WO2005122228A1

WO2005122228A1 - Method for preparing a gap-filling dielectric film

Info

Publication number: WO2005122228A1
Application number: PCT/US2005/018572
Authority: WO
Inventors: Paul J. Popa; Kevin E. Howard; Randy D. Woods
Original assignee: Dow Global Technologies Inc.
Priority date: 2004-06-07
Filing date: 2005-05-25
Publication date: 2005-12-22

Abstract

A patterned substrate containing gaps and suitable for pre-metal dielectric (PMD) or shallow trench isolation (STI) devices can be spin-coated with a solution of a polymer resin of a trihydrolyzable silane and a tetraalkylorthosilicate; upon solvent removal and curing, theresin forms a crosslinked dielectric material that fills the gaps and is virtually free of voids.

Description

METHOD FOR PREPARING A GAP-FILLING DIELECTRIC FILM

Background of the Invention

The present invention relates to a method for preparing a gap-filling dielectric film. The fabrication of integrated circuits requires the deposition of a dielectric material into very small gaps between features patterned over or into silicon substrates. A continuing challenge for applications such as pre-metal dielectric (PMD) and shallow trench isolation (STI) devices is to completely fill these gaps, which have widths on the order of tens of nanometers, depths on the order of hundreds of nanometers, and aspect ratios (depth:width) of four or greater. A further challenge is to fill the gaps with a relatively dense, void-free dielectric material to withstand high temperatures and etch as these steps are required in the process of building the integrated circuit.

Dielectric materials can be deposited by chemical vapor deposition (CVD) or by spin-on processes, but each of these techniques fall short of providing a completely filled void-free dielectric material into the gap. Plasma enhanced chemical vapor deposition (PECVD) provides high deposition rates at comparatively low temperatures, but this technique suffers from a differential deposition rate, which creates structural overhang, thereby leading to undesirable voids.

Other techniques used in PMD applications include depositing phosphosilicate glass or borophosphosilicate glass by atmospheric pressure CVD, sub-atmospheric pressure CVD, or low pressure CVD. Although these vapor deposition methods provide nearly conformal coating, they require long deposition times. Moreover, as requirements for gap widths become smaller, vapor deposition coating methods become less effective in filling gaps.

In US 6,444,495, Leung et al. describes spin-coating, curing, and annealing a colloidal dispersion of a silicon solution onto a wafer to form a crack-free porous film; this step is followed by infiltrating the film with a matrix material such as a boron-doped silsequioxane material to minimize or eliminate the pores. Although the process is said to be effective in filling gaps with no delamination, it requires two separate coatings and, therefore, two series of coating, curing, and annealing. It would, therefore, be an advance in the art of dielectric films for gap-fill applications to provide a dense and virtually void- free dielectric in a single step.

Summary of the Invention

The present invention addresses a need in the art by providing a method comprising the steps of a) coating a substrate that has gaps with a gap-filling solution containing 1) a solvent; and 2) a polymer resin formed by the hydrolysis and condensation of a trihydrolyzable silane and a tetraalkylorthosilicate; b) removing solvent from the solution; and c) curing the resin; wherein the trihydrolyzable silane is represented by the formula R-Si(X)₃, wherein R is either H or a group that contains a carbon atom attached to the Si atom; and wherein each X is independently halo, alkoxy, acetoxy, or acyloxy.

In a second aspect, the present invention is a method of filling gaps comprising the steps of a) spin-coating a solution containing a solvent and a polymer resin having structural units of R-Si0_3/2 and Si0₂ onto a patterned silicon wafer with shallow trench isolation or pre-metal dielectric topography; b) removing solvent from the solution; and c) curing the resin; wherein R is a monovalent group that contains a carbon atom attached to the Si atom.

In a third aspect, the invention is a composite that comprises a patterned silicon wafer with shallow trench isolation or pre-metal dielectric topography, which wafer contains gaps that are filled with a dielectric polymeric resin having structural units of R-Si0_3/2 and Si0₂, wherein a) R is a monovalent group that contains a carbon atom attached to the Si atom; and b) the number of structural units of R-Si0_{3 2} in the resin exceeds the number of structural units of Si0₂.

