JPS61247033A - Taper etching method - Google Patents

Abstract

PURPOSE:To obtain a tapered etching shape without dimensional conversion error by using mixture gas of etching gas containing halogen atoms oxidative gas containing accumulating gas and oxygen for generating a deposited film by discharge. CONSTITUTION:A sample 24 of a substrate 11 to be treated and formed with an etching mask 12 is placed on one of parallel flat plate electrodes 22, 23, CHF3 gas is fed into a vessel 21, a high frequency power is applied to generate a discharge plasma. A resist 13 is removed by another oxygen plasma asher different from a device. Subsequently, the sample is again disposed in the vessel 21, etched by applying a high frequency power in chlorine as etching gas and methane as accumulating gas. Thus, a polymer film (accumulated film) 14 is gradually adhered to the mask 12 and the etched side wall, and a tapered etching groove 15 is formed together. It can prevent the extension 16 of the end of the mask in a large drawing pattern from generating due to the mixture of the oxygen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in dry etching methods, and particularly to a taper etching method for etching a substrate in a tapered manner.

[Technical background of the invention and its problems]

In recent years, with the miniaturization of semiconductor integrated circuits, reactive ion etching technology has been introduced, and a vertical etched shape along a resist pattern has been achieved. However, depending on the process, for example, when etching the first polysilicon in a two-layer polysilicon process or the single crystal 3i in forming a buried element isolation region, it may be desirable to form the etching tapered rather than vertically.

As a method for taper processing using a reactive ion etching device, a method has been proposed in which a hydrocarbon gas such as ethane or methane is added to the etching gas to cause polymer deposition and etching by the hydrocarbon gas at the same time (
Kimizuka et al., Proceedings of the 29th Spring Joint Conference on Biological Sciences P, 3B1
．． 2ad5.1982”).

The mechanism by which a taper is formed by this method will be briefly explained with reference to FIG.

As shown in FIG. 3(a), it is assumed that a 5i02 film 32 is previously formed on the Si substrate 31 as an etching mask material. Then, when a mixed gas of, for example, chlorine and methane is introduced into the container and high frequency power is applied between the electrodes to generate a discharge, methane will first polymerize, as shown in Figure 3(b). As shown in the figure, the entire surface is covered with a polyethylene film 3.
4 is deposited. At the same time, since there is an ion bombardment, the polyethylene film 34 deposited on the surface is destroyed as shown in FIG. 3(C), and etching progresses in this area. However, the polyethylene film 34 on the sidewall of the pattern where ions are not incident remains undestructed. Therefore, the next etch occurs a thickness valve of polyethylene film 34 away from the pattern edge. By repeating this process, a taper is formed in the etched cross section of <S+ as shown in FIG. 3(d). Note that this taper angle can be selected depending on the ratio at which deposition and etching occur, that is, the mixing ratio of chlorine and methane.

However, this type of method often has the following problems. That is, the taper angle depends on the size of the pattern, and while a small pattern as shown in FIG. 4(a) tapers from the edge of the mask,
As shown in b), in a large pattern, the mask tapers from a little distance from the edge. In other words, a protrusion (unetched portion) 36 is generated near the end of the mask.

Such a shape is undesirable because it causes a dimensional conversion error.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a taper etching method that can obtain a tapered etched shape without causing dimensional conversion errors due to pattern size. There is a particular thing.

[ [Summary of the invention]

The gist of the present invention is to remove protrusions at the edges of the mask that occur when the pattern size is large by adding a new oxygen-containing gas as a gas during taper etching.

As a result of intensive research conducted by the present inventors, it was found that the pattern dependence of the taper angle is a type of loading effect. That is, for a small treated pattern, the etched area is small compared to the mask area, while for a large treated pattern, the etched area is very large compared to the mask area. others.

Therefore, the concentration ratio of chlorine and methane in the vicinity of the etching area is such that the larger the pattern, the more methane is present, ie, the atmosphere is more likely to cause deposition.

