JPS62145733A - Etching - Google Patents

Abstract

PURPOSE:To reduce side etching caused by scattered ions substantially by employing mixed gas of heavy reactive gas and light rare gas. CONSTITUTION:A cathode coupling type reactive sputtering apparatus is employed as an etching apparatus and mixed gas composed of Br2 and He mixed in the ratio of 1 to 9 is employed as etching gas. As a result, the depth of side etching is less than 0.1mum and a quite vertically steep side wall can be obtained. When etching ions are scattered in reactive etching, most of the apponents of the collisions of the ions are etching gas molecules themselves. Therefore, in the case of Br2+90%He mixed gas, 10% of Br<+> ions produced by dissociation of Br2 molecules collide against Br2 molecules and 90% collide against He molecules. As the mass ratio of Br<+>/He=20, Br<+> ions which collide against He molecules hardly turn side from the direction of acceleration and enter a specimen surface. Therefore, in this case, the incident angle distribution of Br<+> ions is concentrated near zero degree and such etching is suitable for highly accurate work.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an etching method, and particularly to a dry etching method suitable for forming fine patterns with high precision.

[Background of the invention]

In recent years, in the processing of fine patterns such as semiconductor integrated circuits,
A dry etching method using reactive gas plasma, particularly a reactive sputtering method, is often used. This method is
It is characterized by high-precision processing based on etching selectivity based on gas reactivity (fast etching of only specific materials) and ion directionality (accelerated from the plasma toward the sample).

In order to take advantage of this feature, it is necessary to optimize the type of reaction gas and plasma discharge conditions.

Conventionally, for example, CC141Cli was used for etching Si.
, HC] and a method using a mixed gas of these and Ar (
Japanese Patent Laid-Open No. 52-9648) is known.

However, under conventional conditions, the gas pressure is generally higher than about IPa and the collision and scattering of ions 1 as shown in FIG. . When attempting to deeply process a very fine pattern of 1 μm or less, diagonal horizontal etching caused by such scattered ions becomes an obstacle to high-precision processing.

In contrast, to reduce ion collisions.

If the gas pressure is lowered, the discharge of the reactive sputtering device becomes unstable. There were problems such as unstable gas supply and exhaust.

[Purpose of the invention]

An object of the present invention is to provide an etching method that can significantly reduce side etching caused by scattered ions as described above.

[Summary of the invention]

To achieve the above object, the present invention uses a mixed gas of a heavy reactive gas and a light rare gas to reduce the scattering of etching ions and to maintain stable discharge and exhaust from the etching apparatus.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

A cathode couple type reactive sputtering device was used as the etching device, and the etching gas was a mixture of Brx and He in a ratio of 1:9.

Etching gas was introduced into the etching chamber at a flow rate of 70 cc/min, and exhaust was performed using a mechanical booster pump and an oil rotary pump. At this time, the gas pressure in the erating chamber was 6 Pa. In this state, a power of 600 IJ (0.3 tl/d) was applied using a high frequency power source of 1.3.56 MHz to generate plasma to etch the Si wafer placed in the etching chamber. As a result, S t O
When a hole with a width of 1 μm and a depth of 5 μm was formed using No. 2 as a mask, the cross-sectional shape had a side etch of 0.1 μm or less and a very vertical side wall. In addition, using only Brs+ as the etching gas, 6
When etching was carried out at a gas pressure of Pa, the side wall 6 of the groove had a slightly side-etched "<" shape as shown in FIG. Further, in this case, the side etch tended to increase as the groove width became narrower, or in the case of a thank-you groove that was more circular than a long and narrow groove. Furthermore, as the aspect ratio of the groove (depth 7 width) increases, the problem has become apparent that even if etching is performed for the same amount of time, only a groove shallower than the desired depth can be formed.

Such a difference in the presence or absence of He mixing can be considered as follows. When etching ions are scattered in reactive sputtering, most of the collision partners of the ions are etching gas molecules themselves. Therefore, in the case of a mixed gas of Brz+9Q% He, 10% of Br+ ions generated by dissociation of Brz will collide with Brz and 90% will collide with He.

