Growth management of silicon carbide crystal

Abstract

To provide a method, an apparatus, and a system for growing a silicon carbide (SiC) crystal.SOLUTION: A physical vapor transportation (PVT) system for growing a silicon carbide (SiC) ingot may be improved by adding a movable heating device. The heating device may be either inductive or resistive. By strictly controlling a temperature gradient during a growth and adding an in-situ annealing following a growth stage, a SiC crystal to be obtained may be made taller and contain less defects, resulting in less cracks during a following griding or polishing operation.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims the benefit of U.S. Patent Application No. 18 / 661,875, entitled "Managing Growth of Silicon Carbide Crystals," filed May 13, 2024, which is incorporated herein by reference in its entirety.

[0002] This specification relates to methods and apparatus for growing silicon carbide (SiC) crystals for use in the electronics industry. More particularly, this specification relates to controlled SiC crystal growth in a physical vapor transport (PVT) furnace. [Background technology]

[0003] Silicon carbide can be used as an alternative substrate material to silicon in the manufacture of integrated circuits. Some useful properties of SiC-based microchips, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), include reduced weight, low power consumption, and the ability to sustain high-temperature operation. While silicon devices operate at temperatures up to approximately 120°C, SiC devices can operate at temperatures as high as 500°C–800°C. This is due to SiC's high thermal conductivity, which is approximately 3.5 times higher than that of silicon. Therefore, SiC devices are particularly suitable for power applications such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and solar panels, as well as industrial applications. SiC devices are being introduced into EV production in vehicle components such as DC-DC converters and on-board fast battery chargers. Summary of the Invention

[0004] In some aspects, techniques described herein relate to a method of forming silicon carbide (SiC), the method including disposing a SiC seed crystal in a seed module in an upper region of a crucible containing a SiC precursor, heating the crucible to sublimate the SiC precursor using an induction heater to heat the sides of the crucible and a first movable heater to heat the ends of the crucible, and growing a crystalline SiC ingot by condensing SiC on a bottom surface of the SiC seed crystal.

[0005] In some aspects, techniques described herein relate to methods, wherein heating the crucible to sublimate the SiC precursor includes converting the SiC precursor from a powder to a gas.

[0006] In some aspects, techniques described herein relate to a method, wherein heating the crucible using an induction heater includes energizing a radio frequency (RF) coil wrapped around the side of the crucible.

[0007] In some embodiments, techniques described herein relate to a method, wherein heating the crucible using a first movable heater includes energizing one or more movable induction coils disposed in a plane parallel to the ends of the crucible.

[0008] In some aspects, techniques described herein relate to a method, wherein heating the crucible using a first movable heater includes energizing one or more movable resistive elements disposed in a plane parallel to an edge of the crucible.

[0009] In some embodiments, the techniques described herein relate to methods, wherein heating the crucible increases the temperature of the crucible to within a range of about 1800°C to about 2500°C.

[0010] In some aspects, techniques described herein relate to a method, wherein heating the crucible comprises heating another end of the crucible using a second movable heater.

[0011] In some aspects, the techniques described herein relate to a method for adjusting the growth rate of a crystalline SiC ingot by varying the positions of a first movable heater and a second movable heater.

[0012] In some aspects, the techniques described herein relate to an apparatus that includes a crucible having an upper region and a lower region, a silicon carbide (SiC) precursor disposed in the lower region of the crucible, a SiC seed disposed in the upper region of the crucible, an induction heater surrounding a sidewall of the crucible, a first movable heater disposed at an upper end of the crucible, and a second movable heater disposed at a lower end of the crucible.

[0013] In some aspects, the techniques described herein relate to an apparatus, wherein a first movable heater and a second movable heater are movable along a vertical axis of the crucible.

[0014] In some aspects, the techniques described herein relate to an apparatus, wherein the first and second movable heaters include induction heating elements.

[0015] In some aspects, the techniques described herein relate to an apparatus, wherein the first movable heater and the second movable heater include resistive heating elements.

[0016] In some aspects, the techniques described herein relate to an apparatus, wherein the resistive heating element comprises at least one of tungsten, molybdenum, or graphite.

[0017] In some aspects, the techniques described herein relate to an apparatus, wherein the first and second movable heaters can be independently positioned at different distances from the top and bottom ends of the crucible.

