(252e) New Photodefinable Dielectric Polymer Thin Film Materials for Microelectronics and Optoelectronics Based on Novel Hexafluoralcohol Substituted Monomers

Photodefinable dielectric polymer thin films are a critical and enabling technology in the fabrication and packaging of modern microelectronic and optoelectronic devices. In particular, photosensitive forms of polyimides are widely used in such applications. Current photosensitive polyimide formulations that can be developed in aqueous alkaline developers are based on the use of either (1) soluble poly(amic acid) precursor polymers or (2) polyimides functionalized with hydrophilic groups (e.g. phenol). The use of poly(amic acid) polymers requires the subsequent high temperature thermal cyclization of the polymer after imaging to produce the desired polyimide which can prevent ue of such materials in many applications. However, the use of pre-imidized poliyimides by imparting solubility with the addition of hydrophilic groups to the polymer is also problematic since the presence of such groups in the polymer generally degrades the dielectric constant and water uptake performance of such materials. The goal of our work has been to overcome these problems by developing new low dielectric constant polyimides and other dielectric polymers that can be formulated into photo-definable materials and processed at low temperatures. In this paper, the use of a novel hexafluoroisopropanol (HFA)-substituted diamine to synthesize novel poly(amic-acid) and polyimide polymers is reported. The addition of HFA to the polymers is shown to produce polyimides which are soluble in both common casting solvents and 0.26 N TMAH alkaline developers. First, a photosentitive polyimide composition based on formulation of the HFA-subtituted polyimide with 20 wt% of a DNQ inhibitor is shown to produce high resolution patterns with a sensitivity of 170 mJ/cm2 and a contrast of 1.32 using I-line exposure. The HFA groups in the polymers are contained on a substituent group attached to the main chain by an ester linkage. It is shown that these HFA-substituent side-groups can be easily removed from the polymer after development of the patterned image by thermal treatment of the polymer at temperatures above 280 oC. The cleavage of the HFA side groups produces a polymer which does not swell and is insoluble in aqueous alkaline developers. Polyimide film properties including dissolution rate, dielectric constant, thermal expansion coefficient (CTE), water absorption have been measured and are shown to be strongly dependent on the presence of the HFA side groups. In particular, the dielectric constant of the polyimide is shown to decrease dramatically from 3.20 to 2.60 after thermal cleavage of the HFA side groups using a thermal cure at 350 oC for 30 minutes. In general, the strategy of using solubility enhancing functional groups that can be cleaved from the polymer during or after imaging and development appears to be a very promising strategy for developing photo-definable low dielectric constant polymers that can be processed at low temperatures. This paper will also give an update on recent work, including new polymer structures and properties, directed at using acid catalyzed mechanisms to achieve removal of the HFA substituent groups on the polymer, thus enabling both a chemically amplified patterning mechanism and allowing for side group removal at lower temperatures. Finally, recent results on the development of new polymer backbone structures which serves as alternative low dielectric constant polymers that employ similar strategies will also be discussed.