JPH10233385A - Method for etching nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to etch a nitride semiconductor in an aqueous solution with good reproducibility and with good controllability by a method wherein a crystal defect is increased artificially in the nitride semiconductor and the nitride semiconductor is etched by a wet etching operation. SOLUTION: A sapphire C face 11 is used as a sapphire substrate. By an electron-beam vapor deposition operation and a lift-off operation, a stripe-shaped Al2 O3 film 12 formed in advance on the sapphire substrate which is used for a growth operation. Since the quality of a crystal in the Al2 O3 film 13 which is vapor-deposited on the sapphire substrate is inferior to that of sapphire in the substrate 11, only a linear defect which is extended to the direction of a C-axis exists in a part 14 on a GaN film as a part which is grown directly on the sapphire substrate. However, in addition to the defect in the direction of the C-axis, a defect other than it is generated in a part 15 on the GaN film on the Al2 O3 vapor-deposited film. When the sapphire substrate is etched by a KOH aqueous solution, the part 14 which is grown directly on the sapphire substrate is not etched at all, and the part 15 which is grown on the Al2 O3 vapor-deposited film is hardly etched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for etching a nitride semiconductor.

[0002]

2. Description of the Related Art A nitride semiconductor has a wide band gap of 2 eV or more, is used as a material for a short-wavelength light-emitting device having a wide range from orange to ultraviolet, and performs a stable operation at a high temperature exceeding 100 ° C. Attention has been paid to semiconductors for high-temperature operation. Nitride semiconductors are rarely used as a single film.For example, in the case of manufacturing a laser or the like, it is necessary to grow and stack a plurality of different types of nitride semiconductor films, and to perform a process of etching and forming electrodes. is there. As a method of performing etching, while irradiating ultraviolet rays,
Etching with potassium hydroxide solution (for example,
Proceedings of the 56th Lecture Meeting on Applied Physics 27p-ZE-16
And the like, and a method of etching using a reactive gas (for example, textbooks pp. 9-14 of the 103rd meeting of the Society of Applied Physics, Crystal Engineering Subcommittee, etc.) have been used as general methods. Among them, the method using a reactive gas is not affected by the shape of the end face because the etched end face collapses due to a delicate condition difference or a phenomenon that it is not etched vertically occurs, but etching can be performed with good reproducibility. Such a device (for example, a light emitting diode) is used.

[0003]

However, an etching method that can control the shape and perpendicularity of the end face sufficiently and has good reproducibility has not been established. When etching is performed in an aqueous solution, a phenomenon occurs in which the etching rate changes in the state of the nitride semiconductor, and sometimes etching is not performed at all. Further, it is known that the surface shape after etching may be significantly different even between nitride semiconductors having the same component. As described above, it has been difficult to etch a nitride semiconductor with good reproducibility and controllability. The present invention has been made to solve the above problems, and has as its object to provide a method of etching in an aqueous solution with good reproducibility and controllability.

[0004]

As described above, as a result of searching for the cause of the uncertainty of etching that occurs when etching is performed in an aqueous solution, the speed of wet etching and the state of the surface after etching are determined. Has been found to greatly depend on the defect density in the crystal.

In addition, it has been found that, in particular, it largely depends on the defect density other than the line defect parallel to the C axis of the nitride semiconductor. That is, it is known that the density of line defects parallel to the C-axis of an epitaxially grown film of a nitride semiconductor, except for the interface with the substrate, is as high as about 1.0 × 10 ¹⁰ cm ^−2. It is difficult to control the defect density. However, other defect densities were extremely low in our investigation (1 × 10 ⁴ cm ⁻³ or less), and were found to be within a range that can be controlled sufficiently artificially. Therefore, C
Defects other than line defects parallel to the axis are artificially generated in the epitaxially grown film, and wet etching is performed using an etchant, thereby enabling predetermined etching.

A method for etching a nitride semiconductor according to the present invention is characterized by including a step of artificially increasing crystal defects in the nitride semiconductor and a step of performing etching by wet etching. Thereby, the above object is achieved.

According to the present invention, as a means for artificially increasing crystal defects, a substrate or a lower layer nitride semiconductor is grown on the whole or a part thereof before the nitride semiconductor to be etched is grown. It is characterized in that a treatment for increasing crystal defects of the nitride semiconductor is performed. Specifically, a method of depositing a different kind of substance on a substrate or a lower nitride semiconductor, a method of applying a different kind of substance, or a method of roughening the surface are exemplified. Thereby, the above object is achieved.

Further, the present invention is characterized in that, as means for artificially increasing the crystal defects, a treatment is performed such that the crystal defects are directly increased on the whole or a part of the grown nitride semiconductor. I have. Specific examples include an ion implantation method. Thereby, the above object is achieved.

The operation of the present invention will be described below.

