Materials Challenges and Alternatives for Advanced Photolithographic Patterning: From 193 to 157 nm and Beyond
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Materials Challenges and Alternatives for Advanced Photolithographic Patterning: From 193 to 157 nm and Beyond Elsa Reichmanis, Omkaram Nalamasu, Francis M. Houlihan, Bell Laboratories, Lucent Technologies Murray Hill, New Jersey 07974 ABSTRACT In the last decade, major advances in fabricating electronic devices have placed increasing demands on microlithography, the technology used to generate today’s integrated circuits. Within the next few years, a new form of lithography will be required that routinely produces features of less than 0.1 µm. As the exposing wavelength of light decreases to facilitate higher resolution imaging, the opacity of traditional materials precludes their use; and major research efforts to develop alternate materials are underway. Through understanding of materials structure and its relationship to device process requirements and performance, cycloolefin based polymers provide for sub-0.1 µm imaging capability using 193 nm exposure. Alicyclic monomers such as norbornene are readily copolymerized with other units to afford a wide range of alternative matrices that exhibit transparency at the exposing wavelength and aqueous base solubility. Further reduction in imaging wavelength necessitates renewed research to define alternative materials platforms. Materials transparency is the key issue to be addressed for 157 nm or EUV lithography. Novel polymer architectures including fluorinated polymers will be required to effect sufficient transparency coupled with requisite solubility, sensitivity, contrast etching resistance, shelf life and purity. Each of these issues will be discussed from the perspective of polymer materials chemistry. INTRODUCTION Advanced silicon based semiconductor circuits are complex three-dimensional structures of alternating, patterned layers of conductors, dielectrics and semiconductor films produced by lithographic processes that consist of two steps: i) delineation of the patterns in a radiation sensitive thin-polymer film called the resist, and ii) transfer of that pattern using an appropriate etching technique [1]. In general, device performance is governed by the size of the individual device elements and enhanced performance is expected with decreased feature size. Enabled through advances in both the materials and hardware associated with lithography, device dimensions have decreased by approximately 2 orders of magnitude, or from about 10-12 µm to 300°C), and exhibit good adhesion to silicon device substrates. Matrix Resin
n
O
O
O
Etching resistance Transparency
m
p
O
O
HO
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O
t-BuO
O
O
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O HO
Base solubilizing groups Adhesion
+
Dissolution Inhibitor
H+ ∆
O R’ Ot-Bu
O R’ OH
H
H RO
H
H R’
H RO
H
H R’
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Contrast Etching resistance
Aqueous base insoluble
Photoacid Generator
Ph2 I
Aqueous base soluble
O3S – CF2CF2CF2CF3
hν
HO3S – CF2CF2CF2CF3 + by products
Figure 3 One example of a 193 nm single-layer photoresist based upon norbornenemaleic anhydride matrix resin chemistry, a cholic acid based dissolution inhibitor and an oniu
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