Study On Metrological Traceability Through Fabry-Perot Laser Interferometer Or Atomic Lattice Spacing For Micro Displacement Measurement

Micro displacement is generally defined as the displacement with the nanoscale positioning accuracy in a few millimeters even much smaller range. Nowadays, with the development of nanotechnology, more and more micro displacement sensors need to be measured accurately and more and more methods of micro displacement measurement need to be traced back to the SI unit of length easily. So the accuracy of measurement standards for micro displacement also need much higher accordingly. Although the laser Michelson interferometry is widely used in precision length measurement, the accuracy is often limited by the unknown size of the periodic non-linearity.Firstly, one kind of beating frequency Fabry-Perot laser interferometer is developed, which can trace to laser frequency directly and have no the periodic non-linearity error. In this system, the displacement measuring range is extended to 36μm and the uncertainty is smaller than 3.5nm(when coverage factor k=2). It is specialty that some technologies are used to push the limits of free spectral range in the Fabry-Perot resonant cavity, such as, digital phase locking amplifier technology, laser frequency tuning technology and nanoscale positioning technology, so this kind interferometer can be used to measure metrological characteritics of the nanoscale displacement sensors in the long range.Secondly, for some micro displacement parameters of nanoscale measuring instruments, if they are difficult to be calibrated by the interferometry directly. One traceable approach of micro displacement measuerment is presented, In this metrological traceability chain, the micro displacement parameters of nanoscale measurement instruments can trace to a series of nanoscale thin film thickness standards, which are designed some special step forms, and then trace to the X-ray wavelength and the atomic lattice spacing of monocrystalline silicon by x-ray reflectometry. It is very important for ensuring the uniformity and traceability of the values for the micro displacement parameters of nanoscale measuring instruments. Especially, the uncertainties of the nanoscale film thickness standards are reached to the sub nanoscale level, so the uncertainty values are very higher in the nanoscale length metrology standard system.The main novelties and results are as follows:1.Traditionally the measurement range of beating frequency Fabry-Perot laser interferometer is only about several hundred nanometers, because it was limited by the unbroken frequency range of the tunable laser, so it mainly can be used to measure interferometer nonlinear error. In this paper, based on stabilizing, measurement, locking, modulation of laser frequency and mode change technology, one technical method for enlarging measurement range of the Fabry-Perot laser interferometer fastly is presented. At the same time, a set of measuring setup is established accordingly, so that it can applied to measure micro displacement with nanometer accuracy.2.One traceable approach of micro displacement to the atomic lattice spacing of monocrystalline silicon and the X-ray wavelength is established and implemented. Based on the grazing incidence X-ray reflectometry, one kind of new uncertainty analytical approach for nanoscale thin film thickness are presented, and the standard measurement equipment for thin film thickness is established, where the expanded uncertainty of the thin film thickness H measurement exists U=0.3nm+1.5%H, when there is coverage factor k=2.3.To ensure the uniformity and traceability of the values for the micro displacement parameters of nanoscale measuring instruments, a serial of the nanometer single layer thickness standard with some step form areas were developed, which could be measured by contact instruments such asscanning probe microscopy, confocal laser scanning microscope, stylus contact surface step profiler and so on.