The full spectrum analysis technology of multi-layer film structure using film thickness profiler is a key breakthrough in the current semiconductor, display, and optical device manufacturing fields. This technology achieves synchronous real-time measurement of multi-layer film thickness and three-dimensional surface profile through single exposure spectral resolution interferometry, solving the problems of low point by point measurement efficiency of traditional ellipsometers and difficulty in separating multi-layer reflection signals using white light interferometry.
The core principle is to couple a pixelated polarization camera (PPC) with an imaging spectrometer to construct an optical system that can obtain four sets of phase-shift interferograms in a wide spectral range in a single acquisition. The light source adopts a 400-800nm tungsten halogen lamp, which achieves uniform illumination through Kohler illumination. The polarization state of the beam is controlled by a combination of linear polarizer and achromatic quarter wave plate, so that the orthogonal circularly polarized light reflected by the sample and reference mirror forms a phase shifted interference pattern on the micro polarizer array of PPC. In the data processing stage, spectral phases are extracted from four phase shifted subgraphs using specific formulas, and linear and nonlinear components are separated. The nonlinear phase reflects changes in film thickness, while the linear phase corresponds to surface height. Based on the absolute reflectance data calibrated from bare silicon wafers, an objective function is constructed to optimize the thickness of each layer, and the surface profile is determined by fitting the total phase.
Taking the five layer thin film (Si ∝ N ₄ - SiO ₂ - SioN SiO ₂ - Si ∝ N ₄) as an example, the standard deviation of this technique after 10 measurements is less than 1.6nm, with a maximum deviation of 14nm, which is highly consistent with the results of ellipsometry; Compared with the probe based step meter, the maximum deviation of surface step height reconstruction is less than 12nm. It is based on the horizontal stitching technology of line scanning, which can achieve large-area 3D thickness profile measurement, and is equipped with a 500W pixel high-resolution camera and sub angstrom resolution sensor to ensure accurate measurement without contact damage. This technology has been widely applied in online detection of semiconductor production lines, providing strong technical support for material quality assurance and production efficiency improvement.