JPS62297477A - Micro fabrication method - Google Patents

Abstract

PURPOSE:To easily form a fine pattern without side etching and having a taper cross section by reactive ion-etching a thin oxide placed on an electrode consisting of carbon alone or a material contg. a large amt. of carbon. CONSTITUTION:A reactive gas is introduced into the chamber 7 of a vacuum chamber to keep the chamber at a specified vacuum, and a plasma region 5 is formed by a high-frequency power source 4 between a cathode 2 and an anode 3 which are arranged in parallel. An ion sheath region is formed with the generated active ion or radical by an electric field. The active ion, etc., are allowed to react with the SiO2 film on the Si wafer of a sample 1 placed on the cathode 2, and reactive ion etching is carried out in accordance with an org. resist. The cathode 2 is formed with carbon alone or a material having a high content of carbon such as PP. As a result, large quantity of active species are generated to form a side wall protecting film, and side etching is prevented.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a microfabrication method for tapered etching of an oxide thin film.

[Conventional technology and its problems]

In recent years, with the increasing integration of semiconductor devices, there has been an increasing demand for fine and highly accurate pattern formation, and reactive ion etching (hereinafter abbreviated as RIE) is increasingly being used in the etching process. RIE is performed by reacting active ions or radicals generated in a low-temperature non-equilibrium plasma generated under reduced pressure with a material to be etched or notched, but since the material to be etched is usually placed on the cathode, the active ions are It collides with momentum in the direction perpendicular to the surface to be etched. On the other hand, since the movement of radicals is not affected by the electric field, they move chaotically even near the surface to be etched. Therefore, when etching proceeds mainly by ions, the etched cross section has a steep shape that rises almost vertically downward from the edge of the mask pattern, reflecting the direction of ion movement, achieving so-called anisotropic etching. .

Furthermore, when etching progresses mainly due to radicals, the etching cross section reflects the behavior of the radicals and etching progresses to the back side of the mask pattern, achieving so-called isotropic etching. Therefore, in the case of a material such as an oxide thin film, which has strong ionicity of interatomic bonds and large bond energy, and is etched mainly by ions, the etched cross section tends to have a steep shape. For this reason, 5i (h
When RIE is used to process oxide thin films such as oxides, many studies have been made in the past on attempts to create a tapered slope in the etched cross section using step RIE. Below, taper etching methods using RIE that have been announced so far will be listed.

(1) Method using the tapered shape of the resist mask (2) Method using the difference in etching selectivity and directionality between the material to be etched and the resist mask (3) Method using the sidewall protective film (4) Sputtering incidence Method (5) that utilizes angle dependence; Methods (1) and (2) in which the resist mask and the material to be etched are etched alternately; in both methods (1) and (2), not only the material to be etched but also the resist mask are simultaneously etched during RIB. By utilizing this phenomenon, the shape of a resist mask before etching is transferred to a material to be etched according to the difference in etching selectivity and directionality between the material to be etched and the resist. This method can perform taper etching with good controllability if the conditions are set appropriately.
Since the recession of the resist mask is used to form the tapered shape, there is a drawback that a difference in pattern conversion occurs between the resist pattern dimension and the etching pattern dimension. (3),
(4) is a method of controlling the direction in which etching progresses by locally attaching a polymer film to the etching surface during IIH. However, in method (3), when the material to be etched is an oxide thin film such as SiO□, the polymer film formed on the etched surface is removed by the oxygen generated when the oxide thin film is etched. Therefore, the controllability as an etching process is poor (and method (4) has the disadvantage of increasing the number of steps because it is necessary to perform RIE again after etching is completed and the resist is removed). Method (5) has the disadvantage of increasing the number of steps. In terms of taper formation using the retreat of the resist mask (1)
, similar to (2), a stepped tapered shape is formed by alternately etching the resist mask and etching the material to be etched. With this method, an arbitrary tapered shape can be obtained by setting appropriate conditions, but the process becomes complicated because it is necessary to change etching-related parameters many times during etching. The present invention solves the above-mentioned problems of the conventional methods, particularly regarding taper etching of oxide thin films, and provides a method for easily performing taper etching without side etching.

