Multiple height calibration reference for nano-metrology

Modern nano-metrology instruments require calibration references with nanometer accuracy in the x, y, and z directions. A common problem is the accurate calibration in the z direction (height). For example, it is generally not difficult to obtain accurate x-and y-calibration references for a Scanning Probe Microscope (SPM). It is, however, much more difficult to obtain accurate z-axis results. It is difficult to control z-axis piezo dynamics because during scanning in the xy-plane the x-and y-axes move at a constant rate whiles the z axis does not. Furthermore due to the high cost of producing calibration standards, the microscope is often calibrated at only one height. However, if the relationship between the measured z height and the actual z height is not linear, then the height measurements will not be correct. In this paper, we will present a method for the fabrication of calibration references with: (i) sub-10 nm features and (ii) multiple step heights on one reference, allowing for better calibration of the non-linearity in the z direction.