［ Vacuum Equipment ］

Auto Tuning Vacuum Capacitor(Auto-VC)
Keywords

Vacuum capacitor, Motor integrated type, Static capacitance, High precision

Abstract

22

Yoshiyuki Tanimizu,
Toshimasa Fukai,
Takumi Hayashi

The Variable Vacuum Capacitor (VVC) is a circuit element (a quantitative
attribute characteristic (capacitance) of an electric circuit ) essential for theradio-frequency plasma control of semiconductor and Flat Panel Display (FPD)
thin-ﬁlm processing equipment, such as Chemical Vapor Deposition (CVD)
equipment and etching equipment. The VVC is steadily extending its application
range with the growth of electronic device industries. The Auto tuning Vacuum
Capacitor (Auto-VC) is a modular design product based on an innovative idea.
It is a package design combining the VVC and the control unit. This productfeatures a required static capacitance that can be easily and precisely set up
by using the dedicated controller. Using a simple command, our users (semiconductor manufacturing equipment suppliers) can control the static capacitance via RS-232C (a serial communications interface) or RS-485 (another serialcommunications interface.) The UW Series of the Meiden standard VVCs, the VP
Series for application to large currents, and the VD Series featuring compactness
are currently available. All these products can be converted to Auto-VCs byusing module options.

1 Preface

2 Features

The Variable Vacuum Capacitor (VVC) is anelectrical component that can adjust the static
capacitance. This is done by adjusting the rotating
position of the tuning screw. The major usage of thiscomponent is for the control of a Radio Frequency(RF) matching network. Nowadays, the VVC iswidely used for the High Frequency (HF) plasmamatching network for thin-ﬁlm processing equipment.
In the development of a HF matching networkby using a VVC and conventional method, it wasnecessary to develop a coupling part for the connection between the VVC and the motor. Since thistype of coupler requires high assembly precision,
the occurrence of a mechanical malfunction wasfrequently reported due to lack of accuracy. In order
to eliminate such difﬁculties, the Auto tuning Vacuum
Capacitor (Auto-VC) has been developed. The AutoVC is capable of increasing reliability because theVVC, motor, and connecting part went through themodule design. This paper introduces the featuresof the Auto-VC and its product lineups.

2.1 Easy Introduction

MEIDEN REVIEW Series No.177 2019 No.3

Conventionally, developing a HF RF matching
network using VVC, in addition to the intended main
circuit development, peripheral developments suchas a motor control system are also required. Thismeans the real development costs added up. The
initial introduction of our Auto-VC was easy because
all key components necessary for VVC capacitancecontrol such as the motor, insulation coupling, dedicated controller, etc. are all available in the module
design. Our customerʼs development resources cantherefore, be focused on the HF RF matching networks.
In addition, our Auto-VCs offer a custom design
to meet the customerʼs individual requirements, suchas installation method, etc. In doing so, we haveenhanced its product applicability. Fig. 1 shows
the conﬁguration of the Auto-VC. The Auto-VC uses
the RS-485 (standard speciﬁcation) as the serial
communications interface. By customer request,
another interface, RS-232C, is also available as anoption.

A part where a motor and a VVC is connectedcalls for the performance for complicated and challenging conditions: such as mechanical strength,
high withstand voltage, accuracy “concentricity
ʻhigh-precision parts level toleranceʼ,” and heatresistance. Given above, this connection part tends
to give rise many failure cases.
Fig. 2 shows a structure of the Auto-VC. For
the VVC driving motor, we adopted a two-phase
stepping motor with an optical encoder. With thisencoder, we can detect an unexpected occurrenceof a motor step-out. By means of a built-in program,it can perform the auto recovery mode operation.
For the connection part between the driving
motor and the VVC, we developed a coupler withthe withstand voltage of 10kVp. This coupler isbased on the design of the Oldham coupler. This
coupler realized two factors: absorption of the axial
misalignment and a high insulation level. For anMotor

external insulation tube, we adopted a special plastic material with high toughness, ﬂame resistance,and high insulation. In order to reduce mechanicalstresses to be applied to the VVC, we achieved optimal control on motor acceleration/deceleration.

