GB2372996A - Preparation of silicone resins - Google Patents

Abstract

A silicone resin is prepared by reacting 10-90 mole% of a chlorosilane of the formula RSiCl3 and/or 10-70 mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl and/or 10-80 mole% of a tetrahydroxydisiloxane of the formula (HO)2Si(R)-O-(R)Si(OH)2 with 10-90 mole% of a chlorosilane of the formula R'SiCl3, where R is a thermally labile alkyl, substituted alkyl or cycloalkyl group and R' is H or a thermally stable organic group, in the presence of a dipolar aprotic solvent which is at least partially miscible with water.

Description

PREPARATION OF SILICONE RESINS [0001] This invention relates to a process for the preparation of silicone resins containing thermally labile groups, to the resins prepared thereby, and to a method for making nanoporous silicone resins, including substrates coated with nanoporous silicone resins, from the silicone resins having thermally labile groups. The resulting nanoporous silicone resins have low dielectric constant and improved mechanical properties and are useful as insulating films in semiconductor devices.

[0002] WO-A-98/49721 describes a process for forming a nanoporous dielectric coating on a substrate. The process comprises the steps of blending an alkoxysilane with a solvent composition and optional water; depositing the mixture onto a substrate while evaporating at least a portion of the solvent; placing the substrate in a sealed chamber and evacuating the chamber to a pressure below atmospheric pressure; exposing the substrate to water vapor at a pressure below atmospheric pressure and then exposing the substrate to base vapor, t [0003] JP-A-10-287746 teaches the preparation of porous films from siloxane-based resins having organic substituents

which are oxidized at a temperature of 250oC. or higher. The useful organic substituents which can be oxidized at a temperature of 250oC. or higher given in this document include substituted and unsubstituted groups as exemplified by 3,3, 3-trifluoropropyl, 0-phenethyl group, t-butyl group,

2-cyanoethyl group, benzyl group and vinyl group.

Mikoshiba et al., J. Mat. Chem., 1999, 9, 591 598, report a method to fabricate angstrom size pores in poly (methylsilsesquioxane) films in order to decrease the density and the dielectric constant of the films.

Copolymers bearing methyl (trisiloxysilyl) units and alkyl (trisiloxysilyl) units are spin-coated on to a substrate and heated at 250oC. to provide rigid siloxane matrices. The films are then heated at 450 C. to 500 C. to remove thermally labile groups and holes are left corresponding to the size of the substituents.

Trifluoropropyl, cyanoethyl, phenylethyl, and propyl groups were investigated as the thermally labile substituents.

[0005] WO-A-98/47945 teaches a method for reacting trichlorosilane and organotrichlorosilane to form organohydridosiloxane polymers having a cage conformation and between approximately 0.1 to 40 mole percent carboncontaining substituents. Resins formed from the polymers are reported to have a dielectric constant of less than 3.

WO-A-98/47941, WO-A-98/47942 and WO98-A-47944 have similar disclosures, and WO-A-00/75975 and WO-A-00/75979 prepare siloxane resins by a similar process.

EP-A-786489 describes a curable polymethyl silsesquioxane which is produced by hydrolyzing a methyltrihalosilane and subjecting the product of the hydrolysis to a condensation reaction in a two-phase system consisting of (1) water and (2) a solvent selected from (a) an oxygen-containing organic solvent or (b) an oxygencontaining organic solvent in a mixture containing a hydrocarbon solvent incorporated therein in an amount of less than 50 vol. %.

[0007] A process according to the present invention for the preparation of a silicone resin comprises reacting 10-90 mole% of a chlorosilane of the formula RSiC13 and/or 10-70 mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl and/or 10-80 mole% of a tetrahydroxydisiloxane of the formula (HO) 2Si (R)-O- (R) Si (OH) 2 with 10-90 mole% of a chlorosilane of the formula R'SiC13, where R is a thermally labile alkyl, substituted alkyl or cycloalkyl group and R' is H or a thermally stable organic group, in the presence of a dipolar aprotic solvent which is at least partially miscible with water.

Where a chlorosilane of the formula RSiC13 and/or R2R'SiCl or R3SiCl is reacted with a chlorosilane of the formula R'SiCl3, the reaction is carried out in the presence of water as well as the dipolar aprotic solvent. Reaction

of RSiC13 forms Rosi03/2 units, also known as T units in the silicone resin. Similarly, reaction of R'SiCl3 forms R'Si03/2 T units, and reaction of (HO) 2Si (R)-O- (R) Si (OH) 2 also forms T units. Reaction of R2R'SiCl or R3SiCl forms R2R'SiOl/2 or R3SiOl/2 units, also known as M units. The chlorosilanes can be co-reacted with up to 35 mole% SiCl4, which forms Spi04/2 units, also known as Q units.

