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ADVANCED LIFTOFF PROCESSING

IP.com Disclosure Number: IPCOM000006670D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-22
Document File: 3 page(s) / 187K

Publishing Venue

Motorola

Related People

Ed Fisk: AUTHOR

Abstract

Advance single layer liftoff processing has been developed to reduce the cycle time, minimize process variation and produce an environmentally safe process. This paper will present the key elements of two liftoff processes developed for use in the manufacture of sem- iconductor devices. The advance processes have been labeled "Polyvinyl Alcohol Liftoff' and "Sequential Develop Liioff: Historically the main stay used in single layer photoresist liftoff processing has been the use of a proc- ess described here as "Chlorobenzene liioff' similar to that described by Hatzakis, Canavello, Shawl. Chloro- benzene liftoff processing takes advantage of the use of a solvent in which the surface properties of the resist change during development. The exposed chloroben- zene surface development rate of the novalad positive resist used, AZ 13702, would be reduced with respect to the bulk resist development rate. Increased exposure to chlorobenzene and temperature will promote the "lip" formation at the top of the resist opening to produce a clean Ii!?& protile for metalization masking during dep- osition ofthe metal. This lip will produce the clean break of metal over the photoresist step and allow the removal of the resist with the unwanted metal when placed into resist-soluble solvents after metaliiation. Refer to Fig- ure 1 for the process step diagram for "Chlorobenzene Lift&?' Note: see Figure 4 for resist lip and profile observation.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

ADVANCED LIFTOFF PROCESSING

by Ed Fisk

  Advance single layer liftoff processing has been developed to reduce the cycle time, minimize process variation and produce an environmentally safe process. This paper will present the key elements of two liftoff processes developed for use in the manufacture of sem- iconductor devices. The advance processes have been labeled "Polyvinyl Alcohol Liftoff' and "Sequential Develop Liioff:

  Historically the main stay used in single layer photoresist liftoff processing has been the use of a proc- ess described here as "Chlorobenzene liioff' similar to that described by Hatzakis, Canavello, Shawl. Chloro- benzene liftoff processing takes advantage of the use of a solvent in which the surface properties of the resist change during development. The exposed chloroben- zene surface development rate of the novalad positive resist used, AZ 13702, would be reduced with respect to the bulk resist development rate. Increased exposure to chlorobenzene and temperature will promote the "lip" formation at the top of the resist opening to produce a clean Ii!?& protile for metalization masking during dep- osition ofthe metal. This lip will produce the clean break of metal over the photoresist step and allow the removal of the resist with the unwanted metal when placed into resist-soluble solvents after metaliiation. Refer to Fig- ure 1 for the process step diagram for "Chlorobenzene Lift&?' Note: see Figure 4 for resist lip and profile observation.

  One of the disadvantages of this process includes: total number of processing steps, required is seven, an addition of two steps over standard straight wall non- liftoff process. Other disadvantages with this process are the increased sensitivity to processing parameters: i.e. temperature, humidity, chemical purity and staging time. The parameters reduce the optimum resolution as well as the critical dimension distribution of the process, referred here to as the process capability. Environmentally the use of chlorobenzene and the use of EGMEA (ethyleneglycohnonoethyletheracetate) as found in AZ 1370 series of resist are known carcinogens.

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  The first of the "Advance LXtoff Processing" to be descrii will be the "Polyvinyl Alcohol Liiofl?' followed by "Sequential Develop LiiofY

  Polyvinyl Alcohol Liftoff process takes advantage of the resist modification properties of polyvinyl alco- hol as in the chlorobenzene process at development. Fur- ther development was completed with many resist types. The evaluation found enhanced process capabilities with the use of AZ 52 14E2 resist for lit&% processing. Polyvi- nyl alcohol is applied in a dilute aqueous-based solution for spin coating after resist spin coat and bake. The proc- ess continues with standard UV exposure and metal ion (sodium or potassium hydroxide) containing develop- ment. Refer to Figure 2 for the process step diagram for "Polyvinyl Alcohol Liiofl?...