KR100720537B1 - Growing Method for Nitride Semiconductor Film - Google Patents

Abstract

The present invention is to provide a method for growing a nitride semiconductor film, the local defect is removed after lateral epitaxial overgrowth (LEO) to reduce the potential density due to the difference in lattice constant and thermal expansion coefficient between the substrate and the nitride semiconductor film After that, a method of growing a nitride semiconductor film is performed to improve device performance, such as a laser diode, which is subsequently grown by performing a peneoepitaxy to grow a nitride semiconductor film on the removed portion.

Nitride semiconductor film, laser diode, LEO, pendeoepitaxy

Description

Growing Method for Nitride Semiconductor Film

1A to 1C are cross-sectional views of a nitride semiconductor thin film manufacturing process using a lateral epitaxial overgrowth (LEO) method according to the prior art.

2A through 2C are cross-sectional views of a nitride semiconductor film fabrication process using a peneoepitaxy growth method according to the related art.

3A to 3E are cross-sectional views of a nitride semiconductor thin film manufacturing process according to the present invention.

* Explanation of symbols for main parts of the drawings

1, 11, 21: sapphire substrate 2, 12, 22: first nitride thin film layer

3, 23, 25: dielectric film mask 4, 13, 24: the second nitride thin film layer

26, 27: third nitride thin film layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method for improving the performance of a semiconductor thin film required for fabricating a nitride semiconductor laser, which is attracting attention as a light source of a digital versatile disc (DVD) system. A method for growing a nitride semiconductor thin film.

When growing a semiconductor thin film for fabricating a nitride semiconductor laser, it was common to grow directly on a sapphire substrate, which is a heterogeneous material suitable for growth of a wurtzite structure. This is because the sapphire substrate has advantages of being easier to obtain than other substrates, simple substrate pretreatment process, and stable at high temperature during nitride semiconductor thin film growth. However, there is a fundamental limitation in obtaining a high quality thin film by reducing crystal defects because of the large difference in the nitride semiconductor thin film and the coefficient of thermal expansion and lattice constant.

In general, when a thin film is grown on a heterogeneous substrate, a difference in thermal expansion coefficient and lattice constant between the substrate and the thin film causes a large number of defects such as misfit dislocation. It is important to prevent these defects from propagating during the growth of the upper layer, so a buffer layer may be introduced for this purpose. There is a method of reducing the driving force in which dislocations are transferred and propagated to the upper layer by blocking stress by the buffer film, and there is a method in which a large stress is applied to the buffer film and the defects such as dislocations are removed to the outside through a heat treatment process. There is a limit.

Thus, many studies have been made on growing a primary GaN substrate as a base material for subsequent growth of a laser diode structure, rather than directly growing a semiconductor thin film such as a GaN thin film directly on a sapphire substrate. This is a form in which a thick GaN film is grown on a sapphire substrate and is not a true homoepitaxy in that a GaN thin film is not grown on a GaN-only thick film.

1A to 1C are cross-sectional views of a nitride semiconductor thin film fabrication process using a lateral epitaxial overgrowth (LEO) method according to the prior art, which greatly reduces the crystal defect density of the nitride semiconductor film.

As shown in FIG. 1A, a first nitride thin film layer 2 is formed on the sapphire substrate 1. Thereafter, a dielectric film mask 3 having a predetermined pattern is formed to expose a predetermined region of the first nitride thin film layer 2.

Subsequently, as shown in FIGS. 1B and 1C, the second nitride thin film layer 4 grown through the exposed first nitride thin film layer (Window 2) is allowed to grow sideways so as to cover the upper portion of the dielectric mask mask 3. Thus, the second nitride thin film layer 4 is grown on the front surface.

The laterally grown portion over the portion covered by the dielectric mask 3 reduces the defect density but the second nitride thin film layer 4 grown over the first nitride thin film layer (Window: 2) of the portion not covered by the dielectric mask 3 Defects of the first nitride thin film layer 2, such as a GaN thin film, which is a lower base material, are transferred as they are, so that crystallinity is not excellent.

