113 results about "Heterodyne interferometer" patented technology

The invention discloses a heterodyne point diffraction interferometer based on the phase shift of a low-frequency-difference acousto-optic frequency shifter. The heterodyne point diffraction interferometer based on the phase shift of the low-frequency-difference acousto-optic frequency shifter comprises a light beam adjusting unit, a low-frequency-difference phase shifting unit, a point diffraction unit and an area array detector unit. The light beam adjusting unit is used for adjusting output lasers of a laser device into two laser beams with identical powers. The low-frequency-difference phase shifting unit is used for adjusting the frequencies of the two laser beams obtained by the light beam adjusting unit to obtain two laser beams with the output difference frequency being a low difference frequency lower than 100 Hz. The point diffraction unit is used for dividing the lasers adjusted by the low-frequency-difference phase shifting unit into measuring light and reference light so as to generate interference. The area array detector unit is used for collecting the interference. According to the heterodyne point diffraction interferometer based on the phase shift of the low-frequency-difference acousto-optic frequency shifter, heterodyne interference phase shift of the acousto-optic frequency shifter is adopted to effectively avoid that moving parts exist in the interferometer, the measurement accuracy is improved, the anti-interference performance is good, the low-frequency-difference heterodyne interferometer and the area array detector unit carry out consecutive collection, more abundant information can be obtained, phase position can be solved precisely, and noise influences can be avoided.

In a wafer thickness measuring apparatus and a method thereof, detection values are obtained from a sample piece (for example, a wafer chip) at a plurality of measurement points thereon by first and second detectors for absolute measurement of distances, and at the same time, measurement values of the fluctuations, for relative measurement of distances, are obtained by the optical heterodyne interferometer, and those measurement values are memorized as a plurality of measurement data being related with those measurement values. When measuring the thickness of a wafer, the measurements are performed at measurement points on the wafer which has a front surface and a reverse surface in height lying within the height of the sample piece, on which such a correspondence is obtained, thereby obtaining the detection values of the first and second detectors. Searching conversely from those detection values by referring the correspondence data, the respective detection values are converted into the data of the relative fluctuations therefrom upon the basis of the thickness of the sample piece, thereby obtaining the relative amounts of fluctuation in positions (i.e., the distances) upon the basis of the thickness of the sample piece, respectively. Then, by conducting addition and/or subtraction of the fluctuation amount on the front surface and the reverse surface from the thickness of the sample piece as a reference, it is possible to calculate out the thickness of the wafer to be measured.