JPS6161423A - Dry etching method - Google Patents

Abstract

PURPOSE:To effectively remove the remaining etching residue without damaging the base by a method wherein a directional etching process, a sidewall protective film forming process and an isotropic etching process are combined together. CONSTITUTION:A directional etching is performed on a polycrystalline silicon film 13 to a just etching. At this time, an etching residue 16 remains. Silicon oxide films are formed according to a plasma treatment of o2 and the oxide films are turned into sidewall protective films 17,..., and 18. Then, a semiisotropic etching is performed. In this condition, the film 18 having the horizontal surface among the silicon oxide films 17,..., and 18 formed according to the plasma treatment of O2 is removed by ion bombardment, but chemicals 17, 17...on the side surfaces protect the polycrystalline silicon films 13, 13 without being removed. As a result, any undercut is never generated and the etching residue 16 is removed.

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.

<Technical background of the invention and its problems> In general, reactive ion etching (RIE) is used to perform microfabrication in the manufacturing process of VLSI.
) etc. are performed.

Due to such RIE or the like, the step may be coated, leaving scratches. Further, in directional etching, foreign matter may be generated depending on the etching conditions and the state of the film.

FIG. 3 is a diagram showing an example of etching of a film coated with a conventional step top 1, in which (a) is before etching,
) indicates the state of etching residue. Here, 1 is a base substrate, 2 is a film to be etched, 3 is a mask, 4 is an etching residue at a step portion, and 5 is a foreign substance.

This generation of foreign matter 5 is because the fine foreign matter acts as an etching mask and creates new etching residue.

In conventional etching process, these etching residues were removed by prolonging the etching time (over-etching), but directional etching generally has a problem of damaging the underlying material because the selectivity with the underlying material is low. there were.

Further, when the step has an overhang shape as shown in FIG. 4, the etching residue 6 cannot be removed by directional etching, which adversely affects the reliability of devices such as VLSIs.

<Objective of the Invention> The present invention provides a dry etching method that can eliminate the above-mentioned conventional drawbacks, improve the reliability of the etching process, and greatly contribute to the improvement of the degree of integration and performance of LSI etc. In order to achieve this purpose,
The dry etching method of the present invention includes, in the step of etching a film coated on a step, an etching step for microfabrication and a protective film forming step for forming a sidewall protective film to eliminate pattern dimension changes due to undercuts. and an isotropic etching step for removing etching residues from the directional etching step.

<Embodiments of the Invention> Before explaining embodiments that have not yet been invented, 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/notching and isotropic etching. Directional etching mainly uses reactions with ions.
Only the portions exposed to ion irradiation are etched and no undercuts occur. This method is suitable for microfabrication, but
As mentioned above, there is a drawback that etching remains are likely to occur.

On the other hand, since isotropic etching uses a radical reaction, etching proceeds isotropically and undercuts occur. Although this method is not suitable for microfabrication, it is effective for removing etching residue. The reason for this is that in radical etching/notching, etching proceeds from all directions, so that it is possible to remove etching residues as shown in FIG.

The present invention is based on the combination of these two etching methods to etch the film on the step without leaving any etching residue.First, directional etching is performed, and then isotropic etching is performed to remove the etching residue. Remove. In order to prevent the occurrence of undercuts during isotropic etching, the step of forming a sidewall protective film is inserted between two etching steps.

That is, the dry etching method of the present invention combines a directional etching process, a sidewall protective film forming process to eliminate pattern dimension changes due to undercuts, and an isotropic etching process to remove etching residues. Hereinafter, an embodiment of the dry etching method of the present invention will be described with reference to the drawings, taking as an example the etching of polysilicon (PolySi) on a step.

The conditions and results of the two etching steps used in this actual Mi example are shown in the following table.

In the table above, the condition is directional etching, condition ■
is an etching that is approximately intermediate between directional etching and isotropic etching, and is hereinafter referred to as isotropic etching.

In the above table, the etching directionality is defined as the amount of etching in the lateral direction with respect to the etching base in the depth direction, and is defined by the value 34 in FIG.

1 faJ to (di are diagrams for explaining the steps of an embodiment of the dry etching method of the present invention, in which a step-shaped 5iOz@12 is formed on a Si substrate 11,
This 5i (polysilicon film 13 deposited on the h film 12
is etched using the 5in2 films 14 and 15 as masks (see FIG. 1(a)).

First, the polysilicon film 13 is etched to just etching under condition (2). At this time, since the etching under condition (3) is directional etching, 16 etching residues remain as described above (Fig. 1 (bl)). Next, 02 plasma treatment (020, 6 Torr 600W, 30 minutes) is performed. This 02 plasma As a result of the treatment, a silicon oxide film of approximately 20° is formed, and sidewall protective films 17, 1.7, 1 are formed.
8 (Figure 1 (C)).

Next, perform isotropic etching under condition (2). Under these conditions, the silicon oxide film formed by plasma 17.1
8, the horizontal surface film 18 is removed by tri ion bombardment, but the side surface film 17.17. . . protects the polysilicon film 13.13 without being removed. As a result, the etching residue 16 is removed without causing any undercuts (Fig. 1(d)).

Note that in the etching under condition (2), the etching rate ratio with 5iOz is sufficiently high, so even if over-etching is performed, the underlying 5i02 film 12 will not be damaged. Resist residue that has sunk into the hang-like step 19 can also be removed.

<Effects of the Invention> As described above, the uninvented dry etching method includes a directional etching process, a sidewall protective film forming process to eliminate pattern dimension changes due to undercuts, and an isotropic etching process to remove etching residues. By combining chemical etching, the etching residue that remains after etching the film coated on the step can be effectively removed without damaging the underlying layer, improving the reliability of the etching process. I can do it. As a result, it greatly contributes to improving the yield in VLSI manufacturing, for example, and
This greatly contributes to improving the degree of integration and performance of I.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, but can be widely used for etching a film on a general step.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the steps of the dry etching method according to the present invention (al to Fd), FIG. 2 is a diagram for explaining the directionality of etching, and FIG. 3 is an example of etching by the conventional method. FIG. 4 is a diagram showing etching remains on the overhang portion. 11...Si substrate, 12...5i02 film,
13... Polysilicon film (film to be etched), 14.
15...S i Oz II! (Mask), 16・
...Etching residue, 17.18...Side wall protective film. Agent Patent Attorney Hiko Fuku Tsuchiuke (and 2 others) No. 1 (2)

Claims (1)

[Claims] 1. In the step of etching the film coated on the step, a directional etching step for microfabrication and a step for forming a sidewall protective film to eliminate pattern dimension changes due to undercuts are performed. A dry etching method comprising: a protective film forming step; and an isotropic etching step for removing etching residue in the directional etching step.