JPH1114841A - Organosilicon nanocluster and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily form patterns of silicon thin films and silicon oxidized thin films by forming a silicon nanocluster soluble in an org. solvent, thereby making it possible to form an organosilicon nanocluster. SOLUTION: The silicon nanocluster soluble in the org. solvent is formed. The example of the silicon nanocluster soluble in the org. solvent includes the organosilicon nanocluster. The organosilicon nanocluster refers to an org. silicon compd. which is soluble in the org. solvent and is of 3 to 1.2 eV in the band gap determined by the Tauc plot of a soln. The Tauc plot refers to a method of obtaining the optical band gap from electron spectra with respect to an amorphous semiconductor. This organosilicon nanocluster is produced by bringing a silane tetrahalide and an org. halide into reaction in the presence of an alkali metal or alkaline earth metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organosilicon nanocluster, a method for synthesizing the same, and its application to an electronic device.

[0002]

2. Description of the Related Art Amorphous silicon is used in solar cells and T cells.
Research is progressing as a material for the driving part of the FT-LCD, and its application is being pursued. However, since amorphous silicon is conventionally formed by a vapor phase method, there is a major problem in terms of cost reduction and large area.

On the other hand, organic silane compounds have been widely studied as functional organic materials. However, linear polysilanes that have been generally studied have a problem in terms of stability. Polysilane is expected to have semiconductor properties as low-dimensional silicon, but at present there is no effective means for pn control. In a one-dimensional system, even if a different molecule such as phosphorus or boron is introduced into the main chain skeleton, that portion becomes a trap site and the expected effect cannot be obtained. Further, doping with a Lewis acid or Lewis base significantly impairs stability. The linear polysilane compound cannot be used as a silicon precursor because the main chain is simultaneously decomposed and vaporized when an organic group is eliminated by heating, so that it is vaporized.

The network polysilane is a polysilane having a branched silicon chain, is soluble in an organic solvent, and can easily form a thin film. In this thin film, the side chain organic substitution period hinders the transfer of carriers between silicon skeletons, and no improvement in semiconductor characteristics is observed as compared with the linear type. Since the network polysilane has a network structure, it has excellent heat resistance and can form an amorphous silicon thin film by heating. However, there are problems such as the fact that many organic substituents remain and electrical characteristics are inferior to the original amorphous silicon, and there is no appropriate doping method of phosphorus or boron.

On the other hand, by performing heat treatment using t-butyl octasilacuban as a precursor, amorphous silicon having the same characteristics as those obtained by the conventional gas phase method can be obtained. However, t-butyl octasilacuban is a crystalline compound, and a thin film can be formed only by a vapor phase method by a vapor deposition method, and the formed amorphous silicon thin film is also non-uniform.

As described above, there is no method for easily and efficiently forming an amorphous silicon thin film.

Further, in the integrated circuit industry, as the degree of integration increases, the wavelength of irradiation light used in photolithography for miniaturization has been shortened. Conventionally, photolithography has been performed mainly using g-line (436 nm), which is one of the characteristic luminescence of mercury lamps.
An i-line (365 nm), which is more advantageous for fine processing, has been used. These processes are mainly performed using a photoresist mainly composed of an organic polymer having an aromatic ring in the molecule.

However, conventional photoresists containing an organic material as a main component have a strong absorption at a wavelength of 350 nm or less, and thus are not suitable for lithography using light having a wavelength shorter than 350 nm.

[0009] material of silicon system represented by SiO ₂ is in the SiO ₂ film formation is also a problem in terms of needs productivity using CVD apparatus or the like. To address this problem, there is a siloxane-based "coat-on" material called spin-on-glass (hereinafter abbreviated as SOG). However, SOG has a problem that a film thickness of submicron or more cannot be obtained due to a large film stress at the time of effect, and the workability is poor and cracks are easily generated.

[0010] The network polysilane has excellent heat resistance due to its network structure, and can form a silicon oxide thin film by exposure or heating in the presence of oxygen. However, there is a problem that many organic groups are eliminated and a dense film quality cannot be obtained.

