JPH06104242A - Minute pattern formation method - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to suppress an undercut under a mask pattern in a method for forming a fine pattern by etching. [Structure] After forming a predetermined mask pattern on a thin film to be patterned, this thin film is partially etched in the thickness direction, and the side surface of the step formed by this etching is applied with a resist forming the mask pattern or separately. The resist is selectively covered and then the remaining film is etched. As a method of covering the side surface of the step with a resist, the mask pattern is flown down by heat or a positive resist is applied, and the opaque film under the mask pattern is exposed to the mask to selectively leave the side surface of the step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to patterning a thin film, for example, by etching, and more particularly to forming a fine pattern such as an electrode or wiring in an electronic circuit.

[0002]

2. Description of the Related Art The wiring width can be reduced as the mounting density of components on a circuit board increases. However, in order to avoid the increase of the resistance, the thickness of the conductor thin film that constitutes the wiring is not reduced. Therefore, a patterning method with high anisotropy is required because the aspect ratio of the cross section of the wiring increases.

Usually, copper, gold, and aluminum are often used as wiring materials. Among them, copper is suitable for circuit boards in terms of resistivity and cost. That is, a copper thin film formed on a circuit board is patterned into wiring having a desired shape and width. The copper thin film is patterned by wet etching using ferric chloride solution as an etching agent or Ion milling using argon ions is well known.

Ion milling generally has a low etching rate, for example, about 0.1 μm / min for copper. Therefore, it usually takes several tens of minutes to one hour to pattern a copper thin film having a thickness of about several μm. Also, the ion milling device itself is expensive. For these reasons, ion milling is not suitable for mass production.

[0005]

Therefore, the patterning of the copper thin film on the circuit board is generally performed by wet etching. However, since the wet etching of the copper thin film is isotropic, the side etching cannot be ignored, so that an undercut occurs under the mask. The higher the aspect ratio, the greater the proportion of the area that undergoes side etching, so that copper thin-film wiring cannot maintain low resistance, and there is a high possibility that wire breakage will occur.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to make it possible to reduce the side etching effect in wet etching for forming a pattern having a high aspect ratio.

[0007]

The object is to form a mask pattern made of a resist that covers a defined region on a thin film formed on one surface of a substrate and is made into a fluid state by heating. The thin film exposed from the thin film is wet-etched so that a part in the thickness direction is removed to form a step in the thin film around the mask pattern, and the mask pattern is heated to flow. Cover the step with the converted resist,
Micropattern formation according to the present invention, which comprises the steps of subjecting the thin film exposed from the resist covering the step and the mask pattern to wet etching again to grow the step on the surface side of the substrate. Method, or,
An opaque mask pattern is formed to cover a defined area on a thin film formed on one surface of the substrate, and a part of the thin film exposed from the mask pattern in the thickness direction is removed. Wet etching is applied to form a step on the thin film around the mask pattern, and a positive resist is applied to the surface of the substrate having the thin film on which the step is formed, and then the resist is applied from the mask pattern side to the resist. Light irradiation and development treatment are performed, and the wet etching is performed again on the developed resist and the thin film exposed from the mask pattern to grow the step on the substrate surface side. And a fine pattern forming method according to the present invention.

[0008]

In other words, in the present invention, the thin film on which the mask pattern made of resist is formed is wet-etched only partially in the thickness direction. The side etching on the side surface of the step caused by this is stopped in an amount corresponding to the step. Next, the mask pattern is heated to fluidize it, or the step around the mask pattern is selectively covered with a separately applied resist, and then wet etching is performed again to a predetermined thickness. The thin film is patterned by repeating this process. Since the side surface of the step is covered with the resist, the side etching in the subsequent wet etching is small. Therefore, side etching proportional to the total thickness of the thin film or the total etching time does not occur, and the undercut under the mask pattern is greatly reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view for explaining a process of an embodiment of the present invention described in claim 1.

As shown in FIG. 1 (a), after depositing a thin film 2 on one surface of a substrate 1, a mask pattern 4 made of a resist is formed on the thin film 2 as shown in FIG. 1 (b). To do. Then, the thin film 2 exposed from the mask pattern 4
As shown in Fig. 1 (c),
For example, etch only half the total thickness.

Next, the substrate 1 is heated. Normal resist softens and becomes fluid at 140 ° C to 200 ° C. As a result, the side surface of the step formed in the thin film 2 is covered with the fluidized mask pattern 4 as shown in FIG. 1 (d).

