Over-coating agent for forming fine patterns and a method of forming fine patterns using such agent

Abstract

It is disclosed an over-coating agent for forming fine-line patterns which is applied to cover a substrate having thereon photoresist patterns and allowed to shrink under heat so that the spacing between adjacent photoresist patterns is lessened, further characterized by comprising a water-soluble polymer which contains at least methacrylic acid and / or methyl methacrylate as the constitutive monomer thereof. Also disclosed is a method of forming fine-line patterns using the over-coating agent. The advantages of the invention are that the exposure margin is large, that the dimension control of photoresist patterns can be reflected on the dimension controllability in forming fine-line patterns, that the dimension control and planning of forming fine trace patterns after treatment for thermal shrinkage can be attained with ease in the stage of photoresist patterning, that the original photoresist pattern profile can be kept as such and the top of the photoresist pattern is not rounded after thermal shrinkage, that the degree of thermal shrinkage of the over-coating agent is large and thus the agent is effective in forming fine-line patterns.

Description

BACKGROUND OF THE INVETNION [0001] 1. Field of the Invention [0002] This invention relates to an over-coating agent for forming fine patterns in the field of photolithographic technology and a method of forming fine-line patterns using such agent. More particularly, the invention relates to an over-coating agent for forming or defining fine-line patterns, such as hole patterns and trench patterns, that can meet today's requirements for higher packing densities and smaller sizes of semiconductor devices. [0003] 2. Description of the Related Art [0004] In the manufacture of electronic components such as semiconductor devices and liquid-crystal devices, there is employed the photolithographic technology which, in order to perform a treatment such as etching on the substrate, first forms a film (photoresist layer) over the substrate using a so-called radiation-sensitive photoresist which is sensitive to activating radiations, then performs exposure of the film by selective illumination ...

AI Technical Summary

Benefits of technology

[0071] The photoresist composition serving as a material from which photoresist patterns are formed is not limited in any particular way and any common photoresist compositions may be employed including those for exposure to i- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArF or F2) and those for exposure to EB (electron beams). According to the invention, even in a photoresist having a low thermal flow temperature of around 150° C. or lower, the top of the photoresist pattern can be prevented from being rounded, and while the degree of thermal shrinkage of the over-coating agent is kept as such, the exposure margin may be broadened. Still another advantage of the invention is that the controllability in patterning is good.

[0072] After thusly forming the photoresist pattern as a mask pattern, the over-coating agent for forming fine patterns is applied to cover entirely the substrate. After applying the over-coating agent, the substrate may optionally be pre-baked at a temperature of 80-100° C. for 30-90 seconds.

[0073] The over-coating agent may be applied by any methods commonly employed in the conventional heat flow process. Specifically, an aqueous solution of the over-coating agent for forming fine patterns is applied to the substrate by any known application methods including bar coating, roll coating and whirl coating with a spinner. [b.] Heat Treatment (Thermal Shrinkage) Step

[0074] In the next step, heat treatment is performed to cause thermal shrinkage of the film of the over-coating agent. Under the resulting force of thermal shrinkage of the film, the dimensions of the photoresist pattern in contact with the film will increase by an amount equivalent to the thermal shrinkage of the film and, as the result, the photoresist pattern widens and accordingly the spacing between adjacent photoresist patterns lessens. The spacing between adjacent photoresist patterns determines the diameter or width of the pattern elements to be finally obtained, so the decrease in the spacing between adjacent photoresist patterns contributes to reducing the diameter of each element of a hole pattern or the width of each element of a trench pattern, eventually leading to the definition of a pattern with smaller feature sizes.

[0075] The heating temperature is not limited to any particular value as long as it is high enough to cause thermal shrinkage of the film of the over-coating agent and form or define a fine pattern. Heating is preferably done at a temperature that will not cause thermal fluidizing of the photoresist pattern. The temperature that will not cause thermal fluidizing of the photoresist pattern is such a temperature that when a substrate on which the photoresist pattern has been formed but no film of the over-coating agent has been formed is heated, the photoresist pattern will not experience any dimensional changes. Performing a heat treatment under such temperature conditions is very effective for various reasons, e.g. a fine-line pattern of good profile can be formed more efficiently and the duty ratio in the plane of a wafer, or the dependency on the spacing between photoresist patterns in the plane of a wafer, can be reduced. Considering the softening points of a variety of photoresist compositions employed in current photolithographic techniques, the preferred heat treatment is usually performed within a temperature range of about 80-160° C. for 30-90 seconds, provided that the temperature is not high enough to cause thermal fluidizing of the photoresist. [c.] Over-Coating Agent Removal Step

[0076] In the subsequent step, the remaining film of the over-coating agent on the patterns is removed by washing with an aqueous solvent, preferably pure water, for 10-60 seconds. Prior to washing with water, rinsing may optionally be performed with an aqueous solution of alkali (e.g. tetramethylammonium hydroxide (TMAH) or choline). The over-coating agent of the present invention is easy to remove by washing with water and it can be completely removed from the substrate and the photoresist pattern.

Problems solved by technology

However, in these methods, it is difficult to control the thickness of layers to be formed on the sidewalls of resist patterns.

In addition, the in-plane heat dependency of wafers is as great as ten-odd nanometers per degree Celsius, so it is extremely difficult to keep the in-plane uniformity of wafers by means of the heater employed in current fabrication of semiconductor devices and this leads to the problem of occurrence of significant variations in pattern dimensions.

On the other hand, it is difficult to control the resist deformation and fluidizing on account of heat treatment, so it is not easy to provide a uniform resist pattern in a wafer's plane.

However, polyvinyl alcohol alone is not highly soluble in water and cannot be readily removed completely by washing with water, introducing difficulty in forming a pattern of good profile.

The pattern formed is not completely satisfactory in terms of stability over time.

In addition, polyvinyl alcohol cannot be applied efficiently by coating.

Because of these and other problems, the method disclosed in JP-7-45510 has yet to be adopted commercially.

In the process comprising said two stages, when photoresist patterning is performed by increasing the luminous exposure of light to which a photoresist is exposed in the first stage, the degree of thermal shrinkage of the over-coating agent in the second stage is apt to be larger than the expected degree thereof and, as a result, it is often difficult to anticipate the dimension controllability in forming fine-line patterns in the process.

In view of the shape of photoresist patterns, even when photoresist patterns having a good rectangular cross-sectional profile could be formed in the photoresist patterning stage (first stage), there may occur in the second stage a problematic phenomenon that the top of the photoresist pattern may be rounded owing to the thermal shrinkage of the over-coating agent applied thereto for forming fine patterns.

In particular, when an ArF photoresist is used for forming finer line patterns, the top of the photoresist pattern could not keep the original rectangular profile thereof but is often rounded in the thermal shrinkage step for the over-coating agent applied onto the photoresist pattern.

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