JP2001122611A - Porous silica thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous silica thin film low in hygroscopicity and excellent in mechanical strength. SOLUTION: There is provided a porous silica thin film having high porosity of porous silica, a nanometer sized pore diameter, a specific quantity of Si-CH3 bond in the structure and properly suppressed in the movability of CH3 group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous silica thin film for an insulating thin film, and more particularly, to a porous silica thin film for an insulating thin film.
The present invention relates to a porous silica thin film having a low relative dielectric constant, being extremely excellent in adhesion and mechanical strength, and having a low hygroscopicity and a large thickness for an insulating thin film, and its use.

[0002]

2. Description of the Related Art Porous silica is widely used for structural materials, catalyst carriers, optical materials, etc. because of its excellent properties such as light weight and heat resistance. For example, in recent years, porous silica has been expected to be capable of lowering the dielectric constant. Conventionally, a dense silica film has been generally used as an insulating thin film material for a multilayer wiring structure of a semiconductor element such as an LSI. However, in recent years, the wiring density of LSIs has been steadily miniaturized, and accordingly, the distance between adjacent wirings on a substrate has been reduced. In this case, when the dielectric constant of the insulator is high, the capacitance between the wirings increases, and as a result, the delay of an electric signal transmitted through the wiring becomes significant, which is a problem. In order to solve such a problem, a material having a lower dielectric constant is strongly required as a material of the insulating film for the multilayer wiring structure. Here, since porous silica is a composite with air having a relative dielectric constant of 1, the relative dielectric constant can be significantly reduced from 4.0 to 4.5 of silica itself, and the density is high. It has attracted attention as an ideal insulating film material because it has the same processability and heat resistance as a simple silica film.

[0003] Typical examples of porous silica include silica xerogel and silica aerogel. These materials are produced by a sol-gel reaction. Here, the sol-gel reaction is a reaction in which a colloidal substance in which particles called a sol are dispersed in a liquid is changed into a solid gel as an intermediate. In the case of silica, for example, when an alkoxysilane compound is used as a raw material, a sol is obtained by dispersing particles of a crosslinked structure obtained by hydrolysis and condensation reaction in a solvent, and further, the particles undergo hydrolysis and condensation reactions. The state in which a solid network containing is formed is a gel. When the solvent is removed from the gel, a silica xerogel having a xerogel structure in which only a solid network remains can be produced.

As an example of the formation of a thin film of silica xerogel, as disclosed in JP-A-7-257918, a coating solution of a silica precursor, which is a sol, is once prepared, followed by spray coating, dip coating or spin coating. To form a thin film having a thickness of several microns or less. Then, the thin film is gelled into silica, and dried to obtain a silica xerogel. On the other hand, silica aerogel is different from silica xerogel in that the solvent in silica is removed in a supercritical state, but is similar to silica xerogel in that a coating solution of a silica precursor as a sol is prepared.

Further, as examples of the formation of a silica xerogel thin film, US Pat. No. 5,807,607 and US Pat. No. 5,900,879 disclose that when a silica precursor as a sol is used as a coating solution, A method is disclosed in which a specific solvent such as glycerol is contained to control the pore size and pore size distribution of the silica xerogel obtained through subsequent gelation and solvent removal, and to improve the mechanical strength of the porous body. ing. However, in this example, since a low-boiling solvent is used as the solvent, the solvent is rapidly removed when the hole is formed, and the wall portion surrounding the hole follows the capillary force generated there. No, as a result, the pores shrink. As a result, holes are crushed, micro cracks are generated around the holes,
If an external stress is applied here, this acts as a stress concentration point, and as a result, there is a problem that the silica xerogel does not exhibit sufficient mechanical strength. It is possible to make the removal rate of the solvent extremely slow, but in this case, there is a problem in productivity because it takes a lot of time to obtain silica xerogel.

As a means for improving the above-mentioned problems in the low boiling point solvent, for example, there is an attempt to use an organic polymer instead of the low boiling point solvent. Use of an organic polymer also has the advantage that it is not necessary to strictly control the solvent evaporation rate and atmosphere. For example, JP-A-4-285
No. 081 discloses that a sol-gel reaction of alkoxysilane is carried out in the presence of a specific organic polymer, a silica / organic polymer composite is once produced, and then the organic polymer is removed to obtain a porous material having a uniform pore size. A method for obtaining functional silica is disclosed. JP-A-5-85762 and WO 99/03926 also disclose a method of obtaining porous silica having a very low dielectric constant, uniform pores and pore distribution from a mixed system of an alkoxysilane and an organic polymer. A method for doing so is disclosed. Further, JP-A-10-25359 and JP-B-7-88239
Japanese Patent Application Laid-Open Publication No. H10-15064 discloses a method in which organic polymer fine particles are dispersed in an oligomer of a metal alkoxide containing an alkoxysilane to form a gel, and the organic polymer fine particles are subsequently calcined and removed to obtain porous silica having a controlled pore system. Have also been reported.

