 1000° C, and the pyrometer with a built-in video camera that can detect a video signal from a glowing susceptor. Misalignment of the pyrometer field of view and center of the viewport may sufficiently impact the apparent (averaged over a revolution) temperature reading to be substantially higher than temperature measured in the center. Discrepancy in the temperature readings can produce poor quality crystal and reduce production yield. For example, deviation of a hot zone package from concentricity by approximately 5 mm may impact apparent temperature readings by as much as 15° Celsius.

SUMMARY

[0071 Existing challenges associated with the foregoing, as well as other challenges, are overcome by the presently disclosed hot zone alignment structures and methods for a physical vapor transport system.

[008] In accordance with one aspect of the present disclosure, a physical vapor transport system is described and includes a vacuum chamber having a first view port in a top flange thereof and a second view port in a bottom flange thereof; a heater configured to heat objects within the vacuum chamber; a rotating pedestal configured to rotate around an axis of rotation; and a hot zone support configured to be rotated by the rotating pedestal. The hot zone support supports a hot zone package that includes a crucible surrounded at least in part by insulation; a first hot zone viewport at a first end of the hot zone package and adjacent an open end of the crucible; and a second hot zone viewport at a second end of the hot zone package. The system further includes a first video pyrometer positioned so that a field of view of the first video pyrometer views the first hot zone viewport through the viewport in the top flange of the vacuum chamber, the first video pyrometer measuring a first temperature of the first hot zone viewport and providing a first video feed showing instantaneous positions of the hot zone package as it is rotated; a second video pyrometer positioned to view the second hot zone viewport through the viewport in the bottom flange of the vacuum chamber, the second video pyrometer measuring a second temperature of a center of the second hot zone viewport and providing a second video feed showing instantaneous positions of the hot zone package as it is rotated; and a controller. The controller is configured to receive and analyze the first and second video feeds to determine the concentricity of first and second hot zone viewports relative to the axis of rotation of the rotating pedestal; determine, using the first video feed, how far the field of view of the first video pyrometer deviates from a center of the first hot zone viewport; and adjust a position of the first video pyrometer so that the field of view of the first video pyrometer is aligned with the center of the first hot zone viewport continuously during a process run dynamically compensating for any variation in crucible position.

[009] In aspects, the system further includes a first visible light source illuminating the first hot zone viewport, and a second visible light source illuminating the second hot zone viewport, wherein at least one of the first visible light source or the second visible light source is a collimated, high intensity visible light source.

[0010] In aspects, the second hot zone viewport extends through the insulation to a second end of the crucible.

[0011] In aspects, the controller is further configured to store temperature measurements taken as the field of view of the first video pyrometer traverses across the first hot zone viewport of the hot zone package while the hot zone package is heated within the vacuum chamber but not rotating; determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and based on the determination of how far the field of view of the first video pyrometer deviates from the axis of rotation and on the stored temperature measurements, adjust a temperature within the vacuum chamber.

[0012] In aspects, the controller is further configured to determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and adjust a position of the first video pyrometer in real time.

[0013] In aspects, the controller is further configured to determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and adjust a position of the first and second video pyrometers.

[0014] In aspects, the controller is further configured to determine, using the first video feed, how far the field of view of the first video pyrometer deviates from a center of the first hot zone viewport; and adjust a position of the first video pyrometer so that the field of view of the first video pyrometer is aligned with the center of the first hot zone viewport. [0015] In aspects, the controller is further configured to determine whether the hot zone package is tilted within the vacuum chamber by determining, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; determining, using the second video feed, how far the field of view of the second video pyrometer deviates from the axis of rotation of the rotating pedestal; and comparing how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal relative to how far the field of view of the second video pyrometer deviates from the axis of rotation of the rotating pedestal.

[0016] In aspects, the controller is further configured to rotate the rotating pedestal; image, by the first video pyrometer, a plurality of instantaneous images of the first hot zone viewport over one revolution of the hot zone package; determine, from the plurality of instantaneous images any deviation of a position of the hot zone package from a center of the rotating pedestal; and if the controller determines that the maximum deviation of the position of the hot zone package from the center of the rotating pedestal is larger than a threshold value, adjust the position of the hot zone package.

[0017] In aspects, the controller is further configured to receive and analyze the first temperature of the center of the first hot zone viewport and the second temperature of the center of the second hot zone viewport; and establish and maintain a desired temperature gradient between the open end of the crucible and a second end of the crucible within the vacuum chamber.

[0018] In aspects, the controller is further configured to establish and maintain the desired temperature gradient within the vacuum chamber by adjusting a position of the heater.

[0019] In aspects, the controller is further configured to establish and maintain the the desired temperature gradient within the vacuum chamber by adjusting a position of the crucible.

[0020] In aspects, the controller is further configured to establish and maintain the the desired temperature gradient within the vacuum chamber using a Proportional-Integral-Derivative (PID) control loop.

[0021] In aspects, the physical vapor transport system further includes at least one of a motion stage configured to adjust a position of the rotating pedestal within the vacuum chamber, a motion stage configured to adjust a position of the first video pyrometer relative to the vacuum chamber, or a motion stage configured to adjust a position of the second video pyrometer relative to the vacuum chamber. [0022] In aspects, the physical vapor transport system further includes a cushion positioned between the hot zone support and the rotating pedestal, the cushion includes a recess configured to receive the rotating pedestal; and a centering lock configured to center the cushion with respect to the hot zone support and to reduce slippage of the hot zone support relative to the rotating pedestal, wherein the cushion includes a recess configured to receive the centering lock, and a surface of the hot zone support in contact with the cushion is roughened to reduce slippage between the hot zone support and the cushion.

