Chapter 14
Polarity Change for the Design of Chemical Amplification Resists Hiroshi Ito
Downloaded by YORK UNIV on October 29, 2012 | http://pubs.acs.org Publication Date: April 13, 1993 | doi: 10.1021/bk-1993-0527.ch014
Research Division, Almaden Research Center, IBM Corporation, 650 Harry Road, San Jose, California 95120-6099
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In Irradiation of Polymeric Materials; Reichmanis, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
Downloaded by YORK UNIV on October 29, 2012 | http://pubs.acs.org Publication Date: April 13, 1993 | doi: 10.1021/bk-1993-0527.ch014
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IRRADIATION OF POLYMERIC MATERIALS
polymethacrylates (14) and poly(4-vinylbenzoates) (10). In Figure 8 is presented a T G A curve of poly(2-cyclopropyl-2-propyl 4-vinylbenzoate) (PCPPVB) (15) together with those of PTBVB and PBOCST. Replacement of one of the methyl groups of the f-butyl ester with a cyclopropyl group results in dramatic reduction in the deesterification temperature by ca. 80 °C. Thus, the dimethyl cyclopropyl carbinol ester is even more thermally labile than the tBOC group. However, whereas the thermal deesterification of PBOCST and PTBVB is quantitative, the weight loss (ca. 32 %) that occurs at 160 °C in the case of PCPPVB is smaller than the quantitative loss of 2-cyclopropylpropene (35.7 wt%) accounts for, which is due to concomitant rearrangement to a thermally stable 4-methyl-3-pentenyl ester (ca. 10 %), according to our authentic syntheses and spectroscopic studies (Scheme V) (13). As mentioned earlier, since polyvinylbenzoates have strong U V absorptions below 300 nm, the TPPDPS salt which extends its absorption to 350 nm was used as the photochemical acid generator and the resist film was exposed to 313 nm radiation. The rearrangement of the cyclopropyl carbinol ester is much more pronounced in the presence of acid (Scheme V). The effects of exposure dose and postbake temperature on conversion in terms of remaining film thickness are presented in Figure 9. The PCPPVB film containing 9.4 wt% of TPPDPS is stable when heated without UV exposure at 100 or 130 °C for 5 min and shrinks more upon postbake at higher doses due to loss of more olefin. The 130 °C bake provides a higher conversion than the 100 °C bake at the same dose but the degree of shrinkage saturates at ca. 12 % at about 5 and 50 mJ/cm when postbaked at 130 and 100 °C., respectively. Thus, the shrinkage never reaches the maximum value of 32 % expected from T G A or 35.7 % expected from the quantitative loss of 2-cyclopropylpropene. On the contrary, the 160 °C bake results in almost maximum thinning in the unexposed regions and the exposed film retains more thickness at higher doses, which is clearly due to more pronounced rearrangement in the presence of acid. The shrinkage saturates again at ca 12 % at about 20 mJ/cm when postbake is carried out at 160 °C. The maximum degree of acid-catalyzed rearrangement is estimated to be about 66 % in the solid state. The PCPPVB resist system allows negative imaging either with a nonpolar organic developer or with aqueous base, depending on the postbake temperature as illustrated in Scheme VI and Figure 10. Unexposed films are cleanly soluble in anisole but insoluble in aqueous base when heated below 130 °C because the film consists of the lipophilic PCPPVB. As the film is exposed, more benzoic acid units are generated upon postbake and the film becomes insoluble in anisole at about 3 mJ/cm when postbaked at 130 °C (polarity change). The exposed films never become soluble in aqueous base presumably because the concentration of the vinylbenzoic acid units formed is not high enough (ca. 34 %), failing to provide positive imaging. When postbaked at 160 °C., the PCPPVB resist system behaves completely differently. The 160 °C postbake renders the unexposed film insoluble in anisole but soluble in aqueous base due to the predominant thermal deprotection to convert PCPPVB to PVBA containing only about 10 % of the rearrangement product. The exposed films are insoluble in anisole because of generation of the polar benzoic acid units and become insoluble in aqueous base at about 5 mJ/cm when postbaked at 160 °C because the exposed area mainly consists of the nonpolar rearrangement product with only 34 % of the polar benzoic acid unit. Thus, the polarity is reversed by the high temperature postbake. 2
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In Irradiation of Polymeric Materials; Reichmanis, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
14. ITO Design of Chemical Amplification Resists
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Downloaded by YORK UNIV on October 29, 2012 | http://pubs.acs.org Publication Date: April 13, 1993 | doi: 10.1021/bk-1993-0527.ch014
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Figure 8. T G A of PCPPVB, PTBVB, and PBOCST (heating rate: 5 °C/min). (Reproduced with permission from ref. 15. Copyright 1990 American Chemical Society.)
In Irradiation of Polymeric Materials; Reichmanis, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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IRRADIATION O F P O L Y M E R I C MATERIALS
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