HK1196465A - Process for high-pressure nitrogen annealing of metal nitrides - Google Patents

Description

High pressure nitrogen annealing process for metal nitrides

Cross reference to related applications

The present application claims the benefit of U.S. patent application No.13/171,042 entitled "Process for high-Pressure nitrile analysing of Metal nitriles" filed on 28.6.2011, which is hereby incorporated by reference in its entirety.

Technical Field

The present disclosure relates to a process for reducing nitrogen vacancies in metal nitrides. In particular, the present disclosure relates to a slow annealing process for reducing nitrogen vacancies in bulk crystals, wafers, epitaxial layers, and epitaxial films of metal nitride compounds by post-growth annealing in a high temperature, high pressure environment, resulting in a reduced nitrogen vacancy density and an increased p-type conductivity.

Background

Metal nitride epitaxial layers and films are the basis of many modern electronic devices, such as Light Emitting Diodes (LEDs) and power crystalsA tube. Nitrogen Vacancies (VN) are point defects that affect the chemical bonds between atoms in metal nitrides and are formed by the absence of nitrogen during the production and growth of the metal nitrides. Defects have proven to be an important factor in the weakness of positive (p-type) conductivity in metal nitride compositions, including those used as semiconductors. Generally, nitrogen vacancies are the lowest energy formed in a semiconductor material and can act as mono-or tri-electron donors (VN), respectively₁₊) And (VN)₃₊). Weak p-type conductivity results in high internal resistance and limits the efficiency and performance of metal nitride semiconductor materials. Therefore, it is desirable to reduce nitrogen Vacancies (VN)₁₊And/or VN₃₊) The p-type conductivity of the metal nitride semiconductor material is improved.

It is known that the vapor pressure of nitrogen is high and NH is decomposed₃Is low, nitrogen vacancies are easily generated in the metal nitride. During growth, metal nitrides are often unintentionally doped with nitrogen vacancies. Thus, the quality of the grown composition is impaired because nitrogen vacancies affect the electrical and optical properties of the metal nitride. The nitrogen vacancies contribute to the negative (n-type) conductivity of the metal nitride. n-type conductivity refers to conductivity associated with donor electrons in a semiconductor that are functionally equivalent to negative charges.

Efforts to reduce the benefits of n-type conductivity have included doping materials to increase the p-type conductivity of the materials. More specifically, p-type dopants are incorporated into the metal nitride in an attempt to counteract or "neutralize" the effects of growing impurities and/or defects, including nitrogen vacancies. However, p-type doping also creates nitrogen Vacancies (VN) by an auto-compensating mechanism₁₊And/or VN₃₊)。

Nitrogen vacancies are extremely mobile in the lattice structure of the metal nitride. Thus, it is possible to reduce the density of nitrogen vacancies in the metal nitride by an annealing process that diffuses nitrogen atoms into the metal nitride crystal lattice and extrudes nitrogen vacancies out of the crystal lattice. High temperature annealing has shown promise in improving the crystal structure and conductivity quality of metal nitrides. However, some materials, including group III-V metal nitrides (e.g., aluminum nitride, gallium nitride, and indium nitride), will decompose under rapid thermal annealing, with pressures ranging from vacuum to approximately atmospheric pressure. Therefore, there is a need for a slow High Temperature High Pressure (HTHP) annealing process that can be monitored and adjusted to ensure that crystal relaxation and spatial movement occurs without significant nitrogen decomposition.

Summary of The Invention

The present disclosure relates to a slow, post-growth process for forming metal nitrides of increased p-type conductivity. In one aspect, the process includes placing the grown metal nitride in an annealing apparatus that includes an annealing vessel. The ambient gas is then evacuated from the annealing vessel to create a vacuum in the annealing vessel. A nitrogen overpressure above approximately atmospheric pressure is created in the annealing vessel. The annealing vessel is typically heated to a temperature sufficient to diffuse the nitrogen species into the metal nitride. The metal nitride is then annealed for 1 hour or more to reduce the nitrogen vacancy density in the material. The metal nitride is annealed for 1-100 hours, typically at a temperature ranging from 600 c to 2900 c and a pressure greater than 760 torr (-1 standard atmospheric pressure (ATM)). It is critical that the process use heat and overpressure for a period of time to produce metal nitride with increased p-type conductivity.

