Method and system for continuous growth of group IIIA metal-containing films

Abstract

The present disclosure provides a reaction system for growing a Group IIIA metal-containing film, including a reaction chamber housing a substrate; a first vessel external to the reaction chamber and containing a liquid Group IIIA metal; a second vessel containing the liquid Group IIIA metal within the reaction chamber; a pipe connecting the first vessel to the second vessel; a first gas line connecting an inert gas source with the first vessel; and a second gas line in fluid communication with the first gas line and connecting the inert gas source with the reaction chamber, the second gas line including a valve such that throttling the valve increases the pressure in the first gas line to induce liquid Group IIIA metal flow from the first vessel to the second vessel.

Description

[0001] METHOD AND SYSTEM FOR CONTINUOUS GROWTH OF GROUP IIIA METAL-CONTAINING FILMS

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] This invention was made with government support under grant number DE-AR0000444 awarded by the Advanced Research Projects Agency - Energy (ARPA-E). The government has certain rights in the invention.

[0004] FIELD OF THE INVENTION

[0005] The present disclosure relates to methods and systems for epitaxial growth of films containing Group IIIA metals.

[0006] BACKGROUND OF THE INVENTION

[0007] Gallium nitride and its alloys with AIN and InN are an important family of wide bandgap semiconductor materials currently being utilized for a number of optical, RF, and power electronics applications. As is typical with semiconductor devices produced from other families of materials, a native substrate (e.g., GaN layers grown on GaN substrates as opposed to GaN layers grown on e.g., Si, SiC, or sapphire substrates) is beneficial to realize the ultimate potential of a given material, since the native substrate provides a more perfect crystal lattice and thermal match to the epilayers grown thereon as compared to nonnative substrates. At present, the halide vapor phase epitaxy (HVPE) technique is the most important technique for the production of GaN substrates, in order to minimize manufacturing costs and increase production yields, it is desirable to achieve long-term continuous growth of GaN crystals.

[0008] However, long-term crystal growth can be challenging in an HVPE environment due to the difficulties in maintaining a constant supply of reagents to the crystal growth zone within the reactor. As such, there is a continuing need in the art to extend crystal growth sessions in order to efficiently build substrates with minimal process disruption.

[0009] SUMMARY OF THE INVENTION

[0010] The present disclosure provides an apparatus that allows for a convenient way to refill metal (e.g., gallium) to the internal metal chloride generation vessel in an HVPE reactor. This allows one to better maintain the chemistry inside the HVPE reactor since the quantity of the metal inside the metal chloride generation vessels affect the conversion rate of Ga to GaCl within the system. This allows for HVPE reactors to maintain the necessary chemistry within the crystal growth zone during very long growth campaigns (potentially hundreds of hours) using, in certain embodiments, a feedback mechanism which controls an automatic filling device that adds a metal precursor to the HVPE reactor at, for example, essentially the same rate as it is being consumed during growth. In some embodiments, the reaction system of the present disclosure utilizes inert gas pressure to induce flow of a Group IIIA metal from an external vessel to a vessel within a reaction chamber.

[0011] The present disclosure includes, without limitation, the following embodiments.

[0012] Embodiment 1: A reaction system for growing a Group IIIA metal-containing film, comprising: a reaction chamber housing a substrate; a first vessel containing a liquid Group IIIA metal, such as gallium or indium, and having a gas headspace adjacent to a surface of the liquid Group IIIA metal, the first vessel being external to the reaction chamber; a second vessel containing the liquid Group IIIA metal within the reaction chamber, the second vessel in fluid communication with a source of halogen-containing gas and in fluid communication with a first gas injector positioned to direct a gas produced in the second vessel toward the substrate; a pipe connecting the first vessel to the second vessel such that the liquid Group IIIA metal can flow from the first vessel to the second vessel, wherein the pipe is devoid of a valve capable of reducing flow between the first vessel and the second vessel; a first gas line connecting an inert gas source with the first vessel such that inert gas is present within the gas headspace; and a second gas line in fluid communication with the first gas line and connecting the inert gas source with the reaction chamber, the second gas line including a valve such that throttling the valve increases the pressure in the first gas line to induce liquid Group IIIA metal flow from the first vessel to the second vessel.

[0013] Embodiment 2: The reaction system of Embodiment 1, further comprising a level sensor configured to produce a signal corresponding to a liquid Group IIIA metal level within the second vessel, and a controller configured to receive the signal and control throttling of the valve of the second gas line in response thereto.

[0014] Embodiment 3 : The reaction system of Embodiment 1 or 2, wherein the level sensor comprises a capacitive sensor comprising a first conductor and a second conductor, wherein the first conductor and the second conductor are located adjacent to the second vessel and in spaced relation to each other, and a meter electrically connected to the first and second conductor for applying a voltage and measuring capacitance.

[0015] Embodiment 4: The reaction system of Embodiment 1 or 2, wherein the level sensor comprises a first light pipe for coupling a first light beam to the second vessel such that the first light beam interacts with gas produced in the second vessel and a second light pipe for receiving a second light beam from the second vessel, and a signal detector for measuring a difference between the first and second light beams.