The group R generally contains at least 3 carbon atoms, preferably 4 to 20 carbon atoms, and is preferably a branched alkyl group. We have found that the presence of branched alkyl groups in the silicone resin leads to porous resins of improved strength after controlled thermal degradation. Preferred examples of groups R are t-butyl- C (CH3) 3, which is thermally labile by interaction of the beta-carbon groups present in t-butyl and the Si-C linkage as part of the overall thermal degradation. Alkyl, substituted alkyl and cycloalkyl groups having at least one aliphatic beta-carbon atom bearing H atoms are preferred groups R because of the possibility of this type of thermal degradation. Further examples of preferred branched alkyl

groups R include 2-methylpropyl (isobutyl), 2- (2, 2dimethylpropyl)-4, 4-dimethylpentyl (colloquially known as triisobutyl), 2, 2-dimethylpropyl and 2, 4, 4,-trimethylpentyl (isooctyl). Other examples of groups R are linear alkyl groups such as n-propyl, nonyl, octyl, decyl, dodecyl, hexadecyl or octadecyl. Long chain alkyl groups, for example those having 8 to 20 carbon atoms may be preferred as they lead to nanoporous resins after thermal degradation which have improved porosity and potentially lower dielectric constant. Further examples of groups R are substituted alkyl groups such as 3,3, 3-trifluoropropyl, trimethylsiloxyoctyl, methoxyoctyl, ethoxyoctyl, trimethylsiloxyhexadecyl or chlorooctyl, and cycloalkyl groups such as cyclopentyl. Resins containing a mixture of groups R, for example t-butyl groups and long chain alkyl groups, can be produced by reaction of two different RSiC13 chlorosilanes with R'SiC13.

The group R'preferably has no aliphatic betacarbon atoms bearing H atoms and is most preferably H or methyl, although phenyl is an alternative. HSiC13, forming Si03/2 groups, may be preferred when further reaction of the silicone resin is intended. CH3SiC13 may be preferred when further reaction of the silicone resin is to be avoided. In one preferred process according to the invention, 20-80 mole% of a chlorosilane of the formula RSiC13 is reacted with 20-80 mole% of the chlorosilane of formula R'SiC13. RSiC13 and R'SiC13 can be reacted in the absence of any other chlorosilane to produce a TT resin or

can be co-reacted with up to 35 mole% SiC14 to produce a TTQ resin. Most preferably, 25-50 mole% RSiC13, for example t butyl trichlorosilane or triisooctyl trichlorosilane, is reacted with 50-75 mole% R'SiC13.

[0011] In an alternative process according to the invention, 10-70, preferably 20-40, mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl, preferably a chlorosilane of the formula R2HSiCl such as di-t-butyl monochlorosilane, is reacted with 60-90 mole% of a chlorosilane of the formula R'SiC13, preferably trichlorosilane HSiC13 to produce a TM resin. A mixture of a trichlorosilane, for example t-butyl trichlorosilane, and a monochlorosilane, for example di-t butyl monochlorosilane, each containing thermally labile

groups, can be reacted with HSiC13 to produce a TTM resin.

In another process according to the invention, 1080 mole% (HO) 2Si (R)-O- (R) Si (OH) 2, particularly a tetrahydroxydisiloxane where R is branched alkyl, preferably t-alkyl, is reacted with 20-90 mole% of a trichlorosilane of the formula R'SiCl3, preferably HSiC13. The tetrahydroxydisiloxane is preferably l, 3-di-t-butyl-1, 1, 3,3tetrahydroxydisiloxane (DBDS). The tetrahydroxydisiloxane is preferably reacted with R'SiCl3 in the absence of water, although water can be present and is generally used during isolation of the product.

[0013] The reaction medium in which the reaction takes place comprises a dipolar aprotic solvent which is at least partially miscible with water. The solvent may be fully miscible with water, for example tetrahydrofuran (THF) or dioxane, or may be partially miscible with water, for example a ketone containing 4 to 7 carbon atoms such as methyl isobutyl ketone (MIBK), methyl ethyl ketone or methyl isoamyl ketone. The water miscible solvent can be used in admixture with a solvent which is immiscible with water but miscible with the dipolar aprotic solvent, for example an aromatic hydrocarbon such as toluene or xylene. Such a water immiscible solvent may aid in dissolution of chlorosilane reagents having a long chain alkyl group.

[0014] If the dipolar aprotic solvent is fully miscible with water, water is generally present in a controlled amount, for example from the amount necessary to hydrolyse the Si-Cl groups in the chlorosilanes up to 10 times that amount and most preferably 100-300 mole% based on Si-bonded Cl. If the dipolar aprotic solvent is only partially miscible with water, excess water can be present as a separate phase.