[0023] In aspects, the rotating pedestal, hot zone support and bottom flange are movable relative to the vacuum chamber to permit loading of the hot zone package onto the hot zone support outside of the vacuum chamber.

[0024] In accordance with another aspect of the present disclosure, a method of operating a physical vapor transport system is described and includes rotating a pedestal, the pedestal positioned on a motion stage configured to adjust the position of the rotating pedestal within a vacuum chamber, the pedestal having a hot zone support thereon, the hot zone support having a hot zone package supported thereon; measuring, by a pyrometer, a plurality of instantaneous temperatures of the hot zone package over one revolution of the hot zone package; determining, by a controller, an average temperature value from the plurality of instantaneous temperature measurements over one revolution of the hot zone package; and calculating, by the controller, a maximum deviation of the plurality of instantaneous temperature measurements over one revolution of the hot zone package from the average value of the temperature. If the controller determines that the maximum deviation is larger than a threshold value, the controller adjusts, by the motion stage, the position of the hot zone package within the vacuum chamber. Measuring, determining, calculating, and adjusting occur during a process run while PVT growth of SiC bulk material is occurring.

[0025] In accordance with another aspect of the present disclosure, a method of improving crystal growth in a physical vapor transport (PVT) system is described and includes loading a hot zone package including a crucible surrounded at least in part by insulation onto a rotating pedestal in a vacuum chamber of the PVT system; initiating a process run to grow SiC bulk material in the PVT system including rotating, by a controller, the rotating pedestal and the hot zone package around an axis of rotation of the rotating pedestal; and during the process run, receiving, at the controller, a first video feed and a first temperature from a first video pyrometer positioned so that a field of view of the first video pyrometer views a first hot zone viewport adjacent a top of the crucible, the first video feed showing instantaneous positions of the hot zone package as it is rotated; receiving, at the controller, a second video feed and a second temperature from a second video pyrometer positioned so that a field of view of the second video pyrometer views a second hot zone viewport adjacent a bottom of the crucible, the second video feed showing instantaneous positions of the hot zone package as it is rotated; analyzing, by the controller, the first and second video feeds from first and second video pyrometers to determine the concentricity of first and second hot zone viewports relative to the axis of rotation of the rotating pedestal; and adjusting, by the controller, based on the first and second temperature measurements and the first and second video feeds at least one of a position of video pyrometer, a position of the hot zone package, or a processing temperature during the process run while PVT growth of SiC bulk material is occurring.

[0026] In aspects, the adjusting is done continuously during the process run.

BRIEF DESCRIPTION OF THE FIGURES

[0027] The foregoing and other features of this disclosure will become more fully apparent from the following description, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

[0028] FIG. 1 schematically shows an inductively heated physical vapor transport system in accordance with the present disclosure.

[0029] FIG. 2 shows an example of a pyrometer camera image of the viewport taken at room temperature with the indicator of pyrometer temperature measurement field of view.

[0030] FIG. 2A shows another example of a pyrometer camera image of the hot zone viewport with an indicator of the center of rotation, the center of the pyrometer field of view, the center of the hot zone viewport trajectory during rotation, and an area of acceptable centering based on image processing.

[0031] FIG. 3 schematically shows another physical vapor transport system in accordance with aspects of the present disclosure.

[0032] FIG. 4 schematically shows a viewport in a graphite crucible in accordance with aspects of the present disclosure. [0033] FIG. 5 A shows a top view of the hot zone viewport with the pyrometer field of view aligned precisely with the center of a viewport and the center of rotation of the hot zone package in accordance with aspects of the present disclosure.

[0034] FIG. 5B shows scenario when a hot zone is still centered around the center of rotation, but the pyrometer field is misaligned with the center of rotation.

[0035] FIG. 5C schematically shows case when both a hot zone and a pyrometer are misaligned with respect to the center of rotation.

[0036] FIG. 6A schematically shows the steady state temperature set point (dash line) determined by the average temperature during one or multiple revolutions and immediate temperature measured value (solid line) for the scenario shown in FIG. 5A.

[0037] FIG. 6B shows the steady state set point (dash line) and varying immediate temperature (solid line) caused by misalignment of a hot zone crucible and a pyrometer.

[0038] FIG. 6C shows a graph of temperature measurements taken as the position of pyrometer field of view is transversed in both the x and y directions across the hot zone viewport of a static (not rotating) hot zone package.

[0039] FIG. 7 shows a cross section view of a viewport, with details schematically showing factors contributing to the accuracy and consistency of temperature measurement in accordance with aspects of the present disclosure.

[0040] FIG. 8 shows a system with the pyrometer mounted to an x-y motion stage and the hot zone support and rotation assembly mounted to an x-y motion stage in accordance with aspects of the present disclosure.

[0041] FIG. 9A is a flow chart showing a control algorithm for improved temperature measurement accuracy and consistency in accordance with aspects of the present disclosure.