[0018] In some embodiments, the techniques described herein involve an apparatus where the pressure within the crucible is maintained between about 0.1 Torr and about 50 Torr.

[0019] In some aspects, the techniques described herein relate to an apparatus, wherein the crucible further includes an outer shell, and wherein the first and second movable heaters are disposed inside the outer shell.

[0020] In some aspects, the techniques described herein relate to an apparatus, wherein the crucible further includes an outer shell, and the induction heater is disposed outside the outer shell.

[0021] In some aspects, techniques described herein relate to a system that includes a process chamber for growing a SiC crystal ingot, a fixed heater disposed around a side of the process chamber, a first movable heater disposed at a first end of the process chamber, a second movable heater disposed at a second end of the process chamber, and a processor programmed to control a first temperature of the first movable heater and a second temperature of the second movable heater according to a target schedule.

[0022] In some aspects, the techniques described herein relate to a system, wherein a processor is programmed to energize a fixed heater, a first movable heater, and a second movable heater while growing a SiC crystal ingot.

[0023] In some aspects, the techniques described herein relate to a system, wherein a processor is programmed to energize a first movable heater and a second movable heater to perform an annealing process after growing a SiC crystal ingot. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of a physical vapor transport (PVT) device according to an implementation of the present disclosure. [Figure 2] 1 is a cross-sectional view of a physical vapor transport (PVT) device according to an implementation of the present disclosure. [Figure 3] 1 is a cross-sectional view of a physical vapor transport (PVT) device according to an implementation of the present disclosure. [Figure 4A]FIG. 2 is a top view of an induction heater according to an implementation of the present disclosure. [Figure 4B] 4B is a simulated temperature map of the heater and nearby susceptor shown in FIG. 4A according to an implementation of the present disclosure. [Figure 4C] 4B is a simulated temperature map of the heater and nearby susceptor shown in FIG. 4A according to an implementation of the present disclosure. [Figure 5] 1A and 1B are cross-sectional views illustrating temperature gradients during a crystal growth process according to implementations of the present disclosure. [Figure 6A] 10A-10C are simulated contour plots of temperature across a SiC boule according to implementations of the present disclosure. [Figure 6B] 1 is a simulated contour plot of stress in a SiC boule according to an implementation of the present disclosure. [Figure 6C] 1 is a simulated contour plot of stress in a SiC boule according to an implementation of the present disclosure. [Figure 7] FIG. 1 is a flow diagram illustrating a method for forming a SiC boule according to an implementation of the present disclosure. [Figure 8] FIG. 8 is a system block diagram of a computer system capable of providing feedback control to the process shown in FIG. 7 according to a possible implementation of the present disclosure.

[0025] Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be noted that, according to common practice in the industry, various features have not necessarily been drawn to scale. Dimensions of various features may be arbitrarily increased or decreased for clarity of illustration. In the drawings, the same reference numerals in different views may indicate the same and / or similar components (elements, structures, etc.). The drawings illustrate generally, by way of example, and not by way of limitation, various implementations discussed in the present disclosure.

[0026] Reference numbers shown in one drawing may not be repeated for the same and / or similar elements in related drawings. Reference numbers repeated in multiple drawings may not be specifically discussed with respect to each of those drawings, but are provided for context between the related drawings. Also, when multiple instances of an element are shown, not all of the same elements in the drawings are specifically referenced with a single reference number. DETAILED DESCRIPTION OF THE INVENTION

[0027] Silicon carbide ingots used in the manufacture of integrated circuits can be formed (e.g., grown) in a physical vapor transport (PVT) furnace. A PVT furnace can have the form of a vertical cylindrical chamber, or crucible, with a seed crystal at one end. The crucible can receive silicon and carbon source materials, which are heated until they vaporize. The resulting silicon and carbon gases rise within the chamber, and when they encounter the seed crystal, they crystallize around the seed crystal, causing crystal growth radially outward and axially downward. Such crystal growth forms a cylindrical boule that can be subsequently sliced ​​into SiC wafers used as substrates in semiconductor manufacturing processes.

