JPH0121230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma etching method capable of microfabrication of polycrystalline silicon using plasma of a reactive gas generated by high frequency discharge.

In recent years, a plasma etching method that utilizes plasma generated by high-frequency glow discharge of Freon gas or the like has been widely used as a silicon microfabrication method in the manufacturing process of semiconductor devices.

For plasma etching of polycrystalline silicon
Gases such as CCl ₄ , CCl ₃ F, CCl ₂ F ₂ , CClF ₃ and CF ₄ are often used. The biggest problem with etching using these gases is undercuts. The degree of undercutting varies depending on the etching conditions such as the degree of vacuum, the type of etching gas, and the material of polycrystalline silicon. For example, in the case of CF ₄ or CClF ₃ , undercuts occur that are at least as thick as the polycrystalline silicon film, regardless of the material of the polycrystalline silicon.
In CCl ₄ , CCl ₃ F, and CCl ₂ F ₂ , the degree of undercut is smaller than in the case of CF ₄ and CClF ₃ . However, the amount of undercut is affected by the amount of impurities such as P and As in polycrystalline silicon. Furthermore, the higher the degree of vacuum, the smaller the undercut tends to be.

However, according to the conventional method using such a gas, in the best case, a polycrystalline silicon film with a thickness of 0.5 μm is etched and the undercut is reduced to 0.1 μm.
It was difficult to suppress it below.

On the other hand, semiconductor integrated circuits require increasingly finer patterns, and therefore the requirements for undercuts are also becoming more severe. For example, if the pattern width is 0.7 to 0.8 μm, the amount of undercut
It is thought that the demand for 0.05 μm or less will definitely arise in the near future. Therefore, how to reduce the size of the undercut has become extremely important in etching technology.

Therefore, it can be said that the above-mentioned drawbacks of the prior art are fatal to the etching process in the manufacture of semiconductor integrated circuit devices.

In order to solve these drawbacks, the present invention uses a mixed gas containing at least one of CCl ₄ , CCl ₃ F, CCl ₂ F ₂ , CClF ₃ and CF ₄ and H ₂ as a reaction gas. This provides a plasma etching method that maintains an appropriate etching rate for polycrystalline silicon and eliminates side etching.

In order to achieve the above object, the present invention has an etching chamber equipped with a sample electrode on which a sample to be etched is placed and a counter electrode facing the sample electrode. In the method of etching the sample to be etched using gas plasma generated by applying a high frequency voltage to both the electrodes while maintaining the degree of vacuum in the etching chamber, the reaction gas contains at least CCl ₄ , CCl ₃ F,
At least one of CCl ₂ F ₂ , CClF ₃ and CF ₄
The gist of the invention is a plasma etching method characterized by using a mixed gas containing seeds and H ₂ and in which the amount of H ₂ mixed in the mixed gas is 15 to 50%. It is.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

FIG. 1 is an example of a sectional view of a plasma etching apparatus used in the present invention. In the figure, 1 is a reaction chamber, 2 and 3 are a sample electrode and a counter electrode installed in parallel to each other in the reaction chamber, and 4 is a gas introduction tube attached to the sample electrode 2 to introduce the reaction gas for etching between the two electrodes. , 5 is a gas exhaust pipe that is attached to the reaction chamber 1 and exhausts the gas inside the reaction chamber to the outside, 6 is a material to be etched that is placed on the sample electrode 2, and 7 is an etching pipe that is connected to both electrodes. This is a high frequency power source for generating plasma of reactive gas. Note that the distance between both electrodes is generally 2 to 10 cm.

To etch the material to be etched 6 using the plasma etching apparatus configured as described above, a reaction gas is introduced into the reaction chamber and exhausted from the gas exhaust pipe 5 using a vacuum pump, and the inside of the reaction chamber is heated at 10 ^-3
~Several 100V between both electrodes while maintaining a vacuum of several Torr
A high frequency voltage of ~ several KV and 13.56 MHz is applied to generate plasma by high frequency glow discharge. The active species present in this plasma react with the material to be etched, such as monocrystalline silicon or polycrystalline silicon, producing volatile compounds that
The etching progresses by being exhausted and removed from the etching chamber.

The plasma etching method of the present invention will be explained in detail below using Examples.

The material to be etched 6 is placed on the sample electrode 2 in the reaction chamber, and the reaction chamber is evacuated using a vacuum pump.
After the degree of vacuum has become sufficiently low, for example, CCl ₂ F ₂ is introduced as an etching reaction gas from the gas introduction pipe 4.
Introduce 50 SCCM of H ₂ and 25 SCCM of H 2 and maintain the vacuum level in the reaction chamber at 0.18 Torr. A high frequency power of 400 W (13.56 MHz) is applied between both electrodes to generate plasma of CCl ₂ F ₂ and H ₂ mixed gas to perform etching. When etched under these conditions, the etching rate of the As-doped polycrystalline silicon film as the material to be etched 6 was 540 Å/min. The etching rate for photoresist AZ-1370 (trade name, manufactured by Shippray Co., Ltd.), which is commonly used as an etching mask material, was 170 Å/min. Furthermore, when the cross section of the pattern of the As-doped polycrystalline silicon film after etching was observed with a scanning electron microscope, the undercut was 0.05 μm or less.

For example, in the manufacturing process of a silicon gate type MOS integrated circuit, silicon dioxide is formed as a gate oxide film on a silicon substrate, and an As-doped polycrystalline silicon film is further formed as a gate silicon film. When selectively etching an As-doped polycrystalline silicon layer having such a structure using a resist as a mask, the etching pattern is required to have an appropriate etching rate and no undercuts. In the above example, when the thickness of the As-doped polycrystalline silicon film is 5000 Å, the etching time is about 10 minutes, and the etching rate can be said to be an appropriate value from the viewpoint of practicality and controllability. Also, the undercut of the etching pattern
Since it is 0.05 μm or less, microfabrication with much higher precision than conventional methods can be easily achieved.