[0015] Use of a dipolar aprotic solvent allows smooth reaction producing the silicone resin in high yield. In many cases the reaction proceeds rapidly even when no catalyst is added to the reaction. When a fully water miscible solvent such as THF is used, the reaction usually proceeds rapidly without catalyst at temperatures of 40oC or below, for example at 0-25oC. Chlorosilanes, particularly trichlorosilanes, having less than about 10 carbon atoms are generally soluble in THF. When a partially water miscible solvent such as MIBK is used, the reaction usually proceeds rapidly without catalyst. Preferred temperatures for reactions in MIBK are generally in the range 0-100oC.

[0016] In some cases, particularly for long chain alkyl R groups where an aromatic hydrocarbon has been mixed with the dipolar aprotic solvent, a catalyst may be required. The

preferred catalyst is HCl. The ion exchange resin catalyst used for example in WO98/47941 causes extra complication at the purification step in order to remove trace amount of impurities particularly unsuitable for microelectronic application. The silicone resins produced according to the present invention can generally be isolated from the reaction product by extraction into a water immiscible organic solvent such as toluene followed by water washing then drying over a hygroscopic salt to remove water. The resin is thereby obtained as a solution in the water immiscible organic solvent. This solution can be used as a coating solution but usually the solvent is removed to isolate the resin. The resin can be re-dissolved in an organic solvent for application of the resin to a substrate, for example an electronic component.

[0017] To form a nanoporous silicone resin, the silicone resin is heated at a temperature sufficient to effect curing of the silicone resin and thermolysis of R groups from silicon atoms. Generally the resin is heated at a temperature of greater than 350oC. Usually, the resin is coated on a substrate and the coated substrate is heated to effect thermolysis, thereby forming a nanoporous silicone resin coating on the substrate. The resin is preferably coated on the substrate from solution in an organic solvent.

Such a coating solution may be the purified resin solution reaction product as described above, or the isolated resin can be dissolved in an organic solvent, for example an aromatic hydrocarbon such as toluene, xylene or mesitylene, a ketone such as MIBK, or an ester such as butyl acetate or isobutyl isobutyrate. The concentration of silicone resin in the organic solvent is not particularly critical to the present invention and is any concentration at which the silicone resin is soluble and which provides for acceptable flow properties for the solution in the coating process.

Generally, a concentration of silicone resin in the organic solvent of 10 to 25 weight percent is preferred. The silicone resin is coated on the substrate by standard processes for forming coatings on electronic components such as spin coating, flow coating, dip coating and spray coating.

[0018] The substrate having the silicone resin coating is heated in preferably an inert atmosphere at a temperature sufficient to effect curing of the silicone resin coating and thermolysis of R groups. The heating may be conducted as a single-step process or as a two-step process. In the two-step process the silicon resin is first heated in preferably an inert atmosphere at a temperature sufficient to effect curing without significant thermolysis of R groups. Generally, this temperature is from 20oC. to 350oC.

Then, the cured silicone resin is further heated at a

temperature of greater than 350oC to effect thermolysis. In the single-step process, the curing of the silicone resin and thermolysis of R groups are effected simultaneously by heating the substrate having the silicone resin to a temperature of greater than 350oC. Thermolysis is preferably conducted at a temperature of from greater than

350oC to 600oC, with a temperature of 400oC to 550oC being most preferred. The inert atmosphere can be any of those known in the art, for example, argon, helium or nitrogen.

The nanoporous silicone resin produced has pores less than 20 nm in diameter and usually less than about 5nm diameter, for example the nanoporous coating typically has a pore diameter in the region of 0.3 nm to 2 nm. The nanoporous silicone resins are particularly useful as low dielectric constant films on electronic devices such as integrated chips. The nanoporous silicone resin coatings prepared by the present method generally have a dielectric constant less than 3, preferably less than 2.5, down to below 2.2, and are stronger than previously proposed nanopororous silicone resin low dielectric materials. The nanoporous silicone resin typically has a modulus of above 5GPa, particularly when formed from resins of the invention in which the group R is a tertiary alkyl group.

The nanoporous silicone resins can also be made in particulate form, for example by spray drying the purified resin solution and heating to effect thermolysis as described above. The particulate nanoporous silicone resins can be used in known applications where porous materials are used, for example as packing in chromatography columns.

The following examples are provided to illustrate the present invention.

