RU2578870C2 - Method of growing gallium nitride film - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: substrate is placed in the atmosphere of a gas pumped at a rate of 5-10 l/h, the said gas being in the form of gaseous nitrogen or argon with nitrogen and hydrogen additives, wherein the substrate is heated to 600-1100°C, held at the said temperature for 1-3 hours, followed by cooling the furnace. In special cases of the invention, argon with nitrogen and hydrogen additives contains up to 15% nitrogen and up to 4% hydrogen. Before feeding the gas, the substrate is placed in a tubular alundum crucible which is placed in a quarts vessel, wherein the said gas is pumped while simultaneously heating the substrate, holding and cooling. The substrate is heated to 1050°C.

EFFECT: simple process of growing a film and short duration of the said process, obtaining oriented monocrystalline layers of different types.

4 cl, 3 dwg, 3 ex, 4 tbl

Description

The invention relates to a method for growing a gallium nitride film by auto-segregation of gallium on the surface of a complex semiconductor substrate and can be used in the manufacture of light-emitting diodes, laser LEDs, as well as high-power microwave transistor devices. More specifically, this invention relates to the growth of gallium nitride films in a heated device equipped with a gas pumping system.

The simplest synthesis scheme for gallium nitride is based on the reaction of gallium and nitrogen, however, it is necessary to use high pressure due to the chemical inertness of the nitrogen atmosphere. It is also possible to increase the chemical activity of nitrogen, for example, by translating it into an atomic state. In [1. G.A. Sukach, V.V. Kidalov, M.B. Kotlyarevsky et al. Structure and composition of gallium nitride films obtained by processing gallium arsenide single crystals in atomic nitrogen // Journal of Technical Physics. 2003.V. 7. Issue. 4. P. 59-62] obtained gallium nitride nanolayers by processing gallium arsenide in a high-frequency high-power plasma discharge. The disadvantage of this method is the expensive equipment and the small thickness of the films (island nanolayers).

Gallium nitride films can also be grown by other methods, in particular, molecular beam epitaxy (MBE) [2. A.I. Gusev. Nanomaterials, nanostructures, nanotechnology. - M .: Fizmatlit, 2007. - 416 pp.] And chemical vapor deposition of organometallic compounds (MOCVD) [3. HO Pierson. Handbook of Chemical Vapor Deposition (CVD): Properties, Technology and Applicatioons-NY. 1992. P. 235, 4. Matlox Donald M. Handbook of Physical Vapor Deposition (PVD): Processing Film Formation, Adhesion, Surface Preparation and Contamination Control. Westwood, NJ: Noyes Publication. 1998. ISBN 0-8155-1422-0]. The disadvantage of the MBE method is that for the formation and control of molecular beams, complex equipment and ultrahigh vacuum of ~ 10 ^-8 Pa are necessary. Nevertheless, using this method, layers of GaN filaments were obtained, for example, on silicon substrates [5. N.V. Sibirev, G.E. Tsyrlin, V.G. Dubrovsky et al. Effect of diffusion from the lateral surface on the growth rate of GaN whiskers // Physics and Technology of Semiconductors. 2012. V. 4. No. 6. S. 857-860]. MOCVD is a more preferred deposition method for producing films of sufficiently high quality, including in the manufacture of light emitting diodes. However, in the case of growing gallium nitride films, the MOCVD method has the disadvantage that it requires high synthesis temperatures of the order of 1000 ° C, strict control of the temperature gradient in the reactor, and careful selection of molecular transport agents that must have a low sublimation temperature (less than 300 ° C) and Do not decompose when transported to a cold area.

