JPH0372087A - Dry etching method - Google Patents

Abstract

PURPOSE:To stick an oxidized metal to the side wall of a resist, to prevent the attack of oxygen ions, to enable vertical etching and to improve etching accuracy by adding gas of a metal compd. to oxygen as etching gas and patterning the resist with them. CONSTITUTION:A molybdenum or tungsten compd. such as molybdenum hexafluoride or tungsten hexafluoride is prepd. gas of the metal compd. is added to oxygen as etching gas and a metal oxide film 24 is formed on the side wall of an etched resist 2 so as to prevent etching by reflected ions. The stuck metal oxide 24 is removed by washing after etching.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to an improvement in a method for directional etching of resist.

(Prior Art) In recent years, the minimum pattern size of semiconductor integrated circuits has become extremely fine, 1 micron or less.

As a semiconductor integrated circuit approaches the end of its manufacturing process, its surface becomes more uneven. When a fine pattern of 1 micron or less is formed on an uneven surface, the pattern size is the same as that of the substrate (30) (7), as shown in Figure 3.
The convex portion (30a) is thin, and the concave portion (30b) is thick. That is, since the resist (31) is normally formed as a film, the resist film thickness is thinner at the convex portions (30a) and thicker at the concave portions (30b). When exposed and developed in this state, the convex parts will be overexposed due to the thinness of the resist film.
Over-development occurs.

As a result, the pattern size changes (Figure 1 (b)).

A multilayer resist method was devised to solve these problems. FIG. 4 shows a three-layer resist process, which is an intermittent multi-layer resist method. Film to be etched (40)
A thick resist (43) is applied on the substrate (4I) with the unevenness formed thereon to flatten the unevenness (Fig. 4(a)).
. On top of this, a material (43) resistant to oxygen plasma, such as a silicon oxide film, is deposited, and a resist (44) is again applied thereon (FIG. 4(b)). After that, exposure,
Develop to form a resist pattern. Using the resist pattern thus formed as a mask, the intermediate!
Directional etching (43) is performed, and then the resist (42) is etched by reactive ion etching using oxygen. Finally, the film to be etched (40) is etched using the resist (42) as a mask.

Although this method can accurately form fine patterns on an uneven substrate, it is not without its problems. That is, the biggest problem is etching of the resist (42) using the intermediate layer (43) as a mask.

In resist etching, even if a relatively large pattern is etched vertically, a fine pattern of 1 micron or less is etched as described above, as shown in Figure 5 (a).
), a phenomenon occurs in which the center portion of the pattern (51) formed on the substrate (50) becomes thinner. This is considered to be because ions reflected at the end of the intermediate layer (52), which is an etching mask, impact the middle of the pattern. As a means to prevent sidewall gouging, a method has been proposed in which a gas, such as ethylene, which forms a polymer film by electric discharge is added to the etching gas. However, as shown in Figure 5(b), the plasma polymerized film (5
The film thickness of 3) is thicker at the top of the pattern and thinner at the bottom.

This is simply because the amount of incident chemical species is greater at the top of the pattern. Therefore, if polymerization occurs to the extent that sidewall gouging can be prevented, there is a problem that the entire pattern will overhang. Gases such as Si
Although it is possible to form a thin silicon oxide film on the side wall by adding C474 or the like, another problem arises in that it is difficult to remove the film after etching.

(Problem 8 to be solved by the invention) As described above, in the past, it was extremely difficult to perform vertical resist etching due to the sidewall gouging caused by ions reflected at the edge of the intermediate layer, which is an etching mask. Ta. The present invention has been made in view of the above circumstances, and provides a method for vertically etching a resist.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to form a metal oxide film on the side wall by adding a gas containing metal atoms such as tungsten or molybdenum to oxygen, which is an etching gas. This prevents etching caused by reflected ions. After etching, tungsten oxide or molybdenum oxide adhering to the sidewalls can be removed by washing with water.

