KR100834698B1 - Method of forming gan layer and gan substrate manufactured using the same - Google Patents

Abstract

A method of forming a gallium nitride thin film and a gallium nitride thin film substrate manufactured by the same are provided to reduce a stress due to a thermal coefficient difference between gallium nitride and silicon. A method of forming a gallium nitride thin film includes: forming a first aluminum nitride layer(20) on a silicon substrate(10); an epitaxial gallium nitride layer(30) of the first aluminum nitride layer; forming a gallium aluminum nitride layer(40) on the epitaxial gallium nitride layer; forming a second aluminum nitride layer(50) on the gallium aluminum nitride layer; and a gallium nitride thin film on the second aluminum nitride layer. The first aluminum nitride layer is formed to have a thickness ranging from 2 nm to 100 nm. The step of forming a first aluminum nitride layer on a silicon substrate includes: forming Al coating layer on the silicon substrate; and flowing NH3 gas to an upper portion of the Al coating layer to convert the Al coating layer into an aluminum nitride layer.

Description

Gallium nitride thin film forming method and gallium nitride thin film substrate produced by the method {Method of forming GaN layer and GaN substrate manufactured using the same}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a cross-sectional structural view of a gallium nitride thin film substrate according to a preferred embodiment of the present invention.

2 to 8 are cross-sectional views sequentially illustrating a method of forming a gallium nitride thin film according to a preferred embodiment of the present invention.

9 is a view showing the result of measuring the thickness of the gallium nitride thin film over the entire surface when the gallium nitride thin film is actually formed on the 2-inch silicon substrate according to the present invention.

FIG. 10 is a graph showing the results of analyzing the characteristics of a crystal by measuring a rocking graph of a gallium nitride thin film sample formed according to the present invention using a crystal diffraction apparatus (XRD).

<Main reference number in drawing>

10: silicon substrate B: buffer layer

20, 80: first aluminum nitride layer 30, 90: epi gallium nitride layer

40, 100: gallium aluminum nitride layer 50, 110: second aluminum nitride layer

60, 120: gallium nitride thin film

The present invention relates to a gallium nitride semiconductor with improved quality of a gallium nitride (GaN) thin film and a method of manufacturing the same.

Gallium nitride is a semiconductor material with a direct transition bandgap of 3.4 eV at room temperature, and at 1.9 eV (InN) when combined with other semiconductor materials such as indium nitride (InN) or aluminum nitride (AlN) It has a direct energy bandgap of up to 3.4 eV (GaN) or 6.2 eV (AlN).

Therefore, gallium nitride has a great potential as an optical device in a wide wavelength range from the visible region to the ultraviolet region, and recently, the market for lighting fixtures due to full color display boards or white light emitting devices by red, green, and blue light emitting devices is rapidly growing. As a result, much research is being conducted on gallium nitride. In particular, gallium nitride has attracted great attention as an optical device material of a blue light emitting diode (LED) and a blue laser diode (LD) in a short wavelength band.

In order to fabricate an optical device using gallium nitride, a technique for thickly growing a gallium nitride thin film without crystal defects such as dislocation is important. For thick film growth of a gallium nitride thin film, it is important to select a base substrate on which a gallium nitride and a lattice constant match. This is because when the degree of lattice constant mismatch between the gallium nitride and the substrate is large, there is a limit to the growth of good quality gallium nitride due to the difference in the coefficient of thermal expansion.

In general, substrates that can be used for growing a gallium nitride thin film include a silicon carbide (SiC) substrate and a sapphire (Al ₂ O ₃ ) substrate. Among them, the silicon carbide substrate has a small lattice constant difference with gallium nitride, and is excellent in high temperature characteristics and chemical stability. In addition, when a gallium nitride-based optical device is manufactured using a hydrocarbon substrate, the wafer can be easily divided into chips, and since the substrate itself has conductivity, the chip area can be reduced by distributing electrodes above and below the chip. Therefore, there is an advantage over the sapphire substrate in terms of productivity and manufacturing cost of the optical device. However, the high price of the substrate and the low production volume have problems in smooth substrate supply, and the quality of the gallium nitride thin film grown on the substrate is not excellent compared to the efficiency of optical device manufacturing. For this reason, sapphire substrates are mainly used for growth of gallium nitride thin films rather than silicon carbide substrates.

