Reaction pathways etching

TiCU readily functionalizes hydrophilic polymers such as poly(vinyl alcohol), m-ciesol novolac and methacrylic acid copolymers as well as moderately hydrophobic polymers such as poly(methyl methacrylate), poly(vinyl acetate), poly(benzyl methacrylate) and fully acetylated m-cresol novolac. HCI4 did not react with poly(styrene) to form etch resistant films indicating that very hydrophobic films follow a different reaction pathway. RBS analysis revealed that Ti is present only on the surface of hydrophilic and moderately hydrophobic polymer films, whereas it was found diffused through the entire thickness of the poly(styrene) films. The reaction pathways of hydrophilic and hydrophobic polymers with HCI4 are different because TiCl is hydrolysed by the surface water at the hydrophilic polymer surfaces to form an etch resistant T1O2 layer. Lack of such surface water in hydrophobic polymers explains the absence of a surface TiC>2 layer and the poor etching selectivities. 

The feed gas to the reactor is composed of molecules that contain the etching species. Fluorine containing molecules such as CF4, CF3H, or SiFs are used to etch silicon. Molecules such as H2 or O2 may also be present in the feed gas to control the reaction pathways and will be subsequently discussed. This feed mixture is termed the recipe for the etching process. To etch aluminum or aluminum silicide, which are used to make the electrical contacts to the active device region, a chlorine containing gas such as BCI3 is used. 

Another critical need identified in Database Needs for Modeling and Simulation of Plasma Processing (Database, 1996) is the measurement of thermodynamic data for species of interest in plasmas (radicals and ions). Such data provide benchmarks for comparison with calculated potential energy surfaces, allow energetically unfavorable reaction pathways to be identified, and supply information necessary to estimate unknown reaction rates by transition state theory. Such thermodynamic information is a critical tool in understanding deposition and etching processes and in evaluating the optimum conditions for plasma reactors (Kruis et al, 1992). 

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