JPH03266419A - Four-layer mask pattern - Google Patents

Abstract

PURPOSE:To make it possible to conduct a highly precise working on a microscopic groove by a method wherein, after a first layer has been dry-etched using a resist, a second layer and a third layer as etching masks; the resist, the second layer and the third layer are removed, and a substrate or a thin film is etched using the first layer only as an etching mask. CONSTITUTION:A first layer film 7, a second layer film 8 and a third layer film 9 are formed on a substrate, the third film 9 is coated with a resist, and a pattern 10 is formed. After the first, second and third layers have been dry- etched using the resist pattern 10 as an etching mask, the substrate 1 is etched using the patterned first layer as a mask leaving the first layer only. Accordingly, the resist pattern 10 of the uppermost layer of the mask can be transferred to the lowermost layer 7, and the thickness of the lowest layer 7 can be thinned off to the extent which is suitable for etching of the base substrate. As a result, the decrease in etching speed of the base material, using an etching mask having a high aspect ratio, can be prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method of forming an etching mask, particularly when forming a mask pattern on a high substrate step.
In conventional three-layer mask patterns, the mask thickness is extremely thick at 1.5 to 2.0 μm, so narrow groove or hole patterns with a width of 0.5 μm or less result in high aspect ratio etching, making it difficult to etch. The present invention relates to a mask pattern forming method suitable for preventing this.

[Conventional technology]

Conventionally, when forming a mask pattern on a high level difference, in order to prevent uneven resist coating thickness and uneven exposure, the level difference is flattened and a resist using light, electron beams, X-rays, etc. is applied on top of the level difference. A pattern needed to be formed. For this purpose, for example, a three-layer mask pattern as described in Japanese Patent Application No. 50-32195 has been used. As shown in FIG. 2, when an uneven portion 20 exists on the base substrate 1 or the thin film 2 or 3 (FIG. a),
First, a thick first layer 8 of around 2.0 μm for planarization is formed, and a thin second layer 9 of around 0.1 μm is formed thereon to serve as an etching mask during dry etching of the first layer 8. A resist 10 sensitive to light, electron beams, and X-rays is patterned on the second layer 9 (FIG. b), and the resist pattern is applied to the second layer 9. After transferring to the first layer 8 by dry etching (Figures c and d), use only the laminated film of the first layer 8 and the second layer 9 or the first layer 8 with the second layer 9 removed as an etching mask ( Figure e) Substrate 1 or thin film 2 underlying the first layer 8
, 3 was used. At this time, the first layer 8 is usually made by heating and baking a resist material, and the second layer 9 is made of SOG (spin on glass: 5 pin on glass) or the like, which becomes an etching mask when dry etching the first layer 8. It is an inorganic material such as titanium silica (Ti-5i-○X). The second layer 9 is dry-etched with a gas containing halogen such as fluorine, and the first layer 8 is dry-etched with a gas containing oxygen using the laminated film of the patterned resist 10 and the second layer 9 as an etching mask. . At this time, since the resist pattern 10 is removed by etching at the same time, the second layer 9 serves as a substantial mask. After etching the first layer 8,
Usually, the second layer 9 is removed by etching, but there are cases where the second layer 9 is left and the laminated film of the first layer 8 and the second layer 9 is used as an etching mask for the base material.

[Problem to be solved by the invention]

Dry etching for microfabrication of LSIs has a problem in that the etching speed decreases in deep and narrow grooves or holes. This phenomenon occurs when the groove width or hole diameter is as small as 0.5 μm or less, or when the etching depth is 1.5 μm or less.
It becomes noticeable when the depth becomes 0 μm or more. On the other hand, as the integration of LSIs progresses, the surface structure becomes more complex and uneven, and a three-layer mask pattern as described above is used to pattern a resist thereon. However, in the past, the thickness of the bottom layer for flattening the surface unevenness is as thick as around 2.0 μm, so such a thick film is used for example when the opening width or opening diameter is 0.0 μm.
When attempting to pattern a 2 μm groove or hole, the aspect ratio (height 7 width) becomes 10, resulting in a very thin and deep mask. There was a problem in that etching was performed, and the above-mentioned reduction in etching rate became noticeable.

