JP2932488B2 - Dry etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dry etching method, and more particularly, to a dry etching method for selectively etching an organic layer (resist layer) formed on a base layer. It is related.

[Summary of the Invention] The present invention relates to a dry etching method for selectively etching an organic layer formed on an underlayer, wherein a mixed gas of a chlorine gas and an oxygen gas is used as an etching gas to thereby form an anisotropic organic film. In addition to speeding up the wet processing, it is possible to expand the range of etching conditions such as pressure and flow rate.

[Prior Art] In recent years, with the miniaturization of patterns in semiconductor devices, it has become difficult to respond to miniaturization with a single-layer resist, and multilayer resist technology has become widespread. This multi-layer resist technique generally forms a photoresist layer as an underlayer planarization layer on an underlayer having a step, and forms another layer or two or more layers on this photoresist layer. Patterning is performed, and using this as a mask, a resist that is an underlying flattening layer is to be developed. As a resist developing means serving as the underlayer flattening layer, the underlayer is dry-etched using the patterned upper layer film as a mask.

As this method, for example, as shown in FIG.
A planarization layer 2 is formed on a base layer 1 (substrate, wiring, etc.) having 1a, and an organic film 3 is formed thereon by a photoresist, and then, as shown in FIG. 3 and then, as shown in FIG. 7C,
The flattening layer 2 is dry-etched by using the organic film 3 as a mask (such a two-layer resist method is described in "Electronic Materials", April 47, pp. 47 and 48). ).

8A to 8E show a three-layer resist method. In this method, a lower organic film 5 made of a photoresist also having a function as a flattening film is formed on a base layer 4 such as a substrate (FIG. 8A), and a SiO 2 film is formed thereon by CVD.
₂ , an intermediate layer 6 such as SOG by spin coating or the like is formed, and an upper layer 7 made of a normal resist is further formed (FIG. 8B). As shown in FIG. C, the intermediate layer 6 is patterned by RIE or the like using the upper layer 7 as a mask, as shown in FIG. 8D, and then the base organic film 5 made of photoresist is subjected to RIE using oxygen gas or the like as an etching gas. Patterning (8th
FIG. E) Technology (see “Semiconductor World” (Press Journal), November 1987, pp. 101-105).

In addition, there is a so-called PCM method as a multilayer resist technique.

In the above-described techniques, it is preferable to use a material having good dry etching resistance as a photoresist to be used as an etching mask. However, in the conventionally proposed two-layer resist technique, this mask resist is generally used. For example, a resist material called a Si-containing resist is used. Usually, this resist is subjected to reactive ion etching with oxygen gas or the like to obtain a desired pattern. This principle is believed to be due to oxidation (SiO _x conversion) of the upper Si-containing resist by O ₂ plasma.

As described above, usually, in the lower layer etching process of the multilayer resist, SiO ₂ or ₂ which is the intermediate layer of the three-layer resist is used.
Etching with O ₂ gas is performed using the Si-containing resist of the layer resist as a mask. In this case, to ensure sufficient anisotropy,
Low pressure, high Vdc conditions are essential. Processing of the underlying resist layer is performed under a low pressure and high ion energy with respect to oxygen O _{2 to be} used, due to a problem of reactivity between oxygen radicals O ^* and an organic film such as a resist, in a mode similar to a sputtering reaction by ions. Must be etched.

[Problems to be solved by the invention] However, under such low pressure and high Vdc conditions,
Usually, the concentration of the radical species contributing to the etching is reduced, so that a sufficient etching rate cannot be obtained. However, on the other hand, if conditions for increasing the radical concentration in order to improve the etching rate, that is, conditions of high pressure and low Vdc, are used, an anisotropic shape cannot be obtained under such conditions, and an undercut occurs. There's a problem.

Therefore, a dry etching method capable of increasing an etching rate while securing an anisotropic shape has been desired.

The present invention has been made in view of the above-mentioned problems of the prior art, and maintains the etching shape in an anisotropic shape, particularly while maintaining the etching shape in an anisotropic shape without undercut, and at the same time, has a sufficient etching rate. An object of the present invention is to obtain a dry etching method which can be performed at a high speed.