However, since the a-axis lattice constant of sapphire (hexagonal system) is 4.758Å and the a-axis lattice constant of gallium nitride (hexagonal) is 3.186Å, gallium nitride and sapphire show a lattice constant mismatch of about 30% or more. Therefore, when the gallium nitride thin film is grown on the sapphire substrate, tensile stress may be caused by a-axis lattice constant mismatch. However, when the gallium nitride thin film is actually grown on the sapphire substrate, compressive strain occurs because the effective lattice constant of sapphire is about 14% smaller than the effective lattice constant of gallium nitride. In addition, because sapphire and gallium nitride has a thermal expansion coefficient also show a difference of about 25%, a stress is generated on the boundary between the sapphire substrate and the GaN thin film, as a result, electric potential having a large density of about 10 ¹⁴ / cm ² in the gallium nitride thin film Defects are introduced, which is a barrier to growth of high quality single crystals. In addition, when the gallium nitride thin film is grown to a thickness of 10 μm or more, it is more likely to cause cracks in the gallium nitride thin film due to excessive stress caused by mismatch of crystal lattice constant and difference in thermal expansion coefficient. There is a limit to the growth of gallium nitride to a thickness of 10um or more.

In order to solve the above problems, before the growth of the gallium nitride thin film on the sapphire substrate recently, a buffer layer is formed of a semiconductor material such as AlN, AlGaN, InN, etc. to improve the crystallinity and electrical and optical properties of the gallium nitride thin film Heteroepitaxy has been proposed. However, when the buffer layer for heterojunction is grown to a thickness of about 1 to 500 nm and the gallium nitride thin film is grown on the buffer layer, crystal defects occur in the buffer layer due to lattice constant and thermal expansion coefficient mismatch between the sapphire substrate and the buffer layer. The resulting crystal defects are transferred to the gallium nitride thin film formed on the buffer layer as it is, causing a deterioration in the quality of the gallium nitride thin film. Therefore, there is still a limitation in forming a high quality gallium nitride thin film by the conventional heterojunction growth method.

Meanwhile, when manufacturing a gallium nitride-based optical device using a sapphire substrate, there is a problem in that an electrode forming process is more complicated than other optical devices manufactured using a conductive substrate. Since the sapphire substrate has an insulating property, when a gallium nitride thin film is grown on the sapphire substrate to manufacture an optical device, an ohmic contact for forming an electrode cannot be directly formed on the rear surface of the substrate. As the electrode forming process becomes complicated, not only the manufacturing cost of the optical device increases but also the series resistance of the optical device increases, thereby degrading the performance of the device. In addition, the sapphire substrate can be manufactured up to 4 inches, but since the 2 inch substrate is used in the actual optical device manufacturing process, productivity is expected to be limited in the production of LEDs and LDs, which are expected to be in high demand. Therefore, a large diameter substrate is required to replace the sapphire substrate.

Currently, research on the growth of a gallium nitride thin film using a silicon substrate as an alternative to a sapphire substrate and a silicon carbide substrate is actively conducted. Silicon substrates are inexpensive and easy to secure high quality substrates with large diameters, and can be widely applied to various optical device manufactures because of easy application of integrated processes as well as single optical devices. However, in the case of the silicon substrate as well as the conventional sapphire and silicon carbide substrate, there are still problems caused by the lattice constant mismatch with the gallium nitride and the difference in coefficient of thermal expansion. In other words, the coefficient of thermal expansion and lattice constant of the silicon substrate are 3.7 × 10 ⁻⁶ / K and 3.8403 kPa, respectively. Therefore, compared with gallium nitride (thermal expansion coefficient 5.59 x 10 ^-6 / K, lattice constant 3.189189), it has a difference in thermal expansion coefficient of about 53.6% and a lattice constant of 16.9%. The crystal structures of silicon and gallium nitride are cubic and hexagonal, respectively, and the basic crystal structures are different. Therefore, it is known that dislocation defects having a density of about 10 ¹⁰ / cm ² exist in the gallium nitride thin film formed on the silicon substrate, and when the gallium nitride thin film is thickly formed, cracks are generated because stresses exceed the limit in the thin film. . Therefore, in order for the silicon substrate to be widely used as a substrate for reproducible gallium nitride-based optical devices, it is most important to find a method of reducing crystal defects and preventing cracks caused by the difference in lattice constant with gallium nitride. can do.