Detailed Description of the Invention

The present invention relates to a method comprising a) coating a substrate that contains gaps with a gap-filling solution containing one or more solvents and a polymer resin of a trihydrolyzable silane and a tetraalkylorthosilicate; b) removing the solvent from the solution; and c) curing the resin. The substrate is preferably a patterned silicon substrate with PMD or STI topography. As used herein, a trihydrolyzable silane is a substituted or unsubstituted silane that contains three groups that can be converted to hydroxyl groups by treatment with acid. The trihydrolyzable silane can be represented by the formula R-Si(X)₃, wherein R is either H or a group that contains a carbon atom attached to the Si atom; and wherein each X is independently halo, alkoxy, acetoxy, or acyloxy. Each X is preferably a Cι_-6-alkoxy group, more preferably a methoxy or ethoxy group; and R is preferably a Cι_-6-alkyl, a phenyl, or a vinyl group.

As used herein, a polymer resin of a trihydrolyzable silane and a tetraalkylorthosilicate refers to a resin that is formed from the hydrolysis and condensation of a trihydrolyzable silane and a tetraalkylorthosilicate or a partially hydrolyzed tetralkylorthosilicate.

The polymer resin of the trihydrolyzable silane and the tetraalkylorthosilicate can be prepared by reacting, under hydrolysis, condensation, and polymerization conditions, a trihydrolyzable silane with a tetraalkylorthosilicate. Preferably, the hydrolysis and polymerization is carried out by slow addition of a mixture of a trialkoxysilane and a tetraalkylorthosilicate with an acid and water at a temperature in the range of from about 0° C, more preferably from about 15° C, to about 40° C, more preferably to about 30° C. Examples of suitable acids include Brόnsted acids such as acetic acid, formic acid, propionic acid, citric acid, hydrochloric acid, sulfuric acid, and phosphoric acid. Alternatively, the polymer resin can be prepared by partially hydrolyzing the tetraalkylorthosilicate prior to reaction with the trihydrolyzable silane. Partial hydrolysis can be accomplished, for example, by contacting the tetraalkylorthosilicate with the hydrolyzing acid and water in the presence of the solvent prior to contact with the trihydrolyzable silane. The trihydrolyzable silane can either be unsubstituted or substituted with a group that contains a carbon atom attached to the silicon atom of the trialkoxysilyl group or trihalosilyl group. Examples of unsubstituted trialkoxysilanes include tri- Cι_-6-alkoxysilanes such as triethoxysilane and trimethoxysilane; examples of substituted trialkoxysilanes include alkyltri-Cι_-6-alkoxysilanes; aryltri-Cι_₆-alkoxysilanes; and vinyltri- Cι_-6-alkoxysilanes. Preferred substituted trialkoxysilanes include methyltrimethoxysilane, ethyltrimethoxysilane, triisopropoxysilane, n-propyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, n-propyltriethoxysilane, trimethoxysilane, triethoxysilane, methacryloxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, aminopropyltriethoxysilane, n-phenyl-γ-aminopropyltrimethoxysilane, γ- glycidoxypropyltrimethoxysilane, b-(3,4)-epoxycyclohexylethyltrimethoxysilane; methyltrimethoxysilane and methyltriethoxysilane are more preferred, and methyltrimethoxysilane is most preferred. Examples of unsubstituted trihalosilanes include trichlorosilane and tribromosilane, with trichlorosilane being a preferred unsubstituted trihalosilane; examples of substituted trihalosilanes include methyltrichlorosilane, ethyltrichlorosilane, vinyltrichlorosilane, phenyltrichlorosilane, and n-propyltrichlorosilane.

Examples of suitable tetraalkylorthosilicates include tetraethylorthosilicate (TEOS) and tetramethylorthosilicate (TMOS) with TEOS being preferred. The mole:mole ratio of the trihydrolyzable silane to the tetralkylorthosilicate is preferably not less than 50:50, more preferably not less than 70:30; and is preferably not greater than 95:5.

