Improvement in the measurement of the diffraction pitch for the one dimensional grating

초록

The precision laser diffractometer of the conventional-type has been developed for the 1D grating pitch measurement, and successful precision improvement has been made. At the first stage of this improvement, the rotary arm was set to be as long as 1.2 meter, and the precision goniometer (resolution 0.0001 degree; accuracy 0.001 degree) has been used. Furthermore, a focusing lens has been inserted between the grating sample and the detection plane in order to prevent the measurement error from the beam allignment. The system has been more improved to meet the need for higher accuracy and precision so far. One of the two important modifications is the use of CCD camera-based detection system instead of visual evaluation. And, the precise value of the laser wavelength, with one more digit than before, is used. These two modifications contribute considerably in improving the accuracy of the measurement comparing with the previous one. The correction of axis wearing shift has been accomplished additionally to improve the accuracy at the current stage of the development. The measured values for the grating whose pitch is certified as 288 nm and 700 nm by the manufacturer, are 287.593 and 700.762 nm. The expanded uncertainties with a coverage factor of 2, is now improved to 0.005 and 0.014 nm for the 288 and 700 nm-grating (MXS301CE and MXS701CE, Moxtek), respectively. They are significantly less, about 1/10, than previous ones (0.04 and 0.1 nm each, before modification).