CCl ₄ , CCl ₃ F,
The details of why undercuts do not occur in the material to be etched 6 when CCl ₂ F ₂ , CClF ₃ or a mixed gas of CF ₄ and H ₂ are used are unknown, but the following may be the reason. is estimated. _CCl4 ,
In the glow discharge plasma of CCl ₃ F, CCl ₂ F ₂ , CClF ₃ or a mixed gas of CF ₄ and H ₂ , an etching reaction mainly caused by chlorine ions, radicals, fluorine radicals, etc. occurs, and in parallel with this, CCl ₄ , _CCl3F ,
A plasma polymerization reaction occurs in which carbon atoms, hydrogen atoms, etc. dissociated from CCl ₂ F ₂ , CClF ₃ , CF ₄ , H _{2 ,} etc. are the main factors. On the surface of the material to be etched 6,
Since the etching reaction and the plasma polymerization reaction are carried out in parallel, plasma polymers adhere to the side walls of the resist film and the As-doped polycrystalline silicon film as the etching progresses. On the side walls of the etching pattern, etching is prevented in the lateral direction due to polymers attached thereto, but on surfaces parallel to the substrate surface, growth of polymers is inhibited due to ions incident perpendicularly to the substrate surface. It is assumed that etching progresses. In this example, the material to be etched after plasma etching was observed with a scanning electron microscope, and it was confirmed that a thin film of a polymer was attached to the side wall of the As-doped polycrystalline silicon film.

Figure 2 shows, as an example, the relationship between the etching rate (indicated by broken line A) and the undercut amount (indicated by broken line B) of As-doped polycrystalline silicon when the amount of H ₂ mixed in CCl ₂ F ₂ 50 SCCM is changed. It is something that The etching conditions at this time are RF power
400W and constant pressure 0.18Torr. In the case of CCl ₂ F ₂ alone, the etching rate shows a relatively large value of 770 Å/min, and the amount of undercut also shows a value of 0.16 μm, which is about 30% more than the film thickness of 0.5 μm. on the other hand
When _H2 is mixed into _{CCl2F2 ,} the amount of mixing should be 15 to 50
%, the etching rate is 520 to 500 Å/min, and the amount of undercut is reduced to 0.06 to 0.02 μm. Even when H ₂ is mixed in this way, it is practical because it has an appropriate etching rate, and etching with good controllability is possible, and an etching pattern with almost no undercuts can be formed. Although it is not shown in the figure, if the amount of H ₂ mixed exceeds 50%, the etching rate will decrease rapidly, making it impractical. Furthermore, if the amount of H ₂ mixed in is less than 15%, the effect of suppressing undercuts decreases.

Although FIGS. 1 and 2 show examples of As-doped polycrystalline silicon films, other impurity-doped polycrystalline silicon films such as P-doped polycrystalline silicon films and impurity-free polycrystalline silicon films are also available. A similar tendency is observed for the material to be etched.

In this example, as the etching gas,
Although only CCl ₂ F ₂ was shown, the present invention is intended to actively utilize plasma polymerization as described above.
This allows H ₂ to be mixed in. Therefore, the gases that mix H ₂ are CCl ₄ , CCl ₃ F, CCl ₂ F ₂ ,
CClF ₃ , CF ₄ or a mixture thereof;
Furthermore, even in the case of a mixed gas of these and other N ₂ or Ar, by adjusting the amount of H ₂ mixed in, plasma polymerization can be caused and undercuts can be prevented. However, the present invention is not limited to CCl ₂ F ₂ .

As explained above, the present invention uses a mixed gas containing at least one of CCl ₄ , CCl ₃ F, CCl ₂ F ₂ , CClF ₃ and CF ₄ and H ₂ as an etching reaction gas. Since there is no undercut in the etching pattern of polycrystalline silicon and it is possible to maintain an etching rate with good practicality and controllability, it contributes to improving the yield in the etching process in the manufacture of semiconductor devices.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the plasma etching apparatus used in the present invention, and Figure ₂ is a cross _- sectional view of the plasma etching apparatus used in the present invention.
This is a diagram showing the relationship between the etching rate and the undercut amount with respect to the amount of H ₂ mixed in when an As-doped polycrystalline silicon film is etched by plasma discharge of a mixed gas of H _2. In the figure, A indicates the etching rate and B indicates the amount of undercut. . DESCRIPTION OF SYMBOLS 1...Reaction chamber, 2...Sample electrode, 3...Counter electrode, 4...Gas introduction tube, 5...Gas exhaust tube, 6...
...Material to be etched, 7...High frequency power supply.

Claims (1)

[Claims] 1. A reaction gas is introduced into an etching chamber equipped with a sample electrode on which the sample to be etched is placed and a counter electrode facing the sample electrode while exhausting the etching chamber. In the method of etching the sample to be etched using gas plasma generated by applying a high frequency voltage to an electrode, the sample to be etched is a silicon thin film, and the reaction gas contains at least CCl ₄ ,
Using a mixed gas containing at least one of CCl ₃ F, CCl ₂ F ₂ and CClF ₃ and containing H ₂ ,
The pressure in the etching chamber above is 10 ^-3 Torr to several Torr.
A plasma etching method characterized in that a gas in which the amount of H ₂ mixed in the mixed gas is 15 to 50% is used as the plasma etching method.