Plasma curing of MSQ-based porous low-k film materials

Details Plasma curing of MSQ-based porous low-k film materials Plasma curing of MSQ-based porous low-k film materials

2001-07-16

2004-07-06

Padgett, Marianne (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Pretreatment of substrate or post-treatment of coated substrate

C427S539000, C427S489000, C427S397700, C438S789000

Reexamination Certificate

active

06759098

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to porous dielectric film materials for use in electronic and semiconductor devices, such as integrated circuits. More particularly, the invention relates to plasma cured, porous methylsilsesquioxane (MSQ) based dielectric film materials having an improved elastic modulus and a low dielectric constant and to methods of making such films.
As the semiconductor industry introduces new generations of integrated circuits (IC's) having higher performance and greater functionality, the density of the elements that form those IC's is increased, while the dimensions, size and spacing between the individual components or elements is reduced. While in the past such reductions were limited only by the ability to define the structures photolithographically, device geometries having dimensions as small as 0.25 micron (&mgr;m) or smaller have created new limiting factors, such as the conductivity of the metallic elements or the dielectric constant of the insulating material(s) used between the elements. For example, for any two adjacent conductive paths, as the distance between the conductors decreases, the resulting capacitance (a function of the dielectric constant (k) of the insulating material divided by the distance between conductive paths) increases. This increased capacitance results in increased capacitive coupling between the conductors, increased power consumption, and an increase in the resistive-capacitive (RC) time constant. Therefore, the continual improvement in semiconductor IC performance and functionality is dependent upon developing materials that form a dielectric film with a lower dielectric constant (k) than that of the most commonly used material, silicon oxide, thus resulting in reduced capacitance. As the dimensions of these devices get smaller and smaller, significant reductions in capacitance, into the so-called “ultra low-k” regime (e.g., k<2.5), will be required.
The initial approach for providing reduced-k insulating films was the doping of the silicon oxide material (k~3.9) with other components that would reduce the k value. For example, doping silicon oxide with fluorine typically reduces the value of k, but only to about 3.5-3.9. Processes for forming these doped films often advantageously use the same or similar methods that are used for forming undoped silicon oxide films. Hence the integration of fluorine doped films into the typical process flow is generally easily accomplished. However, as such fluorine doped films offer only a small decrease in k, other solutions having lower dielectric constants are needed. Finally, the stability of such fluorine containing films with regard to moisture is problematic.
A number of families of organic polymers were another preliminary solution for providing low-k dielectric films. Typically, organic polymers can form dielectric films where a k in the range of 2.5 or higher is possible. Generally, such dielectric films are formed by first applying a solution of an appropriate pre-polymer to a substrate. The substrate is then heated until the pre-polymer crosslinks and polymerizes to the degree desired and a solid film formed. As the organic material is applied as a liquid, some degree of surface planarization is provided for and often no additional planarization is needed. However, while such organic polymer films provide both a lower dielectric constant and enhanced planarization as compared to silicon oxide films, formed for example by chemical vapor deposition, for other film properties, such silicon oxide films have advantages. For example, organic materials generally have limited thermal stability above 450 degrees Centigrade (° C.); they often exhibit less adhesion to common metals, such as tungsten (W) and aluminum (Al); and the mechanical strength of such organic films is much less than that of silicon oxide. Finally, such organic films typically provide for k values only in the “low-k” regime (e.g., k=2.7-3.0).
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.
U.S. Pat. No. 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 al., entitled A 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 coating 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.
In an approach for providing a silicon oxide layer having a planar surface, spin-on glass (SOG) compositions have been prepared utilizing polyorganosilsesquioxanes; for example, see U.S. Pat. No. 4,670,299 issued to Fukuyama et al. (Fukuyama '29

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