JP2002319582A - Coating liquid for forming silica based coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating liquid for forming a silica based coating of low permittivity. SOLUTION: A silica based coating having permittivity not higher than 3.2 can be formed on a substrate by adding one kind selected from (a) a condensate obtained by subjecting trialkoxy silane to hydrolysis in an organic solvent under an acid catalyst, and (b) polyalkylene glycol and its end alkylate and a low permittivity can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating liquid for forming a low dielectric constant silica-based coating used in, for example, a damascene method.

[0002]

2. Description of the Related Art The demand for higher integration of semiconductor devices is increasing, and the gate length is approaching the 0.13 μm generation. As a wiring material in this case, a conventional A
It has been found that the use of Cu instead of l can improve the characteristics of the semiconductor element in the following points.

[0003] Cu is superior in resistance to EM (electromigration) compared to Al, and because of its low resistance, it can reduce signal delay due to wiring resistance and can use a high current density. That is, the allowable current density can be reduced by three times or more. In addition, the wiring width can be reduced.

However, since the control of the etching rate of Cu is more difficult than that of Al, the copper damascene (inlaid) method has recently attracted attention as a method of realizing a multilayer wiring of Cu without etching Cu, and many proposals have been made. (JP-A-2000-174,023, JP-A-200
0-174,121).

A copper damascene method will be described with reference to FIG.
First, as shown in FIG. 3A, an interlayer insulating film, which is a low dielectric constant material made of SiO2 or SOG, is formed on a substrate by a CVD method, and a resist mask having a pattern formed thereon is formed thereon. Then, a wiring groove is formed by etching as shown in FIG. 3 (b), and then a barrier metal is deposited as shown in FIG. 3 (c), and the wiring groove is formed as shown in FIG. 3 (d). Cu is buried by electroplating or the like to form a lower wiring, and after the barrier metal and Cu are polished by CMP (chemical polishing), an interlayer insulating film is formed thereon again as shown in FIG. . In the same manner, the interlayer insulating film is selectively etched through a patterned resist mask to form via holes and trenches for upper wiring in the interlayer insulating film as shown in FIG. Damascene), and as shown in FIG.
A barrier metal is deposited in the via hole and the upper wiring groove, and Cu is buried in the via hole and the upper wiring groove by electrolytic plating or the like to form an upper wiring as shown in FIG.

Although the damascene method has been described mainly on copper as a metal forming wiring, the damascene method is also being carried out using aluminum in addition to copper. The present invention is not limited to the copper damascene method, but is widely used in a damascene method using a conductive metal.

[0007]

As described above, when forming a multilayer wiring by the damascene method, it is an essential requirement for miniaturization to increase the aspect ratio (height / width) of the via hole. However, when SiO2 formed by CVD is used as the interlayer insulating film material, the aspect ratio is at most 2 and the dielectric constant of SiO2 is ε =
It is not satisfactory because it is relatively high at 4.1.

It is now known that the dielectric constant of an interlayer insulating film can be lowered by making the interlayer insulating film porous. However, the lower the dielectric constant of the interlayer insulating film, the lower the denseness of the film. Therefore, when the resist film is plasma-ashed in a later step, the interlayer insulating film is damaged or cracked, and a highly reliable semiconductor element is manufactured. It becomes difficult to obtain.

The above-mentioned damage to the interlayer insulating film is caused by the fact that the Si-R group (R is a lower alkyl group or a hydrogen atom) of the interlayer insulating film is decomposed by the ashing (the R group is separated) and a Si-OH bond is generated. It is presumed to be caused by. For example, in the case of organic SOG, the Si-CH3 bond (CH3 is an example) is broken to form Si-OH, and in the case of inorganic SOG, the Si-H bond is broken to form Si-OH.

Therefore, organic or inorganic S having a lower dielectric constant is used.
The use of OG is being considered. Further, further reduction in the dielectric constant of such organic or inorganic SOG is desired. In particular,
The dielectric constant required for the interlayer insulating film used in the damascene method is 3.2 or less.

