JPH11354496A - Dry etching method for semiconductor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an effective dry etching method for Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor. A dry etching method for an Al _x Ga _1-x N (0 ≦ X ≦ 1) semiconductor, wherein the Al _x Ga _{1- x} N (0 ≦ X ≦ 1) semiconductor is substantially free of carbon atoms Etching is performed by using a plasma gas of a substance containing chlorine atoms. The above plasma etching,
Usually, a parallel electrode type device in which electrodes for applying high frequency power are arranged in parallel and an object to be etched is arranged on the electrodes,
This is performed using a cylindrical electrode type device in which electrodes to which high frequency power is applied are arranged in a cylindrical shape, and an object to be etched is arranged in parallel with the cross section of the cylinder, or other devices. The plasma gas of a substance containing substantially no carbon atoms but containing chlorine atoms is, for example, plasma of boron trichloride (BCl ₃ ) gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an Al _x Ga _{1 -X} N (0 ≦ X
≦ 1) The present invention relates to a method for dry etching a semiconductor.

[0002]

2. Description of the Related Art Conventionally, Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductors have been attracting attention as materials for blue light emitting diodes and light emitting elements in a short wavelength region. As with other compound semiconductors, it is necessary to establish etching techniques such as mesas and recesses.

An Al _x Ga _{1 -X} N semiconductor is a very chemically stable substance, and is generally used as an etching solution for other III-V compound semiconductors, such as hydrochloric acid, sulfuric acid, and hydrofluoric acid (HF).
And so on or a mixed solution thereof, so that wet etching using these solutions cannot be used.

[0004] Therefore, the present inventors have proposed carbon tetrachloride (CCl ₄ ).
Alternatively, a method of dry-etching an Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor by plasma of carbon difluoride and carbon dichloride (CCl ₂ F ₂ ) gas was developed (Japanese Patent Laid-Open No. 1-278025, JP-A-1-
No. 278026).

[0005]

However, carbon difluoride (CCl ₂ F ₂ ) is subject to the regulation of chlorofluorocarbon gas and has a problem that its use is difficult. Also, plasma etching using carbon tetrachloride (CCl ₄ )
Compared to etching with carbon chloride (CCl ₂ F ₂ ), there is a problem that the etching rate is slow, and in addition, handling is difficult because the liquid is at room temperature. Furthermore, in plasma etching using a gas containing carbon, there are many reports that a polymer involving carbon is formed on a semiconductor surface and the etching state is deteriorated.

At present, the mechanism of the etching has not been elucidated, and the etching gas used for other semiconductors is not effective for Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductors. After all, it cannot be determined without experimentation. In addition, there is no report of a gas effective for dry etching of Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductors other than the disclosure of the present inventors.

[0007] The inventors of the present invention have repeatedly performed experiments on plasma etching of an Al _x Ga _{1 -X} N semiconductor using another plasma gas, and as a result, have found that boron trichloride (BCl ₃ )
Was found to be most suitable as an etching gas, and the present invention was completed.

[0008]

Configuration of the invention for solving the above object, according to an aspect of is an _{Al x Ga 1-x N (} 0 ≦ X ≦ 1) semiconductor dry etching method, Al _x Ga _1-x An N (0 ≦ X ≦ 1) semiconductor is etched with a plasma gas of a substance containing substantially no carbon atoms and containing chlorine atoms.

The above-mentioned plasma etching is usually performed at a high frequency.
The electrodes to which the wave power is applied are arranged in parallel, and the electrodes
Parallel electrode type device with a switching object, high frequency power
The electrodes to which the voltage is applied are arranged in a cylindrical shape, and the section of the
Cylindrical electrode type device with objects to be etched arranged in rows,
This is performed using an apparatus having another configuration. In addition, carbon atoms
Plasma gas of a substance containing chlorine atoms
If boron trichloride (BCl _Three) Gas plasma. Praz
The parallel electrode type device or cylindrical electrode type device
Is performed by applying high-frequency power between the electrodes.
It is.

[0010]

As will be apparent from the following embodiments,
The Al _x Ga ₁ -xN (0 ≦ X ≦ 1) semiconductor could be efficiently etched by a plasma gas of a substance containing substantially no carbon atoms and containing chlorine atoms. It has also been found that the plasma etching does not cause crystal defects in the semiconductor. Therefore, by using the present invention, Al _x Ga _1
In the production of devices using _-xN (0 ≦ X ≦ 1), their productivity can be greatly improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. The semiconductor used in the method of this example was formed into a structure shown in FIG. 2 by vapor phase growth by metalorganic compound vapor phase epitaxy (hereinafter referred to as "M0VPE"). The gases used were NH ₃ , carrier gas H ₂ and trimethylgallium (G
a (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”) and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”).

