=Paper=
{{Paper
|id=None
|storemode=property
|title=Modeling, Algorithms and Implementation of the Microcontroller Control
System for the Ion Beam Forming Process for Nanostructures Etching
|pdfUrl=https://ceur-ws.org/Vol-1000/ICTERI-2013-p-030-037.pdf
|volume=Vol-1000
|dblpUrl=https://dblp.org/rec/conf/icteri/RaloDKSV13
}}
==Modeling, Algorithms and Implementation of the Microcontroller Control
System for the Ion Beam Forming Process for Nanostructures Etching==
https://ceur-ws.org/Vol-1000/ICTERI-2013-p-030-037.pdf
Modeling, Algorithms and Implementation of the
Microcontroller Control System for the Ion Beam
Forming Process for Nanostructures Etching
Aleksandr Ralo1, Andrii Derevianko1, Aleksandr Kropotov1, Sergiy Styervoyedov1
and Oleksiy Vozniy1
1
V.N. Karazin Kharkiv National University,
Svobody sq. 4, 61022, Kharkiv, Ukraine
ralo-a-n@mail.ru
Abstract. In this work a three-level control system for the vacuum-plasma sys-
tem with the ion source based on high-frequency induction discharge architec-
ture is described. The system is built on smart sensors and specially designed
for operation in high EMI programmable logic controllers (PLCs) in the middle
hierarchical level. The structure of PLC and the algorithms of the system are
presented. Results of comparative simulation of classical management system
and created one, as well as the results of the system applying to obtain beams of
positive and negative ions and beams neutralized particles are reported.
Keywords. Programmable logic controller (PLC), control system, plasma tech-
nology, empirical model
Key terms. InformationTechnology, CommmunicationTechnology, Software-
System, Integration, Process
1 Introduction
Ion beams are an effective means of the surface treatment. Their application can be
found in the industry of the integrated circuits manufacturing, as well as for research
purposes as a powerful tool of micro-and nanoscale structures synthesis. However,
during the materials treatment by ion beams due to effects of similar charges repul-
sion and the charge accumulation near the processed surface, defects are formed in
the form of islet unetched films and vice versa – side etches. There are unwanted and
unpredictable changes in the structure of the processed sample that can irreversibly
change the characteristics of the ware [1]. There are several methods of excluding or
compensating the charge accumulation. One of the most promising technique that can
increase the rate of applicable products during plasma-beam processing is alternately
etching by pulsed beams of ions of different signs and etching by high-energy beams
Modeling, Algorithms and Implementation of the Microcontroller Control System 31
of neutral atoms, where the particle charge is neutralized by the ion beam away from
the treated sample [2], [3], [4].
Short times and complex algorithms that should be taken into account during these
experiments do not allow the operator to process without the use of modern computer
automation systems that work using a process model. Therefore, the aim of this work
was to create the intellectual management and control system, that will meet the re-
quirements of operating conditions of the pulsed plasma-process plant for etching and
micro- and nanostructures formation. An urgent task today is to build a system capa-
ble of independently analysis of historical data, and using them to provide the process
control. Seeing the specifics of the pulsed plasma-ion process system must ensure the
fastest possible response to the effects of interference that is impossible with the use
of information-analytical systems (IAS) based on the classical scheme and used for
the slower process.
2 The Use of Programmable Logic Controllers in Control
Systems
Programmable logic controllers (PLCs) are widely used in such control systems as
industrial automation and automation of scientific research. They provide signifi-
cantly higher reliability than personal computers, and the same flexibility of working.
Difficulties with changes in the operation make popular today microcontroller sys-
tems as not sufficient automation tool.
In order to improve the efficiency of the system it was proposed to build the hard-
ware using three-tier architecture, as it shown in Fig. 1. The lower level consists of
intelligent sensors and control elements, which control the PLC work.
PLCs have a much greater speed and are responsible for getting data from sensors,
filtering, formation of data packets and for communicating with the control centre,
created on the basis of a personal computer.
Algorithmic work of such system can be represented as follows:
1. Information about physical parameters, obtained by sensors, after conversion into
digital codes enters with the corresponding interface to the programmable logic
controller.
2. PLC forms an information packet, transmits the received information to the manag-
ing node (in our case, the system arbiter).
3. The central node addresses for the data needed to the historical data storage, ana-
lyzes them and, if necessary, generate management command. Information re-
ceived from the PLC is also stored in the repository for further analysis.
4. This control command is received with the PLC, which transmits it to the appropri-
ate control element.
