Particle Detection for 100-nm Patterned Wafers by Evanescent Light Illumination – Analysis of Evanescent Light Scattering Using Finite-Difference Time-Domain Method –
Toshie Yoshioka, Takashi Miyoshi, and Yasuhiro Takaya
Department of Mechanical Engineering and Systems, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
Patterned wafer inspection technique is essential to high productivity and reliability in high-yield semiconductor manufacturing. Since circuit features are below 100nm, conventional imaging and light scattering methods cannot be applied to patterned wafer inspection technique due to the diffraction limit and the low S/N ratio. We propose a new particle detection method using annular evanescent light illumination. In this method, a converging annular beam used as a light source is incident to a micro-hemispherical lens. When the converging angle is greater than the critical angle, annular evanescent light is generated on the bottom surface of the hemispherical lens. Evanescent light is localized near the bottom of the hemispherical lens and decays exponentially away from it, so the evanescent light selectively illuminates a particle on the patterned wafer surface because it cannot illuminate the patterned wafer surface. The proposed method evaluates a particle on a patterned wafer surface by detecting scattered evanescent light pattern from the particle. To analyze the fundamental properties of the proposed method, the computer simulation was performed using the finite-difference time-domain (FDTD) method. It is found that the proposed method is effective for detecting 100nm sized particle on a patterned wafer consisting of 100nm lines and spaces, when the evanescent light illumination is done using P-polarized light and line orientation parallel to the incident plane. Finally, the experimental results suggest that 220nm sized particle can be detected on a patterned wafer consisting of about 200nm lines and spaces.
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