The formation of the polymer resin results in the creation of hydrolysis byproducts such as ethanol, methanol, isopropanol, and water. These byproducts are advantageously removed by heat or in vacuo or a combination thereof, preferably with the aid of a solvent, which, as used herein, refers to one or more solvents. Examples of such solvents include C₅-ι₂ linear, branched, or cyclic alkanes such as hexane, heptane, and cyclohexane; ethers such as tetrahydrofuran, dioxane, ethylene glycol diethyl ether, and ethylene glycol dimethyl ether; ketones such as methyl isobutyl ketone, methylethyl ketone, and cyclohexanone; acetates such as butyl acetate, and propylene glycol methyl ether acetate; halogenated solvents such as trichloroethane, bromobenzene, and chlorobenzene; and silicone solvents such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane; and combinations thereof.

A preferred solvent has a boiling point at least as high as that of the highest boiling hydrolysis byproduct; preferably the solvent system contains a solvent having a boiling point of not less than 100° C. A more preferred solvent is a glycol ether ester, such as DOWANOL™ PMA glycol ether acetate (a trademark of The Dow Chemical Company). The concentration of the polymer in the solvent is application dependent but is generally in the range of from about 10 to about 30 weight percent, based on the weight of the polymer and the solvent.

The solution of the polymer of the trihydrolyzable silane and the tetraalkylorthosilicate is coated onto a patterned silicon substrate containing gaps to form a coating of the desired thickness. The coating can be carried out by a variety of techniques, including spin-coating, dip-coating, and spray-coating, with spin-coating being preferred. The solvent is then removed, preferably with heat, to form a composite of a substrate whose gaps (including trenches and vias) have been filled and at least partially planarized with a polymer resin that contains structural units of R-Si0_3/2 (also known as silsequioxanes units) and Si0₂ (sometimes referred to as Si0_4/2), wherein R is a monovalent group that contains a carbon atom bonded to the Si atoms and wherein number of R-Si0_3/2 groups in the resin preferably exceeds the number of Si0₂ group. Preferably, R is methyl or ethyl, more preferably methyl; preferably, the mole:mole ratio of R-Si0_3/2 groups to Si0₂ groups in the resin is from 70:30 to about 95:5.

The resin is then cured and annealed by heating, preferably to a temperature in the range of about 400° C to about 1000° C. The subsequently formed silicon oxide coating is preferably substantially free of voids.

The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example 1 - Me/TEOS Dielectric Resin

Methyltrimethoxysilane (MTMS, 125 g, 0.92 mole) and tetraethylorthosilicate (TEOS, 19.46 g, 0.094 mole) were pre-mixed and added with stirring over 90 minutes at room temperature to flask containing a stoichiometric amount of 3N acetic acid. After completion of the silane addition, stirring was continued for 30 minutes, whereupon DOWANOL® PMA glycol ether acetate (137 g) was added to the flask. A Dean-Stark trap was attached to the flask and the solution was ramped to 125° C with concomitant removal and collection of methanol, ethanol, and water. Once the temperature reached 125° C, heating was discontinued and 75 g of the glycol ether acetate was added to the reaction mixture. The resulting resin (Me TEOS) was found to have a M_w of about 4100 Daltons and a degree of substitution (DS) of 0.91.

The resin was puddled onto a patterned silicon wafer with Shallow Trench Isolation topography having gap widths on the order of 100 nm and gap depths on the order of 400 nm. The resin was spun dry (1500 rpm for 30 seconds) to produce a film of desired thickness. The wafer was then heated to 150° C for 120 seconds in air. The resin was then cured in two steps in a quartz tube furnace. In the first step, air was flowed through the tube at 12 scfh (5.7 L/min) and the wafer was heated to 600° C with a 10 C min ramp and held for 60 minutes. In the second step, the air stream was replaced with a nitrogen purge at 12 scfh (5.7 L/min) and the temperature was held at 600° C for an additional 12 minutes. The furnace was heated with continued nitrogen purge to 1000° C and a 10 C min ramp and held for 60 minutes. The furnace was then cooled under flowing nitrogen at a rate not exceeding 10 C7min. A TEM of the resin-filled gap showed substantially no voids. The thickness of the layer was found to be about 175 nm.

