Grating
Stack Tab
The Grating
Stack Tab provides more or less the functionality of the former stack editor
(until version 2.02.01). In addition, a cross section drawing of the stack can
be shown optionally on the right hand side of the Tab
as shown in Fig. 13. According to the dimensionality (1D or 2D) and to the solution method (RCWA or C-method) there are 4
basic grating types available in Unigit. The
dimensionality and solution method can be chosen when creating a new grating by
clicking the wanted radio buttons. In case, a grating is selected from a
database, these options are detected from the grating file and set
automatically.
As long as
no valid grating is selected, it is indicated with red color in the stack file
group. Similarly, the color changes to red as soon as the grating is changed by
editing one of its parameters. In order to run the grating structure that is
exhibited in the grating editor on the left-hand side of the Tab, one has to
make sure to save it first. After successful saving, the color of the stack
file path turns into black.
In the
following subsections, first the basic features of the stack editor are
explained and then, the four basic grating types along with their implemented
layer types are presented.
Fig. 13: Grating
Stack Tab with cross section drawing of the multilayer stack
1.
Stack
Editor
The stack
editor is integrated into the Grating Stack Tab and facilitates the assembling
of arbitrary multilayer grating structures for each of the four basic grating
types. The types of layers to choose from are context sensitive, i.e., they
depend on the selected solver type and dimensionality. For the editing, a
number of buttons are arranged below the spreadsheet list.
There are
several feasibilities to assemble the stack.
- First, new layers can be inserted by
starting the layer editor clicking the INSERT
button.
- Second, an existing layer can be edited by
clicking the EDIT-button. This action also
launches the layer editor with the selected layer. In order to select a
layer, the cursor has to be positioned at the beginning of the associate
description line.
- Third, the order can be changed by moving
a marked layer up or down.
- Fourth, a layer can be deleted by marking
it and press the DELETE button.
- Layers can be marked by clicking with the
left mouse button and concurrently holding the CTRL or SHIFT key and saved
as a sequence file. The marked layers must not necessarily form a coherent
string, i.e., unmarked lines are permitted between marked lines.
- Marked layers can be copied or cut and
later pasted (this is also possible between different stacks for the
information is stored to the clipboard). For instance, HL (high low
index)-quarter wave stacks can be built in this way.
1.1.
RCWA
1D stacks
For 1D
(line gratings) there are 5 basic types of layers:
- homogeneous flat layer (type 1),
- sinusoidal Rayleigh-Fourier layer (type
2),
- polygonal Rayleigh Fourier layer (type 3),
- discrete RCWA layer (type 4) and
- continuous RCWA (i.e., gradient) layer
(type 5).
In addition
to these basic layer types, so-called composite layers can be input:
- polygonal RCWA layer (type 6),
- sinusoidal RCWA layer (type 7),
- sliced multilayer (RCWA),
- sequence of layers (comprising an arbitrary
number of layers from type 1 through type 7 in an arbitrary order).
A symbolic
layer stack comprising all these layer types is shown in Fig. 14.
As opposed to the sinusoidal or polygonal
Rayleigh-Fourier (/3/) layer, the corresponding composite layers are
automatically decomposed (that means sliced) into discrete RCWA slices of type
4 immediately before being processed. A sequence of layers (also called
sub-stack) has to be stored as a file in the same way as the total stack
description is stored. The only difference between a complete stack and a
sub-stack consists in the fact that the complete stack comprises beside the
stack data the grating period as well as the superstrate and substrate
description. Moreover, a hierarchy of sequences is not permitted, i.e., a
sub-stack must not contain another sub-stack. As for layer editing see section
layer editor.
Fig. 14: Example
for a RCWA 1D layer stack
1.2.
C-Method
1D Stack
This editor enables the assembling of stack
files for the C-method. An unlimited number of non-parallel interfaces is
permitted. The stack editor considers the
interface as a “layer” just like in the same way as it does for
Rayleigh-Fourier interfaces. This arises from the layer-wise processing of
RCWA-slices. Basically, the stack editor enables several choices:
- Plane interface;
- CCM polygon = polygonal
C-method interface;
- CCM sinus = sinusoidal C-method
interface;
- Parallel to previous: meaning
the interface is parallel to the one below;
- Sequential: not yet
implemented;
- CCM Trapezoid: special case of
CCM polygon (with 6 profile sampling points);
- CCM measurement: special case
of CCM polygon where the profile sampling points are obtained from a
measurement file;
- CCM Triangle: special case of
CCM polygon (with 3 profile sampling points);
The interface types are uniquely identified by
its names. Beside the corrugation of the layers, the distances and if existent
the material ID's are shown. Note, that there is no distance entrance for the
uppermost interface (because it would have no meaning). An example of a
multi-layer stack containing all different layer types is shown in Fig. 15.
Fig.
15: Example
for a C-method 1D grating stack
1.3.
RCWA
2D Stack
There are basically 6 types
of layers:
- Thin Film,
- Patches (rectangular),
- Ellipse,
- 3D Cone,
- Fill 2D,
- Sequence.
Here, the
types: thin film, patch, ellipse and fill2d are genuine 2D layers whereas 3D
cone and sequence are composite 3D-shapes formed by the basic 2D types (i.e.,
all 4 types are possible for sequence and ellipse type is used for 3D cone).
An example
of a multi-layer stack containing all different layer types for a RCWA 2d stack
is shown in Fig. 16.
Fig. 16: Example
for a RCWA-method 2D grating stack
1.4.
C-Method
2D Stack
There are basically 4 types
of interfaces for c-method
2D:
- Parallel to Previous
- Pyramide
- Micro-Lens
- Fill 2C.
In the
current implementation, only one out of the types pyramide,
micro-lens and fill2c can be chosen as bottom interface. In addition, only one
interface of type “parallel to previous” can be put on top of it resulting in a
maximum number of two interfaces. Examples are provided in Fig. 17, Fig. 18 and Fig. 19.
Fig. 17: Example
of a 2C stack with a pyramid interface
Fig. 18: Example
of a 2C stack with a micro lens interface
Fig. 19: Example
of a 2C stack with an arbitrary interface (fill2C) load from a file