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3 April 2012 Investigations into an electrostatic chuck design for 450mm Si wafer
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We report on theoretical and experimental investigations into electrostatic chuck designs for use in future e-beam lithography on 450 mm Silicon wafers. Ultra-low thermal expansion glass (ULE) and Si infiltrated Silicon Carbide (SiSiC) designs were evaluated by finite element modeling, subject to a mass budget of 8 kg. In addition to massive chucks, light-weight designs were created by applying bore holes through the chuck body below its surface. Considerable chuck bending under gravity is observed with classical kinematic 3-point mounts. Out-of-plane distortions of about 1250 (650) nm and 400 (200) nm for the massive and light-weight designs of ULE (SiSiC), respectively, were calculated. The corresponding surface in-plane distortions for a chucked Si wafer of standard thickness 925 μm amount to about 3 (1.6) nm for the massive and 1 (0.5) nm for light-weight designs of ULE (SiSiC), respectively. By using the standard 6th order polynomial correction upon e-beam writing, these values can be reduced to ≤0.7 nm for the massive designs with both materials. Various pin-pattern configurations for an ideally flat chuck surface were adopted to determine resulting wafer bending under the influence of electrostatic forces. At a typical electrostatic pressure of about 18 kPa, a square pin pattern of pin-pitch 3.5 mm and pin-diameter 0.5 mm results in wafer in-plane distortions <0.5 nm, which is considered tolerable for obtaining the desired total overlay accuracy of <4 nm. The pin structure manufacturing process for a corresponding ULE chuck surface was experimentally tested and verified. A nearly elliptic ULE plate, slightly larger than the wafer, was structured with a Chromium hard-mask and subjected to low pressure reactive ion etching to generate the pin-pattern. A homogeneity of about 7 % was obtained for the etching process, which is fully sufficient with respect to resulting variations in electrostatic attraction.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Gerhard Kalkowski, Thomas Peschel, Geoffrey Hassall, Helder Alves, and Stefan Risse "Investigations into an electrostatic chuck design for 450mm Si wafer", Proc. SPIE 8324, Metrology, Inspection, and Process Control for Microlithography XXVI, 83242Z (3 April 2012);

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