The present invention was devised to solve the above-mentioned problems of the prior art, and is generated due to a difference in lattice constant mismatch and thermal expansion coefficient between gallium nitride and silicon in forming a gallium nitride thin film on a silicon substrate for fabricating an optical device. Provided is a method of forming a gallium nitride thin film capable of reducing crystal defects and preventing cracking and melt-back even when a gallium nitride thin film is grown thick, and a gallium nitride thin film substrate manufactured by the method. Its purpose is to.

According to another aspect of the present invention, there is provided a method of forming a gallium nitride thin film, including: forming a first aluminum nitride layer on a silicon substrate; Forming an epi gallium nitride layer on the first aluminum nitride layer; Forming a gallium aluminum nitride layer on the epi gallium nitride layer; Forming a second aluminum nitride layer on the gallium aluminum nitride layer; And forming a gallium nitride thin film on the second aluminum nitride layer.

Preferably, the first aluminum nitride layer is formed to a thickness of several nm to 100 nm. And forming a first aluminum nitride layer, forming an Al coating layer on the silicon substrate; And converting the Al coating layer into an aluminum nitride layer by flowing NH ₃ over the Al coating layer.

Preferably, the epi gallium nitride layer is formed to a thickness of 30 to 200nm. The gallium aluminum nitride layer is formed to a thickness of 100 to 300nm. In addition, the second aluminum nitride layer is formed to a thickness of several tens to 100nm.

Preferably, the first aluminum nitride layer, epi gallium nitride layer, gallium aluminum nitride layer and the second aluminum nitride layer are formed by the MOCVD method at a temperature condition of 1000 to 1200 ℃.

Gallium nitride thin film substrate according to the present invention for achieving the above technical problem, the silicon substrate; A buffer layer formed on the silicon substrate, the buffer layer comprising a first aluminum nitride layer, an epi gallium nitride layer, a gallium aluminum nitride layer, and a second aluminum nitride layer sequentially stacked; And a gallium nitride thin film formed on the buffer layer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various equivalents that may be substituted for them at the time of the present application It should be understood that there may be water and variations.

1 is a cross-sectional view of a gallium nitride thin film substrate according to a preferred embodiment of the present invention. As shown in the drawing, the gallium nitride thin film substrate according to the present invention includes a silicon substrate 10, a buffer layer B formed on the silicon substrate 10, and a gallium nitride thin film 60 formed on the buffer layer B. ). The buffer layer B has a structure in which the first aluminum nitride layer 20, the epi gallium nitride layer 30, the gallium aluminum nitride layer 40, and the second aluminum nitride layer 50 are sequentially stacked.

The silicon substrate 10 is a substrate that is most widely used in a general semiconductor process, and is inexpensive and has a feature of making a large wafer and having excellent thermal conductivity. It is preferable that the surface orientation of the silicon substrate 10 on which the buffer layer B according to the present invention is formed is {111}. The surface of the silicon substrate 10 having a plane orientation of {111} has a lattice constant of about 3.8403 Å. On the other hand, the surface of the silicon substrate 10 having a plane orientation of {100} has a lattice constant of about 5.40 Å. Therefore, considering that the lattice constant of gallium nitride is about 3.189 Å, the surface orientation of the silicon substrate 10 is preferably {111}.

