Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-10-04
2004-09-07
Moore, Margaret G. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C428S447000, C524S379000, C524S389000, C528S025000, C528S481000, C106S287130, C106S287160
Reexamination Certificate
active
06787191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating composition for use in producing an insulating thin film. More particularly, the present invention is concerned with a coating composition for use in producing an insulating thin film, which comprises a silica precursor, an organic polymer, water, an alcohol and optionally an organic solvent, wherein the amounts of the water and the alcohol are in specific ranges. The present invention is also concerned with a silica/organic polymer composite thin film produced from the coating composition; a porous silica thin film obtained by removing the organic polymer from the silica/organic polymer composite thin film; a multilevel interconnect in which the porous silica thin film is used as an insulating layer; and a semiconductor device comprising the multilevel interconnect. Further, the present invention is also concerned with methods for producing the thin films.
The silica/organic polymer composite thin film and porous silica thin film of the present invention not only have an improved mechanical strength, and have insulating properties and low dielectric constant, but also exhibit excellent surface smoothness. Therefore, the silica/organic polymer composite thin film and porous silica thin film of the present invention can be advantageously used for producing an excellent multilevel interconnect, an excellent semiconductor device and the like.
2. Prior Art
Conventionally, as a material for an insulating thin film for a multilevel interconnect for a semiconductor device (such as an LSI), a high density silica material having excellent processability and heat resistance has generally been used.
In recent years, the density of the circuit of a semiconductor device (such as an LSI) has become higher and, hence, the distance between mutually adjacent conducting lines in the circuit has become extremely small. Due to this high density circuit, the mutually adjacent conducting lines having insulators therebetween function as a capacitor. This poses a problem that, when the dielectric constant of the insulator is high, the electrostatic capacity of the capacitor formed by the mutually adjacent conducting lines and the insulators present therebetween becomes high, so that the transmission of the electric signals through each of the mutually adjacent conducting lines is markedly delayed. In view of this, as a material for an insulating thin film for a multilevel interconnect, it is desired to use a material having a lower dielectric constant.
As such a material having a lower dielectric constant, a porous silica has drawn attention for the following reason. A porous silica is a composite of silica with air having a dielectric constant of 1, so that a porous silica has not only a dielectric constant which is much lower than that of a silica (from 4.0 to 4.5), but also processability and heat resistance which are comparable to those of a high density silica material. Therefore, a porous silica has drawn attention as a material for an insulating thin film.
Representative examples of porous silica materials include a silica xerogel and a silica aerogel. These porous silica materials are produced by a sol-gel reaction in which a sol (i.e., a colloid-like dispersion of particles in a liquid) is formed as an intermediate and then transformed into a gel in a solid form.
An explanation on a sol-gel reaction is made below, taking as an example a case where the sol-gel reaction is performed using an alkoxysilane compound as a raw material to thereby produce a gel. In this case, an alkoxysilane compound is subjected to hydrolysis and dehydration-condensation reactions in a solvent to obtain a dispersion of particles (having a crosslinked structure) in the solvent. This dispersion is a sol. The crosslinked particles undergo further hydrolysis and dehydration-condensation reactions in the solvent to form a solid network structure containing the solvent. This solid network structure is a gel. When the solvent is removed from the gel without bringing the solvent into a supercritical state, a silica xerogel is obtained. On the other hand, when the solvent is removed from the gel while bringing the solvent into a supercritical state, a silica aerogel is obtained.
Since, as mentioned above, a silica aerogel is obtained by removing the solvent from the gel while bringing the solvent into a supercritical state, the production of a silica aerogel requires not only a prolonged period of time but also extremely complicated steps of operations using specially designed apparatuses, so that it is practically impossible to introduce a production process for an insulating layer containing a silica aerogel thin film into the current process for producing a semiconductor device.
With respect to silica xerogel thin films, methods for the formation thereof are disclosed in several patent documents. For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 7-257918 describes a method which comprises preparing a coating material comprising a sol of a silica precursor, coating the coating material on a substrate by spray coating, immersion coating or spin coating to form a thin film having a thickness of several microns or less on the substrate, subjecting the thin film to gelation to obtain a silica thin film, and drying the silica thin film to obtain a silica xerogel thin film.
U.S. Pat. Nos. 5,807,607 and 5,900,879 also disclose methods for forming silica xerogel thin films. In each of the methods of these patent documents, it is attempted to obtain a silica xerogel having an improved mechanical strength by a method in which a specific solvent, such as glycerol, is used in the preparation of a silica precursor sol so as to appropriately control the pore size and pore size distribution of a silica xerogel which is obtained by effecting gelation of the silica precursor sol and subsequent removal of the solvent. However, each method has the following disadvantages. In each of the methods, as a solvent, a low-boiling-point solvent is used. Therefore, rapid removal of the solvent is likely to occur during the formation of pores in the silica xerogel and, hence, wall portions surrounding the formed pores cannot stand the capillary power generated by the rapid removal of the solvent, thereby causing contraction of the pores. As a result, breakage of the pores and microcracking around the pores occur. Therefore, when an outer stress is exerted on the pores, the action of the stress is concentrated on the pores. Accordingly, the mechanical strength of the silica xerogel becomes unsatisfactory.
In the above-mentioned method, it is possible to extremely lower the rate of the removal of the solvent. However, when the rate of the removal of the solvent is extremely lowered, a very long period of time is necessary for obtaining a silica xerogel, thereby leading to a lowering of the productivity.
In view of this, for producing a silica xerogel thin film, it is attempted to use an organic polymer instead of a low-boiling-point solvent. The use of an organic polymer for producing a silica xerogel thin film is advantageous not only in that the silica xerogel thin film obtained has an improved mechanical strength, but also in that there is no need to strictly control the solvent removal rate (i.e., the solvent volatilization rate) or the atmosphere employed.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 4-285081 discloses a method comprising subjecting an alkoxysilane compound to a sol-gel reaction in the presence of a specific organic polymer to produce a silica/organic polymer composite, followed by removal of the organic polymer, to thereby obtain a porous silica thin film having a uniform pore diameter.
On the other hand, in an attempt to obtain a porous silica thin film having an extremely low dielectric constant, uniform pores and a good pore size distribution, each of Unexamined Japanese Patent Application Laid-Open Specification No. Hei 5-85762 and WO99/03926 discloses a met
Araki Toru
Hanahata Hiroyuki
Nakamura Mikihiko
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Moore Margaret G.
Zimmer Mark S.
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