Example 1 [0022] t-BuSiCl3 (10.9g, 57mmol), HSiC13 (7.7g, 57mmol), and THF (100ml) were charged to a three-necked flask which had been flushed with N2; the flask was equipped with a condenser/inert gas inlet, magnetic stirrer, and pressureequalised dropping funnel. Distilled water (9.23g, 513mmol) and THF (40ml) were charged to the dropping funnel. The chlorosilane solution was cooled to 0 to 5 C in an ice/water bath; the water/THF solution was added over 30mins. The cooling bath was removed and the reaction mixture was stirred for a further lh at ambient temperature. There was no appreciable change (no colour change, no precipitate, water-white solution). Volatiles were removed under reduced

pressure (100mbar/300C) to give thick oily droplets. All the slurry was extracted into toluene (loom) and washed to neutral with distilled water (5 x 100ml). The resulting suspension was dried over anhydrous Na2SO4 ; after filtering, a clear, colourless solution was obtained. All volatiles were removed under reduced pressure (100mbar/30oC, then lmbar/ambient temperature == 200C) to give 8. 0g of a crispy

white solid which was a To. 5TH0. 5 resin.

Example 2 [0023] 135ml of MIBK and 176g of distilled water were charged to a three-necked flask; the flask was equipped with a condenser, magnetic stirrer, and pressure-equalised dropping funnel. A solution of t-BuSiCl3 (42g, 220mmol), HSiCl3 (29.8g, 220mmol), and MIBK (46ml) was charged to the dropping funnel and the chlorosilane solution was added at 0

to 5 C over 45mins. The cooling bath was removed and the reaction mixture was warmed up in an oil bath to 100oC and stirred for a further 3h. There was no appreciable change (no colour change, no precipitation, water-white solution).

The resulting suspension was washed to neutral with distilled water (5 x 200ml). The resulting solution was dried over anhydrous Na2SO4 ; after filtering a clear, colourless solution was obtained. All volatiles were

removed under reduced pressure (lOOmbar/30oC, then lmbar/ambient temperature == 200C) to give 35. 5g of a crispy white solid which was a TtBuo. T Ho. 5 resin.

Example 3 [0024] 46.94g of Cl2SiCl3 (C12=tri-isobutyl) and 62.88g of HSiCl3 mixed into 160ml MIBK were added dropwise into a mixture of 240ml 0.5M HCl/H20 solution, 320ml MIBK and 160ml toluene over 40 minutes at room temperature. The temperature of the reaction mixture rose to 65 to 70oC).

The mixture was left for another hour under constant stirring. The organic layer was separated and washed four times with water until neutral. 100ml was sampled from the solution. Removal of residual water and stripping off the

12 H solvent led to 9. 2g of a white solid which was aTc 0. 75T 0. 25 resin.

Example 4 [0025] A solution of 9.23g (513 mmol) of distilled water and 40 ml of THF was added dropwise into a solution of PrSiCl3 (10. lg, 57mmol; Pr=propyl), HSiCl3 (7.7g, 57mmol), and THF (100ml) under N2 at 0 to 5 C over 30min. The procedure described in Example 1 was then followed to obtain

Pr H 8. 05g of a white solid which was a T 5THo. 5 resin.

Example 5 [0026] A solution of 9.23g (513 mmol) of distilled water and 40 ml of THF was added dropwise into a solution of

Pr (F) SiCl3 (13. 2g, 57mmol, Pr (F) =trifluoropropyl), HSiCl3 (7. 7g, 57mmol), and THF (loom) under N2 at 0 to 5 C over 30min. The procedure described in Example 1 was then followed to obtain 7. 0g of a white solid which was a Pr (F) H T 0. 5T 0. 5 resin.

Example 6 [0027] A solution of 9.23g (513 mmol) of distilled water and 40 ml of THF was added dropwise into a solution of t BuSiCl3 (14g, 73.6mmol), MeSiCl3 (llg, 73. 6mmol), and THF (130ml) under N2 at 0 to 5 C over 30min. The procedure described in Example 1 was then followed to obtain 10. Og of

me a white solid which was aTtBuo. 5T 0. 5 resin.

Example 7 [0028] A solution of 8.86g (492mmol) of distilled water and 40 ml of THF was added dropwise into a solution of

CpSiCIs (11. 14g, 54. 7mmol, Cp=cyclopentyl), MeSiCl3 (8. 2g, 54.7mmol), and THF (100ml) under N2 at 0 to 5 C over 30min. The procedure described in Example 1 was then followed to obtain 10.7g of a white solid which was a Topo. sTo. s resin.

Example 8

[0029] A solution of 16. 36g (908mmol) of distilled water and 80 ml of THF was added dropwise into a solution of i OctSiCl3 (25g, 101mmol, i-Oct=iso-octyl), MeSiCl3 (15. 1g, 101mmol), and THF (200ml) under N2 at 0 to 5 C over 45min. The procedure described in Example 1 was then followed to

me obtain 27g of a white solid which was a Tl o. 5TM'o. 5 resin.

