JPS6191929A - Dry etching method - Google Patents

Abstract

PURPOSE:To etch a film to be etched in a taper form using a vertical photo resist pattern, by isotropic- or semi-isotropic-etching a etching mask, and at the same time by directed-etching the film to be etched. CONSTITUTION:On a film 12 to be etched (a portion of a silicon substrate or a polysilicon film) over the substrate 11, a photo resist film 13 with a vertical cross sectional shape is formed. Next, reactive ion etching is done using SF6+O2 gas. By selecting a concentration of O2 in the etching gas at a appropriate value (about 50%), a film 12 to be etched can be directed-etched and the photo resist 13 can be isotropic- or semi-isotropic-etched. In this way, by employing the photo resist film 13 with a vertical cross sectional shape, the film 12 can be formed in a taper shape 12a. Moreover, by controlling an O2 concentration, cross sectional shape of the processed face can be controlled precisely.

Description

[Detailed Description of the Invention] <Technical Field of the Invention> The present invention relates to an improvement in a dry etching method used, for example, in the manufacturing process of VLSI, and more specifically, to making it possible to obtain a tapered cross-sectional shape. This invention relates to a dry etching method.

<Technical background of the invention and its problems> Generally, in the manufacturing process of VLSI, reactive ion etching (RIE) is used to suppress dimensional shifts.
) etc. are performed. The cross-sectional shape of the film processed by this reactive ion etching becomes a vertical shape with sharp corners as shown in FIG. Here l
2 is a base substrate, and 2 is a film to be etched.

When an LSI or the like is constructed by stacking another film on top of the etched film 2 shown in FIG. Problems such as the occurrence of

In order to solve these problems, the film 2'f is processed into a tapered shape as shown in FIG.

As a taper etching technique, a method of transferring the shape of a photoresist has conventionally been mentioned, and this etching method will be explained together with the seventh drop.

First, a pattern of a normal 7-photoresist 3 is placed on a film to be etched 2 formed on a base substrate 1. formatively 7th
(See Figure (a)), then perform a predetermined heat treatment to soften and flow the photoresist 3 to form a tapered photoresist pattern 3a (see Figure (b)). Selecting conditions in which the etching rates in Step 2 are approximately the same, perform directional etching such as reactive ion etching to transfer the entire shape of the photoresist in step 7 (see 3(c)), then photoresist) in tray 3b. The film is removed to obtain a tapered film 2a to be etched (see FIG. 7(d)).

In such a conventional etching method, the shape of the taper of the film to be etched 2a is determined by the shape of the initial photoresist and the etching rate ratio of the photoresist and the film to be etched during etching. 7. There are problems such as difficulty in controlling the shape of the photoresist. That is, in the process of softening and fluidizing the photoresist by heat, the reproducibility of pattern dimensions and pattern shapes is poor, resulting in poor accuracy of the transferred pattern.

Therefore, the conventional taper etching method described above is suitable for ultra-LS'1 etching, which requires highly accurate control of fine patterns.
This is essentially unsuitable for use in manufacturing processes such as
It has been desired to develop a new etching method to obtain a tapered cross-sectional shape.

<Object of the Invention> The present invention has been made in view of the above points, and is a novel taper etching method that does not require tapering the photoresist, in other words, using a vertical photoresist pattern. The purpose of the dry etching method of the present invention is to provide a dry etching method that makes it possible to perform etching in a tapered shape. Alternatively, etching is performed semi-isotropically and the film to be etched is etched omnidirectionally at the same time to obtain a desired cross-sectional shape. According to this, the film to be etched is substrate silicon or polysilicon, and the etching gas is SF.
6+O2°, and the etching conditions are all set by fully controlling the 02 concentration in this etching gas to obtain a desired cross-sectional shape.

<Embodiments of the Invention> Prior to detailed description of the present invention, the principle of the dry etching method of the present invention will be explained as follows.

Dry etching can be roughly divided into two types: directional etching and isotropic etching. Directional etching mainly uses reactions with ions, and only the areas exposed to ion irradiation are etched; In isotropic etching, a radical reaction is used, so etching proceeds isotropically.

In the present invention, the photoresist is etched isotropically or semi-isotropically by a combination of these two etching methods.
A feature of this method is that by setting etching conditions such that the film to be etched is etched directionally, taper etching is performed using a photoresist having a vertical cross-sectional shape as a mask. In the description of the present invention, it is assumed that semi-isotropic etching (photographic etching) is an etching gas that is approximately intermediate between directional etching and isotropic etching. is the basic operation of the dry etching method of the present invention.
This is an etching process diagram for explaining 11t/'i base substrate, ! 2#''i film to be etched; 13 is an etching resist having a vertical cross section and acting as a t etching mask;

In carrying out the dry etching method of the present invention, first, the film to be etched 12 formed on the base substrate 11 is etched.
-1- of 7 otoresist + of normal cross section or vertical shape
3) (see Ms6(a)), then 7 etching resist is isotropically or photoresist etched as described above, and the film to be etched is set to be etched directionally. Etching is started according to the etching conditions set. Under these conditions, as the etching progresses, the edge of the photoresist +3 recedes as shown in FIGS. As shown, a taper is formed, and by removing the photoresist 13a, a tapered film to be etched +
2a is obtained (see FIG. 1(C)).

