JP3109059B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method useful for taper etching of a material to be etched.

[0002]

2. Description of the Related Art Conventionally, dry etching methods such as plasma etching, sputter etching, and reactive ion etching (RIE) have been used as a method of forming a fine pattern of a highly integrated semiconductor. In order to enable a multi-layered wiring structure, not only forming a fine pattern by a dry etching method but also tapering the fine pattern to improve the coverage of a film stacked on the pattern. That is, so-called taper etching is performed.

Various reports have been made on the taper etching method. For example, as a well-known method of tapering etching of a wiring material, a resist pattern serving as a mask of the wiring material is tapered, and the etching selectivity between the wiring material and the mask is reduced at the time of etching so that the resist recedes. To form a taper in the pattern of wiring material by using
338). FIG. 4 is an explanatory view of such a taper etching method. According to this method, first, as shown in FIG. 4A, an SiO ₂ film 2 is formed on a substrate 1 and an aluminum film as a material to be etched. 3 are sequentially stacked, and a tapered resist pattern 4 is further formed thereon. The tapered resist pattern 4 can be formed by forming a resist pattern by a conventional method and then performing a heat treatment or the like. Then
Using the tapered resist pattern 4 as a mask, etching is performed by reactive ion etching under the condition that the selectivity to resist is about 1, and the taper of the resist pattern 4 is transferred to the aluminum film 3 by resist receding. A wiring pattern is formed as shown in B).

As another taper etching method, a deposition gas is added into an etching chamber,
A method of forming a taper by a competitive reaction between etching and deposition (dry process symposium, 1986, p. 48) has been reported. Recently, a method of forming a taper by controlling the temperature of a wafer (Applied Physics, Spring 1987) Proceedings of the Society, p. 462) have also been reported.

[0005]

However, in the method in which the resist pattern is tapered and the selectivity between the wiring material and the mask is lowered, the pattern of the wiring wiring material is tapered by the receding resist. And the difference between the dimensions of the initial resist pattern and the dimensions of the wiring material after etching is large, making it difficult to control the dimensions. Further, since the pattern width of the wiring material is restricted by the taper width of the resist pattern formed in advance, it is difficult to form a fine pattern on the wiring material. Further, since the taper of the wiring material is formed by transferring the taper of the resist pattern, it is inherently necessary to reduce the resist selectivity. For this reason, it is necessary to form the resist film relatively thick. Therefore, this method cannot cope with pattern formation, which tends to be further miniaturized in the future.

In the method of adding a deposition gas and forming a taper by a competitive reaction between etching and deposition, the deposition gas has a deposition property.
It is feared that a polymer causing particle contamination is generated in the entire etching chamber.

In the method of forming a taper by controlling the temperature of the wafer, it is necessary to strictly control the temperature of the wafer. At present, however, there is a method of accurately evaluating the temperature of the wafer in-process. There is a concern that the reliability of the process may decrease.

Therefore, the conventional taper etching method is insufficient for forming a fine pattern with high precision, and none of them has been put to practical use.

An object of the present invention is to solve the above-mentioned problems in the prior art, and an object of the present invention is to provide a dry etching method which can easily taper even a fine pattern.

[0010]

In order to achieve the above object, the present invention provides a method of forming a mask pattern on a material to be etched and performing dry etching, wherein a cross-sectional shape of the mask pattern is from bottom to center. Wide
And narrows from the center to the top
A dry etching method characterized by being formed in a barrel shape .

According to the method of the present invention, a cross-sectional shape is used as a mask pattern used when performing dry etching.
By using a barrel-shaped member, the material to be etched can be easily tapered etched.

In this case, applicable dry etching methods include reactive ion etching,
Various dry etching methods suitable for forming a fine pattern can be given.

Various mask patterns can be used as the mask pattern. For example, a negative resist or a positive resist can be used. As such a photoresist, particularly when forming a narrow taper required for the taper of a fine pattern,
It is preferable to use one having a relatively small absorption at the exposure wavelength.

In the present invention, the shape of the mask pattern is such that its cross-sectional shape is wider from the bottom to the center.
And narrows from the center to the top
It is assumed that it is formed in a barrel shape . Such cross-sectional shape
It is in the mask pattern, the region where the central portion of the cross-sectional direction is <br/> the eaves, ions or the like for vertically incident during etching the surface of the object to be etched beneath the eaves does not reach form
Re that.

There is no particular limitation on the method of forming such a mask pattern, and the formation method can be appropriately determined according to the type of the resist and the material to be etched. For example, in the case of forming a mask pattern from a positive resist, the best focus at the time of exposure may be shifted slightly above the surface of the material to be etched in a pattern forming method using ordinary photolithography. This makes it possible to easily form a resist pattern having a barrel-shaped cross section on the material to be etched using a conventionally used photolithography apparatus. In addition, when using a high-luminance material having a high reflectance such as aluminum as the material to be etched, the resist usually includes a dye to which a dye is usually added in order to suppress the influence of light scattering at the time of exposure. Although it is used, when a mask pattern having a cross-sectional shape suitable for the present invention is used, the amount of such a pigment to be added may be reduced.