Means for Solving the Problems Accordingly, the present invention provides a dry etching method for selectively etching an organic layer formed on a base layer,
A mixed gas of chlorine gas and oxygen gas is used as an etching gas.

The etching gas in the present invention is obtained by adding oxygen gas (O ₂ ) at a flow rate of 1 to 99% with respect to chlorine gas.

In the present invention, what is etched is the organic film formed on the underlayer.

Here, the underlayer may be any underlayer on which an organic film such as a resist to be etched is to be formed, and is not limited to its type or material. For example, a wiring layer, an interlayer insulating film, a semiconductor layer, It may be a mask material or the like.

In the present invention, as the organic film to be selectively etched, any material can be used as appropriate. For example, a photoresist for forming a photoresist pattern, that is, a photoresist that can be patterned by exposure and development A substance can be used as an object to be etched. In addition, a buffer layer is provided on the underlayer, the multilayer resist including this structure is etched using a mixed gas of chlorine gas and oxygen gas as an etching gas, and the etching of the buffer layer is performed under the same conditions as the organic layer. I do.

[Operation] In the present invention, by using a mixed gas of chlorine gas and oxygen gas as an etching gas, the deposition of a reaction product CClx between the chlorine gas and the organic layer serving as a resist is removed by oxygen gas (O ₂ ). While the etching proceeds, the reaction mechanism becomes a reaction mechanism. For this reason, even in a pressure region where an undercut is usually caused by oxygen radicals (O ^* ), anisotropic processing by the CClx-based side wall protective film becomes possible, and a physical reaction using only ions under low pressure is possible. Anisotropic processing of the resist (organic layer) is achieved at a much higher speed than in the case of etching. Next, a buffer layer is provided on the underlayer, and the multilayer resist including this structure is etched using a mixed gas of chlorine gas and oxygen gas. It can be carried out.

EXAMPLES Hereinafter, details of the dry etching method according to the present invention will be described based on examples shown in the drawings.

First Embodiment FIGS. 1 to 3 show an embodiment in which the present invention is applied to a three-layer resist method.

In the figure, reference numeral 10 denotes a silicon substrate as a base layer, on which a lower resist 11, which is an organic layer, is formed.

Next, SOG (spin-on-glass) is applied on the lower resist 11 by spin coating to form an intermediate layer 12,
Further, an upper layer resist 13 made of a normal resist is formed,
Normal exposure and development are performed, and the upper layer resist 13 is used as a mask by RIE (reactive ion etching) or the like.
Is patterned (FIG. 1).

Next, the lower resist 11 is dry-etched under the following conditions.

The flow ratio of the etching gas is chlorine gas (Cl ₂ ): oxygen gas = 2: (20 SCCM): 3 (30 SCCM), the pressure is 10 mTorr,
Vdc was -300V.

FIG. 2 is a cross-sectional view showing the resulting etched shape, showing complete anisotropy without undercut.

In this embodiment, when the pressure, Vdc, and the total flow rate of the etching gas (50 SCCM) are the same, and the flow rate ratio is set to chlorine gas: oxygen gas = 1: 4, the etching is performed as shown in FIG. In addition, the anisotropy has almost no undercut.

When the pressure, Vdc, and the total amount of etching gas were the same, and only oxygen (O ₂ ) gas was used as the etching gas, as shown in FIG. 4, an undercut occurred, and an anisotropic etching shape was not obtained (comparative). Example 1).

Further, the etching rate in the present embodiment is about 9300Å /
Minutes and fast etching was achieved. In contrast, when only oxygen gas was used as in Comparative Example 1 above,
When trying to achieve an etching of an anisotropic shape without undercut, the gas flow rate was set to about 1/10 of the above example,
The pressure needs to be on the order of 10 ^-4 Torr, and the etch rate at that time is about 600 to 800 ° / min, which is only about 1/5 that of the above embodiment, resulting in extremely slow etching.

By the way, as a reaction process in this example,
With the etching, Cl of chlorine gas reacts with the resist, and the reaction product CClx protects the side wall of the lower resist 11,
An anisotropic etched shape without undercut is achieved.

The etching conditions for achieving the anisotropic processing can be changed as appropriate, and are not limited to the above conditions.

