first layer 52 mask is accomplished using shipley positive resist 1813 processed according to standard procedures the mesa and trench pattern is that depicted in fig6 with the mesas being 140 micrometers wide and the trenches being 60 micrometers wide the trench 44 is etched into the silicon using a mixture of 80 parts by volume nitric acid and 1 part by volume hydrofluoric acid at ambient temperature for about 5 minutes the depth of the trench is about 3 micrometers the second layer 56 is 1000 angstroms of a sublayer of silicon glass deposited from the standard atmosphere of oxygen nitrogen diborane and silane with a diborane to silane ratio of 0 07 and with an overlying sublayer of 2000 angstroms of undoped glass deposited from a silane atmosphere deposition is at a total pressure of 1 atmosphere and a temperature of 400 u00b0 c and is accomplished with a tempress model pyrox 216 apparatus thus in this case the mesa tops become doped n and the bottoms of the trenches become doped p the drive in of phosphorus and boron into the substrate piece is accomplished by heating to a temperature of 1120 u00b0 c for a time of.