JPS61220432A - Etching method - Google Patents

Abstract

PURPOSE:To regulate the cross sectional etching shape and to prevent the pattern dimension from decreasing due to the side face etching, by providing with a mask with given openings on silicon or polysilicon, and by plasma-treating it in SF6+NH3 to form selectively a coating on the mask. CONSTITUTION:On polysilicon 3 lying on SiO2 5, a photo resist mask 1 is formed. At this time, in an atmosphere in which NH3 over 0.06 Pa is added into SF6 of 0.1 Pa, microwave plasma etching in magnetic field forms the new mask 1 on the mask 2 without removing the polysilicon 3. The film forming rate is higher on the side face than on the plane portion, and is higher as the NH3 gas pressure increases. Moreover, under an SF6 gas pressure of 0.1 Pa, the mask 1 is deposited under a less NH3 gas pressure, and over 0.1 Pa, NH3 mixing ratio must be made higher. After the sample is treated under conditions to deposite the mask 1, decreasing the NH3 adding quantity etches the polysilicon or single crystalline silicon 3 into a desired cross sectional etching shape, with the result that treating quality of wiring material can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an etching method, and particularly to an etching method suitable for controlling the cross-sectional shape of polycrystalline silicon and silicon.

[Background of the invention]

As a conventional etching method, carbon and fluorine are used as a mask layer on an insulating film, as described in Japanese Patent Laid-Open No. 59-39048.

A method has been proposed in which a polymer having C--F bonds is deposited on the surface of a sample using plasma using a mixed gas containing hydrogen. However, no consideration was given to conductors such as silicon or polycrystalline silicon, and no consideration was given to deposits other than polymers having C--F bonds.

[Purpose of the invention]

The purpose of the present invention is to control etching cross-sectional shapes, prevent reduction in pattern dimensions due to side etching, and prevent mask pattern broadening in areas that are impossible with beam lithography technology in semiconductor manufacturing processing technology that is becoming increasingly finer. The goal is to provide technology.

[Summary of the invention]

In dry etching technology, it is necessary to be able to perform etching according to the mask dimensions, but in reality, the mask dimensions become smaller during etching and there are undercuts, so the finished dimensions are often smaller than the mask dimensions. As a countermeasure, measures have been taken such as making the mask dimension thicker by the amount of dimension reduction in advance so that the finished dimension is a predetermined dimension. But sub μ
When manufacturing m-dimensional elements, the space width between mask patterns becomes, for example, 0.6 μm or less, which approaches the limit beyond which patterning can be performed by photolithography, and it is no longer possible to widen the mask dimensions. Therefore, in etching, it is absolutely necessary to have a processing method that matches the mask dimensions without any reduction in dimensions. However, as mentioned above, a complete dry etching method has not yet been developed.

Therefore, we investigated a deposition method that deposits only on the mask. With conventional plasma-based polymer deposition methods, it is almost impossible to selectively deposit only on the resist mask, and only carbon and hydrogen can be deposited selectively.

This could not be expected with plasma using a mixed gas such as oxygen. In a mixed gas of SF and NH, which is effective for vertical etching of silicon and polycrystalline silicon, if NH and I are mixed excessively, deposition will occur selectively on the resist mask, and deposition and etching will occur on silicon and polycrystalline silicon. It was also found that this does not occur.

[Embodiments of the invention]

An embodiment of the present invention will be described below. Although a magnetic field microwave plasma etching apparatus is used in this embodiment as a plasma generating apparatus, other plasma etching apparatuses or reactive ion (or sputter) etching apparatuses may also be used. SF in magnetic field microwave plasma etching.

When the etching gas is used as the etching gas, the cross-sectional shape shown in FIG. 2 is obtained. In Figure 2, the mask material is photoresist (AZ
1350J) 1, but dotted line 2 before etching
The dimensions were as shown in . The material to be etched is polycrystalline silicon 3, which was in the state shown by the dotted line 4 before etching. The base of the polycrystalline silicon is silicon oxide Si0.5. In the etched cross-sectional shape of FIG. 2, the bottom of the mask is etched.

This shows a so-called undercut state, and in FIG. 1, a indicates the amount of dimensional shift due to the undercut, and b indicates the amount of dimensional shift from the mask dimension. The magnetic field microwave plasma conditions to obtain the cross-sectional shape shown in Figure 2 are SF, gas pressure 0, IPa, and microwave power 20.
It is 0W. Figure 3 shows the S
F, 0. This is the etched cross-sectional shape when NH and 0.06Pa are added to IPa. In FIG. 3, it appears that the polycrystalline silicon 3 has been etched to match the dimensions of the mask 1, but in reality, the dimensions of the polycrystalline silicon 3 are smaller than the dimensions of the mask 2 before etching. Although the amount of reduction varies depending on the overetching time, in this embodiment, overetching by 30% of the etching time (about 40 seconds) reduces the mask width by about 0.2 μm.

In the normal etching method as mentioned above.

There is an undercut phenomenon in which the mask size decreases or the etching digs into the lower part of the mask, and it is often difficult to obtain processing dimensions that match the mask dimensions before etching.