First, a single-crystal sapphire substrate 1 whose main surface is the c-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of an M0VPE apparatus. Next, the pressure in the reaction chamber was reduced to 5 Torr, and H ₂ was supplied at a flow rate of 0.3 liter /
Sapphire substrate 1 at a temperature of 1100 ° C
Was subjected to gas phase etching.

Next, the temperature is lowered to 800 ° C., H ₂ is flowed at 3 liter / min, NH ₃ is flowed at ₂ liter / min, and TMA is 7 liter / min.
Heat treatment was performed by supplying at a ^{rate of} × 10 ^-6 mol / min. By this heat treatment, the AlN buffer layer 2 was formed to a thickness of about 500 °.
Next, the supply of TMA was stopped, the temperature of the sapphire substrate 1 was maintained at 600 ° C., H ₂ was 2.5 liter / min, and NH ₃ was 1.5 liters.
ter / min, TMG was supplied at 1.7 × 10 ^-5 mol / min.
A 3 μm GaN layer 3 was formed.

Next, as shown in FIG. 3, an SiO ₂ layer 4 was formed on the GaN layer 3 by RF sputtering to a thickness of 5000 °. Next, a photoresist 5 was applied on the SiO ₂ layer 4, and the photoresist at the window A was removed by photolithography.

Next, as shown in FIG. 4, the SiO ₂ layer 4 not covered with the photoresist 5 was removed with a hydrofluoric acid-based etchant. Then, a double layer mask of the SiO ₂ layer 4 having the window A and the photoresist 5 was formed in the etched portion of the GaN layer 3. Next, sample 3 having the structure shown in FIG.
0 was installed in a parallel plate electrode type plasma etching apparatus shown in FIG. 1 to etch the exposed portion of the GaN layer 3.

Next, the structure of the etching apparatus shown in FIG. 1 will be described. In the parallel electrode type electrode device shown in FIG. 1, a stainless steel vacuum vessel 10 forming a reaction chamber 20 is used.
The introduction pipe 12 for introducing an etching gas is
The introduction pipe 12 is provided with a boron trichloride via a mass flow controller 14 capable of varying the gas flow rate.
It is connected to a cylinder 16 storing (BCl ₃ ). Then, boron trichloride (BCl ₃ ) gas is introduced from the cylinder 16 into the reaction chamber 20 via the mass flow controller 14.

The reaction chamber 20 includes rotary pumps 15, 1
7, diffusion pump 19, mechanical booster pump 13
And the degree of vacuum in the reaction chamber 20 is adjusted by the valve 18. On the other hand, an electrode 22 and an electrode 24 that are insulated from the vacuum vessel 10 are disposed in the reaction chamber 20 so as to face in the vertical direction. Then, the electrode 22 is grounded, and the electrode 24 is supplied with high-frequency power. The high-frequency power is supplied from a high-frequency power supply 28 having a frequency of 13.56 MHz to a matching device 2
6.

A quartz plate 25 is mounted on the electrode 24, and the sample 30 shown in FIG.
Is placed. When plasma etching is performed in the apparatus having the above configuration, first, the sample 3 is placed on the quartz plate 25.
After placing 0, the residual gas in the reaction chamber 20 is sufficiently exhausted by the diffusion pump 19, and the degree of vacuum in the reaction chamber 20 is reduced by 5 ×.
Make it about 10 ^-6 Torr. Thereafter, a boron trichloride (BCl ₃ ) gas was introduced into the reaction chamber 20 from the side of the electrode 24 at a flow rate of 10 cc / min by the mass flow controller 14 from the cylinder 16. Then, the reaction chamber 2 is opened by the valve 18.
The vacuum of 0 was adjusted to exactly 0.04 Torr.

In this state, the distance between the electrode 24 and the electrode 22 is 0.4
When a high-frequency power having a density of 4 W / cm ² was supplied, glow discharge was started between the electrodes, and the introduced boron trichloride (BCl ₃ ) gas was brought into a plasma state, and etching of the sample 30 was started. After etching for a predetermined time, the sample 30 was taken out of the reaction chamber 20, and the SiO ₂ layer 4 was removed with hydrofluoric acid to obtain a sample 30 shown in FIG. Then, the etch depth Δ was measured with a step gauge.