[0042] FIG. 9B is a flow chart showing a control algorithm for improved temperature measurement accuracy and consistency in accordance with aspects of the present disclosure.

[0043] FIG. 10A schematically shows further details of the load support assembly in a chamber- closed position in accordance with aspects of the present disclosure.

[0044] FIG. 10B schematically shows the load support assembly of FIG. 10A in a chamber-open position when the end cap with load and load support mechanism is retracted from the process chamber in accordance with aspects of the present disclosure. [0045] FIG. 10C schematically shows a hot zone package with a modified lower viewport in accordance with aspects of the present disclosure.

[0046] FIG. 10D schematically shows a straight, but offset hot zone package within the vacuum chamber in accordance with aspects of the present disclosure.

[0047] FIG. 10E schematically shows a tilted hot zone package within the vacuum chamber in accordance with aspects of the present disclosure.

[0048] FIG. 11 shows further details of a load support assembly in accordance with aspects of the present disclosure.

[0049] FIG. 12A shows an AGV or AMR carrying a load with support arms in accordance with aspects of the present disclosure.

[0050] FIG. 12B shows an orthogonal cross section view of a load illustrating the position of support arms in accordance with aspects of the present disclosure.

[0051] FIG. 13 is a flowchart showing the steps of an example algorithm for controlling the position of the load prior to lowering it over a quartz support pedestal in the PVT tool in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0052] Novel devices and methods for aligning a hot zone within a physical vapor transport system are described herein. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure may be practiced without these specific details.

[0053] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, and drawings are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. [0054] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0055] As seen in FIG. 1, an inductively heated physical vapor transport system in accordance with the present disclosure may include: a quartz vacuum chamber 101; an induction coil 102; top and bottom viewports 103a and 103b formed in top and bottom sealing flanges 104a and 104b, respectively of vacuum chamber 101 ; a video pyrometer 105 for taking temperature measurements and generating a video feed; a hot zone package 106, including a crucible 106a, insulation 106b, and a hot zone viewport 107 formed in insulation 106b to allow viewing of the interior of crucible 106a; a hot zone support 108; and a rotating quartz pedestal 109 which rotates around an axis of rotation “A” thereby rotating hot zone package 106. Operation of the system of FIG. 1 may be automatically controlled by a programmable logic controller (PLC) or a PC (“controller”) 1000 which is not only capable of controlling rotation of pedestal 109, vertical adjustment of induction coil 102 (as shown by arrow “B” in FIG. 1), and other process parameters, but is also capable of image recognition and centering data processing based on the temperature measurements and video feed from video pyrometer 105. FIG. 2 shows an example of a pyrometer camera image of the hot zone viewport 107 taken at room temperature with the indicator of pyrometer field of view 201. As those skilled in the art reading this disclosure will understand, the position of the hot zone viewport 107 reflects the position of the hot zone package 106 (and hence of crucible 106a) relative to the axis of rotation.

[0056] Another pyrometer camera image of the hot zone viewport 107 is shown in FIG. 2A with an indicator of the center of rotation 201, the center of the pyrometer field of view 202, the center of the hot zone viewport trajectory during rotation 203, and the area of an acceptable centering 204 determined based on image recognition and centering data processing performed by controller 1000.

[0057] FIG. 3 schematically shows a possible positions of visible light sources 31, 32, 33 illuminating a hot zone viewport 107 to enable a camera in video pyrometer 105 to detect a position of hot zone viewport 107 and, therefore, alignment of hot zone package 106. It should of course be understood that only a single light source (e g., one of light sources 31, 32, or 33) may be present in the system, although two or more light sources are also contemplated.

[0058] FIG. 4 schematically shows a viewport 501 in a graphite crucible 502. When crucible 502 and pyrometer 105 (see FIG. 3) are both set up precisely on the axis of rotation “A” and vertically aligned, the pyrometer field of view 503 is located exactly in the center of the viewport 501 therefore measuring temperature in a most accurate manner. The pyrometer field of view may also be misaligned to positions 504 or 505 (i.e., pyrometer field of view rotating around axes XI or X2, respectively in FIG. 4) depending on how closely the hot zone package is centered with the axis of rotation and pyrometer centerline.

[0059] FIG. 5 A shows a top view of the hot zone viewport 601 (equivalent to 501 in FIG. 4) with the pyrometer field of view 602 aligned precisely with the center of viewport 601 and center of rotation 603 of the hot zone package.

[0060] FIG. 5B shows a scenario when hot zone viewport 601 is still centered around center of rotation 603 but the pyrometer field of view 602' is misaligned with the center of rotation such that the pyrometer field of view 602' follows the trajectory 605 during one revolution of the hot zone package.

[0061] FIG. 5C schematically shows the case when both a hot zone viewport and a pyrometer are misaligned with respect to the center of rotation 606. In such a case, the system will be measuring immediate temperature values from a pyrometer field of view 602" moving along the trajectory 607 during one revolution of the hot zone package.