[0016] Embodiment 5: The reaction system of Embodiment 4, wherein the liquid Group IIIA metal is gallium, and wherein the first light beam has a wavelength of about 249 nm or about 334 mu.

[0017] Embodiment 6: The reaction system of any one of Embodiments 1 to 2, wherein the level sensor comprises a light pipe for receiving light from the second vessel, and a signal detector for determining intensity of the light received from the light pipe.

[0018] Embodiment 7: The reaction system of any one of Embodiments 1 to 6, further comprising a source of gas comprising oxygen, ammonia, phosphine, or arsine in fluid communication with the reaction chamber via a second gas injector positioned to direct the gas toward the substrate. Embodiment 8: A method growing a Group IIIA metal-containing fdm epitaxially on a surface of a substrate, comprising: providing a substrate in a reaction chamber comprising a crystal growth zone overlying the substrate, the crystal growth zone being at a crystal growth temperature of about 800 °C or above, such as about 850 °C to about 1100 °C, the reaction chamber housing an internal vessel containing liquid Group IIIA metal within the reaction chamber; providing an external vessel containing the liquid Group IIIA metal and having a gas headspace adjacent to a surface of the liquid Group IIIA metal, the first vessel being external to the reaction chamber, wherein the external vessel is in fluid communication with the internal vessel via a pipe devoid of a valve capable of reducing flow between the external vessel and the internal vessel; flowing an inert gas through a first gas line to the gas headspace of the external vessel; flowing an inert gas through a second gas line to the reaction chamber, the second gas line being in fluid communication with the first gas line, the second gas line including a valve; flowing a halogen-containing gas into the internal vessel to produce a Group IIIA metal halide gas; injecting the Group IIIA metal halide gas from the internal vessel toward the substrate and into the crystal growth zone; injecting a gas comprising oxygen, ammonia, phosphine, or arsine toward the substrate and into the crystal growth zone; depositing a Group IIIA metal-containing film on a surface of the substrate; and periodically, throttling the valve in the second gas line to induce flow of liquid Group IIIA metal from the external vessel to the internal vessel to refill the liquid Group IIIA metal in the internal vessel.

[0019] Embodiment 9: The method of Embodiment 8, wherein throttling the valve in the second gas line occurs simultaneously with depositing the Group IIIA metal-containing film on the surface of the substrate such that refilling of the internal vessel occurs without stopping crystal growth.

[0020] Embodiment 10: The method of Embodiment 8 or 9, further comprising determining the level of liquid Group IIIA metal within the internal vessel and throttling the valve to induce flow of liquid Group IIIA metal when the liquid Group IIIA metal within the internal vessel reaches a predetermined level.

[0021] Embodiment 11 : The method of Embodiment 10, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises measuring capacitance across a first conductor and a second conductor located in spaced relation to each other and adjacent to the internal vessel, and correlating a change in the capacitance to a level of liquid Group IIIA metal within the internal vessel.

[0022] Embodiment 12: The method of Embodiment 10 or 11, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises coupling a first light beam to the internal vessel such that the first light beam interacts with gas produced in the internal vessel, receiving a second light beam from the internal vessel, and correlating a difference in the first light beam and the second light beam to a level of liquid Group IIIA metal within the internal vessel.

[0023] Embodiment 13: The method of any one of Embodiments 10 to 12, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises receiving a light beam from the internal vessel, measuring an intensity of the light beam, and correlating a change in the intensity of the light beam to a level of liquid Group IIIA metal within the internal vessel. Embodiment 14: The method of any one of Embodiments 8 to 13, wherein the pressure within the reaction chamber is about 50 to about 550 Torr, such as about 100 to about 300 Torr.

[0024] Embodiment 15: The method of any one of Embodiments 8 to 14, wherein the halogen-containing gas comprises chlorine, such as gaseous HC1 or Ch.

[0025] Embodiment 16: The method of any one of Embodiments 8 to 15, wherein the Group III A metal is gallium and the Group IIIA metal-containing film is a gallium nitride film.

[0026] Embodiment 17: Use of inert gas pressure to induce flow of liquid Group IIIA metal from an external vessel to an internal vessel within a reaction chamber adapted for crystal growth, particularly in the absence of a valve within a line connecting the two vessels.

