Architectures for high-resolution photomask phase metrology

Details Architectures for high-resolution photomask phase metrology Architectures for high-resolution photomask phase metrology

2006-05-09

2006-05-09

Toatley, Jr., Gregory J. (Department: 2877)

Optics: measuring and testing

By light interference

For dimensional measurement

C356S239300, C356S237400

Reexamination Certificate

active

07042577

ABSTRACT:
We disclose several instrument architectures for the measurement of arbitrary phase retardation on advanced lithography photomasks. These architectures combine traditional interferometric techniques with high-magnification UV microscopy. Features are interrogated using a multitude of phase probes, formed by a imaging a number of variable apertures back-illuminated by phase-coherent beams, onto the surface of the photomask with a given demagnification. The size, spacing, and orientation of the phase probes may be adjusted to suit photomask feature geometries. Means are provided to vary the relative optical phase between the phase probes. These phase probes both reflect from and transmit through the photomask; the stationary, non-localized interference fringes, formed in the regions of phase probe electric field overlap, contain information on the optical path difference between the two probes. The spatial resolution of these measurements is limited only by the resolution limit of the UV microscope, which may significantly exceed the capability of existing tools.

REFERENCES:
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patent: 6559953 (2003-05-01), Davids
patent: 2002/0148955 (2002-10-01), Hill
Kusunose et al. “Direct Phase-Shift Measurement with Transmitted Deep-UV Illumination”, in Proceedings of the SPIE vol. 2793 pp. 251-260 (1996).

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