JP2001308089A - Low-permittivity film and semiconductor element having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-permittivity film which has a high mechanical strength, improves the CMP resistance by applying as a layer insulation film for semiconductor elements, can ensure a wide process margin, and attains a high performance, high reliability and high yield of LSI. SOLUTION: The low-permittivity film of 0.5-0.6 μm, formed on a silicon wafer has a hardness of 0.45 GPa or more in DHT115 as measured at a weight of 10 mg and a specific permittivity of 1.0-2.4 as measured at 1 MHz, and the semiconductor element uses this low-permittivity film as a layer insulation film of a multilayer wiring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low dielectric constant film useful as an interlayer insulating film for a semiconductor device and a semiconductor device having this low dielectric constant.

[0002]

2. Description of the Related Art With the miniaturization of wiring due to the high integration of LSIs, an increase in signal delay time due to an increase in capacitance between wirings has become a problem. Conventionally, a SiO ₂ film formed by a CVD method having a relative dielectric constant of about 4.2 has been used as an interlayer insulating film.
In order to improve the operation speed of the device, a film having a lower dielectric constant is required. Low dielectric constant films that are currently in practical use include:
An example is an SiOF film (CVD method) having a relative dielectric constant of about 3.5. As an insulating film having a relative dielectric constant of 2.5 to 3.0,
An organic SOG (Spin On Glass) film, an organic polymer, and the like are considered to be promising, and studies for application to an interlayer insulating film of LSI are being actively conducted. In order to cope with further miniaturized LSIs, an insulating film having a relative dielectric constant of less than 2.5 has been studied.

The characteristics required for a low dielectric constant film applied to an interlayer insulating film of an LSI include characteristics such as heat resistance, plasma resistance, and mechanical strength. In a multilayer wiring process of a miniaturized LSI, CMP is used for global flattening.
(Chemical Mechanical Poli
shing) is essential, and mechanical strength is a particularly important property. Organic polysiloxane and organic polymer, which are considered to be effective as low dielectric constant films having a relative dielectric constant of 2.5 to 3.0, have a lower dielectric constant than SiO ₂ films and SiOF films formed by conventional CVD. The problem is that the mechanical strength of the membrane is low.

[0004] Characteristics that the mechanical strength of the insulating film affects in the CMP process include peeling due to stress during CMP, damage due to foreign matter, erosion during metal CMP in the damascene process (cutting of the insulating film), and the like. Regarding these, it is reported that the characteristics are significantly improved by improving the mechanical strength of the film. In order to achieve high yield and high reliability by using a low-dielectric-constant insulating film that contributes to high performance of LSI, it is strongly desired to improve the mechanical strength of the low-dielectric-constant film.

As a low dielectric constant film having a relative dielectric constant of less than 2.5, JP-B-6-12790 and JP-A-10-25
A porous membrane as shown in JP-A-359-359 is generally used. However, the porous membrane obtained by these methods has a remarkable decrease in mechanical strength.
The problem of insufficient mechanical strength in the CMP process is expected to become a more serious problem. In order to further improve the performance of LSI, it is considered that a relative dielectric constant film having a mechanical strength enough to withstand the CMP process is required even for a low dielectric constant film having a relative dielectric constant of less than 2.5.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a low dielectric constant film having a relative dielectric constant of 1.9 to 2.4 and a mechanical strength enough to withstand the CMP process of an LSI, and an improvement in the performance of an LSI using the same. And a semiconductor device that achieves high reliability and high yield.

[0007]

According to the present invention, a film having a thickness of 0.5 to 0.6 μm is formed on a silicon wafer and a load of 1 to 0.5 μm is formed.
The hardness DHT ₁₁₅ of the film measured at 0 mg is 0.45 G
The relative dielectric constant measured at 1 MHz at Pa or higher is 1.9 to
The present invention relates to a low dielectric constant film having a thickness of 2.4 and a semiconductor device using the low dielectric constant film as an interlayer insulating film of a multilayer wiring.

Since the hardness measurement value of a thin film is affected by the substrate, the value obtained depends on the film thickness even if the film has the same hardness. Therefore, in order to compare the hardness of the thin film, it is necessary to make the film thickness uniform.
The measurement was carried out at 0.6 μm. Therefore, a film thickness of 0.5
The limit of 0.6 μm is a condition for measurement, and does not limit the film thickness when the low dielectric constant film of the present invention is applied.

