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Photodiode Mask for Endpoint Detection System

IP.com Disclosure Number: IPCOM000040895D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Durham, JA: AUTHOR [+2]

Abstract

The use of a mask to avoid unwanted reflections from reaching the photodiode in an endpoint detection system results in improved accuracy and reliability of the system.

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Photodiode Mask for Endpoint Detection System

The use of a mask to avoid unwanted reflections from reaching the photodiode in an endpoint detection system results in improved accuracy and reliability of the system.

In the processing of semiconductor wafers, accurate determination of the etch endpoint is critical to insure product quality. A visually aligned endpoint detection system used on reactive ion etching tools employs a laser to generate a beam which is reflected off the wafer being etched. The reflected beam is detected by a photodiode. An endpoint signal results from the interference of the reflected laser beam from the wafer surface and the interface of a thin film on the wafer as it is being etched.

The reflected laser beam passes through several lenses and beam splitters before reaching the photodiode. The lenses and beam splitters cause unwanted reflections which cause the output of the photodiode to be erratic and often prevents accurate detection of the etch endpoint.

A mask consisting of a stainless steel disk with about a 60 mil hole is mounted in front of the photodiode. The main reflected laser beam is aligned to pass through the hole. This arrangement prevents the unwanted reflections from reaching the photodiode, resulting in a well-defined endpoint.

Disclosed anonymously

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