JP2001118841A - Porous silica - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin porous silica film having a superior mechanical strength. SOLUTION: A thin porous silica film is composed of porous silica having high porosity, contains pores having nanometer-size diameters, and contains a specific amount of residual organic polymer or its modified product in its structure.

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 for an insulating thin film, which has uniform pores of low-density porous silica, and is remarkably excellent in adhesion and mechanical strength, 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,
If 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 an insulating film for a 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 sol are dispersed in a liquid is converted 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 as a sol is once prepared,
Subsequently, it is applied on the substrate 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.

[0006] It is possible to make the removal rate of the solvent extremely slow, but in this case, a large amount of time is required to obtain the silica xerogel, which causes a problem in productivity. As a means for improving the problems in the low-boiling solvent as described above, for example, an attempt has been made to reduce the capillary force by using an organic polymer instead of the low-boiling solvent to delay the removal of the fluid around the pores as much as possible. is there. 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 to produce a silica gel / organic polymer composite, and thereafter the organic polymer is removed. Thus, a method for obtaining porous silica having a uniform pore size is disclosed. JP-A-5-85762 and WO99 /
03926 publication pamphlet also contains alkoxysilane /
There is disclosed a method for obtaining a porous body having a very low dielectric constant, uniform pores, and good pore size distribution from an organic polymer mixed system. 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. It has been disclosed. Further, JP-A-10-25359 and JP-B-7-88239 disclose that organic polymer fine particles are dispersed in an oligomer of a metal alkoxide containing alkoxysilane to form a gel, and then the organic polymer fine particles are dispersed. A method of obtaining a porous body having a controlled pore system by removing it by firing has also been reported.

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 apparent from the above description, an insulating thin film having a low dielectric constant, a high adhesion and a high mechanical strength for a multilayer wiring structure of a semiconductor element has not been obtained.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, in which the porous silica gel thin film has a low dielectric constant, the maximum pore diameter of the pores is 50 nm or less, and the adhesion and mechanical strength are small. The present invention provides a porous silica thin film for an insulating thin film, which is remarkably excellent in performance.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, in a porous silica thin film having a specific porosity, the pore size was reduced to nanometer size. Having a specific amount of an organic polymer having a specific chemical structure and / or a modified organic substance derived from the polymer to such an extent that the relative permittivity is not impaired in the structure. The inventors have found that an insulating film material having extremely excellent strength can be obtained, and have completed the present invention. Therefore, the purpose of the present invention is to
% Porosity, low dielectric constant, maximum pore size of 50 nm or less, narrow pore distribution, remarkably excellent adhesion and mechanical strength, 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 obtained by removing an organic polymer from a complex of silica and an organic polymer obtained by a hydrolysis / condensation reaction of alkoxysilanes, wherein a residue derived from the organic polymer in the gel is 3 to 15%. A porous silica thin film having a porosity of 30 to 80% and a maximum pore diameter of 50 nm or less. 2. (1) The porosity is 40 to 70%. Porous silica thin film. 3. (1) The film thickness is 10 μm or less. Or 2. Porous silica thin film. 4. Including a plurality of insulating layers and wiring formed thereon, at least one of the insulating layers has the above-mentioned 1. ~ 3. A multilayer wiring structure characterized by comprising a porous silica thin film of the above. 5. 4. A semiconductor device comprising the multilayer wiring structure according to the above.