[0027] These and other features, aspects, and advantages of the disclosure will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below. The invention includes any combination of two, three, four, or more of the above-noted embodiments as well as combinations of any two, three, four, or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined in a specific embodiment description herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosed invention, in any of its various aspects and embodiments, should be viewed as intended to be combinable unless the context clearly dictates otherwise.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Having thus described the disclosure in the foregoing general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0030] FIG. 1 illustrates a cross-sectional schematic view of an example reactor with injector apparatus suitable for use in the present disclosure;

[0031] FIG. 2 is a schematic illustration of a reaction system according to an embodiment of the present disclosure;

[0032] FIG. 3 is a top view of an example injector apparatus with refractory metal plates placed on either side of a liquid gallium vessel according to an embodiment of the present disclosure;

[0033] FIG. 4 is a refractory metal plate configuration according to an embodiment of the present disclosure;

[0034] FIG. 5 is a schematic illustration of a level control system using light absorption according to an embodiment of the present disclosure;

[0035] FIG. 6 is a cross-sectional side view of a level control system using a light pipe according to an embodiment of the present disclosure;

[0036] FIG. 7A-7C illustrate different levels of liquid metal in the system shown in FIG. 6;

[0037] FIG. 8 graphically illustrates the change in light intensity associated with Regions I, II, and III of FIGS. 7A-7C; FIGS. 9 A and 9B graphically illustrate the change in capacitance over time from the experiment of Example 1;

[0038] FIG. 10 A graphically illustrates the change in light signal over time from the experiment of Example 2; and

[0039] FIG. 10B graphically illustrates the slope of the light signal compared to HC1 flow from the experiment of Example 2.

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] The present disclosure will now be described more fully hereinafter with reference to exemplary embodiments thereof. These exemplary embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Indeed, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the,” include plural referents unless the context clearly dictates otherwise.

[0042] The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, such as within 5%, or within 1%, or within 0.5%.

[0043] The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0044] “Halogen” refers to elements within IUPAC group 17 of the periodic table, such as fluorine (F), chlorine (Cl), and bromine (Br).

[0045] “Gallium nitride” refers to any phase of GaN (e.g., the wurtzite phase or the cubic phase). The present disclosure also extends to production of alloys of gallium nitride in combination with other elements, including Al or In (such as (AlxGai.x)N or (InxGai.x)N).

[0046] “Gallium oxide” refers to any phase of Ga2O3 (e.g., alpha-phase or beta-phase). The present disclosure also extends to production of alloys of gallium oxide in combination with other elements, including Al or In (such as (AlxGai.x)2O3 or (InxGai.x)2O3).

[0047] Reaction System

[0048] The present disclosure provides a reaction system suitable for use in growing traditional III-V films (e.g., GaAs or GaP) or alloys thereof, III-N films (e.g., GaN) or alloys thereof, or gallium oxide (e.g., b- Ga2O3) films or alloys thereof, particularly using HVPE growth techniques. However, principles of the present disclosure could also be applied to other vapor-phase chemical deposition crystal growth methods wherein elemental metals are utilized as precursors, such as tri-halide HVPE (THVPE) or halogen-free vapor phase epitaxy. The reaction system and method described herein could be applied to HVPE growth of various Group IIIA metal-containing films, such as gallium nitride, indium oxide, or indium nitride. Accordingly, reference to liquid gallium herein could be replaced with other liquid Group IIIA metals, such as indium or aluminum. For the sake of brevity, the detailed description of the present disclosure will focus on gallium nitride fdms.

[0049] The present disclosure overcomes one of the disadvantages of using a reaction system that includes a liquid-containing vessel within a reaction chamber used for crystal growth. Conventional refilling of the liquid-containing vessel requires stoppage of the crystal growth process and cooling of the reaction chamber before the chamber can be opened and the internal liquid-containing vessel refilled. This results in reactor downtime and reduces production throughput.

[0050] In the present disclosure, refilling of the internal liquid-containing vessel is possible without disturbing crystal growth or cooling the reaction chamber. Instead, an external liquid-containing vessel is in fluid communication with the internal liquid-containing vessel and a pressure differential between the two vessels is used to induce flow, which enables refilling of the internal vessel without stoppage of crystal growth. In certain embodiments, real-time monitoring of the liquid level within the internal vessel can be used as a feedback control to enable more precise refilling of the internal vessel in a manner that allows improved control over the level in the internal vessel.

[0051] FIG. 1 provides a schematic view of a portion of an example embodiment of a reactor 10 suitable for use in the present disclosure. The reactor 10 includes a reaction chamber 30 having an injector apparatus 20 positioned therein. The injector apparatus 20 can comprise three concentrically -arranged injectors 22, 24, 26. The centrally-located injector 22 can be used for a first reagent gas, such as a gallium halide gas. The outermost injector 24 can be used for a second reagent gas, such as an ammonia-containing gas or an oxy gencontaining gas such as purified oxygen or air (e.g., where desired substrate film is gallium oxide). The injector 26 in the intermediate position between the reagent gas injectors 22, 24 is optional and adapted for use with a halogen-containing gas, such as a gas containing HC1 or CF. Through such an injector apparatus 20, the reagent gases are delivered to a crystal growth space within the reaction chamber 30 overlying a substrate 40 for subsequent reaction near the surface of the substrate for purposes of growing an epitaxial layer of, for example, GaN.

[0052] As shown, the substrate 40 can be supported by support 45, which is optionally translatable between a raised crystal growth position closer to the injector apparatus 20 (as shown) and a lowered position where the substrate can be accessed and removed / replaced. The reaction chamber 30 can be defined, for example, by an outer wall 65, an inner wall 70 having a portion slanted inward toward the crystal growth space and arranged such that an end of the inner wall is proximal to an end of the injector apparatus 20, and a substate support wall 75 defining a space through which the support 45 can be moved back and forth from the raised crystal growth position to a lowered position for substrate access.