As a means of remedying the above-mentioned problems in low-boiling solvents, for example, an organic polymer may be used instead of the low-boiling solvent to reduce the capillary force by delaying the removal of the fluid around the pores as much as possible. There is an attempt. Use of an organic polymer also has the advantage that there is no need to strictly control the solvent volatilization rate and atmosphere.
For example, JP-A-4-285081 discloses that a sol-gel reaction of an alkoxysilane is carried out in the presence of a specific organic polymer, a silica / organic polymer composite is once produced, and then the organic polymer is removed. A method for obtaining a porous silica having a uniform pore size is disclosed. Japanese Patent Application Laid-Open No. 5-85762 and WO99 / 03936 also disclose from an alkoxysilane / organic polymer mixed system that a porous material having a very low dielectric constant, uniform pores and a good pore size distribution is obtained. A method is disclosed. Japanese Patent Application Laid-Open No. 9-315812 discloses an example in which a coating solution comprising silica fine particles and a specific alkoxysilane and a hydrolyzate thereof is used to improve properties such as adhesion and mechanical strength of an insulating thin film. Is disclosed. Further, Japanese Patent Application Laid-Open No. 10-25359 and
Japanese Patent Application Laid-Open No. 88239/88 discloses a porous body in which fine particles of an organic polymer are dispersed in an oligomer of a metal alkoxide containing an alkoxysilane to form a gel, and the fine particles of the organic polymer are calcined and removed to control the pore system. It has also been reported how to obtain

However, even in these methods, the adhesion and mechanical strength that are practically satisfactory have not yet been developed. Further, Japanese Patent Application Laid-Open No. 9-169845 discloses an attempt to improve the hardness and adhesion of a bulk silica film by controlling the amount of water and the reaction temperature in a sol-forming reaction using an organic trialkoxysilane as a raw material. There is. However, in this production method, only a high-density, that is, a silica body having a high dielectric constant can be obtained, and furthermore, there is no concept of controlling the pore size and pore size distribution. Is extremely difficult. Tokuhei 8
Japanese Patent No. 29952 discloses a method in which an organic polymer is added in a homogeneous system. However, since phase separation occurs in the system at the time of gelation, only submicron-order holes can be obtained in this case. Again, in this case, it is difficult to develop sufficient mechanical strength.

Attempts have been made to improve the mechanical strength and the like of a porous body by adding a metal oxide other than silica. JP-A-7-185306 discloses a method of obtaining an alcogel by hydrolyzing an alkoxysilane, a metal alkoxide other than silicon, and a halide, and then supercritically drying the formed alcogel to obtain an aerogel. Methods for improving strength are disclosed. But,
When such metal alkoxides and halides other than silica are used, the raw materials or / and the hydrolysis / condensates are poorly soluble during the sol-gel reaction, so that the inside of the system may have large particles. In some cases, a slurry may be formed or a precipitate may be formed. In any case, only a heterogeneous gel is obtained. As a result, it is not suitable for use as an insulating film for the same reason as when the organic polymer fine particles are added. As is clear from the above description,
An insulating thin film for a multilayer wiring structure used as a semiconductor element, which has a low dielectric constant, a high adhesion and a high mechanical strength, and a low hygroscopicity, has not been obtained. Furthermore, in the above-mentioned published documents, there is no description about a concept or a specific method regarding thickening of a thin film which is extremely important as a practical characteristic.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and has a low relative dielectric constant of a porous silica thin film, remarkably excellent adhesion and mechanical strength, and a film having low hygroscopicity. It is intended to provide a porous silica thin film for a thick insulating thin film and its use.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have made intensive studies and as a result, the porosity of the porous silica thin film is high, and the porosity of the porous silica thin film is nanometer size. There further structure has Si-CH ₃ bonds of a specific amount in and by movement of the CH ₃ group is moderately suppressed, low moisture absorption in a low dielectric constant, and significantly adhesion and mechanical strength The present inventors have found that an excellent porous insulating film material can be obtained, and that the film thickness can be increased by adjusting the composition of a coating solution for producing a thin film. Thus, the present invention has been completed. Accordingly, an object of the present invention is to provide an insulating film material having a low relative dielectric constant, excellent adhesion and mechanical strength, low moisture absorption, and a practically sufficient film thickness, and its use.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description. To facilitate understanding of the present invention, basic features and preferred embodiments of the present invention are listed. 1. A porous silica thin film having pores in a silica structure, having a porosity of 30 to 80%, a maximum pore diameter of 10 nm or less, and a relaxation time of 0.5 to 10 seconds in the structure.
A porous silica thin film containing at least 2% by weight of a CH ₃ group bonded to an i atom and having a thickness of 0.5 μm to 10 μm. 2. (1) The porosity of the porous silica thin film is 40 to 70%. 3. The porous silica thin film according to 1. 3. (1) The relaxation time of carbon in the CH ₃ group is 0.7 to 3 seconds. Or 2. Porous silica thin film. 4. (1) The film thickness is 0.5 μm to 5 μm. ~ 3. The porous silica thin film of any one of the above. 5. Including a plurality of insulating layers and wiring formed thereon, at least one of the insulating layers has the above-mentioned 1. ~ 4. A multilayer wiring structure characterized by comprising a porous silica thin film of the above. 6. 5. Semiconductor device including the multilayer wiring structure of the above.

