KR19990084402A - GAN single crystal structure manufacturing method - Google Patents

Abstract

A method for producing a GaN single crystal structure is disclosed. It comprises the steps of forming a GaN layer on the step and the Ti _1-x Al _x N layer to form a Ti _1-x Al _x N layer on the ZnO layer to form a ZnO layer on the substrate. The GaN layer manufactured as described above can be used as a substrate for a light emitting device through a ZnO layer removal process, so that defects generated in each layer during manufacturing of the light emitting device can be suppressed, thereby improving lifetime and simplifying the manufacturing process, thereby improving yield.

Description

Baan single crystal structure manufacturing method

The present invention relates to a method of manufacturing a GaN single crystal structure, and in particular, a plurality of buffer layers are provided on a heterogeneous substrate to narrow the difference in lattice constant and coefficient of thermal expansion with a GaN by hetero-epitaxial growth techniques. A method for producing a GaN single crystal structure obtained by forming a desired GaN single crystal on a buffer layer.

The compound semiconductor of In _1-x Ga _x N is a direct transition semiconductor, and has a characteristic that its bandgap energy is varied within a wide range depending on the component ratio of In determined by how much x is. The compound semiconductor of In _1-x Ga _x N having such characteristics varies its bandgap energy in the emission band range from blue violet to red according to the component ratio of In. Such In _1-x Ga _x N semiconductors are used in light emitting semiconductor devices such as color display devices and blue laser diodes. In _1-x Ga _x N crystals having various fields of application by the growth technique, a method of forming a high quality thin film form and from there, the development of various application devices is steadily progressing.

In _1-x Ga _x N thin films were grown by MOCVD on heterogeneous substrates such as sapphire (Al ₂ O ₃ ) or silicon carbide (SiC), and the laser diode fabricated using them succeeded in oscillation, but its life was short. Research results that are not sufficient for commercialization have been published recently by several research institutes. In addition, as a cause for the short life time, it is pointed out that the instability of the structure caused by a series of defects that occur from the interface between the dissimilar substrate and GaN, resulting in chain growth to the growth of the thin film layer subsequently formed thereon. Defects at these interfaces occur because of the large difference in lattice constant and thermal expansion coefficient between the substrate and the growing thin film layer. Therefore, as a solution to effectively solve this problem, a homogeneous substrate, that is, a GaN substrate, may be used as a matrix for growing an In _1-x Ga _x N thin film.

On the other hand, GaN is crystal-grown by the hydrogen vapor phase epitaxy (HVPE) method, which is one of the vapor phase growth methods, so that crystal growth from the liquid phase to the solid phase may be performed under high temperature and high pressure. This HVPE method is a method in which GaN crystals are grown by a reaction between source gases of GaN supplied on a dissimilar substrate such as sapphire or silicon carbide which has been generally applied in the past. In the crystal growth by the HVPE method, the crystal quality is determined by the crystal structure of the applied substrate and the grown film, the degree of matching of the lattice constant, the difference in the coefficient of thermal expansion, and the like.

1 is a cross-sectional view showing a GaN single crystal structure formed by a conventional method.

Referring to the drawings, a GaN layer 20 is formed directly on a heterogeneous substrate 10 such as sapphire (Al ₂ O ₃ ) or silicon carbide (SiC). However, when the GaN layer 20 is formed on the sapphire substrate 20, the sapphire substrate 10 may be formed by lattice constant difference between GaN and sapphire of about 16% and thermal expansion coefficient difference of about 35%. It is difficult to obtain a high quality single crystal due to defect factors caused by strain generated at the interface with In addition, silicon carbide having a small lattice constant and thermal expansion coefficient difference with GaN compared to sapphire has a disadvantage in that the price is expensive, and unwanted micropipes are used in the GaN layer 20 formed on the silicon carbide substrate 10. It is also difficult to obtain high quality crystals by the formation of.

On the other hand, the GaN layer 20 formed directly on the dissimilar substrate 10 has a problem that it is difficult to separate from the substrate 10. The heterogeneous substrates 10 of the above-mentioned materials are chemically stable and are not easily removed by etching, so there are many methods for mechanically removing the substrates. In particular, when the substrate 10 is used without being separated, when the sapphire, which is an insulator, is used as the substrate 10, the electrode layer 21 is formed during the fabrication of the light emitting device due to the disadvantage that it cannot be used as an electrode. First, as shown in FIG. 2, there is a disadvantage in that a process of removing a portion of layers sequentially stacked on the substrate 10, that is, a portion indicated by a dotted line, by etching is added.

