Promixity alignment using polarized illumination and double conj

Details Promixity alignment using polarized illumination and double conj Promixity alignment using polarized illumination and double conj

1990-10-31

1991-12-10

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250225, G01N 2186

Patent

active

050721267

ABSTRACT:
Alignment of two objects such as a mask and a wafer is achieved using crossed polarizer imaging and polarization sensitive targets to enhance signal contrast in proximity alignment. Two linearly polarized illumination beams with electric field polarization axes at oblique angles to each other illuminate and interact with mask and wafer marks. The marks are oriented to induce a partial depolarization of each incident illumination at each plane, i.e. the marks make some of the light visible upon passing through filters and a polarization analyzer. When marks are viewed through a polarization analyzer stray light is rejected and mark contrast greatly improved.

REFERENCES:
patent: 4701606 (1987-10-01), Tanimoto et al.
patent: 4937459 (1990-06-01), Ina

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