[0053] The substrate support 45, outer wall 65, inner wall 70, and substrate support wall 75 can be constructed of any material inert and thermally stable at crystal growth temperatures as noted below. Example materials include quartz, alumina, silicon carbide, tantalum carbide, and the like. The inner wall 70 and the substrate support wall 75 are advantageously positioned proximal to the injected gaseous reagents and can therefore aid in reducing or eliminating deposits on the outer wall 65. In this manner, the inner wall 70 and substrate support wall 75 can be viewed, in certain embodiments, as sacrificial liners that can be replaced as needed while preserving the outer wall 65 for long-term use.

[0054] Surrounding the outer wall 65 is a suitable heater 80 for maintaining the reaction chamber at desired crystal growth temperatures. An example heater 80 can include one or more resistive heating elements, typically surrounding by insulation 85 to reduce heat loss. In certain embodiments, the heater 80 is capable of independent heating control in multiple zones. The total number of zones may vary. As shown, the zones can include a first zone Z 1 in the area of the injector apparatus 20 overlying the crystal growth space, a second zone Z2 in the area of the crystal growth space, and a third zone Z3 below the substrate 40. Additional zones are also possible, such as zones proximal to the top of the reactor and / or an upper portion of the injector apparatus 20 (not shown).

[0055] It is advantageous in certain embodiments to also inject an inert gas into various locations of the reaction chamber 30. As shown, in one embodiment, an inert gas is injected into a first area 90 surrounding the injector apparatus 20 and a second area 95 within the substrate support wall 75. In this manner, deposition of material in undesirable locations of the reaction chamber 30 can be reduced or eliminated. The reactor 10 can also include a suitable exhaust port 100 for removal of gases from the reaction chamber 30.

[0056] Although FIG. 1 shows a reactor 10 with a vertical orientation, the present disclosure is not limited to such an orientation. The same general principles of the present disclosure could be applied to other reactor orientations, such as horizontal reactors where reagents are injected laterally into a reaction chamber. In addition, the present disclosure is not limited to an injector apparatus with concentrically arranged injectors. An injector apparatus with side-by-side injectors could also be utilized without departing from the present disclosure. The relative location of the injector for the two reagent gases could also change from the arrangement shown in FIG. 1 without departing from the present disclosure. For example, the position of injection the two reagent gases could be switched with the ammonia, arsine, phosphine, or oxy gen-containing gas injected through the centrally -located injector 22 and the gallium halide gas injected through the outermost injector 24.

[0057] Still further, even where a concentric arrangement is utilized with one or more injectors configured in a ring-like or annular shape, the concentric arrangement need not be precisely concentric, meaning each injector need not have the same precise center. Instead, the injector apparatus could be substantially concentric, meaning concentric rings with a relatively small offset in the center of each concentric ring are included. The number of rings within a substantially concentric arrangement can also vary. The example embodiment of FIG. 1 illustrates an injector with three concentric injectors. However, other arrangements with additional substantially concentric injectors could also be used.

[0058] Each gas flow entering the injectors is in fluid communication with a source for each gas. The various gas sources may vary. The inert gas source is typically nitrogen or a noble gas, such as argon or other members of IUPAC group number 18 within the Periodic Table. The halogen-containing gas is typically gaseous HC1 or O2, although other halogen gases could also be used. The gallium halide source is typically GaCl, although other gallium halides could be used, such as GaC , or other compounds containing gallium and a different halogen. The gallium chloride is formed in situ within the reaction system by flowing either a combination of CI2 and H2or gaseous HC1 over liquid gallium within an injector apparatus. An inert gas can be combined with any of the other gas sources, such as the GaCl gas, the ammonia, arsine, phosphine, or oxy gen-containing gas, or the halogen-containing gas.

[0059] FIG. 2 schematically illustrates the connection between an external liquid gallium vessel and an internal liquid gallium vessel according to one embodiment of the present disclosure, and can be implemented in conjunction with, for example, the reaction system and injector apparatus set forth in FIG. 1. As shown, a reactor 300 is provided with an internal liquid gallium vessel 302 located within the reactor. The internal liquid gallium vessel 302 is in fluid communication with an externa liquid gallium vessel 304 via line 306. Both the reactor 300 and the external liquid gallium vessel 304 are in fluid communication with an inert gas source 308, such as a course of nitrogen or a noble gas, such as argon or other members of IUPAC group number 18 within the Periodic Table. The line carrying the inert gas to the reactor 300 includes a throttle valve 310, which enables the user to reduce the inert gas flow to the reactor. Throttling valve 310 will create a pressure differential between the inert gas pressure within the headspace of the external liquid gallium vessel 304 and the inert gas pressure within the reactor 300. This difference in pressure will induce flow through a drip port in the external liquid gallium vessel 304 such that liquid gallium flows into the internal liquid gallium vessel 302. The inert gas pressure difference created between the reactor 300 and the external liquid gallium vessel 304 from throttling of the valve 310 can vary, but will typically be about 10 Torr or higher, such as about 15 Torr or higher or about 20 Torr or higher or about 25 Torr or higher (e.g., about 10 to about 50 Torr or about 10 to about 30 Torr). The valve 310 can be throttled periodically as needed, and the periodic nature of the throttling need not be at defined regularly -occurring intervals and, instead, can be based on a feedback level control system as explained more fully below. Accordingly, reference to “periodically” or “periodic” simply means from time to time, rather than according to a predetermined schedule.

