Browse Prior Art Database

Stepper Focus Compensation for Atmospheric Pressure Variations

IP.com Disclosure Number: IPCOM000061986D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Bakeman, PE: AUTHOR [+4]

Abstract

A novel real time focus compensation technique is presented for current reduction step and repeat semiconductor tooling which negates the current need for focus adjustment with changes in barometric pressure.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 67% of the total text.

Page 1 of 1

Stepper Focus Compensation for Atmospheric Pressure Variations

A novel real time focus compensation technique is presented for current reduction step and repeat semiconductor tooling which negates the current need for focus adjustment with changes in barometric pressure.

Focus drift during barometric changes is a major problem in state-of-the-art lithographic printing step and repeat tools. Air pressure changes cause the refractive index (n) of air to change at the lens-air interface resulting in optical property changes in the tool.

Currently there are two ways of coping with the problem of atmospheric pressure variations: 1) Control n by using pressurized lens columns. 2) Generate a pressure-focus chart for each stepper.

The first technique requires an extensive retrofit in order to help existing systems and the second method of generating pressure-focus charts is time consuming. Over time, tools ten drift away from the chart parameters generated and require further efforts to produce another chart set.

By controlling the optical parameter affecting lens performance i.e., the refractive index of the gas around the le stepper focus compensation for atmospheric pressure changes can be effected. A flow of gasses into the stepper environment with the correct mixture to maintain a constant n will provide stepper focus compensation for atmospheric variations in air pressure. A combination of two gases in the correct proportions, one with a higher n and one with a low...