[0028] Process control during SiC crystal growth is difficult. At least one problem that arises during the crystal growth process is that temperature gradients or fluctuations can disrupt crystallization and introduce irregularities or defects, such as dislocations, into the crystal structure of the boule. To reduce (e.g., minimize) the dislocation density within the boule, it is desirable to tightly control the growth process to maintain a constant growth rate and limit both axial and radial temperature gradients. Another method for reducing crystal defects within the boule is to control the crystal-gas interface to maintain a convex shape throughout the growth process. The rate of depletion of the source material can also affect the geometry of the crystal growth.

[0029] To control the temperature gradient, heaters can be disposed at both ends of the chamber and along the chamber walls. The heaters can be induction heaters, e.g., radio frequency (RF) type induction heaters, or resistive heating elements. Temperature control can be adjusted by varying the number of heaters, the type of heaters, their location and spacing, and by modulating the power applied to the heaters. In addition, some heaters can be fixed and others can be movable.

[0030] 1-3 show cross-sectional views of a PVT furnace 100 according to some implementations of the present disclosure. In some implementations, the PVT furnace 100, e.g., a sublimation furnace, may include an outer shell 102, a seed crystal 106, a crucible 105, a side heater 112, a top heater 114, and a bottom heater 116. In some implementations, the outer shell 102 may be a multi-layered cylindrical structure including an outer chamber wall 103 and an insulating sleeve 104 around the crucible 105. In some implementations, the crucible 105 may be an enclosed vessel defining a growth cell 107. The growth cell 107 may be evacuated so that the SiC crystal boule is grown in a high-purity, low-pressure environment. In some implementations, the outer chamber wall 103 may be made of quartz, the insulating sleeve 104 may be made of low-density graphite, and the crucible 105 may be made of high-density graphite. Because graphite is a high conductor of both heat and electricity, the graphite material supports inductive heating of the crucible 105 surrounding the growth cell 107. In some implementations, an air gap 109 may separate the outer chamber wall 103 from the insulating sleeve 104. In some implementations, the thickness of the air gap 109 may range, for example, from about 3 mm to about 7 mm. In some implementations, another inert gas, such as nitrogen gas (N), may be used instead of air in the air gap 109. In some implementations, the SiC seed crystal 106 may have a growth dimension of about 1 mm. In some implementations, the SiC seed crystal 106 may be disposed in a seed module.

[0031] In some implementations, the side heater 112 may be disposed outside the outer shell 102, and the top heater 114 and bottom heater 116 may be disposed inside the outer shell 102, e.g., inside a "hot zone." In some implementations, the top heater 114 primarily controls the temperature of the seed crystal 106, and the bottom heater 116 primarily controls the temperature of the source material. The top heater 114 and bottom heater 116 can be considered vertical heating elements because they affect a temperature gradient in the + / -z direction. In some implementations, the side heater 112 can be considered a horizontal heating element because it affects a temperature gradient in the xy plane, i.e., the radial plane, along the z axis. In some implementations, the side heater 112 is in the form of a stationary RF induction coil that wraps around the outer shell 102 and surrounds the sidewall of the crucible 105, the coil wraps being represented by circles in FIGS. 1-3 . The induction coil of the side heater 112 induces an electric current to flow within the crucible 105 .

[0032] In the PVT furnace 100, the source material is disposed in a lower region of a crucible 105, and the seed crystal 106 is disposed in an upper region of the crucible 105. The SiC source material, e.g., a SiC precursor, can be in the form of a powder having a 1:1 silicon-to-carbon ratio. The crucible 105 can be heated by a bottom heater 116 to a temperature ranging from about 1800°C to about 2500°C, for example, until the solid SiC source material sublimes to form a gas 110. The gas 110 rises within the growth cell 107 toward the seed crystal 106, which is maintained at a lower temperature than the gas 110. When the gas 110 encounters the seed crystal 106, the gas 110 condenses on the seed crystal 106, driving crystal growth radially outward from the seed crystal 106 and axially downward in the -z direction.

[0033] 1-3 show three different configurations of the top heater 114 and bottom heater 116 in a PVT furnace 100 according to some implementations of the present disclosure. FIG. 1 illustrates the use of one or more stationary, e.g., fixed, RF induction coils, e.g., "pancake heaters" (represented by ellipses), for the top heater 114 and bottom heater 116. Pancake heaters are individual localized heating elements that can be operated similarly to induction burners used on kitchen cooktops. The lateral (x-y) distance (e.g., spacing) between the pancake heaters can be designed to control the number of heating elements directly below the crucible 105 and directly above the seed crystal 106. The power applied to the RF coils can also be adjusted to control the rate at which the crucible 105 heats up. One advantage of induction heaters is that they can remain cooler than the target. In some implementations, the RF coils can reach a temperature of approximately 90°C, while the temperature of the crucible 105 is approximately 2000°C.