[0060] In certain embodiments, as shown in FIG. 2, the reaction system can include a level sensor 320 configured to produce a signal corresponding to a liquid gallium level within the internal vessel 302, and a controller 322 configured to receive the signal and control throttling of the valve 310 in response thereto. Use of a level sensor 320 will enable the reaction system to provide a feedback loop for more precise control of the liquid gallium level within the internal vessel 302. In this manner, the controller 322 could be programmed to maintain the liquid gallium within the internal vessel 302 at a predetermined level, such as at a level corresponding to a fill volume of liquid metal expressed as a percentage of total volume of the internal vessel. For example, the controller 322 could be programmed to maintain the liquid metal fill volume within a range, such as about 20% or higher, or about 30% or higher or about 40% or higher, such as a fill volume of about 20% to about 80% or about 30% to about 70% or about 40% to about 60%.

[0061] The controller 322 can vary, but will typically include a processor. The processor can include at least one processor core, microprocessor, coprocessor, or various other computing or processing devices including one or more integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), some combination thereof, or the like. In some examples, the processing circuitry may include memory coupled to or integrated with the processor, and which may store data, computer program instructions executable by the processor, some combination thereof, or the like. In some example embodiments, the processor can be configured to execute instmctions that can be stored in the memory or that can be otherwise accessible to the processor. As such, whether configured by hardware or by a combination of hardware and software, the processor is capable of performing operations according to various embodiments noted herein, such as controlling valve 310.

[0062] The type of level sensor 320 can vary. In one embodiment, the level sensor 320 includes a capacitive sensor comprising a first conductor and a second conductor, wherein the first conductor and the second conductor are located adjacent to the internal liquid gallium vessel (e.g., vessel 302 of FIG. 2) and in spaced relation to each other. Typically, the first and second conductor are located on opposing sides of the internal liquid gallium vessel. A meter electrically connected to the first and second conductor is adapted for applying a voltage and measuring capacitance. FIGS. 3 and 4 relate to an example level sensor configuration of this type. FIG. 3 is a top view of a metal source vessel 404 (e.g., a liquid gallium source) which is formed within a portion of the gas injection apparatus 400. The injection apparatus 400 includes first and second conductors, 402a and 402b, in the form of metal plates, positioned on either side of the liquid gallium chamber 404. The two conductors, 402a and 402b are electrically connected to a meter 408, such as an LCR meter (e.g., a HEWLETT PACKARD® HP4284A Precision LCR meter). The metal used for the conductors, 402a and 402b, can vary, with examples including refractory metals such as molybdenum or tantalum. An example metal plate configuration for the conductors, 402a and 402b, is shown in FIG. 4. The shape of the metal plates can be determined, at least in part, by the shape of the liquid gallium chamber 404 such that the metal plates conform to the outer surface of the chamber.

[0063] During use, the measured capacitance of the metal plates will change as the amount of gallium in the internal chamber 404 changes. Once the capacitance drops below a particular predetermined value, the “fill” signal is activated by the controller 322 and gallium refilling is performed by throttling valve 310 (see FIG. 2). The capacitance that corresponds to a particular gallium level within the vessel 404 will change with the geometry of the metal plates as well as the geometry of the vessel. Once the geometry of the vessel 404 and the metal plates (conductors 402a and 402b) are known, the relationship between capacitance and liquid metal level can be determined by routine experimentation by, for example, measuring capacitance during crystal growth reactions over time and periodically stopping the reaction process to determine liquid gallium level in the internal vessel.

[0064] In an alternative embodiment, the level sensor 320 comprises a first light pipe for coupling a first light beam to the internal gallium vessel (e.g., vessel 302 of FIG. 2) such that the first light beam interacts with gas produced in the vessel and a second light pipe for receiving a second light beam from the vessel, and a signal detector for measuring a difference between the first and second light beams. One example of this embodiment is shown schematically in FIG. 5, which shows use of a light source 502 (e.g., a mercury arc lamp), a light filter 504 that narrows the light wavelength produced to a desired wavelength, an optical chopper 506 (which modulates intensity of a light beam), and a beam splitter 508 for directing the light beam to two locations. The beam splitter 508 enables coupling of the light beam to the internal gallium vessel within a reactor 510 and also coupling of the light beam to a reference signal detector 512. The light beam coupled to the internal gallium vessel through a light pipe 520 will interact with the gallium-containing gas being produced within the vessel such that some light is absorbed therein. The light leaving the vessel via a second light pipe 522 after such interaction is measured suing a second signal detector 514. An example signal detector for use in the present disclosure is a silicon photodetector such Model 918D-UV-OD3R available from Newport Corporation.

