Microloading effect in ultrafine SiO2 hole/trench etching

Abstract

In the search of new etchant gas combinations which address the earth’s environmental concerns, a new C3F6-based plasma etch chemistry is investigated and evaluated for patterning fine SiO2 structures. Trimethylsilane and O2 are added first separately to C3F6 to investigate their respective influence. It is shown that both trimethylsilane and O2 additive gases have beneficial effects on the hole etching process but also result in undesired effects such as enhancement of the microloading effect upon trimethylsilane addition, and poor BPSG/resist selectivity upon O2 addition. When trimethylsilane and O2 are combined and mixed with C3F6, the opening of fine deep holes are achieved. For example, 0.15 μm holes with an aspect ratio of 15 are fabricated using C3F6/8% trimethylsilane/20% O2. The plasma conditions employed are a pressure of 10 mTorr, an rf source power of 500 W, a total flow rate of 30 sccm, and a bias power of 150 W. These plasma conditions allow good control of the hole size, practical resist selectivity for deep hole processing, and microloading-free etching of holes down to 0.15 μm. The C3F6-based plasma etch performance is further evaluated for nanometer-scale patterns using the simpler C3F6/O2 gas system. Line and space and mesh hole patterns delineated by electron lithography are fabricated with dimensions as small as 20 and 70 nm, respectively.