JPS61179440A - Pattern forming organic film and formation of pattern - Google Patents

Abstract

PURPOSE:To obtain a resist pattern true to a mask pattern by using a laminated film consisting of a resist and a water soluble org. film contg. pullulan and an absorber which absorbs light penetrating into the light shielding part of the mask pattern so as to increase the accuracy of a pattern on projections. CONSTITUTION:A laminated film consisting of a resist 3 and a water soluble org. film 8 contg. pullulan and a light absorber which absorbs excess light of <=500nm penetrating into the light shielding part 6 of a mask pattern 5 is formed on a substrate 1 having projections 2. The laminated film 3, 8 is exposed through the mask pattern 5 and developed to obtain a resist pattern 3f, 8a, Electrode wiring or the like can be obtd. by selectively removing an Al film 4 with the pattern 3f, 8a as a mask. The resist pattern 3f, 8a true to the mask pattern 5 and having high accuracy is obtd. independently of the projections 2. Since the resist 3 and the org. film 8 are not miscible with each other, they are easily formed in layers by coating and facilitate the formation of a fine resist pattern during development.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in the manufacture of semiconductor integrated circuits, etc., in particular in photolithography pattern formation, to prevent the adverse effects of excess light passing through a mask pattern, This invention relates to pattern formation using a laminated structure of a radiation-sensitive resin and a water-soluble organic film to improve pattern accuracy and resolution.

Conventional configurations and their problems High integration and high density of integrated circuits have increased due to advances in conventional lithography technology. The minimum line width has become around 1 μm, and in order to achieve this processed line width, there are three methods: ultraviolet exposure using a reduction projection method with a high aperture lens, electron beam exposure that draws directly on the substrate, One example is the proximity exposure method using lines. However, with either method, it is difficult to simultaneously obtain good line width control, high resolution, and good step coverage without sacrificing throughput. In particular, unevenness inevitably occurs on actual integrated circuits, and after coating a radiation-sensitive resin (hereinafter referred to as resist), differences in resist film thickness occur at the uneven parts, making it difficult to control line width. becomes impossible.

This will be explained using FIG. FIG. 1 shows a state in which a single-layer resist film is applied to a stepped portion by a conventional method and patterned across the stepped portion. Figure 1 (8 shows Si○ on substrate 1 such as a semiconductor substrate)
2 is a cross-sectional view of a state in which a step pattern 2a such as a two-layer film 2 is formed and a resist 3 is applied thereon. FIG. In this case, the resist 3 on a flat film without the step pattern 2a
When the film thickness of tRl is applied, the step pattern 72
The film thickness of the resist 3 on a is determined by the viscosity of the resist itself and the number of revolutions during coating. At this time tR1
=tR2, that is, it is physically impossible to completely eliminate the difference in the thickness of the resist film at the uneven portions. FIG. 1B shows a plan view when a resist pattern is formed with a film thickness of tR4 to 'R2 in this manner.

This means that if the pattern width is determined to be 11 at the position of the film thickness tR1 of the resist pattern 3 formed perpendicularly to the step pattern 2a, then at the position of the film thickness tR2 there is a relationship of tRl>tR2. Therefore, the pattern width is l
Since 11>112, a dimensional conversion difference occurs at the stepped portion. However, when a very fine pattern is used, good line width control cannot be obtained, and furthermore, the edge portion 2b of the step 2a becomes substantially thicker than the film thickness tR1 of the flat portion, resulting in a decrease in resolution. Generally, the resolution improves as the resist film thickness becomes thinner. This is because the incident energy is attenuated due to interference and diffraction development when fine gaps are formed due to the wavelength of the radiation itself. In order to reduce the difference in resist film thickness on the stepped object, simply applying a thick layer of resist to reduce the apparent difference in resist film thickness is undesirable in terms of pattern formation because the resolution deteriorates.

Furthermore, the influence of reflection will be explained using FIG. 2.

The second diagram shows a metal film 4, for example A, on a convex step 2 on the substrate 1.
A film is deposited on the entire surface, and a photosensitive resin (hereinafter referred to as
3 is a cross-sectional view of a state where resist 3 is applied and ultraviolet rays are irradiated through chromium 6 of mask 5. FIG. The second diagram shows an enlarged view of the incident state of ultraviolet rays (hereinafter referred to as UV light) at this time.
) in the figure.

