JPS60110122A - Etching method of semiconductor - Google Patents

Abstract

PURPOSE:To prevent the generation of other impurity through reaction of internal wall of reaction tube with HF gas not changed to plasma by supplying inactive gas before supplying or after stopping supply of electrical energy for generating plasma. CONSTITUTION:A substrate 1 to be etched is placed on a holder and the substrate inserted to a quartz reaction furnace 2 is heated by a heater from the outside. Plasma is supplied by a high frequency power supply 13 in such a manner that an electrical energy is applied to a pair of mesh type electrodes 3, 3'. The reaction furnace opens respectively the valves 9, 10 with a vacuum pump 11 for the vacuum exhaustion. Thereafter, hydrogen is supplied from 6 and thereby internal pressure of reaction furnace is set to 0.05-3Torr. The valve 14 is then closed, the valve 8 is opened and the HF gas is supplied from 5. Thereafter, an output is applied from the high frequency power supply 13, plasma etching is carried out with the HF gas, the HF gas is stopped and the power supply (electrical energy supply source) is turned OFF. After the reaction tube is brought to the atmospheric condition with hydrogen, the substrate is taken out from the reaction furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for plasma etching a semiconductor whose main component is silicon or silicon carbide, in particular by using hydrogen fluoride (hereinafter referred to as liver) gas to provide high-quality etching after etching. Concerning a method for obtaining a residue-free surface.

In semiconductor device manufacturing processes, as miniaturization and higher integration progress, dry etching including plasma etching has become important.

Conventionally, plasma etching of silicon or silicon compounds uses CF9+ CHF3, CF,3 as a reactive gas.
A plasma etching process is performed using halogenated hydrocarbons such as 11r and adding auxiliary gases such as hydrogen, nitrogen, and oxygen as necessary.

However, if the semiconductor to be etched is a non-single-crystal or single-crystal silicon such as amorphous, or a semiconductor whose main component is silicon such as silicon carbide, C20° CI, Br, etc. may be present at the same time during plasma etching. Some of the radicals are sputtered and mixed in. However, these mixed Br and CI generate recombination centers, and C and O cause insulation.

It is generally believed that fluorine radicals (F) activated by plasma energy are directly related to the etching reaction, and the remaining carbon (C) and chlorine (C)
1) It is said that bromine (Br) and the like do not participate in the reaction and are exhausted. However, among these, carbon is a non-volatile inert substance and is deposited on reaction tube walls, electrodes, sample stands, and sample surfaces. Much of the carbon deposited is chemically active, generally C→-4F-)CF.

Or, as shown by reaction equations such as C + O → Co (in the presence of oxygen), carbon is thought to be immediately removed, but it is nevertheless deposited and mainly forms silicon or silicon carbide compounds after etching. It is known to have an adverse effect on the physical properties of semiconductors as components.

The present invention performs plasma etching using tIF gas that does not contain malignant impurities such as C + CI + Br as a composition, and introduces hydrogen or an inert gas in the pre- or post-process to prevent the inner wall of the reactor and other parts from becoming plasma. So-called liver gas - characterized by preventing the reaction and generation of other impurities.Especially when the reactor is quartz, plasma-formed HF
There is almost no etching in the atmosphere. On the other hand, however, since it reacts with so-called liver gas that has not been turned into plasma, impurities in the quartz are released by etching. In order to prevent etching of the inner walls of such reactors, it has been extremely important to introduce hydrogen, nitrogen or an inert gas into the pre- or post-process.

Since the present invention performs plasma etching using IIF gas, there is no contamination such as C, O, CI, Br, etc. that accompanies conventional etching, and good etched surface and interface properties can be obtained. It will be done. Furthermore, it has been found that preventing surface contamination by IIF gas after etching is important for preventing contamination of the active surface due to liver gas plasma etching. The present invention has the advantage that hydrogen, nitrogen or an inert gas can be introduced into the reactor in a step before or after plasma etching, thereby completing a non-etching plasma process for the first time.

In particular, it is important to clean the semiconductor with an inert gas after etching. By keeping the nitrogen, hydrogen, and inert gases at atmospheric pressure without mixing oxygen or oxides, there is no possibility that impurities, especially oxides, and carbides will adhere to the surface. A clean semiconductor surface could be obtained.

Examples are shown below.

Example 1 FIG. 3 shows an outline of a plasma etching apparatus used in the present invention.

