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METHOD FOR OFFLINE PHOTOLITHOGRAPHIC EVALUATION ON VARIOUS SUBSTRATES

IP.com Disclosure Number: IPCOM000006245D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-18
Document File: 3 page(s) / 141K

Publishing Venue

Motorola

Related People

Gerald A. Keller: AUTHOR

Abstract

Manufacturing timetables to meet customer demands for integrated circuits can push the process engineer into production with little time for lengthy qualifi,cation procedures. Some equipment, such as SEM and optical critical dimension measuring equip- ment that provide valuable data to the engineer require significant time delays to gather necessary informa- tion. Availability of the critical dimension measuring equipment for develop module setup is also an issue. Because of this, and the need to make adjustments to the equipment in a timely manner anyway, the method described here has found application. In this method a light, uniform exposure dose is applied across the pho- toresist coated wafer substrate and then developed. By observing pattern colorations in the developed film, adjustments to the hardware, etc. are made to optimise develop and process uniformity across the wafer substrate. During the initial setup phase of a photolithographic process, contrast (the slope found by taking the linear regression of the normalized resist thickness versus the logarithm of the exposure dose at a fixed develop process time) and Eo (threshold or the exposure dose at which the photoresist film develops out) are determined (Figure 1).

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MOTOROLA INC. Technical Developments Volume 13 July 1991

METHOD FOR OFFLINE PHOTOLITHOGRAPHIC

EVALUATION ON VARIOUS SUBSTRATES

by Gerald A. Keller

  Manufacturing timetables to meet customer demands for integrated circuits can push the process engineer into production with little time for lengthy qualifi,cation procedures. Some equipment, such as SEM and optical critical dimension measuring equip- ment that provide valuable data to the engineer require significant time delays to gather necessary informa- tion. Availability of the critical dimension measuring equipment for develop module setup is also an issue. Because of this, and the need to make adjustments to the equipment in a timely manner anyway, the method described here has found application. In this method a light, uniform exposure dose is applied across the pho- toresist coated wafer substrate and then developed. By observing pattern colorations in the developed film, adjustments to the hardware, etc. are made to optimise develop and process uniformity across the wafer substrate. During the initial setup phase of a photolithographic process, contrast (the slope found by taking the linear regression of the normalized resist thickness versus the logarithm of the exposure dose at a fixed develop process time) and Eo (threshold or the exposure dose at which the photoresist film develops out) are determined (Figure 1).

  The experienced photo engineer will optimise these factors so that for a given substrate, photoresist thickness will be chosen so that contrast will be at a maximum value and Eo will be at a minimum value. by monitoring developed, stepped exposure wafers with film measurement equipment such as the Nanospec AFT, it is possible to reduce or even elimi- nate dependence on critical dimension measurement. ' The photomask image is developed at roughly twice the time required for Eo. This is accomplished through photomask biasing for particular substrates.

  During contrast and threshold optimization testing that it was noticed that develop irregularities can be seen in the thin film of resist left at low exposure dose, above the Eo of the process. (Figure 2). By applying

this light, uniform exposure dose across the wafer and developing the photoresist film, one can generate pat- terns that represent geometry, temperature stability of the developer and other factors like "drip" faults in the developer setup. Corrective action may involve adjustments using allen wrenches with the ring stand type apparatus that supports the develop spray nozzles on TEL equipment, or a small crescent wrench in the case of an SVG 8100 type developer. Sometimes develop nonuniformities as a result of temperature deviations may be seen. It is sometimes necessary to observe the developer spray pattern and equate this to an observed coloration pattern. For example, in figure 2 example 1.0, a liquid vortex at the center of the wafer with little or no develop may indicate that repo- sitioning of...