Frequently Asked Questions
Who uses the Evactron De-Contaminator?
The Evactron De-Contaminator is used by both scanning electron microscope manufacturers and users to insure pristine conditions for nanometer scale high resolution images. It has also been used with great success in CD-SEMs, nanoprobers and FIBs. It can be used to rid any vacuum chamber of unwanted hydrocarbon contamination such as carbon buildup on EUV windows.
What causes black squares and other kinds of carbon contaminator build-up?
Hydrocarbons diffusing into the area impinged by the electron beam will react with the beam. This reaction will cause the hydrocarbon to polymerize into higher molecular weight compounds. In an SEM the carbon will build up exactly where you are trying to image, and the results are black squares. In EUV systems the carbon will build up on the surface of the mirror and reduce its reflectivity. Even a small amount of contamination in the chamber can cause problems.
Why do I see contamination using a low kV electron beam versus using a high kV electron beam?
High kV electron beams have a lower reactive cross-section with carbon containing molecules than low kV electron beams. They will penetrate through carbon adsorbed on surfaces.
How does the Evactron De-Contaminator clean my electron microscope/vacuum chamber?
The Evactron De-Contaminator lets a small stream of gas, such as room air, oxygen or hydrogen, into the vacuum chamber. The stream of gas passes through a radio frequency (RF) generated, low power plasma. The plasma creates radicals (atoms), which then flow through the chamber and ash the hydrocarbons. If room air or oxygen is used the products of the ashing process are CO, CO2 and H2O, which can be pumped out of the chamber.
Will the Evactron process harm my sensitive detection equipment such as EDS detector, EBSD, or WDS?
Several studies have shown that the Evactron De-Contaminator is almost harmless to EDS detectors, EBSD, and WDS. Only neutral radicals leave the low power RF plasma, not the sputtering ions.
What size is the Evactron De-Contaminator?
There are two parts to the Evactron De-Contaminator. For almost all models, the compact Plasma Radical Source is ~22 x 13 x 13 cm and can easily be attached to a SEM chamber. The Controller, for models C and 25, is 14 x 23 x 18 cm and can fit on any tabletop. Models 40 and 45 are rack-mounted (9 x 49.5 x 18 cm).
How can I determine how contaminated my chamber is? How can I gauge the effectiveness of Evactron cleaning?
Where do I install the Evactron De-Contaminator on my electron microscope or vacuum chamber?
The best place to install an Evactron De-Contaminator is on a port away from the vacuum pump port. For example, if your vacuum pump port is on the bottom of your chamber, put the Evactron De-Contaminator as close to the top of the chamber as possible.
How easy is the Evactron De-Contaminator to install?
The Evactron De-Contaminator is very easy to install. There is a KF40 fitting on the Plasma Radical Source (PRS). XEI Scientific, Inc. sells adapter flanges for almost all ports on an SEM. Contact us if there is a need for a custom adaptor flange. To install, one vents the SEM or vacuum chamber to atmosphere, removes the blank flange to the port on which the Evactron De-Contaminator will be installed, and attaches the adaptor flange and the PRS. Finally, one finds a level and convenient location for the Evactron Controller, plugs the Controller into a wall socket (the Evactron De-Contaminator can be run with almost any standard wall socket, provided the correct power cable is used), and connects the cable between the Controller and the PRS. The Evactron De-Contaminator is now installed and the vacuum chamber is ready to be pumped down.
You recommend using room air. Can I use other gases?
How do I run the Evactron process on my instrument?
At what pressure does the Evactron De-Contaminator work? Why do I need to vent my chamber?
The Evactron De-Contaminator typically runs at pressure in the 0.2 to 1.0 Torr range. The models 25, 40 and 45 can run as low as 50 mTorr. The venting step is an interlock to make sure that the pressure in the vacuum chamber is being raised by the instrument’s evacuation control system and not the Evactron De-Contaminator. This way, unexpected venting of the chamber by the Evactron De-Contaminator will not occur. The venting step can be removed by the user if needed, but the user will need to make sure that the Evactron De-Contaminator will not harm any sensitive instruments in the vacuum chamber. For details on removing the venting step, contact XEI Scientific, Inc.
At what RF power range does the Evactron De-Contaminator work?
The Evactron De-Contaminator runs between 5 and 20 W forward RF power. The use of higher power on the Evactron De-Contaminator would overheat the matching network. Studies have shown that the rate of cleaning levels off as the forward RF power is increased, due to a greater production of nitrogen ions. These ions remove oxygen radicals from the plasma.
How much time should I run the Evactron De-Contaminator? How often?
Still have questions that we did not answer above?
Contact XEI Scientific, Inc. with any further inquiries. We will be glad to help you.
Phone: 1 (650) 369-0133 / Fax: 1 (650) 363-1659