Hereinafter, the present invention will be described in detail. The silica used in the present specification refers to a silicon oxide (Si
In addition to O ₂ ), those represented by the following structural formula having a hydrocarbon or hydrogen atom on silicon are included. 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 aryl group, and 0 ≦ x ≦ 2,
y represents 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 becomes more remarkable 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. In general, when a large hole exists in a porous body, the portion functions as a defect point where stress concentrates, and thus high mechanical strength is not exhibited. In some cases, the formation 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.However, when sols having large particle diameters are aggregated and gelled, or when sols having different particle diameters are aggregated and gelated, the sol is formed. The gaps between the particles tend to be large pores. On the other hand, in the case of the porous silica gel thin film of the present invention, the sol particle size is small and uniform, so that close-packing is possible, and only a pore having a maximum pore size of 50 nm or less exists in the porous body. do not do. Therefore, since the stress is structurally dispersed, the high mechanical strength is hardly impaired. As important as the control of the pore size in increasing the mechanical strength, there is a structural enhancement of the porous gel skeleton. The literature "Sol-Gel Science (C.J.
Brinker & G. W. By Scherer, Ac
Ademic Press, published in 1990) "states that the skeletal strength of silica gel is greatly affected by the bond strength between sol particles, which are constituent units of the gel.

In the porous silica thin film of the present invention, the content of the organic polymer in the structure is 3 to 15% by weight, and high adhesion and high mechanical strength are achieved without impairing the whole dielectric constant. . It is not clear why the high mechanical strength is exhibited, but the bond between the silica sol particles is formed by a direct chemical bond between the silica end group and the polymer, or by a hydrogen bond between the two, or by physical entanglement. It is presumed that they have been reinforced by Ai. This effect is achieved by using a polymer with a specific chemical structure.
It is not damaged even under a high temperature of 300 to 500 ° C. as described later. 3% by weight of polymer in thin film
If it is below, the above reinforcing effect is not exhibited. Conversely 15
If the content is more than 10% by weight, the dielectric constant becomes high, so that it is not suitable as an insulating thin film. The characteristics of the porous silica thin film of the present invention will be described in detail in the section of Examples. As an example, polyethylene glycol monomethacrylate having a molecular weight of 500 and having a methacrylate group at one end is used as an organic polymer.
The porous silica thin film having a thickness of 1 μm obtained by removing most of the polymer at 0 ° C. has a porosity of 53% and a relative dielectric constant of 2.
1. The maximum pore size is 2.9 nm, and the amount of remaining polymer is 5.2.
% By weight. Furthermore, its tensile strength is 50MPa
(The adhesion was 50 MPa or more).

Next, specific examples of the method for producing a porous silica thin film according to the present invention will be described. First, specific examples of the alkoxysilane that can be used in the present invention include tetramethoxysilane, tetraethoxysilane, tetra (n-
(Propoxy) silane, tetra (i-propoxy) silane, tetra (n-butoxy) silane, tetra (t-butoxy) silane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane , Phenyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, bis (trimethoxysilyl) methane, bis (triethoxysilyl) methane, 1,2-bis (trimethoxysilyl) Ethane, 1,2-bis (triethoxysilyl) ethane, 1,4-bis (trimethoxysilyl) benzene, 1,4-bis (triethoxysilyl)
Benzene and the like can be mentioned. Of these, particularly preferred are tetramethoxysilane, tetraethoxysilane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane. A partially hydrolyzed product of alkoxysilanes may be used as a raw material.
These may be used alone or in combination of two or more.

Further, in order to modify the obtained hybrid thin film or porous silica thin film, two to two
It is also possible to mix alkoxysilanes having three hydrogens, alkyl groups or aryl groups with the above alkoxysilanes. For example, trimethylmethoxysilane, trimethylethoxysilane, triphenylmethoxysilane, triphenylethoxysilane, phenyldimethylmethoxysilane, phenyldimethylethoxysilane, diphenylmethylmethoxysilane, diphenylmethylethoxysilane and the like can be mentioned. The mixing amount is set 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.

The organic polymer contained in the composition according to the present invention has a moderately good compatibility with the silica sol, can swell the gel, and can be appropriately decomposed and removed or volatilized by heating as described later. Polymers that are easily removed are preferred. Examples of the polymer corresponding to this include an aliphatic polymer having at least one polymerization functional group in a molecule and an aliphatic polymer having a hydroxyl group at a terminal group. A more preferred example of the polymer whose degree of removal by heating is appropriately controlled is an aliphatic polymer having at least one polymerizable functional group in the polymer molecule. In this polymer, a three-dimensional network structure and / or a graft structure are formed in silica, and physical entanglement with silica is strengthened.
Or it becomes difficult to remove by heating due to a chemical bond or a hydrogen bond with the silica terminal. On the other hand, since the main chain of the organic polymer is an easily decomposable aliphatic polymer, the effects of both are appropriately balanced in the end, and finally, as a part of the organic polymer or as a heated metabolite in the porous silica thin film. Will remain.

