Reflow of BPSG for sensor applications

Borophosphosilicate glass (BPSG) has been investigated for both the surface planarization of plasma-etched and refilled trenches before etchback and structural layer deposition to enable the fabrication of genuine surface-micromachined double clamped beams and the smoothing of bulk-micromachined surfaces up to mirror quality for optical applications. Sufficient reflow has been obtained without an excessive reduction of the etch rate in HF using low-pressure chemical vapour deposition (LPCVD) with 8 sccm BCl3 flow at 950 degrees C.