In an optical device, formation of an optical waveguide is a major technical problem. Conventionally, an organic material such as polyimide has been used because there is no simple method for forming an optical waveguide of a silicon oxide thin film having high transparency. However, these materials had high losses and poor stability.
In addition, workability such as roughness of a side wall due to dry etching is poor, which hinders improvement in performance of an optical device. To solve this problem, there is a silicon network polymer. However, a silicon oxide film using such a polymer has poor transparency and cannot be used as an optical waveguide.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to enable the synthesis of organosilicon nanoclusters under the above-mentioned circumstances, and to easily use a novel organosilicon nanocluster to easily prepare a silicon thin film and silicon. An object of the present invention is to provide a method for forming a pattern of an oxide thin film, and to apply the formed thin film to an electronic device and an optical device.

[0013]

The gist of the present invention for solving the above problems is as follows.

[0014] The above problem is solved by a silicon nanocluster soluble in an organic solvent. Silicon nanoclusters have a three-dimensional structure and their structure and properties are described in WL Wilson, PF Szajowski, LE Brus, S
cience 262, 1242 (1993) ,. KA Littau, PJ Szajow
ski, AR Muller, AR Kortan, and LEBrus, J.
Phys. Chem. 97, 1224 (1993),. S. Frukawa and T. Mi
yasato, Jpn, J. Appl. Phys. 27, L2207 (1989),. T. T
akagi, H .; Ogawa, Y. Yamazaki, A. et al. Ishizaki, and T.
Nalagiri, Appl. Phys. Lett. 56, 2379 (1990),. D. Zh
ang, R. M. Kolbas, P .; D. Milewski, D. J. Lichtenwa
lner, A .; I. Kingon, and J. M. Zavada, Appl. Phys.
Lett. 65, 2684 (1994),. X. Chen, J.S. Zhao, G .; Wang,
X. Shen, Phys. Lett. 212, 285 (1996),. It is described in.

As the silicon nanocluster soluble in an organic solvent, there is an organosilicon nanocluster.

Here, the organosilicon nanocluster refers to an organosilicon compound that is soluble in an organic solvent and has a band gap of 3 eV to 1.2 eV determined by Tauc plot of the solution.

Here, the Tauc plot is a method for obtaining an optical band gap from an electron spectrum generally used for an amorphous semiconductor. In light absorption due to optical transition between bands of an amorphous semiconductor, the relationship between absorbance and photon energy is represented by the following equation.

Α = k (E−E ₀ ) ² / E (k is a constant) Then, the horizontal axis is the photon energy, and the vertical axis is the square root of the product of the absorbance and the photon energy, and a tangent is drawn. The intersection of this tangent and the horizontal axis is the optical band gap (Tatsuo Shimizu, Amorphous Semiconductor, Baifukan (1994). P20
1).

Organosilicon nanoclusters are generally advantageous for applications when they have the composition of Formula 1. (Where y, z, and a are each x with respect to 0.1x ≦ y ≦ 10
x, 0.3x ≦ z ≦ 30x, a ≦ 0.5x) Si x C y H z O a ... ( Equation 1) y is poor solubility in organic solvents is less than 0.1x,
If it exceeds 10x, the film quality of the silicon thin film and the silicon oxide thin film deteriorates. If z is less than 0.3, the solubility in organic solvents is poor, and if it exceeds 30x, the film quality of the silicon thin film and the silicon oxide thin film deteriorates. When a exceeds 5x, the film quality of the silicon thin film and the silicon oxide thin film deteriorates. When a silicon thin film is to be obtained, it is preferable that a <0.5. In the equation, as the values of y, z, and a with respect to x become smaller, the band gap obtained by the Tauc plot becomes smaller, and the value decreases to the value of crystalline silicon of 1.2 eV. However, the solubility in organic solvents is reduced.

On the other hand, as the value of y, z, a with respect to x increases, the band cap increases.

In order to achieve the object of the present invention, from the viewpoint of solubility, the band gap determined by Tauc plot is preferably 1.5 eV or more. The band gap is desirably 3 eV or less from the viewpoint of the characteristics of the obtained silicon thin film and silicon oxide thin film.

