Planar silicon diodes and transistors

In the planar design of diodes or transistors, the device is fabricated to its final shape during the diffusion operations, rather than during a mesa operation subsequent to diffusion. The planar process involves the application of a suitable coating on the silicon surface prior to the diffusion operations so that the junctions emerge from the bulk of the material under the coating and are protected from environmental contamination. Two types of devices made by the process will be described: a planar diode and a planar NPN transistor. Dopants used in both cases are boron and phosphorus and the lateral limitation of the diffused layers is obtained by oxide masking of suitable shape. The outstanding property of planar units is the very tight distribution of diode reverse currents over a large sample of units. Values of these currents are in close agreement with those calculated from bulk reverse currents. Life test data indicate improved reliability at high temperature storage over mesa units of similar characteristics. Data on unencapsulated units will also be presented.