Abstract: The present disclosure pertains to our discovery of a method of etching a shaped cavity in a substrate, where the shaped cavity has a width that is at least as great as its depth. We have discovered that by varying the process chamber pressure during etching of the shaped cavity, we can control lateral etching of the shaped cavity, while allowing the removal of etch process byproducts from the shaped cavity during continued etching. The method of the invention can be used to etch shaped cavities having round or horizontal elliptical shapes. The method of the invention is particularly useful in the etching of buried cavities, where removal of etch byproducts from the cavity can be difficult.