PVT system with active temperature gradient control

Abstract

A physical vapor transport system includes a vacuum chamber and a hot zone package located within the vacuum chamber. The hot zone package includes a crucible and a top hot zone viewport adjacent an open end of the crucible. One or more light sources are positioned to illuminate the top hot zone viewport and, upon activation, adjust a temperature gradient within the crucible.

Description

International Patent ApplicationDocket 2624-44 PCTPVT SYSTEM WITH ACTIVE TEMPERATURE GRADIENT CONTROLCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of, and priority to, U.S. Provisional Patent Application No. 63 / 681,191 filed on August 9, 2024, the entire contents of which are hereby incorporated herein by reference.TECHNICAL FIELD

[0002] The present disclosure generally relates physical vapor transport (PVT) systems and to novel methods of active radial temperature control at the growth front.BACKGROUND

[0003] 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.

[0004] Physical vapor transport (PVT) systems are currently used for growth of single crystal bulk SiC, AIN, ZnSe, ZnSeTe, CdTe, CdS, and ZnTe materials. An example of a PVT system is described in commonly owned International Application No. PCT / US24 / 39699, the entire disclosure of which is incorporated herein by this reference.

[0005] SiC bulk growth by a physical vapor transport (PVT) method involves a hot zone assembly, that includes a support structure (typically a quartz vessel), heat insulation (typically graphite foam and graphite felt), and a graphite crucible containing the source material and a seed SiC material, with the crucible being resistively or inductively heated (typically to above 1800° C e.g., by an induction coil positioned outside the reactor) for seeded sublimation growth. The hot zone package is loaded manually, semi-manually or automatically into the vacuum chamber of the PVT system and is supported by an insulating pedestal, which is, in turn, supported by a metal base that is coupled to a ferrofluidic feedthrough to provide hot zone assembly rotation. Graphite foam parts are normally used as a cushion between the quartz pedestal and the quartz support vessel. Graphite felt is used as heat insulation around the crucible containing the SiC seed and source material. The cylindrical design of the graphite crucible and felt insulation typically provides viewports (made, e.g., from fused silica, sapphire, borosilicate glass, zinc selenide, magnesium fluoride, calciumInternational Patent Application Docket 2624-44 PCT fluoride, etc.) to measure crucible temperature with infrared pyrometers and to monitor any temperature gradients inside of the crucible for sublimation growth.

[0006] For reproducible growth of a SiC boule with consistent defect and residual stress distribution it is advantageous to have repeatable and controllable axial (along the axis of rotation) and radial (from center to the edge of the crucible) temperature gradients inside of the crucible holding the source material and across the growth front over the SiC seed surface. In inductively heated PVT systems, the axial temperature gradient is created by the design of the hot zone assembly, in particular' by the shape and thickness of the insulation material, and by the position of the induction coil with respect to the hot zone assembly. A typical radial temperature gradient at the growth front is about 5-10 °C for a 150mm crystal and slightly more for a 200mm crystal. A typical axial temperature gradient can be 20-30 °C depending on the size of the crucible. The actual temperature gradients inside of the crucible are nonlinear and vary during the growth (due to the mass transfer from source to seed). It can be modeled based on the geometry and properties of hot zone assembly materials and construction with reference to the top and bottom pyrometer measurements of outer crucible surface temperature inside of the viewports.

[0007] The radial temperature gradient at the growth front is also impacted by the construction and materials of the hot zone assembly (crucible and insulation). The radial temperature gradient also varies during the growth run and is difficult to control in inductively heated PVT systems with a single induction coil.SUMMARY

[0008] Existing challenges associated with the foregoing, as well as other challenges, are overcome by the presently disclosed active control of temperature gradient(s) in the crucible of a physical vapor transport system and methods for active control of temperature gradient(s) in the crucible of a physical vapor transport system. Active control of temperature gradient(s) can be provided by the present systems during the growth and / or cool down phases of the SiC boule growth process in the physical vapor transport system.