As a part of overcoming this drawback, as shown in FIG. 3, a ZnO layer 11 having similar material properties as GaN is disposed on the heterogeneous substrate 10 as a complete layer, and the GaN layer 20 on the ZnO layer 11. A method of forming a was proposed. However, in the ZnO layer 11, Zn re-evaporates severely around 1000 DEG C, which is the growth temperature of GaN, and defects are generated on the surface thereof. The GaN layer 20 which is subsequently grown by such thermal instability has a problem in that adhesion to the ZnO layer 11 is separated or lifted off. The method of lowering the growth temperature of GaN to a temperature at which Zn does not re-evaporate is not applicable because GaN growth is not performed normally.

The present invention was devised to improve the above problems, and provides a GaN single crystal structure manufacturing method for forming a GaN layer on the buffer layer, having buffer layers capable of narrowing the difference in lattice constant and thermal expansion coefficient with GaN on a heterogeneous substrate. Its purpose is to.

Another object is to allow the buffer layer to be used as an electrode.

1 is a cross-sectional view showing a GaN single crystal structure formed by a conventional method,

2 is a cross-sectional view showing a light emitting diode made using the GaN single crystal structure of FIG.

3 is a cross-sectional view showing a GaN single crystal structure formed by another conventional method;

4 is a cross-sectional view showing a GaN single crystal structure prepared according to the manufacturing method of the present invention,

FIG. 5 is a cross-sectional view of the GaN single crystal structure of FIG. 4 after removing the ZnO layer which assisted the growth of the substrate and the GaN single crystal for use in fabrication of a light emitting diode. FIG.

<Description of Symbols for Major Parts of Drawings>

10, 50: substrate 11, 60: ZnO layer

20, 80: GaN layer 21: electrode layer

70: Ti _1-x Al _x N layer

In order to achieve the above object, a GaN single crystal structure manufacturing method according to the present invention comprises the steps of forming a ZnO layer on a substrate; Forming a Ti _1-x Al _x N layer on the ZnO layer; And forming a GaN layer on the Ti _1-x Al _x N layer.

The Ti _1-x Al _x N layer includes an AlN layer when the X value for determining the component ratio is 1, that is, the AlN layer.

Preferably, the method further comprises separating the GaN layer from the substrate by removing the ZnO layer by an etching solution.

Hereinafter, a GaN single crystal structure manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a cross-sectional view showing a GaN single crystal structure prepared according to the manufacturing method of the present invention.

Referring to the drawings, a ZnO layer 60 as a first buffer layer, a Ti _1-x Al _x N layer 70 and a GaN layer 80 as a second buffer layer are sequentially stacked on the substrate 50. have.

In order to prevent the evaporation of ZnO when forming the GaN layer 80, the Ti _1-x Al _x N layer 70 as the second buffer layer is formed of an AlN layer having an X value of 1, which determines the component ratio, or ZnO In addition to the prevention of evaporation, the X value may be formed between 0 and 1 so as to be used as an electrode, or may be gradually changed depending on the film growth thickness.

The manufacturing process will be described below.

First, a ZnO layer 60 is formed on the substrate 50 made of sapphire or silicon carbide by an RF sputtering method, with a thickness of 0.1 μm to 1 μm as a first complete layer. Next, the Ti _1-x Al _x N layer 70 is grown on the ZnO layer 60 by the sputtering method or the vapor phase deposition method (MOCVD). In the case of sputtering, the Ti _1-x Al _x N layer 70 is formed while maintaining a selected growth temperature within a range from room temperature (25 ° C.) to 500 ° C. When the Ti _1-x Al _x N layer 70 is formed by vapor deposition (MOCVD), the Ti _1-x Al _x N layer 70 is formed while maintaining a selected growth temperature within a range from 400 ° C to 1100 ° C. When the Ti _1-x Al _x N layer 70 including the Ti component is formed so that the Ti _1-x Al _x N layer 70 can also be used as an electrode, the total thickness is adjusted to be 0.1 μm to 1 μm. . Here, it is preferable to grow such that the x value for determining the mixing ratio gradually increases as the film growth thickness increases when the Ti _1-x Al _x N layer 70 is formed. The surface layer of the Ti _1-x Al _x N layer film finally formed by the gradual increase of the x value is improved by the growth conditions of GaN to be subsequently grown by AlN having almost the same lattice constant as GaN. On the other hand, when forming the Ti _1-x Al _x N layer 70 only by the AlN layer 70 when the X value is 1, it is preferable to form the thickness of 0.1 micrometer-1.5 micrometers.

