U. Paul Kumar

Deformation and shape measurement using multiple wavelength microscopic TV holography

Characterization of deformation and surface shape is an important parameter in quality testing of micro-objects in view of the functionality, reliability, and integrity of the components. Single-wavelength TV holography is widely used for deformation analysis. However, the single-wavelength TV holographic configuration suffers from overcrowding of fringes for large deformation that sets a limitation due to speckle decorrelation for quantitative fringe analysis. Furthermore, shape cannot be determined when using single wavelength. In this paper, we describe a multiple-wavelength microscopic TV holographic configuration that uses sequentially recorded phase-shifted frames at three different wavelengths before and after deformation of the specimen for evaluation of relatively large deformation fields at the effective wavelengths. Use of multiple wavelengths for deformation and shape evaluation is discussed. The design of the system along with the experimental results on small-scale rough specimens under static load is presented.

Microscopic TV shearography for characterization of microsystems

We demonstrate a microscopic TV shearographic configuration for characterization of microsystems by measuring the slope under relatively large out-of-plane deformation. In the optical arrangement, a long working distance zoom imaging system is combined with a conventional Michelson shear interferometer. The experimental results on a microelectromechanical system pressure sensor subjected to external pressure load are presented.

Multiple wavelength interferometry for surface profiling

Interferometry is a well established technique for surface profiling. The conventional interferometric surface profilers using a single wavelength offer excellent vertical resolution, but a serious limitation to their use is that they can only handle smooth profiles and step heights less than half a wavelength. In the situation where the surface profile is discontinuous, white light interferometry has been applied with great success. However the scanning white light interferometry requires large number of frames to be recorded, whereas in spectrally resolved white light interferometry only a line profile of the object is obtained, although the requirement on number of frames is similar to the single wavelength phase shifting interferometry. In this paper we discuss three wavelength interferometry in which a limited number of frames suitable for phase shifting technique are recorded at three laser wavelengths. The phase evaluation at the three wavelengths gives wrapped phase at any pixel corresponding to these wavelengths. The fringe order is obtained considering the fact the variation of phase with wavenumber for a given profile height is linear. The slope of the phase verses wavenumber line gives the absolute value of the profile height and is used to ascertain the fringe order. The fringe order along with the wrapped phase gives the profile height with a resolution given by phase shifting technique. Experimental results on etched silicon samples are presented.

Microscopic TV sherography for microsystems characterization

Microscopic TV holography (MTVH) is widely used for out-of-plane deformation and 3-D surface profile characterization of microsystems. However, the problem of overcrowding of fringes shows up when deformations are large, making quantitative fringe analysis difficult. In this paper, we introduce the use of microscopic TV sherography (MTVS) for microsystems characterization so that under relatively large out-of-plane deformation the slope of deformation is measured, rather than the deformation itself. The optical arrangement consists of a zoom imaging system with a conventional Michelson shear interferometer. We use the digital speckle photography (DSP) technique for precise measurement of magnitude of the lateral shear introduced between the two sheared images.

Deformation analysis on micro objects using multiple wavelength microscopic TV holography

Microscopic TV holography is a reliable and versatile non-contact optical technique for whole-field deformation measurements with interferometric sensitivity for many micro-metrology applications. The technique is based on digital speckle interferometric subtraction correlation. Characterization of deformation and surface shape is an important parameter in quality testing of micro objects related to functionality, reliability and integrity of the components. Single wavelength TV holography is used widely for deformation analysis. However the single wavelength TV holographic configuration suffers from overcrowding of fringes for large deformation that sets in limitation due to speckle de-correlation for quantitative fringe analysis. In this paper, we describe a multiple wavelength microscopic TV holographic configuration that uses sequentially recorded phase shifted frames at three different wavelengths before and after deformation of the specimen for evaluation of relatively large deformation fields at effective wavelengths. Use of multiple wavelengths for deformation and shape evaluation is also discussed. The design of the system along with few experimental results on small scale rough specimens