[0009] In accordance with one aspect of the present disclosure, a light source with an emission wavelength outside of the pyrometer detection band is incorporated outside or inside of the vacuum chamber to provide additional heat flux to the top crucible viewport. The light source heats up the center of the crucible viewport above its quasi steady-state value at a given RF power, coil positionInternational Patent Application Docket 2624-44 PCT and hot zone assembly construction. In aspects, the present system provides additional heat sourcc(s) localized at the crucible viewport area to impact the radial and / or axial temperature gradient inside of the crucible during the growth or cool down part of the process.

[0010] In accordance with another aspect of the present disclosure, additional heating from the light source targets the center of the viewport maintaining mechanical alignment of the hot zone assembly, the pyrometer field of view, and the heated spot independent of alignment with the axis of rotation of the hot zone assembly.

[0011] As used herein, the term “axial temperature gradient” refers to the change in temperature along the vertical axis of the crucible in a PVT system (i.e. , in the direction of the crucible's length, rather than across its width). The term “radial temperature gradient” refers to the change in temperature across the width of the crucible in a PVT system.BRIEF DESCRIPTION OF THE FIGURES

[0012] Fig. 1 schematically shows an inductively heated physical vapor deposition system suitable for incorporation of active control of the radial temperature gradient in accordance with the present disclosure.

[0013] Fig. 2 shows an example of a modeled temperature and flow distribution inside of the crucible of an illustrative PVT system.

[0014] Fig. 3 schematically shows a nearly collimated light source illuminating a hot zone viewport for active control of the radial temperature gradient in the crucible in accordance with the present disclosure.

[0015] Fig. 4a (prior art) shows typical schematic of two detectors implemented a pyrometer.

[0016] Fig. 4b (prior art) shows the operation principle of a two wavelength pyrometer.

[0017] Fig. 5a (prior art) shows examples of the two-color and dual wavelength pyrometers.

[0018] Fig.5b (prior art) shows an example of responsivity curves of a two-color pyrometer.

[0019] Fig. 6 shows examples of possible light source arrangements for incorporation of active control of the radial temperature gradient in a crucible of an illustrative PVT system in accordance with the present disclosure.International Patent ApplicationDocket 2624-44 PCTDETAILED DESCRIPTION

[0020] 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.

[0021] Novel devices and methods for heating a hot zone viewport 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.

[0022] 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.

[0023] Fig. 1 schematically shows an inductively heated physical vapor transport system in which active control of a radial temperature gradient can be achieved in accordance with the present disclosure. The system includes a quartz vacuum chamber 101, an induction coil 102, top and bottom chamber view ports 103a and 103b, top and bottom vacuum flange 104a and 104b, top and bottom pyrometers 105a and 105b for temperature measurements, a hot zone assembly 106, a hot zone top and bottom view ports 107a and 107b, a hot zone support 108, a rotating quartz pedestal 109, a crucible 110, a ferrofluidic feedthrough assembly 111 and a metal support pedestal 112. 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 active control of axial and / or radial temperatureInternational Patent Application Docket 2624-44 PCT gradients within the crucible in accordance with the present disclosure based on the temperature measurements from top and bottom pyrometers 105a and 105b.

[0024] Fig. 2 shows an example of a modeled temperature and flow distribution inside of the crucible 110 schematically indicating the temperature at the growth front in the center 201 and edge 202 of the seed as well as at the location of the top crucible viewport 203. As seen in Fig. 2, hot spots near the bottom of the crucible can be more than 40 °C hotter than the cool area near the top of the crucible. Depending on the size of the crucible, an axial gradient (along the axis of the crucible) can be as much as 20-30 °C. A radial (from center to the edge of the crucible) temperature gradient inside of the crucible holding the SiC seed material can be of the order of 5-10 °C at the growth front. Controllable radial and axial temperature gradients are highly desirable for reproducible growth of a SiC boule with consistent defect and residual stress distribution. The presently described systems provide a solution to this problem.