In one aspect, the metal nitride is annealed at a temperature ranging from 1000 ℃ to 2400 ℃ and a pressure ranging from 3800 torr to 10100 torr for 1-48 hours. Thus, the resulting metal nitride is discernible by a decrease in the density of nitrogen vacancies and an increase in p-type conductivity, as evidenced by a resistivity ranging from approximately 0.0001 Ω -cm to approximately 100 Ω -cm.

In another aspect, the III-V metal nitride is annealed at a temperature of 2200 ℃ and a pressure of 7000 Torr for at least 24 hours. The resulting group III-V metal nitride has a reduced concentration of nitrogen vacancies and an increased p-type conductivity, as evidenced by a resistivity of from about 0.0001 ohm-cm to about 100 ohm-cm. The exact decrease in nitrogen vacancy concentration and increase in p-type conductivity depends on the annealed metal nitride, the level of p-type doping and the p-type dopant used.

The annealing process may be performed by an annealing apparatus. The annealing apparatus includes an annealing vessel having an enclosure defining an interior space for containing a grown group III-V metal nitride. The annealing apparatus also includes a heating system for maintaining a desired temperature in the annealing vessel and a nitrogen gas source for providing nitrogen species to the annealing vessel. The apparatus further includes a vacuum system that generates a near vacuum to purge ambient gas from within the annealing vessel and a pressure control system that provides a constant overpressure of nitrogen species to the annealing vessel. The annealing apparatus also includes a feedback control system that monitors and controls the various systems of the annealing apparatus.

Brief Description of Drawings

Fig. 1 is a flow diagram of a slow annealing process according to an embodiment of the present disclosure.

Fig. 2 is a block diagram depicting an annealing apparatus performing a slow annealing process according to an embodiment of the present disclosure.

Fig. 3 is a block diagram of an annealing vessel for a slow annealing process according to an embodiment of the present disclosure.

Detailed Description

The process of the present disclosure provides a slow method of increasing the p-type conductivity of metal nitrides. As used herein, metal nitride refers to a metal nitride crystal, wafer, epitaxial layer or film, or other composition consisting essentially of a metal nitride compound. Slow as used herein refers to a duration of more than one and a half hours. The method includes heating a metal nitride (including a substrate or epitaxial layer grown on a substrate) in a nitrogen-rich environment at a pressure above atmospheric pressure for at least 1 hour.

The slow High Temperature High Pressure (HTHP) annealing process facilitates diffusion of nitrogen gas into the ingot, wafer, epitaxial layer, and/or epitaxial film to generate a metal nitride containing a reduced concentration of nitrogen vacancies. The diffusion of nitrogen into the metal nitride effectively increases the concentration of nitrogen species in the metal nitride. The increased concentration of nitrogen species increases the stoichiometric ratio of nitrogen atoms in the nitride. Thus, the reduction of nitrogen vacancies improves p-type conductivity by reducing hole trapping effects caused by vacancies, voids, and other imperfections in the metal nitride.

The slow annealing process increases the positive (p-type) conductivity of doped metal nitrides commonly used in the manufacture of semiconductors. The slow anneal is particularly useful for increasing the p-type conductivity of binary, ternary, and quaternary group III-V metal nitrides, including those In the form of AXB1-XN, where A and/or B are group III-V elements such as, but not limited to, B, Al, Ga, or In. After the slow annealing process, the p-type conductivity of the metal nitride will increase, as evidenced by a decrease in resistivity ranging from approximately 0.0001 to 100 Ω -cm, depending on the annealed metal nitride, the doping level, and the dopant used.

p-type conductivity refers to conductivity associated with holes in a semiconductor material. In a semiconductor material, a hole refers to an empty orbital in an otherwise fully charged quantum shell of an atom. In an applied electric and/or magnetic field, the holes act as positive charges e +. Holes may be generated by doping. For example, substituting an atom having less than 3 electrons in the outermost shell (e.g., Mg or Ca) for a group III metal atom in a metal nitride (e.g., Al) creates holes in the material.

The vacancies are identified by one or more atoms that are missing from the crystal structure of the material. Similarly, a space is a cluster of two or more slots. The vacancies contain additional unbound electrons. Thus, to counteract the vacancies, a p-type dopant atom having less than 3 electrons in the outermost shell must be incorporated into each nitrogen vacancy of the metal nitride.