Example 9 [0030] A solution of 16. 36g (908mmol) of distilled water and 80 ml of THF was added dropwise into a solution of i OctSiCis (9. 91g, 40mmol), MeSiCl3 (23.92g, 160mmol), and THF (200ml) under N2 at 25 C over 45min. The procedure described in Example 1 was then followed to obtain 15g of a

me colourless gum which was a Tl cto-2To. 8 resin.

Example 10 [0031] A mixture of Pr (F) SiCl3 (39. 6g, 171mmol), MeSiCl3 (102.7g, 684mmol), and MIBK (90ml) was added dropwise into a solution of distilled water (342g, 19mol) and MIBK (262. 5ml) under N2 at 0 to5 C over 1.5hr. The procedure described in Example 2 was then followed to obtain 86g of a sticky liquid

h. h Pr (F) Me. which was a T'o. 2To. 8 resin.

Example 11 [0032] A solution of 6.93g (385mmol) of distilled water and 300ml of THF was added dropwise into a solution of Pr (F) SiCl3 (39.6g, 171mmol), MeSiCl3 (102.7g, 684mmol), and THF (75ml) under N2 at 0 to 5 C over 1. 5hr. The procedure described in Example 1 was then followed to obtain 77g of a white solid which was a TPr (F) 0. 2To. 8 resin.

Example 12 [0033] 25. 80g of C18H37SiCl3, 29.69g of tBuSiCl3, 30g of HSiC13 mixed into 120ml MIBK were added dropwise into a mixture consisting of 180ml 0. 5M HC1/H20 solution, 240ml MIBK and 180ml Toluene over 40 minutes at room temperature (the temperature of the reaction mixture rising to 65-70 C upon addition). The mixture was refluxed for another two hours under constant stirring. The organic layer was separated and washed four times with water until neutral. A 270ml portion (270ml) of Q was sampled from the solution. Removal of residual water and stripping of the solvent led to 24.16g of a whiteTTTH resin.

Example 13 [0034] A mixtures of 25.2g (132mmol) tbutyltrichlorosilane, 27.8g (205mmol) of trichlorosilane, 19.7g of methyltrichlorosilane (132mmol) and 46ml of MIBK were added dropwise into a mixtures of 176ml water and 135ml MIBK at 25 C over 1. Ohr. The mixtures were kept stirring at 80 C for additional 48hr. The organic layer were separated and washed until neutral, the residual water was removed using a Dean stark. 34.6g solid was obtained after stripped off the solvent under vacuum, which was To. 32To. 36T0. 32 copolymer Example 14.

[0035] A mixtures of 11.16g (29mmol) octadecyltrichlorosilane, 7.8g (58mmol) of trichlorosilane, 4.89g of tetrachlorosilane (29mmol) and 40ml of MIBK were added dropwise into a mixtures of 60ml 0. 5M HCl aqueous solution, 40ml toluene and 80ml MIBK at 25 C over 0. 5hr.

The mixtures were kept stirring at 120oC for additional 12hr. The organic layer were separated and washed until neutral, the residual water was removed using a Dean stark.

8.16g solid was obtained after stripped off the solvent under vacuum, which was a TC180.52TH0.36Q0.12 resin.

Example 15.

[0036] A mixtures of 2. 5g (14mmol) di-tertbutylchlorosilane, 17. 05g (126mmol) of trichlorosilane and 15ml of MIBK were added dropwise into a mixtures of 30ml water and 45ml MIBK at 25 C over 0. 5hr. The mixtures were kept stirring at 60 C for additional 3hr. The organic layer were separated and washed until neutral, then dried over anhydrous NaSO4. 1. 5g solid was obtained after stripped off

H Bu2H the solvent under vacuum, which was a THo. 82MtBU"o. 18 resin.

Example 16 [0037] A mixture of 3. 35g (19mmol) di-t-butylchlorosilane (t-C4H9) 2SiHCl, 10. Og (74mmol) of trichlorosilane and 10ml of MIBK were added dropwise into a mixture of 56ml water and 29ml MIBK at-5oC over 0. 5hr. The mixture was stirred at 90oC for additional 3hr. The organic layer was separated and washed until neutral, then dried over anhydrous Nais04.

3. Og solid MT resin was obtained after stripping off the

solvent under vacuum, which was a THo. 78MtBu2Ho. 22 resin.

Example 17.