Hereinafter, the present invention will be described in detail. The silica used in the present specification is silicon oxide (SiO ₂ ).
And those having a hydrocarbon or hydrogen atom on silicon and represented by the following structural formula. R ¹ _x H _y SiO _{(2- (x + y) / 2)} (wherein, R ¹ represents a linear, branched or cyclic alkyl group having 1 to 8 carbon atoms, or an aromatic group, and 0 ≦ x ≦ 2,
y is 0 or 1. The characteristics of the porous silica thin film obtained by the present invention are as follows.
80% porosity. The porosity at which the effect of the present invention is more remarkably exhibited is 40 to 70%. Although it depends on the chemical structure of silica, if the porosity is 30% or less, the relative dielectric constant becomes too high, and it is not suitable as an insulating thin film. Conversely, if the porosity exceeds 80%, the adhesion and mechanical strength will not reach practical levels.

In order to increase the mechanical strength and adhesion of the porous silica, it is important to control the pore size and pore size distribution peculiar to the porous body. Generally, when a large hole is present in a porous body, the portion becomes a defect point where stress concentrates, and high mechanical strength is not exhibited. In some cases, the generation of microcracks leads to the destruction of the structure itself, which is not preferable. There are various possible causes for the formation of such large pores, but the literature "Sol-Gel"
Science (CJ Brinker & GW.
Academic Press, 1 by Scherer
990), that, when the particle size of the particulate silica sol, which is a constituent unit of silica, is large, large pores are likely to be formed in gaps between the particles. On the other hand, in the case of the porous silica gel thin film of the present invention, only pores having a maximum pore diameter of 10 nm or less are present. However, since the sol particle diameter is small and uniform, close packing between sols is possible. It is thought that it became. In this case, since there is no place where stress concentrates, high mechanical strength is not impaired.

In order to increase the mechanical strength, as important as the control of the pore size, there is a structural reinforcement of the porous gel skeleton. In the porous silica thin film of the present invention, a Si-CH ₃ bond is introduced into the structure for the purpose of improving the hygroscopicity as described later, but the relaxation time of the methyl-based carbon determined from ¹³ C-NMR is determined. Is 0.5 to 10 seconds. More preferably, it is 0.7 to 3 seconds. When the relaxation time of the CH ₃ group falls within such a range, it indicates that the mobility of the porous silica of the present invention is appropriately suppressed, in other words, the silica skeleton structure is dense. For this reason, high mechanical strength is exhibited. If the relaxation time is 0.5 seconds or less, the skeletal strength against external stress is not sufficient, and high mechanical strength is not exhibited. On the other hand, when the relaxation time is 10 seconds or more, the porosity of the porous thin film is reduced to 30% which is the lower limit of the present invention.
Will be smaller than As another feature of the present invention,
CH ₃ derived from Si-CH ₃ bond in silica gel thin film
At least 2% by weight of the group. This significantly improves the hygroscopicity of the thin film. When the content of the methyl group is 2% by weight or less, the hygroscopicity is extremely deteriorated, which is not preferable.

Next, a method for producing a porous silica gel thin film according to the present invention will be described. Specific examples of alkoxysilanes that can be used in the present invention include:
having CH ₃ on the i atom, for example, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane And the like. Further, trimethylmethoxysilane,
Trimethylethoxysilane may be used. These alkoxysilanes are contained in the final product, porous silica gel,
It must be contained at least 2% by weight or more as the weight of the CH ₃ group of Si—CH ₃ . If the amount is less than 2% by weight, the hygroscopicity is significantly deteriorated. If the amount of CH ₃ groups exceeds 22% by weight, the mechanical strength may be impaired, which is not preferable.

In the present invention, preferred alkoxysilanes having a group other than a methyl group include tetramethoxysilane, tetraethoxysilane, tetra (n-propoxy)
Silane, tetra (i-propoxy) silane, tetra (n
-Butoxy) silane, tetra (t-butoxy) silane,
Trimethoxysilane, triethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, bis (trimethoxysilyl) methane, bis (triethoxysilyl) methane, 1,2-bis (tri Methoxysilyl) ethane, 1,2-bis (triethoxysilyl) ethane, 1,4-bis (trimethoxysilyl) benzene,
1,4-bis (triethoxysilyl) benzene and the like. Among these, particularly preferred are tetramethoxysilane, tetraethoxysilane, trimethoxysilane,
Triethoxysilane. A partially hydrolyzed product of alkoxysilanes may be used as a raw material.

