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Structure for Electrical Measurement of Overlay Between P+ Layer and Isolation

IP.com Disclosure Number: IPCOM000038718D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Yee, PL: AUTHOR [+3]

Abstract

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 a┬╣aspect 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.

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Structure for Electrical Measurement of Overlay Between P+ Layer and Isolation

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. However, with misalignment they are not equal, and this results in a larger area for either the emitter or collector window. Such a misalignment is evident in Fig. 2, where w1 3 is greater than w2 4. The terminal base current depends strongly on these areas. Because of the aspect ratio chosen and the very small contacts, the amount of misalignment can be determined from terminal base current measurements. Initially, the base current of the device is measured by having w1

(Image Omitted)

as the emitter and w2 as the collector. The current is measured again, this time after switching the emitter and collector. The change in the base current then helps to determine the centerline overlay by using the current equation of LPNP: IB1 = AncJnc + ApvJpv + (Apv-Anc)Jno = Anc(Jnc-Jno) + Apv(Jpv + Jno)

Apv = (WGL1 + Itol + CL)1 Therefore: IB1 = Anc(Jnc-Jno) + (WGL1 + Itol + CL)1(Jpv + Jno) IB2...