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RF AutoTune System

© 2006
MAT-VAC Technology, Inc.
All Rights Reserved

Last Revision: V1.04 — 09 Aug 06

For those systems purchased with RF sputter or etch capability the systems are provided with an RF AutoTune System that dynamically adjusts the load and tune capacators to maintain optimum power coupling into the targets. This system consists of several major components including:

The RF system is shown here in block diagram form:

The PLC controls and co-ordinates all of the signals. There are a variety of signals to/from the PLC:

Signal	Type	To/ From	Notes
RFENBL	RO	RF PS	This is the master command to enable the RF output from the PLC. This is a dry contact relay output for galvanic isolation
RFOK	DI	RF PS	This is a feedback signal from the RF power supply telling the PLC that it is powered ON
RFTEMP	DI	RF PS	This is a feedback signal from the RF power supply that is asserted when the internal temp of the PS is above safety threshold.
RFOUT	AO	RF PS	This is the analog command signal to the RF power supply. The output of the power supply is proportional to the value of this signal. This is used in conjunction with the `RFENBL` output.
PWRFWD	AI	RF PS	This is a feedback signal from the RF power supply telling the PLC the amount of power being delivered to the load. This signal is also sent to the chassis front panel indicating meter for reference when manually tuning
PWRREV	AO	RF PS	This is a feedback signal from the RF power supply telling the PLC the amount of power being reflected from the load back into the RF power supply. The goal of the AutoTune system is to minimize this value by suitable adjustments of the Load and Tune capacators in the RF enclosure. This signal is also sent to the chassis front panel indicating meter for reference when manually tuning.
RFTUNE	AO	AutoTuner	This is the tune command analog signal from the PLC telling the AutoTune controller the desired tune capacator setting
RFTIN	AI	AutoTuner	This is the feedback signal from the AutoTune controller indicating the position of the RF Tune capacator
RFLOAD	AO	AutoTuner	This is the load command analog signal from the PLC telling the AutoTune controller the desired load capacator setting
RFLIN	AI	AutoTuner	This is the feedback signal from the AutoTune controller indicating the position of the RF Load capacator
RTUNE	DO	AutoTuner	This is the command from the PLC to the AutoTune controller telling it to switch from pre-tune (the outputs directly follow the `RFTUNE` and `RFLOAD` inputs) to AutoTune mode where the outputs are controlled by the phase and magnitude signals from the phase/mag detector
LEARN	DI	Panel Button Adjacent to AutoTuner	This is the command to the PLC telling it that it should save the analog values presented on the `RFTIN` and `RFLIN` inputs and associate them with the currently selected target. These values are then fed out as `RFTUNE` and `RFLOAD` by the PLC when changing targets to allow the AutoTune controller to pre-tune for target ignition prior to switching to AutoTune mode. This button is only enabled when the DMP Maint Key Switch is in the ENABLE position and a target is selected.
RFDCOUT	DO	N/A	Not used in RF only Systems. In systems that have both RF and DC power supplys, this will operate the selector relay to connect either the RF power supply or the DC power supply to the internal target bus.
T1	DO	Target Relay	Connects the power supply to T1. Targets that are not selected will be connected to ground.
T2	DO	Target Relay	Connects the power supply to T2. Targets that are not selected will be connected to ground.
T3	DO	Target Relay	Connects the power supply to T3. Targets that are not selected will be connected to ground.
RF2ETCH	DO	Target Relay	Connects the power supply to the etch platform. Targets that are not selected will be connected to ground.
RFINTLK	Safety Relay	RF PS	This pair of inputs are hard wired from the K1 safety relay to the interlock inputs of the RF power supply. The RF output will be disabled no matter what the state of any other command inputs when there is no connection between these two terminals. The Safety Relay will drop out any time that: CMBVAC (Chamber Vac) is lost. H2OSW (Water Flow Switch) is lost indicating that there is insufficient cooling water flow for the targets, the tuning network (which is water cooled to help absorb the `PWRREV` when the target tuning is not optimum) or for the RF power supply itself. Safety cover switch is opened indicating the operator may be exposed to potentially lethal voltages. +24 power to the chassis is lost.

AutoTune Controller Settings

The PT-II-CE AutoTune controller is manufactured by RF-VII corp and their manual (supplied separately) should be consulted prior to continuing.