[Specific measures to solve the problem]

In the present invention, as a result of numerous studies on the problems with the conventional methods described above, the present invention uses carbon alone or a material containing a large amount of carbon as the cathode electrode, and supplies the material into the reaction tank by etching the cathode electrode itself. It was discovered that by increasing the amount of carbon, a protective film could be formed locally on the etching surface and resist sidewall even in RIH of an oxide thin film, and taper etching without side etching was possible. It has been found that angle control is achieved by adding oxygen gas or an oxidizing gas containing oxygen, or hydrogen gas or a reducing gas containing hydrogen, to the reactive gas.

[Detailed description of the invention]

FIG. 1 is a schematic diagram showing an example of an RIE apparatus used in the present invention. In RIE, active ions or radicals are used as active species during etching, and these active species are generated in the plasma region indicated by 5 in FIG. The ions generated here are accelerated by the electric field applied between the cathode electrode 2 and the anode electrode 3 and collide with the electrode surface. In particular, since the cathode electrode 2 is strongly hit by the incident positive ions accelerated in the ion sheath region shown by 6 in FIG. 1, it is possible to perform anisotropic etching on the etching sample 1 placed on the cathode electrode 2. At the same time, the portions of the cathode electrode 2 not covered by the etching sample 1 are also etched.

Therefore, if the cathode electrode 2 is widely exposed in the chamber 7, the reaction products generated by etching the cathode electrode 2 will also have a large effect on the etching characteristics, like other active species.

If the etching reaction product generated from the cathode electrode 2 can be used as an active species in etching a material to be etched, solid substances can be used in addition to reactive gases as a source of active species, and a wider range of materials can be used. It becomes possible to consider etching conditions. In the present invention, when carbon is used as the cathode electrode 2,
By etching the etching sample 7 under conditions of low gas pressure and high applied power such that the cathode electrode 2 is strongly etched, an active material containing a large amount of carbon that is thought to promote the formation of a sidewall protective film within the chamber 7 is etched. We have discovered that the scale can supply a large amount of seeds and form a stable sidewall protective film even on thin oxide films, for which it has traditionally been difficult to form sidewall protective films with good control using RIE. has the greatest feature.

The present invention deals with active ions or radicals generated by applying a high frequency electric field between two electrode plates placed parallel to each other in a vacuum device into which a reactive gas of 10-1 to 10-3 Torr is introduced. In RIE, which is performed by removing the oxide thin film from the surface as a volatile compound by reacting with the oxide thin film placed on the electrode, carbon is used as the electrode material and organic resist is used as the mask material for the oxide thin film. It is characterized by using Although carbon is the most effective electrode material, similar effects can be obtained by using other polymer materials containing a large amount of carbon as a constituent element, such as Teflon, polypropylene, polycarbonate, and polyphenylene oxide. Also,
Basically, any gas can be used as the reactive gas, but carbon gas tends to form a polymer film during etching.
Chlorinated hydrocarbons such as hClz and CFCh, CHF3
If a fluorinated hydrocarbon having a large C/F ratio such as CzFb, C1Fa, etc. is used, the taper can be formed more easily. Control of the taper angle is also achieved by adding an oxidizing or reducing gas to the reactive gas.

In addition to 0□, the oxidizing gas used at that time is C
O□, NZO, etc. are used as reducing gases, but in addition to H2, C
114, C2H2, C2H4, CzH6, C6116, etc. can also be used. Embodiments of the present invention will be specifically described below with reference to the drawings.

