Browse Prior Art Database

Wafer Conformable Image Mask

IP.com Disclosure Number: IPCOM000044879D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Pittler, MS: AUTHOR [+2]

Abstract

As semiconductor lithography becomes increasingly dense it has become more and more difficult to make masks capable of achieving necessary resolution on a wafer. The problem becomes more difficult when the wafer has significant vertical topography. In this case the limited depth of field of the optical apparatus used to project the mask image on a wafer causes added distortion. The depth of field of a conventional optical system will be less than a micron (10-6m). Modern wafers may have topography of several microns. Electron beam systems have adequate depth of field but are generally too slow to expose wafers directly and hence are used to make masks resulting in the limitations previously described.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 83% of the total text.

Page 1 of 1

Wafer Conformable Image Mask

As semiconductor lithography becomes increasingly dense it has become more and more difficult to make masks capable of achieving necessary resolution on a wafer. The problem becomes more difficult when the wafer has significant vertical topography. In this case the limited depth of field of the optical apparatus used to project the mask image on a wafer causes added distortion. The depth of field of a conventional optical system will be less than a micron (10- 6m). Modern wafers may have topography of several microns. Electron beam systems have adequate depth of field but are generally too slow to expose wafers directly and hence are used to make masks resulting in the limitations previously described.

This invention provides a means of overcoming the depth-of- field problem. It describes a unique combination of the electron beam system's superior depth-of- field and the production efficiency of optical exposure tools.

The principle is to make the mask in the form of a hologram. The hologram can be imaged in a three dimensional form and hence the image can be made to conform to the topography of the wafer.

The method is as follows. A wafer is fabricated so as to have the topography of the wafers to be exposed. A pattern is formed on this wafer having well defined geometry and reflectance far different from the surface. A thin metal film, exposed by electron beam exposure techniques and etched by reactive ion etch, is such a suitable s...