Preventing method of volume expansion of polymer after metal infiltration

Polymeric materials have been utilized in semiconductor industries such as pattern formation materials. One of the drawbacks of such polymers is the lack of etch resistance. Metal infiltration into polymer matrices is an emerging technology that could overcome the issue. The gaseous organo-metal precursors penetrate into polymer matrices where they are oxidized to form stable metal oxides. Thus formed organic-inorganic hybrid material shows superior etch-resistance which enables to form patterns with high aspect ratio [1]. One of the most commonly studied processes is the infiltration of trimethylaluminium (TMA) into polymethylmethacrylate (PMMA). One of the issues of this technology is that increase in volume of the polymer after the infiltration is inevitable, since metal oxides are added to the polymer. For example, we observed over 10 % of volume expansion for the combination of PMMA and TMA [2]. If this technology was dedicated to small feature sizes, it would be preferable to maintain its original shape. Poly(tert-butylmethacrylate) (PtBuMA) has a similar structure to PMMA except that it has a tert-butyl group on its side-chain instead of a methyl group. This polymer is known to decompose above 180 degree Celsius, releasing the butyl group in form of 2-butene. If the out-going of tert-butyl group and the in-coming of TMA occurs simultaneously under ambient temperature, we can expect to see a balance of volumetric shrinkage and expansion. In this paper, a concept using PtBuMA to compensate the volume increase after metal infiltration is described.