[0034] 2 shows a PVT furnace 200 including movable induction heaters 202 for the top heater 114 and the bottom heater 116, according to some implementations of the present disclosure. Each movable induction heater 202 spans the width of the crucible 105. In some implementations of the bottom heater 116, the movable induction heater 202 may be attached, e.g., mounted, to a movable platform 204 configured to change the z-distance between the movable induction heater 202 and the bottom end of the crucible 105. In some implementations of the top heater 114, the movable induction heater 202 may be attached, e.g., mounted, to a movable platform 204 configured to change the z-distance between the movable induction heater 202 and the top end of the crucible 105 that houses the seed crystal 106. The movable induction heaters 202 used as the top heater 114 and the bottom heater 116 may be independently positioned at different distances from the respective top and bottom ends of the crucible 105. In some implementations, the multiple bottom heaters 116 can be movable RF coil heaters that allow for varying the vertical (z-direction) distance between the bottom heaters 116 and the crucible 105 .

[0035] 3 shows a PVT furnace 300 including movable resistive heaters 302 for the top heater 114 and the bottom heater 116 according to some implementations of the present disclosure. Each movable resistive heater 302 spans the width of the crucible 105. In some implementations, the movable resistive heaters 302 may comprise one or more of tungsten, molybdenum, and graphite. In some implementations of the bottom heater 116, the movable resistive heater 302 may be attached, e.g., mounted, to a movable platform 304 configured to change the z-distance between the movable resistive heater 302 and the crucible 105. In some implementations of the top heater 114, the movable resistive heater 302 may be attached, e.g., mounted, to a movable platform 304 configured to change the z-distance between the movable resistive heater 302 and the seed crystal 106.

[0036] In some implementations, the movable induction heater 202 or movable resistance heater 302 can be positioned before starting the crystal growth process. In some implementations, the movable induction heater 202 or movable resistance heater 302 can be repositioned at various times during the crystal growth process. In some embodiments, the growth process for a full SiC ingot can occur over a time interval of about 10 days to about 3 weeks, as opposed to a silicon ingot, which can be fully formed in about 1-2 days. In some embodiments, the SiC boule can withstand temperature fluctuations of about + / - 1 degree during the crystal growth process.

[0037] The use of the movable top heater 114 can improve control of the radial temperature gradient to maintain a stable radial growth rate of the crystal, limiting the radial variation in the boule's electrical resistivity and producing SiC wafers with excellent center-to-edge uniformity. The radial crystal growth rate depends on the temperature, the radial temperature gradient, and the pressure within the growth cell 107. In some implementations, the chamber pressure within the growth cell 107 can range from about 0.1 Torr to about 50 Torr. The movable top heater 114 can be used to dynamically balance the radial temperature gradient. The use of the movable top heater 114 can also help prevent seed depletion. Seed depletion can occur when the seed crystal 106 is consumed by the gas 110 rather than the gas 110 condensing on the seed crystal 106 to continue the crystallization process.

[0038] The use of the movable bottom heater 116 controls the source depletion to maintain a target carbon to silicon ratio in the source material and boule.

[0039] The combination of the movable top heater 114 and the movable bottom heater 116 can provide control of the axial temperature gradient along the z-axis between the source material and the seed crystal. Controlling the axial temperature gradient can help maintain a stable axial growth rate of the crystal, resulting in higher ingots. Controlling the axial temperature gradient can also limit the axial variation in the electrical resistivity of the boule to produce SiC wafers with low wafer-to-wafer variation. Controlling the axial temperature gradient can also help maintain a convex crystal-gas interface shape to reduce defects, such as dislocations, within the boule and ensure the growth of a high-quality boule. Growth on the surface of the seed crystal 106 proceeds radially from the center of the z-axis to the edge of the boule as long as the boule has a convex shape.