Preinstallation Check

Prior to installing the PT-II-CE AutoTune Controller remove the outer cover and remove the jumpers at TB3 and TB4 to set proper preset scaling. Replace the cover and install into rack mount.

Removing the cover from the RF-VII AutoTune controller reveals the interior components.
The TB3 and TB4 jumpers are located behind the TUNE meter on the main PCB.
Both jumper are removed to set the proper I/O scaling.

Control Description

There are two essentially identical control sections on the PT-II-CE AutoTune Controller, one for the Load and the other for the Tune. Both operate identically and the discussion here will apply equally to both sections unless otherwise noted

The PT-II-CE AutoTune controller is rackmounted on the system chassis in a 1U rackmount. The unit itself is a half rack width, and is mounted between two filler plates. On one of the side mounted filler plates, the "LEARN" switch has been installed. This is a normally open momentary pushbutton switch and is used to tell the PLC to store the current load/tune settings for the currently selected target.

On the PT-II-CE AutoTune controller itself, each output (Load or Tune) has a group of controls and indicators listed here:

Mode Switch - Leave in REM position
H and L limit red LED indicators
+- toggle switch
Load or Tune Meter

At the far right of the PT-II-CE AutoTune controller there are several additional controls and indicators:

L and T Preset adjustment - Factory preset, do NOT adjust
Power Switch - Leave ON - Green PWR LED indicator should illuminate
Red Fail indicator LED - Contact RF-VII directly for replacement

The PT-II-CE AutoTune controller is powered by a standard power strip internally mounted to the chassis. The cord to the power strip is connected to the adjacent rack assembly and placed into the AUX outlet box. This box is connected to the 10A single phase AUX breaker in the breaker box.

Teaching the PLC

Each target or combination of targets will have a unique RF impedience that will require individual RFLOAD and RFTUNE presets in order to assure reliable target ignition. When a new target is first installed it is usually necessary to manually determine the optimum starting point for ignition and then by pressing the "LEARN" button, the PLC is instructed to save these settings.

The two chassis front panel indicators are provided to allow the operator to conveniently monitor the PWRFWD and PWRREV signals while manually tuning the system. The operator will place the PT-II-CE AutoTune controller in MAN mode and then use the +- switch to adjust the tuning for optimum values. There is normally some interaction between the Tune and Load settings. Once a good compromise value has been found (as shown on the panel indicator meters) then the operator will press the LEARN button to store those values for the current target.

As part of the RF target selection process the PLC will initially output the stored values to the RFLOAD and RFTUNE analog outputs and leave the RTUNE command selector in the 'pre-tune' state. This causes the PT-II-CE AutoTune controller to send the command signals directly to the capacator tuning motors. After a preset delay (normally around 10 seconds), the PLC will command the RF power supply to come on (using the RFENBL signal) and then change the state of the RTUNE output, making the PT-II-CE AutoTune controller to enter automatic tuning mode. The PT-II-CE AutoTune controller will then use the values presented on it's mag and phase inputs (as sensed by the phase/mag detector) and use those to maximize the power coupled to the targets (maximum PWRFWD value) and simultaneously minimize the reflected power being returned to the RF power supply (minimum PWRREV value).

RF Components

The schematic at the beginning of this document shows the components of the RF section. For those used to normal circuitry the physical size and configuration of the components will come as quite a surprise. Due to the large power levels involved (up to 10kW in some systems) the RF components are physically large and generally water cooled to all them to dissipate the heat generated when the RF coupling is mismatched. The 'wires' in the RF section are actually silver plated copper tubing. This both maximizes the current flow due to 'skin effect', but the hollow tubing allows for cooling water to flow.

Cooling water should be cool but not cold. The water temperature must never be allowed to be so cool as to form condensation on the RF components. Additionally the water used should be filtered to remove impurities. It is possible for contaminated water to conduct sufficiently so that the cooling water forms an ohmic path between targets. This can lead to unexpected sputtering on targets that are not selected. This is more of an issue in DC power systems as in RF systems the unused targets are grounded, however, sneak current paths can reduce plasma efficiency and lead to uniformity problems.

Examination of the RF tuning network shows the following components:

LP π Filter consisting of C1, L1 and C2
Dynamic Tuning Air Variable Capacator C3
5-Turn Series Inductor L2
Dynamic Load vacuum High Voltage Capacator C4
3-Turn Series Inductor L3

The final output is then fed to a series of vacuum high voltage SPDT relays for target selection.