Vapor Deposition of Low-Dielectric-Constant Polymeric Thin Films

Abstract

For devices with feature sizes below 0.18 μm, it is desirable to have materials with a dielectric constant below 2.5 as interlayer dielectrics. Polymeric materials are possible candidates. There are two main strategies to grow polymeric films. The most widely used method is the spin-on technique. The other method is by vapor deposition. Although vapor deposition is less common, it has several attractive features that look quite promising, especially when the wafer size becomes very large.There are several advantages to vapor-deposited polymers:(1) The deposition of the polymers is a dry process. It is solvent-free and does not produce waste. No remedial measures are necessary to take care of the waste. The process is attractive from both energy-conservation and environmental considerations.(2) They can provide an extremely uniform coating over a very large area. For 200-mm wafers, for example, one can achieve better than 2% uniformity for vapor-deposited parylene (a type of polymer to be described later) films. Similar uniformity can be expected for future 300-mm wafers.(3) Many vapor-deposited polymers possess superior gap-filling capability. Small vias and trenches of very high aspect ratios can be filled without voids.There are some shortcomings in vapor deposition of polymeric thin films. First of all, except for some special cases, processing issues for these materials are not well-studied. Manufacturing equipment is not well-developed.