A Simple Approach to Eliminate Occasional Grass FormationIn ICP Backside Via Etch Process

Grass’ formation is the very common defects for via etch process when using a BCl3/Cl2 as basic gases in an inductively coupled plasma (ICP) system. Presence of grass can potentially degrade device performance due to poor metallization coverage. In this study we found that grass formation strongly depends on GaAs surface condition prior to etch. Any surface contaminants, such as photo resist residues and/or scumming can contribute to grass formation. We found that applying suitable chemical clean and O2 plasma descum prior to via etch process would prevent the grass formation. To avoid changes to via profile and/or etch rate, etch parameters were not altered in this study.