The electron beam fabrication of small geometry transistors

Abstract

The present trend in molecular electronics is both to reduce the overall size of the completed circuit and also to go to more complex circuits containing larger numbers of components. Both of these tendencies result in the requirement of smaller component sizes in the circuit. However the planar method normally used to fabricate these components is subject to certain dimensional limitations. This paper describes the fabrication of a planar bipolar transistor with an emitter contact 1 μ 2. This reduction in geometry is made possible by the use of an electron beam for the exposure of the resist rather than the conventional method of defining area by optical exposure of a light sensitive resist through a photographic mask. The problems involved in the location and sequential alignment of these small areas are discussed and a novel method for overcoming these difficulties is described. This technique utilizes the effect of lateral diffusion under the oxide mask to achieve area isolation combined with the definition of small areas by the intersection of narrow stripes. It is possible by these methods to drastically reduce the requirements for sequential alignment. The characteristics of micron size transistors with total active areas only 0·0002 × 0·0006 in. will be presented.