2018-8-16

Overlay of multiframe SEM images including nonlinear field distortions

• Event: SPIE Advanced Lithography, 2018, San Jose, California, United States
• S.Babin, S.Borisov, I.Ivonin, *S. Nakazawa, *Y.Yamazaki
  
  aBeam Technologies, Inc., Hayward, CA, USA
  *NGR Inc, Yokohama Japan

ABSTRACT

To reduce charging and shrinkage, CD-SEMs utilize low electron energies and multiframe imaging. This results in every next frame being altered due to stage and beam instability, as well as due to charging. Regular averaging of the frames blurs the edges; this directly effects the extracted values of critical dimensions. A technique was developed to overlay multiframe images without the loss of quality. This method takes into account drift, rotation, and magnification corrections, as well as nonlinear distortions due to wafer charging. A significant improvement in the signal to noise ratio and overall image quality without degradation of the feature’s edge quality was achieved. The developed software is capable of working with regular and large size images up to 32K pixels in each direction.

Key words: CD-SEM, CD metrology, distortions, multiframe, overlay, critical dimensions, image analysis, tool performance