In the drawing, a substrate (1) to be etched is placed on a holder, and the substrate inserted into a quartz reactor (2) is heated from the outside to room temperature to 300°C, for example 100°C, by a heater. Plasma is generated by high-frequency flR (13).
Electrical energy of 3.56M1lz is transferred to a pair of mesh electrodes (3
) and (3'). The reactor is equipped with a vacuum pump (1
According to step 1), the valves (9) and <10) were opened to perform vacuum evacuation, and the pressure was reduced to 10"4 tor'r or less.

After that, 30 cc of hydrogen was supplied from (6) for 7 minutes, and the pressure inside the reactor was adjusted to 0.05 to 3 torr, here 0.5 torr.
It was set as rr. Next, the valve (14) was closed, the valve (8) was opened, and 30 cc of IIF gas was supplied from (5) for 7 minutes.

After that, 40W output was applied from the high frequency power supply (13), and the I
Plasma etching was performed for 10 minutes using IF gas, the liver gas was stopped, the power source (electrical energy supply source) was turned off, and the inside of the reactor was brought to atmospheric pressure with hydrogen, and then the substrate was taken out from the reactor. The substrate is a single crystal silicon substrate with one thermal oxide film.
The silicon oxide film was formed to a thickness of 1,000 mm thick, selectively leaving silicon oxide, and exposing the silicon in some parts. At this time, single crystal silicon can be artificially etched for 5,000 times, and
i02 was hardly etched at a thickness of 100 Å or less. As in this example, silicon could be plasma-etched to a desired extent using 1115 gas without etching much silicon oxide.

FIG. 1 shows the relationship between etching rate and applied power at a temperature of 25°C.

As described above, the etching rates of amorphous silicon (1) and single crystal silicon (2) are 0 when the applied force is 0, but show a peak on the low output side. On the other hand, the etching speed of 5iOz (3) was about 900 people/min when the applied load was O, but when even a small amount of electric power was applied, the etching rate was almost no longer etched.

Furthermore, as shown in Figure 2, as the etching temperature is increased, amorphous silicon (1'>) and single crystal silicon (2'
), the etching speed decreases. On the contrary, SiOyu (3゛)
The etching speed increased slightly as the temperature increased, but the absolute value of the etching speed was small.

As described above, under the conditions of 25° C. and IOW, the selectivity ratio between amorphous silicon or single crystal silicon and 5iOL was as large as 100 or more.

Furthermore, as a result of observing the silicon surface, it was found that the surface had a mirror surface and no residual substances such as carbon were observed.

As explained above, since the method of the present invention uses liver with a purity of 99% or more, after plasma etching, carbon
No chlorine or bromine residue remains on the etched surface.

For this reason, it has become possible to ensure reliability both in the VLSI (ultra integrated circuit) process and in the fabrication of semiconductor devices using amorphous semiconductors.

Additionally, if oxygen or oxide gases are mixed into HF, or if oxides are mixed in after plasma etching, silicon oxide is formed and acts as a mask material for plasma etching, making the etching surface extremely uneven. have done.

For this reason, it was particularly important to have a 1(F purity of 99% or higher) or to introduce non-oxygenates in the post-process to prevent the formation of such local silicon oxides.

In addition, carbide fluorides such as CF Br have their fluorine radicals (
(also called CF radical) has an extremely long lifespan. This has the disadvantage that the oil in the exhaust pump (FIG. 3 (11)) deteriorates, reducing accuracy and making vacuuming impossible. On the other hand, when using the IF (method of the present invention), another feature is that the deterioration in oil accuracy is not observed even after 100 hours of use.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between etching rate and applied power at 25° C. for I11' gas plasma etching. Figure 2 shows plasma power 10 for liver gas plasma etching.
The relationship between etching rate and temperature in W is shown. FIG. 3 shows an outline of the plasma etching apparatus used in the present invention. Patent applicant: Semiconductor Energy Research Institute, Inc. Representative: Shun Yamazaki Applied t1:l(w) Makoto 11blade 0 100 200 Warm (°C)

Claims (1)

[Claims] 1. In plasma etching a semiconductor whose main component is silicon or silicon carbide using hydrogen fluoride gas, a pre-process of supplying electrical energy for plasma generation or supplying said energy A post-semiconductor etching method characterized by introducing an inert gas such as hydrogen, nitrogen, argon or helium after stopping. 2. In claim 1, hydrogen fluoride gas is 9
A semiconductor etching method characterized by having a purity of 9% or more. 3. A semiconductor etching method according to claim 1, characterized in that after stopping the supply of electrical energy for plasma generation, an inert gas such as hydrogen, nitrogen, argon, helium, etc. is introduced to bring the etching pressure to atmospheric pressure. .