P-type semiconductor materials are typically produced by doping processes that add certain types of atoms to the semiconductor material in order to increase the number of free charge carriers. When a dopant is added, the dopant accepts weakly bound outer electrons from atoms of the semiconductor material. The electron vacancy left by the electron is a hole.

P-type doping is performed to generate hundreds of holes and thus increase the number of functional positive charges. For example, when magnesium and/or beryllium is used as a dopant, at least one electron is removed from the 4 covalent bonds naturally occurring in the group III-V metal nitride lattice. Thus, the dopant can accept electrons from covalent bonds of adjacent atoms, thereby forming holes that act as positive point charges. When a sufficiently large amount of dopant is added, the number of holes greatly exceeds the number of electrons. Thus, holes become majority carriers and electrons become minority carriers in the p-type doped semiconductor material.

Under the slow HTHP anneal, nitrogen atoms may diffuse back into the metal nitride (including the p-type doped metal nitride), thereby reducing nitrogen vacancies, repairing the crystal structure and enhancing the p-type electrical properties of the metal nitride.

By way of example, and not limitation, AlN has been demonstrated to exhibit a rapid diffusion rate of nitrogen vacancies into and out of its lattice structure. The average 1-D diffusion length at 2200 ℃ is up to 1 cm/h. The magnitude of this high diffusion constant is higher than the diffusion length of the commonly used p-type dopant atoms (Mg, Be, Si, etc.). Thus, nitrogen vacancies may diffuse out of the AlN substrate while retaining the p-type dopant atoms.

The p-type conductivity of the metal nitride ingot and/or wafers sliced from the ingot can be increased by a slow HTHP annealing process before and/or after polishing. The electrical conductivity of the diced wafers having one or more epitaxial layers of one or more metal nitrides deposited thereon is also improved by a slow high temperature high pressure annealing process. An annealing process may be performed after each epitaxial layer and/or after selective epitaxial layer growth. An annealing process may also be performed once all of the epitaxial layers have been grown. Although the annealing process is described using a metal nitride ingot, wafer, and/or epitaxial layer, the process may also be performed on an epitaxial film consisting essentially of a metal nitride compound.

Although the HTHP annealing process may be used for all metal nitrides, the process is described with reference to group III-V metal nitrides, including but not limited to aluminum nitride (AlN) and aluminum gallium nitride (AlGaN). Other group III-V elements may be used. The process also promotes relaxation of the metal nitride lattice to improve the crystal structure of the metal nitride, and repairs damage to the wafer after sawing and/or polishing.

Fig. 1 is a flow diagram of a slow growth followed by a high temperature and high pressure annealing process 100. The annealing process 100 is performed on metal nitrides, including metal nitride ingots, wafers, and epitaxial layers and films grown on various substrates. The annealing process 100 includes heating the metal nitride in a high pressure nitrogen rich environment to a desired temperature and maintaining the desired temperature for at least 1 hour to cause nitrogen vacancies to diffuse into the metal nitride. The metal nitride is placed in an annealing apparatus having one or more components and systems including, but not limited to, a vacuum system, a heating system, a pressure control system, a gas source, and a feedback monitoring system. The annealing device controls the parameters and other variables of the annealing process 100 that is performed at a number of steps 102-110.

At step 102, one or more group III-V metal nitrides are placed in an annealing apparatus, such as annealing apparatus 200 shown in FIG. 2. In one aspect, the group III-V metal nitride grown in the vessel of the annealing apparatus is subjected to an annealing process 100 after growth. On the other hand, the annealing process 100 is performed on the group III-V metal nitride grown in another reactor or growth apparatus and then placed in an annealing vessel of an annealing device. Likewise, the group III-V metal nitride may be annealed to reduce nitrogen vacancies (VN3+) and (VN1+) formed during growth, thereby increasing the p-type conductivity concentration of the semiconductor material regardless of how it is grown or produced.

At step 104, the annealing vessel is evacuated. The vacuum system evacuates the annealing vessel to create a high vacuum inside the annealing vessel and to purge the annealing vessel of ambient gases. High vacuum can range from below ambient atmospheric pressure to near full vacuum. In one aspect, the annealing vessel is depressurized to create a high vacuum ranging from 1X 10-5 to 1X 10-9 Torr.