A mixtures of 7. 5g (42mmol) di-tert butylchlorosilane, 13.26g (98mmol) of trichlorosilane and 15ml of MIBK were added dropwise into a mixtures of 30ml water and 45ml MIBK at 25 C over 0. 5hr. The mixtures were kept stirring at 60 C for additional 3hr. The organic layer were separated and washed until neutral, then dried over anhydrous NaSO4. 11. 7g solid was obtained after stripped off the solvent under vacuum, which was a To. 76MtBu2Ho. 24 resin.

Example 18.

A mixtures of 25.2g (132mmol) tbutyltrichlorosilane, 29.8g (220mmol) of trichlorosilane, 15. 73g of di-tert-butylchlorosilane (88mmol) and 46ml of MIBK were added dropwise into a mixtures of 176ml water and 135ml MIBK at 25 C over l. Ohr. The mixtures were kept stirring at 100 C for additional 72hr. The organic layer were separated and washed until neutral, the residual water

was removed using a Dean stark. 28. 16g solid was obtained after stripped off the solvent under vacuum. To. 46 TH MtBu2H T 0. 47M 0. 07 Example 19 [0040] A 300-mL four-necked flask equipped with a condenser, a dropping funnel, and a stirring rod was charged with THF (300 mL) and DBDS (10 g: 0.039 mol) under argon.

The THF suspension turned clear with addition of trichlorosilane (7.1 g: 0.052 mol) in THF (30 ml). Pyridine (12.4 g: 0.15 mol) in THF (30 mL) was added dropwise into the clear solution to form pyridine hydrochloride. The reaction mixture was stirred at room temperature overnight.

After removal of the pyridine hydrochloride, the filtrate

was washed with saturated NaCl aqueous solution, followed by drying with MgSO4. The dried organic solution was evaporated in a rotary evaporator, and then was stripped in vacuo at room temperature. The crude product was dissolved in 50 mL of diethyl ether to remove insoluble materials. The resulting diethyl ether suspension was centrifuged at 3,000 rpm for 10 min. The supernatant was filtered (No. 2, ADVANTEC filter paper). The removal of diethyl ether left 9.92 g of a white solid (87.7 % yield as tBuTo. 614TO. 4 resin) Example 20 [0041] A 2-L four-necked flask equipped with a condenser, a dropping funnel, and a stirring rod was charged with THF

(1500 mL) and DBDS (100 g : 0. 393 mol). The THF suspension turned clear with addition of trichlorosilane (71 g: 0.52 mol) in THF (100 ml). Pyridine (124 g: 1.56 mol) in THF (150 mL) was added dropwise into the clear solution cooling with an ice bath, which formed pyridine hydrochloride. The reaction mixture was stirred at room temperature overnight. After removal of the pyridine hydrochloride, the filtrate

was washed with saturated NaCl aqueous solution, followed by drying with MgS04. The dried organic solution was evaporated in a rotary evaporator, and then was stripped in vacuo at room temperature. The crude product was dissolved in 50 mL of diethyl ether to remove insoluble materials.

The resulting diethyl ether suspension was centrifuged at 3,000 rpm for 10 min. The removal of diethyl ether left 105.6 g of a white solid with a composition of tTo. 6HTo. 4.

Example 21 [0042] A 300mL four-necked flask equipped with a condenser, a dropping funnel, a stirring rod was charged with THF (900 ml) and DBDS (20 g: 0.0787 mol). The THF suspension was refluxed for 30 min. Methyltrichlorosilane (15.7 g: 0.105 mol) dissolved in THF (20 ml) was added dropwise into the suspension, which resulted in formation of a clear solution. Pyridine (24.8 g: 0.315 mol) in THF (30 ml) was added dropwise into the clear solution to form pyridine hydrochloride. The reaction mixture was stirred under reflux for 5 h, and then was stirred at ambient temperature overnight. After removal of the pyridine hydrochloride, the filtrate was washed with sat. NaCl aq. soln. , followed by drying with MgSO4. The dried organic solution was evaporated by a rotary evaporator, and then was stripped in vacuo to give a white crude product. The product was dissolved in toluene to form a cloudy solution.

The solution was centrifuged to remove insoluble materials.

The supernatant was filtered with a filter paper, and subsequently was evaporated. Stripping in vacuo overnight left 10.8 g of a white solid with a composition of mtBu rnMe 0. 6 0. 4.

Example 22 [0043] Example 21 was repeated using phenyltrichlorosilane (22.2 g: 0. 105 mol) in place of the methyltrichlorosilane and only 4 hours reflux. Stripping resulted in 22.8 g of a white solid with a composition of TtBuo. 6TPho. 4.