[0040] In some implementations, the top heater 114 and bottom heater 116 can also provide in-situ crystal annealing to reduce thermal stress within the boule after the crystal growth process. In some implementations, the annealing step can occur after crystal growth is complete. Reducing thermal stress within the boule can prevent cracking during subsequent surface grinding, slicing, and polishing processes of the boule or SiC wafers cut from the boule. Reducing thermal stress can also improve epitaxial growth on the surface of the SiC wafers.

[0041] In some implementations, the movement of the movable induction heater 202 or movable resistive heater 302 can be dynamically adjusted using an automatic feedback control system, as described in more detail below with reference to Figure 8. The feedback control system can sense the temperature at different z coordinates during the crystal growth process and move the heater accordingly to achieve a target temperature set.

[0042] 4A-4C illustrate the effect of a movable induction coil on a nearby target, according to some implementations of the present disclosure. Figure 4A is a photograph showing a perspective view 420 of an example of a movable induction heater 202, e.g., an induction coil pancake heater 400, disposed near a target, e.g., near a graphite susceptor 410. The graphite susceptor 410 may represent, for example, either a graphite seed module onto which a seed crystal 106 is mounted, or the bottom end of a graphite crucible 105 containing source material.

[0043] FIG. 4B shows a simulated temperature map illustrating the effect on the temperature gradient of placing the induction coil pancake heater 400 a distance D1 away from the susceptor 410. In some implementations, the distance D1 may range from about 0.9 inches to about 1.1 inches, for example, within the hot zone of the PVT furnace 100. The simulation inputs further include an applied power of 6.5 kW. The temperature gradient shown in FIG. 4B is generated by a minimum temperature T lo From about 680℃ to about 690℃, the maximum temperature T hiThe induction coil pancake heater 400 operates near the low end of the temperature range, e.g., T lo While the susceptor 410 remains at a low temperature near the maximum temperature of the temperature range, for example, T hi It can be heated to much higher temperatures in the vicinity.

[0044] FIG. 4C shows a simulated temperature map illustrating the effect on the temperature gradient of placing the induction coil pancake heater 400 a distance D2 away from the susceptor 410. In some implementations, the distance D2 may range from about 1.8 inches to about 2.2 inches, for example, within the hot zone of the PVT furnace 100. The simulation inputs further include an applied power of 8.5 kW. The temperature gradient shown in FIG. 4C is generated from a minimum temperature T lo to a maximum temperature T of approximately 700°C to approximately 800°C hi The induction coil pancake heater 400 operates near the low end of the temperature range, e.g., T lo While the graphite susceptor 410 remains at a low temperature near the maximum temperature of the temperature range, e.g., T hi It can be heated to much higher temperatures in the vicinity.

[0045] FIG. 5 is a cross-sectional view of a simulation region 500 within a PVT furnace 100, according to some implementations of the present disclosure. As shown in FIG. 5, the PVT furnace 100 includes an RF coil induction side heater 112, a top heater 114, and a bottom heater 116. The top heater 114 and the bottom heater 116 are each in the form of a movable resistive heater 302. In some implementations, the movable resistive heater 302 may be a resistive pancake heater. The simulation region 500 illustrates the temperature gradient inside the growth cell 107. Specifically, five locations are identified where corresponding temperatures T0, T1, T2, T3, and T4 are monitored during the simulation of SiC growth. T0 monitors the temperature of the crucible 105. T1 monitors the temperature of the seed crystal 106. T1 monitors the temperature of the center of the boule at a point along the z-axis. T2 monitors the edge of the SiC seed. T3 monitors the maximum temperature of the crucible and T4 monitors the temperature at the center of the bottom of the crucible 105.

[0046] The temperature of the bottom heater 116 is set to a minimum temperature T lo and the maximum temperature T of about 2000℃ to about 2200℃ hi The temperature of the upper heater 114 can range between about 1740°C and about 1770°C. lo and the maximum temperature T in the range of about 2000°C to about 2200°C. hi It can be between.

[0047] Inputs to the simulation included a chamber pressure of 0.5 Torr, a power level of 1.5 kW applied to energize the top heater 114, a power level of 1.5 kW applied to energize the bottom heater 116, the crucible temperature (T0) was set to 1920°C, the SiC seed thickness was 1.0 mm, the SiC seed outer diameter (OD) was 150 mm, the SiC boule thickness was 39.0 mm, and the SiC boule outer diameter (OD) was 154 mm.