This design exceeds the performance of classical one, because: first, damaged or
incorrect data can be filtered by a PLC, and second, the PLC data is transferred using
an optimum package format.
Modern PLC consists of three main parts:
PLC processor module
32 A. Ralo, A. Derevianko, A. Kropotov, S. Styervoyedov and O. Vozniy
I/O modules
Programming mechanism
Typically, these parts are combined with the use of crates on a physical level and a
number of tires on the logical one.
Despite the structural similarity of the PLC with the PC, the PLC must have some
specific characteristics. For the experiments, and automation systems building using
PLC, they should be able to work under different, sometimes very hard conditions,
ensuring high availability.
Experimental plant for the
ions and neutral particles
obtaining
Control
Sensors elements
PLC
System Storage
arbiter system
Fig. 1. The structure of the nodes communication using PLC
In the development of the PLC as a system bus selection was made from a list of
the most popular, fully standardized well studied buses. The choice was made in fa-
vour of bus VMEbus [5].
By using this bus is possible to build scalable systems, where it can be increased
both the number of modules that are responsible for input/output, and the number of
processor modules, that makes it possible to distribute the control program in the case
of its complexity.
Block diagram of the created PLC is shown in Fig. 2. As a PLC’s control processor
it has been selected 32-bit microcontroller AT91SAM7S from Atmel.
3 The Model Used
To provide a control on a given algorithm of complex technological processes, that
includes the induction plasma source management, it is necessary to develop a model
of the process. The best way to obtain it is to process the results of passive experiment
that are stored in specially designed storage that provides quick access to historical
data. After receiving the necessary amount of experimental data and the model crea-
tion, the control system can proceed in an active phase, i.e. manage the process.
Modeling, Algorithms and Implementation of the Microcontroller Control System 33
Processor part PLC interface Memory
Application memory
AT91SAM7S128 Front panel Po w e r
sou rce
Time rs L o gic
Indication
USB 2.0
and control System User Data
VME bus memory memory memory
controller
VME bus
Join panel
Input/output modules
Outer bus RS-485
Fig. 2. PLC Block diagram
To construct the control system it was decided to use the model of the 5th class by
Shantikumar [6]. In the proposed model, various simulation results for different initial
conditions are used. In addition, on the basis of these results analytical model is gen-
erated. It is possible to identify the following properties of the model:
Simulation model is used to determine the relationship between variable parame-
ters and target factor
An analytical model is a generalization of the results of various simulations; such
systems are more accurate, than the solutions obtained only by using theoretical
calculations, since they are based on multiple real data
After receiving the analytical solution, which is not changing under the new simu-
lations, this model can be used in the process control system to predict its results
for the given parameters and, hence, it provides accurate information for quick de-
cision-making [7]
The proposed class of models of simulation plays an important role in the investi-
gation of the system behaviour. The results are used to derive analytical models to
predict system performance. There may be a situation when the analytical model
without simplifications can not be created, and the approximate model is not suffi-
ciently accurate. Thus, models of this class are applicable in the cases:
When the correlation between the target factor and the system parameters is not
known that makes the analytical model is very difficult to develop, in this case,
when analytical models are very expensive, unreliable or impractical, simulation
can help in understanding the relationships between all factors that makes it possi-
ble to develop an analytical model
In many practical problems the useful signal is often superimposed with lot of
noise, which is almost impossible to take into account, simulation allows to inves-
tigate the behaviour of dynamic systems and to identify key parameters for evalua-
tion, so that these parameters are then included in the analytical model
The process of a given class model constructing was described in [8]. As a result of
simulation data processing system receives a functional relationship between the ex-
periment factors and coefficients of these relationships. To find a list of dependencies
34 A. Ralo, A. Derevianko, A. Kropotov, S. Styervoyedov and O. Vozniy
there has been used a list of 34 functions [9], that is sufficient to describe the most of
physical processes.
4 Simulation of the Control System
During the system development phase to select the most efficient architecture of its
work simulation was carried out. At the same time a number of software products
used to data networks simulating was observed.
OPNET and NetSim++ – graphical network modelling environment;
SMURPH (University of Alberta) and Ptolemy (Berkeley) use an eclectic language
for describing data lines;
OMNet++ that uses its own language to describe the architecture that is then trans-
lated by the pre-processor to standard C++.
The choice was made in favour of the last instrument, as being open, easy embed-
dable in third-party software products and having multiple trusted code in its compo-
sition.
