Influence of deposition and etching on high aspect ratio patterning

The tailoring of a dry etching process in order to fulfill all requirements in a high yield, low cost production becomes increasingly ambitious. Stringent specifications on plasma induced damage, etching selectivity, linewidth control, and etching uniformity necessitates time consuming and expensive plasma process development. Moreover, uniform etching suffers from unexpected problems depending on aspect ratio and pattern density. The effect of decreasing etchrate with increasing aspect ratio, commonly labeled as microloading, is detected in a wide variety of materials and etching conditions. This includes halogen- as well as oxygen- and hydrogen-based chemistry in low and high pressure plasmas. In different reactor types ranging from RIE diodes, high density plasma sources, magnetically enhanced triodes, and microwave driven systems microloading is observed. A number of approaches explaining microloading consider ion angular distributions, ion and neutral shadowing, charging of micros tructures, and Knudsen transport of neutrals. However, predicting profiles in a specific plasma process requires additional investigations for the understanding of microloading. This contribution focusses on aspect ratio dependent etch rates and profiles in SiO2 as a balance of etching and deposition. Patterning of contact holes down to 0.2mu m with aspect ratios of more than 10:1, the influence of polymer deposition and etching is studied. TEM analysis of patterns gives an insight into process mechanisms identifying polymer deposition in low and high aspect ratio features.