That is, on the average, the defect density decreases, but the parts with high defect density and the parts with local defect density exist at regular intervals. This imposes constraints such that the ridge portion of the laser diode must be aligned on a crystal grown on a dielectric oxide film such as the dielectric mask 3 where the defect density is low in a subsequent process, and also in the average decrease in defect density. There will be some limits.                         

2A to 2C are cross-sectional views of a nitride semiconductor film fabrication process using a peneoepitaxy growth method according to the prior art.

First, as shown in FIG. 2A, a first nitride thin film layer is formed on the sapphire substrate 11. Subsequently, as shown in FIG. 2B, the first nitride thin film layer 12 is formed on the sapphire substrate 11 in the form of a periodic stripe, and later side growth is performed using this portion as a base material during subsequent growth.

Although the defect density of the side where the lateral growth occurred is low, the defect density of the part which is the base material of the lateral growth cannot be changed. Therefore, the overall average defect density cannot be reduced any more. In addition, when there are many defects of the base material, the crystallinity of the side-grown part is not excellent. In the process, there are limitations such that the ridge portion of the laser diode must be aligned on the low defect density portion.

In order to fabricate laser diodes with good characteristics, it is necessary to reduce the defects transmitted to the upper layer. Therefore, a method of obtaining a high quality thin film to reduce the defects transmitted to the upper layer and to manufacture a stable and excellent performance should be sought. That is, since the crystallinity of the thin film greatly influences the overall performance of the device, it can be said that obtaining a high quality thin film is essential for producing a stable and excellent semiconductor laser.

The nitride semiconductor film growth method according to the related art described above has the following problems.                         

The method of directly growing on a sapphire substrate, which is a heterogeneous material suitable for growth of a wurtzite structure according to the prior art, does not reduce the dislocation density due to the difference between the coefficient of thermal expansion and the lattice constant.

The lateral epitaxial overgrowth (LEO) growth method according to the prior art has a limit of decrease in average dislocation density due to poor crystallinity and increased local dislocation density.

According to the prior art peneoepitaxy growth method can reduce the dislocation density of the side growth portion, but can not reduce the dislocation density of the base material.

Therefore, the present invention has been made to solve the above problems, and after removing the high defects after the LEO implementation to reduce the dislocation density of the base material, the laser to be grown later by performing a peneoepitaxy (pendeoepitaxy) It is an object of the present invention to provide a nitride semiconductor film growth method for improving device performance of a diode.

Features of the nitride semiconductor film growth method according to the present invention for achieving the above object is the step of forming a first nitride thin film on the substrate, and forming a first dielectric film having a plurality of bands on the first nitride thin film Forming a second nitride thin film so as to cover the first dielectric film on the first nitride thin film, and forming a second dielectric film having a plurality of band shapes parallel to the first dielectric film on the second nitride thin film. And removing the first and second nitride thin films formed on both sides of the first and second dielectric layers so that the substrate is exposed, and removing the second dielectric layer and removing the first and second nitride thin films. Forming a third nitride thin film.

The first and second dielectric layers are SiO ₂ , It is formed of any one of Si ₃ N ₄ , the width of the first and second dielectric film and the width of the portion where the first and second dielectric film is not formed is formed to 1㎛ to 30㎛.

According to the characteristics of the present invention, the side growth method (LEO) and the pandeo epitaxy (pendeoepitaxy) method is used in combination to remove the high defects after the LEO to reduce the defects by using the less defects Through the Pdio epitaxy, it is possible to grow a nitride film with few defects as a whole.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of the nitride semiconductor film growth method according to the present invention will be described with reference to the accompanying drawings.

3A to 3E are cross-sectional views of a nitride semiconductor film production process according to the present invention.

First, as shown in FIG. 3A, the first nitride thin film layer 22 is formed on the sapphire substrate 21. SiO _{2 on} it A stripe pattern is formed with a dielectric film mask 23 such as Si ₃ N ₄ . The widths W1 and W2 of the pattern are formed to have a range of 1 µm <W1 <30 µm and 1 µm <W2 <30 µm.

Subsequently, as shown in FIG. 3B, a second nitride thin film layer 24 is formed. The portion grown on the dielectric mask 23, which is a side lateral growth, is relatively low in density because it is grown in a state in which defects transmitted from the lower side by the dielectric mask 23 are blocked.

