The FAQs listed below are based on real problems encountered during the commissioning and use of the Model PB3 RF power systems. All data in this file originates from our customer’s experiences and from the Manitou Team. Please feel free to submit your experiences with this product so that this web page can continue to grow as a resource.
Why won’t my PB3 power up?
- Is the unit connected to the correct AC mains voltage?
- Is this circuit live?
- The PB3 uses an IEC (HP) type AC mains input module. This module includes a filter and fuses. Are the fuses OK? Please look on the rear of the enclosure as this is where the necessary AC mains voltage level is displayed. The necessary voltage is 187>240VAC and if only 115VAC is applied, the internal circuits will not operate correctly.
Why won’t the RF-ON and Interlock LEDs light ?
- If the unit powers up; cooling fan runs and LED meters operate (PB3-MD models only) you should verify that the interlock shorting plug is installed. The pre-wired plug provides the proper wiring to enable local RF ON/OFF operation in addition to no external interlock capability. If this plug has been re-wired; please check that the wiring scheme follows the schematic in the PB3 owner’s manual.
How long can I make the RF output cable (PB3 matching network output to sputtering source). (Models PB3-M & PB3-MD only)
- We suggest that a cable no longer than 5 feet in length be used. This recommendation is based on the power loss and RF matching problems that may exist with longer cable lengths. You should also plan to use a high quality Teflon coaxial cable (type RG-400 or RG-393) as it will enable high temperature operation and resist shorting better than polyethylene insulated cables.
- With the above said; we do believe that some customers do use long cable lengths (up to 15 feet in length) with good results. If the RF power level is kept very low (<100 watts as in substrate bias applications) this will work. Type RG-400 coax cable is a good choice for this application.
- With higher power operation, type RG-393 will better handle the RF circulating currents. The component values inside the impedance matching network will need to be modified to enable proper matching of the sputter source. The series inductor tap setting may need to re-set and or an additional fixed shunt capacitor may need to be installed.
Why can’t the Reflected power be tuned to zero watts ?
- If all attempts are made to reduce the Reflected power to zero (or close to zero) watts, then the impedance matching circuit element values may require tweaking. This is covered in the Application Notes listed below. Basically, the circuit may require additional series inductance (when used with 1″ magnetron cathodes) or additional fixed shunt capacitance (when used with long match>cathode cables).
- It may also be possible that there is harmonic energy (generated in the plasma discharge) traveling back towards the RF generator and being displayed as fundamental frequency reflected power. The fix for this condition is to install an extra length of 50 ohm coax cable in between the RF generator output (BNC female connector) and the BNC male pigtail connector (labeled Match input). Please download and review the PB3 Plasma Impedance Matching Problems & Solutions application note.
Why won’t the plasma ignite?
- This condition can be caused by many sub-systems in the process system. We suggest that you verify that all RF cables are properly connected. Is there Forward and Reflected RF power being displayed on the meters? If so, the problem is most likely located somewhere after the the PB3. Likely problems located after the PB3 are typically the RF output cable, the preset process conditions in the vacuum system – pressure, process gas flow & type and target material (sputtering application). A common problem is an electrical short in between a conductive target and the cathode housing – a quick check with an ohm meter will verify that. If the PB3 is part of a complete (OEM manufactured) process system then we should verify the process parameters that the system was test to prior to delivery.
When used in substrate bias applications, is the RF Power or DC Bias control mode best ?
- The PB3-MD model includes a switch to enable forward RF power leveling using either Forward RF power or DC Bias as the control mode. The RF power mode is suggested during process set up and testing. This mode is also necessary when using an insulating substrate.
- The DC bias mode may be used with conductive substrates as the plasma discharge will rectify the RF power and result in a usable DC (bias) signal upon which to control. This mode of operation will also exhibit increased tuning sensitivity and wide swings of RF power. These conditions are considered to be normal.
Why do I need an external interlock connection?
