Image hardenings by uv-, pulsed-electron beams and crosslinking agents

Abstract

For uv-hardening increase in oxygen concentration accelerates crosslinking rate than in air, and uv-exposure in nitrogen retards the reaction. Surfaces of photoresist images are photo-oxidized by intense uv-irradiation in air. However, the oxidized layer never extends over several hundred Å depth as measured by ESCA. Crosslinking extends far deeper, although it depends on the irradiating wavelength. The degree of crosslinkages is far densier near the surface than in the interior. A combination of heating and uv-exposure helps uv-hardening by spreading and acclerate crosslinking in resist images. Deep-uv light never reaches deeper beyond a few micron thick layer of photoresists and of polyamic acids. Thus, uv-hardening has a limit of its application. High aspect ratio images can be fabricated with photoimageable polyamic acid. However, in high temperature curing the images flow, yielding only low aspect ratio images of polyimides. Pulsed electron beam hardening can solve these problems of thick photoresists and of polyamic acids. For both type of images about 200 pulses of electron beams at 25 keV are required, each pulse having a dose from 1 μC/cm2 to 10 μC/cm2 with a duration of about 100 nsec. Another method of resist image stabilization is chemical crosslinking, using various crosslinking agents. These image hardening processes are discussed in terms of advantages and disadvantages of the processes and chemical mechanisms involved. © 1989, The Society of Photopolymer Science and Technology(SPST). All rights reserved.