[0025] Fig. 3 schematically shows a nearly collimated light source 301 illuminating viewport 107a to heat up a viewport surface above the steady-state temperature. In aspects, when light source 301 illuminates viewport 107a, axial and radial temperature gradients inside of the crucible are reduced by several degrees Centigrade or even reversed, if desirable. Light source 301 is aligned such that specular reflected light does not couple with the top pyrometer 105 a. Because the specular reflected light is not incident on top pyrometer 105a, the accuracy of the temperature readings from top pyrometer 105a is not negatively impacted by actuation of light source 301.

[0026] Fig. 6 shows examples of possible light source arrangements for incorporation of active control of the radial temperature gradient in a crucible of an illustrative PVT system in accordance with the present disclosure. Light sources 602 are each directed at respective top chamber viewports 601. In addition, main top chamber viewport 103a permits temperature measurements by top pyrometer 105a. In aspects, bottom light sources 603 are provided at locations compatible with main bottom chamber viewport 103b.

[0027] The present disclosure relates to methods of active radial temperature gradient control in inductively heated PVT systems. In the illustrative system shown in Fig. 3, a light source 301 with a nearly collimated beam, (e.g., a laser source), is aimed at top hot zone viewport 107a. Laser emission from light source 301 is absorbed by the graphite of the crucible causing it to heat up above its quasi steady-state temperature. A substantial portion of the incident power will be radiated out due to high emissivity of graphite at operating process temperatures (e.g.,International Patent Application Docket 2624-44 PCT temperatures around 2000° C) contributing to the temperature measured by and the corresponding signal generated by pyrometer 105a. A nearly collimated beam from light source 301 is aimed at the top hot zone viewport 107a at an angle that does not expose top pyrometer 105a to specular reflection of incident light 302. Thus, the specular reflection of incident light does not contribute to false temperature measurements if the source wavelength falls within the pyrometer sensitivity band(s).

[0028] Fig. 4 and 5 explain the typical operation of dual wavelength and two-color pyrometers suitable for use in PVT systems due to their better accuracy at high temperatures. Specifically, Fig. 4a shows a typical schematic of two detectors implemented into a sandwich structure inside of a known pyrometer. Fig. 4b shows the operation principle of a known two wavelength pyrometer and its improved accuracy. Fig. 5a shows examples of known two-color and dual wavelength pyrometers specifying two distinct bands for dual wavelength pyrometers and partially overlapping bands for two-color pyrometers. Fig.5b shows an example of responsivity curve of a known two-color pyrometer. As evident from Fig. 5a and 5b, typical spectral responsivity of pyrometers is from approximately 0.6 microns to approximately 1.2 microns or to approximately 1.5 microns. In one embodiment, the wavelength of the excitation light source should be outside of the 0.6- 1.5 micron spectral range and can be, for example a visible light in violet (400-450nm), blue (450-495nm), part of green spectral range (495-550nm), or infrared spectral range with wavelengths longer than 1.2 microns and, in aspects, longer than 1.5 microns.

[0029] In another embodiment, a light source 301 and top pyrometer 105a are installed onto an x- y stage (not shown) and continuously aligned with the center of the top hot zone viewport 107a.

[0030] In other embodiments, a light source 301 may be positioned outside of the main top chamber viewport 103a and a dedicated viewport 601 may be used (see Fig. 6). A plurality of combinations can be arranged using multiple light sources 602 exciting the crucible viewport surface through a single or multiple chamber viewports 601 (as shown in the example system of Fig. 6). The location of viewports 601 and positions of light sources 602 are determined by the incidence angle of the incoming beam being smaller than the angle defined by the aspect ratio of the hot zone viewport 107a.

[0031] In yet another embodiment, same or similar light sources 603 can be installed at the bottom chamber viewport to partially heat the bottom hot zone viewport 107b (see Fig. 6).International Patent ApplicationDocket 2624-44 PCT

[0032] To maintain the desired process temperature and axial temperature gradient the process Proportional-Intcgral-Dcrivativc (PID) control can be maintained using at least one of the hot zone viewports 107a or 107b when other the other of viewports 107b or 107a is exposed to heating from an external light source to modify the axial and / or radial temperature gradient within the crucible. When a plurality of the excitation of light sources is used, they can operate at essentially same wavelength or at different wavelengths outside of the spectral responsivity range of pyrometers measuring the temperature of hot zone viewport(s) surface.

