Selective Etching of Phosphosilicate Glass with Low Pressure Vapor HF

A reliable low pressure vapor etch process was developed for the selective removal of phosphorus‐doped silicon oxides. With this process, a high etch rate ratio of phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG) over undoped oxide is obtained. The high etch selectivity is accomplished by controlling the total vapor pressure and/or the partial pressure. Under the low vapor pressure conditions, adsorption on the oxide surface is suppressed, resulting in a low etch rate of the undoped oxide. The etching of (B)PSG is not suppressed even at low vapor pressure, since an layer is formed on the surface and fluorine species dissolve in this layer. Because of this difference in etch mechanisms, high etch rate ratios of (B)PSG to thermal oxide of over 2000 were obtained over a wide range of conditions. Further, the low pressure vapor etch technique was successfully applied for selective damage‐free removal of the core BPSG film from cylindrical capacitor structures in DRAMs. By applying this new process, the number of process steps involved in the formation of a cylindrical capacitor can be reduced.