JP2598524B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a dry etching method used for manufacturing a semiconductor device such as an IC.

(Prior Art) The dry etching method is a technique in which, after depositing various films on a semiconductor substrate made of silicon or the like, the films are selectively etched using gas plasma such as freon.

Various techniques have been developed for the dry etching method. Among them, the chemical dry etching method is widely used because it is legal and can perform highly selective etching.

In this chemical dry etching method, a reactive gas is excited by micro liquid plasma in a plasma generator to generate active species, and the active species is introduced into a reaction chamber to react with an object to be processed. Etching is performed, and selection of a reactive gas for etching is an important key point.

As this reactive gas, a mixed gas of freon gas (CF4), oxygen gas (O2) and nitrogen gas (N2) has been frequently used.

(Problems to be Solved by the Invention) In the conventional chemical dry etching method, when etching a silicon nitride film, there is a disadvantage that it is difficult to selectively etch a silicon oxide film underlying a silicon nitride film. . That is, in the prior art,
The selectivity (silicon nitride film etching rate / silicon oxide film etching rate) was only about 5 obtained.

In particular, recently, the silicon oxide film, which is the base of the silicon nitride film, has been made thinner, and the selectivity is 5 as described above.
If the degree is about, a defect such as a pinhole may possibly occur on the silicon oxide film.

In order to improve the above selectivity, NF3 as a reactive gas
There is a method of using a mixture of gas and chlorine gas.
However, in this method, the selectivity is improved to about 30, but the etching rate of the silicon nitride film is a low value of about 100 Å / min.

(Object of the Invention) The present invention has been made to solve the above-mentioned drawbacks in the prior art, and a dry etching method for increasing the selectivity between an object to be processed and a base and enabling high-speed etching of the object to be processed. The purpose is to provide.

[Configuration of the invention]

(Means for Solving the Problems) According to a dry etching method of the present invention, in order to achieve the above object, an object to be processed having a silicon nitride film is loaded into a vacuum vessel and a reaction activated by a plasma generator is performed. A dry gas method for supplying a reactive gas to the surface of the workpiece to etch the silicon nitride film, wherein the reactive gas includes a gas containing fluorine, an oxygen gas, a chlorine gas, and at least hydrogen. Using a mixed gas with a gas containing at least one of them, controlling the supply amounts of the chlorine gas and the gas containing at least hydrogen to optimize the selectivity between the silicon nitride film and its base and the etching rate of the silicon nitride film. It is characterized by doing.

As the above-mentioned gas containing fluorine, NF3, SF6 and the like can be used in addition to freon gas (CF4). As the hydrogen-containing gas, for example, hydrogen, water, alcohol, methane and the like can be used.

(Operation) As described above, in the dry etching method of the present invention, a mixed gas of a gas containing fluorine, an oxygen gas, a chlorine gas, and a gas containing hydrogen is used as the reactive gas. And the amount of gas containing hydrogen is controlled so that the etching selectivity between the object to be processed and the base is optimized so that the etching selectivity between the object to be processed and the base is reduced. It is possible to greatly increase the etching rate and to etch the object at a high speed.

(Example) Hereinafter, an example of the present invention is described with reference to drawings.

FIG. 1 shows an example of a dry etching apparatus used in the method of the present invention. In an etching chamber of a vacuum vessel 1, a mounting table 3 on which a workpiece 2 is mounted is provided.

Above the vacuum vessel 1, a gas dispersion pipe 4 that opens above the workpiece 2 is provided, and a gas introduction pipe 5 is connected to the gas dispersion pipe. A plasma generator 6 is interposed in the gas introduction pipe 5.

The plasma generator 6 includes a discharge tube 7 made of quartz and a waveguide 8 provided outside the discharge tube 7, and generates plasma by applying a microwave through the waveguide 8.

A gas exhaust pipe 9 for discharging a reactive gas is connected to the bottom wall of the vacuum vessel 1 via a manifold 10, and a vacuum pump (not shown) is connected to the gas exhaust pipe.

In the dry etching apparatus having such a configuration, in the method of the present invention, a mixed gas of a gas containing fluorine, an oxygen gas, a chlorine gas, and a gas containing hydrogen is used as the reactive gas. In this case, as the gas containing fluorine, any one of freon gas (CF4), NF3, SF6 and the like is selectively used as described above. Further, as the gas containing hydrogen, any one of hydrogen, water, alcohol, methane and the like is selectively used.