Roughly, the oxide film such as S i 02 which is a mask is also etched and releases oxygen. In the case of a large grading pattern, since the mask area is small as described above, the amount of released oxygen is small. Oxygen has the effect of oxidizing methane near the etching surface. This low amount of oxygen is also one of the reasons why deposits tend to occur in large handling patterns.

In addition, when using an insulating film such as 5i02 as a mask,
There is a risk that the mask itself will become electrically charged and bend the ions incident on the surface to be etched. In particular, in the case of a large handling pattern, the ions in the vicinity of the pattern sidewalls are strongly influenced by the nearby pattern sidewalls, and the ions are greatly bent. This problem is also considered to be a cause of dimensional conversion errors depending on the pattern size.

Therefore, in order to eliminate the pattern dependence of the taper angle, it is possible to increase the oxygen concentration in a large taper pattern, and it is even more effective if a small amount of oxidizing gas is added. Therefore, the present invention is characterized in that, in addition to the etching gas and the deposition gas such as hydrocarbon, an oxidizing gas is added as a third gas.

That is, in the present invention, a substrate to be processed having an etching mask formed on the surface to be processed is placed between a pair of electrodes, a predetermined gas is introduced between these electrodes, and a discharge is generated between the electrodes. In the taper etching method for etching the substrate to be processed into a tapered shape, the gas is a mixed gas of an etching gas containing halogen atoms, a deposition gas that generates a deposited film by electric discharge, and an oxidizing gas containing oxygen. This is the method used.

[Effects of the Invention] According to the present invention, by adding an oxidizing gas, it is possible to sufficiently increase the oxygen concentration particularly in a large pattern, and the deposited film at the edge of the mask can be etched. Therefore, protrusions at the ends of the mask can be removed. Therefore, pattern size conversion errors can be significantly reduced, which is effective for miniaturization and high integration.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIGS. 1(a) to 1(e) are sectional views showing a taper etching process according to an embodiment of the present invention.

First, as shown in FIG. 1(a), a P-type Si substrate 11 with a plane orientation (100) was wet-oxidized at 1000 ['C] to form an Si 02 film 12 as a mask material on the substrate 11. Subsequently, a positive photoresist 13 was applied onto this SiO2 film 12, and this resist 13 was patterned to form a resist pattern. Here, both a small punching pattern and a large handling pattern were formed in the resist pattern.

Next, using an etching apparatus as shown in FIG.
By reactive ion etching using F3 gas, S
The i02 film 12 was selectively etched to form a mask pattern. Thereafter, the resist 13 was removed using an oxygen plasma asher to obtain the shape shown in FIG. 1(b).

The apparatus shown in FIG. 2 is similar to a normal reactive ion etching apparatus, and in the figure 21 is a vacuum vessel, 22.23
are parallel plate electrodes, 24 is a sample, 25 is a matching circuit,
26 is a high frequency power source, 27 is a gas inlet, and 28 is a gas exhaust port. To perform the above-mentioned etching using this apparatus, first, a sample 2 having the shape shown in FIG.
4 is placed on one of the parallel plate electrodes 22 and 23. Then, while introducing CHF3 gas into the container 21, the electrode 2
A discharge plasma may be generated by applying high frequency power between 2.23 and 2.23. In addition, the removal of the resist 13 is performed on the container 2.
Once the sample 24 was taken out from inside the sample 1, an oxygen plasma asher different from the above-mentioned apparatus was used.

Next, the sample shown in FIG. 1(b) was again placed in the container 21 of the apparatus shown in FIG.
0 [sccm], oxygen 2 [S
CCm], pressure 0.15 [torr], and high frequency power 800 [W] for 90 seconds (condition 1). Etching was also performed in the same manner under Condition 2, except that oxygen gas was removed from Condition 1 above.