Example 2 - 70/30 Me/TEOS Siloxane Resin

A siloxane resin with a DS of 0.70 was prepared by adding (54.74 g, 3.04 mole) of 3N acetic acid to a 500 mL round bottom flask equipped with an addition funnel and maintained at room temperature. MTMS (87.74 g, 0.645 mole) and TEOS (57.52 g, 0.276 moles) were added to the acetic acid with stirring by way of the addition funnel over 100 minutes. After the addition was complete, the material was allowed to mix for an additional 35 minutes, whereupon DOWANOL® PMA glycol ether acetate (120 g) was added to the flask. The flask was re-equipped with a thermometer and a Dean-Stark trap, then ramped up to 125°C with concomitant removal and collection of methanol, ethanol, and water. Once the temperature reached 125°C, an additional 70 g of DOWANOL® PMA was added to the flask and heating was discontinued. The material was allowed to cool and was filtered. The percent non-volatile (solids content) of the polymer resin was 27.7% non-volatiles. The M_w was found to be approximately 13,000 Daltons.

This material was coated on a patterned wafer and processed by placing the wafer on a hot plate at 150°C for 2 minutes in air; then heating the wafer to 750° C for 60 minutes in air; then heating the wafer for an additional 60 minutes at 750° C under a blanket of nitrogen. This wafer also had very good in-feature density with very few small voids within the feature.

Example 3 - 91/9 Me/TEOS Siloxane Resin from Methyltriethoxysilane and TEOS 3N acetic acid (46.90 g, 2.61 moles) was added to a 500 mL round bottom flask equipped with an addition funnel and maintained at room temperature. Methyltriethoxysilane (MTES, 136.82 g, 0.769 mole, obtained from Aldrich, Milwaukee, WI) and TEOS (16.26 g, 0.078 mole) were added to the flask by way of the addition funnel over 90 minutes. After the addition was complete, the material was allowed to mix for an additional 45 minutes, whereupon DOWANOL® PMA glycol ether acetate (135 g) was added to the flask. The flask was re-equipped with a thermometer and a Dean-Stark trap, then ramped up to 125°C with concomitant removal and collection of ethanol and water. Once the temperature reached 125°C, 70 g of DOWANOL® PMA was added to the flask and heating was discontinued. The contents of the flask were allowed to cool, then filtered. The percent non-volatile of the siloxane resin was 25.7%. The M_w was approximately 3900 Daltons. The in-feature density of this material was not evaluated.

Example 4 - 91/9 Me/TEOS Siloxane Resin

A siloxane resin with a DS of 0.91 was prepared from MTMS and TEOS at a mole ratio of 91/9 MTES/TEOS. The TEOS was partially pre-hydrolyzed prior to adding the MTMS. TEOS (19.46 g, 0.094 mole) and DOWANOL™ PMA glycol ether acetate (20 g) were charged into a 500 mL round bottomed flask. 3N acetic acid (3.37 g, 0.187 mole) was added over 30 minutes to the flask, whereupon MTMS (125 g, 0.92 moles) was added to the flask followed by the addition of more acetic acid (52.13 g, 2.90 moles) over 80 minutes. Then, 137 g of DOWANOL® PMA was added to the flask. The flask was re- equipped with a thermometer and a Dean-Stark trap, then ramped up to 125°C with concomitant removal and collection of methanol, ethanol, and water. Once the temperature reached 125°C, 80 g of additional DOWANOL® PMA was added to the flask and heating was discontinued. The contents of the flask were allowed to cool, then filtered. The percent non-volatiles of the siloxane resin was 26%. The M_w was approximately 2900 Daltons. The resin was puddled onto a patterned silicon wafer with Shallow Trench Isolation topography having gap widths on the order of 100 nm and gap depths on the order of 400 nm. The resin was spun dry (1440 rpm for 30 seconds) to produce a film of desired thickness. The wafer was then heated to 150° C for 90 seconds in air. The resin was then cured in two steps in a quartz tube furnace. In the first step, air was flowed through the tube at 12 scfh (5.7 L/min) and the wafer was heated to 600° C with a 10 C7min ramp and held for 60 minutes. In the second step, the air stream was replaced with a nitrogen purge at 12 scfh (5.7 L/min) and the temperature was held at 600° C for an additional 12 minutes. The furnace was heated with continued nitrogen purge to 1000° C and a 10 C7min ramp and held for 60 minutes. The furnace was then cooled under flowing nitrogen at a rate not exceeding 10 C min. This wafer also had good in-feature density with few small voids within the feature.