Further, in order to modify the obtained porous silica thin film, it is also possible to mix an alkoxysilane having two or three hydrogens, alkyl groups or aryl groups on silicon atoms with the above-mentioned alkoxysilanes. It is. For example,
Examples include triethylmethoxysilane, triethylethoxysilane, tripropylmethoxysilane, triphenylmethoxysilane, triphenylethoxysilane, phenyldimethylmethoxysilane, phenyldimethylethoxysilane, diphenylmethylmethoxysilane, diphenylmethylethoxysilane, and the like. The amount to be mixed is adjusted to be 80 mol% or less of the total number of moles of the raw material alkoxysilanes. If it exceeds 80 mol%, gelation may not occur.

In the present invention, an organic polymer suitably used is an organic polymer having at least one polymerizable functional group in a molecule. The organic polymer is not particularly limited as long as it has at least one polymerizable functional group in a molecular chain. Specific examples thereof include polyether, polyester, polycarbonate, and the like.
Polyanhydride, polyamide, polyurethane, polyurea, polyacrylic acid, polyacrylate,
Polymethacrylic acid, polymethacrylic acid ester, polyacrylamide, polymethacrylamide, polyacrylonitrile, polymethacrylonitrile, polyolefin, polydiene, polyvinyl ether, polyvinyl ketone, polyvinyl amide, polyvinyl amine, polyvinyl ester, polyvinyl alcohol, polyvinyl halide , A polyhalide, a polystyrene, a polysiloxane, a polysulfide, a polysulfone, a polyimine, a polyimide, a cellulose, and a polymer having a derivative thereof as a main component. Copolymers of monomers that are constituent units of these polymers or copolymers with any other monomer may be used. One or more organic polymers may be used in combination.

Among the above-mentioned polymers, those preferably used are polyether, polyester, polycarbonate, polyanhydride, polyamide, polyurethane, polyurea, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylic ester,
Polyacrylamide, polymethacrylamide, polyvinylamide, polyvinylamine, polyvinylester, polyvinylalcohol, polyimine, and polyimide are main components. Further, when converted to porous silica by heating and calcination as described below, aliphatic polyether having a low thermal decomposition temperature, aliphatic polyester,
It is particularly preferable to use one containing aliphatic polycarbonate and aliphatic polyanhydride as main components.

Examples of the polymerizable functional group include a vinyl group, a vinylidene group, a vinylene group, a glycidyl group, an allyl group, an acrylate group, a methacrylate group, an acrylamide group,
Examples include a methacrylamide group, a carboxyl group, a hydroxyl group, an isocyanate group, an amino group, an imino group, and a halogen group. These functional groups may be in the main chain, at the terminal, or in the side chain of the polymer, may be directly bonded to the polymer chain, or may be bonded to the polymer chain via a spacer such as an alkylene group or an ether group. May be combined. The same polymer molecule may have one type of functional group, or may have two or more types of functional groups. Among the functional groups listed above, vinyl, vinylidene, vinylene, glycidyl, allyl, acrylate, methacrylate, acrylamide, and methacrylamide groups are preferably used.

Specific examples of the basic skeleton of the organic polymer that can be suitably used in the present invention are shown below. In addition,
In the following, alkylene is methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene,
Hexamethylene, isopropylidene, 1,2-dimethylethylene, 2,2-dimethyltrimethylene, alkyl refers to an alkyl group having 1 to 8 carbon atoms and a phenyl group,
Tolyl group, aryl group such as anisyl group, (meth) acrylate refers to both acrylate and methacrylate, dicarboxylic acid is oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, Refers to organic acids such as azelaic acid and sebacic acid.

Polyalkylene glycol (meth) acrylate, polyalkylene glycol di (meth) acrylate, polyalkylene glycol alkyl ether (meth) acrylate, polyalkylene glycol vinyl ether, polyalkylene glycol divinyl ether, polyalkylene glycol alkyl ether vinyl ether, polyalkylene Glycol glycidyl ether, polyalkylene glycol diglycidyl ether,
An aliphatic polyether having a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, or a glycidyl group at a terminal, such as a polyalkylene glycol alkyl ether glycidyl ether.

Polycaprolactone (meth) acrylate, polycaprolactone vinyl ether, polycaprolactone glycidyl ether, polycaprolactone vinyl ester, polycaprolactone glycidyl ester,
Represented by polycaprolactone vinyl ester (meth) acrylate, polycaprolactone glycidyl ester (meth) acrylate, polycaprolactone vinyl ester vinyl ether, polycaprolactone glycidyl ester vinyl ether, polycaprolactone vinyl ester glycidyl ether, polycaprolactone glycidyl ester glycidyl ether, and the like. Polycaprolactone having a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, and a glycidyl group at one or both terminals.

(Meth) acrylate, di (meth) acrylate, tri (meth) acrylate, vinyl ether, divinyl ether, trivinyl ether, glycidyl ether, diglycidyl ether, triglycidyl ether of polycaprolactone triol. An aliphatic polyester which is a polymer of a dicarboxylic acid and an alkylene glycol and has a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, or a glycidyl group at one or both terminals. An aliphatic polyalkylene carbonate having a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, or a glycidyl group at one or both terminals.

