JPH08203878A - Amorphous Si etching method and semiconductor device manufacturing method using the etching method - Google Patents

Abstract

(57) [Summary] [Purpose] Large a-Si / SiO₂Etching rate
Etching of amorphous Si that can achieve a high ratio
Method and semiconductor device using this etching method
A manufacturing method is provided. [Configuration] The temperature of the object to be etched is set to 45 ° C. or higher, and
CF as etching gas _Four/ O₂The mixed gas of
RF (high frequency) power applied per unit area of pole
Density is 0.66W / cm²Atmosphere converted to plasma
Dry etching with.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device such as a photodiode or a semiconductor laser element, and more particularly to Si.
The present invention relates to a method of selectively etching amorphous Si (hereinafter abbreviated as a-Si) with respect to O ₂ .

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, selective etching with an underlying film is an important elemental technology in view of etching processing. Among them, the technology of selectively etching a-Si with respect to SiO ₂ is not necessary. It's a big one. a-
As an etchant for wet etching capable of etching Si, hydrofluoric acid can be mentioned.
The iO ₂ , InP and GaAs are also etched. Also,
When dry etching a-Si, SF ₆ can be used as an etching gas.
Since the etching rate of iO ₂ and a-Si is about 1: 2 and there is no big difference, it is not suitable for selective etching of SiO ₂ and a-Si.

[0003]

The object of the invention is to be Solved for the SiO ₂ a-
It is difficult to selectively etch Si at a large etching rate, and if only a-Si of the a-Si / SiO ₂ multilayer film is selectively etched, there is a problem that the SiO ₂ film is damaged.

[0004]

The present invention provides an a-Si etching method which solves the above problems, in which the temperature of the object to be etched is 45 ° C. or higher, and the etching gas is CF ₄ / O ₂ . RF (high frequency) power density applied per unit area of electrode is 0.6 using mixed gas
The first invention is dry etching in a plasma atmosphere of 6 W / cm ² or more. Further, by using the etching method of the invention, an amorphous Si film and a SiO ₂ film are formed.
A second invention is a method of manufacturing a semiconductor device, which includes a step of changing a high reflection film formed of a film to a low reflection film at least partially.

[0005]

The present invention is based on the new knowledge obtained from the earnest experiments. That is, the temperature of the object to be etched is set to 45 ° C. or higher, a mixed gas of CF ₄ / O ₂ is used as an etching gas, and the RF power density is 0.66 W / cm ^2.
When dry etching is performed in the above plasma atmosphere, a-Si can be selectively etched with respect to SiO ₂ at a large etching rate. The temperature of the object to be etched is 45 ° C. or higher, and the RF power density is 0.66.
If it is W / cm ² or more, a large a is obtained in the temperature range and the RF power density range in which normal dry etching is performed.
It is possible to realize a -Si / SiO ₂ etch rate ratio. Further, by using this etching method, the manufacturing process of the semiconductor device having the high reflection film and the low reflection film can be simplified.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. A plasma CVD apparatus is used, and a mixed gas of CF ₄ / O ₂ is used as an etching gas.
The etching rate of a-Si with respect to SiO ₂ was measured while changing the F power density. Here, the mixed gas of CF ₄ / O ₂ contains O ₂ with a concentration of about 10%, and the flow rate is 400 scc.
m and pressure were 133 Pa. Also, the electrode substrate spacing is 2
It was 0 mm.

FIG. 1 shows the RF power and a-Si / when the substrate to be etched, which is an InP substrate, is at room temperature.
The relationship between the SiO ₂ etching rate ratios is shown. As can be seen from FIG. 1, when the RF power exceeds 0.57 W / cm ² , the etching rate ratio increases to 0.66 W / c.
Above m ² , the etching rate ratio reaches about 6 and is almost constant.

FIG. 2 shows an RF power of 0.665 W / cm.
Object to be etched substrate temperature when the ² and a-Si / S
The relationship between the iO ₂ etching rate ratios is shown. As shown in FIG. 2, the etching rate increases with the substrate temperature, but when the substrate temperature is 45 ° C. or higher, the etching rate sharply increases.
When the substrate temperature is 50 ° C., a high etching rate ratio of about 28 times can be realized. A-Si at this time
The etching rate was 3.5 nm / sec. Further, the etching rate of the InP substrate itself at this time was below the measurement limit. Therefore, the above etching conditions can be applied to the selective etching of a-Si with respect to the InP substrate.