With this etching, both conditions 1 and 2 are shown in Figure 1 (C) (
As shown in d), a polymer film (deposited film) 14 gradually adhered to the mask 12 and the etching side wall, and a tapered etching groove 15 was formed together with this. However, under condition 2, as shown in FIG. 1(d), a protrusion (unetched part) 16 is generated at the edge of the mask due to the wide handling pattern, whereas under condition 1, the taper angle is large, but the pattern is large. Even in the pattern, there is no protrusion 16. In other words, it is possible to prevent the protrusion of the end portion of the mask in a large punched pattern due to the mixing of oxygen gas.

On the other hand, under condition 3 in which the amount of methane gas was reduced instead of adding oxygen gas, the taper angle increased as shown in FIG. 1(e), and the protrusion 16 at the end of the mask became smaller. If the amount of methane gas is further reduced, the protrusion 16 will be completely eliminated, but the etched cross section will become vertical and it can no longer be called taper etching. That is, the effect of removing the protrusion at the edge of the mask in a large pattern while maintaining the tapered shape can only be obtained by adding the oxygen gas.

As described above, according to the method of this embodiment, by adding oxygen gas to taper etching using chlorine and methane gas, protrusions at the edges of the mask can be removed. Therefore, a desired tapered shape can be achieved without causing dimensional errors due to the size of the mask pattern. Furthermore, the addition of oxygen gas can reduce the amount of polymerized film at the end of etching. Therefore, the step of removing the polymer film after etching can be performed in a single hour. Therefore, great effects can be obtained when applied to various types of etching that require a tapered cross section.

Note that the present invention is not limited to the embodiments described above. For example, the object to be etched is not limited to the 81 substrate, but may also be applied to a poly 3i film, a SiO2 film, or an A2 film. Further, instead of chlorine as the etching gas, any gas containing at least halogen atoms may be used.

Furthermore, instead of methane as the deposition gas, any gas that can generate a deposited film by electric discharge may be used, and hydrocarbons or hydrocarbon compounds other than methane can be used.

In addition, the oxidizing gas to be added to the above gas is not limited to oxygen, but any one of carbon monoxide, carbon dioxide, nitrous oxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide, and water vapor, or multiple types thereof. It may be a mixed gas.

Further, the etching apparatus is not limited to the configuration shown in FIG. 2, but can be modified as appropriate. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIGS. 1(a) to (e) are cross-sectional views showing a taper etching process according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a schematic configuration of a reactive ion etching apparatus used in the method of the above embodiment. , FIGS. 3(a) to 3(d) are cross-sectional views for explaining the mechanism of taper etching, and FIG. 4(a)(
b) is a sectional view for explaining the conventional problems. 11...3i substrate (object to be etched), 12...S
iO2 film (mask), 13... resist, 14...
Polymer film (deposited film), 15... Etching groove, 16...
・Protrusion (unetched part), 21... vacuum container,
22.23... Parallel plate electrode, 24... Sample, 25
...Matching circuit, 26...High frequency power supply, 27.
...Gas inlet, 28...Gas exhaust port. Applicant's agent Patent attorney Takehiko Suzue Figure 1 ^ ^ -, Ω 0

Claims (5)

[Claims] (1) A substrate to be processed with an etching mask formed on the surface to be processed is placed between a pair of electrodes, a predetermined gas is introduced between these electrodes, and a discharge is generated between the electrodes to remove the etching mask. In a taper etching method for etching a treated substrate into a tapered shape, the gas is a mixed gas of an etching gas containing a halogen atom, a deposition gas that generates a deposited film by electric discharge, and an oxidizing gas containing oxygen. A taper etching method characterized by: (2) The taper etching method according to claim 1, wherein chlorine is used as the etching gas. (3) The taper etching method according to claim 1, wherein a hydrocarbon or a hydrocarbon compound is used as the deposition gas. (4) As the oxidizing gas, any one of oxygen, carbon monoxide, carbon dioxide, nitrous oxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide, and water vapor, or a mixture of multiple types thereof was used. The taper etching method according to claim 1, characterized in that: (5) The taper etching method according to claim 1, wherein the pair of electrodes are parallel plate electrodes.