Next, nitrogen species are injected as a gas at step 106. A high pressure pump was used to generate an overpressure of nitrogen gas in the annealing vessel. The inert nitrogen species further purges the interior of the annealing vessel and diffuses into and out of the surface of the group III-V metal nitride to displace nitrogen vacancies formed during the growth of the metal nitride. The gas may consist entirely of nitrogen species or a mixture of nitrogen species and one or more other species. In one example, the overpressure of nitrogen gas may range from about 760 torr to about 3.8 x 108 torr. In another example, the overpressure of nitrogen ranges from about 3800 to about 10100 torr.

In one aspect, a high pressure pump creates a nitrogen overpressure by injecting a gas at a pressure within a desired pressure range. On the other hand, nitrogen gas was injected into the inside of the annealing vessel at a pressure lower than the required pressure. The nitrogen pressure is then increased to the desired range by heating the interior of the annealing vessel.

The interior of the annealing vessel is then heated, as shown in step 108. In one aspect, the interior of the annealing vessel is heated to a temperature ranging from 1000 ℃ to 2500 ℃. On the other hand, the metal nitride is annealed at approximately 2000 ℃.

At step 110, the temperature and pressure within the annealing vessel are maintained within the desired ranges to anneal the metal nitride for at least 1 hour. In one aspect, the metal nitride is annealed for about 1 to about 100 hours, which is long enough to diffuse the N2 gas into and out of the metal nitride surface and reduce the number of nitrogen vacancies and/or other defects. On the other hand, the metal nitride is annealed for approximately 24 hours. The exact pressure and duration of the annealing process depends on the size and type of metal nitride being annealed.

The metal nitride is cooled at step 112. In one aspect, the metal nitride is removed from the annealing vessel and cooled in the ambient. On the other hand, the metal nitride is cooled in a controlled manner in the annealing vessel. In this regard, the temperature and/or pressure in the annealing vessel is varied to control the cooling of the metal nitride. For example, the metal nitride may be cooled slowly over a longer period of time to minimize thermal displacement of the metal nitride. As used herein, thermal displacement refers to contraction and/or expansion of the metal nitride due to heating and/or cooling.

Fig. 2 is a block diagram of an annealing apparatus 200 (see fig. 1) that may be used to perform one or more aspects of the slow annealing process 100. In one aspect, the annealing apparatus 200 includes an annealing vessel 202, a vacuum system 204, a heating system 206, a pressure control system 208, a nitrogen system 210, and a feedback control system 212.

Annealing container

The annealing vessel 202 is a closed vessel in which one embodiment of the slow annealing process 100 is performed. In one aspect, the annealing vessel 202 includes an enclosure adapted to withstand high temperatures and high pressures. For example, the annealing vessel may be an autoclave. The annealing vessel 202 may also be a reactor configured to withstand high temperatures and pressures, such as a crystal growth reactor.

In one aspect, the annealing vessel 202 is insulated to protect the environment around the annealing vessel from the high temperatures that occur as a result of the annealing process. The anneal vessel 202 is configured to maintain structural integrity at various internal pressures ranging from about 1 x 10 "9 torr to about 3.8 x 108 torr and temperatures up to about 2900 ℃ that may occur during the post-growth anneal process 100.

On the other hand, the annealing vessel 202 is capable of containing a number of wafers and/or ingots within the interior of the annealing vessel. For example, the annealing vessel 202 may hold 1-5000 wafers and/or 1-100 bulk crystals. In other examples, the annealing vessel 202 may hold any number of wafers and/or ingots, limited by the size of the annealing vessel.

The annealing vessel 202 is also of sufficient size to accommodate the structure supporting the ingot and/or wafers. In one example, the wafers may be placed in a quartz boat, such as boat 308 shown in fig. 3, prior to being placed in the annealing vessel 200. In other examples, the ingot and/or wafer may also be placed or housed in other structures suitable to withstand the pressure and temperature in the annealing vessel 202. By way of example and not limitation, other structures may be composed of titanium diboride (TiB2), aluminum nitride ceramics, refractory metals, metal carbides, and/or other metal nitrides.

In one aspect, the ingot and/or wafers are placed in a support structure prior to placement in the annealing vessel 202. On the other hand, the support structure remains in the annealing vessel 202 and the group III-V metal nitride to be annealed is loaded into the support structure.

The annealing vessel 202 may be configured in any suitable orientation, including horizontal, vertical, 45 relative to a vertical reference line, and any intermediate orientation depending on the desired use and location of the annealing apparatus 200.