The organosilicon nanocluster of the present invention can be obtained by reacting a tetrahalogenated silane with an organic halide in the presence of an alkali metal or an alkaline earth metal.

The silicon thin film of the present invention can be used to convert organosilicon nanoclusters to 200-10 under the condition that they do not react with oxygen.
It is obtained by heating or irradiating light at 00 ° C. Further, the silicon oxide thin film of the present invention can be obtained by performing the heating or light irradiation under the condition of reacting with oxygen.

Since the silicon thin film and the silicon oxide thin film of the present invention use silicon nanoclusters, they have the same properties as those obtained by the conventional gas phase method, and are used for solar cells, liquid crystal display devices, integrated circuits, etc. It can be used for a semiconductor device.

The present invention has been made as a result of intensive studies on a method of synthesizing a three-dimensional silicon network polymer for the purpose of developing silicon and silicon oxide thin films used for semiconductor devices. ) ₄ -Si
It is a solvent-soluble compound having a bond and a Si-R bond (R is an organic group having 1 or more carbon atoms). Important advantages of this compound include the fact that silicon and silicon oxide thin films can be easily formed under normal pressure, and that the formed silicon and silicon oxide thin films have excellent properties. The organosilicon nanocluster of the present invention is obtained by reacting a tetrahalogenated silane with an organic halide in the presence of an alkali metal or an alkaline earth metal. It is considered that silicon nanoclusters generated by the reaction of the tetrahalogenated silane, and the organic metal generated by the reaction of the organic halide and the metal react with each other to solubilize the silicon nanoclusters. It is considered that the larger the carbon number of the organic group is, the better the solubility is, but even when a methyl group is used as the organic group, a soluble organosilicon nanocluster can be obtained. Therefore, the structure of the organic group is not particularly limited.

In the synthesis, part of the tetrahalogenated silane can be replaced with trihalogenated silane or dihalogenated silane. By using a trihalogenated silane or a dihalogenated silane, an organosilicon nanocluster having extremely high solubility can be obtained. The use of trihalogenated or dihalogenated silanes reduces the size of silicon nanoclusters. Therefore, in order not to lose the properties of the silicon nanocluster, it is desirable that the amount of the trihalogenated silane does not exceed the amount of the tetrahalogenated silane. The content of the dihalogenated silane is desirably 50% or less of the content of the tetrahalogenated silane. The obtained organosilicon nanocluster is soluble in common organic solvents such as hydrocarbons, alcohols, ethers, aromatic solvents, and polar solvents.

When a silicon thin film is to be obtained using organosilicon nanoclusters, it is desirable that the synthesis be performed under dehydration and deoxygenation conditions while avoiding contact with a compound serving as an oxygen supply source. At the end of the synthesis, it is important to stop the reaction with a terminator having no oxygen atom such as an alkyl metal.

When a silicon oxide thin film is to be obtained, the terminating agent is not particularly limited, and the reaction solution may be put into a solvent such as alcohol which can react with silicon halide.

The organosilicon nanocluster thin film can be obtained from a solution in which the organosilicon nanocluster is dissolved in an appropriately selected solvent by a general thin film forming method such as spin coating and dipping.

The silicon thin film can be obtained by heating or irradiating the organosilicon nanoclusters in an atmosphere substantially free of oxygen or in a reducing atmosphere with ultraviolet rays. It is also possible to combine heating and UV irradiation. This is due to the thermal decomposition of the organic component of the organosilicon nanocluster. The decomposition temperature of the organic component varies depending on the structure and the heating time, but when a t-butyl group is used, decomposition is observed at around 200 ° C.
Decomposition of many organic groups, including aromatic groups, is almost complete at up to 500 ° C., although it varies depending on the heating conditions. When the heating temperature is set to 500 ° C. or higher, the thin film gradually changes from amorphous silicon to crystalline silicon, and evaporates at 1500 ° C. or higher. By utilizing this, the properties of silicon can be controlled by the heating temperature. Heating temperature to 600-8
When the temperature is as high as 00 degrees, the crystalline silicon portion increases, and when it is lower than that, amorphous silicon increases. Using this property, the band gap of the thin film obtained can be controlled. The band gap of the silicon thin film can be continuously controlled from about 2.5 V to about 1.2 V by changing the heating temperature and adjusting the amounts of the crystalline portion and the amorphous portion.