This mixed gas is introduced into the discharge tube 7 from the gas introduction tube 5, and is excited by applying a microwave from the waveguide 8 when passing through the gas mixture tube, and is introduced into the vacuum vessel 1 as plasma as plasma. The subject 2 is subjected to chemical dry etching.

FIG. 2 illustrates an object 2 to be processed by chemical dry etching according to the present invention. A silicon oxide film 12 having a thickness of about 500 angstroms is formed on a silicon substrate 11 by a thermal oxidation method. On this silicon oxide film, a silicon nitride film 13 having a thickness of about 1,500 angstroms is deposited by a CVD method. On the silicon nitride film 13, a pattern of a photoresist 14 is formed by photolithography.

As a reactive gas to be sent into the vacuum vessel 1, a mixed gas obtained by mixing a gas containing fluorine (CF4) at 300 SCCM and oxygen gas at 200 SCCM, and adding chlorine gas to alcohol gas as containing hydrogen. It was used.

Using the reactive gas, the object 2 was etched under the conditions of a microwave power of 700 W and a pressure of 50 pa, while changing the addition amounts of the alcohol gas and the chlorine gas.

In the above description, when the flow rate of the alcohol gas is used as a parameter and the addition amount of the chlorine gas is changed from 0 to 80 SCCM, the etching selectivity between the silicon nitride film 13 and the silicon oxide film 12 (= the silicon nitride film etching rate / the silicon oxide film) The relationship between the etching rate) and the etching rate of the silicon nitride film 13 was as shown in FIG.

As is clear from this figure, the addition of the alcohol gas improves the etching rate and the etching selectivity of the silicon nitride film 13, and further increases the etching rate and the etching rate of the silicon nitride film 13 with an increase in the amount of the alcohol gas added. The etching selectivity is further improved.

When the chlorine gas flow rate increases, the silicon nitride film
Although the etching rate of 13 decreases, the etching selectivity increases. This is because the etching rate of the underlying silicon oxide film 12 is much lower than the etching rate of the silicon nitride film 13 due to the addition of chlorine gas.

That is, in the conventional case where etching is performed using a reactive gas in which NF3 gas and chlorine gas are mixed, the silicon nitride film 13 is used.
Is about 100 angstroms / minute, but about 400 angstroms / minute is obtained with the present invention. Also, when the chlorine gas flow rate is about 40 SCCM,
The etching selectivity is 10 or less when no conventional alcohol gas is added, but in the case of the present invention, the alcohol gas flow rate is about 50 at 10 SCCM and about 80 at 20 SCCM.

This is because the silicon nitride film 13
It can be said that this is due to an increase in the etching rate of the silicon oxide film 12 and a decrease in the etching rate of the silicon oxide film 12 due to the addition of chlorine gas.

As described above, according to the method of the present invention, the etching selectivity can be greatly increased, and high-speed etching can be performed.

〔The invention's effect〕

As described above, according to the present invention, as a reactive gas, a mixed gas of at least a gas containing fluorine, an oxygen gas, a chlorine gas, and a gas containing at least hydrogen is used, and a chlorine gas and at least hydrogen are used. Since the supply amount of each of the contained gases is controlled, the selectivity between the silicon nitride film and the underlying layer and the etching rate of the silicon nitride film can both be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a dry etching apparatus used in the method of the present invention, FIG. 2 is a cross-sectional view illustrating a workpiece to which the method of the present invention is applied, and FIG. It is a graph explaining. DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Workpiece, 3 ... Mounting table, 4 ... Gas dispersion tube, 5 ... Gas introduction tube, 6 ... Plasma generator, 7 ... Discharge tube, 8 ... Waveguide, 9 ... Gas exhaust tube , 10: manifold, 11: silicon substrate, 12: silicon oxide film, 13: silicon nitride film, 14: photoresist.

Claims (1)

(57) [Claims] An object having a silicon nitride film is carried into a vacuum vessel, and a reactive gas activated by a plasma generator is supplied to the surface of the object to etch the silicon nitride film. A dry etching method, wherein as the reactive gas, a mixed gas of a gas containing at least fluorine, an oxygen gas, a chlorine gas, and a gas containing at least hydrogen is used, and the chlorine gas and the at least hydrogen are used as the reactive gas. A dry etching method characterized in that a supply rate of each of the contained gases is controlled to optimize a selectivity between a silicon nitride film and a base thereof and an etching rate of the silicon nitride film.