[0062] FIG. 6A schematically shows the steady state temperature set point (dash line) determined by the average temperature during one or multiple revolutions of the hot zone package and the immediate temperature measured value (solid line) for the scenario shown in FIG. 5A, when both the pyrometer and the hot zone viewport are centered perfectly at the center of rotation, or for the scenario shown in FIG. 5B, when hot zone viewport is positioned perfectly at the center of rotation, but the pyrometer is misaligned. In the scenario shown in FIG. 5B, the pyrometer measures temperature at a constant distance from the axis of rotation, so the measurements, while not ideal, nonetheless show a steady state temperature. Controller 1000 can be programmed to detect the distance that the pyrometer varies from the center of rotation and adjust the power (e.g., RF power) from a power supply (not shown) accordingly to achieve a desired process temperature. [0063] FIG. 6B shows the steady state set point (straight dash line) and varying immediate temperature (varying solid and dashed lines) caused by misalignment of both a hot zone package and a pyrometer, such as e.g., for the scenario shown in FIG. 5B. Temperature variations ATI and AT2 are linearly proportional to the deviation of the pyrometer field of view trajectory 607 (see FIG. 5C) from the center of rotation, as long as the pyrometer field of view is continuously located within the hot zone viewport. In the scenario shown in FIG. 5C, the pyrometer measures different temperatures at different distances from the axis of rotation, controller 1000 can be programmed to average either the varying temperatures or the distance that the pyrometer varies from the center of rotation during one or more rotations of the hot zone package and adjust the temperature of the system accordingly to achieve a desired process temperature.

[0064] Controller 1000 may adjust the temperature of the system based on empirical data stored in a memory (not shown) associated with 1000. For example, as shown in FIG. 6C, temperature measurements taken as the position of pyrometer field of view is transversed, e.g., by motion stage 91 (see FIG. 8), in both the x and y directions across the hot zone viewport of a static (not rotating) hot zone package. As seen in FIG. 6C, misalignment of 5mm results in a temperature variation of 15 °C. Given the parabolic nature of the curve shown by the data of FIG. 6C, temperature variations can be extrapolated and saved in the memory of controller 1000. Knowing (e.g., from the video feed) how far the pyrometer field of view deviates from the axis of rotation, controller 1000 can use the stored empirical data of FIG. 6C to know how to adjust the temperature of the system to achieve a desired process temperature. It should, of course, be understood that temperature measurements across the hot zone viewport of a static (not rotating) hot zone package can be taken for fields of view of multiple pyrometers (e.g., a top pyrometer and a bottom pyrometer - see FIGs. 10A-C below, for example) can be such empirical data being stored in a memory (not shown) associated with controller 1000 to determine how to adjust the position of the pyrometer(s) or the temperature of the system to achieve a desired process temperature.

[0065] FIG. 7 shows a cross section view of a hot zone viewport, with details 801-804 schematically showing factors contributing to the accuracy and consistency of temperature measurement, such as flatness (801), roughness (802), concave round (803), or conical (804) finish of the hot zone viewport surface of the inner top surface of the hot zone viewport immediately adjacent crucible 106a. While four specific surfaces 801 - 804 are shown, other surface configurations, or combination of the shown surface features, are also contemplated. [0066] FIG. 8 shows the pyrometer 105 mounted to x-y motion stage 91 and hot zone support 108 and rotation assembly 109 to be mounted to x-y motion stage 92. Stage 91 can be used to adjust the pyrometer field of view to coincide with the axis of rotation of the hot zone viewport, based, e.g., on the video feed from pyrometer 105. Stage 92 can be used to adjust the position of the hot zone package to coincide with the center axis of the vacuum chamber based, e.g., on the video feed from pyrometer 105. The x-y motion stages are automatically controlled by a programmable logic controller (PLC) or PC (“controller”) 1000 which controls a motor (not shown) to adjust the position of the stages 91, 92 based on information provided to the controllers from one or more sensors or cameras, such as video pyrometer 105 (see FIG. 1). In aspects, the controller may process such information (e.g., temperature measurements and video feed from video pyrometer 105) and compare it to information stored on a memory (not shown) to which the controller also has access. The controller may control the position of the stages 91, 92 in any suitable manner, including, but not limited to according to the control algorithms described below in connection with FIGs. 9A and 9B.

[0067] FIG. 9A is a flow chart showing a control algorithm 900 for improved temperature measurement accuracy and consistency based on the minimization of the immediate temperature variation AT below a predetermined threshold value by in situ adjusting the x-y position of at least one of the pyrometer or the hot zone package. At 902, a programmable logic controller (PLC) or PC (“controller”) measures instantaneous temperatures by the top pyrometer. At 904, the controller collects the variation of instant temperatures over one revolution of the crucible. At 906, the controller calculates the maximum deviation from the average value of the temperature over one revolution of the hot zone package containing the crucible. At 908, the controller determines if the deviation is larger than a threshold value. If so, at 910 the controller adjusts the x-y position of the hot zone package or the pyrometer. If the deviation is not larger than a threshold value, then at 912 the controller adjusts the process temperature setpoint by a predetermined value based on the offset (see discussion of FIG. 6C, supra), and the process returns to 902.

