Laser Step Alignment For A Wafer Stepper

Optical displacement metrology using alternating direction Moire

“…1 Under this assumption, the laser spot can produce a significant amount of scattered light even for small wedge shapes in Moire photoresist images. Experiments are performed to validate the ADM precision of the 1-D alignment optics equipped with an exposure apparatus and a laser step alignment (LSA) measurement system installed in a Nikon NSR-1755iA (NA ¼ 0.50, illumination NA ¼ 0.30), which is an i-line exposure apparatus.…”

“…In the process of the stage scans, the light signal consists mostly of light diffracted by the columns of marks. 1,17,18 In the discussion below, the ORMS precision σ is multiplied by a factor of three. In the 3σ expression, all measured values lie within 3 sigma of the mean, or approximately 99.7%.…”

“…The first limitation relates to one-dimensional (1-D) laser spot sensors. 1 When a wafer must be moved beneath a fixed optical sensor, 1 a scanning stage for providing object movement is required for 1-D scanning optical sensors. The error in the position of the laser metrology system for stage monitoring is generally larger than that of the optical sensor due to air temperature fluctuations and high frequency vibrations of machine components, 2 which are beyond the frequency response of laser metrology, so the measurement precision can never be small when using conventional metrological methods.…”