Claims

WHAT IS CLAIMED IS:

1. A method comprising the steps of a) coating a substrate that has gaps with a gap-filling solution containing 1) a solvent; and 2) a polymer resin formed by the hydrolysis and condensation of a trihydrolyzable silane and a tetraalkylorthosilicate; b) removing solvent from the solution; and c) curing the resin; wherein the trihydrolyzable silane is represented by the formula R- Si(X)₃, wherein R is either H or a group that contains a carbon atom attached to the Si atom; and wherein each X is independently halo, alkoxy, acetoxy, or acyloxy.

2. The method of Claim 1 wherein the substrate is a silicon wafer with shallow trench isolation or pre-metal dielectric topography; and wherein each X is Cι_-6- alkoxy; and R is C_1-6-alkyl, phenyl, or vinyl.

3. The method of Claim 2 wherein the polymer resin is prepared by contacting a mixture of a tetraalkylorthosilicate and a trihydrolyzable silane with an acid and water.

4. The method of Claim 2 wherein the polymer resin is prepared by contacting the trihydrolyzable silane with a partially hydrolyzed tetraalkylorthosilicate, the solvent, an acid, and water.

5. The method of Claim 1 wherein the solvent includes a compound having a boiling point of not less than 100° C.

6. The method of Claim 1 wherein the trihydrolyzable silane is methyltrimethoxysilane or methyltriethoxysilane; and the tetraalkylorthosilicate is tetraethylorthosilicate or tetramethylorthosilicate.

7. The method of Claim 2 wherein the polymer contains structural units of R- Si0_{3 2} and Si0₂, wherein R is a monovalent group that contains a carbon atom attached to the Si atom and wherein the number of R-Si0₃/₂ groups exceeds the number of Si0₂ groups.

8. The method of Claim 7 wherein R is methyl or ethyl.

. The method of Claim 8 wherein the solvent includes a glycol ether ester.

10. A method of filling gaps comprising the steps of a) spin-coating a solution containing a solvent and a polymer resin having structural units of R-Si0_3/2 and Si0₂ onto a patterned silicon wafer with shallow trench isolation or pre- metal dielectric topography; b) removing solvent from the solution; and c) curing the resin; wherein R is a monovalent group that contains a carbon atom attached to the Si atom.

11. The method of Claim 10 wherein R is C_1-6-alkyl or phenyl and wherein the number of structural units of R-Si0_{3 2} in the resin exceeds the number of structural units of Si0₂.

12. The method of Claim 11 wherein R is methyl or ethyl; and wherein the ratio of structural units of R-Si0_3/2 to Si0₂ is not less than 70:30 and not greater than 95:5.

13. A composite that comprises a patterned silicon wafer with shallow trench isolation or pre-metal dielectric topography, which wafer contains gaps that are filled with a dielectric polymeric resin having structural units of R-Si0_3/2 and Si0 , wherein a) R is a monovalent group that contains a carbon atom attached to the Si atom; and b) the number of structural units of R-Si0_3/2 in the resin exceeds the number of structural units of Si0₂.

14. The composite of Claim 13 wherein R is methyl or ethyl and the ratio of structural units of R-Si0_{3 2} to Si0₂ in the resin is 70:30 to 95:5.