The structure formed from the substrate to the Ti _1-x Al _x N layer 70, which is the second buffer layer, is charged into the HVPE reaction furnace, and the GaN layer 80 is formed on the Ti _1-x Al _x N layer 70 by the HVPE method. To form. The GaN layer 80 is grown at a temperature maintained at 950 to 1200 ° C.

In this lamination process, the Ti _1-x Al _x N layer serves to suppress the re-evaporation of Zn from the ZnO layer 60 when the GaN (80) layer is formed. Compared to the sapphire substrate 50, the Ti _1-x Al _x N layer 70 whose lattice constant is close to the lattice constant of the GaN layer 80 is formed on the Ti _1-x Al _x N layer 70. The defect of the grown GaN layer 80 is suppressed. For this reason, the quality of the GaN layer 80 formed on the Ti _1-x Al _x N layer 70 is improved compared with the prior art.

In order to use the fabricated GaN layer 80 as a substrate of the light emitting device, the ZnO layer 60 is removed with an etchant, and as shown in FIG. 5, the Ti _1-x Al _x N layer 70 and the GaN layer ( Only 80) is left. When the Ti _1-x Al _x N layer 70 separated from the substrate 50 together with the GaN layer 80 is manufactured by gradually increasing the X value, it may be used as an electrode layer. In this case, a fabrication example of a laser diode using the GaN layer 80 as a substrate is shown. The GaN layer 80 is used as a substrate, and a GaN lower cladding layer, an AlGaN lower optical waveguide layer, a GaN or InGaN active layer, an AlGaN upper optical waveguide layer, The GaN upper cladding layer and the upper electrode layer are sequentially stacked. Here, the light emission is achieved when the upper electrode layer and the Ti _1-x Al _x N layer 70 are used as the positive electrode terminals. In this case, since the Ti _1-x Al _x N layer 70 under the GaN layer 80 made for use as a homogeneous substrate can be used as an electrode when fabricating a light emitting device, there is an advantage in that a process of separately forming a lower electrode layer is also reduced.

<Example 1>

First, the sapphire substrate 50 was immersed in TCE, acetone, alcohol, distilled water (DI water) for 15 minutes, in a solution of H ₂ SO ₄ and H ₃ PO ₄ in a 3: 1 mixture for 10 minutes, and finally 10% Pretreatment was performed on the substrate 50, which was immersed in a hydrogen fluoride (HF) solution and distilled water (DIwater) in order. The sapphire substrate 50 washed by the pretreatment was mounted in an RF sputtering device to deposit a ZnO layer 60 to a thickness between 100 and 1000 mW. The target used was a ZnO ceramic disc, and the discharge gases were Ar and O ₂ . 3000 Å to use Ti _1-x Al _x N layer 70 as an electrode while gradually increasing the X value by sputtering at a temperature of room temperature to 500 ° C. on the ZnO layer 60 deposited on the sapphire substrate 50. Was deposited to a thickness of. The sample thus prepared was charged into an HVPE apparatus, and the GaN thick film single crystal layer 80 was grown. At this time, GaCl ₃ gas was used as the gallium material and NH ₃ gas was used as the nitrogen material in the HVPE reaction furnace, respectively. During growth, N ₂ was supplied as a carrier gas into the HVPE reaction furnace. The grown GaN layer 80 was taken out of the HVPE reaction furnace at room temperature, immersed in aqua regia, and the GaN layer 80 was etched by acid etching the ZnO layer 60 using an ultrasonic cleaner while heating the aqua regia to 100 ° C. 50) to obtain a GaN single crystal wafer having a Ti _1-x Al _x N electrode layer 70 thereunder.

<Example 2>

Under the same conditions as in Example 1, the ZnO layer 60 was formed on the sapphire substrate 50 in the same manner, and the AlN layer 70 was spun at about 3000 kPa over the ZnO layer 60 at a temperature from room temperature to 500 ° C. Was deposited to a thickness of. The GaN single crystal wafer having the AlN layer 70 thereunder was obtained through the same process as the post-process described in Example 1 on the sample thus prepared.

