Photoimageable Polyimide: A Dielectric Material For High Aspect Ratio Structures

Jay M. Cech; Modest M. Oprysko; Peter L. Young; Kin Li

doi:10.1117/12.963642

9 July 1986 Photoimageable Polyimide: A Dielectric Material For High Aspect Ratio Structures

Jay M. Cech, Modest M. Oprysko, Peter L. Young, Kin Li

Proceedings Volume 0631, Advances in Resist Technology and Processing III; (1986) https://doi.org/10.1117/12.963642
Event: 1986 Microlithography Conferences, 1986, Santa Clara, United States

Abstract

Polyimide has been identified as a useful material for microelectronic packaging because of its low dielectric constant and high temperature stability. Difficulties involved with reactive ion etching (RIE), a conventional technique for patterning thick polyimide films (thickness greater than 5 microns) with vertical walls, can be overcome by using photimageable polyimide precursors. The processing steps are similar to those used with negative photoresists. EM Chemical's HTR-3 photosensitive polyimide has been spun on up to a thickness of 12 microns. Exposure with a dose of 780 mJcm^-2 of ultraviolet light, followed by spin development produces clean patterns as small as 5 microns corresponding to an aspect ratio of 2.4. When the patterned precursor is heated, an imidization reaction occurs converting the patterned film to polyimide. Baking to ca. 400 degrees C results in substantial loss in the thickness and in line width. However, shrinkage occurs reproducibly so useful rules for mask design can be formulated. Near vertical wall structures can be fabricated by taking advantage of the optical and shrinkage properties of the polyimide precursor. After development, an undercut wall profile can be produced since the bottom of the film receives less exposure and is hence more soluble in the developer. During heating, lateral shrinkage pulls the top of the film inward producing a vertical wall since the bottom is fixed to the substrate by adhesion. As a result, fully cured polyimide structures with straight walls and aspect ratios greater than one can be obtained. Dielectric properties of the fully imidized films were investigated with capacitor test structures. A relative dielectric constant of 3.3 and a loss tangent of .002 were measured at 20 kHz. It was also found that the dielectric constant increases as a linear function of relative humidity.

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Jay M. Cech, Modest M. Oprysko, Peter L. Young, and Kin Li "Photoimageable Polyimide: A Dielectric Material For High Aspect Ratio Structures", Proc. SPIE 0631, Advances in Resist Technology and Processing III, (9 July 1986); https://doi.org/10.1117/12.963642

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