The above-described etching was performed by changing the etching time in various ways, and the relationship between the etching depth Δ and the etching time was measured. The results are shown in FIG. From the measurement result, the etching rate was 490 ° / min. Further, an image of the etched surface was measured by a scanning electron microscope (SEM). The magnification is 5000 times. The etched portion is a region indicated by W in FIG. 7 (b) showing the outline of the image shown in FIG. 7 (a). No foreign matter such as a deposit is seen on the surface, and it can be seen that the form of the surface is flat.

For comparison, carbon difluoride (C 2
FIGS. 8 (a) and 9 (b) show SEM images of the etched surface of the GaN layer 3 by plasma etching with Cl ₂ F ₂ ).
FIG. 8 (b) shows the outline of the etched surface,
In FIG. 9 (b), it is a region X and a region Y. It can be seen from the image of FIG. 8 (a) that a recess has appeared. Also, from the image of FIG. 9 (a), it can be seen that a polymer involving carbon is formed and the etched surface is disturbed.

Before and after the etching with boron trichloride, the sample was cooled to 4.2 K, and irradiated with a helium cadmium laser at 3250 ° to measure the photoluminescence intensity of the etching surface of the GaN layer 3. The result is the tenth
This is shown in FIG. FIG. 10 shows the characteristics before etching, and FIG. 11 shows the characteristics after etching. In the characteristic diagram, no change was observed in the waveform peak wavelength, half width, and photoluminescence intensity. From this, it was found that the above-mentioned etching did not change the crystallinity of the GaN layer 3.

When this etching is sufficiently performed, the lower layer Al
It can be seen that the N layer is etched, and Al other than X = 0
It was found that the method can be applied to etching of _x Ga _1-X N.
Next, a light emitting diode was manufactured using the present dry etching method. The method is described below.

The dry etching method of the present invention is used, for example, at the time of forming electrodes when manufacturing the light emitting diode 40 having the structure shown in FIG. In FIG. 12, the light emitting diode 40 has a sapphire substrate 41, on which a 500-nm AlN buffer layer 42 is formed. The buffer layer 42
On top of this, a high carrier concentration n ⁺ layer 43 made of GaN with a thickness of about 4.5 μm and a low carrier concentration n layer 44 made of GaN with a thickness of about 1.5 μm are sequentially formed. Zn-doped GaN having a thickness of about 0.25 μm on the n-layer 44
I layer 45 is formed. And the i-layer 45
And an electrode 48 made of aluminum and connected to the high carrier concentration n ⁺ layer 43.

Next, a method of manufacturing the light emitting diode 40 having this structure will be described. The light emitting diode 40 includes:
It was manufactured by vapor phase growth by metal organic compound vapor phase epitaxy (hereinafter referred to as "M0VPE"). The gas used was NH
₃ and the carrier gas H ₂ and trimethylgallium (Ga (CH _{3) 3)}
(Hereinafter referred to as "TMG") and trimethylaluminum (Al
(CH ₃ ) ₃ ) (hereinafter referred to as “TMA”), silane (SiH ₄ ), and diethylzinc (hereinafter referred to as “DEZ”). First, a single-crystal sapphire substrate 41 whose main surface is the c-plane cleaned by organic cleaning is mounted on a susceptor placed in a reaction chamber of an M0VPE apparatus.

Next, the sapphire substrate 1 was subjected to gas phase etching at a temperature of 1100 ° C. while flowing H ₂ at a flow rate of ₂ liter / min at normal pressure. Next, the temperature is reduced to 400 ° C. and H ₂
Flow rate 20 liter / min, NH ₃ flow rate 10 liter / min, TMA
The buffer layer 42 of AlN was formed at a thickness of about 500 ° at a supply of 1.8 × 10 ^-5 mol / min.

Next, the temperature of the sapphire substrate 41 is set to 1150 ° C.
Held in the H ₂ 20liter / min and NH ₃ 10liter / min, TMG
1.7 × 10 ^-4 mol / min, silane diluted with H ₂ to 0.86ppm a (SiH ₄₎ was supplied at a rate of 200ml / min, a film thickness of about 2.2 mu
A Si-doped high carrier concentration n ⁺ layer 43 made of GaN having a carrier concentration of 1.5 × 10 ¹⁸ / cm ³ was formed.