[Means to solve the problem]

In order to solve the above-mentioned problem, in the present invention. Form a four-layer mask pattern. The formation method is to first form a first layer film on the surface of a substrate or thin film, then to form a second layer film on the first layer film.
Furthermore, a third layer film is formed on top of that, and a resist sensitive to light, electron beams, or X-rays is coated on the third film. After forming a pattern by irradiating one of them, the third layer is dry etched using the resist pattern as an etching mask. Next, the patterned resist and the third layer are used as an etching mask, and the second layer is dry-etched, and then the patterned resist, the third layer, and the second layer are used as an etching mask, and the first layer is dry-etched. , the third layer and the second layer are removed, leaving only the first layer, and the substrate or thin film is etched using only the patterned first layer as an etching mask.

[Effect]

According to the present invention, the resist pattern on the uppermost layer of the mask can be transferred to the lowermost layer with high precision, and the thickness of the lowermost layer can be made thin enough to be convenient for etching the underlying substrate.

【Example】

(Example 1) A four-layer mask pattern was formed by the procedure shown in FIG. First, CVD was applied on the polysilicon 3 with a thickness of 0.3 μm formed on the step 20 of silicon oxide with a thickness of 1 μm.
Silicon oxide is grown to 0.2 μm using the (chemical vapor deposition) method.
forming a deposited first layer of film 7;
A photoresist (phenol novolak resin, such as Shipley AZ1350J) is coated on the film to a thickness of 2.0 μm, and heated at a temperature of 200 to 250° C. to form a second layer film 8. Furthermore, on top of that, a 0.1 μm thick SO
A third layer film 9 made of G is formed, an electron beam resist (for example, PMMA-polymethyl methacrylate) 10 is applied on the third layer 9, and patterning is performed by electron beam irradiation, development, and baking. (Figure a). Using this resist pattern 10 as an etching mask, the SOG of the third layer 9 is anisotropically dry-etched using CF and gas plasma (Fig. b). Then, using the patterned resist 10 and 5OG9 as an etching mask, the baked resist is etched. The second layer 8 was anisotropically dry etched with a gas containing oxygen as the main component (Figure c).
The uppermost layer of resist 10 was simultaneously etched and disappeared. Subsequently, using the two-layer film of 5OG9 and bake resist 8 as a mask, the first layer silicon oxide 7 was anisotropically dry etched with CHF□ (Figure d). The third layer of 5OG9 was etched away at the same time. Thereafter, the second layer 8 was removed by ashering with oxygen plasma, and a silicon oxide mask 7 with a thickness of 0.2 μm was formed (
Using this as an etching mask, the underlying polysilicon was dry etched with C1□, and a fine groove with a width of 0.2 μm could be processed with high precision. (Example 2) In Example 1, a four-layer mask pattern having a structure in which the first layer of silicon oxide 7 was replaced with polyimide resin was formed. The procedure is shown below. A 0.5 μm thick polyimide isoindoquinazolinedione resin (polyimide resin) 7 is applied to the polysilicon surface on the silicon oxide step 20 similar to that in Example 1.
It was cured by heating at 50°C. Thereon, a second layer 8 made of bake resist, a third layer 9 made of SoG, and an uppermost resist film 10 are formed in the same manner as in Example 1, and then the resist 10 is patterned by electron beam lithography, The steps up to dry etching of SOG9 were performed in the same manner as in Example 1. Thereafter, the second layer 8 and first layer 7 were successively dry etched using a gas containing oxygen as a main component using the uppermost resist layer 10 and 5OG9 as masks. Next, the SOG film 9 is coated with hydrofluoric acid (HF).
The second layer resist 8 was further removed with a resist solvent containing a resist developer or the like. At this time,
The first layer pattern 7 made of the polyimide isoindoquinazolinedione resin was almost insoluble in this solvent. As a result, a polyimide isoindoquinazolinedione resin mask pattern 7 having a width of 0.2 μm was formed. Using this mask, we were able to dry-etch the underlying polysilicon with high precision. In addition to the embodiments described here, the present invention has the following versatility. In addition to the above-mentioned polysilicon, the base material may be silicon or Ga.
A s substrate, any material constituting an LSI such as aluminum, tungsten, silicon oxide, silicon nitride, titanium nitride, tungsten silicide, etc. may be used;
The first layer of the mask pattern is made of silicon oxide, polyimide isoindoquinazoline dione resin, other polyimide resins, silicon nitride, aluminum, tungsten, molybdenum, titanium, tantalum, and oxides and nitrides of these metals. It can also be things. The second layer may be made of polyimide resin or the like in addition to bake resist. The third layer is made of titanium silica (Ti-8i-0x) in addition to SOG.
), titanium, tantalum, tungsten, and oxides and nitrides of these metals. In addition, ions may accumulate on the mask and become electrically charged, causing the etched shape of the underlying film to become sloped. In such cases, using a conductive metal material such as titanium as a mask will reduce the electrical charge on the mask. In some cases, this problem was prevented and the slope of the underlying film etching shape was improved. Further, in the dry etching of the first to third layer films, the effects of the present invention remain the same even if the gas type and etching conditions are different.

