Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2001-03-19
2003-05-06
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S536000, C427S439000, C427S397700, C438S789000
Reexamination Certificate
active
06558755
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to coatings for use in electronic devices. More particularly, the invention relates to coatings having an improved elastic modulus and a low dielectric constant and to methods of making such coatings.
Thin film dielectric coatings on electric devices are known in the art. For instance, U.S. Pat. Nos. 4,749,631 and 4,756,977, to Haluska et al., disclose silica based coatings produced by applying solutions of silicon alkoxides or hydrogen silsesquioxane, respectively, to substrates and then heating the coated substrates to a temperature between 200 and 1000° C. The dielectric constant of these coatings is often too high for certain electronic devices and circuits.
U.S. Pat. Nos. 4,847,162 and 4,842,888, to Haluska et al., teach the formation of nitrided silica coatings by heating hydrogen silsesquioxane resin and silicate esters, respectively, to a temperature between 200 and 1000° C. in the presence of ammonia. These references teach the use of anhydrous ammonia so that the resulting coating has about 1 to 2% by weight nitrogen incorporated therein.
Glasser et al., Journal of Non-Crystalline Solids, 64 (1984) pp. 209-221, teaches the formation of ceramic coatings by heating tetraethoxysilane in the presence of ammonia. This reference teaches the use of anhydrous ammonia and that the resulting silica coatings are nitrided.
U.S. Pat. No. 4,636,440, to jada, discloses a method of reducing the drying time for a sol-gel coated substrate comprising exposing the substrate to aqueous quaternary ammonium hydroxide and/or alkanol amine compounds. Jada requires that the coating be dried prior to heating. It is specifically limited to hydrolyzed or partially hydrolyzed silicon alkoxides and does not teach the utility of the process on coatings having Si—H bonds.
U.S. Pat. Nos. 5,262,201, to Chandra, and U.S. Pat. No. 5,116,637, to Baney et al., teach the use of basic catalysts to lower the temperature necessary for the conversion of various preceramic materials, all involving hydrogen silsesquioxane, to ceramic coatings. These references teach the removal of solvent before the coating is exposed to the basic catalysts.
U.S. Pat. No. 5,547,703, to Camilletti et al., teaches a method for forming low dielectric constant Si—O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin successively under wet ammonia, dry ammonia, and oxygen. The resultant coatings have dielectric constants as low as 2.42 at 1 MHz. This reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,523,163, to Balance et al., teaches a method for forming Si—O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin to convert it to a Si—O containing ceramic coating and then exposing the coating to an annealing atmosphere containing hydrogen gas. The resultant coatings have dielectric constants as low as 2.773. The reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,618,878, to Syktich et al., discloses coating compositions containing hydrogen silsesquioxane resin dissolved in saturated alkyl hydrocarbons useful for forming thick ceramic coatings: The alkyl hydrocarbons disclosed are those up to dodecane. The reference does not teach exposure of the coated substrates to basic catalysts before solvent removal.
U.S. Pat. No. 6,231,989 to Chung et at., entitled METHOD OF FORMING COATINGS, discloses a method of making porous network coatings with low dielectric constants. The method comprises depositing a coating on a substrate with a solution comprising a resin containing at least 2 Si—H groups and a solvent in a manner in which at least 5 volume % of the solvent remains in the coating after deposition. The costing is then exposed to an environment comprising a basic catalyst and water. Finally, the solvent is evaporated from the coating to form a porous network. If desired, the coating can be cured by heating to form a ceramic. Films made by this process have dielectric constants in the range of 1.5 to 2.4 with an elastic modulus of about 2-3 GPa.
It has now been discovered that instead of plasma treating, porous network coatings can be plasma cured, eliminating the need for prior furnace curing.
However, there remains a need for a method of making a porous network coating having an improved elastic modulus.
SUMMARY OF INVENTION
The present invention produces a coating with a low dielectric constant and an improved elastic modulus. The method of making the coating involves providing a porous network coating produced from a resin containing at least 2 Si—H groups. The coating is plasma cured to reduce the amount of Si—H bonds remaining in the coating. Plasma curing of the porous network coating yields a high elastic modulus of greater than or about 4 GPa.
The plasma cured coating can optionally be annealed. Themial annealing of the plasma cured coating reduces the dielectric constant of the coating while maintaining the increase in the elastic modulus as compared to the elastic modulus before the anneal. The annealing temperature is typically less than or about 475° C., and the annealing time is typically no more than or about 180 seconds.
The annealed, plasma cured coating has a dielectric constant in the range of from about 1.1 to about 3.5 and an elastic modulus that is generally greater than or about 4 GPa, and typically in the range of from about 4 CPa to about 10 GPa.
Accordingly, it is an object of the present invention to produce coatings having improved elastic modulus and low dielectric constant.
DETAILED DESCRIPTION
The manufacture of ultra low dielectric constant coatings having a dielectric constant of about 1.5 to about 2.4 is described in U.S. Pat. No. 6,231,989, which is incorporated herein by reference for its teaching on how to produce coatings having ultra low dIelectric constants. This patent describes a process in which pores are introduced into hydrogen silsesquloxane (HSQ) based films. HSQ based films produced according to the method taught in U.S. Pat. No. 6,231,989, which have been cured under thermal conditions, contain about 20 to about 60% Si—H bonds density. When the dielectric constant of the coating is about 2.0, the coating has an electric modulus of between about 2 and about 3 GPa. The present invention is based on the discovery that plasma cunng porous HSQ based films increases the elastic modulus of the film without the necessity of thermally curing the film. Plasma curing reduces the amount of Si—H bonds remaining without losing the low density structure of the film.
Plasma curing can generate a notable amount of polar species in the film, which can be undesirable in some applications. The present invention is also based on the discovery that applying thermal annealing to plasma cured coatings produces a low dielectric constant, improved modulus material.
The methods of the present invention are particularly applicable to the deposition of coatings on electronic devices or electronic circuits where they can serve as interlevel dielectric layers, doped dielectric layers to produce transistor like devices, pigment loaded binder systems containing silicon to produce capacitor and capacitor like devices, multilayer devices, 3-D devices, silicon on insulator devices, super lattice devices, and the like. However, the choice of substrates and devices to be coated by the instant invention is limited only by the need for thermal and chemical stability of the substrate at the temperature and pressure used in the present invention. As such, the coatings of the present invention can be used on substrates such as plastics including, for example, polyimides, epoxies, polytetrafluoroethylene and copolymers thereof, polycarbonates, acrylics and polyesters, ceramics, leather, textiles, metals, and the like.
As used in the present invention, the expression “ceramic” includes ceramics such as amorphous silica and ceramic-like materials such as amorphous silica-like materials that are not fully free of car
Berry, III Ivan L.
Bridgewater Todd
Chen Wei
Han Qingyuan
Moyer Eric S.
Dow Corning Corporation
Killworth, Gottman Hagan & Schaeff LLP
Padgett Marianne
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