JPH01291428A - Taper etching of silicon film - Google Patents

Abstract

PURPOSE:To accurately form a taper shape of the side end of a silicon film with good reproducibility by introducing mixture gas into a chamber, generating a plasma to produce ions, further applying a high frequency voltage with specific power, and etching the silicon film of a sample. CONSTITUTION:When the pressure of mixture gas becomes constant, a microwave oscillated by a magnetron 5 is transmitted into a chamber 2. A current flows to a coil 7 surrounding the chamber 2 to generate a magnetic field in the chamber 2. A plasma is generated in the mixture gas to generate ions by the synergistic operation of the magnetic field and an electric field by the microwave. Further, a high frequency voltage is applied by a high frequency power source 8 to a sample base 3 to accelerate the ions, thereby etching the silicon film 11 of a sample 1 to be etched. In this case, the power of the high frequency to be applied to the base 3 to accelerate the ions is set to 150 to 400W, thereby forming the shape of the side end 11a of the film 11 in a tapered state.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a dry etching method, and more specifically, a taper etching method for etching a silicon sample to be etched so that the side edges of the sample are tapered. Regarding the etching method.

<Prior Art> In the semiconductor manufacturing process, as shown in the cross-sectional view of FIG. 4(a), an oxide film 52. After sequentially forming a thin film 53 and forming a pattern of a resist 54 to serve as an etching mask on the thin film 53, a dry etching process is performed as shown in FIG. 4(b).
The film 53 is etched. At this time, if the side edge 51a of the silicon film 51 is in a vertical state, etching residue 55 will be generated on the side edge 51a, which will cause a short circuit between elements and destroy the function of the device. There was a problem.

One way to prevent the etching residue 55 from occurring is to make the side end 51a of the silicon film 51 tapered. Conventionally, methods for making the side edges 51a tapered include adding oxygen to etching gas and recessing the side edges of the resist, or undercutting by wet etching. There is a method of forming a tapered shape using this method.

The cross-sectional view in FIG. 5 shows a taper etching method that utilizes the recession of the resist. According to this method, the resist 56 is removed by adding oxygen to the etching gas.
The etching speed of the side edges 5 of the resist 56 increases.
The amount of retraction of 6a increases. As the side end 56a of the resist 56 recedes, the side end 51a of the silicon film 51 becomes tapered.

The cross-sectional views in FIGS. 6(a), 6(b), and 6(c) show a process in which a tapered shape is obtained by using both wet etching and try etching. Silicon film 51 and N
Of the thin films having a two-layer structure with the SC film (non-doped CVD oxide film) 57, the NSC film 57 is first wet-etched with a 5% HF solution using the resist 56 as a mask.

Wet etching is isotropic etching, so NS
A large undercut occurs in the C film 57 as shown in FIG. 6(b), creating a space 58, and the side edge S7
a has a tapered shape. Next, when the silicon film 51 is etched using a dry etching method, the above-mentioned space 58 exists between the resist 56 and the silicon film 51.
As shown in Figure (c), the side end portion 51a of the silicon film 51 is tapered.

<Problems to be Solved by the Invention> However, in the conventional taper etching method described above, the amount of side etching on the upper part of the taper becomes large, which may cause defects in the pattern or cause problems in the size and shape of the pattern. The disadvantage was that it was difficult to control.

SUMMARY OF THE INVENTION An object of the present invention is to provide a taper etching method capable of eliminating the above-mentioned drawbacks and forming a tapered shape at the side end portion of a silicon film with high precision, good controllability, and good reproducibility.

<Means for Solving the Problems> The present invention provides a method of dry etching that forms the side edges of a silicon film into a tapered shape when etching a silicon film of a sample to be etched placed on a sample stage in a chamber. It's a method. In order to achieve the above purpose, a gas mixture of a gas that acts on etching and a gas that acts on deposition is introduced into the chamber, and the mixed gas is interacted with a magnetic field and an electric field generated by microwaves. By turning into plasma and generating ions, the ions are accelerated by applying a high frequency voltage with a power of 150 to 400 W to the sample stand, thereby etching the silicon film of the sample on the sample stand.

<Operation> By changing the power of the high frequency, the conversion difference from the resist, that is, the dimension of the bottom of the etched silicon film with respect to the resist dimension changes. By setting this high frequency power in the range of 150 to 400 W, the conversion difference from the resist becomes a positive value, that is, the bottom dimension of the silicon film becomes larger than the resist dimension, and the side edges of the silicon film become larger. Becomes tapered.

<Example> Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic diagram of a microwave plasma etching apparatus used to carry out the taper etching method of the present invention. A ready-made device can be used as this microwave plasma etching device.

