DESCRIPTION

[0001] This invention pertains to silicone resins having the general formula [(PE)(CH2)3Siθ3/2]u(RSiθ3/2)v (03/2Si(CH2)nSi03/2)w(Si04/2)x where PE is a polyether group containing at least 8 carbon atoms and at least 4 oxygen atoms; R is selected from H, vinyl, phenyl or an alkyl group having 1 to 6 carbon atoms; n has a value of 0 to 3; u has a value of 0 to 0.3; v has a value of 0 to 0.5, w has a value of 0.15 to 0.5; x has a value of 0 to 0.4 and u + v + 2w + x « 1. The resins are used to form porous ceramics or porous thing films on semiconductor devices. [0002] Semiconductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements forming an integrated circuit (IC). The interconnect levels are typically separated by an insulating or dielectric coating. The coatings may be formed by chemical vapor deposition or by spin-on techniques. For example, U.S. Patent No. 4,756,977 discloses the use of hydrogen silsesquioxane resins to form coatings on electronic devices. [0003] As the size of the circuit elements and the spaces between such elements continues to decrease, there is a need for insulating materials that have a lower dielectric constant. In particular, materials that can provide a dielectric constant below 3 are desirable. One means for producing coatings that have a dielectric constant below 3 is to use spin-on materials that are silicon based and that when cured produce pores in the film. [0004] Silicon containing spin-on materials have been described in U.S. Patent Nos. 5,010,159 to Bank et al., U.S. Patent No. 6,022,814 to Mikoshiba et al., and U.S. Patent Nos. 6,143,855 and 6,177,199 to Hacker et al. [0005] It has now been found that resins having the formula [(PE)(CH2)3Siθ3/2]u(RSiθ3/2)v(O 3/2Si(CH2)nSiO3/2)w(Siθ4/2)x where PE is a polyether group containing at least 8 carbon atoms and at least 4 oxygen atoms; R is selected from H, vinyl, phenyl or an alkyl group having 1 to 6 carbon atoms; n has a value of 0 to 3; u has a value of 0 to 0.3; v has a value of 0 to 0.5, w has a value of 0.15 to 0.5; x has a value of 0 to 0.4 and u + v + 2w + x « 1 ; can be used to produce coatings on electronic devices, in particular semiconductor devices. These resins can be used to produce films having a dielectric constant of 1.7 to 2.2. [0006] In the resin PE is a polyether group containing at least 8 carbon atoms and at least 4 carbon atoms. The polyether group may be exemplified by, but not limited to, [H(OCH2CH2)O1(OCH2CHMe)nO], {[CH3C(O)](OCH2CH2)m(OCH2CHMe)nO} and

[Me(OCH2CH2)m(OCH2CHMe)nO] where Me represents a methyl group, m is 0 to 30, n is 0 to 30 and m + n > 3. The PE group may be endcapped with a hydrogen (H), alkyl, acetate or any other capping group. Typically the PE group is endcapped with a hydrogen or methyl group. [0007] R is a groups selected from hydrogen, vinyl, phenyl or an alkyl group with 1 to 6 carbon atoms. The alkyl groups may be exemplified by, but not limited to methyl, ethyl, propyl, butyl, iso-butyl and others. Typically R is methyl. [0008] In the resins u has a value of 0 to 0.3, alternatively 0.03 to 0.2; v has a value of 0 to 0.5, alternatively 0.15 to 0.4 ; w has value of 0.15 to 0.5, alternatively 0.2 to 0.3 ; x has a value of 0 to 0.4, alternatively 0.1 to 0.3 ; u + v + 2w + x « 1. [0009] The resins may be further exemplified by, but not limited to resins having the formulas: [(PE)(CH2)3Siθ3/2]u(θ3/2Si(CH2)nSiO3/2)w(Siθ4/2)x

[(PE)(CH2)3Siθ3/2]u(RSiθ3/2)v(O3/2Si(CH2)nSiθ3/2)w

(RSiθ3/2)v(θ3/2Si(CH2)nSiO3/2)w(Siθ4/2)x

(RSiO3/2)v(θ3/2Si(CH2)nSiO3/2)w [0010] Resins having the formula [(PE)(CH2)3Siθ3/2]u(RSiθ3/2)v(O3/2Si(CH2)nSiθ3/2)w(Siθ4/ 2)x where PE, R, n, u, v, w, and x are defined above are produced by (I) combining (A) 0 to 30 mole% of a silane having the formula (PE)(CH2)3SiX3;