[0068] FIG. 9B is a flow chart showing a control algorithm 950 for improved temperature measurement accuracy and consistency based on the minimization of the deviation of the pyrometer field of view from the center of rotating viewport below a predetermined threshold value by in situ adjusting x-y position of the pyrometer or the hot zone package. At 952, a programmable logic controller (“controller”) measures any radial deviation of the pyrometer field of view from the center of the hot zone viewport. At 954, the controller collects any instant temperature variations over one revolution of the hot zone package containing the crucible. At 956, the controller calculates the maximum deviation from the average value of the temperature over one revolution of the hot zone package. At 958, the controller determines if the deviation is larger than a threshold value. If so, at 960 the controller adjusts the x-y position of the hot zone package or the pyrometer. If the deviation is not larger than a threshold value, then at 962 the controller adjusts the process temperature setpoint by a predetermined value based on the offset (see discussion of FIG. 6C, supra), and the process returns to 952.

[0069] During processing, to assist with proper mass transport from Si+C or SiC source material to a single crystal SiC boule deposited on the seed at the top of crucible, it may be advantageous to establish and maintain a variable temperature gradient within the vacuum chamber. Having accurately measured top and bottom temperatures of the hot zone package, the controller can be programmed to analyze the temperature measurements received from the top and bottom pyrometers and to adjust the settings of the system to establish and maintain a desired temperature gradient within the vacuum chamber. For example, the controller may adjust the position of a heater (e.g., move induction coil 102 in the direction indicated by arrow “B” in FIG. 1) based on pyrometer readings to establish and/or maintain a desired temperature gradient. In aspects, the controller may employ a Proportional-Integral-Derivative (PID) control loop to maintain a predetermined vertical temperature gradient between the temperature measured in the center of the first or top viewport and the temperature measured in the center of the second or bottom viewport during the process by adjusting the heater element (induction coil) position during the process.

[0070] As seen in FIG. 10A, with the load support assembly in a chamber-closed position, hot zone support pedestal 301 rests on a metal pedestal assembly 302 which is supported by the rotation feedthrough 303 that has a bottom viewport 304. Rotation feedthrough 303 includes a ferrofluidic feedthrough to permit rotation of metal pedestal assembly 302 and hot zone support pedestal 301 on which the hot zone package 106 is positioned. FIG. 10B schematically shows load support assembly of FIG. 10A in a chamber-open position when end cap 104a with hot zone package 305and hot zone support pedestal 301 retracted from the vacuum chamber 101. The chamber-open position allows convenient positioning of hot zone package 106 on hot zone support pedestal 301. Using lower video pyrometer 311, the position of hot zone package 106 relative to the axis “A” of rotation of pedestal assembly 302 can be determined by viewing lower viewport 107a.

[0071] In embodiments, lower viewport 107a extends through insulation 106b to the bottom of crucible 106a as shown in FIG. 10C, permitting a more accurate reading of the temperature of crucible 106a as the hot zone package rotates.

[0072] The position of hot zone package 106 can be determined at room temperature before or after the load support assembly is raised into vacuum chamber 101. For example, as with the operation of the system of FIG. 1, controller 1000 is not only capable of controlling rotation of pedestal assembly 302 and vertical movement of the load support assembly into and out of vacuum chamber 101 (as shown by arrow “C” in FIG. 10B) but is also capable of image recognition and centering data processing based on the temperature measurements and video feed from lower video pyrometer 305. If the positioning of hot zone package 106 is undesirably off-center from axis “A”, the hot zone package 106 can be lifted and re-positioned on pedestal assembly 302 prior to sealing of vacuum chamber 101 and prior to the start of any processing. Once load support assembly is raised into and seals vacuum chamber 101, the position of both hot zone viewport 107 and lower viewport 107a can be monitored simultaneously by video pyrometers 105 and 305, respectively as the hot zone package 106 is rotated.

[0073] When monitoring the position of both hot zone viewport 107 and lower viewport 107a simultaneously, if the offset of viewports 107 and 107a from axis “A” is determined to be the same at the top and bottom (based on image recognition and centering data processing based on the temperature measurements and video feed from video pyrometers 105 and 305), it can be concluded that the hot zone package 106 is straight, but offset from the axis as shown in FIG. 10D, and controller 1000 can make appropriate adjustments of the position of video pyrometer and/or hot zone package, or adjust the processing temperature. In FIG. 10D the trajectory during rotation of hot zone viewport 107 (Ti) and the trajectory during rotation of lower viewport 107a (T2) are equivalent indicating a straight, but offset scenario. If, however, the offset from axis “A” is determined to be the different at the top compared to the bottom (based on image recognition and centering data processing based on the temperature measurements and video feed from video pyrometers 105 and 305), it can be concluded that the hot zone package 106 is tilted within vacuum chamber 101 as shown in FIG. 10E. In FIG. 10E the trajectory during rotation of hot zone viewport 107 (Ti) is greater in size than the trajectory during rotation of lower viewport 107a (T2) indicating a tilt scenario. Tilt of the hot zone package can be tracked run-to-run by the controller for statistical analysis and process control. Some threshold amount of package tilt may be determined by the controller to be tolerable based on the statistical analysis. If package tilt exceeds the tolerable threshold, system process conditions may be adjusted by the controller to bring package tilt below the threshold. If changes to the system process conditions are unsuccessful to bring package tilt below the threshold, the controller may automatically shut the process down.

