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Thermal Acceleration of UV Hardening for Diazoquinone/Novolak Resist

IP.com Disclosure Number: IPCOM000042750D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Babie, WT: AUTHOR [+2]

Abstract

Plasma hardening is conventionally used to stabilize photoresist prior to high temperature processing. The technique is employed to maintain image dimension and profile, which can degrade with simple baking. Even though plasma treatment stabilizes photoresist to a substantial degree, the images still incur wrinkling and some dimensional changes. Such distortion becomes critical in high definition lithography. Resist stabilization from UV (ultraviolet) exposure has been reported for several years. Reported performance indicates significantly improved stabilization over plasma techniques. However, the required exposure times have been too long for implementation in manufacturing.

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Thermal Acceleration of UV Hardening for Diazoquinone/Novolak Resist

Plasma hardening is conventionally used to stabilize photoresist prior to high temperature processing. The technique is employed to maintain image dimension and profile, which can degrade with simple baking. Even though plasma treatment stabilizes photoresist to a substantial degree, the images still incur wrinkling and some dimensional changes. Such distortion becomes critical in high definition lithography. Resist stabilization from UV (ultraviolet) exposure has been reported for several years. Reported performance indicates significantly improved stabilization over plasma techniques. However, the required exposure times have been too long for implementation in manufacturing. The use of higher intensity sources has decreased the required exposure time somewhat, but further decrease is necessary for economical implementation. Further increase in source power is limited by the high operating temperature of such sources, damaging the resist image before stabilization can be achieved. Resist stabilization by deep UV sources can be categorized by the behavior of the resist upon a high temperature postbake (PB) The stabilization passes through several distinct phases, depending on the thickness of the UV hardened skin of the resist. The phases are shown schematically in the drawings.

The final phase is optimum for maintaining resist dimensions. The ability to achieve the final phase has been observed to depend on the resist type, thickness and wavelength distribution of the UV source.

It is accessible for 1.0 u thick diazoquinone/novolak resists using a medium pressure mercury lamp for UV exposure. The time required to achieve the final phase of resist stabilization was observed to depend on the equilibrium wafer temperature during exposure. The following experimental matrix was performed to demonstrate the dependence. Resist imaged 1.0 u thick samples were used in the matrix, and the exposures were done using two 700 W medium pressure mercury lamps. Exposure temperature was controlled by limiting air flow through the exposure chamber. Exposure temperatu...