(B) 0 to 50 mole % a silane having the formula RSΪX3,

(C) 15 to 50 mole% of a disilane having a formula of X3Si(CH2)nSiX3 and (D) 0 to 40 mole% of a silane having the formula SiY4

where X is CH3CH2O, CH3O or Cl; Y is CH3CH2O or CH3O; R is H, methyl, ethyl, vinyl, propyl or phenyl; in the presence of (E) solvent (F) water and (G) a hydrolysis catalyst; (II) reacting the combination (I) at a temperature and for a time sufficient to form the resin. [0011 ] Silane (A), (PE)(CH2)3 SiX3 , is typically used in an amount of 0 to 30 mole % based on the moles of (A), (B), (C) and (D), alternatively 3 to 20 mole%. Examples of Silane (A) include [H(OCH2CH2)m(OCH2CHMe)nO](CH2)3 Si(OEt)3,

[H(OCH2CH2)m(OCH2CHMe)nO](CH2)3Si(OMe)3,

[H(OCH2CH2)m(OCH2CHMe)nO](CH2)3SiCl3,

{[CH3C(O)](OCH2CH2)m(OCH2CHMe)nO}(CH2)3Si(OEt)3,

{[CH3C(O)](OCH2CH2)m(OCH2CHMe)nO}(CH2)3Si(OMe)3,

{[CH3C(O)](OCH2CH2)m(OCH2CHMe)nO}(CH2)3SiCl3,

[Me(OCH2CH2)m(OCH2CHMe)nO](CH2)3Si(OEt)3, where m has a value of 0 to 30; n has a value of 0 to 30; and m + n > 3 and Et represents an ethyl group. [0012] Silane (B), RSiX3, is typically used in an amount of 0 to 50 mole% based on the moles of (A), (B), (C), (D), alternatively 15 to 40 mole%. Examples of silane (B) include MeSi(OMe)3, MeSi(OEt)3, MeSiCl3, ViSi(OEt)3, HSi(OEt)3, and EtSi(OEt)3.

[0013] Silane (C), X3Si(CH2)nSiX3, is typically used in the amount of 15 to 50 mole % based on the moles of (A), (B), (C), and (D), alternatively 20 to 30 mole %. Examples of Silane (C) include Cl3SiSiCl3, (MeO)3 SiSi(OMe)3, (MeO)3SiCH2Si(OMe)3, and

(EtO)3 Si(CH2)2Si(OEt)3 where Vi represents a vinyl group. [0014] Silane (D), SiY4, is typically used in an amount of 0 to 40 mole% based on the moles of (A), (B), (C), and (D), alternatively 10 to 30 mole%. Examples of Silane (D) include Si(OMe)4 and Si(OEt)-J. [0015] Solvent (E) is any suitable organic or silicone solvent that does not contain a functional group that may participate in the reaction and is a sufficient solvent for silanes (A), (B), (C), and (D). The solvent is generally used in the amount of 40 to 98 weight percent based on the total weight of solvent and silanes (A), (B), (C), and (C), alternatively 70 to 90 weight percent. The organic solvent may be exemplified by, but not limited to, saturated aliphatics such as n-pentane, hexane, n-heptane, and isooctane; cycloaliphatics such as cyclopentane and cyclohexane; aromatics such as benzene, toluene, xylene, mesitylene; cyclic ethers such as tetrahydrofuran and dioxane; ketones such as methyl isobutyl ketone (MIBK), and cyclohexanone; halogen substituted alkanes such as trichloroethane; halogenated aromatics such as bromobenzene and chlorobenzene; esters such as isobutyl isobutyrate and propyl propronate. The silicone solvents may be exemplified by, but not limited to, cyclic siloxanes such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane. A single solvent may be used or a mixture of solvents may be used. Typically the solvent is 2-etoxyethanol. [0016] Component (F) is water. The water is added in an amount sufficient to effect essentially complete hydrolysis of X and Y in silanes (A), (B), (C) and (D) without an excess so great that results in an ineffective rate of reaction. Typically the water is present in an amount of 0.5 to 2.0 moles of water per mole of X and Y in silanes (A), (B), (C) and (D), alternatively 0.8 to 1.5 moles. [0017] Component (G) is a hydrolysis catalyst and can be any of those hydrolysis catalysts known in the art to catalyze the hydrolysis of X and Y on silanes (A), (B), (C) and (D), in the presence of water. Known hydrolysis catalysts include inorganic bases such as ammonium hydroxide, potassium hydroxide and sodium hydroxide; organic bases such as trimethylamine; inorganic acids such as hydrogen chloride, sulfuric acid and nitric acid; and organic acids such as trifluoroacetic acid. Hydrolysis catalyst (G) is present in an amount sufficient to catalyze the hydrolysis of X and Y in silanes (A), (B), (C) and (D). The optimal amount will depend upon the chemical composition of the catalyst as well as the temperature of the hydrolysis reaction. Generally, the amount of hydrolysis catalyst will be between 0.00001 to 0.5 moles per moles of silanes (A), (B), (C) and (D), alternatively 0.1 to 0.3 moles. [0018] In the process for making the resin it is preferred to combine silanes (A), (B), (C) and (D) with solvent (E). The water (F) and hydrolysis catalyst (G) are thereafter added, either separately or as a mixture to the first mixture. The reaction can be carried out at any temperature so long as it does not cause significant gelation or cause curing of the resin. Typically the reaction is carried out at a temperature in the range of 150C to 1000C, alternatively at ambient temperature. [0019] The time to form the resin is dependent upon a number of factors such as temperature and the specific amounts of silanes (A), (B), (C) and (D), among others. Typically the reaction time is from several minutes to several hours. One skilled in the art will be able to readily determine the time necessary to complete the reaction. [0020] Following completion of the reaction the hydrolysis catalyst may be optionally removed. Methods for removing the hydrolysis catalyst are well known in the art and include neutralization, stripping, water washing or combinations thereof. Removal of the hydrolysis catalyst is suggested because the catalyst may negatively impact the shelf life of the resin, especially when in solution. [0021] After the reaction is complete, volatiles may be removed from the silicone resin solution under reduced pressure. Such volatiles include alcohol by-products, excess water, catalyst and solvents. Methods for removing volatiles are known in the art and include, for example, distillation. [0022] The resins produced herein are particularly useful in forming ceramic materials, ceramic membranes, or porous coatings on a substrate, in particular an electronic substrate. By electronic substrate it is meant to include silicon-based devices and gallium arsenide- based devices intended for use in the manufacture of a semiconductor component. In particular, the resins are useful in forming porous coatings in integrated circuits. The silicone resins can be used to produce thin coatings having a dielectric constant in the range of 1.7 to 2.2 thereby making the silicone resin particularly useful in the formation of interlayer dielectrics films. [0023] The resin may be used to prepare a porous coating on a substrate by (I) coating the substrate with a resin having a formula [(PE)(CH2)3Siθ3/2]u(RSiθ3/2)v(O 3/2Si(CH2)nSiθ3/2)w(Siθ4/2)x where PE is a polyether group containing at least 8 carbon atoms and at least 4 oxygen atoms; R is selected from H, vinyl, phenyl or an alkyl group having 1 to 6 carbon atoms; n has a value of 0 to 3; u has a value of 0 to 0.3; v has a value of 0 to 0.5, w has a value of 0.15 to 0.5; x has a value of 0 to 0.4 and u + v + 2w + x * 1; (II) heating the coated substrate at a temperature sufficient to cure the resin and produce a cured resin coating, and (III) further heating the cured resin coating at a temperature sufficient to remove [(PE)(CH2)3- groups from the cured resin coating thereby forming a porous coating on the substrate. [0024] The resin is typically applied to the substrate as a solvent dispersion. Solvents that may be used include any agent or mixture of agents that will dissolve or disperse the resin to form an essentially homogeneous liquid mixture. The solvent is typically a solvent or mixture of solvents that are used in the reaction to produce the silicone resin, described above. Preferred solvents include cyclohexanone, isobutyl isobutyrate, 1-methoxypropanol and mesitylene. The amount of solvent is not particularly limited but is typically present in an amount of 40 to 98 % by weight, preferably 70 to 90 % based on the weight of silicone resin and solvent. [0025] Specific methods for application of the resin to the substrate include, but are not limited to, spin-coating, dip-coating, spay-coating, flow-coating, screen-printing and others. The preferred method for application is spin coating. [0026] When a solvent is used the solvent is removed from the coated substrate following application. Any suitable means for removal may be used such as drying, the application of a vacuum, and/or the application of heat (i.e. such as passing a coated wafer over hot plates). When spin coating is used, the additional drying method is minimized since the spinning drives off most of the solvent. [0027] Following application to the substrate, the coated substrate is heated at a temperature to cure the resin ("curing step"). A resin is essentially insoluble in a solvent which may be used for it application to the substrate. Typically the coated substrate is heated to a temperature in the range of 20 0C to 350 0C to cure the resin. [0028] The cured resin on the substrate is then further heated to a temperature sufficient to remove the (PE)(CH2)3- groups from the cured resin coating thereby forming a porous coating on the substrate ("removal step"). Typically the cured resin is heated to a temperature in the range of 350 0C up to the temperature at which the backbone of resin decomposes. Typically the cured resin is heated to a temperature in the range of 350 0C to 500 0C, alternatively 400 0C to 450 0C. Essentially all of the (PE)(CH2)3- groups are cleaved during this step. However, residual small alkyl groups such as methyl or ethyl resulting from (PE)(CH2)3- groups may remain in the coating. The weight percentage of (PE)(CH2)3- groups removed will affect the dielectric constant of the film as well as the porosity. It is suggested to heat for a period of time sufficient to remove most of the (PE)(CH2)3- groups (i.e. 90% by weight) from the cured resin. [0029] The curing step and removal step may be carried out separately or in a single step wherein the curing takes place as the coated substrate is being heated to the temperature for removal. [0030] Typically the curing step and removal step are carried in an inert environment. Inert atmospheres useful herein include, but are not limited to nitrogen and argon. By "inert" it is meant that the environment contain less than 50 ppm and preferably less than 10 ppm of oxygen. The pressure at which the curing and removal steps are carried out is not critical. The curing and removal steps are typically carried out at atmospheric pressure however, sub or super atmospheric pressures may work also. [0031] Any method of heating may be used during the curing and removal steps. For example, the substrate may be placed in a quartz tube furnace, convection oven or allowed to stand on hot plates. [0032] By this method it is possible to produce porous coatings on a substrate. Preferably the porous coatings have a thickness of 0.3 to 2.5 μm, more preferably 0.5 to 1.2 μm. The porous coatings have a dielectric constant in the range of 1.7 to 2.2. The amount of porosity in the films is dependent upon the amount of (PE)(CH2)3- groups in the starting resin and the degree to which they are removed. Typically the porous coatings will have a porosity of 20 to 60%. [0033] Porous ceramics or ceramic membranes may be produced by heating the resin at a temperature sufficient to cure the resin and further heating the cured rein at a temperature sufficient to remove (PE)(CH2)3- groups from the cured resin coating thereby forming a porous ceramic or porous ceramic membrane. The process conditions are similar to those described herein above for producing the porous coating on a substrate absent coating the substrate with the resin. However, in the step of removing (PE)(CH2)3- groups, the temperature can be much higher such as 800 0C, and oxidative atmosphere can be used to minimize residual alkyl group. [0034] The following non-limiting examples re provided so that one skilled in the art may more readily understand the invention.

Example 1. [0035] 1 weight part of (EtO)3 Si(CH2)2 Si(OEt)3, 0.41 weight parts of an 8.4 wt% HCl aqueous solution, and 4.8 weight parts of 2-ethoxyethanol were mixed in a flask, heated at reflux for 10 minutes, and vacuum stripped until the nonvolatile content reached 13%. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 0C for 1 hour in nitrogen, a crack-free film with a thickness of 609 nm and a refractive index of 1.38 was formed.

Example 2. [0036] 1.55 weight parts of Si(0Et)4,l .04 weight parts of water and 10.4 weight parts 2-

ethoxyethanol were mixed in a glass flask. 1 weight part Of Cl3SiSiCl3 in 3 weight parts of ethanol was added to the flask. The resulting solution was heated to reflux for 10 minutes, and vacuum stripped until the nonvolatile content reached 10.5%. 0.42 weight parts water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minute. After curing at 700°C for 1 hour in steam and oxygen, a crack-free film with a thickness of 279 nm and a refractive index of 1.46 was formed.

Example 3. [0037] 1 weight part of (EtO)3Si(CH2^Si(OEt)3, 0.50 weight parts of Si(OEt)4, 0.65 weight parts of an 8.4 wt% HCl aqueous solution, and 8.65 weight parts of 2-ethoxyethanol were mixed in a glass flask, heated at reflux for 10 minutes, and vacuum stripped until the nonvolatile content reached 8.8%. 0.62 weight parts water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 0C for 1 hour in nitrogen, a crack-free film with a thickness of 273 nm and a refractive index of 1.44 was formed. 5 Example 4. [0038] 0.33 weight parts of MeSi(OMe)3, 1 weight part of (EtO)3 Si(CH2^Si(OEt)3, 0.45 weight parts of an 8.4 wt% HCl aqueous solution, and 3.43 weight parts of 2-ethoxyethanol were mixed in a glass flask, stirred at 25 °C for 10 minutes, and vacuum stripped until the 10 nonvolatile content reached 14.2%. 0.36 weight parts of water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 °C for 1 hour in nitrogen, a crack-free film with a thickness of 551 nm and a refractive index of 1.42 was formed.

J 15 Example 5. [0039] 0.5 weight parts of ([CH3C(O)](OCH2CH2)I0(OCH2CHMe)4O)(CH2)SSi(OEt)3, 1

* weight part of (EtO)3Si(CH2)2Si(OEt)3, 0.45 weight parts of an 8.4 wt% HCl aqueous solution, and 4.81 weight parts of 2-ethoxyethanol were mixed in a glass flask, heated to reflux for 30 minutes, and stripped until the nonvolatile content reached 19.6%. 0.37 weight 20 parts of water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 °C for 1 hour in nitrogen, a crack-free film with a thickness of 757 nm, a refractive index of 1.24 and a dielectric constant of 1.98 was formed.

25 Example 6. [0040] 0.74 weight parts of ([CH3 C(O)] (OCH2CH2) I0(OCH2CHMe)4O }(CH2)3 Si(OEt)3,

0.38 weight parts MeSi(OMe)3, 1 weight part (EtO)3Si(CH2)2Si(OEt)3, 0.67 weight parts of an 8.4 wt% HCl aqueous solution, and 7.30 weight parts 2-ethoxyethanol were mixed in a glass flask, and stripped until the nonvolatile content reached 21.7%. 0.48 weight parts water 30 was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 °C for 1 hour in nitrogen, a crack-free film with a thickness of 741 nm, a refractive index of 1.25 and a dielectric constant of 1.99 was formed.

Example 7. [0041] 1.1 weight parts of ([CH3C(O)](OCH2CH2)I0(OCH2CHMe)4O)(CH2)SSi(OEt)3,

0.51 weight parts MeSi(OMe)3, 15.3 weight parts acetone were mixed in a glass flask. 1

weight part Cl3SiSiCl3 and then 0.73 weight parts water was added to the flask. The solution was stirred at 25 °C for 10 minutes. 14.7 weight parts 2-ethoxyethanol was added, and the solution was stripped until the nonvolatile content reached 19.6%. 0.72 weight parts water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 °C for 1 hour in nitrogen, a crack-free film with a thickness of 624 nm, a refractive index of 1.21 and a dielectric constant of 2.04 was formed.

Example 8. [0042] 1.45 weight parts of {[CH3C(O)](OCH2CH2)i0(OCH2CHMe)4O}(CH2)3Si(OEt)3,

0.73 weight parts Of MeSi(OMe)3, 1 weight part of (EtO)3 Si(CH2)2Si(OEt)3, 1.12 weight

parts Si(OEt)4, 1.44 weight parts of an 8.4 wt% HCl aqueous solution, and 14.1 weight parts 2-ethoxyethanol were mixed in a glass flask, and heated to reflux for 30 minutes. The solution was then vacuum stripped until the nonvolatile content reached 21.7%. 0.95 weight parts water was added to the product. A clear thin film was obtained by spin-coating the resulting resin solution on silicon wafer at 2000 rounds per minutes. After curing at 425 °C for 1 hour in nitrogen, a crack-free film having a thickness of 779 nm, a refractive index of 1.22 and a dielectric constant of 1.92 was formed.