For measuring the hardness of the thin film of 0.5 to 0.6 μm, a commercially available device called a nano indentation tester can be used. In this method, the hardness of the film is calculated from the load and the pressing depth when the diamond indenter is pressed into the surface of the thin film with a small load. The hardness is defined as “hardness = test load / contact area between sample and indenter”, and hardness DHT ₁₁₅ when using a triangular pyramid indenter with an edge angle of 115 ° is used.
Is calculated from the “indentation load” and “indentation depth” obtained by the measurement according to the following formula. DHT ₁₁₅ = 0.0379 F / (h ² ) (Pa) F: Indentation load (N) h: Indentation depth (m)

As a low dielectric constant film having a relative dielectric constant of less than 2.5, a film obtained by reducing the density of an organic polysiloxane film or an organic polymer film is considered to be effective, but from the viewpoint of mechanical strength, SiO ₂ A low-density organic polysiloxane film having a skeleton is more advantageous. As a coating liquid for the organic polysiloxane film, a solution of a partially hydrolyzed condensate of alkoxysilane is used. As a method for producing a coating liquid, for example, there is a method in which water is added to an alkoxysilane in the presence of a solvent and a catalyst to cause a hydrolytic condensation reaction. In this case, heating may be performed if necessary. As a catalyst, hydrochloric acid,
Inorganic acids such as nitric acid and sulfuric acid, and organic acids such as formic acid, oxalic acid and acetic acid can be used. Usually, the molecular weight of the product is 500 to 1 in terms of standard polystyrene-equivalent weight average molecular weight determined by gel permeation chromatography (GPC).
It is preferable to set in the range of 0000 from the viewpoint of compatibility with the thermally decomposable polymer and solubility in a solvent. Then, if necessary, water present in the system is removed by distillation or the like,
Further, the catalyst may be removed with an ion exchange resin or the like.

As the alkoxysilanes, for example, the following can be used. Tetramethoxysilane, tetraethoxysilane, tetraalkoxysilanes such as tetrapropoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane,
Monoalkyl trialkoxysilanes such as phenyltrimethoxysilane, vinyltrimethoxysilane, monoalkenyl trialkoxysilanes such as vinyltriethoxysilane, trifluoromethyltrimethoxysilane,
Trifluoropropyltrimethoxysilane, pentafluorobutyltrimethoxysilane, nonafluorohexyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, heptadecafluoroundecyl Trimethoxysilane, (4-perfluorobutylphenyl) trimethoxysilane, (4-perfluorohexylphenyl) trimethoxysilane, (4-perfluorooctylphenyl)
Fluorine-containing alkoxysilanes such as trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ
Epoxysilanes such as glycidoxypropyltriethoxysilane, aliphatic aminosilanes such as γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, aminophenyltrimethoxysilane, aminophenyltriethoxysilane, N -Aromatic-containing aminosilanes such as phenyl-γ-aminopropyltrimethoxysilane.

As the solvent used for the hydrolysis-condensation reaction and the coating solution, for example, the following can be used. Methanol, ethanol, propanol, alcoholic solvents such as butanol, methyl acetate, ethyl acetate, propyl acetate,
Acetate solvents such as butyl acetate; glycol acetate solvents such as ethylene glycol monomethyl acetate and ethylene glycol diacetate; amide solvents such as N, N-methyl-2-pyrrolidone; glycol ether solvents;

As a method for producing an organic polysiloxane film, a spin coating method of an organic polysiloxane coating solution is generally used. For example, after spin coating, prebaking is performed on a hot plate, and finally, final curing is performed using a furnace. Prebake is usually at a temperature of 50-350 ° C,
It is carried out stepwise from a low temperature using two or three hot plates. The final curing temperature is 400 to 450 ° C., and the atmosphere is usually a nitrogen atmosphere to prevent decomposition of organic groups.

It has been clarified that a low-density organic polysiloxane film can be obtained by adding a monohydric alcohol or a dihydric alcohol having a boiling point of 250 ° C. or more at 1 atm to an organic polysiloxane coating solution (hereinafter referred to as “organic polysiloxane”). In this case, monohydric alcohol is alcohol and dihydric alcohol is diol).
In this method, since the solubility of the alcohol or diol in the solvent used for the organic polysiloxane is good, a solvent having good coatability can be selected. Further, since the molecular weight is uniform, there is no remarkable decrease in mechanical strength, which is a problem when the density is reduced by using a polymer.

The amount of the alcohol or diol to be added is preferably in the range of 0.1 to 1.0 part by weight with respect to 1.0 part by weight of the nonvolatile matter of the organic polysiloxane. Can be set to here,
The calculation of the nonvolatile content of the organic polysiloxane is based on the assumption that all the hydrolyzable groups of the siloxane oligomer are condensed and Si-O-Si
Are used assuming that a bond is formed. In the following, the same calculation method is used.