Subsequently, the temperature of the sapphire substrate 41 is raised to 1150
℃, H_TwoTo 20 liter / min, NH _ThreeTo 10 liter / min,
1.7 x 10 TMG^-FourMol / min.
μm, carrier concentration 1 × 10^Fifteen/ cm^ThreeGaN low key
A carrier concentration n layer 44 was formed. Next, the sapphire substrate
41 to 1000 ° C and H_TwoTo 20 liter / min, NH_ThreeThe 10li
ter / min, TMG 1.7 × 10^-FourMol / min, DEZ 1.5 × 10
^-FourSupply 0.2 mol / min Zn-doped
An i-layer 45 made of GaN was formed.

In this manner, a multilayer structure as shown in FIG. 13 was obtained. Next, as shown in FIG. 14, a photoresist is applied on the i-layer 45, and the photoresist layer 5 patterned so that the photoresist remains on the portion (window) to be etched by photolithography.
Form 3

Next, as shown in FIG. 15, the surfaces of the photoresist layer 53 and the i-layer 45 are made uniform at a pressure of 5 × 10 ⁻³ To
The SiO ₂ layer 51 was formed to a thickness of 100 ° by sputtering under the conditions of rr, high-frequency power of 300 W, and a film forming rate of 27 ° / min. Subsequently, an Al ₂ O ₃ layer 52 having a thickness of 2500 ° was formed on the SiO ₂ layer 51 by sputtering under the conditions of a pressure of 5 × 10 ⁻³ Torr, a high frequency power of 300 W, and a film forming rate of 26 ° / min.

Next, the sample shown in FIG. 15 is immersed in a photoresist stripper (eg, acetone), and the SiO ₂ layer 5 immediately above the photoresist layer 53 together with the photoresist layer 53.
1 and the Al ₂ O ₃ layer 52 were removed to form an SiO ₂ layer 51 and an Al ₂ O ₃ layer 52 having a window A as shown in FIG.

[0032] Next, as shown in FIG. 17, SiO ₂ layer 51
And a part of the upper surface of the i-layer 45 at a portion (window A) not covered by the Al ₂ O ₃ layer 52 and the lower carrier concentration n-layer 44 and the higher carrier concentration n ⁺ layer 43 under a vacuum of 0.04 Torr, Etching was performed with BCl ₃ gas at a high frequency power of 0.44 W / cm ² and a flow rate of 10 cc / min for 40 minutes, followed by dry etching with Ar for 5 minutes. At this time, the Al ₂ O ₃ layer 52 serving as a mask is also etched. The total thickness of the Al ₂ O ₃ layer 52 and the SiO ₂ layer 51 is
This is a thickness that can withstand the etching in the etching of the GaN semiconductor. At the end of the etching of the semiconductor, the Al ₂ O ₃ layer 52 may remain thin without exposing the SiO ₂ layer 51.

Next, as shown in FIG. 18, the SiO ₂ layer 51 remaining on the i-layer 45 was removed with hydrofluoric acid (HF). At this time, even if there are still the Al ₂ O ₃ layer 52 on the SiO ₂ layer 51, with the SiO ₂ layer 51 is peeled off from the i layer 45
The Al ₂ O ₃ layer 52 is removed. At this time, the lower GaN layer is not corroded by hydrofluoric acid. Next, the 19th
As shown in the drawing, an Al layer 54 was formed on the entire surface of the sample by vapor deposition. Then, a photoresist 55 is applied on the Al layer 54, and the photoresist 55 is coated with the high carrier concentration n ⁺ layer 43 and the i layer 4 by photolithography.
A pattern was formed in a predetermined shape so that the electrode portion for No. 5 remained.

Next, as shown in FIG. 19, using the photoresist 55 as a mask, the exposed portion of the lower Al layer 54 is etched with a nitric acid-based etchant to form a photoresist 55.
Was removed with acetone to form an electrode 48 of the high carrier concentration n ⁺ layer 43 and an electrode 47 of the i layer 45.

Thus, the gallium nitride based light emitting device having the MIS structure shown in FIG. 12 can be manufactured. In the dry etching method according to the present embodiment, a silicon dioxide (SiO ₂ ) layer and an aluminum oxide (Al ₂
O ₃ ) layer, and the lowermost photoresist layer is stripped and removed with a photoresist stripper such as an organic solvent to form a mask pattern having a predetermined shape. As described above, since the window of the mask is formed by removing the photoresist, disorder of the window shape such as undercut is prevented.