Vacuum system

[0042] The vacuum system 204 removes ambient gases from the annealing vessel 202 and then anneals the group III-V metal nitride disposed therein. In one aspect, the vacuum system 204 may be any pumping system capable of generating a high vacuum. As used herein, high vacuum refers to a pressure of approximately 1X 10-5 to 1X 10-9 Torr.

The vacuum system 204, on the other hand, generates a high vacuum through a two-stage pumping process. The process includes a first stage of reducing the base pressure of the annealing vessel 202 to-1 x 10-4 torr. The first stage may be accomplished by a mechanical vacuum pump. Other vacuum pumps may be used.

In one aspect, when using the annealing vessel 202 as a growth reactor for ingots and/or epitaxial layers on substrates, the first stage of the vacuum system 204 may include a butterfly valve to achieve and maintain a pressure suitable for crystal growth. Once the crystal growth is complete, a second stage of vacuum system 204 may be used to create a high vacuum prior to post-growth annealing of the growing crystal and/or epitaxial layers.

The second stage of the vacuum system 204 reduces the base pressure of the annealing vessel 202 to-1 x 10-9 torr. The second stage may include a turbomolecular pump and/or a diffusion pump. Other pumps capable of generating high vacuum may be used.

Heating system

A heating system 206 provides and maintains a high temperature in the annealing vessel 202 to anneal the grown group III-V metal nitride. Any process that generates heat may be used in the heating system 206. By way of example and not limitation, the heating system 206 may heat the annealing vessel 202 by induction heating of the graphite assembly in the annealing vessel, resistive heating, and/or focused microwave heating. Other heating systems or devices may be used.

In one embodiment, the heating system 206 comprises a radio frequency induction heater. The radio frequency induction heater further comprises a susceptor constructed from a single piece of refractory material. For example, the susceptor may be composed of graphite. Other refractory materials suitable for use in the heating system 206 include tantalum carbide, zirconium nitride, and zirconium boride. In other aspects, suitable refractory materials also have good thermal conductivity and/or susceptibility to induction heating.

In one aspect, the heating system 206 is capable of generating and maintaining a temperature of at least 600 ℃ in the annealing vessel 202. On the other hand, the temperature of the annealing container 202 is maintained at a temperature ranging from 600 ℃ to 2900 ℃. On the other hand, the temperature in the annealing vessel 202 is maintained between 1000 ℃ to 2200 ℃ during the annealing process 100.

Pressure control system

After the vacuum system 204 evacuates the annealing vessel, the pressure control system 208 provides a nitrogen overpressure to the annealing vessel 202. In one aspect, the pressure control system 208 may include one or more gas supply tubes coupled to the annealing vessel 202 and the nitrogen system 210. The pressure control system 208 may further include a manual or electrically controlled pressure valve to control the flow of nitrogen gas into the annealing vessel 202. The pressure control system 208 may also include another manual or electrically controlled pressure valve to bleed nitrogen gas from the annealing vessel 202 to maintain the desired overpressure. The gas supply pipe and pressure valve may be constructed of any suitable material.

In one embodiment, the pressure control system 208 is capable of delivering nitrogen at a pressure ranging from about 760 torr to about 3.8 x 108 torr. The pressure control system 208 also provides and maintains a nitrogen overpressure equal to or greater than 3800 torr and preferably within the range of 3800 and 10100 torr. In another embodiment, the gas is delivered at a lower pressure such that the nitrogen pressure is increased due to the heating of the annealing vessel 202.

Nitrogen system

The nitrogen system 210 supplies nitrogen that is delivered to the annealing vessel 202 via the pressure control system 208. By way of example and not limitation, gas source system 208 may include a nitrogen generator capable of separating nitrogen from ambient air, a compressed nitrogen tank or cylinder, and/or any suitable system that converts stored liquid nitrogen to nitrogen.

In one embodiment, nitrogen system 210 and pressure control system 208 may be integrated into a single system. Thus, a single integrated system provides and controls a nitrogen overpressure to the annealing vessel 202.

Feedback control system

The feedback control system 212 monitors and interacts with the other systems 204 and 210 of the annealing device 200. The feedback control system 212 includes one or more sensors that monitor one or more measurable parameters in the annealing vessel 202. By way of example and not limitation, parameters include temperature, pressure, nitrogen flow, duration of heating, and duration of annealing. Any suitable sensor may be used to monitor the parameters of the HTHP annealing process 100, including but not limited to thermocouples, pyrometers, thermistors, and piezoelectric pressure sensors.