[0065] The difference in the light signal to the two signal detectors (reference signal detector 512 and second signal detector 514) can be correlated to the level of liquid gallium within the vessel and the controller 516 receiving the signals can use the difference to control refilling of the vessel using the system described above in FIG. 2.

[0066] The light pipes used to couple the light beam to the internal vessel and receive a light beam from the internal vessel must be constructed by a material capable of withstanding the conditions of the reactor. In one embodiment, the light pipes are quartz rods, which are UV transparent and have sufficient thermally stability.

[0067] The desired wavelength used in this embodiment will depend on the Group IIIA metal. For gallium nitride films, where gallium chloride is being produced in the internal liquid gallium vessel, the wavelengths of about 249 nm and about 334 nm are appropriate as GaCl will absorb light at these wavelengths. In use, as the level of gallium is depleted within the internal vessel, the amount of GaCl being produced in the headspace of the vessel will change. This change in GaCl partial pressure within the vessel will cause a change in the amount of light absorbed within the vessel. Thus, the difference in light signals leaving the internal vessel and the reference detector can be correlated to liquid gallium level using routine experimentation by, for example, measuring light absorption during crystal growth reactions over time and periodically stopping the reaction process to determine liquid gallium level in the internal vessel.

[0068] The same general approach can be used for other liquid metals. For example, for an indium-containing vessel, one can utilize wavelengths of 266 nm or 216 nm, which are efficiently absorbed by InCi or InCT,. respectively.

[0069] In a further embodiment, the level sensor 320 comprises a light pipe (e.g., a quartz rod as discussed above) for receiving light from the internal liquid gallium vessel (e.g., vessel 302 of FIG. 2), and a signal detector for determining intensity of the light received from the light pipe. In this manner, the intensity of the detect light can be correlated to liquid gallium level within the vessel. An example schematic representation of such a system is shown in FIGS. 6 and 7A-C. As shown, a light pipe 544, supported by support plate 540, is placed such that a light signal can be received by the light pipe from a liquid gallium vessel 542. The light signal is transmitted to a signal detector 546, such as a silicon photodetector described above. As illustrated in FIGS. 7A-7C and FIG. 8, when the liquid gallium 550 level is low, as exemplified by Region I in FIGS. 7A and 8, the light pipe receives a light signal of maximum intensity. As the liquid gallium level rises into Region II of FIGS. 7B and 8, the light signal intensity declines, and ultimately the minimum light intensity level of Region III (FIGS. 7C and 8) is reached. The light intensity received by the light pipe can be correlated to liquid gallium level using routine experimentation by, for example, measuring light intensity during crystal growth reactions over time and periodically stopping the reaction process to determine liquid gallium level in the internal vessel.

[0070] Gallium Nitride Crystal Growth Process

[0071] The present disclosure also provides a method growing a GaN-based single crystal film epitaxially on a surface of a substrate. The method can be practiced, for example, with the reaction systems described above. The method involves providing a substrate in a reaction chamber comprising a crystal growth zone overlying the substrate, the crystal growth zone being at a crystal growth temperature. Example crystal growth temperatures include about 800 °C or above, such as about 850 °C to about 1100 °C or about 900 to about 1000 °C. The pressure within the reaction chamber during crystal growth is typically about 50 to about 550 Torr, such as about 100 to about 300 Torr. However, higher pressures, including up to atmospheric pressure, could also be used.

[0072] The substrate used for crystal growth may vary, but is typically either sapphire or a freestanding GaN substrate. The crystalline orientation of the GaN substrate may vary, with one advantageous example being the (0001) orientation. Substrate sizes may vary, with typical diameter ranges including about 1 to about 8 inches, such as about 2 to about 4 inches.

[0073] Prior to growth, the substrate wafers are typically cleaned using a series of solvents to remove organic residues, as well as a series of acids, for example aqueous HC1 and / or HF acid, to remove metallic impurities or reconstructed suboxides from the wafer surface. Substrate wafers are subsequently rinsed in deionized water and blown dry with nitrogen before being loaded into the reactor.

[0074] The method involves injecting a gallium halide gas toward the substrate and into a first region of the crystal growth zone and injecting an ammonia-containing gas toward the substrate and into a second region of the crystal growth zone. Still further, the method optionally includes injecting a halogen-containing gas toward the substrate and into a third region of the crystal growth zone, the third region being between the first region and the second region. For example, the halogen-containing gas can be injected through an injector positioned between the ammonia-containing gas and the gallium halide gas as described above. In this manner, the halogen-containing gas provides “excess” halogen to the crystal growth zone in a buffer region between the points of injection of the ammonia-containing gas and the gallium halide gas, which is believed to suppress undesirable vapor phase pre-reactions that can lead to particle defects in the grown film. In certain embodiments, the reaction chamber has a vertical orientation such that the gallium halide gas, the ammonia- containing gas, and the halogen-containing gas are injected above the substrate, and wherein the first region of the crystal growth zone is proximal to a center of the substrate and the second region is proximal to an outer edge of the substrate.

