GB1278052A - Semiconductor devices and methods of making them - Google Patents

Abstract

1278052 Semi-conductor devices WESTERN ELECTRIC CO Inc 21 May 1969 [21 May 1968] 25938/69 Heading H1K The impurity concentration profile near the surface of a semi-conductor wafer is adjusted by heating the wafer in an oxidizing atmosphere under such conditions that the rate of increase in thickness of the oxide is greater than the rate of diffusion of an impurity. Impurities which have a greater affinity for the semi-conductor than for the oxide are concentrated in the semiconductor near the oxide-semi-conductor interface by this process forming an enhanced impurity concentration layer, while impurities which have a greater affinity for the oxide than for the semi-conductor are absorbed into the oxide forming a depleted impurity concentration layer. A plurality of Zener diodes are produced by forming an oxide layer (12) on the surface of an N-type Si slice (11) heavily doped with Sb, photomasking and etching to form a plurality of apertures (13) in the oxide, predepositing and driving-in B to form a heavily doped P-type region (14) and removing the glassy layers formed in the apertures. The wafer is then heated in a wet oxidizing atmosphere to redistribute the impurities. The Sb atoms are pushed ahead of the advancing oxide layer to form a layer 16 of enhanced conductivity at the surface of the N- type region. The B atoms are absorbed into the oxide layer to form a layer 17 of depleted conductivity at the surface of the P-type regions. This redistribution of impurities results in a decrease in the reverse breakdown (Zener) voltage while maintaining a hard breakdown characteristic. A window is opened in the oxide layer (15) formed in each of the original windows and contacts 18 are deposited on the P-type regions 14, a layer of Ag is applied to the lower face of the slice 11 which is then scribed and broken into individual diode wafers. If it is found that the breakdown voltage has been reduced too far the slice may be heated at a higher temperature (1250‹ C.) which results in the mobility of the impurities being greatly increased to a value greater than the rate of oxidation of the semi-conductor so that the impurity concentration and the breakdown voltage return to their original values. The wafer may then be re-processed to reduce the breakdown voltage to the desired value. It is stated that Al segregates into the oxide, Ga, In, As, P and Sb segregate into the semiconductor and B may do either or remain unaffected depending upon the conditions.