If a silicon nanocluster containing a phosphorus atom or the like is used as an organic group, doping is possible at the same time as firing. Doping can also be performed by co-existing the silicon nanocluster with the compound to be doped and firing. In this case, if the atoms to be doped are included in the polymer in some form, efficient doping becomes possible.

Therefore, this silicon thin film is a material suitable for use in a thin film transistor or a solar cell used in a liquid crystal display or the like.

When the organosilicon nanocluster is heated or irradiated with ultraviolet rays in an oxidizing atmosphere, silicon oxide can be obtained. The heating temperature at that time is desirably 200 ° C. or higher as in the case of obtaining a silicon thin film in order to efficiently obtain a silicon oxide thin film. At 1500 ° C. or higher, evaporation occurs (ultraviolet irradiation and heating can be combined).

The decomposition of the organic group is substantially carried out at 200 ° C. to 50 ° C.
Occurs between 0 ° C. It is also possible to obtain a silicon or silicon oxide thin film partially leaving an organic group by adjusting the decomposition temperature. By leaving the organic group, an insulating thin film having a relative dielectric constant of 3 or less can be obtained. This lowering of the dielectric constant is remarkable when a fluorinated alkyl group or a fluorinated allyl group is used as the organic group. Further, the refractive index can be adjusted by adjusting the remaining amount of the organic group. Increasing the remaining amount of the organic group lowers the refractive index.

Since the silicon oxide thin film has excellent insulating properties and small film stress, it can be used as an insulating layer in the field of microelectronics such as an interlayer insulating film of a semiconductor integrated circuit.

The organosilicon nanoclusters are also converted to silicon oxide by irradiating ultraviolet rays under the condition that oxygen is present. By utilizing this property, pattern formation by light becomes possible. The portion of the organosilicon nanocluster thin film that has been irradiated with ultraviolet light and has become silicon oxide cannot be dissolved in the solvent. Therefore, a negative pattern can be obtained by developing with a solvent after irradiation. In addition, by heating in an atmosphere substantially free of oxygen or in a reducing atmosphere after irradiation with ultraviolet rays, a pattern in which exposed portions are silicon oxide and unexposed portions are silicon can be formed. Since the silicon oxide thin film thus formed uses silicon nanocrystals, it has high transparency and does not absorb light at wavelengths longer than 200 nm. Therefore, the silicon oxide thin film according to the present invention is suitable as an optical waveguide material. As described above, the refractive index of the oxide film can be controlled by heating. Also, the pattern shape becomes an optical waveguide with little loss without side surface roughness seen when formed by dry etching, thereby providing a high-performance optical device. When network polysilane is used, transparency is poor and it cannot be used for a waveguide.

By subjecting the obtained thin film to the above heat treatment, a silicon thin film or a silicon oxide thin film can be obtained. In particular, a silicon thin film has conventionally been obtained only by a gas phase method. The present invention is also revolutionary in that a pattern consisting of an insulating portion and a semiconductor portion can be formed only by coating, exposing, and heating. Furthermore, the present invention is also revolutionary in that it provides a waveguide that can be applied to high-performance optical devices with excellent shape without surface roughness, by combining exposure and development and, if necessary, heating without relying on dry etching. It is.

[0038]

Next, the present invention will be described specifically with reference to examples.