[0075] As noted above, the gallium halide gas can be produced by introducing a halogen-containing gas into an internal liquid gallium vessel. During crystal growth, the level of liquid gallium within the internal vessel can be monitored using, for example, one of the techniques described above, and the internal vessel can be refilled as needed.

[0076] The partial pressure of the reagent gases during crystal growth can vary. Example partial pressures for GaCl include from about 0.10 Torr to about 10 Torr, such as about 0.2 to about 2.5 Torr. The amount of ammonia injected into the reaction chamber can be defined as a molar ratio of NH3to GaCl, with example ranges including ratios of about 5 to about 50 or about 10 to about 20. The amount of added halogencontaining gas can be expressed as a molar ratio of added halogen (e.g., CL) to GaCl, with example ranges including ratios of about 0.01 to about 1.0 or about 0.02 to about 0.25.

[0077] Quality of the grown film can also be measured using X-Ray diffractometer (XRD) analysis. In certain embodiments, the grown film exhibits a full-width at half-maximum (FWHM) of the (004) reflection of about 35 arcsec or less, such as about 30 arcsec or less or about 25 arcsec or less, with example ranges including about 15 to about 35 arcsec or about 20 to about 30 arcsec.

[0078] The thickness of the grown film can vary and will depend on the desired application for the film. In certain embodiments, the method of the present disclosure can be used to produce films having an average thickness as measured by weight of at least about 100 pm to about 10 mm, such as a range of about 400 pm to about 4 mm.

[0079] EXERIMENT AL

[0080] Example 1: Capacitance-Based Level Control

[0081] A reaction system as described in FIG. 2 was used with the level control system described in FIGSs. 3 and 4. Capacitance was measured during two 1-hour GaN crystal growth runs with varying HC1 flow through the liquid gallium vessel, starting at 100 seem, then dropping to 25 seem, and finally 50 seem. The results are set forth in FIGS. 9A (first run) and 9B (second run), which graphically illustrates the change in capacitance (in Farad) over time. As can be seen, the capacitance clearly changed during the course of each crystal growth run and the slope of the capacitance was different for each HO flow rate. At the highest HC1 flow rate (100 seem), as expected, the capacitance changed more sharply as the liquid gallium level dropped more quickly in correlation to the reaction rate within the vessel. At the lowest HC1 flow rate (25 seem), the capacitance changed very little since the liquid gallium level changed very little at the much lower reaction rate. The slope of the capacitance change at the mid-level HC1 flow of 50 seem was between the slope at the high and low HC1 flow rates as expected. This experiment proves that a capacitance-based system can be used to monitor the level of liquid gallium within the injector apparatus.

[0082] Example 2: Light Absorption Level Control A reaction system as described in FIG. 2 was used with the level control system described in FIG. 5. A light beam at a wavelength of about 250 nm was coupled to the internal liquid gallium vessel and a light signal leaving the vessel was measured and compared to a reference 250 nm light beam over two GaN crystal growth mns with varying HC1 flow through the liquid gallium vessel, starting at over 90 seem, then dropping to around 23-24 seem, and finally about 46-48 seem. The results are set forth in FIG. 10A, which graphically illustrates the change in the difference between the light signal received from the vessel and the reference 250 nm signal. As can be seen, the light signal difference changed during the course of each crystal growth run. At the highest HC1 flow rate (over 90 seem), as expected, the light signal difference was at its highest due to large amounts of GaCl formed in the vessel (resulting in greater light absorbance). At the lowest HC1 flow rate (below 25 seem), the light signal difference was much lower due to the much lower reaction rate. The magnitude of the light signal difference at the mid-level HC1 flow of around 46-48 seem was between the signal at the high and low HC1 flow rates as expected. The change in light signal according to this method varies approximately linearly as shown in FIG. 10B, which shows the slope of the curve of the light signal compared to HC1 flow rate into the liquid gallium vessel, with larger signals associated with higher HC1 flow rate. This experiment proves that a light absorption based system can be used to monitor the level of liquid gallium within the injector apparatus.

[0083] Many modifications and other aspects of the disclosure set forth herein will come to mind to one skilled in the art to which the disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific aspects disclosed and that modifications and other aspects are intended to be included within the scope of the claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

What is claimed is:

1. A reaction system for growing a Group IIIA metal-containing film, comprising:(i) a reaction chamber housing a substrate;(ii) a first vessel containing a liquid Group IIIA metal, such as gallium or indium, and having a gas headspace adjacent to a surface of the liquid Group IIIA metal, the first vessel being external to the reaction chamber;(iii) a second vessel containing the liquid Group IIIA metal within the reaction chamber, the second vessel in fluid communication with a source of halogen-containing gas and in fluid communication with a first gas injector positioned to direct a gas produced in the second vessel toward the substrate;(iv) a pipe connecting the first vessel to the second vessel such that the liquid Group IIIA metal can flow from the first vessel to the second vessel, wherein the pipe is devoid of a valve capable of reducing flow between the first vessel and the second vessel;(v) a first gas line connecting an inert gas source with the first vessel such that inert gas is present within the gas headspace; and(vi) a second gas line in fluid communication with the first gas line and connecting the inert gas source with the reaction chamber, the second gas line including a valve such that throttling the valve increases the pressure in the first gas line to induce liquid Group IIIA metal flow from the first vessel to the second vessel.

