JPH0245325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to the manufacturing of semiconductor integrated circuits, particularly in the pattern formation of photolithography.
Related to pattern formation using a laminated structure of radiation-sensitive resin and water-soluble organic film to prevent the negative effects of excess light passing through the mask pattern, improve pattern accuracy on steps, and increase resolution. It is.

Conventional Structures and Their Problems High integration and high density of integrated circuits have been increasing due to advances in conventional lithography technology. The minimum line width has also 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 method 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 an actual integrated circuit, and after coating a radiation-sensitive resin (hereinafter referred to as resist), differences in resist film thickness occur at the uneven parts.
Good line width control becomes impossible.

This will be explained using FIG. Figure 1 shows a single-layer resist film applied to the stepped portion using the conventional method.
This figure shows a state in which patterning is performed across the stepped portion. FIG. 1A is a cross-sectional view of a step pattern 2a such as a SiO ₂ film 2 formed on a substrate 1 such as a semiconductor substrate, and a resist 3 coated thereon. In this case, when the resist 3 is applied to a thickness of t _R1 on a flat film without the step pattern 2a, the step pattern 2a
The film thickness of the resist 3 on the surface a is determined to be the film thickness t _R2 based on the viscosity of the resist itself and the number of revolutions during coating.
At this time, it is physically impossible to set t _R1 = t _R2 , that is, to completely eliminate the difference in the thickness of the resist film at the uneven portions. The top view when a resist pattern is formed with a film thickness of t _R1 〓 _{t R2} in this way is shown in the first diagram.
Shown in Figure B.

This is the film thickness _tR1 of the resist pattern 3 formed perpendicularly to the step pattern 2a.
If the pattern width is determined as l ₁ at the position, the film thickness t _R2
At the position, there is a relationship of t _R1 > t _R2 , so the pattern width is l ₂ and l ₁ > l ₂ , resulting in a dimensional conversion difference at the stepped portion. In other words, if the pattern becomes very fine, good line width control cannot be obtained, and furthermore, the edge portion 2b of the stepped object 2a is substantially thicker than the film thickness t _R1 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 other words, in order to reduce the resist film thickness difference on the stepped object, even if the resist is simply coated thickly to reduce the apparent resist film thickness difference, the resolution deteriorates, which is not preferable in terms of pattern formation.

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

FIG. 2A shows a metal film 4 on a convex step 2 on a substrate 1.
For example, this is a cross-sectional view of a state in which an Al film is deposited on the entire surface and a photosensitive resin (hereinafter referred to as resist) 3 is coated on top, and ultraviolet rays are irradiated through the chromium 6 of the mask 5. The ultraviolet rays at this time (hereinafter referred to as UV
FIG. 2B is an enlarged view of the incident state of light).
Of the incident UV light 7, it is incident on the flat part 3a
The reflected light 7b of the UV light 7a is accurately reflected at an angle of 180°, but the UV light is incident on the stepped portion of the Al film 4.
The light 7c is reflected from the side surface of the Al film 4 and becomes reflected light 7d.
This reflected light 7d enters the unexposed resist region 3b and is redundant light for resist pattern formation, and the resist cross section 3c after development is actually wider than the width of the chrome portion 6 of the mask 5. The pattern becomes narrower and the pattern accuracy deteriorates. Furthermore, depending on the distance between the steps and the end of the resist pattern, the resist pattern may disappear and pattern breakage may occur.

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 with high light intensity, the resolution due to the extra light,
For example, when forming a wiring pattern on Al with steps, the pattern accuracy decreases significantly.
The following pattern dimensions always cause disconnection.

Purpose of the Invention The present invention facilitates the formation of fine patterns without damaging a 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.

Structure of the Invention The present invention comprises coating and forming a water-soluble anti-reflection organic film soluble in a greenhouse containing a water-soluble organic substance, a substance that absorbs light of 500 nm or less, a crosslinking agent, and water on a substrate having steps, a step of performing heat treatment, a step of coating and forming an organic solvent-based positive radiation-sensitive resin on the water-soluble antireflection film, a step of selectively exposing the light, and a step of selectively exposing the selectively exposed radiation-sensitive resin. The pattern forming method includes a step of developing and removing the water-soluble antireflection organic film directly under the exposed radiation-sensitive resin, in which pullulan is used as the main component of the water-soluble organic substance.