OMNet++ is not a programming language – it’s just a class library for the simula-
tion. These classes are: modules, gateways, connections, settings, reports, histograms,
assemblers, precision registers, etc.
First of all, it was composed a system model, built using “common bus” architec-
ture with a central arbitration. The algorithm works as follows: arbiter sends a request
to the sensors. The intensity of the queries depends on the particular sensor. The re-
quest is broadcast, thus it contains the sensor’s address. Sensor, recognizing the ad-
dress, sends the data back. The size of datagram is also dependent on the sensor’s
type.
The appearance of the simulation software modelling the system is shown Figure 3
(a).
(a) (b)
Fig. 3. OMNet++ work for simplified systems
Modeling, Algorithms and Implementation of the Microcontroller Control System 35
To simulate the operation using the PLC part of the terminal devices was con-
nected to an intermediate device, which operates as a PLC. The appearance of the
resulting system in the program OMNet presented in Figure 3 (b).
Time and composition of each message sent and received is saved in a special vec-
tor file, that is then processed to obtain statistical information. As a result, basing on
multiple system runs and changing the parameters such as: number of devices, data
rate, processing time, etc. it was found that the use of PLC increases the productivity
of an average of 1.5 times. Figure 4 shows the number of posts at different loads on
the media for the cases of classical architecture and the use of the PLC. The fact that
the use of OMNet++ allows programming in C++, made it possible to produce a bust
of the parameters automatically.
Fig. 4. Dependence of the sent messages number from the bus bandwidth
5 The Results of the Developed System Application
Concrete implementation of information management system was worked out for the
experimental setup of vacuum-plasma nanostructures etching, schematically depicted
in Figure 5 [10].
The vacuum chamber is a cylindrical volume of diameter 600 mm and length
800 mm. On the side flange of the chamber it was mounted an RF ion source based on
the inductive discharge. With the ions extracted passage through the electrode system
the beam of desired particle charge or neutral particles is formed. In front of the
source a quadrupole mass spectrometer with an integrated energy analyzer with a
resolution of 0.1 eV mounted. Plasma excitation is done with an inductor connected to
the RF generator operating at a frequency of 13.56 MHz.
The management system’s task was a search for optimal etching parameters and
the stabilization of these parameters to ensure the repeatability of the experiment, as
well as to change the programmable modes of control elements.
Modes of RF discharge source and power blocs forming voltages on the beam ex-
traction system are controlled by PLC, that uses the internal bus commands to control
elements, responsible for setting the pulse’s amplitude, polarity, duration and duty
36 A. Ralo, A. Derevianko, A. Kropotov, S. Styervoyedov and O. Vozniy
cycle. PLC via USB 2.0 was connected to the computer where the accumulation of
experimental data and the search for functional relationships between them was done.
The system supports the operator control mode and independent search of optimal
parameters for this type of beams and maintains these parameters constant. The user
interface and the corresponding signals taken from the outputs of power blocks are
shown in Figure 6.
AD RFS
GIS
S
M
IND G1-3
Q
VC
- PB +
+ PB -
- PB + MMS
+ PB -
Fig. 5. Structural diagram of the setup for nanostructures etching. VC – vacuum chamber for
ion-plasma treatment, QMS – quadrupole mass spectrometer with energy analyzer, RFS – RF
source, AD – agreement device, PB – power blocks IND – inductor, G1-3 tree-grade electrode
system, GIS – gas inlet system, MMS – microcontroller management system.
Fig. 6. The user interface and the corresponding control signals
Modeling, Algorithms and Implementation of the Microcontroller Control System 37
6 Conclusion
Three-level information management system of vacuum-plasma system with the ion
source based on high-frequency induction discharge is designed to produce beams of
positive and negative ions and neutralized beam of particles used in the nanostruc-
tures etching. On the middle hierarchical level of the system there are specially de-
signed programmable logic controllers based on a 32-bit microcontroller from Atmel
AT91SAM7S, that have increased noise immunity characterized, advanced comput-
ing power and optimal capacity for a given task. PLCs make the primary information
processing and greatly accelerate the process of information exchange, particularly at
high pulse loads.
Despite the overall effectiveness of the method of constructing process models to
manage them based on statistical data accumulated, in practice, large amounts of data
to process and requirements for high-speed make this method not always usable.
Therefore, the task of modelling and process control between the main control
mechanism and the PLC allocation is important.
Testing of the system to manage the real process has shown its efficiency and al-
lowed to obtain an adequate empirical model of the controlled ion source based on
high-frequency discharge from tree-grades control.
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