Simultaneous measurement method of total and self-interference for the volumetric thickness-profilometer

Abstract

A simultaneous measurement method for the total interference and self-interference of a sample is proposed. The proposed method is capable of making separate measurements of the thickness and surface profile of micro-patterned thin film. The system is an extension of a full-field wavelength scanning interferometer with a single acousto-optic tunable filter (AOTF) as a spectral imaging device. Separate measurements are realized via the polarization-sensitive diffraction of non-collinear acousto-optic interaction. That is, the diffraction angle of an AOTF is separated into different directions depending on the polarization state of the incident light. In so doing, the polarization states of a reference and a sample light were manipulated differently so that a single AOTF can generate the total interference and the self-interference signal in different directions simultaneously. Thus, a compact and light-efficient system is realized with an AOTF, a beam splitter and two CCDs. Thus, a compact system with light-efficiency of two to four times higher than the previously reported system is realized with an AOTF, a beam splitter and two CCDs. Details of the calibration procedures such as wavelength-frequency relation, image shift and registration between two CCDs are provided for the proposed setup. Experimental results are provided and compared to those using commercial equipment that demonstrate the efficiency of the proposed system for the high-speed measurements of the thickness and the surface profile of micro-patterned thin film.

Recent Progress on Optical Tomographic Technology for Measurements and Inspections of Film Structures

“…In recent years, the approaches to combine distinct measurement principles have been mostly attempted in film metrology to overcome the limitation of each measurement system [ 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 ]. Ellipsometry and reflectometry have the ability of measuring film thicknesses, but the topographic height of the film specimen cannot be determined.…”

“…In order to overcome this limitation, interferometric techniques were introduced in the hybrid measurement system. The combination of the reflectometry and SRI realized the full analysis of a film structure including topographic and tomographic film thicknesses [ 87 , 88 , 89 , 90 , 91 ]. Because the optical configuration of the spectroscopic reflectometry can be modified from that of SRI, the hybrid system was conveniently configured, as shown in Figure 11 A.…”

Electro-Optic Swept Source Based on AOTF for Wavenumber-Linear Interferometric Sensing and Imaging

“…It has been known that the filtered AOTF has the physically linearized relation between the optical frequency and acoustic frequency [16,17]. It means that only a simple triangular drive function is needed to ensure a linearly sweeping wavenumber in the time domain, instead of a specially programmed drive function with respect to time [18][19][20][21][22]. Moreover, the AOTF filter exhibits more attractive characteristics of accurate wavelength selection, high stability, and non-mechanical actuation [19,20].…”

“…It means that only a simple triangular drive function is needed to ensure a linearly sweeping wavenumber in the time domain, instead of a specially programmed drive function with respect to time [18][19][20][21][22]. Moreover, the AOTF filter exhibits more attractive characteristics of accurate wavelength selection, high stability, and non-mechanical actuation [19,20]. We also demonstrate that the electro-optic operation of a swept source is useful to apply any types of drive function and to improve environmental stability, compared with FFP-TF.…”