Closest to the claimed is a method of chemical deposition from the gas phase with removed plasma (RPECVD), which can be used to grow films of metal nitrides of group (III) metals [6. Patent RU 2391444 METHOD AND DEVICE FOR GROWING METAL NITRIDE FILM OF GROUP (III)]. In this method, reactive nitrogen plasma is formed at a distance from the substrate, and then transferred through the lock chamber to the reaction zone. The method is a variant of the RPECVD process and includes heating an object selected from the group in the form of a substrate in the growth chamber, the formation of active neutral nitrogen components in a nitrogen plasma located at a distance from the growth chamber, and moving active neutral nitrogen components through the lock chamber for growing. The reaction mixture is formed in a growth chamber, this reaction mixture contains a group (III) metal component capable of reacting with the nitrogen component in such a way as to form a group (III) metal nitride film on a heated object. In an RPECVD apparatus, a metal nitride film was grown under vacuum in a growth chamber using a reaction mixture of reagents such as ammonia (and / or nitrogen) and trimethyl gallium. The substrate is heated from below with a stationary heater. Nitrogen plasma is generated in the removal and fed into the chamber for growing. Depending on the technology used, the growing temperature was from about 630 ° C to about 1400 ° C.

The device also includes a heater located in the growth chamber for heating the object, a system for evacuating the growth chamber, a plasma holding tube, and a high-frequency means for regulating the pressure in the growth chamber. The device also further comprises means for generating nitrogen plasma from nitrogen gas. The surface morphology of the samples was studied by atomic force microscopy (AFM) in the intermittent contact mode, which showed that GaN films were usually polycrystalline with an average grain diameter of about 20-25 nm.

The disadvantage of this method is, firstly, the complex expensive equipment for creating a zone of excitation and plasma confinement using high vacuum to provide magnetron and microwave processes, including a lock device, a synthesis zone. Secondly, the disadvantage is the length of the process: from tens of hours to several days. A significant drawback is also the polycrystalline nature of the structure of the obtained films, since for various applications it is necessary to have diverse and oriented morphological single crystal forms: needles, threads, etc.

An object of the invention is to simplify the process of growing films and reduce its duration, obtaining oriented single-crystal layers of various types (needles, threads, plates).

The solution to the technical problem is achieved by the practical implementation of the totality of the features of the claimed invention.

The invention consists in the following.

The method proposed by the authors is implemented on simple equipment. A high-temperature reaction of gaseous nitrogen with the fresh surface of a layer of liquid gallium, which is formed as a result of surface autosegregation of gallium arsenide, was used [7. Yu.Ya. Tomashpolsky, N.V. Sadovskaya, G.A. Grigoryeva. Nanoscale features of thermostimulated surface auto-segregation on the surface of covalent crystals: gallium arsenide // Surface: X-ray, synchrotron and neutron studies. 2013. No9. S. 95-101].

Surface auto-segregation of chemical and phase composition, atomic-electronic and supratomic structure of materials makes it possible to form new phases. Additional new opportunities arise as a result of surface reactions of segregants with foreign components (heterosegregation). The use of heterosegregation, in particular, allows for the directed synthesis of multifunctional surface structures. In this case, the formation of a gallium nitride film occurs as a result of nitrogen diffusion through a layer of liquid gallium and begins at the interface between a drop of liquid and the surface of a single crystal. The nuclei of the new phase that have arisen grow orientedly within the droplet perpendicular to the substrate or at an angle to it, while part of the droplet remains at the end of the growing nanocrystallite all the time. The ingress of liquid material on the end face of the grown microcrystallite initiates additional growth of nanometer needles. Elongated nanocrystallites consist of a few drops of growth material.

The orthogonal orientation of growing crystallites is determined by the symmetry of the single-crystal substrate, while the orienting effect of the substrate increases with increasing temperature. In the case of the nucleation of a new phase inside the liquid gallium layer on defective parts of the matrix, where the orienting effect of the substrate is weakened, the direction of growth of microcrystallites is not ordered, and various non-oriented forms of the gallium nitride phase are formed: individual microcrystallites, needles, threads, plates, etc.

To implement the method does not require high vacuum, the device is made of quartz glass. The substrates are loaded into a tubular alundum crucible, which is placed in a quartz ampoule, after which the device pumps gas: nitrogen or argon with the addition of nitrogen and hydrogen while heating the substrate, holding and cooling in a gas atmosphere. Such conditions block the oxidation processes in the substrate and the film. The high rate of the synthesis reaction allows you to get a coating of gallium nitride of micron scale in 3 hours.

The lower and upper limits of the temperature of the substrate and the exposure times proposed in the invention are justified by the following.

