US Patent 7163641 Method of forming high aspect ratio apertures

A plasma etch process for etching BPSG employing two primary etchants at low flows and pressures, and a relatively low temperature environment within the etch chamber, which includes a fluorine scavenger in the form of silicon. The two primary etchant gases are CHF3 and CH2F2, delivered at flow rates on the order of between about 10 and 40 sccm for CHF3 and between about 10 and 40 sccm for CH2F2. Small quantities, on the order of 10 sccm or less, of other gases such as C2HF5 and CF4 may be added.