remaining in the side walls of the original moat 28 is removed by a suitable wet etch such as a fifty to one h 2 o hf mixture the resultant is shown in fig2 f as seen the buried open cavity 32 includes the intact unwidened neck portion 34 whose lateral dimensions essentially are those of the hole 26 in the masking layer 24 next the wafer 20 is exposed to an ambient suitable for the growth of epitaxial monocrystalline silicon laterally within the neck portion 34 to fill it and thus define a sealed and buried or sealed buried cavity 16 the deposition conditions are chosen to favor lateral growth rather than vertical growth so that the neck opening 34 can be filled without materially affecting the remainder of cavity 16 typical conditions for such deposition are 950 u00b0 c 50 torr pressure 80 liters minute h 2 3 6 liters minute hcl and 1 8 liters minute dichlorosilane in some instances it may proves advantageous to improve the quality of the crystal structure in the diaphragm portion deposited by known laser melt and regrowth techniques by including such a technique there may be formed monocrystalline diaphragm portions of larger area than might otherwise be conveniently grown without it after the removal of the original masking layer 24 the structure shown in fig2 g results it comprises a monocrystalline silicon chip 12 which is still a portion of wafer 20 and that includes a sealed and buried cavity 16 below the front.