[0074] While verification of alignment of the hot zone package in the chamber and of the pyrometer is typically done at the beginning of the growth process when crucible temperature is above 1000° C, it should be understood that alignment of the hot zone package can be verified during some or all of the process run while PVT growth of SiC bulk material is occurring. As those skilled in the art reading this disclosure will understand, typical growth rate of SiC bulk material is of the order of 0.2-0.5mm/hr typically with the aim of growing crystals that are up to or greater than 30mm thick. This requires the hot zone to be at high temperature (typically above 2000 °C) for over 100 hours, and alignment verification can be done continuously during the process run or intermittently at specific times during the process run. Verifying alignment of the hot zone package during the process run can improve crystal quality and increase production yield.

[0075] During the process run, the graphite felt insulation surrounding the crucible is exposed to high temperature and may degrade, losing its thickness and/or density. For example, the inner layer of the felt insulation may get thinner (e.g., from about 1/8” to about 1/16”) and may become denser. As a result the crucible which was initially tightly wrapped in the insulation may become “loose” during the process run and thus the crucible (or just the lid of the crucible with the upper viewport) can shift or sag during the process run. This degradation of the insulation may result in a shift in the position of the crucible during the process run and incorrect temperature measurements. Based on the temperature measurements and video feed from video pyrometers 105 and 305 (see FIG. 10C) taken during the process run during PVT growth of SiC bulk material as the insulation degrades an/or the hot zone package shifts, controller 1000 can make appropriate adjustments of the position of video pyrometer and/or hot zone package, and/or can make appropriate adjustments to the processing temperature during the process run. Active video feedback and real time x-y pyrometer position adjustment enables the temperature to always be measured in the center of the viewport thereby enabling use of a smaller viewport diameter which, in turn, promotes a radial temperature profile beneficial for growth of SiC with reduced defect density.

[0076] For example, the position of both hot zone viewport 107 and lower viewport 107a can be monitored simultaneously by video pyrometers 105 and 305, respectively as the hot zone package 106 is rotated (see FIG. 10C) during the process run while PVT growth of SiC bulk material is occurring. Based on image recognition and centering data processing based on the temperature measurements and video feed from video pyrometers 105 and 305, controller 1000 can make appropriate adjustments of the position of video pyrometer and/or hot zone package during the process run while PVT growth of SiC bulk material is occurring, and/or can make appropriate adjustments to the processing temperature during the process run. Continuous compensation of the misalignment of the hot zone package during the PVT SiC growth or cooldown after the deposition may enable improvements of SiC material quality, reduced residual stress, or both.

[0077] As seen in FIG. 11 , quartz hot zone support pedestal 401 rests on a metal pedestal assembly 402 which is supported by the shaft 403 with a rotation feedthrough 415 mounted to the bottom sealing flange 404. Rotation feedthrough 415 includes a ferrofluidic feedthrough to permit rotation of metal pedestal assembly 402 and hot zone support pedestal 401 on which the hot zone package 106 is positioned. The load support assembly has a spring-loaded mechanism 405 that supports the above assembly on the frame part 406. Rotation drive 407 and rotation motor 408 are also mounted to the frame part 406. A hollow shaft 403 has a transparent window 409. Translation stage 410 supports bottom video pyrometer 411 with a light source 412. Translation stage 410 can provide manual or motorized translation of the load support assembly in the X, Y, and Z directions. [0078] As seen in FIG. 12A, an AGV or AMR carries a load with support arms 1502. Automated loader 1501 is capable of docking to the frame of the PVT tool for rough positioning and has a fine adjustment of support arms 502 for positioning the load before lowering it over a quartz pedestal. Loader 1501 is also capable of communicating with the PVT tool over wireless interface, such as Wi-Fi or Bluetooth or similar, to provide fine position adjustments based on the lower pyrometer camera video feedback. FIG. 12B shows an orthogonal cross section view of a load illustrating position of support arms 1502. It should be noted that mechanical, vacuum or other methods can be used for gripping and supporting the quarts load assembly by support arms 1502. The number of support arms may be one or two or more while the number of contact points with the quartz load assembly can be two, four, six or more. [0079] FIG. 13 depicts a possible algorithm 1100 for controlling the position of the load prior to lowering it over a quartz support pedestal in the PVT tool.

[0080] At 1102, the lower and upper pyrometers and cameras are calibrated to be aligned to center of rotation. At 1104, the loader carrying the hot zone package docks to a PVT tool. At 1106, the loader aligns a hot zone package to a pedestal with feedback from the lower and upper cameras. At 1108, the loader lowers the hot zone package onto a support pedestal and retracts the supporting arms. At 1110, the processor (PLC/PC) starts load rotation to verify concentricity of the hot zone. At 1112, the PLC/PC measures any radial deviation of the hot zone center from the axis of rotation. At 1114, the control circuit collects any variation of instant position deviation over one revolution of the crucible. At 1116, the control circuit calculates the maximum deviation from the average value. At 1118, the controller determines if the maximum deviation from the average value is larger than a stored threshold value. If the threshold value is exceeded, at 1120 the process returns to 1 102 and the loading procedure is repeated. If the threshold value is not exceeded, at 1122 the loader is undocked from the PVT tool and the system proceeds with a growth run.

[0081] The example algorithms presented in the flowcharts of FIGs. 9A, 9B, and 13 include various operations, actions, or functions as illustrated by one or more of blocks. Although illustrated as discrete blocks, various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation.

