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 How to prevent Veeco-Commonwealth MkI & MkII gridless ion source problems

Simple routine preventative maintenance procedures employed with MKI & MKII End-Hall Gridless Ion Sources can often prevent major failures of both ion source and power supply (controller) hence avoiding unnecessary loss of production downtime. The following points are intended as a guide.

1. Is your process chamber clean?

A well electrically earthed chamber and/or chamber shielding is required. Deposition processes using dielectric materials can build up insulating layers on chamber walls and disrupt ion source operation.

2. Regularly change insulators!

The insulators in the MKI and MKII source are exposed to high temperatures and contamination during use, and will eventually break down causing damage to the ion source controller. 10-32M and sapphire ball insulators should be regularly replaced. Contaminated sapphire ball insulators in the MKI source will also lead to rapid erosion of the gas distributor.

3. Cathode filament supports

These need to be checked regularly for tightness of fit and ‘pinched up’ with pliers when needed.

4. Cathode connectors (The domed end rods on which the above fits)

These can deteriorate rapidly through poor electrical contact with the cathode filament support. If there are signs of erosion through arcing – replace them.

5. Flexy ‘in vacuum’ power leads

These can often fail at the end (by the push-on connector), resulting in an anode to ground or cathode to ground short circuit. This problem is often masked by the stainless steel braiding and lead construction. Routinely carry out ohmmeter checks on leads to verify electrical integrity. Push-on connectors should also be checked for tightness and ‘pinched up’ if necessary.

6. Pumping speed & gas flow

Ion source Instability in operation, or ‘hunting’ is often caused by a conflict of chamber pump speed and gas flow requirements for the source. A low demand on gas flow < 5 sccm may give operational problems if the gas mass flow control valve is ranged at 50 sccm. If instability is allowed to continue, it is very likely that the ion source controller will suffer damage.

7. Ion source gas leaks

Gas leaks in gas lines or unions ‘in-vacuum’ feeding the source can often cause strange operational problems due to the ion source being starved of gas. The plug-in faces of the ion source body to its mounting socket should be highly polished with the surface free from scratches as this is a gas seal, and gas unions both internal and external to the ion source body should be checked for tightness. The flexy stainless steel gas line is easily perforated during process chamber maintenance.

8. Anode and gas distributor

Use the correct materials to suit the process. Use graphite for inert gases, stainless steel for reactive gases. Titanium or tantalum alternatives are available for critical optical coating applications to match the native deposition materials being used. Never use graphite components if oxygen is a process gas as graphite will rapidly decompose in an oxygen rich plasma. A clean anode surface is necessary for problem free gridless ion source start up. Clean regularly using abrasive material.

9. Cathode filaments

Always handle with a gloved hand. Skin oils will cause premature failure. Correctly pre-formed and annealed high purity tungsten filaments may cost a little more – but will last much longer in use.

10. Electrical vacuum feedthroughs

Electrical feedthroughs can overheat with the current load carried. The polymer insulation on the atmospheric side can degrade as a result, and cause electrical breakdown. Routinely check electrical insulation integrity.

11. Changing process gas bottles

Always take time to purge gas lines after changing the process gas cylinder or breaking gas lines during maintenance. This will avoid ion source start up and instability problems.

12. Hollow cathode (HCES 5000)

Gas purging on venting and prior to pumpdown are essential if you wish to obtain maximum operational lifetimes. Clean and high purity gas delivery and handling lines are also essential. A white or yellow/white deposit at the end of the cathode tip or on the inside surface of the keeper plate indicates incorrect purging or possible air leak in the gas line. Observing correct procedures will dramatically improve the lifetime of the HCES.

13. MKI Ion Source - common issues

Do not overtighten hold down rods and nuts during maintenance – you will shear the threaded section off.

Always ensure sapphire ball insulators are clean, or replace frequently. If they become contaminated, rapid erosion of the gas distributor will result. Check the gas distributor for erosion. If this becomes perforated, replacement radiation shield discs and magnet will probably be required.

14. If you should still have problems?

If all else fails, why not switch over to our new ‘next generation’ End-Hall Gridless Ion Sources and Controllers. Totally redesigned by the original MKI and MKII patentee - for greatly improved reliability, providing higher output, wider operational parameter range - with lower operational costs.

 View our range of 'next generation' gridless ion sources