[0048] The simulations model the temperature response to the use of various combinations of heaters. Simulation results indicate that monitored temperatures T1, T2, and T3 are all within approximately 20% of 2100°C. However, examination of the temperature differences, e.g., temperature gradients T2-T1 and T3-T1, reveals that the smallest temperature gradient occurs when both the top heater 114 and the bottom heater 116 are in use, and the largest temperature gradient occurs when the top heater 114 is not in use. Thus, the benefits of the top heater 114 and the bottom heater 116 are demonstrated. Conversely, the largest temperature gradient occurs when the power applied to energize the side heater 112 is highest, and the smallest temperature gradient occurs when the power applied to energize the side heater 112 is lowest. These results suggest that the use of the side heater 112 exacerbates temperature fluctuations.

[0049] The simulation also models the annealing process during the cooling stage after boule growth. The purpose of annealing is to relieve stress within the crystalline structure to reduce defects and prevent cracking. It is shown that when a maximum power level of approximately 9 kW is applied to energize the side heater 112, while the top heater 114 and bottom heater 116 are powered off (0 kW), both shear stress and von Mises stress remain at their maximum values. This result demonstrates the futility of attempting to anneal the boule using only the fixed induction side heater 112. Both shear stress and von Mises stress are minimized when the top heater 114 and bottom heater 116 are each powered at 1.5 kW, while the side heater 112 is at its minimum power of approximately 4.7 kW. This result demonstrates the benefits of annealing a crystalline boule using the top heater 114 and bottom heater.

[0050] 6A-6C show simulation results characterizing a SiC boule according to some implementations of the present disclosure. The simulation results shown in FIGS. 6A-6C correspond to a PVT furnace 100 configured as shown in FIG. 5. FIG. 6A is a 2D contour plot showing the temperature change ΔT across the SiC boule. FIG. 6B is a 2D contour plot showing the shear stress applied to the SiC boule, which can generate defects such as basal plane dislocations (BPDs). FIG. 6C is a 2D contour plot showing the von Mises stress within the SiC boule, which can lead to cracking in subsequent processing operations.

[0051] As shown in Figure 6A, the temperature of the SiC boule ranges from about 1950°C to about 2250°C. As shown in Figure 6B, the simulated values ​​of shear stress reach a minimum value σ of about 0.45 mega-Pascals (MPa). lo ~Maximum value σ of approximately 0.86 MPa hi As shown in Figure 6C, the simulated value of the von Mises stress reaches a minimum value σ of about 14 MPa. lo ~Maximum σ of approximately 24 MPa hi The range is.

[0052] FIG. 7 is a flow diagram illustrating a method 700 for forming a SiC boule according to some implementations of the present disclosure. Operations 702-708 of method 700 may be performed to form a SiC boule according to some implementations such as those described above with reference to FIGS. 1-3, 4A, 4B, 4C, 5, 6A, 6B, and 6C. The operations of method 700 may be performed in a different order or not at all, depending on the particular application. Note that method 700 may not completely form a SiC boule. Therefore, it should be understood that additional processes may be provided before, during, or after method 700, and that some of these additional processes may be briefly described herein.

[0053] At 702, the method 700 includes providing a crucible containing a SiC precursor, such as the crucible 105 of a sublimation furnace, such as the PVT furnace 100. In some implementations, the crucible 105 can have an upper region and a lower region, and the SiC precursor is provided in the lower region.

[0054] At 704 , the method 700 includes disposing a SiC seed crystal, such as seed crystal 106 , in a seed module suspended in an upper region of the crucible 105 .

[0055] At 706, the method 700 includes heating the crucible 105 to sublimate the SiC precursor using a first heater and a second heater, for example, a bottom heater 116 and a top heater 114. Alternatively, the first heater can be the side heater 112 and the second heater can be the bottom heater 116, or the first heater can be the side heater 112 and the second heater can be the top heater 114. In some implementations, at least one of the first heater and the second heater is disposed inside the outer shell of the PVT furnace 100. In some implementations, at least one of the first heater and the second heater is movable.

[0056] At 708, the method 700 includes growing a crystalline SiC ingot using a first heater and a second heater to control a temperature gradient during the growth process. The use of the first heater and the second heater during and / or after the growth process can result in a longer ingot with lower defect density and lower stress than can be obtained using only one heater or only a fixed heater.

