Development of a double sided stitching interferometer for wafer characterization

doi:10.1016/S0007-8506(07)60481-8

CIRP Annals

Volume 55, Issue 1, 2006, Pages 555-558

https://doi.org/10.1016/S0007-8506(07)60481-8 Get rights and content

Abstract

A pre-prototype measurement machine for measuring the geometry of double side polished wafers has been developed. The measurement principle is based on a scanning double sided Fizeau interferometer with which the front side and the back side flatness of a wafer are measured simultaneously. Both flatness maps are used to derive the wafer thickness variation. Field distortion of the optical system, alignment errors and the thickness variations of the reference cavity are compensated by self-calibrating techniques in order to achieve a measurement uncertainty in the order of several nanometers.

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Cited by (21)

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One of the possible solutions is to perform multiple measurements and stitch the results together to form a dataset with a larger area to reveal the large topographic information without losing the high resolution information to characterize the micro-structure pattern [2]. Stitching has been reported for a sub-aperture stitching interferometer for both spherical and flat surface measurements [3–6]. Preibisch et al. [7] used a phase-correlation method to find the translation matrix between image pairs and performed global optimal stitching.
Optical instruments are widely used for precision surface measurement. However, the dynamic range of optical instruments, in terms of measurement area and resolution, is limited by the characteristics of the imaging and the detection systems. If a large area with a high resolution is required, multiple measurements need to be conducted and the resulting datasets needs to be stitched together. Traditional stitching methods use six degrees of freedom for the registration of the overlapped regions, which can result in high computational complexity. Moreover, measurement error increases with increasing measurement data. In this paper, a stitching method, based on a Gaussian process, image registration and edge intensity data fusion, is presented. Firstly, the stitched datasets are modelled by using a Gaussian process so as to determine the mean of each stitched tile. Secondly, the datasets are projected to a base plane. In this way, the three-dimensional datasets are transformed to two-dimensional (2D) images. The images are registered by using an (x, y) translation to simplify the complexity. By using a high precision linear stage that is integral to the measurement instrument, the rotational error becomes insignificant and the cumulative rotational error can be eliminated. The translational error can be compensated by the image registration process. The z direction registration is performed by a least-squares error algorithm and the (x, y, z) translational information is determined. Finally, the overlapped regions of the measurement datasets are fused together by the edge intensity data fusion method. As a result, a large measurement area with a high resolution is obtained. A simulated and an actual measurement with a coherence scanning interferometer have been conducted to verify the proposed method. The stitching result shows that the proposed method is technically feasible for large area surface measurement.
A technique to measure the flatness of next-generation 450 mm wafers using a three-point method with an autonomous calibration function
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Citation Excerpt :
Currently, the primary methods used to inspect wafer flatness are interferometer systems or scanning probe systems. Interferometer systems [1–5] have the advantage of a high accuracy. However, there are certain drawbacks in production efficiency due to the influence of environment, which can have an effect through: (a) disturbance light, (b) vibration, and (c) changes in the temperature.
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Stitched Acousto-Optic Modulator Stroboscopic Interferometry for characterizing larger microstructures
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Large field of view with higher resolution has become a strong requirement for the present measurement technology. Currently used sub-aperture stitching methods are suffering from the inaccuracies of computer controlled stages. In this work three different simplified stitching methods are presented. The stitching process proposed here is based on Acousto-Optic Modulator Stroboscopic Interferometry (AOMSI) of fixed field of view (FOV) and it does not require any computer controlled stage. A large microcantilever was tested in two stages, one from the root and the other from the tip portions separately, and the complete profile of the cantilever was extracted using the proposed stitching methods. The same cantilever also was tested using a commercial profilometer with a full field of view. There was a good agreement between the results from the proposed methods and a commercial profilometer. Obtaining extremely low amount of variation using the presented stitching methods validates the proposed stitching methods for large microstructures.
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Citation Excerpt :
Progress in miniaturisation of components requires dimensional micro- and nanometrology [1]. The presented probing system is based on a Fizeau interferometer [2,3], which is normally used in surface testing [4]. The information given by the interference pattern is the orientation of the surface under test relative to the reference surface as well as the form deviation of the surface under test relative to the reference surface.
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A Novel 3D Topography Stitching Algorithm Based on Reflectance and Multimap
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Development of a double sided stitching interferometer for wafer characterization

Abstract

Opt. Lasers Eng.

Annals of the CIRP