WO2025049130A1

WO2025049130A1 - Pvt system with improved crucible design

Info

Publication number: WO2025049130A1
Application number: PCT/US2024/042629
Authority: WO
Inventors: Yu Yang; Samuel J. WRIGHT; Maxim S. Shatalov
Original assignee: CVD Equipment Corp
Current assignee: CVD Equipment Corp
Priority date: 2023-08-25
Filing date: 2024-08-16
Publication date: 2025-03-06
Anticipated expiration: 2026-02-25

Abstract

Structures for providing a more uniform temperature at the bottom of an inductively-heated crucible of a PVT system include a specialized electrically conductive component having a cavity in an upper surface thereof. The conductive component may be added as a separate component to the bottom of an existing crucible or may be formed as a unitary structure with the crucible. The electrical conductivity of the component may be equal to or less than the electrical conductivity of the crucible. The shape of the cavity is designed to impact the magnetic field excited at the bottom of the crucible, thereby changing the overall radial temperature profile within the crucible.

Description

PVT SYSTEM WITH IMPROVED CRUCIBLE DESIGN

TECHNICAL FIELD

[0001] The present disclosure generally relates physical vapor transport (PVT) systems and to improved crucible designs within the system.

BACKGROUND

[0002] 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.

[0003] Physical vapor transport (PVT) systems are currently used for growth of single crystal bulk SiC, AIN, ZnSe, ZnSeTe, CdTe, CdS, and ZnTe materials. Examples of PVT systems are described in commonly owned International Application No. PCT/US24/39699, the entire disclosure of which is incorporated herein by this reference.

[0004] Traditional inductively heated crucibles suffer from notable radial and axial thermal gradients, with the highest temperature near the crucible’s bottom in proximity to the wall of the reaction chamber. In a conventional PVT system with a cylindrical hot zone containing a crucible and an insulation, these temperature gradients can be controlled only by coil position and geometry, and by design of the crucible and insulation. This nonlinear and varying temperature distribution causes non-stoichiometric evaporation of the SiC powder charge and Si-depletion in high-temperature areas, leading to smaller granules and graphitization, which becomes more pronounced particularly when the crucible is made of graphite. This alters the charge powder composition, density, permeability, and thermal conductivity. Consequently, the thermal field distribution and mass transport pathways with the powder charge change significantly during longterm SiC growth.

[0005] Known system designs mainly focused on remedying such issues by making adjustments to the existing PVT chamber. One approach is to introduce an external heating source (e.g., adding a resistor heater at the bottom of the PVT graphite chamber), to compensate for the temperature uniformity, such as disclosed by U.S. Publication No. 2019/0323145 Al. However, this may increase the complexity of control and assembly. Another approach is to use various coating methods and materials to isolate the SiC powder from direct contact with the inner walls of the graphite chamber, thereby mitigating the graphitization phenomenon, as disclosed in TW Publication No. 202114968-A and EP Publication No. 4186881-Al. However, the radial thermal gradient still exists and remains unresolved. The third approach, which is even more passive, involves using various filter concepts to block the unwanted particles caused by the radial temperature gradient, leading to carbonization, from reaching the growth front of the seed. This can be achieved through designs within the SiC powder, such as a double side wall design with a selectively permeable inner wall to allow only Si-rich source transport through, as disclosed in CN Publication No. 107059130B and CN Publication No. 115182038-A. Alternately, the filter design can be implemented in the flow path between the raw SiC powder and the seed to minimize the carbon inclusion in the gas, as disclosed in U.S. Publication No. 2019/249332-Al, U.S. Patent No. 8741413-B2, CN Publication No. 110424052A. While effective, they do not tackle the underlying problem of the temperature uniformity. Apart from the mentioned remedies, there have been designs that aim to modify temperature profile by directly changing the magnetic field through altering the shape of the inductive work piece in the PVT process. For instance, a study introduced manipulating the axial temperature gradients by adjusting the crucible wall thickness, but addressing the radial temperature gradient, especially at the bottom of the chamber, remains unexplored so far.

SUMMARY

[0006] Existing challenges associated with the foregoing, as well as other challenges, are overcome by the presently disclosed improved crucible designs for a physical vapor transport system.