[0033] The present systems can provide active control of temperature gradient(s) during the growth and / or cool down phases of operation of the physical vapor transport system. Stress causing defects in a crystal, can accumulate during the crystal cool down, since edges of the crystal may cool slower than the center. In such case, the laser power can be applied to the viewport of the crucible to reduce radial temperature gradient accumulated during the cool down stage. Thus, active control of temperature gradient(s) during the cool down phase can minimize, offset, or eliminate any differential cooling of the edges versus the center of the crystal.

[0034] In a typical control algorithm for adjusting the axial temperature gradient within the crucible of a PVT system, a programmable logic controller (PLC) or PC (“controller”) measures instantaneous temperatures by the top pyrometer and the bottom pyrometer. The controller calculates any deviation in temperature within the crucible and then determines whether the deviation in temperature is larger than a threshold value (e.g., 2 °C). If it is determined that the deviation between the top and bottom temperatures is below the threshold value, the light source(s) are not activated and the process returns to the measuring step. If a deviation between the top and bottom temperatures larger than the threshold value is detected, the controller activates the light source(s) to thereby increase the temperature near the top of the crucible and the process returns to the measuring step. It should, of course, be understood that this process can be employed to actively control the axial temperature gradient during the growth phase of operation of the physical vapor transport system, or the cool down phase of operation of the physical vapor transport system, or both.

[0035] Rather than relying on actual measurements, modeling can be used for adjusting the axial or radial temperature gradient within the crucible of a PVT system. In such a process, a model of the expected temperatures within the crucible is prepared (see, e.g., Fig. 2) based on the physical characteristics of the crucible, the insulation, coil position, etc. The light source(s) can then beInternational Patent ApplicationDocket 2624-44 PCT activated throughout the crystal growth, cooldown, or both, based on the modelled temperature distribution. The crystal grown can then be recovered and analyzed for the distribution of defects caused by stresses and other characteristics to determine the effectiveness of the temperature gradient control. Data from multiple runs can be fed into a machine learning model to improve the accuracy of the temperature gradient control over multiple operations of the PVT system.

[0036] The present systems can be used in connection with other technologies to provide active control of temperature gradient(s) during the growth and / or cool down phases of operation of the physical vapor transport system. For example, in addition to the systems described herein an electrically conductive component may be incorporated into the bottom of the crucible to change the overall radial temperature profile within the crucible as described in commonly owned International Application Publication W02025 / 049130, the entire contents of which are incorporated herein by this reference. As another example, in addition to the systems described herein mechanisms to improve hot zone package alignment and / or to adjust the temperature gradient within the vacuum chamber (e.g., by adjusting a position of the heater based on pyrometer readings), as described in commonly owned International Application Publication W02025 / 029610 and International Application No. PCT / US25 / 13925, the entire contents of both of which are incorporated herein by this reference.

[0037] 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.

[0038] 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 theirInternational Patent Application Docket 2624-44 PCT 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.

[0039] 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.

[0040] Embodiment 1 is a physical vapor transport (PVT) system that includes a vacuum chamber; a hot zone package located within the vacuum chamber, the hot zone package including a crucible and a top hot zone viewport and adjacent an open end of the crucible; and a light source positioned to illuminate the top hot zone viewport and to adjust a temperature gradient within the crucible.

[0041] Embodiment 2 is a PVT system of embodiment 1, wherein the light source is a laser.

[0042] Embodiment 3 is a PVT system of either of embodiments 1 or 2, wherein the light source adjusts a radial temperature gradient within the crucible.International Patent Application Docket 2624-44 PCT

[0043] Embodiment 4 is a PVT system of either of embodiments 1 or 2, wherein the light source adjusts an axial temperature gradient within the crucible.

