A method of forming openings in a polymer layer includes positioning a layer of a material over a cavity such that a portion of the first material lies over a cavity, ablating the portion of the material at a first shape, and ablating the portion of the material at a second shape, wherein the second shape lies within the first shape. A method of forming openings in a polymer layer includes positioning a layer of a first material over a second material having a cavity such that a portion of the first material lies over the cavity, ablating the portion of the first material over the cavity at a first shape, and ablating the portion of the second material over the cavity at a second shape, wherein the second shape lies within the first shape.