Chemical etching solutions for air gap formation using a sacrificial oxide/polymer approach

The formation of intra metal level ''air cavities'' using a sacrificial oxide in a Dual Damascene copper interconnect structure was investigated for different HF solutions. In this approach, HF solutions diffuse throughout a porous polymer membrane to realise the cavities within the interconnect stack. Results were discussed in terms of silicon dioxide etching rate, vertical and lateral diffusion behaviour in the porous membrane for three different chemistries. The formation of two oxide levels in the same operation with very short process times (in the range of few minutes) was demonstrated. Main limitations on the current architecture have been evaluated in terms of copper and diffusion barrier integrity and alternative solutions have been proposed to overcome them.