A self comparison method to measure distortions of fine gratings and to characterize electron beam systems

We present a nondestructive method using no special markers to measure distortions in gratings, which is useful in the fabrication process as a monitoring procedure. The method consists of a comparison of a part of the grating, which is used as a reference, with an other part of the same grating. The second recording is printed after moving the full field grating. Both images are recorded on the same film by a double exposure. As a result moire' stripes are obtained which reveal the differences of the compared grating areas. Evaluation of the moire' pattern gives the magnitude of the distortions in the fabricated structure. This procedure allows to judge gratings which can not be resolved in the light microscope. Scanning microscopy can be employed to measure distortions of finer gratings with a similar procedure.