Example 1 16 mmol of tetrachlorosilane was dissolved in tetrahydrofuran and reacted at 0 ° C. for 3 hours while irradiating ultrasonic waves in the presence of magnesium metal. Thereafter, 16 mmol of t-butyl bromide is added and reacted at 50 ° C. for 2 hours. The obtained reaction solution was poured into methanol to obtain a yellow-orange powder (A, yield 43%).
The composition obtained based on elemental analysis and ¹ H-NMR was Si ₁ C _1.19 H _3.07 O _0.07 . The ratio of butyl group and methoxy group to Si atom is 0.28 and 0.2.
07 (PtBuSi1). Figure 1 shows the CP / MA of A
S ²⁹ Si NMR was shown. 15,0, -50, -95pp
There is a broad absorption at m. These absorptions are attributed to Si atoms having 1, 2, 3, 4 Si-Si bonds, respectively.

Using THF as an eluent, the molecular weight was determined by GPC in terms of polystyrene as Mw = 1770, Mw / Mn = 2.9.
Met. The elution curve is shown in FIG. The distance between both ends of the standard polystyrene corresponding to the elution range is 0.2 to 1.5 n.
m.

FIG. 3 shows the visible ultraviolet absorption spectrum of A. The spectrum is the result in a 0.5 mM THF solution. The absorption edge extending to a longer wavelength side than 400 nm is due to the amorphous nature of this compound. The band gap determined from the Tauc plot was 2.57. The value of 2.57 V is substantially equal to the value of silicon nanocrystals and silicon nanoclusters obtained by pyrolysis of monosilane gas by a gas phase method.

(Example 2) 10 g of 1 g of A in Example 1
Was dissolved in toluene, and a thin film was formed on a quartz substrate by spin coating. This was dried at 100 ° C. for 5 minutes and then heated in a vacuum furnace (2 × 10 ⁻⁵ torr) for 1 hour. The visible ultraviolet absorption spectrum measured after cooling to room temperature was measured, and the band gap determined by Tauc plot was 1.8 eV when the heating temperature was 500 ° C. and 1.6 eV when the heating temperature was 800 ° C.

Example 3 A thin film formed in the same manner as in Example 2 was heated at 500 ° C. in air. As a result, a colorless and transparent thin film was obtained. Its visible ultraviolet absorption spectrum has 2
No absorption at a wavelength longer than 00 nm was observed. A similar experiment was performed with the substrate replaced by a silicon wafer. The infrared absorption spectrum of the obtained thin film was measured. A strong absorption based on the stretching vibration of Si-O was observed around 950 cm-1, confirming the formation of the silicon oxide thin film. Was done.

Example 4 16 mmol of tetrachlorosilane was dissolved in tetrahydrofuran and reacted at 0 ° C. for 3 hours while irradiating ultrasonic waves in the presence of magnesium metal. Thereafter, 16 mmol of t-butyl bromide is added and reacted at 50 ° C. for 2 hours. 50 mmol of n-
A hexane solution of BuLi is added and reacted at room temperature for 12 hours. This solution was poured into n-hexane to obtain a yellow-orange powder (B, yield 70%). The composition obtained based on elemental analysis and ¹ H-NMR was Si ₁ C _0.5 H _1.5 . (Example 5) The same experiment as in Example 4 was performed, except that metallic magnesium was replaced with metallic lithium. The yield of the powder obtained is 7
5% (C). The composition obtained based on elemental analysis and ¹ H-NMR was Si ₁ C _0.4 H _1.2 . The band gap determined by Tauc plot from the visible ultraviolet absorption spectrum of the solution of C measured in the same manner as in Example 1 was 2.4 eV.

Example 6 A C thin film formed in the same manner as in Example 2 was dried at 100 ° C. for 5 minutes, and then dried in a vacuum furnace (2 ×
Heat at 500 ° C. for 1 hour at 10 ⁻⁵ torr). After cooling to room temperature, the visible ultraviolet absorption spectrum was measured, and the band gap determined by Tauc plot was 1.3 eV.

Example 7 The same organosilicon nanocluster as in Example 4 was synthesized and a 20% toluene solution was prepared. This solution was spin-coated on an n ^- type silicon substrate to form an organosilicon nanocluster thin film.
This was heat-treated at 600 ° C. for 1 hour under vacuum to obtain an amorphous silicon film. This was doped with phosphorus as an impurity to form a pn junction of n ⁻ -type silicon and p ⁻ -type amorphous silicon thin film. FIG. 4 shows this voltage-current curve.

