Detailed Information
RCRefSimW is a state of the art program to simulate reflectivity curves (XRR) of thin layers and diffraction curves (HRXRD) of single crystals with thin strained layer structures including an automatic curve fitting procedure.
1. RCRefSimW: Full version for diffraction and reflectivity
2. RCRefSimW.diff: A reduced version for diffraction only
3. RCRefSimW.ref : A reduced version for reflectivity only
Features of RCRefSimW:
RCRefSimW is a program to simulate HRXRD reflection/rocking curves of single crystals
with thin strained surface layers and XRR reflectivity curves of thin layer systems within
one common frame. RCRefSimW allows an automatic fitting of experimental and
calculated curve with given deformation (diffraction) and layer (reflectivity) models that
can be varied within broad limits.
RCRefSimW is a windows program written in Delphi. It is the successor of the older DOS
program RC_Ref_Sim5.
RCRefSimW uses by choice the dynamical theory (algorithm of Wie et al., J. Appl. Phys.
59, 3743, (1986)) or the semi-kinematical theory ( algorithm of Kyutt et al.,
phys.stat.sol.(a) 60, 381 (1980)) to calculate the diffraction curves of single crystals with
strained surface layers in symmetrical and asymmetrical Bragg case geometry.
RCRefSimW is provided with data files for CuKa radiation. However, any other radiation
can be used, if parameters for constructing the necessary data files are known.
RCRefSimW uses the most important reflections (111, 220, 400, 440 [and 200 and 600
for A3B5]). Other reflections are also possible (see above).
RCRefSimW (diffraction) allows the simulation for (multi)layer structures and superlattice
structures. Four different types of deformation models are provided. These can be
modified in many ways.
RCRefSimW uses the SIMPLEX algorithm for fitting. The number of free parameters
depends on the model used. The fitting process can be interrupted at any time. When
fitting begins, a random generator modifies the parameters arbitrarily, so that even with
equal starting parameters exactly the same result may not necessary be reached. The
fitting process is stopped automatically when a certain limit of the SIMPLEX parameters
is reached. Different features guaranty the convergence if fitting.
RCRefSimW allows fitting of experimental curves as well as a simple simulation of a
diffraction or reflectivity curve with a given deformation or layer model.
The substrate peak position can be corrected to 'zero' automatically or manually.
Experimental curves given in intensity values can be normalized to reflectivity values
automatically or manually.
RCRefSimW considers different collimator arrangements and double or triple crystal
setups.
RCRefSimW considers by choice s- and p-polarization, or only one of the two
(e.g. for synchrotron radiation).
RCRefSimW considers the influence of diffuse background scattering according to four
different models, where an optimization is possible with up to four changeable
parameters. The background can be included in the fitting procedure as a free
parameter by choice.
Experimental curves can be smoothed with different algorithms.
What does RCRefSimW do better than other commercially available programs?
Experimental files (ASCII) from different diffractometer manufacturers can be read
(adaptation of new file types is possible).
The points that are to be used for fitting the experimental curve can be selected
explicitly. This selection can be changed at any time if necessary.
Up to five profile parameters can be scanned within adjustable limits in order to find the
absolute minimum of the fitting parameter.
During the fitting process, the approach of simulated to experimental curve or the
modification of the deformation profile can be followed.
Deformation profiles obtained can be shown graphically and printed out or saved into
files for further use as a strain profile or as concentration profiles of an alloy component
(e.g. Ge concentration in SiGe layers).
There is an option available to analyze the experimental curve of a simple layer system
to receive a sensible deformation profile to start the fitting.
It is possible to create different archives (according to the areas of interest) with curves
analyzed already and the corresponding deformation profiles or layer model. A new
experimental curve can be compared with all the curves in an archive, and the profile or
model of the one, which is most similar to the new curve, will be used as the starting
profile for the fitting procedure. Especially for more complex structures this allows fast
finding of optimal start parameters.
Depending on the layer system, deformation profiles can be constructed very flexibly
and intelligently. The free variation of any lamella thickness allows for the development
of deformation profiles which do not have to follow any analytical function.
It is possible to simulate and fit XRD and XRR curves of the same sample with the same
layer model (XRD to XRR cross-over).
For superlattice structures, an additional variation of SL lattice constant and
deformation is considered over the layer stack.
It is possible to consider only a partial covering of the surface with the investigated
layer structure. This is important, if for example measurements were carried out in only
partly SiGe covered transistor arrays.
The error limits of all fitting parameters are obtained and directly shown after fitting
together with the layer parameters.
Special wishes of a customer may be considered to some extent.
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