In the epitaxial growth film of the nitride semiconductor,
By artificially increasing the density of defects other than the line defects parallel to the C-axis, the effect of performing wet etching with good reproducibility only on the portion where the defects are increased is used.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention utilizes the characteristic that wet etching can be performed by artificially generating crystal defects in an epitaxially grown nitride semiconductor film.

(Example 1) Metal organic chemical vapor deposition (MOC)
GaN which is a nitride semiconductor film grown by the VD method)
An example of etching the film will be described below with reference to FIG.

The GaN film is made of M at normal pressure (760 Torr).
It was produced by the OCVD method. The growth temperature of the GaN film is 10
00 ° C, the raw material is trimethylgallium (TM
G) using ammonia (NH ₃ ), NH ₃ : TMG = 5
Growth was performed for 1 hour under the condition of 000: 1. A sapphire C-plane substrate (11) was used as the substrate. The sapphire substrate used for growth has a stripe shape and a thickness of 1 in advance.
An Al ₂ O ₃ film (12) of about 00 Å was formed by electron beam evaporation and lift-off. The Al ₂ O ₃ film deposited on sapphire is sapphire (A
Since the quality of the crystal is inferior to l ₂ O ₃ ), the GaN film (13) grown on the deposited film is parallel to the C axis ((00 · 1)).
Direction) Line defects and surface defects other than the line defect (14) occur (region 15). The growth rate of GaN under these conditions is 2μ
m / h. Only the line defect extending in the C-axis direction exists in the portion of the GaN film directly grown on the sapphire substrate,
Its density was about 5.0 × 10 ⁹ cm ⁻² . Also, A
The GaN film on the l ₂ O ₃ deposited film has a defect in the C-axis direction,
Many line defects and surface defects extending in the (10.0) or (11.0) direction were observed. Main growth film at 80 ° C, 10m
As a result of etching for about 3 hours with an ol / L KOH aqueous solution, the portion directly grown on the sapphire substrate was not etched at all, but the portion grown on the Al ₂ O ₃ deposited film was almost completely etched. Was. In this embodiment, an example is shown in which Al ₂ O ₃ is deposited on a sapphire substrate, but the deposited film is not necessarily limited to the Al ₂ O ₃ film. But,
In the case of the Al ₂ O ₃ film, since the sapphire as the substrate has the same component, there is an advantage that it is not necessary to consider the influence of impurity diffusion on the grown film. Other substances include AlN,
The use of SiO ₂ or the like showed the same tendency.

Embodiment 2 A second example is shown in which Ga ions are implanted into a GaN film epitaxially grown on a sapphire substrate by an ion implantation method and then wet etching is performed.
This is shown below with reference to the drawings. A GaN film (2) directly grown on a sapphire substrate (21) in the same manner as in Example 1
2) A 50 μm wide, 1 μm thick striped Si
An O ₂ film mask (23) was formed by an electron beam evaporation method and a lift-off method, and thereafter, Ga ions were implanted by an ion implantation method (region 25). The ion implantation conditions were an acceleration voltage of 100 kV and an implantation amount of 1 × 10 ¹⁵ cm ⁻² . After removing the mask of the SiO ₂ film of this sample, 80
As a result of performing etching for about 3 hours with a 10 mol / L KOH aqueous solution at a temperature of about 300 n
It was etched to a depth of m (region 27), but the masked portion was not etched at all. G
The portion of the GaN film into which the a ion has been implanted is discolored to yellow, which indicates a defect (2
6). The ions to be implanted need not be limited to Ga, but N, Al, In, Mg,
Any material other than ions that directly adversely affect the nitride semiconductor, such as Be and Ca, may be used.

Embodiment 3 An example of etching a regrown GaN film is shown below.

A GaN film (32) was grown on a sapphire substrate (31) under the same conditions as in Example 1, and ions were implanted under the same conditions as in Example 2 (region 36). ( ₂ ) After removing the mask (33), the substrate was sufficiently washed with a weak acid or an organic solvent, and then a GaN film was regrown on the present GaN film under the same conditions as in Example 1 for 1 hour (37). ). Regrown GaN film
80 ° C., 10 mol / L result of about 3 hours etched with aqueous solution of KOH, GaN regrowth layer of a portion of SiO ₂ mask was not etched, the regrown never been part of the SiO ₂ mask The film was etched (38 areas). This is because the defect (36) in the GaN film caused by the ion implantation penetrates into the regrown film, thereby facilitating the etching.