[0007] In accordance with aspects of the present disclosure, an electrically conductive component is added to the bottom of the crucible of a PVT system. The electrical conductivity of the component can be equal to or less than that of the crucible. The geometry of the electrically conductive component is specially modified by removing a part to create a cavity and carefully calculating and designing the shape of the cavity. By adding this conductive component, the magnetic field excited at the bottom of the crucible can be altered, thereby changing the overall radial temperature profile. Such a technique can compensate for colder regions at the center of the crucible and generate a uniform radial temperature distribution. [0008] The geometry of the conductive component is designed to alter the magnetic field distribution at the bottom of the inductively-heated crucible. In the absence of this component, the induced magnetic field line direction is parallel to the crucible floor, resulting in less electromotive force and inefficient inductive heating at the bottom. Heat primarily conducts from the sidewalls to the center, causing a radial temperature gradient. With inclusion of this modified design, the magnetic field line becomes perpendicular to the crucible floor, resulting in a more uniform and efficient heating at the bottom of the crucible. The electromagnetic heating in combination with heat transfer and surface radiation computational modelling, utilizing commercial simulation software, have verified the efficacy of the design.

[0009] According to one aspect of the present disclosure, a physical vapor transport (PVT) system is disclosed and includes a crucible and an electrically conductive component adjacent a bottom surface of the crucible and having a cavity in an upper surface thereof.

[0010] Implementations of the above embodiment may include one or more of the following features. According to one aspect of the above embodiment, the electrically conductive component may be added as a separate component to the bottom surface of the crucible. In another aspect of the above embodiment, the electrically conductive component may be formed as a unitary structure with the crucible.

[0011] According to another aspect of the above embodiment, an electrical conductivity of the electrically conductive component may be equal to the electrical conductivity of the crucible. In another aspect of the above embodiment, the electrical conductivity of the electrically conductive component may be less than the electrical conductivity of the crucible. In aspects, the electrical conductivity of the electrically conductive component may be up to 25% less than the electrical conductivity of the crucible. In aspects, both the electrically conductive component and the crucible are made of graphite.

[0012] According to yet other aspects of the above embodiment, the cavity in the upper surface of the electrically conductive component may be an inverted conical cavity. In aspects, an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity may be from about 87° to about 30°. In aspects, an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity may be from about 75° to about 45°. In aspects, an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity may be from about 70° to about 50°.

[0013] According to yet other aspects of the above embodiment, a width of the electrically conductive component may be equal to a width of the crucible. In aspects, the width of the electrically conductive component may be +/- 20% of the width of the crucible. Also in aspects, a height of the electrically conductive component may be from about 5% to about 25% of a height of the crucible. In aspects, the height of the electrically conductive component may be from about 10% to about 15% of the height of the crucible. In other aspects, a depth of the cavity may be from about 50% to about 99% of a depth of the electrically conductive component. In yet other aspects, the depth of the cavity may be from about 85% to about 95% of the depth of the electrically conductive component.

[0014] In another embodiment, a bottom viewport opening in the crucible insulation may propagate through the entire thickness of insulation to the bottom surface of the conductive part. In aspects, the conical shape of the conductive part can be modified according to such modification to still achieve a desired resulting radial temperature gradient at the bottom of the crucible via heating of the conductive part.

BRIEF DESCRIPTION OF THE FIGURES

[0015] 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.

[0016] Fig. 1 schematically shows a schematic sectional view of a conventional PVT growth apparatus (prior art).

[0017] Fig. 2 is a sectional view of an example crucible modification following the principles described herein.

[0018] Fig. 2A is a sectional view of a PVT growth apparatus with a viewport that extends to a bottom of a modified crucible following the principles described herein.

[0019] Fig. 3 is a sectional view of the inductively heated component of Fig. 2 alone. [0020] Figs. 4a and 4b show a comparison between the simulated temperature contour maps of the crucible during heating of a conventional PVT apparatus (Fig. 4a) versus a PVT apparatus in accordance with the present disclosure (Fig. 4b).

[0021] Fig. 5 represents a comparison of the radial temperature plots on the inner bottom wall of the crucible during the heating process between the conventional PVT apparatus and a modified design of the crucible in accordance with the present disclosure, derived from simulations.

[0022] Figs. 6a and 6b display the distribution of normalized magnetic field vectors in a sectional view for both the conventional design (Fig. 6a) and a modified design in accordance with the present disclosure (Fig. 6b), as simulated.