[0011]

In order to solve the above-mentioned problems, a coating solution for forming a silica-based film according to the present invention forms a silica-based film having a dielectric constant of 3.2 or less (preferably 2.7 or less). A (a) condensate obtained by hydrolyzing a trialkoxysilane in an organic solvent under an acid catalyst, and (b) one selected from a polyalkylene glycol and a terminal alkylated product thereof. Including the configuration.

As the component (a) of the coating solution, in particular, trialkoxysilane is dissolved in an alkylene glycol dialkyl ether at a concentration of 1 to 5% by weight in terms of SiO2. 5
After adding 3.0 mol of water and carrying out hydrolytic condensation in the presence of an acid catalyst, it is preferable to adjust the content of alcohol produced by the reaction in the reaction mixture to 15% by weight or less.

In the above description, the reason why the concentration of trialkoxysilane is set to 1 to 5% by weight in terms of SiO2 is that an interlayer insulating film having a ladder structure is obtained. Regardless of whether it is organic or inorganic, a ladder structure is preferable because a dense film is formed and the dielectric constant is low as described above.

Examples of the trialkoxysilane include trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, diethoxymonomethoxysilane, monomethoxydipropoxysilane, dibutoxymonomethoxysilane, ethoxymethoxypropoxysilane, Monoethoxydimethoxysilane, monoethoxydipropoxysilane, butoxyethoxypropoxysilane, dimethoxymonopropoxysilane, diethoxymonopropoxysilane, monobutoxydimethoxysilane and the like can be mentioned. Among these, practically preferred compounds are trimethoxysilane, triethoxysilane,
Tripropoxysilane and tributoxysilane are preferred, and among them, trimethoxysilane and triethoxysilane are particularly preferred.

Next, it is necessary to use an alkylene glycol dialkyl ether as a solvent in order to enhance storage stability. By using this, it is possible to suppress the decomposition reaction of the H-Si group of the trialkoxylan and the reaction in which the hydroxyl group of the silanol generated in the middle is replaced with the alkoxy group in the conventional method using the lower alcohol as the solvent, Gelling can be prevented.

Examples of the alkylene glycol dialkyl ether include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, and propylene glycol. Examples thereof include dialkyl ethers of alkylene glycol such as dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, and propylene glycol dibutyl ether. Preferred among these are dialkyl ethers of ethylene glycol or propylene glycol, especially dimethyl ether. These organic solvents may be used alone or 2
It may be used in combination of more than one kind. With respect to the amount of use, it is used in a ratio of 10 to 30 mole times with respect to 1 mole of alkoxysilane.

Water for hydrolyzing trialkoxysilane is used in an amount of 2.5 to 1.5 mol per mol of trialkoxysilane.
It is necessary to use an amount in the range of 3.0 moles, preferably 2.8 to 3.0 moles, in order to increase the degree of hydrolysis. If the amount is less than this range, the storage stability increases, but the degree of hydrolysis decreases, the content of organic groups in the hydrolyzate increases, and gas is generated during film formation,
On the other hand, if the amount is too large, the storage stability deteriorates.

Even if at least one selected from alkylene glycol dialkyl ethers is used without using an alcohol as a solvent, the alcohol corresponding to the alkoxy group is inevitably generated in the hydrolysis of alkoxysilane. The resulting alcohol must be removed from the system. Specifically, it is necessary to remove the alcohol to 15% by weight or less, preferably 8% by weight or less in the coating solution. If the alcohol content remains in excess of 15% by weight, the H-Si group reacts with the generated alcohol to generate an RO-Si group, which lowers the crack limit and generates gas during film formation, This may cause the trouble described above.

