JP3237082B2 - Method of forming resist pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a resist pattern, and more particularly to a method of forming a resist pattern by, for example, a lift-off method.
And a method of forming a resist pattern for producing a gate electrode.

[0002]

2. Description of the Related Art In recent years, demands for higher performance and higher integration of semiconductor integrated circuits and the like have been further increased. For this reason, efforts have been made to establish an ultra-fine pattern processing technique by lithography using electron beams, soft X-rays, ion beams, or the like, instead of conventional photolithography using ultraviolet rays. In particular, shortening the gate length is effective for increasing the frequency and improving the performance of the compound field effect transistor, and a fine gate electrode is formed by a lift-off method.

For this purpose, a resist is coated on a substrate 20, exposed and developed, and then, as shown in FIG. 2A, a resist pattern 21 having a vertical or forward tapered cross section.
However, as shown in FIG. 2B, a gate metal 22 is vapor-deposited on the resist pattern 21 and then, as shown in FIG.
Dissolves and removes unnecessary burrs 2 at the end of the gate electrode 23.
4 or the gate electrode 23 itself is destroyed during lift-off.

In order to avoid such a problem, it is necessary to use a resist pattern 35 having an inverse tapered shape (or overhang shape) as shown in FIG. As one conventional method for obtaining such an inversely tapered resist pattern, a resist surface is alkali-treated to make it hardly soluble in a developing solution, and a desired developing rate is obtained by utilizing a difference in developing speed from the inside of the resist. A method for obtaining a resist cross-sectional shape has been proposed (JP-A-3-119720). That is, as shown in FIG. 3A, a positive resist 31 is applied on a substrate 30, and the surface thereof is subjected to an alkali treatment to form a surface hardly-solubilized layer 32 as shown in FIG. 3B. Then, as shown in FIG. 3C, the resist 31 is baked on a hot plate 33, and then, as shown in FIG. 3D, a desired pattern is formed by light, electron beam, ion beam, Exposure is performed using X-rays or the like 34, and then, as shown in FIG.
Can be obtained. Thereafter, as shown in FIG. 3F, a gate metal 36 is deposited or sputtered on the resist pattern 35, and then, as shown in FIG. Is formed. In this case, since the opening cross section of the resist pattern 35 has an inversely tapered shape, there is no burr or the like at the end of the completed gate electrode 36, and since the lower portion of the gate electrode 36 is not peeled off by lift-off, the gate electrode 36 is broken. It will not be done.

[0005]

However, this conventional method for making the resist surface hardly soluble requires an extra step for making the resist surface hardly soluble.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a lift-off method in which the opening cross section is inversely tapered without using any extra steps by merely devising a baking process. An object of the present invention is to provide a method for forming a resist pattern for producing a fine gate electrode.

[0007]

In general, when a resist layer is formed on a substrate, a resist is applied using a spinner or the like, and then the adhesion between the substrate and the resist is improved.
And, baking is performed for the purpose of removing insoluble solvents in the resist, but in the case of a positive resist, the sensitivity varies depending on the baking temperature, specifically, those baked at a high temperature are reduced at a low temperature. It is known that the sensitivity is lower than the baked one.

The present invention utilizes this characteristic of a positive type resist. In a resist pattern forming step, when baking is performed after applying a resist on a substrate,
A substrate is placed on a temperature-controllable plate, and a gas or heat ray higher than the plate temperature is applied from the resist surface side to create a temperature difference within the resist thickness, and obtain a reverse tapered shape from the sensitivity difference due to it. It was completed after finding that it became possible.

That is, the method of forming a resist pattern according to the present invention is a resist pattern having an inverted tapered shape in which the cross section of the opening narrows toward the surface, and the method of forming a resist pattern for producing a fine gate electrode by a lift-off method. In, apply a resist on the substrate, when baking before exposure, put the substrate on a temperature-controllable plate, and apply hot air or heat rays from the resist surface side,
By cooling relatively from the substrate side, making a temperature difference within the resist thickness and baking to form a sensitivity difference within the resist thickness, the resist has a reverse tapered opening cross section after exposure and development. The method is characterized by forming a pattern.

In this case, the resist is preferably a positive resist.