[0082] The systems described herein may utilize one or more controllers to receive various information and transform the received information to generate an output. The controller may include any type of computing device, computational circuit, or any type of processor or processing circuit capable of executing a series of instructions that are stored in a memory. The controller may include multiple processors and/or multicore central processing units (CPUs) and may include any type of processor, such as a microprocessor, digital signal processor, microcontroller, programmable logic device (PLD), field programmable gate array (FPGA), or the like. The controller may also include a memory to store data and/or instructions that, when executed by the one or more processors, causes the one or more processors to perform one or more methods and/or algorithms.

[0083] Any of the herein described methods, programs, algorithms or codes may be converted to, or expressed in, a programming language or computer program. The terms “programming language” and “computer program,” as used herein, each include any language used to specify instructions to a computer, and include (but is not limited to) the following languages and their derivatives: Assembler, Basic, Batch files, BCPL, C, C+, C++, Ladder Logic, Delphi, Fortran, Java, JavaScript, machine code, operating system command languages, Pascal, Perl, PL1, scripting languages, Visual Basic, metalanguages which themselves specify programs, and all first, second, third, fourth, fifth, or further generation computer languages. Also included are database and other data schemas, and any other meta-languages. No distinction is made between languages which are interpreted, compiled, or use both compiled and interpreted approaches. No distinction is made between compiled and source versions of a program. Thus, reference to a program, where the programming language could exist in more than one state (such as source, compiled, object, or linked) is a reference to any and all such states. Reference to a program may encompass the actual instructions and/or the intent of those instructions.

[0084] The storage and/or memory device may be one or more physical apparatus used to store data or programs on a temporary or permanent basis. In some embodiments, the controller may include volatile memory and requires power to maintain stored information. In some embodiments, the controller includes non-volatile memory and retains stored information when it is not powered. In some embodiments, the non-volatile memory includes flash memory. In some embodiments, the non-volatile memory includes dynamic random-access memory (DRAM). In some embodiments, the non-volatile memory includes ferroelectric random access memory (FRAM). In some embodiments, the nonvolatile memory includes phase-change random access memory (PRAM). In some embodiments, the controller is a storage device including, by way of nonlimiting examples, CD-ROMs, DVDs, flash memory devices, magnetic disk drives, magnetic tapes drives, optical disk drives, and cloud computing based storage. In some embodiments, the storage and/or memory device is a combination of devices such as those disclosed herein. Code or instructions contained thereon can be represented by carrier wave signals, infrared signals, digital signals, and by other like signals.

[0085] It should be understood that the foregoing description is only illustrative of the present disclosure. Various alternatives and modifications can be devised by those skilled in the art without departing from the disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications, and variances. The embodiments described with reference to the attached drawing figures are presented only to demonstrate certain examples of the disclosure. Other elements, steps, methods, and techniques that are insubstantially different from those described above and/or in any appended claims are also intended to be within the scope of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A physical vapor transport system comprising: a vacuum chamber including a first view port in a top flange of the vacuum chamber and a second view port in a bottom flange of the vacuum chamber; a heater configured to heat objects within the vacuum chamber; a rotating pedestal configured to rotate around an axis of rotation; a hot zone support configured to be rotated by the rotating pedestal; a hot zone package supported by the hot zone support and including: a crucible surrounded at least in part by insulation; a first hot zone viewport at a first end of the hot zone package and adjacent an open end of the crucible; and a second hot zone viewport at a second end of the hot zone package; a first video pyrometer positioned so that a field of view of the first video pyrometer views the first hot zone viewport through the viewport in the top flange of the vacuum chamber, the first video pyrometer measuring a first temperature of the first hot zone viewport and providing a first video feed showing instantaneous positions of the hot zone package as it is rotated; a second video pyrometer positioned to view the second hot zone viewport through the viewport in the bottom flange of the vacuum chamber, the second video pyrometer measuring a second temperature of a center of the second hot zone viewport and providing a second video feed showing instantaneous positions of the hot zone package as it is rotated; and a controller configured to: receive and analyze the first and second video feeds to determine the concentricity of first and second hot zone viewports relative to the axis of rotation of the rotating pedestal. determine, using the first video feed, how far the field of view of the first video pyrometer deviates from a center of the first hot zone viewport; and adjust a position of the first video pyrometer so that the field of view of the first video pyrometer is aligned with the center of the first hot zone viewport continuously during a process run dynamically compensating for any variation in crucible position.

2. The physical vapor transport system of claim 1, further comprising: a first visible light source illuminating the first hot zone viewport; and a second visible light source illuminating the second hot zone viewport, wherein at least one of the first visible light source or the second visible light source is a collimated, high intensity visible light source.

3. The physical vapor transport system of claim 1, wherein the second hot zone viewport extends through the insulation to a second end of the crucible.

4. The physical vapor transport system of claim 1, wherein the controller is further configured to: store temperature measurements taken as the field of view of the first video pyrometer traverses across the first hot zone viewport of the hot zone package while the hot zone package is heated within the vacuum chamber but not rotating; determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and based on the determination of how far the field of view of the first video pyrometer deviates from the axis of rotation and on the stored temperature measurements, adjust a temperature within the vacuum chamber.

5. The physical vapor transport system of claim 1, wherein the controller is further configured to: determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and adjust a position of the first video pyrometer in real time.

6. The physical vapor transport system of claim 1, wherein the controller is further configured to: determine, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; and adjust a position of the first and second video pyrometers.