In one embodiment, the feedback control system 212 includes one or more computing devices having a processor and a memory. In this regard, the signals generated by the one or more sensors may be received and monitored at a processor of the feedback control system 212. In response to the signals received from the sensors, the computing device may generate one or more commands to the system 204 and 210 of the annealing apparatus 200 to change the parameters of the annealing process 100. The interaction between the feedback control system 212 and the other components of the annealing apparatus 200 may be based on any suitable control scheme, including but not limited to linear or non-linear control strategies.

The commands generated by the feedback control system 212 may change or otherwise maintain one or more parameters of the annealing process 100. For example, the feedback control system 212 may generate commands to the induction heaters of the heating system 206 to decrease the voltage of the applied electric field in response to an increase in temperature in the annealing vessel 202 that is outside of a desired temperature range. By way of example and not limitation, the modifiable parameters include nitrogen overpressure provided by the pressure control system 208, nitrogen flow from the gas source 210, temperature in the annealing vessel 202, and vacuum pressure in the annealing vessel prior to annealing the group III-V metal nitride.

In one embodiment, the feedback control system 212 receives a number of signals from a number of locations in the annealing vessel 212. For example, the feedback control system 212 may obtain a number of temperature readings from a number of locations in the annealing vessel 202 to ensure consistent temperature throughout the annealing vessel. In another example, the feedback control system 212 may be used to generate a temperature gradient in the annealing vessel 202. Alternatively, the feedback control system 212, sensors, and other systems 204 and 210 of the annealing device 200 may transmit and receive signals and commands via wired and/or wireless communication.

In another embodiment, the feedback control system 212 may be used to automate and control the post-growth annealing process 100. For example, after the annealing process based on the instructions received at the feedback control system 212, the feedback control system 212 may automatically control the ramp-up time of the heating system 206, the soak time of the annealing process 100, and the cool-down time of the annealing vessel 202 and the group III-V metal nitrides therein. The instructions may be provided manually by an operator of the annealing apparatus 200 or by a software program executing on the feedback control system 212 or another computing device in communication with the feedback control system.

Fig. 3 is a block diagram of one embodiment of an annealing vessel, shown generally at 300. In one embodiment, the annealing vessel 300 is not used to grow the ingot and/or epitaxial layers on the substrate. In this regard, the annealing vessel 300 is used to anneal group III-V metal nitrides grown or prepared in separate reactors. The annealing vessel 300 includes an outer shell 302 defining an interior space 304. The interior space 304 is adapted to contain a large or substantial volume of a group III-V metal nitride. For example, the interior space 304 may hold a number of wafers 306 already loaded into a boat 308. In this example, wafers 306 are loaded into a wafer boat 308 prior to inserting the boat into the housing 302.

After the boat 308 is placed in the enclosure 302, the annealing vessel is sealed using an enclosure cover 310. The housing cover 310 may be constructed of the same material as the housing 302 or other material suitable for maintaining structural integrity at pressures ranging from about 1 x 10 "9 torr to about 3.8 x 108 torr and temperatures up to about 2900 ℃. The outer housing shell 310 may include one or more sealing elements (not shown) to provide a thermal, fluid, and/or high pressure seal separating the interior space 304 from the external environment. The enclosure cover 310 may be removably coupled to the annealing vessel using any process or device sufficient to withstand the temperature and pressure ranges experienced in the enclosure 302. By way of example and not limitation, housing cover 310 may be secured with threaded hermaphroditic fittings, bayonet mounts, or bolts. Other fastening methods or devices may be used.

The annealing vessel 300 also incorporates a gas outlet 312. The gas outlet 312 is used to purge ambient gas from the interior space 304 of the annealing vessel 300. The air outlet 312 also provides a means for creating a high vacuum within the interior space 304. In one aspect, air outlet 312 includes a suitably configured conduit and/or other conduit. One end of the gas outlet 312 is in fluid communication with the interior space 304 of the annealing vessel 300, while the other end of the gas outlet is in fluid communication with a vacuum system, such as the vacuum system 204 (see fig. 2). The vacuum system 204 creates a high vacuum in the interior space 304 via the air outlet 312. The air outlet 312 may also include one or more manual or electrically controlled pressure valves that regulate and/or seal the air outlet.

