Research Of High-resolution Measuring System Based On Differentialphase-shifting Interference Microscopy

In the surface topography measuring field, phase-shifting interference microscopysystem has many outstanding advantages, for example, simple construction, high abilityof resisting against environmental disrupt, the implementation of3D non-contactquantitative measurement, high resolution and so on. Thus, it is widely used in everyfield for measuring micro surface topography.In the past phase-shifting interference measurement, laser is usually used as thelight source. Because of its good direction and long interference length, the system hashigh resolution and big measuring range. But, just for laser’s strong coherence, the straylight scattered by defects or impurities from optical elements or even by the dust in theair, which still has certain coherence, will cause interference on the receiving screen andproduce coherent noises or speckle noises. These noises which are difficult to beremoved by algorithm seriously impact on measuring precision.In this thesis, the differential phase-shifting interference microscopy system hasbeen set up, based on illumination by partially coherent light source (LED). Bycollimating and filtering, LED’s coherence is improved. Not only can the improvedbeam satisfy the condition of coherent light for measurement, but also the scatteredstray light can’t interfere. Coherent noises and speckle noises get to be well restrained.And the measuring precision of the system is improved.The system has been used to measure several samples. As a result, the feasibility ofthe improved scheme of system is proved. Firstly, by measuring the plate of sapphirewhose evenness is known, the measuring result can match well the actual value, whichshows the high resolution of the system. Secondly, by measuring the rod-like structureswhich are regularly arranged on the hard disk, the result displays that the system hasstrong capability of reconstructing the surface topography. Then by measuring thesmooth region of the hard disk, the roughness is about2nm, which indicates that thesystem can execute the measurement of nano-scal high smooth surface. At last, bymeasuring the aluminum metal plate, the evenness is submicron. Theoretically, thesystem’s biggest measuring evenness is micrometer. Thus, the system is proper tomeasure micro-nano surface. In order to test the reliability of the system, the repeatedmeasuring precision is examined. The result shows that the repeated measuringprecision of the system is subnanometer.