A polymer of a dicarboxylic anhydride,
Acrylate group, methacrylate group, vinyl group,
Aliphatic polyanhydride having a polymerizable functional group such as glycidyl group. Polyacrylic esters and polymethacrylic esters having a functional group such as a vinyl group, a glycidyl group, or an allyl group in a side chain, such as polyglycidyl (meth) acrylate, polyallyl (meth) acrylate, and polyvinyl (meth) acrylate; Polyvinyl cinnamate, polyvinyl azidobenzal, epoxy resin, etc. Among these, the aliphatic polyethers, aliphatic polyesters, aliphatic polycarbonates, aliphatic polycarbonates, and the like, which are easily converted to porous silicon oxide by heating and firing as described below, are particularly preferable. Used for

The molecular weight of the organic polymer is from 100 to 100
Preferably, it is one million. It should be noted here that the pore size of the porous silica thin film is extremely small and uniform without depending much on the molecular weight of the organic polymer. This is extremely important for achieving high mechanical strength. The amount of the organic polymer added in the present invention is 10 ⁻² to 10 based on 1 part by weight of the alkoxysilane.
0 parts by weight, preferably 10 ^-1 to 10 parts by weight, more preferably 10 ^{-1 to} 5 parts by weight. If the amount of the organic polymer is less than 10 ^-2 parts by weight or more than 100 parts by weight, the properties of the porous body do not appear and the practicability is poor.

In the present invention, water is required for the hydrolysis of alkoxysilanes. Water is generally added to the alkoxysilane in a liquid state or as an alcohol or an aqueous solution, but may be added in the form of water vapor. If water is added rapidly, hydrolysis and condensation may be too fast depending on the type of alkoxysilane to cause precipitation, so take sufficient time for adding water and use a solvent such as alcohol for homogenization. Are used alone or in combination. In the present invention, a substance that functions as a catalyst for accelerating the hydrolysis and dehydration condensation reaction of alkoxysilane may be added. Specific examples of the substance that can function as a catalyst include hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid,
Acids such as oxalic acid and maleic acid are preferred.

The addition amount of these catalysts is 1 mol or less, preferably 10 ^-1 mol or less, per 1 mol of alkoxysilane. If it is more than 1 mol, a precipitate may be formed, and a uniform porous body may not be obtained. In the present invention,
The thin film is formed by applying the mixture obtained by the above method on a substrate. The film can be formed by a well-known method such as casting, immersion, or spin coating, but spin coating is suitable for use in manufacturing an insulating layer for a multilayer wiring structure of a semiconductor element. The thickness of the thin film can be adjusted by changing the viscosity and rotation speed of the composition.
It can be controlled in the range of 0.1 μm to 10 μm. If the thickness is more than 10 μm, cracks may occur. As an insulating layer for a multilayer wiring structure of a semiconductor element, usually 0.5 μm
It is used in the range of ５5 μm.

In the production of the porous silica thin film of the present invention, the presence of a solvent is not indispensable. However, as long as it dissolves both the alkoxysilanes and the organic polymer, it is referred to as the thick porous body of the present invention. It can be used to the extent that the characteristics are not impaired by dilution of the entire solution by the addition of solvent. Examples of the solvent used include monohydric alcohols having 1 to 4 carbon atoms, dihydric alcohols having 1 to 4 carbon atoms, ketones such as acetone and methyl ethyl ketone, glycerin and the like, and ethers or esters thereof, for example, diethylene glycol, ethylene. Glycol monomethyl ether, ethylene glycol dimethyl ether, 2-ethoxyethanol, propylene glycol, monomethyl ether, propylene glycol methyl ether acetate or formamide,
N-methylformamide, N-ethylformamide,
N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylpyrrolidone, N-formylmorpholine, N- Amides such as acetylmorpholine, N-formylpiperidine, N-acetylpiperidine, N-formylpyrrolidine, N-acetylpyrrolidine, N, N'-diformylpiperazine, N, N'-diacetylpiperazine, and γ-butyrolactone Lactones,
Ureas such as tetramethylurea and N, N'-dimethylimidazolidinone. These alone,
Alternatively, they may be used as a mixture. Among them, acetone, methyl ethyl ketone, a monohydric alcohol having 1 to 4 carbon atoms, and the like are preferable as a solvent which evaporates immediately after spin coating and is preferable in terms of increasing the film thickness. Other, if desired
For example, a photocatalyst generator for imparting photosensitivity, an adhesion improver for increasing the adhesion to the substrate, and an optional additive such as a stabilizer for long-term storage, the present invention may be used within a range not to impair the purpose of the present invention. Can be added to the composition.

As the substrate, a semiconductor substrate of silicon, germanium or the like, a compound semiconductor substrate of gallium-arsenic, indium-antimony, or the like can be used, or a thin film of another substance can be formed on these surfaces before use. Is also possible. In this case, as the thin film, aluminum,
In addition to metals such as titanium, chromium, nickel, copper, silver, tantalum, tungsten, osmium, platinum, and gold, silicon dioxide, fluorinated glass, phosphorus glass, boron-phosphorus glass, borosilicate glass, polycrystalline silicon, and alumina , Titania, zirconia, silicon nitride, titanium nitride, tantalum nitride, boron nitride, inorganic compounds such as silsesquioxane hydride, methyl silsesquioxane, amorphous carbon, fluorinated amorphous carbon, polyimide, and any other organic polymer A thin film can be used.