2. The reaction system of claim 1, further comprising a level sensor configured to produce a signal corresponding to a liquid Group IIIA metal level within the second vessel, and a controller configured to receive the signal and control throttling of the valve of the second gas line in response thereto.

3. The reaction system of claim 2, wherein the level sensor comprises a capacitive sensor comprising a first conductor and a second conductor, wherein the first conductor and the second conductor are located adjacent to the second vessel and in spaced relation to each other, and a meter electrically connected to the first and second conductor for applying a voltage and measuring capacitance.

4. The reaction system of claim 2, wherein the level sensor comprises a first light pipe for coupling a first light beam to the second vessel such that the first light beam interacts with gas produced in the second vessel and a second light pipe for receiving a second light beam from the second vessel, and a signal detector for measuring a difference between the first and second light beams.

5. The reaction system of claim 4, wherein the liquid Group IIIA metal is gallium, and wherein the first light beam has a wavelength of about 249 nm or about 334 nm.

6. The reaction system of claim 2, wherein the level sensor comprises a light pipe for receiving light from the second vessel, and a signal detector for determining intensity of the light received from the light Pipe.

7. The reaction system of any one of claims 1 to 6, further comprising a source of gas comprising oxygen, ammonia, phosphine, or arsine in fluid communication with the reaction chamber via a second gas injector positioned to direct the gas toward the substrate.

8. A method growing a Group IIIA metal-containing film epitaxially on a surface of a substrate, comprising: providing a substrate in a reaction chamber comprising a crystal growth zone overlying the substrate, the crystal growth zone being at a crystal growth temperature of about 800 °C or above, such as about 850 °C to about 1100 °C, the reaction chamber housing an internal vessel containing liquid Group IIIA metal within the reaction chamber; providing an external vessel containing the liquid Group IIIA metal and having a gas headspace adjacent to a surface of the liquid Group IIIA metal, the first vessel being external to the reaction chamber, wherein the external vessel is in fluid communication with the internal vessel via a pipe devoid of a valve capable of reducing flow between the external vessel and the internal vessel; flowing an inert gas through a first gas line to the gas headspace of the external vessel; flowing an inert gas through a second gas line to the reaction chamber, the second gas line being in fluid communication with the first gas line, the second gas line including a valve; flowing a halogen-containing gas into the internal vessel to produce a Group IIIA metal halide gas; injecting the Group IIIA metal halide gas from the internal vessel toward the substrate and into the crystal growth zone; injecting a gas comprising oxygen, ammonia, phosphine, or arsine toward the substrate and into the crystal growth zone; depositing a Group IIIA metal-containing film on a surface of the substrate; and periodically, throttling the valve in the second gas line to induce flow of liquid Group IIIA metal from the external vessel to the internal vessel to refill the liquid Group IIIA metal in the internal vessel.

9. The method of claim 8, wherein throttling the valve in the second gas line occurs simultaneously with depositing the Group IIIA metal-containing film on the surface of the substrate such that refilling of the internal vessel occurs without stopping crystal growth.

10. The method of claim 8, further comprising determining the level of liquid Group IIIA metal within the internal vessel and throttling the valve to induce flow of liquid Group IIIA metal when the liquid Group IIIA metal within the internal vessel reaches a predetermined level.

11. The method of claim 10, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises measuring capacitance across a first conductor and a second conductor located in spaced relation to each other and adjacent to the internal vessel, and correlating a change in the capacitance to a level of liquid Group IIIA metal within the internal vessel.

12. The method of claim 10, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises coupling a first light beam to the internal vessel such that the first light beam interacts with gas produced in the internal vessel, receiving a second light beam from the internal vessel, and correlating a difference in the first light beam and the second light beam to a level of liquid Group IIIA metal within the internal vessel.

13. The method of claim 10, wherein determining the level of liquid Group IIIA metal within the internal vessel comprises receiving a light beam from the internal vessel, measuring an intensity of the light beam, and correlating a change in the intensity of the light beam to a level of liquid Group IIIA metal within the internal vessel.

14. The method of any one of claims 8 to 13, wherein the pressure within the reaction chamber is about 50 to about 550 Torr, such as about 100 to about 300 Torr.

15. The method of any one of claims 8 to 13, wherein the halogen-containing gas comprises chlorine, such as gaseous HC1 or Ch.

16. The method of any one of claims 8 to 13, wherein the Group IIIA metal is gallium and the Group IIIA metal-containing film is a gallium nitride film.

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