The water-soluble organic film mentioned above contains a water-soluble organic substance such as pullulan, which is a polysaccharide, as a main component.
Substances that absorb light (ultraviolet light) of 500 nm or less, such as those containing acidic or basic dyes; crosslinking agents for adjusting the rate of dissolution in water, etc., such as dialdehyde starch, dichromate, diazide compounds,
It may contain an azide compound, an aldehyde compound, etc., 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 pullulan, which is a polysaccharide, will be described. The structure of pullulan is shown below.

The molecular structure of pullulan is different from polysaccharides such as starch and cellulose, which are mainly composed of glucose units. 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. In addition, the pullulan aqueous solution is stable for a long time, and no gelation or aging phenomenon is observed. Furthermore, the film also has the property of not being easily dissolved in organic solvents. In other words, it has the property of being easily coated in layers with organic solvent-based radiation-sensitive resins (hereinafter referred to as resists) used in lithography 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, the dye is an acid dye, but the pullulan aqueous solution is
It is a stable aqueous solution that is not affected by pH.

The developer (alkaline aqueous solution) and rinse solution (water) in the development process of resist pattern formation.
In order to control the dissolution rate of the pullulan membrane, a small amount of dialdehyde starch, for example, may be mixed as a crosslinking agent. After resist development, the pullulan film in the area where the resist was removed is also dissolved and removed by the developer and rinse solution used in the resist development process. At this time, if the pullulan film is removed too quickly, the area under the remaining resist pattern will be removed. The side etch of the pullulan membrane increases. In order to eliminate this, a crosslinking agent is appropriately added and heat treatment is performed after coating to appropriately reduce the dissolution rate of the pullulan film. Dialdehyde is produced by oxidizing starch with periodic acid to change the constituent units of starch to 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, azide compounds (photosensitive),
It is also good to react with aldehyde compounds.

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 c.c. of pure water (deionized water) into a beaker, keep the temperature at room temperature, and adjust the average molecular weight with enough heavy metals.
Add 200,000 g of pullulan while stirring,
gDissolve. On the other hand, add acid dye (dye that absorbs ultraviolet light below 500 nm) to 100 c.c. of warm water at a temperature of 80°C.
Dissolve 2.5g while stirring. Next, the pullulan aqueous solution and the dye aqueous solution were mixed to prepare a dye-containing pullulan aqueous solution. Next, several cc of dialdehyde starch aqueous solution (10%) were mixed with the pullulan aqueous solution containing the dye. In this state, gelation is not observed and the quality does not change at all even after a long period of time.
Spread this solution onto a quartz glass plate using a spinner.
When spin-coated at 3000 rpm, a uniform film thickness of 5000 Å was obtained, and the ultraviolet transmission characteristics were less than 50% at wavelengths less than 500 nm, making it suitable for ultraviolet exposure in semiconductor manufacturing to sufficiently absorb excess light during positive resist exposure. It had the effect of absorbing Further, after coating this water-soluble organic film, when an organic solvent-based positive resist was coated on this organic film, there was no dissolution, and this resist could be laminated very easily. The dissolution rate of this water-soluble organic film in the solution used for resist development is about 10 times slower than that without a crosslinking agent, and is slower than the dissolution rate of the resist in the developer after exposure. The side etch of the organic film can be reduced.

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 period of time and its solubility is also easy to control, and the film does not easily dissolve in organic solvents and is heat resistant. It also has high transparency against UV rays.

Note that the amounts of pullulan, dye, and crosslinking agent can be arbitrarily selected depending on the coating thickness, amount of ultraviolet absorption, and 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 an Al film 4 that will become a wiring, is deposited.
Then, the water-soluble organic film 8 described above is applied (FIG. 3A). 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, the thickness was 2000.
A thin film was formed by coating .

Next, apply a positive UV resist 3 [for example, S-
1400 (manufactured by Shippray), OFPR-800 (manufactured by Tokyo Ohka), etc.] 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]. When applying this layered coating,
No extra steps are required, and the layered coating step can be easily performed. This is an excellent process advantage since there is no need to change the normal semiconductor integrated circuit process.

Then, ultraviolet rays 7 of 436 nm are exposed through the chrome pattern 6 of the photomask 5 using a reduction projection exposure method with an energy of 150 mJ/cm ² . 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 absorbed by the ultraviolet absorber in the water-soluble organic film 8, so that the unexposed areas 3e of the six chrome patterns are An image is formed (Figure 3C).

