The present invention relates generally to a new apparatus and method for forming cavities in semiconductor substrates without the necessity of using an insert. More particularly, the invention encompasses an apparatus and a method for fabricating cavities in semiconductor substrates wherein a coated membrane sheet is placed over the cavity prior to lamination and caused to conform to the contour of the cavity, thus preventing collapse of, or damage to, the cavity shelves during the lamination process. After the lamination process, the coated membrane is conveniently removed without causing damage to the cavity shelves or paste pull-outs.