【Effect of the invention】

According to the present invention, even when the surface unevenness becomes large due to the progress of high integration of LSI, a highly accurate resist pattern can be formed due to the flattening effect of the second layer film, and the resist pattern that is finally formed can be The thickness can be determined only by the thickness of the first layer, regardless of the degree of unevenness on the LSI surface, that is, the thickness of the second layer. The thickness can be set to be convenient for etching the underlying substrate or thin film. Due to this effect, it is possible to prevent the etch rate of the underlying material from decreasing due to a high aspect ratio etching mask by setting the first layer thickness to typically about 0.5 μm, and it is possible to prevent the etching rate of the underlying material from decreasing due to a high aspect ratio etching mask. High-precision micromachining can be achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a pattern forming process using a four-layer mask pattern according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a pattern forming process using a conventional three-layer mask pattern. Explanation of symbols 1...Silicon substrate, 2...Silicon oxide step, 3
... Polysilicon film, 4... First layer bake resist, 5... Second layer SOG, 6... Third layer resist pattern (top layer), 7... First layer silicon oxide, 8...
・Second layer bake resist layer, 9...Third layer SOG, 1
0...1st figure Atsushizu

Claims (1)

[Claims] 1. In the step of forming an etching mask on a substrate or thin film to be etched, a first layer of film is first formed on the surface of the substrate or thin film, and then a first layer of the film is formed on the surface of the substrate or thin film. A second layer film is formed on the film, a third layer film is formed on top of that, and a resist that is sensitive to light, electron beams, or X-rays is applied on the third film. After forming a pattern by irradiating the resist with light, electron beams, or X-rays, the third layer is dry-etched (also called plasma etching) using the resist pattern as an etching mask.
Then, dry etching the second layer using the patterned resist and the third layer as an etching mask, then dry etching the first layer using the patterned resist, the third layer, and the second layer as the etching mask. , the resist, the third layer, and the second layer are removed to leave only the first layer, and the substrate or thin film is etched using only the patterned first layer as an etching mask. Pattern formation method. 2. The four-layer mask pattern forming method according to claim 1, wherein the second layer has a thickness of 1 μm or more. 3. The four-layer mask pattern forming method according to claim 1 or 2, wherein the third layer has a thickness of 0.5 μm or less. 4. The four-layer mask pattern forming method according to any one of claims 1 to 3, wherein the first layer has a thickness of 1.0 μm or less. 5. The four-layer mask pattern forming method according to any one of claims 1 to 4, wherein the third layer is made of either an inorganic material or a metal material. 6. The four-layer mask pattern forming method according to any one of claims 1 to 5, wherein the second layer is a heat-treated organic polymer material. 7. The first layer is made of silicon oxide, silicon nitride, polyimide resin (including polyimide isoindoquinazoline dione resin), aluminum, tungsten, molybdenum, titanium, tantalum, and oxides and nitrides of these metals. Claim 1 characterized in that:
6. The method for forming a four-layer mask pattern according to items 6 to 6. 8. The four-layer mask pattern forming method according to claim 7, wherein the first layer is a polyimide resin (including a polyimide isoindoquinazolinedione resin). 9. The four-layer mask pattern forming method according to any one of claims 1 to 8, wherein the second layer is a photoresist material subjected to heat treatment. 10. The four-layer mask pattern forming method according to any one of claims 1 to 9, characterized in that the first layer and the second layer are dry-etched successively. 11. The four-layer mask pattern forming method according to any one of claims 1 to 10, wherein the etching gas for dry etching the first layer and the second layer in succession contains oxygen gas.