Abstract: The method of the present invention comprises the steps of: (a) laying on a prior layer, a first oxide layer doped in one form; (b) laying on said first oxide layer, a second oxide layer doped in a different form; (c) patterning said layers; (d) etching the second layer with an etchant having high selectivity to said second doped oxide layer; and (e) etching the first layer with an etchant having high selectivity to said first doped oxide layer. As the etch rate is higher for the highly doped oxide than that for the lightly doped oxide, high selectivity of etching between such layers can therefore be attained. A lightly doped silicon oxide layer may therefore be used to stop etching at an optimal thickness over the complicated layer of substrate. The lightly doped silicon oxide area may be covered with a layer of highly doped silicon oxide layer which may be etched with a specific etchant.

Abstract: The method of the present invention comprises the steps of: (a) laying on a prior layer, a first oxide layer doped in one form; (b) laying on said first oxide layer, a second oxide layer doped in a different form; (c) patterning said layers; (d) etching the second layer with an etchant having high selectivity to said second doped oxide layer; and (e) etching the first layer with an etchant having high selectivity to said first doped oxide layer.