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. Further, it may be directly bonded to the polymer chain, or may be bonded via a spacer such as an alkylene group or an ether group. The same polymer molecule may have one type of functional group, or may have two or more types of functional groups. Among the above functional groups, vinyl group, hydroxyl group, vinylidene group, vinylene group, glycidyl group, allyl group, acrylate group, methacrylate group, acrylamide group,
Methacrylamide groups are preferably used.

Hereinafter, specific examples of the polymer preferably used in the present invention are described. In the above, alkylene alkylene glycol refers to two hydrogen atoms that are not bonded to the same carbon atom of an alkane having 2 or more carbon atoms. Refers to a dihydric alcohol obtained by substituting each with a hydroxyl group. (Meth) acrylate refers to both methacrylate and acrylate. Further, the dicarboxylic acid refers to an organic acid having two carboxyl groups such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. Specific examples of the aliphatic polyether having a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, and a glycidyl group at a terminal include:
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, polyalkylene glycol alkyl ether glycidyl ether and the like.

An acrylate group at one or both ends;
Examples of polycaprolactone having a polymerizable functional group such as a methacrylate group, a vinyl group, and a glycidyl group include polycaprolactone (meth) acrylate, polycaprolactone vinyl ether, polycaprolactone glycidyl ether, polycaprolactone vinyl ester, polycaprolactone vinylidyl ester, Examples include 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, and polycaprolactone glycidyl ester glycidyl ether.

An acrylate group at one or both ends,
Examples of the aliphatic polyester having a polymerizable functional group such as a methacrylate group, a vinyl group, and a glycidyl group include:
(Meth) acrylate, di (meth) acrylate, tri (meth) acrylate, vinyl ether, divinyl ether, trivinyl ether, glycidyl ether, diglycidyl ether of polycaprolactone triol,
Aliphatic polyalkylene carbonate or dicarboxylic acid 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, such as a polymer of triglycidyl ether or dicarboxylic acid and alkylene glycol. It is a polymer of an acid anhydride, and includes an aliphatic polyanhydride having a polymerizable functional group such as an acrylate group, a methacrylate group, a vinyl group, or a glycidyl group at a terminal.

Among these polymers, particularly preferably used polymers include polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol monomethacrylate, polypropylene glycol dimethacrylate, polyethylene adipate monomethacrylate, and polyethylene carbonate monomethacrylate. No. Further, aliphatic polymers in which the polymer terminal groups are hydroxyl groups are also suitable. Examples of aliphatic polyethers include polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol,
Examples thereof include alkylene glycols such as polypentamethylene glycol, polyhexamethylene glycol, polydioxolan, and polydioxepane.

Examples of the aliphatic polyester include polycondensates of hydroxycarboxylic acids such as polyglycolide, polycaprolactone, polycaprolactone thiol, and polypivalolactone, and ring-opening polymers of lactones, and polyethylene oxalates and polyethylenes. Succinate, polyethylene adipate, polyethylene sebacate, polypropylene adipate, polycondensates of dicarboxylic acids and alkylene glycols such as polyoxydiethylene adipate,
In addition, an aliphatic polyester having a hydroxyl group as a terminal group in a ring-opening copolymer of an epoxide and an acid anhydride may be used. Examples of the aliphatic polycarbonate include polycarbonate such as polyethylene carbonate, polypropylene carbonate, polypentamethylene carbonate, and polyhexamethylene carbonate.

