In some embodiments, silicon-filled openings are formed having no or a low occurrence of voids in the silicon fill, while maintaining a smooth exposed silicon surface. In some embodiments, an opening in a substrate may be filled with silicon, such as amorphous silicon. The deposited silicon may have interior voids. This deposited silicon is then exposed to a silicon mobility inhibitor, such as an oxygen-containing species and/or a semiconductor dopant. The deposited silicon fill is subsequently annealed. After the anneal, the voids may be reduced in size and, in some embodiments, this reduction in size may occur to such an extent that the voids are eliminated.