JPS6044825B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an etching method suitable for selective etching using a photoresist as a mask during the manufacture of semiconductor devices.

2. Description of the Related Art In the manufacturing process of semiconductor devices, it is known to perform selective etching by ion beam etching using a photoresist as a mask to form patterns of semiconductors, various insulating films, and metal films.

Ion beam etching is performed by irradiating an ion beam of an inert gas such as argon, and is suitable for forming fine patterns because the side etching phenomenon is minimal. However, in ion beam etching, there is no difference in the etching speed for different materials, and photoresist, which is normally used as an etching mask, is removed at the same speed as the etched materials such as semiconductors and various insulating films. Therefore, when the etching depth is large, the resist film thickness is required to be equal to or greater than the etching depth, and it becomes difficult to miniaturize the photoresist pattern used as a mask, so that the original advantage cannot be fully exploited. Therefore, the present invention aims to provide an ion beam etching method in which the etching rate is selective depending on the material.
In particular, it is an object of the present invention to provide an etching method suitable for forming fine patterns by selectively etching polycrystalline silicon using a photoresist as a mask.

In the etching method of the present invention, polycrystalline silicon is
It is characterized by being placed in a 3 to 10-4 Torr(7) Cl2 or CF4 gas plasma, irradiating polycrystalline silicon with an ion beam, and performing an etching process using a photoresist as a mask. Explain in detail. FIG. 1 shows one side of an etching apparatus for carrying out the etching method of the present invention.

This etching apparatus has a sample support stage 3 in a vacuum container 1, as well as a plasma generation power source 4 and a plasma generation electrode 5, like a normal ion beam etching apparatus. The plasma generating electrode 5 may be arranged outside the container 1, and may be of an inductive type instead of the dielectric type shown in FIG. When the plasma generation electrode 5 is of a dielectric type as shown in FIG. 1, the plasma generation power source 4 may be not only a high frequency power source but also a direct current or low frequency power source. When etching is performed using the apparatus shown in FIG. 1, the substrate 6 to be processed is placed on the support stand 3, the pressure inside the vacuum container 1 is reduced, and halogen gas, halogen compound gas, or a mixture thereof is introduced. The gas is introduced through the port 7 and the gas plasma is generated by the plasma generation power source 5 and the electrode 4, and an ion beam is generated from the ion gun 2 and irradiated onto the substrate 6.

The halogen gas to be introduced is preferably chlorine gas, and the halogen compound gas is preferably halogenated carbon compound gas such as CF4, CCl4, CCl2F2, and the pressure in the container 1 is 10-3 to 10-4T0rr or lower. It is desirable to do so. This gas is preferably continuously supplied from the gas inlet 7 during the etching process and exhausted from the gas outlet 8 to maintain the pressure within the container 1 at the above-mentioned level. Although any ion source can be used, it is preferable to use an inert gas such as argon in order to prevent damage to the ion gun. High-energy ions such as argon coming from the ion gun 2 collide with halogen or halogen compound plasma particles and impart kinetic energy, so that the plasma particles also impact the substrate 6 with directionality.

Therefore, the amount of etchant that wraps around under the edges of the photoresist used as a mask is small, and only a small amount of side etching occurs. Furthermore, since the halogen or halogen compound gas plasma etches the photoresist only slowly, there is no need to make the photoresist as a mask thicker. For example, when selectively etching polycrystalline silicon using CF4 plasma as a gas plasma, the etching rate of polycrystalline silicon reaches 10 to 2 times that of photoresist. Therefore, a thin photoresist film can be used as a mask, making it easy to form fine patterns. After etching is completed. Generation of the ion beam is stopped, oxygen is introduced from the gas inlet 7, and the vacuum vessel 1 is
By creating an oxygen atmosphere of 10 -3 to 10 -4 T0rr inside, and generating oxygen plasma, the semiconductor substrate 6 and the insulating film, metal film, etc. on its surface can be etched without etching. Only otoresist can be removed rapidly.
FIG. 2 shows another example of an etching apparatus used in the etching method of the present invention, in which the same parts as those in the apparatus of FIG. 1 are designated by the same numbers.

This apparatus differs from the apparatus shown in FIG. 1 in that the plasma generation chamber 9 is provided apart from the substrate placement section. Further, this device uses an induction type generator for plasma generation, and generates plasma by passing a high frequency current from the plasma generation power source 4 to the high frequency coil 10.
In order to guide the gas plasma generated in the plasma generation chamber 9 onto the substrate 6, a gas inlet 7 and a gas outlet 8 are used as shown in the figure.
halogen and/or halogen compound gas may be introduced and discharged continuously. In order to improve the uniformity of etching within the substrate 6, it is desirable to rotate the sample support stage 3. With this apparatus, etching can be carried out in the same manner as the etching apparatus shown in FIG. 1, and fine patterns can be formed by selective etching using a photoresist as a mask. Next, the effects of the etching method of the present invention will be explained using examples.