The coating solution obtained as described above is formed into a thin film, and the silica sol in the obtained thin film is reduced to 50 to 30.
By gelling at 0 ° C., a silica / organic polymer composite (hybrid) thin film can be obtained.
A more preferred gelling temperature range is 60 to 200 ° C.
By performing gelation in this temperature range, gelation proceeds sufficiently. If the temperature is lower than 50 ° C., gelation does not proceed sufficiently, so that shrinkage occurs, the strength of the structure is insufficient, and no mechanical strength is obtained. In addition, seepage of the organic polymer may occur. If the temperature is higher than 300 ° C., unnecessary voids may be generated in the hybrid body, which is not preferable.

The role of the organic polymer in forming the hybrid obtained in the present invention is important. I mean,
Even when the organic polymer transitions from a sol to a gel at 50 to 300 ° C., it substantially remains in the reaction system, so that the sol particles may become a gel while maintaining their size and shape in a swollen state. When the organic polymer is removed from the hybrid body in a subsequent step to form a porous body, the porosity of the porous body can be sufficiently increased. further,
Since the polymer has at least one or more polymerizable functional groups in the molecule, the polymer is grafted or IPN (three-dimensional network structure) in the sol, resulting in a moderate entanglement between the sol and the polymer. . This entanglement densifies the structure of the hybrid, and this state is maintained in the gel, so that the silica skeleton after the organic polymer is removed is densified.

The porous silica thin film in the present invention can be obtained by applying heat of 300 to 500 ° C. to the hybrid thin film to remove only the organic spacer by heating. Depending on the type of organic polymer, there are those that are simply removed by evaporation and those that are calcined and removed with polymer decomposition,
Although the removal temperature varies, a more preferred temperature is 300-450.
° C. If the temperature is lower than 300 ° C., the removal of the organic spacer is insufficient, and the impurities of the organic substance remain, so that there is a risk that a porous silica thin film having a low dielectric constant cannot be obtained. Conversely 500
Although it is preferable to perform the treatment at a temperature higher than ° C. from the viewpoint of strength development, it is impossible to use this temperature in the LSI manufacturing process. The heating time is preferably in the range of 1 minute to 24 hours. If the time is less than 1 minute, the evaporation and decomposition of the polymer do not proceed sufficiently, so that an organic substance remains as an impurity in the obtained porous silica thin film, and the characteristics are deteriorated. Further, since pyrolysis and transpiration are usually completed within 24 hours, firing for a longer time does not make much sense.

The removal of the organic polymer may be carried out in an inert atmosphere such as nitrogen, argon or helium, or in an oxidizing atmosphere such as in air or by mixing oxygen gas. Generally, the use of an oxidizing atmosphere tends to reduce the removal temperature and time. Also, if ammonia, hydrogen, etc. are present in the atmosphere, the silanol groups remaining in the silica will simultaneously react and be hydrogenated or nitrided, reducing the hygroscopicity of the porous silica thin film and increasing the dielectric constant. Can also be suppressed.

When the obtained porous silica thin film is treated with a silylating agent, the water absorption is suppressed, the dielectric constant can be stabilized, and the adhesion to other substances can be improved. Examples of silylating agents that can be used include trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethylethoxysilane, methyldiethoxysilane, dimethylvinyl Alkoxysilanes such as methoxysilane, dimethylvinylethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, methyldichlorosilane,
Dimethylchlorosilane, dimethylvinylchlorosilane,
Methylvinyldichlorosilane, methylchlorodisilane,
Chlorosilanes such as triphenylchlorosilane, methyldiphenylchlorosilane and diphenyldichlorosilane, hexamethyldisilazane, N, N'-bis (trimethylsilyl) urea, N-trimethylsilylacetamide, dimethyltrimethylsilylamine, diethyltriethylsilylamine, and trimethylsilylimidazole; Silazane and the like. The silylation method is performed by a method such as coating, dipping, and steam exposure.