As a method for removing the alcohol, a degree of vacuum of 3
0 to 300 mmHg, preferably 50 to 200 mmH
g, a method of performing distillation under reduced pressure at a temperature of 20 to 50 ° C. for 2 to 6 hours is preferable. The coating liquid thus obtained shows that the film-forming component after solvent removal shows an increase in weight when measured by thermogravimetry (TG), and that the film-forming component has an infrared absorption spectrum of 30%.
It is characterized by having no peak at 00 cm-1. In the case of a conventional coating solution such as the coating solution described in JP-A-4-216827, upon thermogravimetry, the weight loss is indicated,
In the infrared absorption spectrum, it has a peak near 3000 cm -1, indicating that a residual alkoxy group is present.

On the other hand, in the coating solution,
It is necessary to include one selected from polyalkylene glycol and its terminal alkylated product. By including these, the interlayer insulating film is made porous and the dielectric constant is lowered.

Examples of the polyalkylene glycol include poly-lower polyalkylene glycols such as polyethylene glycol and polypropylene glycol. The term "alkylated at the terminal" means that the hydroxyl group at one or both terminals of the poly-lower alkylene glycol is a methyl group or an ethyl group. ,
It has been alkoxylated with a lower alkyl group such as a propyl group.

Here, the addition amount of one kind selected from polyalkylene glycol and its terminal alkylated product is from 10% by weight to 500% by weight, preferably from 50% by weight to 200% by weight, based on the solid content of the coating solution. % By weight. The weight average molecular weight of the polyalkylene glycol and its terminal alkylated product is 100 to 10,000, preferably 2
00 to 5,000. Within this range, a low dielectric constant can be easily achieved without impairing the compatibility of the coating solution.

An example of a method for manufacturing a semiconductor device using the coating liquid according to the present invention comprises the following steps. (1) A step of forming a silica-based coating having a dielectric constant of 3.2 or less (preferably 2.7 or less) on a substrate. (2) A step of providing a resist pattern on the silica-based coating. (3) A step of etching the silica-based coating using the resist pattern as a mask. (4) A step of treating the silica-based coating with plasma derived from an inert gas such as helium gas. (5) a step of subjecting the resist pattern to an ashing process using plasma induced from oxygen gas.

The silica-based coating is formed by, for example, applying a coating solution onto a substrate such as a semiconductor substrate, a glass substrate, a metal plate, or a ceramic substrate by a spinner method, a roll coater method, an immersion pulling method, a spray method, or a screen printing method. Then, it is applied by a brush coating method or the like, and dried to disperse the solvent to form a coating film. Next, it is formed by firing at a temperature of 250 to 500C. (2), (3) and (5)
May be a conventional means conventionally performed.

Conditions for treating the silica-based coating with plasma derived from an inert gas such as helium gas include a plasma processing apparatus capable of generating a plasma gas from the gas (for example, TCA- manufactured by Tokyo Ohka Kogyo Co., Ltd.). 7
822) at a pressure of 10 to 600 mTorr (millitorr), preferably 100 to 500 mTorr, and 30 to 30 mTorr.
Plasma treatment is performed for 0 second, preferably 30 to 120 seconds.

The plasma processing apparatus is TCA-782
2, but is not limited to this device.
As the inert gas, in addition to helium, neon, argon, and the like are also preferable.

[0027]

Embodiments of the present invention will be described below. (Preparation of Coating Solution) Reference Example 1 (Coating Solution 1) Triethoxysilane 7 having a concentration of 3% by weight in terms of SiO2
3.9 g (0.45 mol) was dissolved in 799.0 g (8.87 mol) of ethylene glycol dimethyl ether and stirred. Next, a mixture of 24.2 g (1.34 mol) of pure water and 5 ppm of concentrated nitric acid was added dropwise while slowly stirring, followed by stirring for about 3 hours, and then allowed to stand at room temperature for 6 days to obtain a solution. 120-140m of this solution
Vacuum distillation was performed at mHg and 40 ° C. for 1 hour to prepare a coating solution having a solid content of 8 wt% and an ethanol concentration of 3 wt%. This solution was used as coating solution 1. The dielectric constant of the coating formed from this coating liquid 1 was 3.1.