Example 8 The same organosilicon nanocluster as in Example 1 was synthesized, and its 30% toluene solution was spin-coated on a silicon wafer on which an aluminum pattern having a wiring width, spacing and height of 1 μm was arranged. As a result, a film having a thickness of 2 μm was formed. This film is placed in air 40
After treatment at 0 ° C for 1 hour, chemical mechanical polishing (CMP)
The surface of the coating film was flattened. Even after polishing, the film did not crack and a tough insulating film was obtained. The withstand voltage of this insulating film was 650 V / μm, and the relative dielectric constant was 3.4.
FIG. 5 schematically shows a cross section of an aluminum two-layer wiring obtained by repeating the above steps. Aluminum wiring and vias were formed by usual etching of aluminum deposited by sputtering. An integrated circuit can be obtained by forming a wiring on a silicon wafer on which a transistor is formed.

Example 9 A thin film was formed from a toluene solution of A in Example 1 on a quartz substrate by spin coating. This was dried at 100 ° C. for 5 minutes, exposed through a light-shielding mask using a 500 W ultra-high mercury lamp for 3 minutes, and developed with toluene. As a result, a pattern having a smooth surface having a width of 1 μm and a thickness of 1 μm and having no deformation was formed. This thin film had no absorption on the longer wavelength side than 200 nm and was suitable as an optical waveguide for a high-performance optical device.

[0049]

The present invention provides an organosilicon nanocluster and a method for synthesizing the same. Further, a silicon and silicon oxide thin film using the same and a high-performance semiconductor device using the same are provided.

[Brief description of the drawings]

FIG. 1. C of synthesized organosilicon nanoclusters
Is a P / MAS ²⁹ SiNMR spectrum.

FIG. 2. G of synthesized organosilicon nanoclusters
It is a PC elution curve.

FIG. 3 is a visible ultraviolet absorption spectrum of a synthesized organosilicon nanocluster.

FIG. 4 is a diagram showing voltage-current characteristics of an n ⁻ type silicon substrate-amorphous silicon thin film.

FIG. 5 shows aluminum 2 formed on a silicon wafer.
It is a cross section of a layer wiring.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon wafer, 2 ... Aluminum wiring, 3 ... Aluminum via, 4 ... Insulating film.

Claims (13)

[Claims] 1. A silicon nanocluster soluble in an organic solvent. 2. The silicon nanocluster soluble in an organic solvent according to claim 1, which is an organosilicon nanocluster. Here, the organosilicon nanocluster refers to an organosilicon compound that is soluble in an organic solvent and has a band gap of 3 eV to 1.2 eV determined by Tauc plot of the solution. 3. It has the composition of Formula 1, is soluble in an organic solvent, and has a band gap of 3 determined by Tauc plot of the solution.
An organosilicon compound having an eV of 1.22 eV. (Where y, z, and a are each x with respect to 0.1x ≦ y ≦ 10
x, 0.3x ≦ z ≦ 30x, a ≦ 0.5x) Si x C y H z O a ... ( Equation 1) 4. A method for producing an organosilicon nanocluster, comprising reacting a tetrahalogenated silane with an organic halide in the presence of an alkali metal or an alkaline earth metal. 5. A silicon thin film using an organosilicon nanocluster as a precursor. 6. A method for producing a silicon thin film, comprising heating an organosilicon nanocluster at 200 to 1500 ° C. under conditions that do not react with oxygen. 7. The method for producing a silicon thin film according to claim 5, wherein the organosilicon nanocluster is heated at 200-1500 ° C. in a reducing atmosphere. 8. A method for producing a silicon oxide thin film, comprising heating an organosilicon nanocluster at 200 to 1500 ° C. under a condition for reacting with oxygen. 9. An electronic device using the silicon thin film according to claim 5. 10. A silicon oxide thin film using an organosilicon nanocluster as a precursor. 11. An electronic device using the silicon oxide thin film according to claim 10. 12. An optical waveguide comprising the silicon oxide film according to claim 10. 13. An optical device using the optical waveguide according to claim 12.