The porous silica thin film obtained by the above method has a large porosity, a small and uniform pore size, and a strong silica skeleton. Therefore, the adhesion and the mechanical strength are extremely low. Since it is high, exhibits low moisture absorption, and can be made thicker, it is most suitable for an LSI multilayer wiring substrate or an insulating film of a semiconductor element. As an example, the film thickness is 1.0 μm, the porosity is 51%, the dielectric constant is 2.0, the average pore size is 2.4 nm, there is substantially no pore of 10 nm or more, and the tensile strength is 40 MPa (adhesion force). Is 40MPa
As described above, a practically excellent porous silica insulating thin film was obtained. The relative dielectric constant after exposure to an atmosphere having a relative humidity of 100% for 24 hours was 2.05, and hardly changed. The porous silica thin film obtained by the present invention is a bulk porous silica body other than a thin film, such as an optical film or a catalyst carrier as well as a heat insulating material, an absorbent, a column filler, a caking inhibitor, a thickener, a pigment, It can also be used as an opacifier, ceramic, smoke suppressant, abrasive, dentifrice and the like.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
The scope of the present invention is not limited by these. The evaluation of the porous silica thin film was performed using the following apparatus. (1) Porosity, average pore size, pore size distribution: A thin film on a silicon wafer was scraped off and measured using a nitrogen adsorption porosimeter (Autosorb 1 manufactured by Quantachrome). The porosity was determined by comparison with the density of a previously prepared bulk body. The maximum pore diameter used was a pore diameter having a V / r value of 10 ^-3 or less. (2) Relative permittivity: After forming a porous film on a silicon wafer having TiN formed on its surface, a SUS
Aluminum was vapor-deposited through a (stainless steel) mask to form an electrode having a diameter of 1.7 mm, and the relative dielectric constant (k) at 1 MHz was determined using an impedance analyzer.

[0039] (3) CH ₃ content rate: Calculation of the content of CH ₃ were mixed with a known amount of powder scraped from the silicon wafer, a NaHCO ₃ was added at a constant weight ratio to this,
The mixture was subjected to solid-state ¹ H-NMR measurement and determined from each signal area. ¹ H-NMR measurements were performed with magic angle rotation (10000 Hz), pulse width of 5 (μsec), delay time of 10 (sec), and 100 integrations. (4) Relaxation time (T1ρC) of CH ₃ group carbon: T1ρC
Was calculated by nuclear magnetic resonance analysis (MSL400, manufactured by Bruker) of a powder scraped from a silicon wafer. Measurements of T1ρC is ¹ H- ¹³ C cross polarization (CP), magic-angle spinning (5000H
z), ¹ H irradiation decoupling method was used in combination. Delay time 4
s, the contact time was 1 ms, the spin lock time was variously changed, and each was performed 200 times, and T1ρC was determined from the obtained signal intensity.

(5) Mechanical strength (adhesiveness, tensile strength): The adhesiveness and tensile strength of the film were measured by sputtering titanium on a film on a silicon wafer to a thickness of 10 nm, and tacking the titanium film with an epoxy resin. Were adhered to prepare five materials, and evaluated as an average value of the five materials by a tensile tester. The measurement temperature is 25 ° C. (6) Hygroscopicity: Judgment was made based on the difference in relative dielectric constant before and after exposure to an atmosphere having a relative humidity of 100% for 24 hours.

[0041]

Example 1 1.2 g of tetraethoxysilane (5.8 m
mol), 6.3 g of methyltrimethoxysilane (46.
2 mmol) and 5.2 g of polyethylene glycol monomethacrylate (molecular weight 400) were added to 8.0 parts of methanol.
g, 3.0 g of γ-butyrolactone and 2.0 g of propylene glycol methyl ether acetate were dissolved in the mixed solvent, and 2.5 g of water and 1.5 g of 0.1 N sulfuric acid were added to the solution, followed by stirring at room temperature for 2 hours. After adding 0.01 g of dicumyl peroxide to 3 g of this solution, a silicon nitride thin film was spin-coated at 1300 rpm for 10 seconds on a 6-inch silicon wafer previously formed by a chemical vapor deposition method. . Next, on a hot plate, in the atmosphere 120
After heating for 3 minutes at 200 ° C for 1 hour at 200 ° C under a nitrogen atmosphere,
Then, heat treatment was performed in a curing furnace at 450 ° C. for 1 hour to obtain a porous silica thin film having a thickness of 1 μm.

The porosity of the obtained porous silica thin film determined by nitrogen adsorption was 51%, and the average pore diameter was 2.4.
It was found that pores with a diameter of 10 nm or more were practically absent. The dielectric constant at 1MHz of the porous film formed on the TiN film in the same manner is 2.0, SiO ₂
Was significantly lower than the dielectric constant of 4.5. The relative dielectric constant after exposure to an atmosphere having a relative humidity of 100% for 24 hours was 2.05, and hardly changed. The CH ₃ group concentration in the silica thin film was 19.7% by weight, the relaxation time of CH ₃ carbon was 1.5 seconds, and it was found that the silica skeleton was sufficiently strong. Further, the adhesiveness and tensile strength of the obtained thin film are 40 MPa (since the fracture is a cohesive failure of the material, the adhesive force can be determined to be 40 MPa or more). This porous silica thin film has a preferable thickness as a semiconductor interlayer insulating film material, It has dielectric constant, pore size, pore distribution, high mechanical strength and low hygroscopicity.

[0043]

Example 2 A coating solution was prepared in the same manner as in Example 1 except that 4.8 g (23.0 mmol) of tetraethoxysilane and 4.2 g (30.8 mmol) of methyltrimethoxysilane were used. A 1 μm porous silica thin film was obtained. The relative dielectric constant of the porous film formed on the TiN film was 2.2, and the relative dielectric constant after exposure to an atmosphere having a relative humidity of 100% for 24 hours was 2.25. The average pore size of the thin film obtained by coating on a silicon wafer is 3.1 n.
There were no pores larger than 10 nm in m. CH in thin film
_{3 The} content is 11.5% by weight, the relaxation time of CH ₃ carbon is 2.5 seconds, and the silica skeleton is sufficiently strong. Furthermore, the tensile strength is 45MPa (adhesion strength is 45M
Pa or more). Therefore, the obtained porous silica thin film has preferable characteristics as a semiconductor interlayer insulating film material.