The buffer layer B is formed due to a lattice constant mismatch between the gallium nitride thin film 60 and the silicon substrate 10 and a difference in coefficient of thermal expansion during formation of the gallium nitride thin film 60 on the silicon substrate 10. Reduces crystal defects (mainly dislocation defects), relieves stress caused in the gallium nitride thin film 60 to prevent cracks in the gallium nitride thin film 60, and melts by chemical action of the silicon substrate 10 The back-etch is prevented to prevent Ga atoms of the gallium nitride thin film 60 from penetrating into the silicon substrate 10.

More specifically, the first aluminum nitride layer 20 determines an initial crystal growth condition for forming the buffer layer (B) structure, and the Ga valence melt back included in the epi gallium nitride layer 30 formed thereon. It is prevented from penetrating into the silicon substrate 10 by the development. In addition, the first aluminum nitride layer 20 reduces crystal defects caused by lattice constant mismatch between the gallium nitride thin film 60 and the silicon substrate 10 and prevents crack generation. In view of such a function, the thickness of the first aluminum nitride layer 20 is preferably several nm to 100 nm.

The epi gallium nitride layer 30 improves the quality of the gallium nitride thin film 60 by controlling crystal defects of the gallium nitride thin film 60 formed thereon. On the other hand, since the epi gallium nitride layer 30 is formed close to the lower silicon substrate 10, Ga atoms contained in the epi gallium nitride layer 30 may be penetrated into the silicon substrate 10 by the melt back phenomenon. have. Therefore, the thickness of the epi gallium nitride layer 30 is formed to a thickness that does not cause the penetration of the silicon substrate 10 of Ga atoms. Preferably, the epi gallium nitride layer 30 has a thickness of 30 to 200 nm.

The gallium aluminum nitride layer 40 blocks Ga atoms contained in the gallium nitride thin film 60 formed thereon from penetrating into the lower silicon substrate 10 by a melt back phenomenon, and the silicon substrate 10 and the silicon substrate 10. The stress caused by the difference in thermal expansion coefficient between the gallium nitride thin film 60 is alleviated to prevent cracks from occurring in the gallium nitride thin film 60. The gallium aluminum nitride layer 40 is preferably formed to a thickness of 100 to 300nm for the penetration of the silicon substrate 10 and stress relaxation of the Ga atom.

The second aluminum nitride layer 50 directly controls the defect density of the gallium nitride thin film 60 formed thereon to determine the quality of the gallium nitride thin film 60. In addition, the second aluminum nitride layer 50 may reduce the stress caused by the crystal lattice mismatch and thermal expansion coefficient difference between the gallium nitride thin film 60 formed on the upper portion and the silicon substrate 10 on the lower portion. To prevent cracking). In view of such a function, the second aluminum nitride layer 50 is preferably formed to a thickness of several tens to 100 nm.

Next, a method of forming a gallium nitride thin film according to a preferred embodiment of the present invention for manufacturing a gallium nitride thin film substrate having the above-described structure will be described in detail.

2 to 8 are cross-sectional views illustrating a sequential flow of a gallium nitride thin film forming method according to a preferred embodiment of the present invention.

Referring to FIG. 2, first, chemical pretreatment is performed on a silicon substrate 10 having a plane orientation of {111}. That is, the first SC1 cleaning is performed to remove organic contaminants, fine particles, etc. present on the upper surface of the silicon substrate 10. Then, the native oxide film formed on the silicon substrate is removed using dilute hydrofluoric acid (diluted HF).

Referring to FIG. 3, when the chemical pretreatment of the silicon substrate 10 is completed, the silicon substrate 10 is loaded into a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, and then heat using hydrogen at a high temperature of 1000 to 1200 ° C. FIG. Carry out the cleaning process.

Thereafter, an Al coating process using a TriMethlyAlluminum (TMAl) source is performed at a temperature condition where the thermal cleaning process is performed to form an Al coating layer 70 on the upper surface of the silicon substrate 10. The reason for forming the Al coating layer 70 is to prevent the Si atoms on the upper surface of the silicon substrate 10 and the N atoms of NH ₃ from reacting with each other in the subsequent first aluminum nitride layer forming process. Preferably, the deposition process of the Al coating layer 70 proceeds for at least 10 seconds to 1 minute.