The following can be used as the alcohol or diol having a boiling point of 250 ° C. or higher at 1 atm. Dodecanol, tetradecanol, hexadecanol, octadecanol, 1,2-decanediol, 1,2-dodecanediol, 1,2-tetradecanediol, 1,
2-hexadecanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, 1,16-
Hexadecanediol.

A diol has a higher solubility in an organic polysiloxane solvent than an alcohol, and a good coating film can be obtained. Diols have two types of isomers, 1,2- and 1, n-, but 1,2- is cheaper and easily available. In addition, even if these alcohols and diols are used alone,
Two or more types may be used in combination.

As a method for producing a low-density organic polysiloxane film by using a coating solution in which an alcohol or a diol is dissolved in an organic polysiloxane coating solution, a spin coating method can be used. For example, after spin coating, prebaking is performed on a hot plate, and finally, final curing is performed using a furnace. The pre-bake is usually performed at a temperature of 50 to 350 ° C. and stepwise from a low temperature using two or three hot plates. The final curing temperature is 400 to 450 ° C., and the atmosphere is usually a nitrogen atmosphere to prevent decomposition of organic groups.

By pre-baking the organic polysiloxane at 200 ° C. or higher, crosslinking proceeds to such an extent that the film does not shrink any more. When an alcohol or diol having a boiling point of 250 ° C. or more is added, the crosslinking of the organic polysiloxane proceeds in a state where the alcohol or diol remains in the film, so that the density of the obtained film is considered to decrease. Therefore, 200 to 25
Performing prebaking at 0 ° C. is effective in obtaining a low-density film. In the prebaking step, the diol is more suitable for obtaining a low dielectric constant film because the diol is more likely to remain in the film by hydrogen bonding than the alcohol.

In the following study, the coating film is formed by a spin coating method, and is heated in a vertical furnace under a nitrogen atmosphere.
A final cure at 5 ° C. for 30 minutes was performed. Hardness measurement is EN
It performed using T-1100 (made by Elionix). The measurement was performed five times for one sample, and the average value was obtained. For the measurement of the relative dielectric constant, a wafer having a cured film of 0.5 to 0.6 μm formed on a low-resistance silicon wafer of 0.1 Ω · cm or less was used. An Al electrode was formed on the cured film, the capacitance of a capacitor formed of the Al electrode and the Si wafer was measured, and the relative dielectric constant was calculated from the film thickness and the electrode area. The capacity measurement was performed at 1 MHz.

When reducing the density of the organic polysiloxane,
Naturally, the higher the mechanical strength of the organic polysiloxane before the reduction in density and the lower the dielectric constant, the higher the mechanical strength of the resulting low-density film and the lower the dielectric constant. The dielectric constant of the organic polysiloxane film generally decreases as the organic content increases, but when the organic content increases, the strength of the film decreases. Therefore, in order to achieve both low dielectric constant and high mechanical strength, it is important to optimize the composition.

An alcohol or diol having a composition in which 0 to 0.5 mol of tetraalkoxysilane is added to 1 mol of methyltrialkoxysilane and having a boiling point of 250 ° C. or more at 1 atm is added to the nonvolatile component of the organic polysiloxane coating solution. When 0.4 to 0.7 part by weight is added to 1.0 part by weight, a low dielectric constant film having a relative dielectric constant of 1.9 to 2.4 and a hardness of 0.45 GPa or more can be obtained. .

The low dielectric constant film made of a polysiloxane having an organic group having a relative dielectric constant of less than 2.5 measured at 1 MHz has a relative dielectric constant of 1.9 to 2.4 and a film thickness on a silicon wafer. A film having a thickness of 0.5 to 0.6 μm is formed, and a load of 10
The hardness DHT ₁₁₅ , measured in mg, is between 0.45 and 0.5.
A film of 88 GPa is excellent as an interlayer insulating film of LSI.

[0024]

EXAMPLES Examples 1 to 5 Hydrolytic condensation reaction using tetraethoxysilane in a ratio of 0, 0.1, 0.2, 0.4, 0.5 mol per mol of monomethyltriethoxysilane Thus, polysiloxane coating liquids 1 to 5 were obtained. Monomethyltriethoxysilane and tetraethoxysilane were mixed in a flask with propylene glycol monopropyl ether as a solvent, and acetic acid diluted with water was added dropwise with stirring to carry out a reaction.
At this time, the temperature of the laboratory was 23 ° C., and the temperature of the flask was not controlled. The amount of water added was equimolar to the alkoxy group of the alkoxysilane used, and acetic acid was 0.01 mol per 1.0 mol of alkoxysilane. The non-volatile content of the coating solution is 10 to 20 so that a required film thickness can be obtained.
It was adjusted in the range of weight%. After completion of the dropwise addition of water and the catalyst, the mixture was stirred for about 2 hours, then transferred to a sealed container and left at 23 ° C. for 2 days. As a result of measuring the molecular weight of the siloxane oligomer at that time by GPC, the molecular weight was almost the same regardless of the sample, and the number average molecular weight in terms of polystyrene was about 1,000 and the weight average molecular weight was about 1500. Thereafter, it was stored in a freezer (−18 ° C.).

