Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Processing feature prior to imaging
Reexamination Certificate
1998-11-30
2001-10-09
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Processing feature prior to imaging
C430S322000, C430S324000
Reexamination Certificate
active
06300043
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a resist film on a surface of the substrate or on a layer formed on a substrate such as a semiconductor layer, an insulating layer or an electrode layer.
In a photolithography process, a photoresist film is formed on a semiconductor wafer or a glass substrate for a liquid crystal display device (LCD substrate), followed by exposing the photoresist film to light in a predetermined pattern and subsequently developing the patterned photoresist film. Where the photoresist film is formed on the substrate, employed is a spin coating method disclosed in, for example, U.S. Pat. No. 5,002,008 or U.S. Pat. No. 5,688,322.
In recent years, the semiconductor wafer or the LCD substrate tends to be enlarged, with the line width of the circuit pattern becoming finer and finer. As a result, the photoresist film is required to be made thinner. The wafer size and the pattern line width have undergone various changes in the manufacture of a semiconductor device. Specifically, the pattern line width was 0.5 to 0.8 &mgr;m in a 6-inch wafer. In this case, the corresponding resist film was about 1.0 &mgr;m thick. Also, the pattern line width was 0.3 to 0.2 &mgr;m in an 8-inch wafer. In this case, the corresponding resist film was about 0.8 to 1.0 &mgr;m thick. Further, the pattern line width was 0.18 to 0.22 &mgr;m in a 12-inch wafer. In this case, the corresponding resist film is considered to be about 0.3 to 0.5 &mgr;m thick.
The thickness of the resist film formed by the spin coating method is greatly dependent on the rotating speed of the substrate and on the viscosity (concentration and temperature) of the resist solution. In order to make the resist film thinner, it is necessary to lower the viscosity of the resist solution and to increase the rotating speed of the substrate. For example, with change in the wafer diameter from 6 inches to 8 inches, the viscosity of the resist solution is lowered from 10 cP to 5 cP. Also, the wafer rotating speed is increased from, for example, 2,000 rpm to 3,000 rpm.
In a 12-inch wafer which is expected to be put to a practical use in future, the thickness of the resist film is to be decreased to below 0.5 &mgr;m, making it necessary to further lower the viscosity of the resist solution and to further increase the wafer rotation speed. However, the lowest viscosity of the resist solution which can be used in the manufacture of a semiconductor device is about 3 cP. In order to form a resist film in a thickness of about 0.5 &mgr;m by using a resist solution having a viscosity of about 3 cP, it is necessary to set the wafer rotation speed at about 4,000 rpm. However, the resist film formed by a spin coating method with such a high rotation speed is greatly non-uniform in thickness. Also, an excessively large load is applied to the spin chuck driving mechanism for rotating a large substrate at such a high speed, with the result that the spin chuck driving mechanism is required to be put to maintenance frequently. It follows that it is difficult to carry out a stable treatment uniformly.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of forming a resist film having a small thickness.
According to a first aspect of the present invention, there is provided a method of forming a resist film, comprising, the steps of, (a) forming a resist film on a substrate, and (b) removing a surface region of the resist film formed in the step (a) so as to decrease the thickness of the resist film.
In the step (b), an acid component is applied to the surface of the resist film so as to make the surface region of the resist film soluble in alkali, followed by applying an alkaline solution to the surface of the resist film so as to permit the surface region of the resist film to be dissolved in the alkaline solution and, thus, to remove the surface region. It is desirable to use an aqueous solution containing a compound having a sulfonic group as the acid component.
In the step (a), the substrate is coated with a resist solution containing a first solvent, followed by heating the resist film so as to evaporate the first solvent from the resist film. Then, in the step (b), a second solvent lower in its dissolving characteristics than the first solvent is supplied to the surface of the resist film so as to permit the surface region of the resist film to be dissolved in the second solvent and, thus, to remove the surface region. It is desirable to use a mixture consisting of 85% by volume of isopropyl alcohol and 15% by volume of MMP (3-methoxymethyl propionate) as the solvent having the low dissolving characteristics.
In the step (b), it is possible to apply a mechanochemical polishing treatment to the surface of the resist film for removing the surface region of the resist film. In performing the mechanochemical polishing treatment, a polishing member is brought into contact with the surface of the resist film while supplying a chemical polishing agent onto the surface of the resist film, and the polishing member is moved relative to the substrate. It is desirable for the polishing member to be formed of polyurethane. Also, it is desirable to supply, for example, a colloidal silica, which is a weakly alkaline slurry containing silica as a main component, as the polishing agent.
In the step (a), it is possible to supply a resist solution onto the substrate while rotating the substrate. Also, in the step (b), it is possible to supply a liquid material containing the acid component onto the substrate while rotating the substrate. It is also possible to supply in the step (b) a solvent having a low dissolving power onto the substrate while rotating the substrate. Each of the resist solution, the acid component solution, the solvent and the chemical polishing agent can be dispersed uniformly over the entire surface of the substrate by employing a spin coating method so as to ensure uniformity of processing.
In the step (a), an alkali-reactive group brings about an acid catalyst reaction under heat, making it possible to coat the substrate with a chemically amplified resist in which the portion where the acid catalyst reaction has taken place is made soluble in alkali. It is possible to use as the chemical amplification type resist polyhydroxy styrene (PHS) having an acetal protective group (see FIG.
7
), PHS having t-BOC protective group or polyvinyl phenol having the hydroxyl group within the polymer blocked by an alkyl group.
According to a second aspect of the present invention, there is provided a method of forming a resist film, comprising:
a first step of forming on a surface of a substrate a chemically amplified resist film, which, if heated in the presence of an acid component, permits the acid component to be diffused so as to bring about an acid catalyst reaction, the portion where the acid catalyst reaction has taken place being made soluble in alkali;
a second step of supplying the acid component to the surface of the resist film after the first step;
a third step of heating the substrate so as to cause the acid component to bring about an acid catalyst reaction within the resist film to make the surface region of the resist film soluble in alkali; and
a fourth step of supplying an alkaline solution onto the surface of the substrate so as to dissolve and remove the surface region of the resist film.
The thickness of the resist film can be decreased to a desired level by repeating a plurality of times the second to fourth steps.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: Re. 35821 (1998-06-01), Niki et al.
patent: 3793106 (1974-02-01), Grunwald et al.
patent: 4861438 (1989-08-01), Banks et al.
patent: 5002008 (1991-03-01),
Hirose Keizo
Konishi Nobuo
Duda Kathleen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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