Next, the thin film 2 is etched again. Since the side surface of the step of the thin film 2 is covered with the mask pattern 4, the progress of etching is slow. Note that this etching may be performed until the substrate 1 is exposed around the mask pattern 4 as shown in FIG. 1 (e), or may be performed so that the thin film 2 remains around the mask pattern 4. Good.
Finally, the mask pattern 4 is removed as shown in FIG.

Undercutting under the mask pattern 4 can be suppressed as described above. Figure 1
In the above, the case where the thin film 2 is a single layer is shown, but it is needless to say that the same can be applied when the thin film 2 is composed of, for example, three layers of chromium-copper-chrome.

FIG. 2 is a sectional view for explaining a process of an embodiment of the present invention as set forth in claim 2. Figure 2 (a)
As shown in, the thin film 2 with a large film thickness is formed on one surface of the substrate 1.
And a thin film 3 having a small film thickness are deposited. An opaque material is used for the thin film 3. After that, as shown in FIG. 2B, a mask pattern 4 made of a resist is formed on the thin film 3.

Next, the thin film 3 exposed from the mask pattern 4 is selectively etched and patterned as shown in FIG. 2 (c). Since the thin film 3 has a small film thickness, side etching in this etching can be ignored.

Next, as shown in FIG. 2D, the thin film 2 exposed from the mask pattern 4 is etched from its surface by a predetermined thickness, for example, 1/2 of the total thickness. Then, as shown in FIG. 3E, a positive resist layer 5 is applied to the surface of the substrate 1. And for the resist layer 5,
After irradiating light from the front surface side of the substrate 1, development processing is performed. Since the resist layer 5 in the undercut portion under the mask pattern 4 is shielded by the opaque thin film 3, it remains after the developing process as shown in FIG. Needless to say, it is necessary to select the solvent and the developing solution for the resist layer 5 so that the mask pattern 4 is not dissolved during the above-mentioned application and during the development of the resist layer 5.

Then, the thin film 2 is etched again. Since the side surface of the step of the thin film 2 is covered with the resist layer 5, the progress of etching is slow. This etching may be performed until the substrate 1 is exposed around the mask pattern 4 as shown in FIG. 3 (g), or may be performed so that the thin film 2 remains around the mask pattern 4. Good.

Next, as shown in FIG. 3H, the resist layer 5 is selectively removed. Needless to say, it is necessary to select a stripping solution for the resist layer 5 so that the mask pattern 4 is not dissolved in this removal.

Next, as shown in FIG. 3 (i), the thin film 3 is selectively etched. This etching is for preventing the eaves of the thin film 3 from remaining on the patterned thin film 2. Finally, the mask pattern 4 is removed as shown in FIG.

In this way, the undercut under the mask pattern 4 can be suppressed. In addition,
When it is not necessary to leave the thin film 3 on the patterned thin film 2, the mask pattern 4 and the thin film 3 may be sequentially removed after FIG. 3 (h).

A more detailed embodiment will be described below. Figure 1
With reference to, the thickness of 0.1
A thin film 2 consisting of a 6 .mu.m thick copper film sandwiched by two .mu.m chromium films is formed. Then, a cyclized rubber negative resist is formed on the thin film 2 to a thickness of 2 μm.
A mask pattern 4 is formed by applying m on m, exposing it to a predetermined light pattern, and then developing it.

Next, the upper chromium film of the thin film 2 exposed from the mask pattern 4 is etched using a mixed solution of sodium hydroxide and potassium ferricyanide.
The side etching of the chromium film at this time is so small that it is difficult to measure. Then, the copper film forming the thin film 2 is etched to a thickness of about 3 μm using a mixed solution of hydrogen peroxide solution and sulfuric acid.

Next, the substrate 1 is heat-treated at 150 ° C. for 30 minutes. As a result, the mask pattern 4 is fluidized and covers the side surface of the step formed in the thin film 2. Then, the copper film is etched again using a mixed solution of hydrogen peroxide and sulfuric acid until the underlying chromium film is exposed around the mask pattern 4. Finally, the lower chromium film is etched using a mixed solution of sodium hydroxide and potassium ferricyanide, and then the mask pattern 4 is removed.

Thin film 2 patterned in this way
The side etching amount corresponding to the undercut under the mask pattern 4 was about 3 μm. On the other hand, when the present invention is not applied, the side etching amount is about 6 μm,
The remarkable effect by this invention was shown.

