The present invention relates to a novel silicon-containing polymer and a novel photosensitive material containing siloxane linkages, which is useful for resist having photosensitive groups responsive to electrons, X-rays, UV light and deep UV light as are used when producing semiconductor integrated circuits, and which is also usable as an insulation film or a protective film.
The silicon-containing polymers are used in a variety of fields for the reasons that they exhibit excellent heat resistance and cold resistance, that the electric characteristics thereof are stable over a wide range of temperature, and the like. Moreover, silicon-based polymers provided with photosensitive group have been recently developed and their uses are spreading out in electronic materials.
In the electronic field, particularly in the production of semiconductors (integrated circuits), the processing of substrates at high levels of precision has become more complicated and higher precision has been required as the degree of circuit integration has become higher. Accompanying this, techniques for performing processing at a sub-micron scale on substrates at different levels have been proposed and various methods have been tried. As one of them, a two-layer resist technique using a silicon-based resist as a top layer has been proposed, and has recently received much attention. This technique will now be explained.
A resin or resist having resistance to halogen gas is spin-coated onto a bottom layer, which is subject to soft- or hard-baking. Then, a silicon-based resist is spin-coated onto the top layer. Using an exposure device, the top layer resist is exposed to light and only the top layer is developed. Then, using the patterned area of the top layer resist as a mask, the bottom layer resist is etched with O.sub.2 gas plasma. Finally, using the bottom layer resist as a mask, the substrate is etched with halogen gas.
The functions needed for the top layer resist are as follows:
(1) To be excellent in resistance to O.sub.2 plasma. PA1 (2) To be excellent in flatness. PA1 (3) To have a high glass transition temperature. PA1 (4) To have high resolution. PA1 (5) To have high sensitivity.
Silicon-containing resist materials are excellent in resistance to O.sub.2 plasma and some resist materials using them are known. As representatives thereof, a method of attaching a silyl group directly or indirectly to the benzene rings of Novolak resin or polystyrene, a method utilizing a polysilane linkage, and, in particular, recently, a method utilizing a ladder polymer (silsesquioxane linkage) have been proposed.
In the case of the type where a silyl group is attached directly or indirectly to the benzene rings, however, the problem that the resistance to O.sub.2 plasma is insufficient exists because the content of Si is low and Si is introduced into a side chain. Moreover, in the case of the polysilane type, poor coating property and stability are generally encountered, though the content of Si may be increased depending on the kind of compounds. Furthermore, in the case of silsesquioxane type polymers, there is a problem that the sensitivity is not enough though the resistance to O.sub.2 plasma is excellent.
As described above, at present resist materials with excellent resistance to O.sub.2 plasma and excellent flatness which have a high Tg, high resolution and high sensitivity have not been developed.
The present invention was made to overcome the problems as above and the purpose thereof is to provide a novel silicon-containing polymer and a photosensitive material using the same which is excellent in resistance to O.sub.2 plasma, has excellent flatness and which has high Tg, high resolution and high sensitivity.
As a result of diligent studies against such background, the inventors have found that by using a polymer having a single siloxane cyclic compound as a repeating unit or a copolymer having various siloxane cyclic compounds as repeating units, a resist material which is highly sensitive, highly flat and excellent in resistance to O.sub.2 plasma and yet having a high Tg can be obtained, leading to the completion of the present invention.