When the photoresist 13 is vertical, the shape of this taper is determined by the ratio of the lateral etching rate of the photoresist 13 and the etching rate of the film 12 to be etched. In the case of etching, the dry etching method of the present invention will be explained in more detail with respect to the gold side.

In carrying out the dry etching method of the present invention,
It is important to set etching conditions such that the photoresist is etched isotropically or phototropically 1 and the substrate silicon is etched directionally.

One of the etching methods that satisfies this condition is using SF6+O as the etching gas. The present inventors have newly developed reactive ion etching using gas.

The relationship between the etching rate of the substrate silicon and the 7-photoresist and the undercut of the substrate silicon in this reactive ion etching using SFG+O2° gas is shown in FIG. The relationship shown in Figure 2 is gas SF6+O2□,
The etching conditions shown are a pressure of 90 mTorr and an RF power of 0.08 W/-.

In addition, in FIG. 2, the undercut is defined as the amount of etching in the lateral direction relative to the amount of etching in the depth direction, and the undercut of the substrate silicon 21 in FIG.
It is defined by the value of /A.

As is clear from Fig. 2, 02 in the etching gas
The addition of gas reduces undercutting of the substrate silicon 21 and achieves directional etching. This phenomenon occurs because the side surfaces of the silicon 21 are oxidized by the addition of rfiO2, and the oxide film prevents undercuts caused by fluorine radicals. Incidentally, the horizontal surfaces of the silicon are also oxidized, but since the horizontal surfaces are exposed to ion bombardment, etching is not prevented.

On the other hand, the etching rate of the photoresist (2) increases with the addition of 2. That is, in the case of photoresist, unlike in the case of silicon, the film is removed by oxidation, so that etching progresses in a photographic manner. Evaluating the lateral etch rate of the photoresist from changes in resist pattern dimensions, the etch gas SF6+O
2° (50%), pressure 90mTorr, RF power 0
．． 08 The etching rate in the vertical direction was approximately 60% of the etching rate in the vertical direction under the etching conditions of Wlcrl.0 When the substrate was re-etched under the above etching conditions, the shape as shown in FIGS. 4(a) and (b) was obtained. Taper etching of the substrate silicon is realized using a vertically shaped 7-photoresist pattern, and the cross-sectional shape of the substrate silicon can be controlled by changing the 0□ concentration of gold.

In the gIJ4 diagram, 31 is the taper-etched substrate silicon, 32 is a vertical photoresist pattern, and (a) shows the 02 concentration at 40%, and (b) shows the 0° concentration. This figure shows the etching state when 60%.

In the above embodiment, the case of f+- par etching of substrate silicon has been described, but the present F3JJ is not limited to this (it goes without saying that it can also be applied to taper etching of polysilicon).

<Effects of the Invention> As described above, according to the etching method of the present invention, it is possible to control the cross-sectional shape of the surface processed by etching with high precision, and as a result, for example, in the VLSI manufacturing process, fine patterns can be formed. It can be processed with high reliability and greatly contributes to improving the performance and yield of LSI devices.

[Brief explanation of the drawing]

Figures 1 (a) to (c) are diagrams for explaining the steps of the dry etching method according to the present invention, and Figure 2 shows the relationship between the etching rate and the 0° concentration of undercut used in the present invention. 3 is a diagram for explaining the definition of an undercut, FIGS. 4(a) and 4(b) are diagrams showing the shape of a substrate etched according to the present invention, and FIG. 5 is a diagram for explaining the definition of an undercut. Figure 6 shows the cross-sectional shape of the film to be etched by conventional ion etching. Figure 6 is a diagram for explaining taper etching of the film to be etched. Figures 7 (a) to (d) It is a figure for explaining a process. 11... Base substrate, 12... Cutting film, 1
3...7 otregis with vertical cross section), 12a...
Taper etched film to be etched. Agent Patent Attorney Aihiko Fuku (2 others) Figure 1 Figure 3 Figure 2 (7!L) (b) Ward 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. The etching mask is etched isotropically or semi-isotropically, and the film to be etched is simultaneously etched in a directional manner. A dry etching method characterized by the following. 2. The film to be etched is substrate silicon or polysilicon, the etching gas is SF_6+O_2, and the O_2 concentration in the etching gas is controlled to set the conditions to obtain a desired cross-sectional shape. A dry etching method according to claim 1, characterized in that: