Defect-free dielectric coatings and preparation thereof using polymeric nitrogenous porogens

#This invention relates generally to dielectric materials and their use in electronic devices such as integrated circuits. More particularly, the invention pertains to defect-free dielectric coatings and preparation thereof using nitrogen-containing polymers as pore-generating agents. The dielectric coatings so prepared are useful in a number of contexts, for example in electronic devices such as integrated circuit devices and integrated circuit packaging devices.

#As semiconductor devices are becoming smaller and on-chip device density is correspondingly increasing, both signal delays due to capacitive coupling and crosstalk between closely spaced metal lines are increasing. These problems are exacerbated by the need to keep conductor lines as short as possible in order to minimize transmission delays, thus requiring multilevel wiring schemes for the chip. The problems have been ameliorated to some extent by the switch to copper metallurgy, but as feature sizes go below 0.25 μm, this alone will not provide a solution. The use of an insulator with a lower dielectric constant than the currently used SiO2 (k=3.9-4.2) would also, clearly, improve the situation. Current integration demands for insulators used with, for example, Al(Cu) wiring, also require thermal stabilities in excess of 400° C., good mechanical properties, resistance to crack generation and propagation, low defect densities, low water uptake, chemical resistance, processability by photolithographic techniques and gas phase etching procedures, and capacity for planarization.

#Accordingly, considerable attention has focused on the replacement of silicon dioxide with new materials, particularly materials having lower dielectric constants, since both capacitive delays and power consumption depend on the dielectric constant of the insulator. This is not a simple matter given the complexities and demands of current semiconductor integration processes. Of the existing materials with demonstrated ultra-low dielectric constants, the highly fluorinated materials (e.g., Teflon) have the longest history. For example, attempts have been made to reduce the dielectric constant of polyimides by incorporating perfluoroalkyl-containing comonomers into the polymer structure (see, e.g., Haidar et al. (1991) Mater. Res. Soc. Symp. Proc. 227:35; Critchlen et al. (1972) J. Polym. Sci. A-I10 1789; and Harris et al. (1991) Mater. Res. Soc. Symp. Proc. 227:3). The synthesis of polyimides based on 9,9-disubstituted xanthene dianhydrides, e.g., 6FXDA/6FDA (9,9-bis(trifluoromethoxy)xanthenetetracarboxylic dianhydride/2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane), as well as polyimides based on the TFMOB monomer (2,2′-bis(trifluoromethyl)benzidine), has been reported (see Muraka (March 1996) Solid State Tech 83 and Jang et al. (1994) Mater. Res. Soc. Symp. Proc. 337:25). Although fluorinated alkane polymers such as these have the lowest dielectric constants of any homogeneous polymers and substitution with fluorine decreases the dielectric constant of any polymer, there are many liabilities. Current integration requirements call for exceptional thermal stability at temperatures in the range of 400-450° C. This temperature region is a problem for most organic polymers, and particularly for many fluorocarbons. Also, adhesion of fluorinated materials (self-adhesion, adhesion to metals, dielectrics, ceramics, etc.) is a problem without some prior surface pretreatment. Further, the stability of fluorinated materials due to interaction with interconnect metallurgy at elevated temperatures is problematic. The mechanical properties of many known fluorinated materials (particularly fluoroalkanes) are not ideal; they usually have large thermal expansion coefficients and are intrinsically soft materials. The latter creates a problem for chemical mechanical polishing (CMP) procedures. Finally, the methodology to develop other highly fluorinated materials such as fluorinated polyimides is limited by synthetic difficulties associated with the incorporation of a substantial number of pendant perfluoroalkyl groups.

#FIG. 1 is a high magnification optical photomicrograph illustrating a substantially defect-free methylsilsesquioxane (MSSQ) coating prepared using the method of the invention.

#FIGS. 2A-2C represent the prior art, wherein FIGS. 2A and 2B are high magnification and low magnification optical photomicrographs, respectively, illustrating defects in a coating of neat MSSQ resin near the edge of a wafer, while FIG. 2C is a high magnification optical photomicrograph illustrating defects in a coating of neat MSSQ resin at the center of a wafer.

#FIG. 3 is a graph illustrating the change in viscosity over time of an MSSQ coating solution containing dimethylamino ethyl isobutyrate, dimethylamino ethanol, and a poly(methyl methacrylate-co-dimethylaminoethyl methacrylate) (poly(MMA-DMAEM)) copolymer as porogens.

#Before describing the present invention in detail, it is to be understood that unless otherwise indicated this invention is not limited to specific substrates, coating compositions, or process steps, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

#It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a porogen” includes mixtures of porogens, a “host polymer” includes combinations of host polymers, “a solvent” includes mixtures of solvents, and the like.

#In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.