Examples of the aliphatic polyanhydride include polymalonyl oxide, polyadipoyl oxide,
Polycondensates of dicarboxylic acids such as polypimeloyl oxide, polysuberoyl oxide, polyazela oil oxide, and polysebacoil oxide are exemplified. Among these, it is preferable to use polyethylene glycol, polypropylene glycol, polycaprolactone triol, polyethylene carbonate, polypentamethylene carbonate, polyhexamethylene carbonate, polyadipoyl oxide, polyazela oil oxide, and polysebacoil oxide.

The above organic polymer may be used alone or in combination.
May be mixed. Also, organic polymer
Are other than the above as long as the effects of the present invention are not impaired.
Including a polymer chain having an arbitrary repeating unit of
Is also good. Furthermore, in addition to the above polymers, removal by heating
A polymer that is hardly removed may be partially mixed and used. this
Polymers falling under the category of
, Polyamide, polybenzimidazole, polyurea,
Examples include polysulfone and polysiloxane. Departure
The amount of organic polymer added in the light
10 parts by weight per class^-2~ 100 parts by weight, preferably 1
0^-1-10 parts by weight, more preferably 10 ^-1~ 5 parts by weight
It is. 10 organic polymer added^-2Less than parts by weight
To obtain a porous body, and more than 100 parts by weight
However, porous silica having sufficient mechanical strength cannot be obtained,
Poor practicality.

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 is extremely small and uniform, independent of the molecular weight of the organic polymer. This is extremely important for achieving high mechanical strength. 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 functioning 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, oxalic acid,
Acids such as 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 production of a porous silica thin film via a hybrid as in the present invention, the presence of a solvent is not always essential, but it is not particularly limited as long as it dissolves the alkoxysilanes and the organic polymer. It can be used without. Examples of the solvent used include monohydric alcohols having 1 to 4 carbon atoms, dihydric alcohols having 1 to 4 carbon atoms, 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.

In addition, if desired, optional additives such as a photocatalyst generator for imparting photosensitivity, an adhesion enhancer for enhancing adhesion to a substrate, and a stabilizer for long-term storage may be added to the present invention. It can be added to the composition of the present invention within a range that does not impair the purpose. In the present invention, the formation of the thin film is performed by applying the mixture obtained by the above-described production method onto a substrate. Casting, immersion,
It can be performed by a well-known method such as spin coating,
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 is 0.1 μm to 10 μm by changing the viscosity and rotation speed of the composition.
It can be controlled in the range of 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, it is usually used in a range of 0.5 μm to 5 μm.

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.

A thin film is formed by molding the composition obtained as described above, and the silica precursor (sol) in the obtained thin film is gelled at 50 to 300 ° C. to obtain a silica gel / organic polymer. A composite (hybrid) thin film is obtained. A more preferred gelling temperature range is 60 to 200 ° C. By performing gelation in this temperature range, gelation proceeds sufficiently and the silica skeleton becomes strong. If the temperature is lower than 60 ° C., gelation does not proceed sufficiently, so that shrinkage occurs and the silica skeleton is fragile. As a result, the mechanical strength of the porous thin film cannot be 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. The porous silica thin film of the present invention has a hybrid thin film of 30%.
It is obtained by removing most of the organic spacer by applying heat of 0 to 500 ° C. By controlling the heating temperature in this range, the amount of the residue derived from the organic polymer in the porous silica thin film becomes 3 to 15% by weight. It is considered that the composition of the residue is composed of a substance that remains without being decomposed even by heating, a decomposition product, and a mixture thereof. A more preferred temperature is 350-425C.

If the temperature is lower than 300 ° C., the removal of the organic spacer is insufficient, and a large amount of organic substances remain in the porous silica thin film, so that there is a risk that a porous silica thin film having a low dielectric constant cannot be obtained. Conversely, processing at a temperature higher than 500 ° C. cannot be used in an LSI manufacturing process. The heating time is preferably in the range of 1 minute to 24 hours. If it is less than 1 minute, the evaporation and decomposition of the polymer do not proceed sufficiently, so that a large amount of organic substances remain in the obtained porous silica thin film, and the properties are deteriorated. In addition, since thermal decomposition 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. In addition, when ammonia, hydrogen, and the like are present in the atmosphere, the silanol groups remaining in the silica simultaneously react to be hydrogenated or nitrided, thereby reducing the hygroscopicity of the porous silica thin film and reducing the dielectric constant. The rise 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 sufficiently low dielectric constant, a uniform pore diameter, and a strong silica skeleton. Therefore, adhesion and mechanical strength are extremely high. As an example, the porosity is 53% and the average pore size is 2.
A porous silica thin film having a thickness of 9 nm and substantially no pores of 10 nm or more and having a tensile strength of 50 MPa (adhesion force of 50 MPa or more) can be mentioned, and is most suitable for an LSI multilayer wiring substrate or an insulating film of a semiconductor element. . The porous silica thin film obtained by the present invention is a bulk porous silica body other than the thin film, for example, a heat insulating material such as an optical film and a catalyst carrier, 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 Hereinafter, the present invention will be described by way of examples, but the scope of the present invention is not limited by these examples. The evaluation of the porous silica thin film was performed using the following apparatus and method. (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 in comparison with the density of a previously prepared bulk body. As the maximum pore diameter, the pore diameter when the V / r value became 10 ⁻³ or less was adopted. (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.

(3) Mechanical strength (adhesiveness and tensile strength): The adhesiveness and tensile strength of the film were determined by sputtering SiO ₂ to a thickness of 10 nm on the film on the silicon wafer.
Five materials were prepared by bonding tacks with an epoxy resin on the iO ₂ film, and evaluated with a tensile tester as an average value of the five materials. The measurement temperature is 25 ° C. (4) Residue content: A porous silica thin film on a silicon wafer was scraped off, and a thermogravimetric analyzer manufactured by Shimadzu Corporation:
The temperature was raised from room temperature to 425 ° C. at a rate of 20 ° C./min using TGA-50, and the weight difference was obtained before and after holding at 425 ° C. for 120 minutes.

[0040]

Example 1 7.0 g of methyltrimethoxysilane and polyethylene glycol monomethacrylate (molecular weight: 50
0) After dissolving 5.2 g in a mixed solvent of 10.0 g of ethanol and 2.0 g of propylene glycol methyl ether acetate, 3.0 g of water and 1.5 g of 0.1 N sulfuric acid were added to this solution, and the mixture was stirred at room temperature for 2 hours. Stirred. 2 g of this solution
Was dropped onto a 6-inch silicon wafer on which a silicon nitride thin film had been coated in advance by a chemical vapor deposition method, and was applied by rotating at a speed of 1500 revolutions per minute. Next, after heating at 120 ° C. for 1 minute in the air on a hot plate, a heat treatment is performed at 200 ° C. for 1 hour and then at 425 ° C. for 1 hour in a curing furnace under a nitrogen atmosphere to obtain a porous silica having a thickness of 1.01 μm. A thin film was obtained.

The porosity of the obtained porous silica thin film obtained by the nitrogen adsorption method was 53%, and the average pore size was 2.
It was found that pores of 9 nm, 10 nm or more were virtually absent. The relative dielectric constant at 1 MHz of the porous film formed on the TiN film was 2.1, which was much lower than the dielectric constant of SiO ₂ of 4.5. The amount of the residue determined by TGA (thermogravimetric analysis) was 5.2% by weight. Further, in the mechanical strength test of the obtained thin film, cohesive failure of the material occurs, and the value is 50 MPa (therefore, the adhesiveness is 50 MPa or more). This porous silica thin film has a preferable dielectric constant as a semiconductor interlayer insulating film material, It has pore diameter, pore distribution and mechanical strength.

[0042]

Example 2 In Example 1, the organic polymer was changed to polyethylene glycol dimethacrylate (molecular weight: 400).
In the same manner except that the amount was set to 5.2 g, the film thickness was 0.95 μm.
m of porous silica thin film was obtained. The relative permittivity of the porous film formed on the TiN film is 1.9, and the average pore size is 3.5 n.
There were no pores larger than 10 nm in m. The residue by TGA was 4.9% by weight. The cohesive failure strength of the material was 55 MPa (adhesion force was 55 MPa or more). Therefore, the obtained porous silica thin film has preferable characteristics as a semiconductor interlayer insulating film material.

[0043]

EXAMPLE 3 The same method as in Example 1 was repeated except that the organic polymer was 5.2 g of polyethylene adipate monoacrylate (molecular weight: 400) and the heating temperature in a curing furnace was 450 ° C. A porous silica thin film was obtained. The relative dielectric constant of the porous film formed on the TiN film is 2.5
Yes, the average pore size was 3.5 nm, and no pores of 20 nm or more were present. 12.5% by weight of residue by TGA
Met. The cohesive failure strength of the material was 45 MPa (adhesion force was 45 MPa or more). Therefore, the obtained porous silica thin film has preferable characteristics as a semiconductor interlayer insulating film material.

[0044]

Example 4 In Example 1, 12.0 g of tetraethoxysilane (58.
0 mmol), and a porous silica thin film having a thickness of 0.98 μm was obtained in the same manner as in Example 1 except that 10.4 g of polyethylene glycol monomethacrylate (molecular weight 500) was used. The obtained porous silica thin film had a dielectric constant of 2.2, an average pore diameter of 6.2 nm, and had no pores of 30 nm or more. The weight loss on TGA was good at 6.3% by weight. In addition, the tensile strength is 48MP
a (adhesion force was 48 MPa or more).

[0045]

Comparative Example 1 In Example 1, the organic polymer was changed to polyethylene glycol dimethyl ether (molecular weight: 500).
A porous silica thin film having a thickness of 0.89 μm was obtained in the same manner as in Example 1 except that the amount was changed to 5.2 g. The dielectric constant was 2.0 and the average pore size was 3 nm. In the mechanical strength measurement test, this material peeled off at the interface with the substrate, and the adhesion in this case was 15 MPa (cohesive failure strength was 15 MPa
Above), which is not satisfactory as a material for a semiconductor interlayer insulating film.

[0046]

Comparative Example 2 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. 0.5 g of dicumyl peroxide is added to this solution, and a silicon nitride thin film is spin-coated on a silicon wafer which has been coated in advance by a chemical vapor method at a speed of 1500 revolutions per minute, at 120 ° C. for 1 hour. , Heated at 180 ° C for 1 hour, 0.41μ thick
m was obtained. This sample was placed under a nitrogen atmosphere for 45 minutes.
The mixture was baked at 0 ° C. for 1 hour to burn off the organic polymer, thereby obtaining a porous silica thin film having a thickness of 0.23 μm. The residue amount was 1.8% by weight. The cohesive failure strength in this case is 25
MPa (adhesion force is 25 MPa or more), which is not satisfactory as a material for a semiconductor interlayer insulating film.

[0047]

The porous silica thin film obtained by the present invention has a high porosity, a low dielectric constant, a uniform pore diameter,
In addition, since the silica skeleton is strong, the adhesion and the tensile strength are remarkably improved as compared with the conventional product.

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Claims (5)

[Claims] 1. A porous silica thin film obtained by removing an organic polymer from a composite of silica and an organic polymer obtained by a hydrolysis / condensation reaction of alkoxysilanes, wherein the silica-derived residue is derived from an organic substance in the silica. Is 3 to 15% by weight
Having a porosity of 30 to 80% and a maximum pore diameter of 50 n.
m or less. 2. The porous silica thin film according to claim 1, wherein the porosity is 40 to 70%. 3. The porous silica thin film according to claim 1, wherein the thickness is 10 μm or less. 4. 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.
3. A multilayer wiring structure, comprising the porous silica thin film according to any one of 3. 5. A semiconductor device comprising the multilayer wiring structure according to claim 4.