In Fig. 3a, a 3-inch silicon substrate is thermally oxidized at 400A, non-doped polycrystalline silicon 11 is grown at 5000A, AZl35OJ resist is applied on this to a thickness of 1.8μm, and exposed and developed to obtain a resist pattern 12 with a width of 2μm. This is a cross-section of the object. In addition, due to film peeling due to exposure and development,
The resist film thickness at this point was 1.4 μm. Third
The pattern in Figure a was etched using an argon ion beam etching system at a pressure of 2 x 10-4T0rr1 and an ion voltage of 50.
When two powder etching was performed under the conditions of 0V1 ion current density and 0.75n1A/CIL, the polycrystalline silicon was etched.

The remaining resist film at this time was 5000 Å, and the cross section of the pattern was as shown in FIG. 3b. The cross section of the pattern has a tapered shape due to the large amount of resist being reduced.

The etching rate of polycrystalline silicon at this time was 250A.
/771. The selectivity for the in1 resist was 0.56. Figure 3c shows a 3-inch silicon substrate thermally oxidized at 400A, and then non-doped polycrystalline silicon 11 is applied at 5000A.
A is grown, and 1.2μ of AZl35OJ resist is applied on top of this.
A cross section of a resist pattern with a width of 1.5 μm obtained by coating the resist pattern with a resist pattern of 1.5 μm and developing it with light is shown.

Due to film wear due to exposure and development, the resist film thickness at this point was 1.12 μm.

Next, the pattern shown in FIG.
When etching was carried out for 3 minutes at an output of 200 W, the remaining resist film was 1.0 μm and the cross section of the pattern was as shown in FIG. 3d.

The etching is isotropic and undercut.

The etching rate of polycrystalline silicon at this time was 1300.
At A/Min, the selectivity to resist was 4.2.

FIGS. 3E and 3F show cross sections of the resist pattern shown in FIG. 3C, which has been etched using the apparatus shown in FIG. 2 of this specification.

The wafer is held perpendicular to the argon ion beam and Cl. Introduce gas, pressure 1.5 x 10-2
When an argon ion beam with an ion voltage of 500 V and a current density of 0.75 mA/CIL was irradiated with plasma discharge at T0rr and I00W, the polycrystalline silicon was etched in one shot.

At this time, the remaining resist film was 1.1 μm, and the cross section of the pattern was as shown in FIG. 3e. The etching is isotropic and undercut.

The etching rate of polycrystalline silicon at this time was 500A.
/Min, and the selectivity to resist was 25.

Figure 3f shows a cross section of the pattern to which the etching method of the present invention is applied.The wafer is held perpendicular to the argon ion beam, CI2 gas is introduced from the inlet, and the pressure is 8 x 1.
0-4T0rr1 Plasma discharge with output 100W, ion voltage 500, current density 0.75TT1A/Cr
The polycrystalline silicon was etched in 12 minutes when irradiated with 1 liter of argon. The etching was anisotropic and a vertical cross section was obtained. The etching rate at this time was 420A.
/Minl resist was 12.5. Similarly, etching was carried out by introducing Cl2 gas through the inlet and changing the pressure. The results are summarized in Table 1.

At 8.times.10@-6 T0rr, the etching rate became small because a sufficient ion current could not be obtained.

For 8×10 −4 T0rr and 8×10 −5 T0rr, patterns with vertical cross-sectional shapes and conforming to the mask pattern were obtained.

Next, Tables 2 and 3 show the results when the gas for forming the gas plasma was changed to chlorine, SF6, and CF4+02 (10%), respectively.

Among the above examples, a pattern (aspect ratio 0.33) having a substantially vertical cross-sectional shape as shown in FIG. 3F by the method of the present invention and conforming to the mask pattern was obtained.

As is clear from the above description, according to the present invention, selective etching can be performed without using a thick photoresist as a mask, and the side etching phenomenon can be suppressed, so there is an advantage that fine patterns can be formed. can get.

[Brief explanation of the drawing]

1 and 2 show an example of an etching apparatus used to carry out the etching method of the present invention. FIG. 3 shows an explanatory diagram for showing the effects of the present invention. In the drawing, 2 is an ion gun, 4 is a plasma generation power source, and 5 is an ion gun.
1 is a plasma generation electrode, 6 is a substrate to be processed, and 10 is a plasma generation coil.

Claims (1)

[Claims] 1 Polycrystalline silicon 10^-^3~10^-^4To
placed in a Cl_2 or CF_4 gas plasma of rr;
An etching method characterized in that the polycrystalline silicon is irradiated with an ion beam and etching is performed using a photoresist as a mask.