Of the UV light 7 that enters, the UV light 7 that enters the flat portion 3a
The reflected light 7b of a is reflected at an angle of exactly 18o0, but
The UV light 7C incident on the stepped portion of the Al film 4 is reflected from the side surface of the Al film 4 and becomes reflected light 7d.
The light d penetrates into the unexposed resist region 3b and is unnecessary light for resist pattern formation, and the resist cross section 3c after development is actually narrower than the width of the chrome part 6 of the mask 5, resulting in poor pattern accuracy. to degrade. Furthermore, depending on the distance between the steps and the end of the resist pattern, the resist pattern may disappear, causing pattern breakage.

As described above, extra light passing through the photomask pattern is caused to wrap around due to steps on the substrate, reducing pattern accuracy and posing a major obstacle to miniaturization.

Particularly in the reduction projection exposure method where the light intensity is high, the resolution due to the extra light.

The pattern accuracy is significantly lowered, and, for example, when forming a wiring pattern on Al having a step, a pattern dimension of 2 μm or less always causes wire breakage.

Purpose of the Invention The present invention facilitates the formation of fine patterns without damaging the resist suitable for fine pattern formation and without complicating the process. It is an object of the present invention to provide a stable pattern-forming organic film suitable for preventing a decrease in resolution and a decrease in pattern accuracy due to the influence of light, and a pattern-forming method using the same.

Components of the Invention The present invention includes a light absorber, an alkaline aqueous solution as a developer of the resist, and pullulan which is soluble in water and is soluble at room temperature and can be laminated with an organic solvent-based resist. After coating and forming a laminated film of the resist and the water-soluble organic film on the substrate using a water-soluble organic film, selectively exposing to radiation of 500 nm or less, such as ultraviolet rays, deep ultraviolet rays, and X-rays, A laminated film consisting of a resist exposed to light and a water-soluble organic film is simultaneously developed and removed to form a pattern.

That is, the present invention provides a resist, a water-soluble organic film containing pullulan, and a light absorber that absorbs excess light of 500 nm or less that enters the light-shielding portion of the mask pattern out of the light that passes through the mask pattern during resist exposure. A pattern-forming organic film having a laminated structure with a substrate, and furthermore, on a substrate having steps, excess light entering the light-shielding portion of the mask pattern out of the light during exposure of the positive resist that has passed through the resist and the mask pattern is removed. a step of forming a laminated film with a water-soluble organic film containing an absorbing light absorber and pullulan; a step of selectively exposing the patterned organic film through the mask pattern; and a step of exposing the resist and the water-soluble organic film to light through the mask pattern. The present invention provides a pattern forming method that includes a step of developing and removing the irradiated area at the same time.

The above-mentioned water-soluble organic film contains a water-soluble organic substance such as pullulan, which is a polysaccharide, as a main component, and contains a substance that absorbs light (ultraviolet rays) of SOOnm or less, such as an acidic or basic dye. It may contain a crosslinking agent such as dialdehyde starch, dichromate, diazide compound, azide compound, aldehyde compound, etc. to adjust the dissolution rate, and water.

DESCRIPTION OF EMBODIMENTS First, a water-soluble organic film of the present invention, which is particularly easily soluble in cold water and whose main component is PULLA, which is a polysaccharide, will be described.

The structure of pullulan can be shown as follows (in the margins below). Pullulan is a starch mainly composed of glucose units.
It has a different molecular structure from polysaccharides such as cellulose. Moreover, their properties are also different. For example, starch and cellulose are difficult to dissolve in cold water, whereas pullulan is easily soluble in cold water, and its aqueous solution has a lower viscosity than that of an aqueous solution of water-soluble polymers at the same concentration and molecular weight. It is one.

The pullulan aqueous solution is stable for a long time, and no gelation or aging phenomenon is observed. Furthermore, the film has the property of not being dissolved at all in organic solvents. In other words, it has properties that allow it to be easily coated in layers with organic solvent-based radiation-sensitive resins (hereinafter referred to as resists) used in phosphorography technology in semiconductor manufacturing.

Furthermore, a dye or the like as a material that absorbs radiation such as ultraviolet rays is dissolved in the pullulan aqueous solution. At this time, although the dye is an acidic material, the pullulan aqueous solution is completely unaffected by pH and is a stable aqueous solution.

