A method of forming a semiconductor device, comprising: forming a layer of dielectric material, wherein an upper portion of the layer of dielectric material has a first etch rate with respect to an etchant and a lower portion of the layer of dielectric material has a second etch rate with respect to the etchant; forming a layer of semiconductor material over the layer of dielectric material; forming an opening in the layer of semiconductor material and exposing the layer of dielectric material through the opening; etching with the etchant, the layer of dielectric material through the opening to remove a portion of the layer of dielectric material underneath the layer of semiconductor material with the etchant, wherein the upper portion of the layer of dielectric material is removed by etching with the etchant at a faster rate than the lower portion of the layer of dielectric material is removed by the etching with the etchant such that a remaining side wall of the layer of dielectric material defined by the etching underneath the layer of semiconductor material is non planar with an upper portion of the remaining side wall extending laterally farther from the opening than a lower portion of the remaining side wall extending laterally from the opening; forming a structure of semiconductor material in a location where the layer of dielectric material was removed by the etching, wherein the structure extends underneath the layer of semiconductor material to contact a bottom surface of the layer of semiconductor material underneath the layer of semiconductor material, the structure having a structure side wall with an upper portion corresponding to the upper portion of the remaining side wall that extends farther underneath the layer of semiconductor material than a lower portion of the structure side wall that corresponds to the lower portion of the remaining side wall, characterized in that forming the layer of dielectric material includes: in-situ introducing dopants during the latter part of the deposition of said layer of dielectric material, to provide the upper portion of the layer of dielectric material with a higher concentration of the dopants than the lower portion of the layer of dielectric material, such that the first etch rate is faster than the second etch rate. forming a layer of dielectric material, wherein an upper portion of the layer of dielectric material has a first etch rate with respect to an etchant and a lower portion of the layer of dielectric material has a second etch rate with respect to the etchant; forming a layer of semiconductor material over the layer of dielectric material; forming an opening in the layer of semiconductor material and exposing the layer of dielectric material through the opening; etching with the etchant, the layer of dielectric material through the opening to remove a portion of the layer of dielectric material underneath the layer of semiconductor material with the etchant, wherein the upper portion of the layer of dielectric material is removed by etching with the etchant at a faster rate than the lower portion of the layer of dielectric material is removed by the etching with the etchant such that a remaining side wall of the layer of dielectric material defined by the etching underneath the layer of semiconductor material is non planar with an upper portion of the remaining side wall extending laterally farther from the opening than a lower portion of the remaining side wall extending laterally from the opening; forming a structure of semiconductor material in a location where the layer of dielectric material was removed by the etching, wherein the structure extends underneath the layer of semiconductor material to contact a bottom surface of the layer of semiconductor material underneath the layer of semiconductor material, the structure having a structure side wall with an upper portion corresponding to the upper portion of the remaining side wall that extends farther underneath the layer of semiconductor material than a lower portion of the structure side wall that corresponds to the lower portion of the remaining side wall, characterized in that forming the layer of dielectric material includes: in-situ introducing dopants during the latter part of the deposition of said layer of dielectric material, to provide the upper portion of the layer of dielectric material with a higher concentration of the dopants than the lower portion of the layer of dielectric material, such that the first etch rate is faster than the second etch rate.