7. The physical vapor transport system of claim 1, wherein the controller is further configured to: determine, using the first video feed, how far the field of view of the first video pyrometer deviates from a center of the first hot zone viewport; and adjust a position of the first video pyrometer so that the field of view of the first video pyrometer is aligned with the center of the first hot zone viewport.

8. The physical vapor transport system of claim 1, wherein the controller is further configured to: determine whether the hot zone package is tilted within the vacuum chamber by: determining, using the first video feed, how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal; determining, using the second video feed, how far the field of view of the second video pyrometer deviates from the axis of rotation of the rotating pedestal; and comparing how far the field of view of the first video pyrometer deviates from the axis of rotation of the rotating pedestal relative to how far the field of view of the second video pyrometer deviates from the axis of rotation of the rotating pedestal.

9. The physical vapor transport system of claim 1, wherein the controller is further configured to: rotate the rotating pedestal; image, by the first video pyrometer, a plurality of instantaneous images of the first hot zone viewport over one revolution of the hot zone package; determine, from the plurality of instantaneous images any deviation of a position of the hot zone package from a center of the rotating pedestal; and if the controller determines that the maximum deviation of the position of the hot zone package from the center of the rotating pedestal is larger than a threshold value, adjust the position of the hot zone package.

10. The physical vapor transport system of claim 1, wherein the controller is further configured to: receive and analyze the first temperature of the center of the first hot zone viewport and the second temperature of the center of the second hot zone viewport; and establish and maintain a desired temperature gradient between the open end of the crucible and a second end of the crucible within the vacuum chamber.

11. The physical vapor transport system of claim 10, wherein the controller establishes and maintains the desired temperature gradient within the vacuum chamber by adjusting a position of the heater.

12. The physical vapor transport system of claim 10, wherein the controller establishes and maintains the desired temperature gradient within the vacuum chamber by adjusting a position of the crucible.

13. The physical vapor transport system of claim 10, wherein the controller establishes and maintains the desired temperature gradient within the vacuum chamber using a Proportional- Integral-Derivative (PID) control loop.

14. The physical vapor transport system of claim 1, further comprising at least one of a motion stage configured to adjust a position of the rotating pedestal within the vacuum chamber, a motion stage configured to adjust a position of the first video pyrometer relative to the vacuum chamber, or a motion stage configured to adjust a position of the second video pyrometer relative to the vacuum chamber.

15. The physical vapor transport system of claim 1, further comprising: a cushion positioned between the hot zone support and the rotating pedestal, the cushion includes a recess configured to receive the rotating pedestal; and a centering lock configured to center the cushion with respect to the hot zone support and to reduce slippage of the hot zone support relative to the rotating pedestal, wherein the cushion includes a recess configured to receive the centering lock, and a surface of the hot zone support in contact with the cushion is roughened to reduce slippage between the hot zone support and the cushion.

16. The physical vapor transport system of claim 1, wherein the rotating pedestal, hot zone support and bottom flange are movable relative to the vacuum chamber to permit loading of the hot zone package onto the hot zone support outside of the vacuum chamber.

17. A method of operating a physical vapor transport system, the method comprising: rotating a pedestal, the pedestal positioned on a motion stage configured to adjust the position of the rotating pedestal within a vacuum chamber, the pedestal having a hot zone support thereon, the hot zone support having a hot zone package supported thereon; measuring, by a pyrometer, a plurality of instantaneous temperatures of the hot zone package over one revolution of the hot zone package; determining, by a controller, an average temperature value from the plurality of instantaneous temperature measurements over one revolution of the hot zone package; calculating, by the controller, a maximum deviation of the plurality of instantaneous temperature measurements over one revolution of the hot zone package from the average value of the temperature; and if the controller determines that the maximum deviation is larger than a threshold value, adjusting, by the motion stage, the position of the hot zone package within the vacuum chamber, wherein the measuring, determining, calculating, and adjusting occur during a process run while PVT growth of SiC bulk material is occurring.

18. A method of improving crystal growth in a physical vapor transport (PVT) system, the method comprising: loading a hot zone package including a crucible surrounded at least in part by insulation onto a rotating pedestal in a vacuum chamber of the PVT system; initiating a process run to grow SiC bulk material in the PVT system including rotating, by a controller, the rotating pedestal and the hot zone package around an axis of rotation of the rotating pedestal; and during the process run, receiving, at the controller, a first video feed and a first temperature from a first video pyrometer positioned so that a field of view of the first video pyrometer views a first hot zone viewport adjacent a top of the crucible, the first video feed showing instantaneous positions of the hot zone package as it is rotated; receiving, at the controller, a second video feed and a second temperature from a second video pyrometer positioned so that a field of view of the second video pyrometer views a second hot zone viewport adjacent a bottom of the crucible, the second video feed showing instantaneous positions of the hot zone package as it is rotated; analyzing, by the controller, the first and second video feeds from first and second video pyrometers to determine the concentricity of first and second hot zone viewports relative to the axis of rotation of the rotating pedestal; and adjusting, by the controller, based on the first and second temperature measurements and the first and second video feeds at least one of a position of video pyrometer, a position of the hot zone package, or a processing temperature during the process run while PVT growth of SiC bulk material is occurring.

19. The method of claim 18, wherein the adjusting is done continuously during the process run.