The lower limit of the substrate temperature, gallium arsenide (600 ° C), is determined by the onset of the formation of liquid-phase gallium on the GaAs surface as a result of autosegregation. This temperature is the starting point for the start of the reaction of liquid Ga with gaseous nitrogen.

The upper limit of the temperature of the substrate, gallium arsenide, is determined, on the one hand, by enhancing the efficiency of the chemical reaction of liquid Ga with gaseous nitrogen at t> 1000 ° C. On the other hand, taking into account the melting point of GaAs equal to 1238 ° C, the upper temperature of the substrate should not exceed 1200 ° C. Based on this, the upper limit of the temperature of the substrate should lie above 1000 ° C, but below 1200 ° C, that is, in the region of 1100 ° C. The optimum substrate temperature is 1050 ° C.

The exposure time determines the thickness of the layer of the new phase of gallium nitride and the formation of structural forms of the new phase: crystallites, needles, threads, ribbons. At an exposure time of less than 1 hour, the film thickness is too small, and the particles of the new phase do not have the above characteristic shapes. When holding for more than 3 hours, the growth processes of crystalline forms of the new phase are inhibited due to the restriction of the supply of material to the surface reaction zone. Based on this, the optimum exposure time is 1-3 hours, at which the thickness of the gallium nitride layer reaches a micrometric scale, and the structural forms become clearly expressed.

The elemental and phase composition of the obtained films is measured by X-ray spectral microanalysis, and the micro- and nanostructures are determined by scanning electron microscopy. The elemental composition is taken as the ratio of concentrations in atomic percent of gallium to arsenic or to nitrogen in atomic percent. For morphologically heterogeneous surface areas, local measurements are performed. The area of local sections of measurements on crystals ranged from 5 × 5 to 40 × 40 sq. Km. The surface morphology of polished sections of crystals is observed in a scanning electron microscope up to maximum magnifications × 100,000 with a resolution of several nm, using a cathode with cold field emission.

The proposed invention allows to grow films of gallium nitride with high adhesion, to use simple equipment, to reduce the growth time by several times, to obtain a variety of single-crystal morphological forms of films in the form of needles, threads, ribbons and plates.

Example 1

A polished {001} sample of a section of a GaAs single crystal grown by the Czochralski method is placed in a tubular alundum crucible, which is installed in a quartz installation heated by a furnace. Simultaneous pumping of nitrogen gas over the sample at a rate of 5-10 l / h, heating the sample to 970 ° C for 3 hours and cooling with the furnace. After cooling at different sites, the local elemental composition of the surface of the initial (table 1) and annealed (table 2) samples is measured and a nano- and microstructure are observed in a scanning electron microscope (Fig. 1a, b).

Table 1 The values of the elemental local composition of the initial surface of gallium arsenide crystals according to x-ray spectral microanalysis Structure 1 plot 2 plot 3 plot Ga, at.% / As, at.% 1.13 0.95 1,04

table 2 The elemental composition of local surface areas of gallium arsenide after annealing at 970 ° C for 3 h in a nitrogen atmosphere according to x-ray microanalysis Structure Plot 1 Plot 2 Section 3 Ga, at.% / As, at.% 3.2 12.0 8.4 Ga, at.% / N, at.% 1,5 1,5 1.4

From table 1 it follows that the composition of the initial samples corresponds to gallium arsenide, there is no nitrogen, the surface is smooth and homogeneous.

From table 2 it follows that after annealing at 970 ° C for 3 h in a nitrogen atmosphere, a gallium layer segregates on the surface, which reacts with nitrogen to form a thin film of gallium nitride. The film consists of needle and filamentous microcrystallites. In this case, the gallium nitride film grows from the gallium layer as a substrate, which ensures high adhesion of the film.

Example 2

A polished {001} sample of a section of a GaAs single crystal grown by the Czochralski method is placed in a tubular alundum crucible, which is installed in a quartz installation heated by a furnace. Simultaneous pumping of nitrogen gas over the sample at a rate of 5-10 l / h, heating the sample to 1050 ° C for 1 h and cooling with the furnace. After cooling at different sites, the local elemental composition of the surface of the annealed sample is measured (Table 3) and the nano- and microstructure are observed in a scanning electron microscope (Fig. 2a, b, c, d).

