JP2611254B2 - Dry etching method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method used for a so-called trench etching technique when forming a trench capacitor or the like constituting a DRAM (dynamic RAM).

(Summary of the Invention) The present invention uses Cl ₂ and N ₂ as an etching gas when selectively etching a Si semiconductor, and performs dry etching at a predetermined etching rate.
An object of the present invention is to provide a dry etching method capable of forming a trench having a desired shape.

[Conventional technology]

In recent years, along with the high integration of semiconductor elements, the necessity for element isolation or reduction of the two-dimensional area of the capacitor cell has been increasing, and fine holes or grooves having a high aspect ratio have been formed in a silicon substrate constituting the semiconductor element. The so-called trench etching technique for forming is attracting attention. In particular, it is a very important technology that can be reliably incorporated into high megabit DRAMs of 4 Mbit and higher.

Conventionally, when forming a capacitor on a semiconductor substrate,
Mainly planar capacitors have been used. However, in order to obtain a certain capacitance with a planar type capacitor, it is necessary to increase the capacitor area, which has been a great obstacle to reducing the cell size. For example, the cell size of 1MDRAM having a planar type capacitor is about 30 to 40 μm ²
Met. On the other hand, in a trench cell formed by using the dry etching method, the cell size can be reduced to about 20 μm ² . In other words, a capacitor having a conventional planar structure can also be formed three-dimensionally in a deep hole to reduce a two-dimensional area, reduce a cell size, and cope with high integration of a semiconductor element. It is possible to do.

As the etching gas used in the dry etching method, various etching gases such as a Cl-based gas, an F-based gas, and a mixed gas thereof have been reported and put to practical use. The common point of the dry etching method using the above-mentioned etching gas is that in order to achieve anisotropic processing with a high aspect ratio, a gas system that easily causes deposition in the above-mentioned etching gas must be added. It must be.

In other words, in the dry etching method, a unique undercut occurs directly under the mask due to scattering of active species at the end of the mask used for forming the trench, influence of obliquely incident ions from the sheath, chemical reaction due to radicals, and the like, There is a problem that the formed trench has a shape having a so-called bulge called so-called bowing.
Therefore, in order to solve these problems and prevent undercut and bowing, a sidewall protective film is formed on the sidewall of the trench by using a deposition gas.

In the conventional dry etching method, a deposition gas such as a carbon-based gas such as CCl ₄ , CCl ₂ F ₂ , or CHF ₃ or a SiCl ₄ gas is used to form the sidewall protective film. Thus, carbon, silicon, and other deposition components from the above gases have been used.

[Problems to be solved by the invention]

However, with the problem of the increase of particles in the chamber due to the use of the above gas system and the demand for the formation of finer trench holes, the formation of the sidewall protective film by the addition of the deposition gas causes the trench holes to be formed. There is a possibility that a desired trench shape may not be obtained due to blockage or the like due to abnormal deposition at the opening, so that a dry etching method that does not add a gas that easily causes deposition has been desired.

Therefore, the present invention has been proposed to solve the above-described problems, and has a predetermined shape without using a deposition gas and without closing a trench hole opening with a sidewall protective film. It is an object of the present invention to provide a dry etching method capable of forming a trench hole having the following.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a dry etching method for selectively etching a Si semiconductor, wherein etching is performed at an etching rate of 4000 Å / min or more using an etching gas containing Cl ₂ and N _2. Thus, SiCl _x is generated, and the SiCl _x is further reacted with N ₂ to generate Si _x N _y .

In the present invention, Cl used as an etching gas
₂ + N ₂ based gas, the ratio 1: 8 to 8: It is preferable to 1. In principle, if the N ₂ gas is slightly added, a sidewall protective film will be formed, but if the N ₂ gas is less than this range, a film having a good function as the sidewall protective film will be formed. If the N ₂ gas is more than this range, it acts as a diluent gas, and a predetermined side wall protective film cannot be formed.

Further, the etching rate in the present invention is preferably 4000 ° / min or more. This etching rate is 4000Å / min
If slower is, N ₂ of Cl ₂ + N ₂ based gas is used as the etching gas in the present invention because no better contribute to the sidewall protective film formation. That is, C ₂ + N ₂ gas
Although l ₂ contributes as an etchant of Si, N ₂ does not contribute to the formation of the sidewall protective film in this state because N ₂ is not a deposition gas. Therefore, by generating a large amount of SiCl _x by the reaction of Si and Cl ₂ at a high etching rate of 4000Å / min or more, this SiCl _x and N ₂ are reacted to form Si _x N _y and serve as a sidewall protective film. It contributes favorably. As an apparatus used when performing an etching at a high speed of 4000 ° / min or more, a single wafer type etcher is preferable. In a batch type etcher, the etching rate is low, and the N ₂ gas does not contribute to the formation of the side wall protective film, and bowing or the like occurs.