In one aspect, the gas outlet 312 communicates with the interior space 304 of the annealing vessel 302 through one or more openings in the annealing vessel hood 310. In this aspect, the gas outlet 312 may be incorporated into the construction of the annealing vessel enclosure 310.

In one aspect, the gas outlet 312 communicates with the interior space 304 of the annealing vessel 302 through one or more openings in the enclosure 302. In this regard, the air outlet 312 may be incorporated into the construction of the housing 302.

The annealing vessel 300 also incorporates a gas outlet 314. The gas outlet 314 is used to provide nitrogen gas to the interior space 304. In one aspect, air outlet 314 comprises a suitably configured conduit and/or other conduit. One end of the air outlet 314 is in fluid communication with the interior space 304, while the other end of the air outlet is in fluid communication with a pressure control system, such as the pressure control system 208. The pressure control system 208 creates a nitrogen overpressure by injecting nitrogen into the interior space 304. The air outlet 312 may also include one or more manual or electrically controlled pressure valves that regulate and/or seal the air outlet 312.

The inner space 304 may be injected with nitrogen gas at a pressure ranging from about 760 torr to about 3.8 x 108 torr. Alternatively, nitrogen is injected at a lower pressure, followed by heating to raise the nitrogen to the desired pressure range.

In one aspect, the gas outlet 314 communicates with the interior space 304 of the annealing vessel 302 through one or more openings in the enclosure 302. In this aspect, the air outlet 314 may be incorporated into the construction of the housing 302.

The interior space 304 of the annealing vessel 302 is heated with a resistive heater 316 to a temperature ranging from 600 ℃ to 2900 ℃. The resistive heater 316 may comprise any resistive heating element known in the art suitable for producing the desired temperature and capable of withstanding the pressure range provided to the interior space 304.

In one aspect, the resistive heater 316 is constructed of a refractory material. Suitable refractory materials are less or not chemically reactive with the nitrogen gas injected into the annealing vessel 300. In addition, suitable refractory materials have good thermal conductivity and/or susceptibility to induction heating. By way of example and not limitation, suitable refractory materials for the resistive heater 316 include tungsten, tungsten carbide, tantalum carbide, zirconium carbide, zirconium nitride, zirconium boride, molybdenum, niobium, and alloys thereof.

In one aspect, the resistive heater 316 is configured as a coil or cylinder surrounding the interior space 304. Alternatively, the resistive heater 316 may include one or more continuous or discrete segments disposed along the inner surface of the housing 302. The segments of the resistive heaters may be monitored and controlled by an external system, such as the heating system 206 or the feedback control system 212. In one aspect, the temperature in enclosure 302 is maintained by means of a bubble graphite or refractory metal insulation material 318.

The housing 302 and/or the housing cover 310 may incorporate one or more openings as feedback ports 320. The feedback port 320 allows communication between thermocouples and/or other monitoring sensors located in the interior space 304 and the feedback system 212 and/or other components of the annealing apparatus 200 to monitor and control various parameters of the annealing process 100 in the annealing vessel 300. In one aspect, the feedback port 320 includes a seal and a wiring harness or other electrical connector that allows communication between one or more sensors in the annealing vessel 300 and the feedback system 212. On the other hand, the feedback port 320 includes a transmitter that transmits wireless communications to the feedback system 212 and/or other components of the annealing device 200.

In one aspect, the slow HTHP annealing process diffuses nitrogen species into the metal nitride at a near 1:1 stoichiometric ratio. Doped group III-V metal nitrides and compositions thereof contain no more than 1018cm-2 nitrogen vacancies and have p-type conductivity concentrations as high as 1020 cm-3. For example, the p-type conductivity of p-doped AlGaN and AlN epitaxial layers grown on a substrate, including but not limited to SiC, GaN, AlN, sapphire (Al2O3), ZnO, or refractory metals, will increase due to the reduction of nitrogen vacancies and other imperfections in the epitaxial layers. In another example, AlN wafers with defect densities less than 106cm "2 may be produced by a slow HTHP annealing process.

In one aspect of the annealing process 100, a wafer boat holding a plurality of p-type doped group III-V metal nitride wafers is placed in an annealing vessel. The interior of the annealing vessel was evacuated to a vacuum pressure of 1 x 10-9 torr to purge the annealing vessel of ambient gases or any fluent gases trapped in the crystal. The annealing vessel was then filled with nitrogen to create an overpressure of approximately 7000 torr and heated to a temperature of approximately 2000 ℃. The wafer is annealed at a constant temperature and pressure for approximately 24 hours to 48 hours to drive nitrogen gas into the wafer to diffuse nitrogen vacancies out of the wafer. In one embodiment, the wafer is then removed from the annealing vessel and allowed to cool.