(Function) According to the present invention, molybdenum oxide and tungsten oxide are formed by the reaction between a gas containing tungsten and molybdenum and oxygen, which is the main etching gas. Since these do not react with oxygen anymore, just a thin layer attached to the side walls of the resist sufficiently prevents attack of oxygen ions and enables vertical etching. Furthermore, since these are water-soluble, they can be easily removed by washing with water, and there is no problem that they are difficult to remove.

(Example) An example of the present invention will be briefly described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an etching apparatus used in carrying out this example. An electrode (2) is provided in a vacuum container (1), and a high frequency power of 13.5 [3 MHz] is applied from a high frequency power source (4) via a matching box (3). Etching gas is introduced from the gas introduction pipe (5) and exhausted from the exhaust port (6). A water-cooled tube (7) is passed through the electrode (2) to cool it. The wafer (8) to be etched is
) is placed on top.

Here, a silicon substrate (20
) was coated with a resist (21) to a thickness of 1.8 microns, and after baking at 200°C, coated spin-on glass (SOG) was coated as an intermediate layer (22).
After beta at ℃, form a resist pattern (23),
A sample is prepared in which the SOG film (22) is etched using CF4 plasma using this resist (23) as a mask. The sample was introduced into the above-mentioned etching apparatus, and
After drawing a vacuum below Torr, 308 ccI of oxygen gas was added.
11 was introduced, the pressure was maintained at 5 mTorr, and high frequency power of IW per unit electrode area was applied to perform etching of the resist. Next, as an example of the present invention, a new sample was placed in an etching apparatus, and 30 sec of oxygen and 2 sec of molybdenum hexafluoride were introduced, and the resist was etched. When both were broken and the cross section was observed using an SEM, it was found that when etching was done with only oxygen gas,
As shown in Figure 2(b), there are gouges (2
On the other hand, when molybdenum butoxide was added, a thin # (24) was formed on the side wall and vertical etching was achieved, as shown in Figure 2 (C). This was confirmed. Next, this fractured sample was subjected to oxygen plasma ashing for only 30 seconds, the resist was slightly retracted from the cross section, and SEM observation revealed that a thin adhesion film was certainly formed and remained even after oxygen plasma ashing. was confirmed.

In addition, the remaining fractured sample was washed with water, and then oxygen plasma ashing was performed for 30 seconds to slightly etch the resist on the cross section to create a contrast with the sidewalls and SEM
As a result of tlJ inspection, no deposits were observed on the side walls.
It was confirmed that it was removed by washing with water.

Further, in this example, molybdenum hexafluoride was used, but other molybdenum compounds or tungsten compounds may be used.

[Effects of the Invention] As described above, by using the present invention, vertical processing of the resist becomes possible, and in the three-layer resist method, etc.,
Machining accuracy is significantly improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the etching apparatus used to carry out the present invention, FIG. 2 is a diagram for explaining the present invention in detail, and FIG. 3 is a case in which a resist pattern with unevenness is formed on a substrate. 4 is a diagram showing an outline of the three-layer resist method, and FIG. 5 is a diagram showing the conventional problems in resist etching during the process of the three-layer resist method. 1... Vacuum container, 2... Electrode, 3...
・Matching box, 4...High frequency power supply, 5...Gas introduction pipe, 6
...Exhaust port, 7...Water cooling pipe, 8...
・Wafer 20...Silicon substrate, 21
...Resist, 22...Spin-on glass, 23...Resist, 24...Side wall protective film,
30... Silicon substrate, 31... Resist, 40...
... Material to be etched, 41 ... Silicon substrate, 42
...Resist, 43...Middle layer, 44...
- Resist, 50... Silicon substrate, 53... Plasma polymerized film.

Claims (3)

[Claims] (1) A dry etching method characterized by patterning a resist using a mixed gas of a metal compound gas and a gas containing oxygen. (2) The dry etching method according to claim 1, wherein the metal compound gas is a compound of molybdenum or tungsten. (3) The dry etching method according to claim 1, wherein the oxygen-containing gas is oxygen.