Example 23

[0044] A 300mL four-necked flask equipped with a condenser, a dropping funnel, a stirring rod was charged with THF (200 ml) and DBDS (5 g: 0.0196 mol). The THF suspension was refluxed for 30 min. Methyltrichlorosilane (1.95 g: 0.013 mol) dissolving in THF (10 ml) was added dropwise into the suspension, which resulted in formation of a clear solution. Pyridine (3.08 g: 0.039 mol) in THF (10 ml) was added dropwise into the clear solution to form pyridine hydrochloride. The reaction mixture was stirred at room temperature overnight. After removal of the pyridine hydrochloride, the filtrate was purified as described in Example 21 to leave after stripping 3.16 g of a white solid

me with a composition of TtBuo. 7T 0. 3.

Example 24 [0045] A 300mL four-necked flask equipped with a condenser, a dropping funnel, a stirring rod was charged with THF (200 ml) and DBDS (5g: 0.0196 mol). The THF suspension was refluxed for 30 min. Phenyltrichlorosilane (8.29 g: 0.0392 mol) dissolving in THF (20 ml) was added dropwise into the suspension, which resulted in formation of a clear solution. Pyridine (6.19 g: 0.0783 mol) in THF (20 ml) was added dropwise into the clear solution to form pyridine hydrochloride. The reaction mixture was stirred at r. t. overnight. After removal of the pyridine hydrochloride, the filtrate was purified as described in Example 21 to leave after stripping 5.11 g of a white solid with a composition of TtBU TPh T@@@0.5T@@0.5.

[0046] The number average Mn and weight average Mw molecular weights of most of the above resins was evaluated by gel permeation chromatography. The values are listed in Table 1 Table 1

Mn Mw Examplel 1110 2836 Example2 1543 2472 *Example4 4490 243300 Example6 1317 2805 Example713303090 Example814401940 Example9 2190 4460 ExamplelO21984286 Examplell 2346 4585 Examplel223003850 Example 13 1160 31100 Example 16 990 15900 Example 18 710 1910 *triple detector Preparation of Nanoporous silicone resins

[0047] The silicone resins produced in Examples 1-21 were each pyrolysed in bulk at 450oC for 2hr under nitrogen (Examples 2 and 19 were also cured at 250oC) before porosity measurements were carried out using the nitrogen sorption method on a Quantachrome Autosorb 1MP instrument (Table 2). Table 2

BET surface Total Pore rea (m2/g) volume (cc/g) Examplel 396 0. 278 Example2 424 0.270 Example 2 (250oC) 149 0. 233 Examples3 6860. 409 Example4 159 0. 172 Example5 173 0. 166 Example6 314 0. 259 Example7 95 0. 102 Example8 159 0. 253 Example9 469 0. 404 Example10 136 0. 178 Example11 180 0. 224 Example12 63 0. 361 Example13 383 0. 279 Example14 552 0. 397 Example15 290 0. 232 Example16 462 0. 279 Example74910. 294 Example18 329 0. 291 Example94440. 320 Example9 (250oC) 395 0. 259 Example 20 417 0. 240 Example 21 337 0. 245 [0048] The surface areas were calculated using the BET equation, which is considered to give the total internal and external surface area of the material. Total pore volume is derived from the amount of vapor adsorbed at a relative pressure close to unity, by assuming that the pores are then filled with liquid adsorbate. Pore size distributions in the mesopore region are determined by B. J. H. method. (E. P.

Barrett, L. G. Joyner and P. D. Halenda, J. Am. Chem. Soc.

1952,73, 373). A high total pore volume increases the likelihood of a low dielectric constant.

The porosity measurement results on these resins show all of the above examples give porous material after pyrolysis at 450oC, and the two examples of TtBUTH resins (example2 and 19) also give porous materials at a lower temperature of 250oC. The TT resin'examples bearing larger sacrificial R groups (with over 8 carbons, example 3,9, 12, and 14) give a high porosity (over 0.35cc/g). The TM and TTM resins (example 15,16, 17 and 18) give a similar level of porosity to those of the TT'resins. BJH pore size distributions shows the majority of the pores in these pyrolysed resin are smaller than 5nm.

[0050] The silicone resins produced in Examples 2,3, 6, 10,12, 13,18 and 20-22 were each dissolved in MIBK at 20% and spin-coated onto silicon wafers and pyrolysed at 450oC to produce a nanoporous silicone resin coating. The thickness, refractive index, dielectric constant dK, modulus and hardness of each coating were measured. Modulus and hardness values were measured using a Hysitron TriboscopeD nanomechanical testing instrument. A Berkovich diamond indenter was used for all measurements. Hardness and reduced modulus values were determined at a penetration depth of-15%. The reduced modulus (ER = E/ (1-O2), where E and U are the Young's modulus and Poisson's ratio respectively, was determined from the slope of the unloading curve. The values reported were the average of three indents measured at different areas of the film. (Table 3). Table3

