JPH0651915B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an etching method using NF ₃ .

Reactive ion etching using a parallel plate electrode type reactor is used to obtain highly accurate etching required in the LSI process. In the etching, high selectivity, high etching speed and anisotropic etching are required. At present, particularly in the silicon gate technology, high selectivity of etching Si on SiO ₂ and high etching speed are drawing attention.

The study of etching silicon with NF ₃ was first carried out by Eisele, Ianno, etc. in 1980. Eisel has found that NF ₃ is a powerful etching agent for Si, while etching a little SiO ₂ . The Iano etc. compares the etching of the discharge in CF ₃ and NF _3, reported on the reaction mechanism regarding the negative ions occur through cowpea in NF ₃ discharge.

Bower recently compared the etching of polycrystalline silicon on SiO ₂ with CCl ₄ and NF ₃ to show that CCl ₄
It is reported that the etching pattern was almost isotropic in the case of NF ₃ as compared with the above, but the etching pattern was almost isotropic.

Although the etching of Si by NF ₃ is known as described above, the present inventors have a method of further increasing the etching rate of Si relative to the etching rate of SiO ₂ , that is, Si and
We have conducted intensive studies on a method of increasing the etching rate ratio of SiO ₂ and a method of obtaining an excellent anisotropic etching pattern even at a high etching rate.

Then, reactive ion etching with NF ₃ was performed under conditions of various pressures and gas flow rates using a parallel plate electrode type reactor.High selectivity of etching, high etching rate and It has been found that excellent anisotropic etching is achieved.

The present invention is an etching method for etching Si with NF ₃ under parallel plate electrode discharge, wherein the pressure of NF ₃ is 20 to 130 Pa and the flow rate of NF ₃ is 0.1 to 0.4 sccm.
The present invention relates to an etching method characterized by being performed under the condition of / cm ² .

The present invention will be described in detail below. FIG. 1 shows a parallel plate electrode type reaction device (SPF-210B,
It is a system diagram of NEVA and Nichiden Varian Co., Ltd. The diameter of the stainless steel electrode (1) is 10 cm. (1a) is a cathode and (1b) is an anode, and the distance between both electrodes is 6 cm. (2) is a trap using liquid N ₂ , (3) is an oil diffusion pump, and the etching agent is 1 × 10 ⁻³ Pa (pascal).
The following vacuum can be applied. (4) is a rotary vacuum pump. Water can be removed by heating the room to 200 ° C. The NF ₃ gas is introduced through the inset between the electrodes. The gas pressure was measured with a Pirani gauge (5) and a Schultz gauge (6). (7) is an alternating high frequency voltage generator.

Si and SiO ₂ are used as an object to be etched, a p-type of a (100) plane Si wafer is used as a Si sample, and a Si wafer having a diameter of 2 inches is 1200 as a sample of SiO _2.
The one which was thermally oxidized at 0 ° C. to form a SiO ₂ film of about 1 μm was used. The sample was placed on the cathode (cathode), and the cathode was cooled to 120 ° C. or lower with cooling water.

Next, FIG. 2 shows the pressure dependence of the etching characteristics. That is, Table 2 shows the results of measuring the etching rate of NF ₃ of Si and SiO ₂ under various pressures using a parallel plate electrode type reactor having an inner diameter of 25 cm. The flow velocity, high frequency, and output of NF ₃ are 100 sccm (standard cubic centim), respectively.
eter per minute, 0.2sccm / cm ² per unit area) and
13.56MHz, 50W, Etching time is about 0.5-2
0 minutes. From FIG. 2, the etching rate of Si increases with the increase of the pressure of NF ₃ , increases sharply from around 20 Pa, reaches its maximum around 70 Pa, and then decreases rapidly. On the other hand, the etching rate of SiO ₂ is much less dependent on the pressure of NF ₃ . Therefore, considering the etching speed ratio of both Si and SiO ₂ , the preferable pressure range is 20 to 130.
Pa, and an even more preferable range is 30 to 100 Pa.

3 and 4 show the dependence of the NF ₃ gas flow rate on the etching rates of Si and SiO ₂ . NF ₃ pressure is 40, 70
Alternatively, it was set to 130 Pa, the high frequency was 13.56 MHz, the output was 50 W, and the etching time was about 0.5 to 20 minutes. As a result of changing the gas flow rate in the range of 0.1 to 0.8 sccm / cm ² ,
From the figure, the etching rate of Si increased rapidly with the increase of the NF ₃ flow rate. However, when the flow velocity exceeded 0.4 sccm / cm ² , the etching pattern changed from anisotropic to isotropic. On the other hand, the etching rate of SiO ₂ did not change much with the change of gas flow rate, but rather decreased with the increase of flow rate. Therefore, in view of the etching speed ratio and the etching pattern of both, the preferable NF ₃ flow rate is 0.1 to 0.4 sccm /
The range of cm ² is 0.15 to 0.3 sccm / cm ² , and the particularly preferable range is 0.15 to 0.3 sccm / cm ² , and the maximum value of the etching speed ratio of both reached 100 or more by selecting the conditions.

The etching method of the present invention is characterized in that it is carried out under the conditions of the pressure and flow velocity of the specific NF ₃ gas as described above. still,
The etching method can be carried out according to the usual etching method using NF ₃ , for example, placing a sample on the cathode of a parallel plate electrode type reactor and adjusting the pressure and flow rate of NF ₃ for high frequency electrolysis on both electrodes. Can be applied. The high frequency is preferably in the range of about 0.1 to 100 MHz, and the output is preferably in the range of about 0.1 to 1 W / cm ² .

The present invention will be described below with reference to Examples and Comparative Examples.

Example 1 Under conditions of a pressure of NF ₃ of 70 Pa, a flow rate of 0.20 sccm / cm ^{2, a} high frequency of 13.56 MHz, and an output of 50 W, an Al vapor deposition film was used as a mask material for a line and space pattern.
When etching of Si was carried out for 5 minutes, an etching rate of 0.2 μm / min was obtained. The etching pattern at this time is shown in FIG. 5, and it was a clean anisotropic pattern.

Comparative Example 1 Etching of Si was carried out for 1 minute in the same manner as in Example 1 under the conditions of a pressure of NF ₃ of 70 Pa, a flow rate of 0.82 sccm / cm ^{2, a} high frequency of 13.56 MHz and an output of 50 W, and the etching speed was 2.3 μm. / min, but the etching pattern is the sixth
As shown in the figure, the pattern was isotropic.

[Brief description of drawings]

FIG. 1 is a system diagram of a parallel plate electrode type reactor, FIG. 2 is a graph showing NF ₃ pressure dependence of etching speed, and _{3 to} 4
The figure is a graph showing the dependency of the etching speed on the NF ₃ flow rate, and FIGS. 5 to 6 are sectional views of the etching patterns obtained in Example 1 and Comparative Example 1, respectively.

Claims (1)

[Claims] 1. An etching method for etching Si on SiO ₂ by NF ₃ under parallel plate electrode discharge, comprising:
₃ pressure is 20 ~ 130Pa, NF ₃ flow rate is 0.1 ~.
An etching method characterized in that the etching is performed under a condition of 0.4 sccm / cm ² .