In the present invention, as the organic film to be selectively etched, any material can be used as appropriate. For example, a photoresist for forming a photoresist pattern, that is, a photoresist that can be patterned by exposure and development A substance can be used as an object to be etched.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 5A and 5B.

This embodiment is an example in which a three-layer resist is provided on a wiring layer having a step.

First, SiO ₂ films 14 and 15 are formed on a silicon substrate 10, a step is formed by the SiO ₂ film 15, and a wiring layer 16 (base layer) made of aluminum is formed thereon. Then, as shown in FIG. 5A, after forming a buffer layer 17 made of molybdenum (Mo) on the wiring layer 16, a patterned three-layer resist structure similar to that of the first embodiment is formed (lower layer). Resist 11, intermediate layer 12, upper layer resist 13).

Then, Cl ₂ gas: O ₂ gas = 2: 3 as an etching gas
Flow rate (total flow rate 50 SCCM), pressure 10mTorr, Vdc-300V
When dry etching is performed under the conditions described above, a shape as shown in FIG. 5B is obtained. That is, by dry etching, etching can be continuously performed up to the buffer layer 17 under the same conditions as the organic layer.

In this embodiment, the molybdenum of the buffer layer 17 reacts with the etching gas by etching, and the oxychloride Mo _x O
It is quickly removed in the form of _y Cl _z . For this reason, no reattachment is generated on the side wall to be etched.

Further, in the case of overetching the wiring layer 16 made of aluminum with a chlorine-based gas, an undercut occurs even if the wiring layer 16 is etched. But Mo buffer layer
By arranging as 17, only the buffer layer 17 is etched at the time of overetching, and does not affect the wiring layer 16. Note that the remaining buffer layer 17 may be removed by fluorine radicals F ^* after the patterning of the wiring layer 16.

6A and 6B are comparative examples showing a case where the buffer layer 17 is not provided in this embodiment.

In this comparative example, as shown in FIG. 6B, the deposit (Al ₂ O ₃ ) 18 adheres to the side wall (shallow side) by etching, and the generation of the deposit 18 is prevented even when chlorine gas is added. I can't.

In addition, Al ₂ O
_In order to prevent the formation of ₃ , it is necessary to use only a chlorine-based gas as the etching gas at the time of over-etching.
Etching is performed in two steps, which is complicated.

In the second embodiment, molybdenum is used as the buffer layer 17, but the present invention is not limited to this. Any material that can generate oxychloride as a reaction product can be appropriately changed.

In this embodiment, the re-adhesion of the underlying aluminum wiring at the time of over-etching in the multilayer resist patterning process can be prevented, and the undercut of the underlying aluminum layer (wiring layer) at the time of over-etching can be prevented.

The resist material and the like used in the second embodiment are the same as those in the first embodiment.

[Effects of the Invention] As is clear from the above description, claims 1
In the dry etching method described in the section, the anisotropic processing of the resist, which was conventionally achieved only by the physical reaction mainly by ions, can be achieved by the process using the sidewall protective film, and the wide etching conditions This has the effect of increasing the speed below.

According to the dry etching method described in claim 2, a buffer layer is provided on the underlayer, and the multilayer resist including this structure is etched using a mixed gas of chlorine gas and oxygen gas. The etching can be continuously performed from the organic layer to the buffer layer under the same conditions as the layer.

[Brief description of the drawings]

1 to 3 are sectional views showing a first embodiment of a dry etching method according to the present invention, FIG. 4 is a sectional view showing a comparative example, and FIGS. 5A and 5B are second embodiments. A sectional view showing the
6A and 6B are cross-sectional views showing a comparative example, and FIG.
7 to 7C are cross-sectional views illustrating a two-layer resist method, and FIGS. 8A to 8E are cross-sectional views illustrating a three-layer resist method. 10: silicon substrate, 11: lower resist, 12: intermediate layer, 13: upper resist, 16: wiring layer, 17: buffer layer.

Claims (2)

(57) [Claims] 1. A dry etching method for selectively etching an organic layer formed on an underlayer, wherein a mixed gas of chlorine gas and oxygen gas is used as an etching gas. 2. A dry etching method for selectively etching an organic layer formed on a base layer, comprising: providing a buffer layer on the base layer; A dry etching method characterized by etching using a mixed gas of the above, and further etching the buffer layer under the same conditions as the organic layer.