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The optical beam path of the Phame system is comparable to that of an immersion scanner with a 1.6 NA. Its 193 nm laser combined with a low sigma illumination unit generates a coherent on-axis illumination of the mask, which is handled face down. The tools high precision imaging optics with a 0.4 NA, being 1.6 NA scanner equivalent, enables full compatibility with future 193 nm immersion scanners down to the 32 nm node. Phase information is obtained through dedicated phase manipulation by a pupil filter and software algorithms.
The CCD-camera is in the same position as the wafer in an
actual scanner. In addition to in-die phase, the tool also measures in-die transmission.
Furthermore off-axis illumination can be applied. The required partial coherent illumination settings of a scanner are sampled in consecutive measurements of adjustable intervals, allowing phase control under scanner relevant illumination settings. By realizing on- or off-axis illumination all types of PSM`s can be measured.
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