In order to control the dissolution rate of the pullulan film in the developing solution (alkaline aqueous solution) and rinsing solution (water) in the development step of resist pattern formation, a small amount of dialdehyde starch, for example, may be mixed as a crosslinking agent. Dialdehyde is produced by oxidizing starch with periodic acid.
It is made by replacing the constituent units of starch with dialdehyde. This dialdehyde starch reacts with the above-mentioned pullulan to form an acetal bond and exhibits poor solubility in water.

Similarly, dichromates, diazide compounds, and azide compounds (photosensitive) are used to make them poorly soluble in water, and to make them photosensitive, esterified, and etherified.

It is also possible to react with an aldehyde compound or the like.Detailed examples will be described below.

First, a method for synthesizing an example of a water-soluble organic film as a light-absorbing film used in the present invention and its properties will be described.

Pour 100 cc of pure water (deionized water) into a beaker, and while keeping the temperature at room temperature, add pullulan with an average molecular weight of 200,000, which contains enough heavy metals, with stirring to dissolve 20 parts. On the other hand, add acid dye (5%
2.5 g of a dye that absorbs ultraviolet light below 00 nm is dissolved with stirring.

Next, the pullulan aqueous solution and the dye aqueous solution were mixed to prepare a dye-containing pullulan aqueous solution. Next, several CCs of dialdehyde starch aqueous solution (10%) were mixed with the dye Cipululan aqueous solution. In this state, gelation is not observed and the quality does not change at all even after a long period of time. When this solution was spin coated on a quartz glass plate at 300o rpm using a spinner, a uniform film thickness of 5000A was obtained, and the ultraviolet transmission property was 500 nm or less at a wavelength of 500nm or less. It had the effect of sufficiently absorbing excess light during positive resist exposure. Furthermore, after coating this water-soluble organic film, an organic solvent-based positive resist was coated on this organic film, and there was no dissolution.
It was possible to layer this resist extremely easily. The dissolution rate in water was also about 10 times slower than without a crosslinking agent, and it was also easier to control in semiconductor manufacturing.

The aforementioned pullulan has a different molecular structure from other polysaccharides and is easily soluble in cold water. The aqueous solution has one of the lowest viscosity and the molecular weight can be easily controlled, and as mentioned above, it is stable for a long time and its solubility is easy to control, and the film does not dissolve at all in organic solvents and is heat resistant. It also has high transparency against ultraviolet rays.

The amount of pullulan, dye, and crosslinking agent depends on the coating thickness,
It can be arbitrarily selected depending on the amount of ultraviolet absorption and the rate of dissolution in water. Furthermore, in order to control the solubility in water, it is also possible to ether or esterify pullulan itself.

An example of a pattern forming method using this water-soluble organic film will be described with reference to FIG.

Similar to FIG. 2 used to explain the conventional example, a step 2 made of an insulating material or the like is formed on a semiconductor substrate 1, and a metal film having a high reflectance, such as a mulch film 4 that will become a wiring, is deposited.

Then, the water-soluble organic film 8 described above is applied (Figure 3).

The thickness of the water-soluble organic film at this time is appropriately set depending on the amount of energy applied during subsequent exposure, but in this example, a thin film was obtained by coating the film at 200°C.

Subsequently, a positive UV resist 3 is applied onto the water-soluble organic film 8. At this time, it was possible to apply the positive UV resist 3 and the water-soluble organic film 8 uniformly without dissolving each other [FIG. 3B].

In this laminated coating, no extra steps are required, and the laminated coating process can be easily performed. This is an excellent process advantage since there is no need to change the normal semiconductor integrated circuit process.

Then, 1som of 436 nH ultraviolet rays 7 is transmitted through the chrome pattern 6 of the photomask 5 by the reduction projection exposure method.
Expose with an energy of J/z.

At this time, the reflected light from the side surfaces and the surface of the step, that is, the excess light that enters the light-shielding part of the mask pattern is removed by the water-soluble organic film 8.
Since it is absorbed by the ultraviolet absorber therein, latent images of six chrome patterns in the unexposed areas 3e are formed (FIG. 3C).

Next, positive UV was exposed using a normal alkaline developer.
At the same time as developing and removing the resist 3, the exposed water-soluble organic film was removed in a rinsing process, and the butter/3f was removed.

8 & was obtained [Figure 3 D]. Normally, patterning of a positive resist involves development with an alkaline developer followed by a rinsing process with water, and it is possible to form a pattern on this laminated film without changing this normal process. This step can also be carried out without any modification to the normal semiconductor process, which is extremely convenient.

