Abstract

A single laser is used to provide light for both dark and bright field detection. The laser beam is split into two beams by a Wollaston prism and both beams are directed towards a sample to be inspected to illuminate two areas of the sample. The light reflected by or transmitted through the sample at the two spots is then combined by the same or a different Wollaston prism and the phase shift caused by any anomaly of a sample is detected as a phase shift between the two beams by a bright field detector. Light scattered by the sample at the two spots is detected by a dark field detector. A halfwave plate is used to orient the polarization plane of light from the laser incident on the Wollaston prism so that one of the two beams incident on the sample has a much higher intensity than the other and so that the sensitivity and the detection operation of dark field is not altered by the presence of two illuminated spots on the sample. A transparent dielectric at a suitable angle to the incident beam and the reflected or transmitted beam may be used to enhance bright field detection.

Other References

• "Wafer Inspection With a Laser Scanning Microscope," J. de la Rosa et al., AT&T Technical Journal, 65 (1986), Jan.-Feb., No. 1, Short Hills, NJ, U.S.A., pp. 68-77
• "Reticle Particle Detection System," T. Nishino et al., 8297 Hitachi Review 40(1991), Dec., No. 6, Tokyo, Japan, pp. 395-400
• "Linear Imaging in Scanning Polarisation/Interference Contrast Microscopy," by C.W. See and M. Vaez-Iravani, Electronics Letters, Sep. 25, 1986, vol. 22, No. 20, pp. 1079-1081
• "Linear and Differential Techniques in the Scanning Optical Microscope," by M. Vaez Iravani and C.W. See, Proc. SPIE, vol. 897, 43 (1988)
• "Detection and Refractive Index Identification of Sub-micron Particles on Surfaces," by Taubenblatt and Batchelder, SPIE vol. 1821, 152, (1992)
• "Measurement of the Size and Refractive Index of a Small Particle Using the Complex Forward-Scattered Electromagnetic Field," by Taubenblatt and Batchelder, Applied Optics, vol. 30, No. 33, Nov. 20, 1991
• "Phase Contrast and Amplitude Pseudoheterodyne Interference Near Field Scanning Optical Microscopy," by Vaez-Iravan and Toledo-Crow, Appl. Phys. Lett., vol. 62, No. 10, Mar. 8, 199