DETAILED DESCRIPTION

[0023] Novel crucible designs for 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.

[0024] 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.

[0025] The present disclosure relates to structures for providing a more uniform temperature at the bottom of an inductively-heated crucible of a PVT system. More uniform temperature is provided in accordance with the present disclosure by including a specialized electrically conductive component as part of, or in association with, the crucible. In embodiments, the conductive component is added as a separate component to the bottom of an existing crucible. In embodiments, the conductive component and the crucible are formed as a unitary structure. The electrical conductivity of the component can be equal to or less than the electrical conductivity of the crucible. This component geometry is specially modified, by removing a part to create a cavity. The shape of the cavity is designed such that the magnetic field excited at the bottom of the crucible can be altered, thereby changing the overall radial temperature profile. This component geometry can compensate for colder regions at the center of the crucible and generate a uniform radial temperature distribution.

[0026] A schematic sectional view of a conventional PVT growth apparatus (prior art) is presented in Fig. 1. The diagram illustrates a graphite growth crucible 12 surrounded by thermal insulation 14 with top and bottom viewports (15, 25) for temperature measurements inside of the crucible basket 11 using one or more pyrometers (not shown). Exterior heating coils 13 are subjected to a specific working power and frequency to inductively heat the crucible, such that the raw SiC powder charge inside reaches its sublimation temperature. Operation of the system of FIG. 1 may be automatically controlled by a programmable logic controller (PLC) or a PC (not shown) which is capable of controlling process parameters (e.g., power supplied to and vertical adjustment of heating coils 13).

[0027] Fig. 2 is a sectional view of an example crucible modification following the principles described herein. The conductive part (and inductively heated component) 22 underneath the crucible 12' is a cylinder, with an inverted conical cavity 24 on top. Fig. 2A shows a PVT growth apparatus having a crucible modification following the principles described herein, but where a bottom viewport opening 25’ propagates through the entire thickness of insulation 14 to the bottom surface of the conductive part 22. Fig. 3 is a sectional view of the conductive part 22 alone. Hie conductive component can be made using any technique suitable for shaping the material from which the conductive component is being made, such as, machining, molding, drilling, extrusion, vibromolding, isostatic pressing, and the like. For example, the conductive part may be machined from a graphite block. Operation of the systems of Figs. 2 and 2A may be automatically controlled by a programmable logic controller (PLC) or a PC (not shown) which is not only capable of controlling process parameters (e.g., power supplied to and vertical adjustment of heating coils 13), but is also capable of active control of temperature gradients in accordance with the present disclosure based on the temperature measurements at top viewport 15 and bottom viewport 25, 25’.

[0028] The cavity 24 can be conical as shown, although other shapes (e.g., semi-spherical) that can alter the magnetic field at the bottom of the crucible to change the overall radial temperature profile are also contemplated. In embodiments, the angle between the inner surface 26 of the cavity 24 of the conductive part 22 and an axis “A” of rotation of the cavity 24 can be from about 87° to about 30°; in embodiments from about 75° to about 45°; in yet other embodiments from about 70° to about 50°. In embodiments, the width of the conductive part 22 can be equal to the width of the crucible 12', or in embodiments can be +/- 20% of the width of the crucible 12'. In embodiments, the width of the cavity 24 can be equal to the width of the crucible 12', or in embodiments can be +/- 20% of the width of the crucible 12'. In embodiments, the height of the conductive part 22 can be from about 5% to about 25% of the height of the crucible 12'; in embodiments, from about 10% to about 15% of the height of the crucible 12'. In embodiments, the depth of the cavity 24 can be from about 50% to about 99% of the depth of the conductive part 22; in embodiments, from about 85% to about 95% of the depth of the conductive part 22.

[0029] As noted above, the electrical conductivity of the conductive part 22 can be equal to or less than the electrical conductivity of the crucible 12'. Thus, for example, both the conductive part 22 and the crucible 12' can be made of graphite. In such embodiments, the conductive part 22 and the crucible 12' can be made as a unitary structure. In other embodiments, the electrical conductivity of the conductive part 22 can be up to 25% less than the electrical conductivity of the crucible 12'. In such embodiments, since the conductive part 22 and the crucible 12' are made of different materials, the conductive part 22 can be made as a unitary structure or formed separately from the crucible 12' and then either attached to or assembled with the crucible 12'. The conductive part 22 may be made from graphite or any suitable electrically conductive fiber reinforced polymer composite materials (e.g., pyrolithic graphite) having an electrical conductivity lower than or comparable to the electrical conductivity of the material of construction of the crucible.