[0057] FIG. 8 illustrates an example computing system 800 capable of providing feedback control for implementations of the present disclosure. The computing system 800 may be any known computing system capable of performing the functions and operations described herein. For example, without limitation, the computing system 800 may provide a hardware platform for implementing the process control schemes described above. The computing system 800 may be used, for example, to perform one or more operations in the method 700 illustrating the example method for forming a SiC boule. In some implementations, the computing system 800 may function as a feedback control system for the PVT furnace 100. For example, the computing system 800 may be implemented as a controller coupled to the PVT furnace 100. The controller may be configured to monitor one or more temperatures associated with the PVT furnace 100 and accordingly adjust the operation of the heaters, particularly the movable heaters described above, to provide enhanced process control during the crystal growth process and / or post-annealing processes.

[0058] Computing system 800 includes one or more processors (also referred to as central processing units, or CPUs), such as processor 804. Processor 804 is connected to a communications infrastructure or bus 806. Computing system 800 also includes input / output devices 803, such as a monitor, keyboard, and pointing device, that communicate with communications infrastructure or bus 806 via input / output interface 802. Processor 804 can receive instructions via input / output device 803 to perform the functions and operations described herein, such as method 700 of FIG. 7 . For example, processor 804 can be programmed to energize one or more of side heater 112, top heater 114, or bottom heater 116 while growing a SiC crystal ingot or while performing an annealing process after growing the SiC crystal ingot. Computing system 800 also includes a primary or main memory 808, such as random access memory (RAM). Main memory 808 may include one or more levels of cache. Main memory 808 stores control logic (e.g., computer software) and / or data therein. In some implementations, the control logic (e.g., computer software) and / or data may include one or more of the operations described above with respect to method 700 of FIG.

[0059] Computing system 800 may also include one or more secondary storage devices or secondary memories 810. Secondary memory 810 may include, for example, a hard disk drive 812 and / or a removable storage device or drive 814. Removable storage drive 814 may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive.

[0060] The removable storage drive 814 can interface with a removable storage unit 818. The removable storage unit 818 includes a computer-usable or readable storage device that stores computer software (control logic) and / or data. The removable storage unit 818 can be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, thumb drive, and / or any other computer data storage device. The removable storage drive 814 reads from and / or writes to the removable storage unit 818 in well-known fashion.

[0061] In some implementations, secondary memory 810 may include other methods, means, or other techniques for allowing computer programs and / or other instructions and / or data to be accessed by computing system 800. Such methods, means, or other techniques may include, for example, removable storage unit 822 and interface 820. Examples of removable storage unit 822 and interface 820 may include program cartridges and cartridge interfaces (such as those found in video game devices), removable memory chips (such as EPROMs or PROMs) and associated sockets, memory sticks and USB ports, memory cards and associated memory card slots, and / or any other removable storage units and associated interfaces. In some implementations, secondary memory 810, removable storage unit 818, and / or removable storage unit 822 may include one or more of the operations described above with respect to method 700 of FIG. 7.

[0062] In some implementations, computing system 800 may further include a communications or network interface 824. Communications interface 824 enables computing system 800 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referred to as remote devices 828). For example, communications interface 824 may enable computing system 800 to communicate with remote devices 828 over communications path 826, which may be wired and / or wireless and may include any combination of a LAN, a WAN, the Internet, etc. Control logic and / or data may be transmitted to or received from computing system 800 via communications path 826.

[0063] The operations in the above-described implementations may be implemented in a wide variety of configurations and architectures. Thus, some or all of the operations in the above-described implementations, e.g., method 700 of FIG. 7, may be performed in hardware, software, or both. In some implementations, a tangible apparatus or article of manufacture comprising a tangible computer-usable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, tangible articles of manufacture embodying computing system 800, main memory 808, secondary memory 810, and removable storage units 818 and 822, as well as any combination of the above. Such control logic, when executed by one or more data processing devices (e.g., computing system 800), causes such data processing devices to operate as described herein.

[0064] As discussed above, the addition of top and bottom heaters to a PVT system, such as PVT system 100, can assist in controlling SiC crystal formation, especially if the top and bottom heaters are movable. The benefits of tighter process control can be obtained primarily by reducing axial and radial temperature variations, e.g., temperature gradients across the boule. Post-growth annealing operations have been shown to reduce both shear and Van Mises stresses in the boule, which can reduce defects and prevent breakage in subsequent processing steps.