Thickness Refractive dK Modulus Hardnes (nm) Index (GPa) s (GPa) Example2554 1. 301 2. 36 5. 3 0. 69 Example3 631 1. 260 2. 09 5. 5 0. 72 Example6 1015 1. 330 2. 66 ExamplelO 390 1. 356 2. 87 ? Examplel2 715 1. 342 2. 10 3. 6 0. 56 Example13 1015 1.330 2.66 / / Examplel8 365 1. 308 2. 64 8. 7 1. 25 Example 516 1. 298 2. 55 20 Example 316 1.391 2.37 / / 21 Example 208 1.431 2.50 / / 22 [0051] The films were observed to be good quality, crackfree thin films. The deviation in thickness of each film was below 5%. The dK of these resins is in general low ( < 3), and the modulus of these resins was high ( > 3. 5Gpa).

The combination of low dK and high modulus shown by the nanoporous resins of Examples 3 and 12 in particular shows them to be very suitable for interlayer dielectric application.

Claims (21)

1. CLAIMS 1. A process for the preparation of a silicone resin comprising reacting 10-90 mole% of a chlorosilane of the formula RSiCl3 and/or 10-70 mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl and/or

   10-80 mole% of a tetrahydroxydisiloxane of the formula (HO) 2Si (R)-O- (R) Si (OH) 2 with 10-90 mole% of a chlorosilane of the formula R'SiCl3, where R is a thermally labile alkyl, substituted alkyl or

   cycloalkyl group and R'is H or a thermally stable organic group, in the presence of a dipolar aprotic solvent which is at least partially miscible with water.
2. 2. A process according to claim 1, characterised in that

   10-90 mole% of a chlorosilane of the formula RSiCl3 and/or 10-70 mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl is reacted with 10-90 mole% of a chlorosilane of the formula R'SiCl3 in the presence of water and the dipolar aprotic solvent.
3. 3. A process according to Claim 2, characterised in that

   20-80 mole% of a chlorosilane of the formula RSiCl3 is reacted with 20-80 mole% of the chlorosilane of formula R'SiCl3.
4. 4. A process according to Claim 3, characterised in that RSiCl3 and R'SiCl3 are reacted in the absence of any other chlorosilane.
5. 5. A process according to Claim 2 or Claim 3, characterised in that the chlorosilanes are co-reacted with up to 35 mole% SiC14.
6. 6. A process according to Claim 2, characterised in that

   10-70 mole% of a chlorosilane of the formula R2R'SiCl or R3SiCl is reacted with 30-90 mole% of the chlorosilane of the formula R'SiCl3.
7. 7. A process according to Claim 6, characterised in that

   10-40 mole% of a chlorosilane of formula R2HSiCl is reacted with 60-90 mole% of the chlorosilane of formula R'SiCl3.
8. 8. A process according to any of Claims 1 to 7, characterised in that R is a branched alkyl group having at least 4 carbon atoms.
9. 9. A process according to Claim 8, characterised in that R is a t-butyl group.
10. 10. A process according to Claim 8, characterised in that R is a 2- (2, 2-dimethylpropyl)-4, 4-dimethylpentyl group.
11. 11. A process according to any of Claims 1 to 7, characterised in that R is a linear alkyl group having 8 to 20 carbon atoms.
12. 12. A process according to any of Claims 1 to 11, characterised in that the solvent is fully miscible with water.
13. 13. A process according to Claim 12, characterised in that the solvent is tetrahydrofuran.
14. 14. A process according to any of Claims 1 to 11, characterised in that the solvent is partially miscible with water.
15. 15. A process according to Claim 14, characterised in that the solvent is a ketone containing 4 to 7 carbon atoms.
16. 16. A process according to any of Claims 1 to 15, characterised in that no catalyst is added to the reaction.
17. 17. A silicone resin prepared by the process of any of Claims 1 to 16.
18. 18. A method for making a nanoporous silicone resin coating on a substrate, characterised in that a silicone resin according to Claim 17 is coated on the substrate and the coated substrate is heated at a temperature sufficient to effect curing of the silicone resin and thermolysis of R groups from silicon atoms thereby forming a nanoporous silicone resin coating on the substrate.
19. 19. A method according to Claim 18, characterised in that the silicone resin of Claim 17 is applied to the substrate from a solution in a dipolar aprotic solvent.
20. 20. A method according to Claim 18 or Claim 19, characterised in that the coated substrate is heated in a first step at a temperature of from 20 C to 350oC and heated in a second step at a temperature of greater than 350oC to 600oC.
21. 21. A nanoporous silicone resin prepared by the method of any of Claims 18 to 20 having a total pore volume of 0.15 to 0.5 cc/g.