Eliminator ^TM RF Pass & Blocking Filter Modules  

Eliminator filter modules are used to provide attenuation of unwanted harmonic RF 

energy without significant introducing losses. They may be installed at the input 

to the impedance matching network or at the output of the RF generator. 

Eliminator ^TM Low Pass RF Filters

Eliminator RF Low Pass models are typically installed in the 50 ohm coaxial transmission line at the input of the impedance matching network. They function to attenuate harmonic energy without affecting the fundamental frequency or introducing significant phase shift. 

Harmonics are generated in the plasma discharge and usually kept from returning back to the RF generator by the inherent filtering action of the matching network. However, the impedance of some plasmas require matching circuits that may not completely filter these harmonics. The symptoms may include un-stable or non-repeatable (automatic) impedance matching network operation and the  inability to achieve low reflected power. 

In some cases the measured reflected power may not be able to be "tuned out" because this reflected power is actually harmonic energy traveling back through the coaxial cable to the RF generator's power detector. Most Forward/Reflected power detectors now in use are not frequency selective and therefore cannot resolve whether the detected signal is based on the fundamental or the harmonic energy. Since this detector is a key component in maintaining the forward power set-point and protecting the RF power circuits during excessive reflected power conditions, it is important that it sees only fundamental RF energy. 

The electrical topology used in these off the shelf filters is typically a "PI" configuration using two shunt capacitors and a series inductor. These models are constructed within an RF tight aluminum enclosure with high quality coaxial connectors. These low pass filter designs are electrically "symmetrical" and therefore can be installed in either direction.

Click here to view a typical 13.56 MHz frequency vs attenuation plot - 

Model LPF131-N

In some RF delivery systems the low pass filter is used as an "isolator" enabling proper operation of multiple RF generator / impedance matching systems connected into a common vacuum process system. For example, the most common application is in an RF biased magnetron sputtering system where 2 complete RF systems (RF generator & impedance matching network) are used simultaneously to power a magnetron cathode and a substrate holder (stage). The filter module is connected to the 50 ohm input of the matching network only - see image below left. The result is dramatic! The entire system will now operate as originally intended with both RF systems maintaining their RF output power control as well as each automatic impedance matching network properly tuning. 

It should also be noted that RF generators in a multiple system require that their common exciter (master/slave I/O) be connected. This will enable all RF generators to be operating on a common frequency. All cable lengths should also be calculated to introduce the proper phase shift. System level phase shift calculations are discussed on the "Cables" page on this website.      

Eliminator RF Low Pass filters may also be installed directly onto the output connector of an RF generator and used to further attenuate harmonic energy for the purpose of meeting strict CE compliance standards. These filter designs typically include 4 or more "poles" to provide a deep attenuation slope. The measured insertion loss at the fundamental frequency is typically 0.2dB or lower. High power models (>3kW) are forced air cooled using a 24VDC axial fan. All penetrations into the enclosure are RF shielded using an aluminum honeycomb waveguide beyond cutoff material that allows airflow and blocks RF leakage. 

The spectral plots below document the typical attenuation of a 4 element low pass filter model. The image on the left is an unfiltered signal. The image on the right is filtered. Notice that the 2nd harmonic is 53dB down from the fundamental frequency (in the filtered image). 

The models listed below represent products that we currently have designed with some available from stock. All models (unless specified) have a maximum 3000 volt RMS rating and are designed for use in a 50 ohm system. Application specific versions are available upon request. Please contact the sales department to discuss your application. 

Include details such as:

Eliminator ^TM RF Blocking / DC Pass Filters

Manitou Systems offers off the shelf designs in addition to custom/OEM designs. These low pass isolation filters are used to pass either AC or DC power or control & sensor signals to and from a plasma process system while providing a high degree of isolation between the input and output ports. Their use results in keeping the RF energy inside the "process" instead of leaking out and radiating. Radiation of RF energy may cause coupling to adjacent system cabling and interference with the connected hardware.