[0065] In the foregoing description, when an element, such as a layer, region, or substrate, is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled with another element, it will be understood that it can be directly disposed on, connected to, or coupled with the other element, or that one or more intervening elements may be present. Conversely, when an element is referred to as being directly on, directly connected to, or directly coupled with another element or layer, no intervening elements or layers are present. Throughout the detailed description of the present invention, the terms directly, directly connected, or directly coupled may not be used, but elements shown as being directly on, directly connected, or directly coupled may be referred to as such. The claims of this application may be amended to describe the example relationships described herein or shown in the figures.

[0066] As used herein, the singular can include the plural unless the context clearly dictates otherwise. Spatially relative terms (e.g., throughout, above, above, below, lower, underneath, lower, top, bottom, etc.) are intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the drawings. In some implementations, the relative terms above and below can include vertically above and vertically below, respectively. In some implementations, the term adjacent can include laterally adjacent or horizontally adjacent.

[0067] Some implementations may be implemented using various semiconductor processing and / or packaging technologies, such as, but not limited to, silicon (Si), silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), and / or other types of semiconductor processing technologies associated with semiconductor substrates.

[0068] While certain features of the described implementations have been illustrated as described herein, those skilled in the art will now recognize numerous modifications, substitutions, changes, and equivalents. For example, features illustrated with respect to one implementation may, where appropriate, be included in other implementations. It will therefore be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the implementations. These have been presented by way of example only, and not limitation, and it will be understood that various changes in form and detail may be made. Any portions of the apparatus and / or methods described herein may be combined in any combination except mutually exclusive combinations. The implementations described herein may include various combinations and / or subcombinations of functions, components, and / or features of the different implementations described.

Claims

1. 1. A method for forming silicon carbide (SiC), comprising: disposing a SiC seed crystal in a seed module in an upper region of a crucible containing a SiC precursor; heating the crucible to sublimate the SiC precursor using an induction heater to heat the sides of the crucible and a first movable heater to heat the ends of the crucible; growing a crystalline SiC ingot by condensing SiC on a bottom surface of the SiC seed crystal; and varying the positions of the first and second movable heaters to adjust a growth rate of the crystalline SiC ingot.

2. heating the crucible to sublimate the SiC precursor includes converting the SiC precursor from a powder to a gas; or Heating the crucible using the induction heater includes energizing a radio frequency (RF) coil wrapped around the side of the crucible; or heating the crucible using the first movable heater includes energizing one or more movable induction coils disposed in a plane parallel to the ends of the crucible; or heating the crucible using the first movable heater includes energizing one or more movable resistive elements disposed in a plane parallel to the end of the crucible; or Heating the crucible raises the temperature of the crucible to within a range of about 1800°C to about 2500°C; or The method of claim 1 , wherein heating the crucible uses a second movable heater to heat another end of the crucible.

3. 1. An apparatus comprising: a crucible having an upper region and a lower region; a silicon carbide (SiC) precursor disposed in the lower region of the crucible; a SiC seed disposed in the upper region of the crucible; an induction heater surrounding the sidewall of the crucible; a first movable heater disposed at an upper end of the crucible; a second movable heater disposed at a lower end of the crucible.

4. the first and second movable heaters are movable along a vertical axis of the crucible; or the first and second movable heaters include induction heating elements; or the first and second movable heaters comprise resistive heating elements; or the resistive heating element comprises at least one of tungsten, molybdenum, or graphite; or the first and second movable heaters may be independently positioned at different distances from the top and bottom ends of the crucible; or the pressure within the crucible is maintained at about 0.1 Torr to about 50 Torr; or the crucible further includes an outer shell, and the first and second movable heaters are disposed inside the outer shell; or The apparatus of claim 3 , wherein the crucible further comprises an outer shell, and the induction heater is disposed outside the outer shell.

5. 1. A system comprising: a process chamber for growing a SiC crystal ingot; a stationary heater disposed around a side surface of the process chamber; a first movable heater disposed at a first end of the process chamber; a second movable heater disposed at a second end of the process chamber; a processor programmed to control a first temperature of the first movable heater and a second temperature of the second movable heater according to a target schedule.

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