[0030] A comparison was made between the simulated temperature contour maps of the crucible during heating of a conventional PVT apparatus versus a design in accordance with the present disclosure. The simulation utilized the geometries described in Fig. 1 and Fig. 2 as examples. The corresponding results are represented as 31 and 32 in Figs. 4a and 4b, respectively. The temperature is in degrees Celsius. It is evident from the simulated temperature contour maps that the modified crucible design in accordance with the present disclosure (Fig. 4b) exhibits a much more uniform temperature distribution at the bottom of the crucible.

[0031] In addition, a comparison (derived from simulations) of the radial temperature plots on the inner bottom wall of the crucible during the heating process between the conventional PVT apparatus and the modified design of the crucible in accordance with the present disclosure, was made. The plots of Fig. 5 demonstrate a noticeable decrease in temperature gradient in the modified design of the crucible in accordance with the present disclosure.

[0032] The distribution of normalized magnetic field vectors in a sectional view is shown for the conventional design 61 (Fig. 6a) and the modified design 62 (Fig. 6b), as simulated. It can be observed that near the bottom of the crucible, the direction of magnetic field line vectors in the conventional design 61 is nearly parallel to the crucible wall (see, Fig. 6a). However, due to the incorporation of this special inductive component in accordance with the present disclosure, in 62, the magnetic field line vectors around the bottom wall of the crucible are predominantly perpendicular to it as shown in Fig. 6b.

[0033] 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.

[0034] 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 (PVT) system comprising: a crucible; and an electrically conductive component adjacent a bottom surface of the crucible, the electrically conductive component having a cavity in an upper surface thereof.

2. The PVT system of claim 1 wherein the electrically conductive component is added as a separate component adjacent to the bottom surface of the crucible.

3. The PVT system of claim 1 wherein the electrically conductive component is formed as a unitary structure with the crucible.

4. The PVT system of claim 1 wherein an electrical conductivity of the electrically conductive component is equal to an electrical conductivity of the crucible.

5. The PVT system of claim 1 wherein an electrical conductivity of the electrically conductive component is less than an electrical conductivity of the crucible.

6. The PVT system of claim 1 wherein an electrical conductivity of the electrically conductive component is up to 25% less than an electrical conductivity of the crucible.

7. The PVT system of claim 1 wherein both the electrically conductive component and the crucible are made of graphite.

8. The PVT system of claim 1 wherein the cavity in the upper surface of the electrically conductive component is an inverted conical cavity.

9. The PVT system of claim 1 wherein an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity is from about 87° to about 30°.

10. The PVT system of claim 1 wherein an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity is from about 75° to about 45°.

11. The PVT system of claim 1 wherein an angle between an inner surface of the cavity in the upper surface of the electrically conductive component and an axis of rotation of the cavity is from about 70° to about 50°.

12. The PVT system of claim 1 wherein a width of the electrically conductive component is equal to a width of the crucible

13. The PVT system of claim 1 wherein a width of the electrically conductive component is +/- 20% of a width of the crucible.

14. The PVT system of claim 1 wherein a height of the electrically conductive component is from about 5% to about 25% of a height of the crucible.

15. The PVT system of claim 1 wherein a height of the electrically conductive component is from about 10% to about 15% of a height of the crucible.

16. The PVT system of claim 1 wherein a depth of the cavity is from about 50% to about 99% of a depth of the electrically conductive component.

17. The PVT system of claim 1 wherein a depth of the cavity is from about 85% to about 95% of a depth of the electrically conductive component.

18. A physical vapor transport (PVT) growth apparatus comprising: a crucible surrounded by thermal insulation; top and bottom viewports for temperature measurements; a heating coil configured to inductively heat the crucible; and an conductive component adjacent a bottom surface of the crucible, the conductive and having a cavity in an upper surface thereof.

19. The PVT growth apparatus of claim 18 wherein the bottom viewport propagates through an entire thickness of the thermal insulation to a bottom surface of the conductive component.