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IR Phase Contrast Technique for Identifying and Locating Defects in Passivation Layers

IP.com Disclosure Number: IPCOM000050119D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Hopper, GS: AUTHOR [+3]

Abstract

Defocussed infrared (IR) transmission images of passivation layers on silicon wafers are used to identify defects in the layers.

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IR Phase Contrast Technique for Identifying and Locating Defects in Passivation Layers

Defocussed infrared (IR) transmission images of passivation layers on silicon wafers are used to identify defects in the layers.

Recent investigations have shown that passivation defects can be very important in determining the reliability of underlying conductor stripes. A major problem is, however, that defects in the passivation are difficult to detect. Since glass is transparent, and the silicon chip is opaque, the defects are invisible in reflected light and, since they are not surface defects, they cannot be detected by a scanning electron microscope (SEM).

However, because of the fortuitous property of silicon that is transparent in the infrared, one can observe the passivation layers in transmission.

In transmission one can obtain contrast around a defect by defocussing the image slightly. The slight defocus allows the wave front, diffracted from the defect, to interact in a series of additive and subtractive interferences. Thus, in the underfocussed condition, a pore will appear as a light spot surrounded by a dark ring. This contrast reverses upon going to the overfocussed condition. In addition, an inclusion will appear with opposite contrast to that of a pore. Thus, the nature (pore or inclusion) and the vertical location of the defect can be determined by bringing the image through focus from the under to the overfocussed condition.

When in focus the object will di...