Structure for Electrical Measurement of Overlay Between P+ Layer and Isolation
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Feb-01
The method electrically measures the centerline overlay of P+ diffusion to isolation in semiconductor devices. This was previously accomplished by means of manual optical measurements. An isolation defined LPNP is the measurement device used which consists of a symmetric lateral PNP with emitter 1 (Fig. 1) and collector 2 with a diffusion window a¹aspect ratio (1/w) made up of length 5 and width 3,4. This is specifically adjusted and is especially sensitive to variations in dimension w1 3 or w2 4. It has very small, but always equal, contacts 10. The illustration depicts the P+ diffusion 6 mask level, the isolation 7 mask level, the base 8 mask level, and the reach through 9 mask level. Nominally, w1 - w2.