Microlithographic systems rely on precision alignment and a high-level of dimensional stability to achieve required performance. In critical applications, immunity to thermally induced dimensional changes is achieved by the use of low linear coefficient of thermal expansion (hereafter referred to as CTE and denoted by a) materials such as ULE in components such as reflective optics and machine structures. ULE has a CTE that is typically in the 0 + 30 ppb K-1 range and it may be engineered to achieve a specific value. A high-accuracy determination of the CTE is essential for both process control and for providing an essential input to the design of such systems for error budgeting purposes. Currently, there is a need for CTE determination with an expanded uncertainty U(a)(k=2) < 1 ppb K-1 in the 273-373 K temperature range. A survey of the state-of-the-art of high-accuracy absolute measurement of CTE is presented along with a discussion of the significant error sources in each of the current techniques. The metrology techniques, sample design and instrumentation are described along with uncertainty estimates for representative instruments. The design philosophy and prospects for a new instrument that satisfies the above mentioned need are described.

Date Published: 1 July 2002
PDF: 12 pages
Proc. SPIE 4688, Emerging Lithographic Technologies VI, (1 July 2002); doi: 10.1117/12.472323

Published in SPIE Proceedings Vol. 4688:
Emerging Lithographic Technologies VI
Roxann L. Engelstad, Editor(s)