Dresden 2003 – scientific programme
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DF: Dielektrische Festkörper
DF 1: Elektrische und optische Eigenschaften I
DF 1.9: Talk
Monday, March 24, 2003, 12:30–12:50, HSZ/403
The weak optical anisotropy in the cubic crystal CaF2: Caused by exciton dispersion? — •Martin Letz1, Alexander Gottwald2, Mathias Richter2, and Lutz Parthier3 — 1Schott Glas, Research and Development, D-55014 Mainz — 2Physikalisch-Technische Bundesanstalt, D-10587 Berlin — 3Schott Lithotec AG, Otto-Schott Str. 13, D-07745 Jena
The need for miniaturization in the semiconductor industry forces lithographers to build optical systems and related processes for very small wavelengths. 157 nm lithography is currently considered to be the technology to build semiconductors with feature sizes of 65 nm and less. The material of choice to build refractive optical systems is CaF2 since it simultaneously fulfills the necessary requirements for absorption, radiation stability, chemical durability and mechanical properties for lithographers needs. Despite its perfect cubic crystalline structure it shows a weak optical anisotropy [1] already at 193 nm but more pronounced at 157 nm. We investigated this spatial dispersion induced optical anisotropy [2] and connect it to the deep excitonic state of the Γ-exciton around 112 nm. Using dispersed synchrotron radiation (SR) for reflection measurements on oriented surfaces we investigate the dispersion of the exciton-polariton. The analytic properties of dynamic response functions, namely Kramers-Kronig relations, allow to connect the exciton dispersion around 112 nm to the weak optical anisotropy at 157 nm.
[1] J.H. Burnett et al., Phys. Rev. B 64 241102R (2001)
[2] V.L. Ginzburg, JETP, 34, 1593 (1958)