[0011]

In the present invention, when baking before exposure, the substrate is placed on a temperature-controllable plate, hot air or heat rays are applied from the resist surface side, and relatively cooled from the substrate side. By forming a temperature difference within the resist thickness and baking to form a sensitivity difference within the resist thickness, a resist pattern having a reverse tapered opening cross section after exposure and development is formed. This is a simple process that simply devises the baking process that is always performed in the process, without adding extra and complicated processes such as surface insolubilization, and forming an inverse tapered resist pattern that is optimal for lift-off formation of fine gate electrodes. It can be formed reliably.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for forming a resist pattern according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing steps of a method for forming a resist pattern according to the present invention. First, as shown in FIG.
Positive resist 1 containing polymethyl methacrylate as a main component (trade name; OEBR- manufactured by Tokyo Ohka Co., Ltd.)
1000) is applied by a spinner, and hot air or a hot wire 3 of 150 ° C. is applied to the resist surface so that a temperature difference occurs within the thickness of the resist film 1 as shown in FIG. Cool on the cool plate 4. This process is performed for 30 minutes, and as shown in the figure, a low sensitivity portion 5 is formed relatively on the exposed side of the resist film 1 and a high sensitivity portion 6 is formed relatively on the deep side (sensitivity difference formation).

Next, as shown in FIG. 1C, a gate having a width of 0.25 μm is formed on the resist film 1 by using an electron beam of an electron beam lithography apparatus, or light, ion beam, or X-ray 7. A resist pattern for forming a pattern is drawn.

After the completion of drawing with an electron beam or the like, the resist film 1 together with the substrate 2 was immersed in a developing solution at a mixing ratio of methyl isobutyl ketone and isopropyl alcohol of 1: 3 at about 23 ° C. for 1 minute and developed. Thereafter, the substrate 2 together with a rinse solution of isopropyl alcohol at about 23 ° C.
By immersion cleaning for about a second, a resist pattern 8 having an inversely tapered cross section as shown in FIG.

Using the resist pattern 8 thus obtained as a mask, aluminum is deposited by sputtering to form a gate electrode metal film 9 as shown in FIG. Then, the resist film 8 is dissolved and removed, and the gate length is 0.25 μm as shown in FIG.
Al gate electrode 10 was formed.

The obtained Al gate electrode 10 was clean with no burrs or the like at the ends and was not broken.

Although the method of forming a resist pattern according to the present invention has been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications are possible.

[0018]

As is apparent from the above description, according to the method for forming a resist pattern of the present invention, when baking is performed before exposure, the substrate is placed on a temperature-controllable plate, and Exposure after exposure and development by applying hot air or heat rays from the substrate and relatively cooling from the substrate side, creating a temperature difference within the resist thickness and baking to form a sensitivity difference within the resist thickness Since a resist pattern with a reverse-tapered cross section is formed, it is a simple process that only devises the baking process that is always performed in the resist pattern forming process, and does not increase extra and complicated processes such as surface insolubilization. In addition, it is possible to reliably form a resist pattern having an inverse tapered shape that is optimal for lift-off formation of a fine gate electrode.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the steps of one embodiment of a method for forming a resist pattern according to the present invention.

FIG. 2 is a sectional view showing a conventional lift-off process in a forward tapered shape.

FIG. 3 is a cross-sectional view showing steps of a conventional method for forming a resist pattern having a reverse tapered cross section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive resist 2 ... Substrate 3 ... Hot air or heat ray 4 ... Cool plate 5 ... Low sensitivity part 6 ... High sensitivity part 7 ... Electron beam, light, ion beam, X-ray 8 ... Resist pattern 9 ... Metal film for gate electrode 10 ... Gate electrode

Claims (2)

(57) [Claims] In a method of forming a resist pattern for forming a fine gate electrode by a lift-off method, a resist is applied to a substrate, the resist pattern having an inverse tapered shape in which an opening cross section narrows toward a surface side. When baking before exposure, the substrate can be temperature controlled.
Put on a rate , apply warm air or heat rays from the resist surface side, cool relatively from the substrate side, make a temperature difference within the resist thickness and bake to form a sensitivity difference within the resist thickness Forming a resist pattern having a reverse tapered cross section of the opening after exposure and development. 2. The method according to claim 1, wherein the resist is a positive resist.