AN UNDERCUT FREE 1 MICRO THICK AZ-5200 POSITIVE E-BEAM RESIST PROCESS FOR HIGH CURRENT DENSITY APPLICATIONS
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-29
Publishing Venue
Motorola
Related People
B. R. Stallard: AUTHOR [+2]
Abstract
AZ-5200 positive resist is found to have a sensitivity (20 microcoullcm') and a contrast (gamma=3) which make it very attractive fore-beam lithography. Unfortunately, when coated in a thickness of 1.0 micro or greater, this and other novalac based e-beam resists exhibit severe undercutting if exposed with a high current density instrument and slightly overdeveloped (see Fig. 1). Until this problem was solved, AEBLE-150 e-beam lithography was unacceptable for a P-tub implant layer of a CMOS device and for some ASIC applications.
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MOTOROLA Technical Developments Volume 8 October 1988
AN UNDERCUT FREE 1 MICRO THICK AZ-5200 POSITIVE E-BEAM RESIST PROCESS FOR HIGH CURRENT DENSITY APPLICATIONS
by 8. R. Stallard, J. N. Helbert and A. J. Gonzales
AZ-5200 positive resist is found to have a sensitivity (20 microcoullcm') and a contrast (gamma=3) which make it very attractive fore-beam lithography. Unfortunately, when coated in a thickness of 1.0 micro or greater, this and other novalac based e-beam resists exhibit severe undercutting if exposed with a high current density instrument and slightly overdeveloped (see Fig. 1). Until this problem was solved, AEBLE-150 e-beam lithography was unacceptable for a P-tub implant layer of a CMOS device and for some ASIC applications.
A study of all pertinent variables uncovered the fact that the undercut could be eliminated by switching the baseline LSI developer used to the metal-ion-free developer MF-312 (see Fig. 2). A study of other variables such as developer strength, e-beam dose, and pre-exposure bake conditions demonstrated that these variables have little or no effect on the degree of undercut. The critical difference between the two developers is the size of the cation in the basic solution. In the case of the LSI developer the cation, Na+, is small, while for the MF-312 developer the cation, (cH1)4~+, is larger.
It has been observed that gases which are evolved when the resist is exposed produce micro-porosity that dramatically increases the solubility of the exposed resist (l-3). Since the solubility rate of the exposed resist is about 3 times lower for the large cation c...