First, the sample 1 to be etched is placed on the sample stage 3 in the chamber 2, and then evacuated by the vacuum evacuation device 4. After the inside of the chamber 2 reaches a predetermined pressure, a gas that acts on etching, such as S, is introduced from a gas inlet (not shown).
F, and a gas acting on the deposition, e.g. C2C1
2F, which mixed gas to introduce. The advantages of using such a fluorine-based gas include: (1) It is easy to handle, (2) It does not corrode piping unlike chlorine-based gas, and (2) There are fewer exhaust gas regulations than chlorine-based gas.

Next, when the pressure of the mixed gas becomes constant,
Microwaves of 2.45 Gtlz oscillated by the magnetron 5 are sent into the chamber 2 through the waveguide 6. Further, a current is passed through the coil 7 surrounding the chamber 2 to generate a magnetic field of 875 gauss within the chamber 2.

The interaction between this magnetic field and the electric field generated by the microwave turns the mixed gas into plasma and generates ions.

Further, a high frequency voltage is applied to the sample stage 3 by the high frequency power source 8 to accelerate the ions, as shown in FIG. 2(a).
) and (b), the silicon film 11 of the sample 1 to be etched is etched.

FIG. 2(a) is a cross-sectional view showing an example of a sample 1 to be etched before etching. As shown in FIG. Form an oxide film 13 and further LPC
A silicon film 11 made of polysilicon is grown to a thickness of 100 OA by the VD method, and a resist 14 is patterned thereon by photolithography.

And SF, gas flow rate 73CCM, C10 sentence 2F
4 gas flow rate 633CCM, etching pressure 10m
Torr, the microwave power was set to 3SOW, and the high frequency power applied to the sample stage 3 was varied in the range of 50 to 400 W to perform etching of the silicon film 11.

FIG. 2(b) is a sectional view showing an example of the sample 1 to be etched after etching. By changing the high frequency power, the conversion difference from the resist, that is, the dimension Y of the bottom of the etched silicon film 11 with respect to the resist dimension X changes.

FIG. 3 is a characteristic diagram showing changes in the conversion difference from the resist with respect to changes in the high frequency power. When patterning the silicon film 11 by a normal dry etching method, the value of the conversion difference is O or negative, that is, the dimension Y of the bottom of the silicon film 11 is equal to or smaller than the resist dimension X. However, as shown in FIG. 3, when the high frequency power is 150 to 400 W, the conversion difference from the resist has a positive value, that is, the bottom dimension Y of the silicon film 11 becomes larger than the resist dimension X, and the silicon The side end portion 11a of the membrane 11 also has a tapered shape. This is considered to be because the etching prevention effect of the deposition film is stronger than the etching effect of the ions.

As mentioned above, in the dry etching of the silicon film 11 using the microwave plasma etching apparatus, the high frequency power applied to the sample stage 3 to accelerate the ions is 1.
By using 50 to 40 openings W, the side end portion 11a of the silicon film 11 can be tapered as shown in FIG. 2(b). Moreover, it is also possible to control the taper shape of the side end portion 11a by changing the high frequency power within the range of 150 to 400W.

(Effects of the Invention) As explained in detail above, according to the taper etching method of the present invention, the side edges of the silicon film can be tapered with high precision, good controllability, and good reproducibility without undercutting. It can be etched. Moreover, it can be carried out by a simple process using an off-the-shelf microwave plasma etching apparatus.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a microwave plasma etching apparatus used to carry out the present invention, and Figures 2 (a) and (b).
) is a cross-sectional view showing the state of the sample to be etched before and after etching, FIG. 3 is a characteristic diagram showing changes in conversion difference from the resist with respect to changes in high-layer power, and FIGS. 4(a) and (b) are , a cross-sectional view illustrating etching residues at side edges of a silicon film. FIG. 5 is a sectional view illustrating a conventional example, and FIG. 6 is a sectional view illustrating another conventional example. 1... Sample to be etched, 11... Silicon film. 11a...Side end portion, 2...Chamber. 3...Sample stand. 0 100 200 3C0400 (W14A
MiPor, ShaFigure 3Figure 4Figure 5Figure 6

Claims (1)

[Scope of Claims] A dry etching method for forming side edges of a silicon film in a tapered shape when etching a silicon film of a sample to be etched placed on a sample stage in a chamber, the method comprising: A mixed gas of a gas that acts on etching and a gas that acts on deposition is introduced into the chamber, and the mixed gas is turned into plasma by interaction with a magnetic field and an electric field generated by microwaves to generate ions. A silicon film taper etching method, characterized in that the silicon film of the sample on the sample stage is etched by applying and accelerating a high frequency voltage with a power of 150 to 400 W to the sample stage.