These products are typically installed in between the DC sputtering power supply output and the magnetron cathode. A short coaxial cable is needed to place the filter in series with the cathode. They are useful in blocking RF energy conducted through the plasma back to the DC power supply in an RF biased system.

The electrical topology used in these off the shelf filters is typically an "L" configuration using a shunt capacitor (on the DC power supply or control side) and a series inductor connected to the output connector (plasma side). All models are constructed in an RF tight aluminum enclosure with high quality coaxial connectors. All RF Blocking filters are not electrically "symmetrical" and need to be installed with the shunt capacitor side connected to the DC process power supply.

Application specific filter designs are also available to solve demanding RF interference problems. These include two-stage versions for increased RF attenuation and special thermocouple filters using thermocouple wire throughout for minimal intrusion to the bi-metallic junction.

The chart below lists typical filters that are designed to operate in a 13.56 MHz RF power environment. All models (unless specified) have a maximum 3000 volt DC or RMS rating. Models for use with other frequencies and higher currents are available upon request.

Include details such as:

• Your application

• Physical size limitations

• Required RF performance 

• RF power level

• I/O connector type & position

Eliminator ^TM RF Blocking / AC-DC Pass Filters for Heaters  

High current heater filters are typically installed on the atmospheric side of a 1" diameter vacuum feed through. They are used to isolate the heater array located inside a plasma processing system from the controls and AC power line on the atmospheric side. Use of the heater module will attenuate the RF energy conducted from a source of plasma to the heater as it exits the vacuum system. An "L" topology effectively isolates and shunts unwanted RF energy to ground. 

The model shown above is our PN 00001026 and is rated at 40 amps continuous current (AC or DC) @ 5KV maximum voltage. The enclosure size is 12" long X 3" high X 3" wide. A 1" diameter hole is provided on the output (connection to the vacuum chamber) and a 1/2" conduit (7/8" actual) hole is provided on the input (to power controller). It is suggested that the input wiring be enclosed in a flexible Sealtite type conduit for proper compliance and safety. Input and output connections are made via 10-32 threaded studs, nuts & lock washers. The user will need to install ring type terminals to mate with the studs.  

Manitou also offers a dual section filter, with the same specifications as above, that enables isolating both lines of a heater. The module will include two of the typical filters illustrated in a single enclosure. The size is 12" X 3" high X 7" wide. Input/Output connection holes are sized and located based on a customer specification. Part number for this model is 00001003.

Click Here To Download Vacuum System Heater Filter Module Installation Notes

The model image to the left illustrates an application specific, OEM model with multiple filter elements (4 discrete filters) designed to mount onto the side of a vacuum process chamber and connect to two separate heater elements. This specific version provides the necessary RF isolation with an ability to easily pass 20 amps of AC current. It has an overall size of 7.5"L x 4.7"W x 3"H and constructed in an aluminum die-cast enclosure. Call us with your specific requirement.  

Eliminator ^TM RF Blocking Filters

Manitou also offers RF Blocking filters that enable both RF and DC power to be connected to a magnetron sputtering cathode. This is desirable to achieve certain deposited thin film characteristics. The filter topology is typically a multi element  "L" enabling a high degree of fundamental frequency attenuation. The output of this filter is connected to the magnetron cathode in parallel with the output of an RF impedance matching network. The filter's input is connected to the DC sputtering power supply. It should be noted that the DC energy is blocked from entering the matching network by the network's series capacitor. As with all Manitou filter modules, this unit is constructed in a metal enclosure with coaxial I/O connectors.

Application specific versions are always available upon request. Please contact the sales department to discuss your application. 

Include details such as:

• your application 

• physical size limitations

• required RF/DC performance

• voltage levels

• current passing specification 

• I/O connector types

• Request Literature

• Download Eliminator Filter Module Owner's Manual (3mb)

Images on this web page are for illustration purposes only. Actual product may differ from these images. Contact Manitou for the actual image or drawing file.

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Manitou Systems Inc.
18 Commerce Road, Newtown, CT. 06470
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This website has been revised as of 03.25.07

Any technical specification described on this website is subject to change without prior notice.

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