Method for formation of siliceous film and siliceous film formed by the method

1. A method for formation of a siliceous film, comprising

(A) a first coating step, in which a polysilazane composition is applied on a substrate surface having concaved portions and convex portions to form a coating layer having a thickness of 10- 1000 nm,

(B) a covering film-formation step, in which said coating layer is hardened only from the surface of the substrate out to 1-50 nm from the surface of the substrate, where the thickness that is hardened is less than the entire thickness of the coating layer, thereby forming a 1 to 50 nm hardened covering film having homogeneous fill along the shape of said substrate surface having concaved portions and convex portions, and

(C) an unhardened layer-removal step, in which the polysilazane composition that remains in said coating layer in a part not hardened in the above covering film formation step is removed.

2. The method according to claim 1 for formation of a siliceous film, further comprising

(D) a covering film-hardening step, in which said covering film is further hardened right after the above unhardened layer-removal step.

3. The method according to claims 2 for formation of a siliceous film, wherein the covering film-hardening step (D) is performed under a heated condition in an inert gas or oxygen gas atmosphere containing steam.

4. The method according to claim 1 for formation of a siliceous film, furthermore comprising

a final coating step, in which another polysilazane composition is applied on said covering film to fill in said concaved portions, and

a final hardening step, in which said polysilazane composition applied in the above final coating step is converted and densified into silicon dioxide.

5. The method according to claim 4 for formation of a siliceous film, wherein the final hardening step is performed under a heated condition in an inert gas or oxygen gas atmosphere containing steam.

6. The method according to claim 1 for formation of a siliceous film, wherein said substrate is prepared by engraving a flat substrate with grooves having a width of 1 to 100 nm and a depth of 10 nm to 10 μm.

7. The method according to claim 1 for formation of a siliceous film, wherein said covering film-formation step is performed according to at least one procedure selected from the group consisting of

(B1) heating said substrate at a temperature of 35 to 120° C.,

(B2) exposing said polysilazane composition applied substrate to light of such a wavelength that said substrate absorbs the light but said coating layer of polysilazane does not, and

(B3) exposing said substrate to high-energy radiation before the first coating step (A) so as to hydroxylate said substrate surface, and thereafter applying the polysilazane composition thereon.

8. The method according to claim 7 for formation of a siliceous film, wherein said covering film-formation step is performed according to a combination of two or more of (B1) to (B3).

9. The method according to claims 1 for formation of a siliceous film, wherein the steps of (A) to (C) are repeated to form two or more covering films.

10. The method according to claim 1 for formation of a siliceous film, wherein said polysilazane composition contains perhydropolysilazane.

11. The method according to claim 1 , where the siliceous film contains nitrogen atoms in a concentration of 1×10 19 atoms/cm 3 or less.