Hereinafter, a photodiode (hereinafter, referred to as PD) is formed by using the a-Si selective etching method according to the above method.
An example in which the manufacturing process is simplified will be shown. The PD described here has a non-reflective coating on the light-receiving portion and a high-reflective coating on the portion other than the light-receiving portion in order to obtain a high light-reception sensitivity ratio between the light-receiving portion and other portions. This element is effective when performing alignment with an optical fiber in an automatic alignment device.

3A to 3D are explanatory views of the manufacturing process of the PD, and the process is as follows. That is, 1) First, the n-InP substrate 1 is formed by metalorganic vapor phase epitaxy.
On top, n-InP buffer layer 2 and undoped InGa
The As light absorption layer 3 and the n-InP window layer 4 are sequentially grown (FIG. 3A). 2) Next, a Zn diffusion region 5 is formed by vapor phase or solid phase diffusion to a position where it enters the light absorption layer 3, and then a SiO _x film 6 and an a-Si film 7 are formed to 1/4 in optical thickness by PCVD method.
A film having a thickness corresponding to the wavelength is formed (FIG. 3B). Wavelength 1.3
In the case of μm, the film thickness of the SiO _x film 6 is about 220 nm, a−
The Si film 7 is about 100 nm. This gives a reflectance of about 80% on the surface of the epitaxial wafer. 3) Next, cover the part other than the blind part with a resist mask 8,
Only the a-Si film 7 is etched using the plasma CVD apparatus by the method described above (FIG. 3C). The time required for etching at this time was about 35 seconds. As a result, only the SiO _x film 6 having a thickness corresponding to a quarter wavelength of the optical film thickness remains in the cutout portion, and the reflectance of this portion becomes about 4%. 4) Further, the SiO _x film 6 in the peripheral portion of the cutout portion is removed by photolithography and wet etching, and p
The electrode 9 is formed, and the n-electrode 1 is formed on the back surface of the n-InP substrate 1.
0 is formed into a device (FIG. 3D).

By adopting such a step, the step of forming the low reflection film again after forming the high reflection film can be omitted, and the process can be performed with the surface of the light receiving portion protected by the SiO _x film. You can proceed.

[0012]

As described above, according to the method for etching amorphous Si of the present invention, the temperature of the object to be etched is set to 45 ° C. or higher, and CF ₄ / O is used as the etching gas.
_In order to perform dry etching in a plasma atmosphere in which the RF (high frequency) power density applied per unit area of the electrode is 0.66 W / cm ² or more using the mixed gas of ² ,
There is an excellent effect that a large a-Si / SiO ₂ etching rate ratio can be realized. Further, the use of this etching method has an effect that the manufacturing process of a semiconductor device having a high reflection film and a low reflection film can be simplified.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between RF power and a-Si / SiO ₂ etching rate ratio.

[FIG. 2] Substrate temperature to be etched and a-Si / SiO ₂
It is a figure which shows the relationship of an etching rate ratio.

3 (a) to 3 (d) are explanatory views of a manufacturing process of a PD using an embodiment of the method for etching amorphous Si according to the present invention.

[Explanation of symbols]

1 substrate 2 buffer layer 3 the light-absorbing layer 4 window layer 5 Zn diffusion regions 6 SiO _x film 7 a-Si film 8 resist mask 9 p electrode 10 n electrode

Claims (2)

[Claims] 1. An RF (high frequency) applied per unit area of an electrode, wherein a temperature of an object to be etched is 45 ° C. or higher, a mixed gas of CF ₄ / O ₂ is used as an etching gas.
A method for etching amorphous Si, characterized by dry etching in a plasma atmosphere having a power density of 0.66 W / cm ² or more. 2. A method of manufacturing a semiconductor device, comprising the step of changing a highly reflective film composed of an amorphous Si film and a SiO ₂ film at least partially into a low reflective film by using the method for etching amorphous Si according to claim 1. Method.