In the present invention, SF, 0. 0.06 Pa to I Pa
In this example, the cross-sectional shape shown in FIG. 1 was obtained by adding the above NH3 gas, the polycrystalline silicon 3 was not etched, and a new mask 1 deposited on the mask 2 before etching was formed. has been done. The characteristic of the deposited film here is that the film formation rate is faster on the side surface than on the flat surface, and this phenomenon is a selective deposition phenomenon due to differences in surface materials.
, +NH, mixed base gas This is a characteristic phenomenon in the case of polycrystalline silicon or silicon single crystal and a photoresist mask. For example, when using photoresist with other materials such as silicon oxide or tungsten, it is not possible to selectively thicken the mask by depositing it on the entire surface.

For selectively depositing SF, +NH, and mixed gas on photoresist on polycrystalline silicon or silicon single crystal, SF is 0.06 when the gas pressure is 0.1 Pa.
It occurs when NH3 gas is added above Pa, and the higher the NH3 gas pressure, the higher the deposition rate.
When the NH3 gas pressure is lower than Pa, the above SF and N
Even if the ratio of H is lowered, it becomes easier to deposit. For example, SF.

When the pressure is 0.05 Pa, deposition occurs above 0.02 Pa.

On the contrary, SF, if the gas pressure is higher than 0.1 Pa, NH
By selectively depositing only on the mask with a mixing ratio of 0 or more, which requires a high mixing ratio, it is possible to perform mask widening, and it is possible to overcome the limit of openings in the mask using lithography technology (for example, 0.6 μm openings). The hole is even smaller (0.6μ by the optical lithography process) than the hole that is said to be the smallest in the current optical process.
If this patented method is applied to a sample with a hole of 0.6μ
It is possible to make the opening size smaller than m.

If etching is then performed using this newly deposited mask under conditions that reduce the amount of the mask, it is possible to process the mask to a size larger than the initial mask size. In addition, if it is an opening, as shown in FIG.
Etching is possible. By using this method, even if the etching method causes undercutting, the finished dimension d of the polycrystalline silicon 3 can be controlled to the initial mask dimension 2, as shown in FIG.

Although it is not clear what the material of this deposited film is.

This deposit is SF, gas or SF, with a small amount of NH added to it.
, and has the characteristic of being etched at a higher rate than a photoresist mask by a mixed gas. therefore,
After processing the sample under the deposition conditions, the amount of NH and gas added is reduced.

As shown in the etched cross-sectional shapes shown in FIGS. 6a, b, and a, a desired etched cross-sectional shape can be obtained by controlling the method. By controlling polycrystalline silicon or silicon single crystal in the manner described above to obtain an etched cross-sectional shape, it is possible to prevent electrical shorts between wiring lines, for example, in actual LSI manufacturing. That is, as shown in FIG. 7a, the glabellar insulating film (for example, Sin
, , P53G, etc.) 7 is formed, on which a second wiring material 8 (eg polycrystalline silicon) is formed.

tungsten, silicide, aluminum etc.) is formed, and when the second wiring material 8 is etched, an etched residue 9 of the second wiring material is formed in the constricted part when the insulating film is formed between the eyebrows. If the etched cross-sectional shape of the polycrystalline silicon is set to 6 vAa in advance using this patented method, a wedge can be formed in the glabella insulating film 7 as shown in Figure 7 above. Since no portion of the second wiring material remains after etching (9 in FIG. 7a), a good etching process is possible.

〔Effect of the invention〕

According to the present invention, it is possible to create a fine aperture mask that is impossible with photolithography, and for example, it is possible to create fine contact holes or through holes in a correlative insulating film. By performing taper etching, it is possible to drastically reduce the problem of electrical short circuits between wirings, which often occur when etching wiring materials, and at the same time significantly improve the yield in semiconductor manufacturing and improve the quality of microfabrication. effective.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing selective deposition on a mask in the present invention, Fig. 2 is a cross-sectional view of polycrystalline silicon etched using only SF and gas, and Fig. 3 is a cross-sectional view of polycrystalline silicon etched using SF, NH, and a mixed gas. FIG. 4 is an etched cross-sectional view after selective deposition, and FIG. 5 is an etched cross-sectional view under undercut conditions after selective deposition.
FIG. 6 is a cross-sectional view of etching deposits and polycrystalline silicon simultaneously or in a controlled manner after selective deposition, and FIG. 7 is a cross-sectional view of a multilayer wiring. DESCRIPTION OF SYMBOLS 1...Mask after etching, 2...Mask before etching, 3...Polycrystalline silicon, 4...Before etching...Interlayer insulating film, 8...Second wiring material, 9.・
- Etching residue of second wiring material. Tea 1 Figure Z Figure 'IfJ3 Illustration 4 Iris 5 Figure ￥J 6 Figure (12-) (b) (c) Kudzu 7 Figure

Claims (1)

[Claims] 1. A film is selectively formed on the mask layer by a step of forming a mask layer having a predetermined opening on the surface of silicon or polycrystalline silicon and a step of plasma treatment. Etching method. 2. Claim 1, characterized in that the gas used for plasma treatment is a gas containing fluorine, nitrogen, and hydrogen.
Etching method described in section. 3. The etching method according to claims 1 and 2, characterized in that the gas containing fluorine is SF_6 gas, and the gas containing nitrogen and hydrogen is NH_3 gas.