〔Example〕

Si is deposited on the silicon wafer 10 by sputtering method.
An O□ film 9 with a thickness of 1.0 μm is formed, and a photoresist l-MP1400-27 (product name of Sysopray Co., Ltd., USA) is formed on the top layer.
An organic resist mask 8 was formed in a desired shape using a method (see FIG. 2(a)). The film thickness of the resist mask 8 was 1.6 μm. Using this sample as a reactive gas, CF2
Using Cl2, gas pressure 20 mTorr, gas flow ff
l 20 s ccm, applied power density 0.32 W/cm
Etching was carried out at a discharge frequency of R13,56Ml1z. A carbon plate (isotropic graphite) measuring 350 mm x 350 mm was used as the cathode electrode. Figure 2 shows the cross-sectional shape of the etching in Example before etching, during etching, and etching. As shown in Figure 2(a), the edges of the resist mask 8 stand almost vertically before etching, but after 5 minutes have elapsed from the start of etching, the edges of the resist mask 8 stand up almost vertically as shown in Figure 2(b). As shown, the shoulder part of the resist mask 8 is scratched off.However, in this case, the resist mask 8 is not entirely scraped and receded, but the bottom part is scratched by the protective film 11 attached to the side surface of the resist mask 8. Therefore, as the etching progresses, the actual dimensions of the resist mask 8 become thicker. FIG. 2(b) schematically shows the formation of this sidewall protection film 11. The dotted line indicated by 8 is the resist shape before etching. Therefore, in this case, the taper angle 12 is formed between the sidewall protective film 11 and 5.
Formation speed of protective film at the boundary of iOz film 9 and 5i02
This is thought to be caused by the ratio between the etching rate and the etching rate.

In this way, it was finally possible to form an etching pattern having a taper angle of approximately 50'' as shown in FIG. 2(c).

Next, apply 0□ or H to cttctz under the same conditions as above.
2 was added to control the taper angle. 0□ in Figure 3
and shows the relationship between the amount of H2 added and the taper angle.

By adding 4 sccm of 02, about 60 ug
It can be seen that by adding 8 sccm of , a taper angle of approximately 45@ is obtained. A steeper taper angle can be formed by further increasing the amount of Oz added, but in that case, the etching rate of the resist increases as the amount of At added increases, so the resist film thickness must be adjusted in advance. It needs to be thick. Note that the etching rate of the SiO□ film under the above conditions is constant at 31r+n+/min regardless of the addition of 0□ or H2, and
The etching selectivity ratio between the resist and the resist was about 0.8 when no additive gas was added.

In the etching patterns formed in this example, the position of the hem of the resist before etching corresponds accurately to the position of the upper end of the tapered portion, so that a tapered shape can be obtained without side etching.

〔Effect of the invention〕

The present invention is a microfabrication method as described above, and according to the present invention, a protective film is easily deposited on the side walls of the resist mask and the etched cross section even during the etching of the oxide thin film, which is different from that seen in conventional methods. In this way, the etching pattern size is not reduced compared to the resist pattern size, and in fact, the width of the resist pattern before etching can be made close to the upper end of the tapered part of the etching pattern, without causing side etching. A tapered etching pattern is obtained. Moreover, there is no need to add a special process to attach the protective film to the sidewalls (and the process conditions are not difficult to control at all compared to the difficulty of conventional methods. Furthermore, oxidizing gas Alternatively, the taper angle can be adjusted by introducing a reducing gas during etching, and the present invention is extremely superior in practical terms.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a reactive ion etching apparatus used in the present invention. Figure 2 (a), (b
) and (c) are schematic cross-sectional views showing the morphology of etching samples before, during, and after etching, respectively, according to examples of the present invention. Figure 3 shows
FIG. 2 is a graph diagram showing the relationship between the flow rate and the taper angle when 02 or H2 is added to CF2Cl2 gas. 1. Etching titfl 7. chamber 2,
Cathode electrode 8. Resist mask 3, anode electrode 9, S i 0zFli 4, high frequency power supply 10. Silicon wafer 5, plasma region
11. Sidewall protective film 6, ion sheath region 12. Taper angle τ Fig. 1 Fig. 2 02 ← →H2 (sccm) Fig. 3

Claims (1)

[Claims] 1) Active ions or radicals generated by applying a high frequency electric field between two electrode plates placed facing each other in parallel in a vacuum device into which a reactive gas is introduced, and active ions or radicals placed on the electrodes. In reactive ion etching, which is performed by removing the oxide thin film from the surface as a volatile compound by reacting with the oxide thin film that has been removed, side etching can be achieved by using carbon alone or a material containing a large amount of carbon as the electrode material. A microfabrication method that is characterized by forming a pattern with a tapered cross-sectional shape. 2) The microfabrication method according to claim 1, characterized in that an organic resist is used as an etching mask. 3) The microfabrication method according to claim 1, wherein the taper angle is controlled by adding an oxidizing gas or a reducing gas to the reactive gas as an additive gas.