Referring to FIG. 4, after formation of the Al coating layer 70 is completed, NH ₃ is flowed to the upper surface of the silicon substrate 10 at a temperature of 1000 to 1200 ° C. and a hydrogen atmosphere to form the Al coating layer 70 and NH ₃ . By reacting, the first aluminum nitride layer 80 is formed. Since the first aluminum nitride layer 80 is formed at the same temperature condition as that of forming the Al coating layer 70, the thermal expansion coefficient difference between the last gallium nitride thin film to be formed and the silicon substrate 10 is different. It acts to relieve the generated stress. Meanwhile, the first aluminum nitride layer 80 may be formed to have a thickness of several nm to 100 nm to prevent Ga atoms of the epi gallium nitride layer formed in a subsequent process from penetrating into the silicon substrate 10 by a melt back phenomenon. desirable.

Referring to FIG. 5, after the first aluminum nitride layer 80 is formed, TMGa (TriMethlyGalium) and NH ₃ are flowed to the surface of the first aluminum nitride layer 80 at a temperature of 1000 to 1200 ° C. and a hydrogen atmosphere. The gallium nitride layer 90 is formed. The epi gallium nitride layer 90 controls the crystal defects of the gallium nitride thin film formed on the top to improve the quality of the gallium nitride thin film. On the other hand, since the epi gallium nitride layer 90 is formed close to the lower silicon substrate 10, if the thickness is not properly controlled, the Ga atoms contained in the epi gallium nitride layer 90 are formed by the melt back phenomenon. There is a risk of penetration into the silicon substrate 10. Therefore, the epi gallium nitride layer 90 is preferably formed to a thickness of 30 to 200nm so as not to cause the penetration of the silicon substrate 10 of Ga atoms.

Referring to FIG. 6, after the epi gallium nitride layer 90 is formed, TMAl, TMGa, and NH ₃ are flowed to the upper surface of the epi gallium nitride layer 90 at a temperature of 1000 to 1200 ° C. and a hydrogen atmosphere to form gallium nitride. An aluminum layer 100 is formed. The gallium aluminum nitride layer 100 formed as described above may prevent a Ga atom from penetrating into the lower silicon substrate 10 by controlling a melt back phenomenon in a subsequent gallium nitride thin film formation process. In addition, the stress caused by the lattice constant mismatch between the silicon substrate 10 and the gallium nitride thin film and the difference in thermal expansion coefficient is alleviated. In view of such a function, the gallium aluminum nitride layer 100 is preferably formed to a thickness of 100 to 300nm.

Referring to FIG. 7, after forming the gallium aluminum nitride layer 100, TMAl and NH ₃ are flowed to the upper surface of the gallium aluminum nitride layer 100 under a hydrogen atmosphere and at a temperature of 1000 to 1200 ° C. to form first aluminum nitride. The second aluminum nitride layer 110 is formed thicker than the layer 80 to complete the structure of the buffer layer B. The second aluminum nitride layer 50 formed as described above directly controls the crystal defects of the gallium nitride thin film formed thereon to determine the quality of the gallium nitride thin film. In addition, the second aluminum nitride layer 110 may relieve stress caused by the crystal lattice mismatch and thermal expansion coefficient difference between the gallium nitride thin film formed on the upper portion and the silicon substrate 10 on the lower portion, thereby causing cracks in the gallium nitride thin film. To prevent them. In view of this point, the second aluminum nitride layer 110 is preferably formed to a thickness of several tens to 100 nm.

Referring to FIG. 8, when the structure of the buffer layer B is completed by forming the second aluminum nitride layer 110, TMGa is formed on the upper surface of the second aluminum nitride layer 110 at a temperature of 1000 to 1200 ° C. and a hydrogen atmosphere. And NH ₃ are flown to form a gallium nitride thin film 120. At this time, since the stress generated by the crystal lattice mismatch between the silicon substrate 10 and the gallium nitride thin film 120 and the difference in thermal expansion coefficient is alleviated by the buffer layer B, the gallium nitride thin film 120 having good quality without cracks is It can be formed thicker than 1.5um, and furthermore, Ga atoms can be prevented from penetrating into the silicon substrate 10 by the melt back phenomenon.

