Scatterometry or optical CD metrology (OCD) has become one of the most common techniques in quantitative wafer
metrology within the recent years. Different tool configurations are either available in commercial inspection tools or
subject of recent and present research activities. Among these are normal incidence reflectometry, 2-θ scatterometry,
spectroscopic ellipsometry and angle resolved Fourier scatterometry. The two latter techniques appear to be promising
for future use in semiconductor fabs. Spectroscopic ellipsometry is well established, and Fourier scatterometry has
become of increasing interest within the recent time. Line edge roughness, i.e. an edge position variation of printed lines
in lithography, has been of less importance up to now, as its amplitude could largely be neglected with respect to the
feature dimensions. This will, however, not be the case for future nodes, as on the one hand CDs are getting smaller and
smaller, and on the other hand, even the absolute amplitude is expected to increase due to the higher complexity of
lithography and etch processes. In this paper a comparison of scatterometric reconstructions in both spectroscopic and
angle resolved techniques considering LER afflicted samples is presented. The validity and benefit of a simple effective
medium model is investigated.
In Fourier modal methods like the RCWA and the Differential Method the Li-rules for products in truncated Fourier
space have to be obeyed in order to achieve good convergence of the results with respect to the mode number. The Lirules
have to be applied differently for parts of the field that are tangential and orthogonal to material boundaries. This is
achieved in the Differential Method by including a field of vectors in the calculation that are normal to the material
boundaries. The same can be done laterally in each layer of an RCWA calculation of a 2-D periodic structure. It turns out
that discontinuities in the normal vector field can disturb the computation especially when metallic materials are
dominant in the structure which would make the usefulness of the normal vector method questionable. So it is of great
importance to investigate how normal vector fields can be established with as few discontinuities as possible. We present
various methods for the 2-D RCWA and the 1-D and 2-D Differential Method and compare the respective convergence
behaviors. Especially we emphasize methods that are automatic and require as few user input as possible.
The optical defect identification on wafer still remains a useful tool, even if the structure sizes have the order of
magnitude of the used wavelengths of the light and far beyond it. Structures are not resolved in this way, but one
receives a contrast in the microscopic image of a defect with a certain illumination configuration. We show simulations
of such images at structures relevant for practice and present methods to accelerate the computations. These
accelerations can cause a loss of accuracy, but they can give hints to useful illumination configurations.
Scatterometry proved to be a powerful technique for CD and profile metrology. In contrast to alternative methods like
scanning electron microscopy (SEM) it is an integral method that reconstructs structure parameters from a comparison
between measured and simulated spectra. It is well established in the field of line / space gratings and gaining importance
for crossed grating structures. The simulation tool MicroSim, which was developed at the Institute for Technical Optics
(ITO) in Stuttgart, has recently been extended to arbitrarily shaped crossed grating structures. Besides the shape also the
pitches and mode numbers in the two directions of periodic continuation can be selected freely. In this article, different
measurement configurations are discussed regarding as an example an asymmetric crossed grating structure. The depth
of an asymmetric etch ought to be measured as well as its width. For the depth a conventional spectroscopic
ellipsometric setup can be applied, whereas for the width an angle scan is proposed. In this configuration the wavelength
remains constant while the sample is rotated around its normal.
We present a measurement setup for the acquisition of topographic and 3-D point cloud data using the depth-scanning fringe projection technique (DSFP). We describe the signal generation, its processing using techniques known from short coherence interferometry and discuss a direct 3-D calibration method. Our measurement system delivers an absolute phase map of the scene under measurement. Calibration procedures for macroscopic measurement methods like fringe projection and / or photogrammetry consider the principal distance (that is to say the distance between the center of projection and the image plane) as a constant. This is feasible as long as no focusing and zooming are performed during measurement. Consequently the depth of the measurement volume is limited by the depth of sharpness of the imaging system. By focusing through the whole depth of the measurement volume, our system overcomes this problem, and offers a virtually unlimited measurement depth. However, we have to take the issue of focusing into consideration in order to calibrate our system. The well-known direct calibration method has been adapted to our DSFP setup in order to deal with the problem of geometrical aberrations and to provide a 3-D point cloud. It has been completed to a set of three polynomial transformations, which allow to include the depth-scanning principle in the calibration of the system.