Example (Coating solution 2) Coating solution 1 was prepared by adding both terminal methylated products of polyethylene glycol having a weight average molecular weight of 200 to 100% by weight based on the solid content.
The mixture was added and sufficiently stirred to obtain a uniform solution. This solution was used as coating solution 2. The dielectric constant of the film formed from this coating solution 2 was 2.6.

Reference Example 2 (Coating solution 1 + He treatment) The coating solution 1 was spin-coated on a substrate to form a film having a thickness of 4500 °. The refractive index of this film was 1.40. Next, a resist pattern is formed on the film,
Etching was performed using this resist pattern as a mask to form a wiring groove. Next, a helium gas concentration of 700 sc
Plasma treatment was performed at a pressure of 500 mTorr for 30 seconds. Thereafter, ashing was performed by oxygen plasma at a pressure of 1000 mTorr for 300 seconds using a batch type plasma ashing apparatus (OPM-EM1000, manufactured by Tokyo Ohka Kogyo Co., Ltd.). FIG. 1 shows an infrared absorption spectrum of the coating after the ashing. In FIG. 1, a peak indicating Si-R (R is a hydrogen atom) clearly appears, which indicates that the coating film is not damaged.

Reference Example 3 (coating solution 2 + He treatment) In Reference Example 2, except that the coating solution was changed from 1 to 2,
Ashing was performed in the same manner as in Reference Example 2. FIG. 2 shows an infrared absorption spectrum of the coating after the ashing. In FIG. 2, a peak indicating Si-R (R is a hydrogen atom) clearly appears, indicating that the coating film is not damaged.

[0031]

As described above, according to the coating liquid of the present invention, (a) a condensate obtained by hydrolyzing a trialkoxysilane in an organic solvent in the presence of an acid catalyst; b) A silica-based coating having a dielectric constant of 3.2 or less can be formed on a substrate by including one selected from a polyalkylene glycol and a terminal alkylated product thereof. The dielectric constant of the system coating is reduced, which is advantageous for miniaturization.

[Brief description of the drawings]

FIG. 1 is an infrared absorption spectrum of a coating formed in Reference Example 2 after the resist on the coating is subjected to ashing.

FIG. 2 is an infrared absorption spectrum of a coating formed in Reference Example 3 after the resist on the coating is subjected to an ashing process.

FIGS. 3A to 3H are diagrams illustrating a process of forming a multilayer wiring structure by a copper damascene method.

Continued on the front page F term (reference) 5F033 HH11 JJ11 MM02 MM12 MM13 NN06 NN07 QQ00 RR04 RR09 RR25 RR29 SS22 5F058 BA20 BC05 BF46 BF47 BH01

Claims (6)

[Claims] 1. A coating liquid for forming a silica-based coating having a dielectric constant of 3.2 or less, comprising: (a) a condensate obtained by hydrolyzing a trialkoxysilane in an organic solvent under an acid catalyst; b) A coating solution for forming a silica-based film, which comprises one selected from polyalkylene glycols and their terminal alkylated products. 2. The coating solution for forming a silica-based film according to claim 1, wherein the content of the polyalkylene glycol and its terminal alkylated product is 10 to 500% by weight based on the solid content of the coating solution. A coating solution for forming a silica-based film, characterized in that: 3. The coating solution for forming a silica-based film according to claim 1, wherein the weight average molecular weight of the polyalkylene glycol and its terminal alkylated product is 100 to 10,
A coating solution for forming a silica-based film, which is in the range of 000. 4. The coating solution for forming a silica-based film according to claim 1, wherein the organic solvent is an alkylene glycol dialkyl ether. 5. The coating solution for forming a silica-based film according to claim 1, wherein the coating solution has an alcohol content of 15%.
A coating liquid for forming a silica-based film, which is not more than 10% by weight. 6. The coating liquid for forming a silica-based coating according to claim 1, wherein the obtained silica-based coating has a ladder structure.