[0016]

According to the dry etching method of the present invention,
The cross-sectional shape of the mask pattern provided on the material to be etched is
As the width increases from the bottom to the center,
It is formed in a barrel shape that becomes narrower from the top to the top . Therefore, for example, as shown in FIG.
When a SiO ₂ film 2 and an aluminum film 3 to be etched are sequentially laminated on a substrate 1, and a resist pattern 5 having a narrow bottom portion 5 a and a wide central portion 5 b as a mask pattern is formed thereon. In the region 3a of the aluminum film below the central portion 5b of the resist pattern, the central portion 5b of the resist pattern 5 becomes an eaves during etching so that vertically incident ions (a ⁺ ) cannot reach and obliquely incident ions (b ⁺ ) Can be reached. On the other hand, oblique incident ions (b) are applied to the region 3b of the aluminum film 3 which does not enter under the eaves of the wide central portion 5b of the resist pattern 5.
⁺ ) As well as vertically incident ions (a ⁺ ). Therefore, the etching rate of the region 3a of the aluminum film 3 is lower than that of the region 3b, and when the etching is advanced to the intended state and terminated, as shown in FIG. The taper 3c is formed in the region. At the end of the etching, the aluminum film 3
The resist pattern 5 remaining on the pattern can be easily removed by a conventional method. In this way, it is possible to form a tapered pattern with a small conversion ratio with the resist pattern on the aluminum film 3.

Therefore, according to the method of the present invention, even if the pattern formed on the material to be etched is fine, it is possible to form a fine taper corresponding to the pattern.

When tapering the pattern, it is not necessary to use a deposition gas as in the prior art, so that particle contamination does not occur.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. In each of the drawings, the same reference numerals represent the same or equivalent components. Embodiment 1 FIG. 1 is an explanatory diagram of an embodiment of the present invention. In this embodiment, the surface of the silicon substrate 1 is coated with Si as an insulating film.
An O ₂ film 2 was formed, an aluminum film 3 to be subjected to fine processing was further formed thereon, and then a barrel-shaped resist pattern 5 was formed with a positive resist (FIG. 1A).

Next, the aluminum film 3 was etched using the resist pattern 5 thus formed as a mask. As an etching method, a microwave plasma etching apparatus was used, and boron trichloride (BCl 3) was used as a reactive gas.
₃ ) Gas and chlorine gas were used at a flow ratio of 60 sccm to 90 sccm. The pressure was set to 16 mTorr, the microwave power was set to 800 W, and the RF bias was set to 40 W. In such microwave plasma etching, the etching proceeds by radical species and ionic species generated by the discharge. However, as described with reference to FIG. 3, since the wide central portion 5b of the resist pattern 5 becomes an eave, the aluminum film is formed. The region 3a of No. 3 does not reach vertically incident ions, and etching proceeds by obliquely incident ions. For this reason, the etching is advanced to the initial state, then the etching is terminated, and the resist pattern 5 is removed, thereby removing the upper corner and removing the tapered aluminum film 3 as shown in FIG. 1B. A pattern was obtained. Embodiment 2 FIG. 2 is an explanatory view of another embodiment of the present invention. In this embodiment, an SiO ₂ film 2 is formed as a gate oxide film on the surface of a silicon substrate 1, and a polycrystalline silicon film 6 and a tungsten silicide (WSi _x , x = 1-3) membrane 7
Were sequentially formed, and then the same resist pattern 5 as in Example 1 was formed (FIG. 2A).

Next, the polycide film 8 composed of the polycrystalline silicon film 6 and the tungsten silicide film 7 was etched. As an etching method, a reactive ion etching apparatus was used, and as a reaction gas, a hydrogen bromide gas and a sulfur hexafluoride gas were used at a flow ratio of 50 sccm to 5 sccm. The pressure was set to 30 mTorr, and the microwave power was set to 300 W.

As a result, as shown in FIG. 2B, a pattern was obtained in which the upper end of the tungsten silicide film 7 had a sharp corner.

[0023]

According to the dry etching method of the present invention, even when a fine pattern is formed on the material to be etched, the pattern can be easily tapered or the corner of the pattern end can be formed. Becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of another embodiment of the present invention.

FIG. 3 is an explanatory diagram of the operation of the dry etching method of the present invention.

FIG. 4 is an explanatory view of a conventional taper etching.

[Explanation of symbols]

Barrel-shaped resist pattern of first substrate 2 SiO ₂ film 3 of aluminum film 4 resist pattern 5 present invention was subjected conventional taper

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 H01L 21/3213

Claims (2)

(57) [Claims] In a method of forming a mask pattern on a material to be etched and performing dry etching, a cross-sectional shape of the mask pattern becomes wider from a bottom to a center.
With the barrel narrowing from the center to the top
A dry etching method characterized by being formed in a mold . 2. The dry etching method according to claim 1, wherein said mask pattern is made of a positive resist.