- The External Interlock connection is both a safety and functional interlock used to protect the user from the equipment and the process from the user. The connections should be connected to a system interlock circuit or a combination of series connected, vacuum and water flow switches. This will inhibit operation of the RF power output if: 1) the chamber is not under vacuum and 2) the cathode cooling water is not flowing. This protests the user from electrical shock and the cathode from overheating.
What are the Common Exciter (Rear mounted BNC connectors) for?
- The Common Exciter circuit enables the simultaneous operation of multiple RF power systems powering multiple plasma loads inside a common vacuum chamber. Typically, the Output of one PB3 will connect to the Input of the next (and so on). The Common Exciter circuit is used to keep all RF generator’s output frequencies synchronized helping the impedance matching process.
- Also note that the Model PB3 RF system has been delivered to the field with two types of common exciter circuits:
- The early version does require a jumper. Please install a jumper (BNC>BNC) to enable the RF output power.
- The newer models do not need an external jumper to enable the RF power stage. This version has been shipping since 1998. If a jumper is connected between the Input & Output, the RF output power will automatically be disabled.
What type of signal can be used with the Common Exciter Input ?
- The Common Exciter input will accept both sine & square wave signals. In most applications, this signal is available from the 2nd (master) RF generator’s CEX output. Remember, that you should keep in mind that the length of the jumper cable will introduce phase shift into the 2 generator “system”. The CEX Input compliance is 250 ohms. A square wave (digital) CEX input signal should be 0 to +5V (Do Not however exceed -0.5 to +5.5V)
What frequency can be used with the Common Exciter Input ?
- The typical frequency is 13.56 MHz. In some applications it may be desirable to operate the PB3 at a center frequency other than the rated 13.56 MHz. This can be accomplished by ordering the unit with a special output frequency or using an external RF signal generator to drive the Common Exciter input at the desired frequency. For safe operation, please use a 10dB 50 ohm pad (attenuator) between the external signal generator and the CEX input.
- We have tested the PB3 models below for wide band operation. The test is to operate the unit at full power into a 50 ohm load while adjusting the frequency of the signal generator above and below the 13.56 MHz center frequency. The usable band edge is defined as the point where the output power starts to drop. Please note that reduced output power operation (outside the typical frequency window) is possible without harm to the PB3. The output control set-point will need to be set lower than full power to maintain a constant level.
Model Comments Common Exciter Sine Wave Input level w/o pad Common Exciter Sine Wave Input level with10dB pad Bandwidth
PB3-100 This model does not use a low pass filter after the RF amplifier. +5 to +8 dBm +20 to +26 dBm 11 to 14 MHz
Please click on these links to download the available application notes.
PB3 RF System – Installation of additional series inductance in the matching network section
PB3 RF System – Installation of additional fixed shunt capacitors
Converting the PB3 Impedance Matching Network from “L” > “PI”
PB3 Plasma Impedance Matching Problems & Solutions
Contacting Manitou Systems for help troubleshooting a problem not listed above
Please have the answers to these questions handy:
- Product model and serial number
- Has the system worked in the current configuration and with the current operational parameters before? (Ie, is this a problem that has suddenly cropped up in a previously working system, or a new system or process?) If the system was previously functioning, has anything changed? (The replacement of a process gas bottle or a sputter target, for example.)
- What is the process? (Sputtering, etching, etc.) What gas(es) and pressure is used in the process? Is it a reactive or non-reactive process?
- What is the plasma source? (Electrode configuration, sputter head size and manufacturer, target material.)
- What is the nature of the problem? (Lack of plasma ignition, inability to tune out reflected power, etc..) If tuning is an issue and plasma can be established, note and record the position of the tuning capacitors and the inductor tap position when the load is tuned to minimum reflected power.
- What are the lengths of the RF cables connecting the various parts of the system?
- If there is no RF at all, check the simple things- is the unit connected to the correct AC mains, and is power present?
- Are input fuses on the device blown?
- Are all interlocks properly satisfied?