GB1218603A - Improvements in and relating to semiconductor devices - Google Patents

Abstract

1,218,603. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 15 Jan., 1968 [18 Jan., 1967], No. 2135/68. Heading H1K. A semi-conductor device such as an integrated circuit comprises a semi-conductor body having a portion 1 of one conductivity type and one or more islands 2 of the opposite type adjoining one surface of the body and forming electrically separating PN junctions 3 with the portion, at least one semi-conductor circuit element (e.g. transistor, diode, resistor, capacitor or multi-layer structure) incorporating a zone 5 of the one conductivity type being formed in at least one island and the breakdown voltage of the junction 3 being lower than the breakdown voltage between the zone 5 and the island. The breakdown voltage of the junction 3 is determined by a local, more highly doped, zone of the portion 1, preferably in the form of a separation channel 7, and a local, more highly doped, buried zone 8 of the island, the more highly doped zones being separated by, and defining part of, the PN junction 3 and the impurity concentration characteristic of the one conductivity type in the zone 7 having a maximum adjacent the part of the junction defined by the zones 7 and 8. In one method of making the device, arsenic is vapour-deposited on one surface of a silicon wafer 1 and diffused into the wafer in an oxygen atmosphere to form the highly doped zone 8 and an oxide layer (9, Figs. 3-7, not shown). A channel (10) enclosing the island 2 is etched in the oxide layer, the exposed silicon is etched to a depth of a few tenths of a micron, and boron is vapour-deposited to form a highly doped region (11) which is then diffused through the zone 8 to reach the portion 1. This is possible because boron diffuses about ten times as fast as arsenic. The oxide layer is then removed, an epitaxial layer 4 is grown on the surface, and a further oxide layer 12 is formed on the layer 4 and provided with a channel (13) immediately above the region (11). Boron is vapour deposited in the channel (13) and diffused into the layer 4 to meet the region (11) to form the highly doped separating channel 7, and simultaneously with this diffusion, or subsequently, boron is diffused through a suitable opening in the oxide layer to form the base zone 5 of a transistor. Phosphorus is then diffused-in to form the emitter zone 6 and collector contact zone 28 and finally aluminium is deposited to form contacts 18-20. The circuit is connected to voltage sources V 1 , V 2 in such a way that the voltage difference V 1 between the portion 1 and the base zone 5 is smaller than the difference between the breakdown voltages defined above. When the voltage V 2 is increased the junction 3 breaks down before the breakdown voltage between the base zone 5 and the collector zone 4 is reached so that damage to the transistor is prevented.