Study On Measurement And Control With Period And Wavefront Of Interference Fringes For SBIL

Diffraction grating is a kind of important optical device, which used widely in many scientific fields and engineering applications. The need for large-size diffraction gratings is particularly urgent. Scanning beam interference lithography, SBIL for short, has become an important technical means of manufacturing large size diffraction gratings with its high accuracy, high efficiency and flexibility. The difficulty of SBIL lies in how to realize exactly exposure stitching in the overlapping scanning and make sure that the grating lines could have uniform exposure, high contrast and good phase linearity.In order to achieve accurate exposure stitching, the following works have been done in this paper:Firstly, the set of interference fringes is required to be overlapped and scanned, so that the small size of the interference fringes can be recorded in the large area of photoresist during the exposure. Because the target step of stage is an integer multiple of the interference fringes period in the direction of perpendicular to the interference fringes, the accurate value of the interference fringe period is an important prerequisite in SBIL. In this paper, I got the accurate value of the interference fringe period by using a method similar to periodic counting method. The measurement accuracy of the method is at 10pm level. Secondly because of the limited and nonadjustable accuracy of a single stage, the double stages model has been built up, expected to get the required accuracy by using the additional pose correction method. I proposed a pose correction method for the double stages based on least-squares polynomial fitting to improve accuracy of the double stages. After the pose correction, the positioning accuracy is in ±10nm and yaw can be controlled in±0.073 ?rad in step motion with 100 interference fringe periods, which provides a good accuracy for SBIL. Thirdly, the Gaussian beam interference fringes is not strictly parallel equidistant line in SBIL, the residual phase nonlinear error will reflect in grating lines directly. Therefore, the wavefront of interference field was measured to calculate the nonlinear error of phase by using phase shifting interference, the PV value of the wavefront is about 0.05?.The measurement of interference fringe period, the pose correction of the stage and the wavefront measurement are very important in SBIL and this paper plays an active role in the building of the system based on SBIL.