Table 3 The elemental composition of the surface areas of gallium arsenide after annealing at 1050 ° C for 1 h in a nitrogen atmosphere according to x-ray microanalysis Plot Ga, at.% / N, at.% Plot 1 1.12 Plot 2 1,0 Section 3 1.17 Section 4 1,0 Section 5 1.13 Section 6 1,0

From table 3 it follows that after annealing at 1050 ° С for 1 h in a nitrogen atmosphere, a thick gallium nitride film forms on the surface, which has various single-crystal morphological forms: needle-shaped microcrystallites with nano needles at the ends, isotropic microcrystallites, ribbon microcrystallites. Since the film grows from the gallium layer as a substrate, high adhesion of the film is ensured.

Example 3

A polished {001} sample of a section of a GaAs single crystal grown by the Czochralski method is placed in a tubular alundum crucible, which is installed in a quartz installation heated by a furnace. Simultaneous pumping over the sample of gaseous technical argon containing up to 15% nitrogen, with the addition of hydrogen (4%) at a rate of 5-10 l / h, heating the sample to 1050 ° C for 1 h and cooling with the furnace. After cooling at different sites, the local elemental composition of the surface of the annealed sample is measured (Table 4) and the nano- and microstructure are observed in a scanning electron microscope (Fig. 2a, b).

Table 4 The elemental composition of the surface areas of gallium arsenide after annealing at 970 ° C for 3 h in the atmosphere of technical argon according to X-ray microanalysis Plot Ga, at.% / N, at.% Plot 1 1,07 Plot 2 1.12 Section 3 1,0 Section 4 0.95

It is known that the reaction of the formation of gallium nitride from the gas phase is more effective when using a nitrogen-hydrogen mixture [8. IN AND. Osinsky, N.P. Sling. The initial stages of epitaxy of III-nitrides on sapphire // Solid State Electronics. Thematic issue "Electronics and Nanotechnology". Part 2. 2009. S. 23-27]. From table 4 it follows that the nitrogen content on the surface after annealing at 970 ° C in an argon atmosphere exceeds its amount after a similar annealing in a nitrogen atmosphere, which confirms the active influence of the nitrogen-hydrogen mixture and hydrogen in argon on the synthesis of the gallium nitride phase also in liquid phase. In FIG. Figure 3 shows the surface morphology of a gallium arsenide single crystal after annealing at 970 ° C × 3 h in the atmosphere of industrial argon. Against the background of a matrix of rounded gallium grains of dark contrast, isotropic microcrystallites of gallium nitride of regular forms of light contrast were obtained, as well as anisotropic crystallites of gallium nitride. It can be assumed that, at high temperatures, a reaction of nitrogen with hydrogen occurs with the formation of ammonia, in which nitrogen more actively enters the subsequent reaction with gallium.

Thus, in the process of heterosegregation, highly adhesive films of gallium nitride were obtained on the surface of gallium arsenide from the liquid phase of gallium and gaseous nitrogen and argon, consisting of various, including oriented, morphological forms, which is the basis for the development of new simple methods for the synthesis of gallium nitride in technologies epitaxial heterostructures.

Claims (4)

1. A method of growing a gallium nitride film by auto-segregation on the surface of a gallium arsenide semiconductor substrate, comprising placing the substrate in an atmosphere of gas pumped at a speed of 5-10 l / h in the form of nitrogen gas or argon with nitrogen and hydrogen additives, while the substrate is heated to a temperature of 600-1100 ° C, holding at the indicated temperature for 1-3 hours and cooling in an oven. 2. The method according to p. 1, characterized in that argon with additives of nitrogen and hydrogen contains up to 15% nitrogen and up to 4% hydrogen. 3. The method according to p. 1, characterized in that before pumping the gas, the substrate is placed in a tubular alundum crucible, which is placed in a quartz ampoule, while the gas is pumped while heating the substrate, holding and cooling. 4. The method according to p. 1, characterized in that the heating of the substrate to 1050 ° C.

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