[0044]

Example 3 In Example 1, the organic polymer was changed to polyethylene glycol dimethacrylate (molecular weight: 400).
With the same method except that the weight is 5.2 g, the thickness is 0.95 μm.
Was obtained. The relative dielectric constant of the porous film formed on the TiN film was 1.9, and the relative dielectric constant after exposure to an atmosphere having a relative humidity of 100% for 24 hours was 1.95.
The thin film obtained by coating on a silicon wafer had an average pore diameter of 2.5 nm and no pores of 10 nm or more were present. The content of CH ₃ in the thin film was 20.3% by weight, the relaxation time of CH ₃ carbon was 1.1 seconds, and the skeleton strength of silica was:
It is satisfactory in exhibiting high mechanical strength. Further, the tensile strength was 41 MPa (adhesion force was 41 MPa or more). Therefore, the obtained porous silica thin film has a preferable film thickness, dielectric constant, pore size, pore size distribution, and excellent mechanical strength as a semiconductor interlayer insulating film material.

[0045]

Comparative Example 1 In Example 1, 12.0 g (57.6 mmol) of alkoxysilane was added to tetraethoxysilane and polyethylene glycol monomethacrylate (molecular weight: 4).
00) A 1.1 μm-thick silica thin film was obtained in the same manner as in Example 1 except that the amount was changed to 10.4 g. The obtained silica thin film has a dielectric constant of 2.0 and a tensile strength of 43 MPa.
(The adhesion was 43 MPa or more), but the relative dielectric constant after a lapse of 24 hours was 3.5, which is inappropriate for a semiconductor interlayer insulating film material.

[0046]

Comparative Example 2 The organic polymer in Example 1 was changed to polypropylene glycol dimethyl ether (molecular weight: 500).
A silica thin film having a thickness of 0.98 μm was obtained in the same manner as in Example 1 except that the amount was changed to 5.2 g. CH ₃ content is 2
At 2.1% by weight, the relaxation time was 0.41 seconds. The adhesion is 15 MPa (the tensile strength is 15 MPa or more), which is not satisfactory as a semiconductor interlayer insulating film material.

[0047]

Comparative Example 3 12.0 g of tetraethoxysilane (58 m
mol), 6.8 g of polyethylene glycol monomethacrylate (average molecular weight 360) and 3.4 g of polyethylene glycol dimethacrylate (average molecular weight 540).
-Methylpyrrolidone was dissolved in a mixed solvent of 20.0 g and propylene glycol methyl ether acetate 10.0 g, and 7.5 g of water and 1.5 g of 0.1 N nitric acid were added to this solution, followed by stirring at room temperature for 2 hours. To this solution was added 0.5 g of dicumyl peroxide, spin-coated on a silicon wafer at a speed of 1500 revolutions per minute, and heated at 120 ° C. for 1 hour and at 180 ° C. for 1 hour to obtain a thickness of 0.1 μm. A 41 μm composite thin film was obtained. This sample was placed at 450 ° C under a nitrogen atmosphere.
For 1 hour to burn off the organic polymer and obtain a porous silica thin film. In this case, only a very thin film having a thickness of 0.23 μm was obtained. Further, the relative dielectric constant before and after the elapse of 24 hours greatly changed from 2.3 to 4.2.

[0048]

The porous silica thin film obtained by the present invention has a large porosity, a small and uniform pore size, and a strong silica skeleton. Since it is extremely high and can be made thicker with low moisture absorption, it is most suitable for an LSI multilayer wiring substrate or an insulating film of a semiconductor element.

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Claims (6)

[Claims] 1. A porous silica thin film having pores in a silica structure, having a porosity of 30 to 80% and a maximum pore diameter of 1
0 nm or less, and the relaxation time in the structure is 0.5 seconds to 10 seconds.
A porous silica thin film containing at least 2% by weight of a CH ₃ group bonded to a Si atom, and having a thickness of 0.1 μm to 10 μm. 2. The porosity of the porous silica thin film is 40 to 70.
% Of the porous silica thin film according to claim 1. _3. The carbon of the CH ₃ group has a relaxation time of 0.7 to ₃ times.
3. The porous silica thin film according to claim 1, wherein the time is seconds. 4. The porous silica thin film according to claim 1, wherein the thickness of the porous silica thin film is 0.5 μm to 5 μm. 5. The method according to claim 1, further comprising a plurality of insulating layers and a wiring formed thereon, wherein at least one of the insulating layers is formed.
5. A multilayer wiring structure comprising the porous silica thin film according to any one of 4. 6. A semiconductor device comprising the multilayer wiring structure according to claim 5.