Browse Prior Art Database

High Pressure Alignment Detector

IP.com Disclosure Number: IPCOM000073792D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Bojman, W: AUTHOR

Abstract

An alignment method is presented which is suitable for mask to wafer alignment in photoresist procedure. A rosette pattern is scanned in a circular path generating a signal which has alignment information in the frequency modulation of the signal. The signal is analyzed by standard FM processing circuits. The scanning is accomplished by projecting the rosette pattern on a vidicon tube screen with the scanning electron beam controlled to travel in a circle. It can be shown that a low resolution identification or reference mark and simple electronics yield dimensional resolutions of the order of less than 5 microinches. Direction and magnitude of the misalignment are generated in a convenient format.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

High Pressure Alignment Detector

An alignment method is presented which is suitable for mask to wafer alignment in photoresist procedure. A rosette pattern is scanned in a circular path generating a signal which has alignment information in the frequency modulation of the signal. The signal is analyzed by standard FM processing circuits. The scanning is accomplished by projecting the rosette pattern on a vidicon tube screen with the scanning electron beam controlled to travel in a circle. It can be shown that a low resolution identification or reference mark and simple electronics yield dimensional resolutions of the order of less than 5 microinches. Direction and magnitude of the misalignment are generated in a convenient format.

As illustrated in Drawing A, the reference mark is a rosette made of alternating and contrasting segments of a ring. The dimensions shown illustrate a range within which the method will operate. The reference mark is magnified until it covers substantially the active area of the vidicon tube screen. The electron beam in the vidicon is caused to describe a circle of constant diameter at a constant speed. The vidicon output current is then amplified and analyzed.

When the vidicon is perfectly aligned with the reference mark, the output signal is a square wave of frequency Nn, where N is the number of segments on the reference mark and n the frequency of the signal controlling the electron beam of the vidicon. The time of dwell on any segment is 1 over 2Nn.

If the vidicon is misaligned relative to the reference mark, the time of dwell of the electron beam on individual segments, and on spaces between them, of the rosette will vary in a harmonic mode about the average which is still 1 over 2Nn. The frequency of this variation is also n.

From Drawing B it is seen that when the vidicon beam travels closest t...