To the polysiloxane coating liquids 1 to 5, 0.7 or 0.4 parts by weight of 1,2-tetradecanediol was added to 1 part by weight of the non-volatile content of the polysiloxane coating liquid and dissolved. A coating solution was prepared. Using this coating solution, a coating film was formed by a spin coating method. The substrate used was a bare silicon wafer. The coating rotation speed was adjusted for each coating liquid so that the film thickness after final curing (425 ° C.) was 0.5 to 0.6 μm. After spin coating, 80 ° C / 90sec, 150 ° C /
The baking was performed continuously for 90 sec at 250 ° C./90 sec. Final curing is performed in a nitrogen atmosphere using a vertical furnace.
The treatment was performed at 425 ° C./30 min.

The hardness and relative permittivity of the obtained film were measured. Hardness was measured using a nano indentation tester ENT-1100 manufactured by Elionix, with a maximum load of 10 m.
g at a loading rate of 1 mg / sec. The measurement was performed five times per sample, and the average value was obtained. The relative permittivity is
An Al electrode having a diameter of 2 mm was formed on the film, the capacitance of the capacitor formed of the Al electrode and the silicon wafer was measured, and calculated from the film thickness and the area of the Al electrode. The capacitance was measured at 1 MHz using an impedance analyzer. The film thickness was measured using ellipsometry.

Table 1 shows the measurement results of the hardness and the relative permittivity.
It can be seen that a low dielectric constant film having a relative dielectric constant of 1.9 to 2.4 with a hardness of 0.45 GPa or more can be obtained. If the addition amount of 1,2-tetradecanediol is increased from 0.7 parts by weight in order to obtain a film having a lower dielectric constant, the density of the film is increased and the moisture absorption of the film is increased. Increases, and a sharp increase in the relative dielectric constant occurs. Further, when the addition amount of tetraethoxysilane is increased from the coating solution 5 in order to obtain a film having higher hardness, the inorganic component increases, so that the moisture absorption of the film increases and the relative dielectric constant increases. .
Therefore, within the range of the formulation in Table 1, the relative dielectric constant is 2.
A good film having a relative dielectric constant of 1.9 to 2.4 and a hardness of 0.45 to 0.88 GPa, which is a low dielectric constant film of less than 5, can be obtained.

Particularly excellent as an interlayer insulating film of LSI is that the addition amount of alcohol and diol is 0.4 to 0.7 parts by weight with respect to 1 part by weight of the non-volatile content of the polysiloxane coating solution. 5 is used. At this time, the film hardness is 0.52 to 0.88 GPa,
A relative dielectric constant film having a relative dielectric constant of 2.0 to 2.4 and excellent in mechanical strength can be obtained.

In the coating solutions 1 to 5, instead of tetraethoxysilane, trialkoxysilane HSi (OR) ₃
Similar results were obtained when (R is an alkyl group having 1 to 5 carbon atoms). In that case, the heat resistance of the film is slightly reduced,
This is a range applicable as an interlayer film of an LSI.

[0030]

[Table 1]

[0031]

Since the low dielectric constant film of the present invention has a high mechanical strength, it can be applied as an interlayer insulating film of a semiconductor device, thereby improving the CMP resistance, securing a wide process margin, and improving the performance of an LSI. And high reliability and high yield are achieved.

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Nobuko Terada 4-3-1 Higashicho, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Office F-term (reference) 5F033 QQ48 RR23 RR25 SS21 WW02 WW09 XX35 5F058 AA08 AC03 AD05 AF04 AG01

Claims (4)

[Claims] 1. The method according to claim 1, wherein the thickness of the silicon wafer is 0.5 to 0.5.
A low dielectric constant film having a film thickness of 6 μm, a hardness DHT ₁₁₅ of 0.45 GPa or more when measured at a load of 10 mg, and a relative dielectric constant of 1.9 to 2.4 measured at 1 MHz. 2. The low dielectric constant film according to claim 1, which is a film made of polysiloxane having an organic group. 3. The low dielectric constant film according to claim 1, wherein the low dielectric constant film is formed by a spin coating method using an organic polysiloxane coating solution containing a monohydric alcohol or a dihydric alcohol having a boiling point of 250 ° C. or more at 1 atm. . 4. A semiconductor device using the low dielectric constant film according to claim 1, 2 or 3 as an interlayer insulating film of a multilayer wiring.