[Action]

In the present invention, the deposition gas used conventionally is not used, and Cl ₂ + N is used as an etching gas for dry etching.
_{A second} gas was used. The Cl ₂ gas contributes as an etchant for Si. On the other hand, since the N ₂ gas is not a deposition gas, the sidewall protective film is not formed well in this state, and the Si trench cannot be etched.

Here, in the present invention, the etching rate is set to 4000 ° / min or more. With such a high etching rate, Si and Cl
_A large amount of SiCl _x , which is an etching reaction product with the _two gases, is generated.

When a large amount of the above-mentioned etching reaction product, SiCl _x , is generated, the N ₂ gas acts as a reaction gas without using a deposition gas, so that a sidewall protective film that is not easily unevenly deposited is formed. can do. That is, a large amount of SiCl _x reacts with the N ₂ gas to form Si _x N _y , which becomes the sidewall protective film. Therefore, the N ₂ gas does not act as a diluent gas, but acts as a reaction gas.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, as shown in FIG. 1, a Si substrate (1) having a predetermined thickness was prepared, and a mask (2) was formed on the Si substrate (1) at an opening (2) at a predetermined position. 3) was overlaid. The mask (3) is formed by depositing a CVD SiO ₂ film on the Si substrate (1) and forming a contact hole pattern (opening) thereon.
Is formed.

Then, as shown in FIG. 2, a trench hole for forming a trench capacitor is formed on the Si substrate (1) provided with the mask (3) by using a dry etching method according to the following conditions. (4) was formed.

Etching equipment: Single wafer type etcher capable of forming high-density plasma using magnetron discharge Pressure: 5 mTorr Cl ₂ + N ₂ gas total flow rate: 85 SCCM Etching rate: 1 μm / min. )
As shown in FIG. 2, the hole was excellent in verticality. Further, a sidewall protective film (6) was adhered to the sidewall (5) of the trench hole (4) at a constant thickness.

As described above, the formation of the sidewall protective film could be achieved by using the N ₂ gas without using the deposition gas. Further, according to this dry etching method, it is also possible to form a side wall protective film having a predetermined thickness at a necessary portion.

It should be noted that the other conditions were not changed and only the etching rate was adjusted.
In the case of 800-1000Å / min, the etching could not be performed well, bowing occurred near the opening, and the trench hole was left and right asymmetric.

Comparative Example First, as shown in FIG. 3, a Si substrate (1) having a predetermined thickness was prepared, and a mask (2) was formed on the Si substrate (1) at an opening (2) at a predetermined position. 3) was overlaid. The mask (3) is obtained by depositing a CVD SiO ₂ film on the Si substrate (1) and forming a contact hole pattern (opening) thereon.

Then, as shown in FIG. 4, a trench hole (4) for forming a capacitor is formed on the Si substrate (1) provided with the mask (3) by dry etching according to the following conditions. Was formed.

Etching equipment: Single wafer type etcher capable of forming high-density plasma using magnetron discharge Pressure: 5 mTorr Cl ₂ total flow rate: 85 SCCM Etching rate: 1 μm / min As shown in FIG. 4, bowing (7) occurred in the trench hole (4), resulting in the left and right asymmetrical trench hole (4). In addition, the reaction product of SiCl ₄ and oxygen from the mask SiO ₂ , which seemed to be a secondary reaction product, were unevenly adhered partially to the side wall of the trench hole (4).

〔The invention's effect〕

As is apparent from the above description, in the present invention, Cl ₂ and N ₂ are used as the etching gas, and the etching rate is 4000
Since it is not less than Å / min, the sidewall protective film can be formed without using a deposition gas such as SiCl ₄ . Therefore, a trench gas having an excellent vertical shape can be formed without uneven deposition of the deposition gas at the opening of the fine trench hole.

Further, generation of particles in the chamber can be suppressed.

Further, as compared with the SiCl ₄ process, the Cl ₄ + N ₂ process has an advantage in that a necessary protective film is formed at a necessary place.

Therefore, it is possible to provide a dry etching method capable of forming a trench hole having an excellent vertical shape without using a deposition gas such as SiCl ₄ .

[Brief description of the drawings]

1 and 2 are enlarged cross-sectional views of a main part showing a manufacturing process of a trench hole using the dry etching method of the present invention. FIG. 1 shows a mask forming process, and FIG. 2 shows a dry etching process, respectively. ing. 3 and 4 are enlarged cross-sectional views of a main part showing a process of manufacturing a trench hole using a dry etching method using only Cl ₂ gas as an etching gas. FIG. Indicates a dry etching step. DESCRIPTION OF SYMBOLS 1 ... Si substrate 2 ... Opening 3 ... Mask 4 ... Trench hole 5 ... Side wall 6 ... Side wall protective film 7 ... Boing

Claims (1)

(57) [Claims] In a dry etching method for selectively etching a Si semiconductor, an etching gas containing Cl ₂ and N ₂ is used at an etching rate of 4000 Å / min or more to generate SiCl _x , A dry etching method, further comprising reacting the SiCl _x with N ₂ to generate Si _x N _y .