Benzocyclobutene dry etch with minimized byproduct redeposition for application in an InP DHBT process

• Reduced dry etch byproducts after structuring Benzocyclobutene with resist in a sulfur hexafluoride/oxygen (SF6/O2) plasma
• Dry etch tests with different substrate carrier materials (PEEK, Al, Ti) shown different behavior in terms of redeposition, etch rate and bias
• Redeposition consists of aluminium, oxygen and fluorine
• Origin of redeposition origin is most probable the substrate carrier clamp
• Redeposition can be removed residue free with TMAH-based developer (MF-26 A)

In this article we report on the reduction of redeposition during inductively coupled plasma (ICP) etching of benzocyclobutene (BCB) with a soft mask in a sulfur hexafluoride/oxygen (SF6/O2) plasma. We have developed an anisotropic ICP recipe to fabricate vertical interconnects through BCB for our indium phosphide (InP) transferred-substrate DHBT technology. In this context the new recipe has an etch inhomogeneity on 3 in. wafer of < 1% 3-sigma based on the total BCB thickness. The origin of residuals post resist ashing consisting of Al, F, and O was traced back to reactor chamber parts made from Al2O3. The amount of redeposition appears to be minimized with lower chamber pressure. We saw an impact of different substrate carrier materials on the amount of redeposition, etch rate, and bias. Remaining deposits could be removed in a wet chemical final rinse, which was based on diluted tetramethylammonium hydroxide (TMAH). With the new high density plasma recipe the BCB etch rate could be increased fivefold while maintaining excellent lateral structure fidelity and minimizing etch byproduct redeposition.

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