In another embodiment, the wafer is cooled in an annealing vessel under an overpressure of nitrogen. In yet another embodiment, the wafer is cooled under a nitrogen overpressure that is higher than the pressure used during the annealing process. The additional overpressure further promotes the reduction of voids in the metal nitride.

In another embodiment, the metal nitride is rapidly quenched by mechanical removal from the high temperature environment while still in the nitrogen rich environment.

While the present invention has been explained with respect to exemplary aspects and embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. It is, therefore, to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims (19)

1. A process for forming a metal nitride having a p-type conductivity ranging from about 0.0001 Ω -cm to about 100 Ω -cm, the process comprising:

placing the grown metal nitride in an annealing container;

evacuating the ambient gas to provide a vacuum;

adding an overpressure of nitrogen gas comprising a nitrogen species to the evacuated vessel such that the overpressure of nitrogen gas is at a higher pressure than atmospheric pressure;

heating the metal nitride to a temperature sufficient to diffuse the nitrogen species into the metal nitride; and is

Annealing the metal nitride for at least 1 hour to form an annealed metal nitride.

2. The process of claim 1, wherein the metal nitride is selected from the group consisting of a wafer, an ingot, an epitaxial film, a wafer having at least one epitaxial layer deposited thereon.

3. The process of claim 1, wherein the metal nitride consists essentially of a group III-V metal nitride compound.

4. The process of claim 3, wherein the metal nitride is selected from binary, ternary, and quaternary group III-V metal nitrides.

5. The process of claim 1, wherein the metal nitride is p-type doped AlN.

6. The process of claim 1, wherein the metal nitride is a p-type doped Al-rich AlGaN alloy.

7. The process of claim 6, wherein the group III-V metal nitride is a_xB_1-xForm N, wherein A or B is a group III element.

8. The process of claim 1, wherein the ambient gas is evacuated to provide a pressure ranging from about atmospheric pressure to about 1 x 10^-9Vacuum of the tray.

9. The process of claim 1, wherein the overpressure of nitrogen gas ranges from about atmospheric pressure to about 3.8 x 10⁸And (4) supporting.

10. The process of claim 1, wherein the overpressure of nitrogen gas ranges from about 1400 torr to about 10100 torr.

11. The process of claim 1, wherein the overpressure of nitrogen gas is above about 3800 torr.

12. The process of claim 1, wherein the metal nitride is heated to a temperature ranging from about 1000 ℃ to about 2200 ℃.

13. The process of claim 1, wherein the metal nitride is annealed for 1 hour to 100 hours.

14. The process of claim 13 wherein the temperature of the metal nitride is constant throughout the process.

15. The process of claim 1 wherein the annealed metal nitride has a nitrogen vacancy density of less than 10¹⁸cm^-2。

16. The process of claim 1 wherein the group III-V annealed metal nitride has a p-type conductivity concentration of up to 10²⁰cm^-3。

17. A process for increasing the p-type conductivity of a post-growth group III-V metal nitride by reducing nitrogen vacancies, the process comprising:

heating the group III-V metal nitride in a nitrogen environment for at least 1 hour, the nitrogen forming an overpressure above atmospheric pressure.

18. A process for increasing the p-type conductivity of a post-growth group III-V metal nitride, the process comprising:

heating the group III-V metal nitride to a temperature greater than 1000 ℃ in a nitrogen environment;

pressurizing the nitrogen environment to at least 3800 torr; and is

Annealing the group III-V metal nitride for 1 to 48 hours to reduce the nitrogen vacancy density of the metal nitride.

19. A process for increasing the p-type conductivity of a post-growth group III-V metal nitride by reducing nitrogen vacancies, the process comprising:

heating the group III-V metal nitride to a temperature of about 2000 ℃ in a nitrogen environment;

pressurizing the nitrogen environment to about 7000 torr; and is

Annealing the group III-V metal nitride for at least 24 hours to reduce the nitrogen vacancy density of the metal nitride and to reduce the resistivity of the metal nitride to between about 0.0001 ohm-cm and about 100 ohm-cm.