As described above, according to the GaN single crystal structure manufacturing method according to the present invention, the difference in lattice constant and thermal expansion coefficient of GaN for heterogeneous sapphire substrates is alleviated by the Ti _1-x Al _x N layer, which is a buffer layer. A suppressed GaN single crystal layer can be obtained. The thus-obtained for blue light emitting elements are created by a GaN single crystal substrate after the step of forming the In _1-x Ga _x N thereon difference lattice constant and thermal expansion coefficient between the GaN substrate and the In _1-x Ga _x N thin film layer marginally A growth effect close to homoepitaxy can be obtained, and thus a high quality light emitting device can be manufactured, and in addition, it can be used as a substrate for various light emitting devices containing GaN as a main component. In addition, since Ti _1-x Al _x N, whose component ratio is determined to include Ti, is in the range of 4000 to 7000 μΩ-cm, whose electrical conductivity can be used as an electrode, there is no need for an etching process for making an electrode when manufacturing a light emitting device. Therefore, in the case of a light emitting device manufactured using a GaN single crystal structure, defects generated in each layer during device fabrication are suppressed, thereby improving lifetime and simplifying a manufacturing process, thereby improving yield.

Claims (25)

Forming a ZnO layer on the substrate; Forming a Ti _1-x Al _x N layer on the ZnO layer; And Forming a GaN layer on the Ti _1-x Al _x N layer; GaN single crystal structure comprising a. The method of claim 1, The substrate is a GaN single crystal structure manufacturing method characterized in that the sapphire material. The method of claim 1, The ZnO layer is a GaN single crystal structure manufacturing method characterized in that formed to a thickness of 0.1μm to 1μm. The method of claim 1, The Ti _1-x Al _x N layer is a GaN single crystal structure manufacturing method characterized in that formed to a thickness of 0.1μm to 1μm. The method of claim 1, The ZnO layer is grown by the sputtering method, GaN single crystal structure manufacturing method. The method of claim 1, The Ti _1-x Al _x N layer is grown by the sputtering method GaN single crystal structure manufacturing method. The method of claim 6, The Ti _1-x Al _x N layer is a GaN single crystal structure manufacturing method characterized in that the growth temperature is maintained at 25 ℃ to 500 ℃. The method of claim 1, The Ti _1-x Al _x N layer is a GaN single crystal structure manufacturing method characterized in that the growth by vapor deposition (MPCVD). The method of claim 8, wherein the Ti _1-x Al _x N layer is grown at 400 ° C. to 1100 ° C. while maintaining its growth temperature. The GaN single crystal structure manufacturing method according to claim 1, wherein the GaN layer is grown by HVPE. The method of claim 10, The GaN layer is grown at 950 to 1200 ℃ while maintaining the growth temperature of the GaN single crystal structure manufacturing method. The method of claim 1, Separating the substrate from the GaN layer by removing the ZnO layer by an etchant; and further comprising GaN single crystal structure. The method of claim 1, The Ti _1-x Al _x N layer is a GaN single crystal structure manufacturing method characterized in that the growth of the film growth thickness so that the x value to determine the mixing ratio is gradually increased. The method of claim 1, Method of producing a GaN single crystal structure characterized in that the step of forming the Ti _1-x Al _x N layer is the X value to determine a mixing ratio of _1-x Al _x N to form Ti an AlN layer as one of AlN. The method of claim 14, The substrate is a GaN single crystal structure manufacturing method characterized in that the sapphire material. The method of claim 14, The ZnO layer is a GaN single crystal structure manufacturing method characterized in that formed to a thickness of 0.1μm to 1μm. The method of claim 14, The AlN layer is a GaN single crystal structure manufacturing method characterized in that formed to a thickness of 0.1μm to 1.5μm. The method of claim 14, The ZnO layer is grown by the sputtering method, GaN single crystal structure manufacturing method. The method of claim 14, The AlN layer is grown by the sputtering method, GaN single crystal structure manufacturing method. The method of claim 19, The AlN layer is a GaN single crystal structure manufacturing method characterized in that the growth is maintained at 25 ℃ to 500 ℃. The method of claim 14, The AlN layer is grown by vapor phase deposition (MPCVD) method of manufacturing a GaN single crystal structure. The GaN single crystal structure manufacturing method according to claim 21, wherein the AlN layer is grown while maintaining its growth temperature at 400 ° C to 1100 ° C. The method of claim 14, The GaN layer is grown by HVPE method, characterized in that the GaN single crystal structure manufacturing method. The method of claim 23, wherein The GaN layer is grown at 950 to 1200 ℃ while maintaining the growth temperature of the GaN single crystal structure manufacturing method. The method of claim 14, Separating the substrate from the GaN layer by removing the ZnO layer by an etchant; and further comprising GaN single crystal structure.