Example 4 The results of an experiment for investigating the effects of InGaN and AlGaN are shown below with reference to FIGS. 4 and 5. For the InGaN film, a C-plane sapphire substrate is used as a substrate, and about 2 μm of GaN is formed thereon using TMG and ammonia.
After growing the film, an InGaN film was grown thereon. Using trimethylindium (TMI), trimethylgallium (TMG) and ammonia as raw materials,
It grew at 750 ° C. The growth rate of InGaN is about 0.5
At μm / h, the growth time is one hour. The composition ratio of In was controlled by changing the input amount of TMI. Also, A
For the lGaN film, a C-plane sapphire substrate is used as a substrate, and about 2 μm
After growing the GaN film of m, an AlGaN film was grown thereon. As a raw material, trimethylgallium (TM
G), trimethylaluminum (TMA), and ammonia were used to grow at 1000 ° C. The growth rate of InGaN is about 2 μm / h, and the growth time is 30 minutes. Al
Was controlled by changing the input amount of TMA. As a method of artificially increasing crystal defects, In
A GaN growth film (4) for growing GaN or AlGaN
In 3), a sapphire substrate (4
1, 51) forming a stripe-shaped Al ₂ O ₃ film (42) to generate a defect in the GaN film and causing the defect (45) to penetrate the upper InGaN film or AlGaN film (44), As in Example 2, InG was
The method (57) for directly generating defects in the aN film or the AlGaN film (53), or InG as in the third embodiment.
After defects are generated by performing ion implantation on the aN film or the AlGaN film, InGaN or AGaN is further formed thereon.
A sample was prepared by a method of regrowth of lGaN, and wet etching was performed. In each case, only the portions where defects were generated (regions 46 and 57) were etched.
7, 58), the other parts were not etched at all.

(Example 5) KO was used as an etching solution.
When an aqueous alkaline solution such as NaOH or the like is used as an etchant in addition to the aqueous H solution, the portions where defects are artificially generated are etched, although the etching speed is different. However, the most remarkable reaction to the presence or absence of a defect is when KOH is used, and the dislocation density other than the line defect parallel to the C axis is 1 × 1
0 easily was possible to control the etching in ⁴ cm ^-2 order of the defect density. In addition, although immersion in the etchant was sufficient, the etching rate could be increased by irradiating ultraviolet rays. In addition, the temperature is also sensitive to the temperature of the aqueous solution, and increasing the temperature tends to increase the etching rate.

[0019]

According to the method for etching a nitride semiconductor according to the present invention, crystal defects are artificially generated in the nitride semiconductor.
Thereafter, by performing the etching by the wet etching method, there is an effect that the etching can be performed only in the portion where the crystal defect is artificially generated.

[Brief description of the drawings]

FIG. 1 is a diagram showing an etching method according to a first embodiment of the present invention.
FIG. 5 is a diagram showing an example in which etching is performed thereafter.

FIG. 2 is a diagram illustrating an etching method according to a second embodiment of the present invention, and illustrates an example in which etching is performed after a defect is generated in a grown film by an ion implantation method.

FIG. 3 is a diagram illustrating an etching method according to a third embodiment of the present invention, and is a diagram illustrating an example in which a regrown film is etched.

FIG. 4 is a view showing an etching method according to a fourth embodiment of the present invention, wherein I is grown while artificially generating defects;
FIG. 4 is a diagram showing an example in which an nGaN film and AlGaN are etched.

FIG. 5 is a diagram showing an etching method according to a fourth embodiment of the present invention, wherein an InGaN film and an Al film are formed by an ion implantation method.
FIG. 3 is a diagram illustrating an example in which a GaN film is etched.

[Explanation of symbols]

11 substrate 12 Al ₂ O ₃ film 13 partially removed by a number generator portion 16 wet etching defects the influence of crystal defects 15 Al ₂ O ₃ film extending in GaN growth layer 14 C axis

Claims (5)

[Claims] 1. A method for etching a nitride semiconductor, comprising generating a crystal defect in a nitride semiconductor crystal, and thereafter etching the nitride semiconductor crystal using an etchant. 2. A material which increases the crystal defect density of a grown film by performing crystal growth on the whole or a part of the substrate on which the crystal growth of the nitride semiconductor is to be performed. The method according to claim 1, wherein, after performing the etching, the growth film is etched using an etchant. 3. Implanting ions into part or all of the surface of the nitride semiconductor to increase the crystal defect density of a predetermined part of the nitride semiconductor crystal,
The method for etching a nitride semiconductor according to claim 1, wherein the nitride semiconductor crystal is etched using an etchant. 4. An ion implantation is performed on a part or all of the surface of the nitride semiconductor to increase the crystal defect density of a predetermined portion of the nitride semiconductor crystal, and thereafter, a new portion is formed on the nitride semiconductor crystal. 4. The method for etching a nitride semiconductor according to claim 1, wherein the nitride semiconductor is re-grown, and the nitride semiconductor crystal is etched using an etchant. 5. The method for etching a nitride semiconductor according to claim 1, wherein an aqueous solution of potassium hydroxide (KOH) is used as the etching solution.