In the above embodiment, the buffer layer B and the gallium nitride thin film 120 were formed using the MOCVD method. However, the buffer layer B and the gallium nitride thin film 120 may use other methods known in the art, such as molecular beam epitaxy (MBE) and hybrid vapor deposition (HVPE). It can be formed by the obvious.

Figure 9 shows the result of measuring the thickness of the thin film over the entire substrate when growing a gallium nitride thin film after forming a buffer layer in accordance with the present invention on a 2 inch silicon substrate. Referring to the drawings, it can be seen that the gallium nitride thin film was grown to a thickness of 1.5 um or more.

FIG. 10 is a graph showing the results of analyzing the characteristics of a crystal by measuring a rocking graph of a gallium nitride thin film sample formed according to the present invention using a crystal diffraction apparatus (XRD). Referring to the drawings, since the full width at half max (FWHM) of the gallium nitride thin film is 580 or less, it can be seen that the crystal defects are effectively controlled by the buffer layer B, thereby improving the crystal quality of the thin film.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

 According to the present invention, a crystal lattice between a gallium nitride thin film and a silicon substrate is formed by forming a gallium nitride thin film after forming a buffer layer having a structure in which an epigallium nitride layer and a gallium aluminum nitride layer are interposed between the first and second aluminum nitride layers. It is possible to form a gallium nitride thin film having a thickness of 1.5 μm or more by reducing stress caused by mismatch and coefficient of thermal expansion and effectively controlling crystal defects such as dislocations.

According to another aspect of the present invention, the gallium aluminum nitride layer included in the buffer layer may prevent Ga atoms from penetrating into the silicon substrate by a melt back phenomenon during gallium nitride thin film formation, thereby preventing deterioration of the quality of the gallium nitride thin film.

Claims (12)

(a) forming a first aluminum nitride layer on the silicon substrate; (b) forming an epi gallium nitride layer on the first aluminum nitride layer; (c) forming a gallium aluminum nitride layer on the epi gallium nitride layer; (d) forming a second aluminum nitride layer on the gallium aluminum nitride layer; And (e) forming a gallium nitride thin film on the second aluminum nitride layer. The method of claim 1, The first gallium nitride layer is formed with a thickness of 2 nm to 100 nm. The method of claim 2, wherein step (a) comprises: Forming an Al coating layer on the silicon substrate; And And converting the Al coating layer into an aluminum nitride layer by flowing NH ₃ gas on top of the Al coating layer. The method of claim 1, The epi gallium nitride layer is formed of a gallium nitride thin film, characterized in that formed in a thickness of 30 to 200nm. The method of claim 1, The gallium nitride layer is formed of a gallium nitride thin film, characterized in that formed in a thickness of 100 to 300nm. The method of claim 1, The second aluminum nitride layer is formed of a gallium nitride thin film, characterized in that formed in a thickness of 20 to 100nm. The method of claim 1, The first gallium nitride layer, the epi gallium nitride layer, the gallium nitride layer and the second aluminum nitride layer is formed by a MOCVD method at a temperature condition of 1000 to 1200 ℃. Silicon substrates; A buffer layer formed on the silicon substrate, the buffer layer comprising a first aluminum nitride layer, an epi gallium nitride layer, a gallium aluminum nitride layer, and a second aluminum nitride layer sequentially stacked; And Gallium nitride thin film substrate, characterized in that it comprises a gallium nitride thin film formed on the buffer layer. The method of claim 8, The first gallium nitride layer has a thickness of 2 nm to 100 nm. The method of claim 8, The epi gallium nitride layer is a gallium nitride thin film substrate, characterized in that having a thickness of 30 to 200nm. The method of claim 8, The gallium nitride layer is a gallium nitride thin film substrate, characterized in that having a thickness of 100 to 300nm. The method of claim 8, The gallium nitride thin film substrate, characterized in that the second aluminum nitride layer has a thickness of 20 to 100nm.

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