Aluminum oxide (Al ₂ O ₃ ) substantially functions as a mask. Aluminum oxide (Al ₂
O ₃ ) has almost the same film forming rate as silicon dioxide (SiO ₂ ), but the etching rate by dry etching is 1/3 or less. Therefore, a mask layer having a thickness that can withstand etching may be 1/3 of the thickness of the case where the mask layer is formed of a single layer of silicon dioxide (SiO ₂ ), and the mask formation time is reduced. .

Further, it is necessary to remove the mask layer after the dry etching of the semiconductor, but aluminum oxide (Al ₂ O ₃ )
It is difficult to form a mask with a single layer of aluminum oxide (Al ₂ O ₃ ) because there is no stripping solution to easily remove only the mask. However, in the above embodiment, silicon dioxide (S
Since iO ₂ ) is used, the mask can be easily removed with hydrofluoric acid (HF). Thus, silicon dioxide
(SiO ₂ ) is used for facilitating the removal of the mask, and therefore may be sufficiently thinner than the aluminum oxide (Al ₂ O ₃ ) of the upper layer.

The light emitting diode of the above embodiment has a double layer structure of a low carrier concentration n layer and a high carrier concentration n ⁺ layer in order from the side where the n layer is joined to the i layer. It may be a layer. Further, a double layer structure of a low impurity concentration i-layer and a high impurity concentration i-layer may be used in order from the side where the i-layer is joined to the n-layer.

As described above, the blue light emission intensity of the light emitting diode could be increased by forming the n layer into the double layer structure. In addition, when the i layer has a double-layer structure, the blue light emission intensity of the light emitting diode can be similarly increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an apparatus for realizing an etching method according to a specific embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of an etching sample.

FIG. 3 is a cross-sectional view showing a relationship between an etching sample and a mask.

FIG. 4 is a cross-sectional view showing a relationship between an etching sample and a mask.

FIG. 5 is a cross-sectional view of a sample after etching.

FIG. 6 is a measurement diagram showing an etching rate.

7A is a micrograph showing a crystal structure of a surface of an etched surface of GaN, and FIG. 7B is a plan view showing an outline of an image in the photograph.

FIG. 8 (a) is a micrograph showing the crystal structure of the etched surface of GaN by plasma etching using carbon difluoride (CCl ₂ F ₂ ), and FIG. 8 (b) is an image in the photograph. The top view showing the outline.

9A is a micrograph showing the crystal structure of the etched surface of GaN by plasma etching using carbon difluoride (CCl ₂ F ₂ ), and FIG. The top view showing the outline.

FIG. 10 shows the frequency characteristics of the photoluminescence intensity of GaN before etching.

FIG. 11 shows the frequency characteristics of the photoluminescence intensity of GaN after etching.

FIG. 12 is a configuration diagram showing a specific configuration of a light emitting diode manufactured by using the method of the present invention.

FIG. 13 is a sectional view showing the manufacturing process of the light-emitting diode of the example.

FIG. 14 is a sectional view showing a manufacturing step of the light-emitting diode of the example.

FIG. 15 is a sectional view showing the manufacturing process of the light-emitting diode of the example.

FIG. 16 is a sectional view showing a manufacturing step of the light-emitting diode of the example.

FIG. 17 is a sectional view showing the manufacturing process of the light-emitting diode of the example.

FIG. 18 is a sectional view showing the manufacturing process of the light-emitting diode of the example.

FIG. 19 is a sectional view showing a manufacturing step of the light-emitting diode of the example.

[Brief description of reference numerals]

1 sapphire substrate 2 buffer layer 3 GaN layer 4 mask 10 vacuum chamber 12 introduction pipe 14 mass flow controller 16 cylinder 19 diffusion pump 18 conductance valve 22, 24 electrode 28 high frequency power supply 40 emission diode 41─ sapphire substrate 42─ buffer layer 43─ high carrier concentration n ⁺ layer 44─ low carrier concentration n layer 45─i layer 47,48─ electrode 51─SiO ₂ layer 52─Al ₂ O ₃ layer 53─ photoresist layer

Continued on the front page (72) Inventor Masahiro Kotaki 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Inside (72) Inventor Masaki Mori 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Inside Toyota Central Research Laboratory

Claims (1)

[Claims] 1. A _{Al x Ga 1-x N (} 0 ≦ X ≦ 1) semiconductor dry etching method, the _{Al x Ga 1-x N (} 0 ≦ X ≦ 1) semiconductor,
Al _x Ga _1-x characterized by being etched by a plasma gas of a substance containing substantially no carbon atoms and containing chlorine atoms
A dry etching method for N (0 ≦ X ≦ 1) semiconductor.