2. Field Threshold Implant and Field Oxidation [Fig. 4.17(b)]. Nitride (Si3N4) is deposited, masked, then etched. The etched nitride regions define the location of the field threshold ion plant [Fig. 4.17(b)] and the locations where oxide Si02 is permitted to grow during field oxidation [Fig. 4.17(c)]. Areas where nitride remains mask (prevent) oxide growth. These regions are where transistors will be built. The thick (approximately 6000 A) field oxide isolates adjacent transistors in ord