Next, the exposed portion of the positive UV resist 3 is developed and removed by a development step using an alkaline developer and a rinse solution. In this development process, the water-soluble anti-reflection organic film directly under the exposed area is also removed, and pattern 3
f, 8a was obtained [Fig. 3D].

The rate of dissolution of the organic film 8 in the developing solution and the rinsing solution can be freely controlled by the amount of crosslinking agent added, as described above, and is set by the thickness of the upper resist layer. Further, in order to promote the crosslinking reaction of the crosslinking agent, it is desirable to apply heat treatment after coating the organic film 8.

After FIG. 3D, the Al film 4 is selectively removed using the patterns 3f and 8a as a mask 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 shape of the step 2 on the base substrate 1 did not change, and the positive type
In the UV resist 3, variations in film thickness occur in the vicinity of steps, and pattern accuracy eventually deteriorates. 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 UV resist 3 (for example, S-1400 (manufactured by Shippray Co., Ltd.), OFPR-800 (manufactured by Tokyo Ohka), etc.) is applied flatly, so that fluctuations in resist film thickness are completely eliminated. By adding exposure, development, and rinsing steps, patterns 3f and 8a with high pattern accuracy and high aspect ratios were obtained as shown in (B). At this time, the water-soluble organic film 8 was formed by applying an aqueous solution in which 5% by weight of dialdehyde starch aqueous solution, which is a crosslinking agent, was added to a dye-containing pullulan aqueous solution, and was further subjected to a low-temperature heat treatment at 100° C. for about 90 seconds. . Organic film 8 with optimally added crosslinking agent in this way
The dissolution rate in the developing solution becomes appropriate, and optimal dissolution is possible regardless of the film thickness. Therefore, the pattern 8a of the remaining organic film 8 can have a good shape in which the resist pattern 3f is faithfully transferred.

Specifically, experimental data according to the present invention is shown in FIG. The horizontal axis represents the distance S from the stepped edge to the chrome pattern edge which is the light-shielding portion of the mask pattern in FIG. 1, and the vertical axis represents the resist pattern after pattern formation, which is a transfer of the mask pattern. According to this, in the curve 11 of the conventional example, S (distance from the step) is 1.
At a distance of ~2 μm, the resist pattern becomes disconnected or tends to disconnect due to reflection from the underlying Al. For example, when S is 0.5 μm,
The resist pattern was thinned to 0.5 μm. On the other hand, the present invention shown by curve 10 is
Regardless of the distance of S, a 1 μm pattern could be formed without any variation in the resist pattern.

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 coats and forms a water-soluble anti-reflection organic film on a substrate having steps, which is made by mixing an aqueous solution containing pullulan as a main component with a substance that absorbs light of 500 nm or less and a crosslinking agent, and On top of this is an organic solvent-based positive radiation-sensitive resin (positive resist).
After coating and heat treatment, a resist and organic film pattern is formed by selective exposure to the light, making it possible to form a highly accurate resist pattern that is faithful to the mask pattern. Furthermore, according to the present invention, when an organic solvent-soluble resist is used, it does not dissolve with the water-soluble organic film, so multilayer coating is easy, and selection can be made in the development and rinsing process that is applied to ordinary resists. Pattern formation can be performed automatically, and fine resist patterns can be easily obtained without changing the development process. In addition, when a water-soluble organic film containing pullulan is used, it is easily soluble in cold water, has stable quality, and is easy to apply, making it extremely effective in the semiconductor photolithography process. It is something that demonstrates its value.

[Brief explanation of the drawing]

Figures 1A and B are cross-sectional views and plan views after pattern formation by conventional processes, Figures 2A and B are cross-sectional views of conventional resist pattern formation processes, and Figures 3A to D.
4A and 4B are sectional views of the pattern forming process of the second embodiment of the present invention, and FIG. 5 is a comparison between the present invention and the conventional example. It is a figure showing data. 1...Substrate, 2...Step, 3...Resist, 8
...Water-soluble organic film.

Claims (1)

[Claims] 1. Water-soluble organic matter and
A step of coating and forming a water-soluble anti-reflection organic film that is soluble at room temperature and containing a substance that absorbs light of 500 nm or less, a crosslinking agent, and water, and heat-treating the organic film; a step of coating and forming an organic solvent-based positive radiation-sensitive resin; a step of selectively exposing the radiation-sensitive resin; A pattern forming method comprising a step of developing and removing a water-soluble antireflection organic film, the pattern forming method comprising using pullulan as a main component of the water-soluble organic substance.