B that is incident on the surface of the etching sample after such a collision.
FIG. 2 shows the calculation results of the incident angle distribution of r+ ions. Since the mass ratio of 10 Br to Bra is 1:2, the Br+ ions collided with Brz are likely to be scattered in a direction largely deviating from the acceleration direction. Therefore, the incident angle (the angle between the normal to the sample surface and the ion incident direction) is distributed from 0 degrees (normal incidence) to nearly 90 degrees.

We believe that if there are many ions with large incident angles, problems will occur when processing microgrooves, such as making it difficult for the ions to reach the bottom of the groove and making it easier for the opposing sidewalls to be id-etched by ions reflected from the sidewalls. It will be done. On the other hand, Br+ that collided with Hθ has a mass ratio of Br+/
Since He=2Q, the beam almost never deviates from the direction of acceleration and enters the test slope. Therefore, in this case Br
+ has an incident angle distribution concentrated near 0 degrees and is suitable for high-precision machining. From the above, even if the gas pressure is the same, that is, the probability of collision is almost the same, mixing a large amount of Hs with a pure Brz gas will align the directionality of the ions much better, allowing vertical machining. It should be noted that although He+ ions collide with He or Br2 and have a relatively large incident angle distribution, it is thought that because the sputtering effect of H8+ is small, it does not contribute much to side etching.

Even in a method using only Brz gas, the gas pressure can be lowered and ion scattering can be reduced by reducing the gas flow rate to, for example, several c c /min.

However, when the amount of gas introduced into the etching chamber was reduced, the etching chamber became susceptible to the influence of impurity gas released from the etching chamber wall during discharge, and the reproducibility of etching was significantly impaired. Since the operating pressure of the pump is higher when He is mixed, the flow rate of Br2 can be increased at the same partial pressure. Furthermore, when the gas pressure in the etching chamber was significantly lowered using an oil diffusion pump or the like, the discharge became unstable. This is because the gas molecules have become so sparse that the ionization necessary to start and maintain discharge cannot be stabilized in the etching chamber.

In this example, by mixing a large amount of Ha, the directionality of the ions can be aligned while keeping the gas supply/exhaust and discharge conditions stable. did it.

The reaction gas to be mixed with Ha is preferably one that generates ions having a sufficiently large mass compared to H8, and compounds of heavy halogen elements such as CI, Br, or ■ are suitable.

Among F compounds, F x r S F s +CF4 is unsuitable for SJ high-grade processing not only because the F ions are light but also because side etching is likely to occur due to neutral F radicals. The reaction gases that were mixed with He and successfully processed were CC1,4.

CC1a+Ox, SiC]a, HCl, C1z,
HBr.

) (Br 2+ and CC1a, CC12Fz +CC1, which are also chlorides and bromides but also contain F in the form of CF
, sF, CBrFg, CzBrzFa, etc.

Further, the mixing effect of He was significantly observed when the reaction gas was diluted with He by a factor of 10 or more. That is, 10
Under low gas pressure etching conditions of less than Pa, the mean free path of ions is substantially reduced by 1 by diluting He.
By increasing the number of orders of magnitude, it is possible to significantly improve machining accuracy.

Note that the method of mixing a large amount of Ha was similarly effective in high-precision machining not only of Si but also of other materials such as S i O2 and A1.

〔Effect of the invention〕

As described above, according to the present invention, etching can be performed with higher accuracy and stability even with the same etching equipment, and fine patterns of materials such as Si can be processed according to the mask dimensions, thereby facilitating miniaturization of semiconductor devices.・It has a great effect on high integration and high performance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a processed part showing the state of etching, and FIG. 2 is a curve diagram showing the principle of the present invention. 1...Ion, 2...Gas molecule, 3...Si, 4
... Square 1st closed 2nd opening

Claims (1)

[Claims] 1. In this method, the workpiece placed in a vacuum container is etched by bringing the workpiece into contact with plasma of a reactive gas until the depth becomes greater than the pattern width. . An etching method, wherein the reaction gas contains 90% or more of He. 2. The etching method according to claim 1, wherein the workpiece is silicon and the reaction gas is chloride/bromide.