The dissolution rate of the water-soluble organic film 8 in water in the development and rinsing step can be freely controlled by post-coating heat treatment and the amount of crosslinking agent added, and may be set by the thickness of the upper positive UV resist.

After FIG. 3(D), the Al film 4 is selectively removed using the patterns 3f and Bh as masks to form electrode wiring.

Next, a second embodiment will be explained using FIG. 4.

In the case of the first embodiment, since the water-soluble organic film 8 was made to have the minimum thickness to prevent reflected light of the exposure energy, the underlying substrate 1
The shape of the step 2 does not change, and the film thickness of the positive UV resist 3 fluctuates near the step, ultimately deteriorating the pattern accuracy. In order to prevent this, in the second embodiment, the water-soluble organic film 8 is applied thickly and formed flat (FIG. 4A). After this, the positive type U"/resist 3 is applied flatly, so there is no variation in the resist film thickness. Then, by adding exposure, development, and rinsing steps, the pattern accuracy is high and the aspect ratio is high as shown in (B). Patterns 3f and sa were obtained. At this time, because the water-soluble organic film 8 was heat-treated at a low temperature and the amount of crosslinking agent added was optimized, the dissolution rate in water was very high, and the film thickness was very high. Since there is no dependence, it is faithfully transferred to the upper layer of positive UV resist pattern 3f.

Specifically, experimental data according to the present invention is shown in FIG. The horizontal axis shows the distance S from the step edge to the chrome pattern edge which is the light-shielding part of the mask pattern in FIG. 1, and the vertical axis shows the resist pattern after pattern formation.
This is a transfer of a mask pattern. according to this,
In the case of the conventional example shown by curve 11, when S (distance from the step) is 1 to 2 μm, the resist pattern is disconnected or broken due to reflection from the substrate l.
The wire tends to break. For example, when S was 0.5 μm, the resist pattern was thinned to 0.6 μm.

On the other hand, in the case of the present invention shown by curve 1o, a 1 μm pattern could be formed without fluctuation in the resist pattern regardless of the distance S.

In the above embodiments, a positive type resist was used, but it goes without saying that the present invention can also be applied to a case where a negative resist is used.

Effects of the Invention The present invention performs pattern formation using a laminated film of a water-soluble organic film containing pullulan and an absorber that absorbs excess light that enters the light-shielding portion of the resist and mask pattern. It becomes possible to form a highly accurate resist pattern that is faithful to the mask pattern without being affected by steps.

Furthermore, according to the present invention, when an organic solvent-soluble resist is used, it does not dissolve with the water-soluble organic film;
Laminated coating is easy, and patterns can be selectively formed in a developing and rinsing process applied to ordinary resists, and a fine resist pattern can be easily obtained without changing the developing process. When using a water-soluble organic film containing pullulan,
It dissolves easily in cold water, has stable quality, and is easy to apply.
The present invention is extremely effective in semiconductor photolithography processes, and exhibits excellent industrial value in manufacturing fine semiconductor devices.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are a cross-sectional view and a plan view after pattern formation by a conventional process, Figures 2 (M) and (B) are a cross-sectional view of a conventional resist pattern formation process, and Figure 3 (A). )
-(D) are cross-sectional views of the pattern forming process of the first embodiment of the present invention, FIGS. 4(A) and (B) are cross-sectional views of the pattern forming process of the second embodiment of the present invention, and FIG. FIG. 3 is a diagram showing comparative data between the present invention and a conventional example. 1... Board, 2... Step, 3...
...Resist, 8... Water-soluble organic film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure ridge Figure 2 Figure 3 Figure 31 Figure 4 Figure 5

Claims (4)

[Claims] (1) Lamination of a resist and a water-soluble organic film containing pullulan and a light absorber that absorbs excess light of 500 nm or less that enters the light-shielding portion of the mask pattern among the light that passes through the mask pattern during resist exposure. A pattern-forming organic film characterized by having a structure. (2) The pattern-forming organic film according to claim 1, wherein the resist is an organic solvent-based resist. (3) A water-soluble organic film containing a resist, a light absorber that absorbs excess light that enters the light-shielding portion of the mask pattern out of the light that has passed through the mask pattern during resist exposure, and pullulan, on a substrate having steps. a step of selectively exposing the laminated film through the mask pattern; and a step of simultaneously developing and removing the resist and the water-soluble organic film to form a resist pattern. Characteristic pattern formation method. (4) The pattern forming method according to claim 3, wherein the substrate is a semiconductor substrate and the resist is an organic solvent resist.