Referring to FIG. 2, on a surface of a substrate 1 made of glass, a 0.1 μm-thick chromium underlayer film, a 6 μm-thick copper film 2 and a 0.1 μm-thick chromium film 3 are formed. Are sequentially formed. Then, a cyclized rubber type negative resist is applied to the chromium film 3 to a thickness of 2 μm, and a predetermined light pattern is exposed to the resist and then developed to form a mask pattern 4.

Next, the chromium film 3 exposed from the mask pattern 4 is etched using a mixed solution of sodium hydroxide and potassium ferricyanide. The side etching of the chromium film 3 at this time is so small that it is difficult to measure. Then, the copper film forming the thin film 2 is etched to a thickness of about 3 μm using a mixed solution of hydrogen peroxide solution and sulfuric acid.

Then, a novolac resin-based positive resist layer 5 is applied on the surface of the substrate 1, and then the entire surface of the resist layer 5 is irradiated with ultraviolet rays from the surface side of the substrate 1. The resist layer 5 in the undercut portion under the mask pattern 4 is shielded from ultraviolet rays by the chromium film 3. After that, the resist layer 5 is developed with a weak alkaline solution. The mask pattern 4 made of the cyclized rubber resist has resistance to an alkaline solution.

Next, the copper film is etched again using a mixed solution of hydrogen peroxide and sulfuric acid until the chromium underlayer film is exposed around the mask pattern 4. Then, the resist layer 5 is removed using an alkaline solution. Finally, after etching the chromium underlayer film using a mixed solution of sodium hydroxide and potassium ferricyanide, mask pattern 4 was formed.
To remove.

In this way, a thin film pattern having a three-layer structure of a chromium-copper-chromium film is formed. The side etching amount corresponding to the undercut of the patterned thin film 2 under the mask pattern 4 is about 3 μm, and the side etching amount when the present invention is not applied is about 6 μm, the remarkable effect of the present invention is shown. Was done.

In the above embodiments, the case where the present invention is applied to the patterning of a metal thin film has been described, but it goes without saying that the present invention can also be applied to the patterning of a thin film other than metal.

[0031]

According to the present invention, it becomes possible to form a fine pattern with a high aspect ratio by wet etching,
This has the effect of contributing to improved productivity and cost reduction of circuit boards and semiconductor integrated circuits.

[Brief description of drawings]

FIG. 1 is a process explanatory view of an embodiment of the invention of claim 1;

FIG. 2 is a process explanatory view (1) of an embodiment of the invention of claim 2;

FIG. 3 is a process explanatory view (No. 2) of an embodiment of the invention of claim 2;

[Explanation of symbols]

 1 Substrate 2, 3 Thin film 4 Mask pattern 5 Resist layer

Claims (8)

[Claims] 1. A first step of forming a mask pattern made of a resist, which covers a defined region on a thin film formed on one surface of a substrate and changes into a fluid state by heating, and exposing from the mask pattern. A second step of forming a step on the thin film around the mask pattern by performing wet etching so that a part of the thin film in the thickness direction is removed; and heating the mask pattern The third step of covering the step with the resist fluidized by the above, and the thin film exposed from the resist covering the step and the mask pattern is wet-etched again to form the step on the substrate surface side. A fourth step of growing the fine pattern. 2. The fine pattern forming method according to claim 1, wherein the third step and the fourth step are circulated and repeated. 3. The fine pattern forming method according to claim 1, wherein the wet etching performed on the thin film in the fourth step is performed until the surface of the substrate is exposed. 4. A first step of forming an opaque mask pattern covering an area defined on a thin film formed on one surface of a substrate, and a thickness of the thin film exposed from the mask pattern. The second step of forming a step in the thin film around the mask pattern by performing wet etching so that a part in the vertical direction is removed, and a positive step is performed on the substrate surface having the thin film in which the step is formed. A third step of applying light and developing treatment to the resist from the mask pattern side after applying a resist of a mold, and to the resist and the thin film exposed from the mask pattern subjected to the developing treatment. And wet etching again to grow the step on the surface side of the substrate, the fourth step. 5. The method for forming a fine pattern according to claim 4, wherein the third step and the fourth step are circulated and repeated. 6. The method for forming a fine pattern according to claim 4, wherein the wet etching applied to the thin film in the fourth step is performed until the surface of the substrate is exposed. 7. The method for forming a fine pattern according to claim 4, wherein the mask pattern comprises an opaque lower layer and an upper layer made of a transparent resist. 8. After the step of performing wet etching on the thin film until the surface of the substrate is exposed, the lower layer is selectively etched so that one side surface continuous to the side wall of the step is formed. 8. The method for forming a fine pattern according to claim 7, further comprising: