JP2002217190A - Thin film and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film which has periodic structure with low dielec tric constant and reduces residual high impurity concentration to a level fit in an application of semiconductor, and its manufacturing method. SOLUTION: An insulating film includes the periodic structure in which a cycle is 0.5 nm or more but not more than 50 nm, and has chlorine impurity concentration and sodium impurity concentration being not more than 10 ppm respectively. The manufacturing method of the thin film includes a manufacturing process of precursor including components of the insulating film, a process of applying precursor and a process of hardening a coating film, and converting it into the thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film having a periodic structure on the order of nanometers and a method for manufacturing the same. The thin film of the present invention can be applied to low dielectric constant interlayer insulating films for semiconductors, optical waveguides, Gretzell-type solar cells, photocatalysts, catalyst carriers, and the like.

[0002]

2. Description of the Related Art A thin film containing silica as a main component and having a periodic structure on the order of nanometers is expected as an insulating material having a low dielectric constant. For example, Am. Chem. Soc. , 122,
pp 5258-6261 (2000) discloses a method for producing the same. The thin film having the above structure is formed by using a sol solution containing a surfactant, a catalyst, water and a solvent in addition to a silica component as a precursor, and forming the thin film on a desired substrate by spin coating or dip coating. However, since a surfactant and a catalyst used contain a halogen element and sodium, impurities based on these elements tend to remain in a film to be formed, which is disadvantageous for semiconductor applications.

[0003]

SUMMARY OF THE INVENTION The present invention provides a low dielectric constant thin film having the above-mentioned periodic structure, wherein the residual impurity concentration is reduced to a level suitable for semiconductor use, and a method of manufacturing the same.

[0004]

According to the present invention, [1] an insulating film including a periodic structure having a period of 0.5 nm or more and 50 nm or less, wherein a halogen impurity and a sodium impurity are each 10 ppm or less. It is a thin film.
Preferably, each of the halogen impurity and the sodium impurity is 1 ppm or less. [2] The thin film according to [1], wherein cavities having a periodic structure of 1 nm or more and 50 nm or less are regularly arranged. [3] The thin film according to the above [1] or [2], wherein the symmetry determined from X-ray diffraction of the thin film is cubic or hexagonal. This has the effect of improving the stability of the thin film after heat treatment and the mechanical strength. [4] The thin film according to any one of the above [1] to [3], wherein the thin film contains silica. In consideration of semiconductor process compatibility, an insulating material containing silica is preferable, and it is more preferable that the insulating material contains substantially only silica. [5] The above [1], wherein the dielectric constant of the thin film is 2.5 or less.
Or a thin film according to any one of the above [4]. As the constituent material of the thin film, any material can be basically used as long as it is an insulator having a low dielectric constant, but the dielectric constant is preferably 2.5 or less. The low dielectric constant is achieved by introducing a cavity into the material, and the cavity having the periodic structure of the present invention plays a role. [6] The thin film according to any one of [1] to [5], wherein silica is a main component. Further, the present invention provides the above [1] to [6], which includes [7] a step of producing a precursor containing an insulating film component, a step of applying the precursor, and a step of curing the applied film to form a thin film. A method for producing a thin film according to any one of the above. [8] 0.1 ppm of sodium impurities in the precursor
The following is a method for producing a thin film according to the above [7]. [9] 1000 ppm of halogen impurities in the precursor
A method for producing a thin film according to the above [7] or [8], which is as follows. [10] The method for producing a thin film according to any one of [7] to [9], wherein the precursor is applied after being treated with an ion scavenger in the step of producing the precursor. . [11] The method for producing a thin film according to any one of [7] to [10], wherein a step of reducing halogen impurities and sodium impurities is added in the step of curing to form a thin film. [12] The method for producing a thin film according to the above [11], wherein the step of reducing the halogen impurities and the sodium impurities is a step of performing treatment with hot water or hot alcohol at 80 ° C to 150 ° C for 1 minute or more. [13] The method for producing a thin film according to the above [12], wherein the hot water or the hot alcohol contains an ion scavenger.

The method for producing a thin film having a cavity having a periodic structure can utilize the self-organizing effect of micelles formed with a surfactant. For the purpose of stably forming the above structure, a cationic surfactant is preferable as the surfactant. In this case, a halogen anion such as chlorine or bromine is preferable as a counter ion, but is not preferable for semiconductor applications. In the case of unavoidable use or particularly in the case of obtaining a high-purity thin film, it is preferable to perform a treatment step for reducing impurity ions in a step after forming the thin film, for example, elution treatment in hot water or hot alcohol at 80 ° C. to 150 ° C. Furthermore, the purifying effect is enhanced by allowing the ion-trapping agent to be present in the elution solution. In any case, it is preferable that the amount of halogen impurities contained in the precursor is as small as possible, and is preferably 1000 ppm or less. Further, since sodium impurities are concentrated in the step of thinning, the content is preferably 0.1 ppm or less.

For the purpose of reducing halogen ion and sodium ion impurities in the precursor, as a surfactant,
Nonionic activators are preferred. Even when a cationic activator is used, it is preferable to use a hydroxyl group or an organic anion as a counter ion. As the catalyst, various organic acids are preferable in addition to nitric acid, phosphoric acid and sulfuric acid. Additives can be added to the precursor for the purpose of controlling the size and structure of the regularly arranged cavities, but for the purpose of the present invention additives containing these impurities should be avoided as far as possible.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The period is 0.5 nm or more and 50 nm
The following insulating film mainly composed of silica having a periodic structure is formed by applying a liquid precursor (sol liquid) containing a silica raw material, a surfactant, a catalyst, water and a solvent by a spin coating method or a dip coating method. The film is manufactured through a curing process such as drying and heat treatment.

As the silica raw material, various metal alkoxides, particularly silicone alkoxides and derivatives thereof are preferable. Silicone monoalkyl trialkoxides such as silicone monomethyl trialkoxide, silicone dialkyl dialkoxides such as silicone dimethyl dialkoxide, as well as crosslinked silsesquioxane monomers are effective. Alternatively, polysiloxane or the like can be used.

It is preferable to use a nonionic surfactant as a material containing no halogen ion or sodium ion impurities. For example, various fatty acid glycerin esters, various fatty acid glycol esters, in particular, polyethylene oxide adducts thereof, various fatty acid sucrose esters, various alcohol and ethylene oxide condensates, various higher fatty acids and ethylene oxide condensates, various fatty acid amide ethylene oxide condensates , Alkylphenol polyethylene oxide condensate, pluronics, etc., have an effect. When a cationic surfactant is used, a hydroxyl ion is preferred as a counter ion.

As the catalyst, various organic acids are effective in addition to nitric acid, phosphoric acid and sulfuric acid.

The organic acid used in the present invention is a compound having an acidic functional group. Examples of the acidic functional group include a carboxyl group, a phosphone group, a sulfone group, a sulfine group, a phenol group, an enol group, a thiophenol group, an imide group, an oxime group, an aromatic sulfamide group, a primary and secondary nitro group. And the like.

The organic acid having a carboxyl group includes
Monocarboxylic acids, dicarboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids and the like, and specifically, monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid , Lauric acid, myristic acid, palmitic acid, stearic acid, pyruvic acid, etc., and dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, phthalic acid, etc., and hydroxycarboxylic acid. Gluconic acid, tartaric acid, glycolic acid, lactic acid,
Examples of citric acid and malic acid include aminocarboxylic acids such as ethylenediaminetetraacetic acid and nitrilotriacetic acid. Examples of the organic acid having a phosphon group include 1-hydroxyethylidene-1,1-diphosphonic acid, and examples of the organic acid having a sulfone group include methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid,
Examples of the organic acid having a sulfin group include benzenesulfinic acid and p-toluenesulfinic acid. Among these, monocarboxylic acids, dicarboxylic acids, hydroxycarboxylic acids and aminocarboxylic acids are preferred, and acetic acid, oxalic acid, succinic acid, glycolic acid, lactic acid, citric acid, malic acid, tartaric acid, gluconic acid, ethylenediaminetetraacetic acid, nitrilotri Acetic acid is more preferred. These organic acids may be used alone or in combination of two or more. The molecular weight of these organic acids is preferably less than 500. Particularly, an organic acid having a proton dissociation constant of 2 or less is preferable.

As the solvent, alcohols, glycols and esters can be used. Among alcohols, methanol, ethanol, propanol and butanol are particularly preferred. The ion scavenger used in the present invention is, as an inorganic ion exchanger, aluminosilicate condensed zeolite, silica gel, alumina, montmorillonite of activated clay, IXE-600 which is an antimony bismuth-based compound (trade name of Toa Gosei Chemical Industry Co., Ltd.) IX), a magnesium aluminum-based compound, IXE-700 (trade name, manufactured by Toa Gosei Chemical Industry Co., Ltd.), and a zirconium compound, IXE
-100 (manufactured by Toa Gosei Chemical Industry Co., Ltd.) and DH as hydrotalcite
T-4A (trade name, manufactured by Kyowa Chemical Industry Co., Ltd.) or the like can be used. An ion-trapping agent is added to the precursor containing the insulating film component to trap ions, and the ion-trapping agent is separated by filtration.
ppm or less of the precursor. Further, halogen impurities and sodium impurities can be reduced by using an ion scavenger for each raw material. Further, the thin film can be washed by adding an ion scavenger to hot water or hot alcohol.
These can also be combined. Hereinafter, the present invention will be described specifically with reference to Examples.

[0014]

<Example 1> 208 g of tetraethoxysilane as a silicone raw material and C as a nonionic surfactant
25 g of ₁₈ H ₃₃ (CH ₂ CH ₂ O) ₁₀ OH, 0.83 g of maleic acid as a catalyst, 72 g of water, 720 g of ethanol as a solvent
Were mixed at room temperature (20 ° C.) to prepare a sol solution. Next, the sol solution was treated with IXE600 (manufactured by Toagosei Co., Ltd.) as an ion trapping agent at 5 wt% for 8 hours, followed by filtration. An aliquot of the obtained furnace liquid was analyzed by ion chromatography to find that chlorine and sodium impurities were 10 pp.
m or less. Next, using the remaining furnace liquid as a coating liquid, a silicon wafer is coated and formed on a silicon wafer by spin coating.
Dried at 0 ° C. The obtained dried membrane was treated with hot water of 80 ° C. containing 5% by weight of the above-mentioned ion scavenger for 2 minutes, and then dried at 120 ° C.
And dried. Subsequently, a heat treatment was performed at 400 ° C. for 12 minutes to obtain a cured film. The obtained film was examined by X-ray diffraction.
As shown in FIG. 3, three diffraction lines were observed.

[0015]

[Table 1]

A strong peak corresponding to a d value of 40.1 ° was observed. This is perpendicular to the resulting film of 4.0.
This shows that a thin film having a periodic structure of nm was obtained. Further, the index is composed of only h00 of hkl, and it is estimated that the film has a strong orientation. From these indices, the crystal symmetry of the film is either cubic or hexagonal. Further, when the obtained film was observed with a transmission electron microscope, a lattice image with a pitch of 4 nm was confirmed. Further, when the pore distribution was measured by a nitrogen gas adsorption method, it was found that a mesopore centered on 3 nm was present. Next, the thin film was treated with pressurized hot water at 120 ° C. to extract impurities and analyzed by ion chromatography,
Both sodium impurities and chlorine impurities were 1 ppm or less, which proved to be suitable for semiconductor applications.

<Example 2> A thin film was prepared under the same conditions as in Example 1 to obtain a dried film. When the IR spectrum of the obtained dry film was measured, in addition to the absorption peak derived from CH ₃ in the vicinity of 2900 cm ^-1 of the absorption peak derived from SiO ₂ to 1100 cm ^-1 was observed. Then at 400 ° C for 1
The film was heat treated for 2 minutes, and the IR spectrum of the obtained film was measured. As a result, an absorption peak derived from SiO ₂ was observed.
The peak derived from H ₃ had disappeared. From this, 40
It was found that the film fired at 0 ° C. was a thin film substantially composed of silica. Further, when the refractive index of the thin film was measured using an ellipsometer, it was 1.12, which was 1.1 for a normal SiO ₂ film.
It was lower than 45. This indicates that cavities have been introduced into the film. Next, a film was formed on a low-resistance Si wafer under the same conditions as in Example 1 to obtain a cured film at 400 ° C. When an AI electrode was formed and the dielectric constant was measured,
0 (measurement frequency 100 KHz).

[0018]

According to the present invention, a high-purity and low-dielectric-constant film suitable for semiconductor use can be obtained.

Continued on front page F term (reference) 4G072 AA25 BB09 GG01 GG03 MM01 RR12 TT19 TT20 TT30 UU01 UU02 UU15 UU17 5F033 HH08 RR09 RR29 SS22 VV00 WW01 WW03 WW04 WW09 XX01 XX24 5F058 AF04

Claims (13)

[Claims] 1. An insulating film having a periodic structure with a period of 0.5 nm or more and 50 nm or less, wherein a halogen impurity and a sodium impurity are each 10 ppm or less. 2. The thin film according to claim 1, wherein cavities having a periodic structure of 1 nm or more and 50 nm or less are regularly arranged. 3. The thin film according to claim 1, wherein the symmetry of the thin film determined by X-ray diffraction is cubic or hexagonal. 4. The composition according to claim 1, wherein said thin film contains silica.
A thin film according to claim 3. 5. The thin film according to claim 1, wherein the dielectric constant of the thin film is 2.5 or less. 6. The thin film according to claim 1, wherein said thin film contains silica as a main component. 7. The thin film according to claim 1, comprising a step of producing a precursor containing an insulating film component, a step of applying the precursor, and a step of curing the applied film to form a thin film. Manufacturing method. 8. The method according to claim 8, wherein the sodium impurity in the precursor is 0.1%.
The method for producing a thin film according to claim 7, wherein the content is 1 ppm or less. 9. The method according to claim 1, wherein the precursor has a halogen impurity of 100.
9. The method for producing a thin film according to claim 7, wherein the content is 0 ppm or less. 10. The method for producing a thin film according to claim 7, wherein the precursor is applied after treating with an ion scavenger in the step of producing the precursor. 11. The method for producing a thin film according to claim 7, wherein a step of reducing halogen impurities and sodium impurities is added in the step of curing to form a thin film. 12. The method according to claim 1, wherein the step of reducing halogen impurities and sodium impurities is a step of treating with hot water or hot alcohol at 80 ° C. to 150 ° C. for 1 minute or more.
2. The method for producing a thin film according to 1. 13. The method for producing a thin film according to claim 12, wherein an ion scavenger is contained in the hot water or hot alcohol.