On the other hand, the portion not covered by the dielectric film mask 23 has a high defect density because defects such as threading dislocation are transmitted as they are. Thus, a second nitride thin film layer 24 such as a GaN film having a high defect density part and a low defect part periodically is formed through the lateral epitaxial overgrowth (LEO) method as described above.

Next, as shown in FIG. 3c, SiO ₂ or A stripe pattern is formed with a second dielectric film mask 25 such as Si ₃ N ₄ .

Subsequently, as illustrated in FIG. 3D, portions having a high defect density, which are not covered by the dielectric masks 23 and 25, are removed through an etching mask pattern forming process and an etching process. This process leaves parts obtained through lateral growth, which are parts with low defect density.

Next, as shown in FIG. 3E, the sidewall growth is removed from the second nitride thin film layer 24 formed on the dielectric film mask 23, which is a portion obtained through side growth by removing the dielectric film mask 25 using PANDIO epitaxy. The third nitride thin film layers 26 and 27, such as GaN, are formed on the entire surface.

The second nitride thin film layer 24 formed on the dielectric film mask 23, which is a non-etched portion, also has a better crystallinity than when grown by a conventional Pdio epitaxy method having a high defect density. Since it also has a low defect density, it is possible to obtain third nitride thin film layers 26 and 27 such as GaN films whose defect density is greatly reduced as a whole.

It should be noted that not only the third nitride thin film layer 27 formed on the side of the second nitride thin film layer 24, but also the third nitride thin film layer 26 formed on the side of the first nitride thin film layer 22, as shown in FIG. It is the fact that it is formed by growth. However, in the case of the third nitride thin film layer 26 formed on the side of the first nitride thin film layer 22, as the third nitride thin film layer 27 formed on the side of the second nitride thin film layer 24 adheres, the gas supply decreases and thus is adhered to the drawing. Although visible, it is not coalesced as much as the third nitride thin film layer 27 formed on the side of the second nitride thin film layer 24. The degree of adhesion does not affect the properties of the third nitride thin film layer 27 formed on the side surface of the second nitride thin film layer 24. The space between the third nitride thin film layer 26 formed on the side of the first nitride thin film layer 22 and the third nitride thin film layer 27 formed on the side of the second nitride thin film layer 24 also depends on the growth conditions but ultimately remains on top. The characteristics of the third nitride thin film layer 27 formed on the side surface of the second nitride thin film layer 24 are not significantly affected. Since the device is formed using the third nitride thin film layer 27 formed on the side surface of the second nitride thin film layer 24 as a result, the device may be formed on the film where the defect density is greatly reduced.

The nitride semiconductor film growth method according to the present invention as described above has the following effects.

Growing a nitride semiconductor film directly on the sapphire substrate does not reduce the dislocation density any more because of the difference between the coefficient of thermal expansion and the lattice constant.

By using the LEO growth method in which a nitride semiconductor film with low defects and a nitride crystal film with poor crystallinity and many defects are formed at the same time, the potential density is reduced by removing the defected nitride semiconductor film portion, followed by PANDIO epitaxy growth. Since the lateral growth is performed using the portion where the dislocation density is reduced by using the method, a nitride semiconductor thin film in which the dislocation density is reduced as a whole can be obtained.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (3)

Forming a first nitride thin film on the substrate, Forming a first dielectric layer having a plurality of band shapes on the first nitride thin film; Forming a second nitride thin film on the first nitride thin film so as to cover the first dielectric film, and forming a second dielectric film having a plurality of band shapes parallel to the first dielectric film on the second nitride thin film; Removing the first and second nitride thin films formed on both sides of the first and second dielectric layers to expose the substrate; Removing the second dielectric layer and forming a third nitride thin film in a portion where the first and second nitride thin films are removed. The method of claim 1, wherein the first and second dielectric layers comprise SiO ₂ , A nitride semiconductor film growth method, characterized in that formed of any one of Si ₃ N ₄ . The nitride semiconductor film growth method according to claim 1, wherein the widths of the first and second dielectric films and the widths of the portions where the first and second dielectric films are not formed are 1 µm to 30 µm.

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