2.3 High Accuracy (Static Capacitance)
Fig. 3 shows an example of the mechanicalcapacitance setting accuracy of the VVC. Regarding
the static capacitance of the VVC, each device has anerror of ±5% or less due to its mechanical accuracy.
Fig. 4 shows capacitance setting accuracy ofthe VVC by the Auto-VC (same sample unit used inFig. 3.) In the case of the Auto-VC, a mechanical54
Static capacitance error (pF)

2.2 High Reliability

Controller

3210－1－2－3－4－5

Conductor
covering
moving partconductors

Metal fitting

VVC

Insulation tube

Fig. 301000
2000
3000
4000
Mechanical VC position (400 ＝ 1 turn)Mechanical Capacitance Setting Accuracy of VVC

The graph shows an example of measured data: static capacitance error and the screw turning position of VVC (Part No.
SCV-125H65UW)

5＋1%

Configuration of Auto-VC

Metal ﬁttings and a conductor covering moving parts can becustomized.

10kVp DC/AC
insulation coupler

Static capacitance error (pF)

4Fig. 1

3＋0.5%

2
10－1－2－0.5%－3－4－5

Stepping motor withan encoder

Fig. 2Insulation tube

5000－1%
0100

200
300
400
500
Specified capacitance value (pF)

600

VVC

Structure of Auto-VC

The structure is simple, but various elements are assembled.

Fig. 4

Capacitance Setting Accuracy of VVC by Auto-VC

The graph shows an example of measured data on a static
capacitance error when the capacitance is automatically set upby the Auto-VC (using the same sample unit.)

MEIDEN REVIEW Series No.177 2019 No.3

23

Table 1 Product Lineups of Auto-VC SeriesSpeciﬁcations of the Auto-VC Series are shown.
VVC series200pF…

RS485

Compact

Standard Large-current

VD45/55

UW55/65

VP65～VP130

No. of motor steps

3600 steps 4000 steps 5400 steps

Motor2-phase motor (with an encoder)

Motor speed

240min−1

Motor resolutions

400 steps/turnInterface

RS-485/RS-232C

Controller

Exclusively designed controller

Communication rate

9600bps

Controller power supply DC24V (1A)

Fig. 5Auto-VC Network Connection

The network connecting Auto-VCs is shown (Max. 16 units).

error is offset by individually calibrating the VVC
capacitance. According to the graph, it is understood that Auto-VC achieved a capacitance accuracy of ±0.5% by this compensation method.

2.4 Ease of Operation (Easy Setting ofCapacitance)
A dedicated controller was developed toremotely control the VVC capacitance. For thecontrol communications interface, we adopt theRS-485 which is strong against noise.
By giving a preset command from the host PC
to the linked Auto-VC by serial communications, thesetting of the VVC capacitance and data retrieval ofthe process value can be controlled.
Fig. 5 shows an example of the Auto-VC network connection. Up to 16 Auto-VCs can be networked. When performing large-area plasma excitation, control of the surface of the plasma can berealized by connecting and controlling the distributed VVCs in a network.

3 Product Lineups
Table 1 shows product lineups of our Auto-VC
Series: for standard VVC series – the UW Series,
for large current application – the VP Series, and forcompact model – the VD Series. All our VVC series
could be turned to an Auto-VC conﬁguration byapplying other module units previously discussed
in 2.1.
As a feature of our VVC products, the driving
torque value of each series VVCs is almost thesame. Due to this reason, when the customer wants
to make an Auto-VC unit out of above VVC series,

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MEIDEN REVIEW Series No.177 2019 No.3

Static capacitancesetup accuracy±0.5% or less ( Typical)

the same motor and driving part can be applied.

4 Our Current Development Program
We are currently developing the EtherCATcompliant Auto-VC. The EtherCAT (Ethernet forControl Automation Technology) is an Ethernetbased real-time ﬁeldbus system. The applicationof the EtherCAT is rapidly spreading in the semiconductor manufacturing ﬁeld. For our Auto-VC, inorder to realize more ﬂexible plasma control, weexpect the EtherCAT will be a new type platform
based on the CANopen protocol and on the Ethernet
speciﬁcally optimized for industrial automation control.

5 Postscript
We have developed an Auto-VC as a new functional device of our VC offerings. Going forward,
we will work on more user-friendly products byimproving the current offering of our Auto-VCs.
In addition, we would like to express my gratitude to those who have greatly contributed to thedevelopment of this product.
We would like to express our appreciation forthe people relating to this development project forkind support and cooperation.
・EtherCAT is the registered trademark of Beckhoff Automation
GmbH, Germany.
・CANopen is a registered trademark of the CAN in Automation
Userʼs Group.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.