[0044] Embodiment 5 is a PVT system of any of embodiments 1 to 4, wherein the light source includes a first light source and a second light source both positioned to illuminate the top hot zone viewport and to adjust a temperature gradient within the crucible

[0045] Embodiment 6 is a PVT system of any of embodiments 1 to 5, further including a chamber viewport in a top flange of the vacuum chamber, the light source positioned to illuminate the top hot zone viewport through the chamber viewport.

[0046] Embodiment 7 is a PVT system of any of embodiments 1 to 6, further including a pyrometer positioned so that a field of view of the pyrometer views the top hot zone viewport; and a controller configured to activate the light source based on temperature measurements from the pyrometer.

[0047] Embodiment 8 is a PVT system of embodiment 7, wherein the light source operates at a wavelength outside of the spectral responsivity range of the pyrometer.

[0048] Embodiment 9 is a PVT system of embodiment 7, wherein the pyrometer is a two wavelength pyrometer.

[0049] Embodiment 10 is a PVT system of embodiment 7, wherein the controller uses Proportional-Integral-Derivative (PID) control to activate the light source to adjust a temperature gradient within the crucible.

[0050] Embodiment 11 is a PVT system of any of embodiments 1 to 10, further including a bottom hot zone view port; and a lower light source positioned to illuminate the bottom hot zone viewport to adjust a temperature gradient within the crucible.

[0051] Embodiment 12 is a PVT system of embodiment 11, further including a lower pyrometer positioned so that a field of view of the lower pyrometer views the bottom hot zone viewport.

[0052] Embodiment 13 is a PVT system of any of embodiments 1 to 12, wherein activation of the light source adjusts radial temperature gradient inside of the crucible to be less than 10 °C.

[0053] 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.International Patent Application Docket 2624-44 PCTOther elements, steps, methods, and techniques that are insubstantially different from those described above and / or in any appended claims arc also intended to be within the scope of the disclosure.

Claims

International Patent ApplicationDocket 2624-44 PCTWHAT IS CLAIMED IS:

1. A physical vapor transport system comprising: a vacuum chamber; a hot zone package located within the vacuum chamber, the hot zone package including a crucible and a top hot zone viewport adjacent an open end of the crucible; and a light source positioned to illuminate the top hot zone viewport and to adjust a temperature gradient within the crucible.

2. The physical vapor transport system of claim 1, wherein the light source is a laser.

3. The physical vapor transport system of either of claims 1 or 2, wherein the light source adjusts a radial temperature gradient within the crucible.

4. The physical vapor transport system of either of claims 1 or 2, wherein the light source adjusts an axial temperature gradient within the crucible.

5. The physical vapor transport system of any of claims 1 to 4, wherein the light source includes a first light source and a second light source both positioned to illuminate the top hot zone viewport and to adjust a temperature gradient within the crucible6. The physical vapor transport system of any of claims 1 to 5, further comprising: a chamber viewport in a top flange of the vacuum chamber, the light source positioned to illuminate the top hot zone viewport through the chamber viewport.

7. The physical vapor transport system of any of claims 1 to 6, further comprising: a pyrometer positioned so that a field of view of the pyrometer views the top hot zone viewport; and a controller configured to activate the light source based on temperature measurements from the pyrometer.International Patent ApplicationDocket 2624-44 PCT8. The physical vapor transport system of claim 7, wherein the light source operates at a wavelength outside of the spectral responsivity range of the pyrometer.

9. The physical vapor transport system of claim 7, wherein the pyrometer is a two wavelength pyrometer.

10. The physical vapor transport system of claim 7, wherein the controller uses Proportional- Integral-Derivative (PID) control to activate the light source to adjust a temperature gradient within the crucible.

11. The physical vapor transport system of any of claims 1 to 10, further comprising: a bottom hot zone view port; a lower light source positioned to illuminate the bottom hot zone viewport to adjust a temperature gradient within the crucible.

12. The physical vapor transport system of any of claims 1 to 11, further comprising: a lower pyrometer positioned so that a field of view of the lower pyrometer views the bottom hot zone viewport.

13. The physical vapor transport system of any of claims 1 to 12 wherein activation of the light source adjusts radial temperature gradients inside of the crucible to be less than 10 °C.

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