Ronald Vane, President
Scanning Electron Microscopy (SEM) was commercialized over 60 years ago, and performance has grown with the need to examine the surface of objects with ever greater magnifications including those of the then new semiconductor devices many times over. A focused electron beam scans the surface, and the secondary electrons can be used to image the surface. Field emission beam began to be used in 1980s to highly focus beams of lower energies to achieve higher resolution and magnification. But low voltage beams ionized hydrocarbon vapor in the vacuum and the hydrocarbon positive ions followed the electron beam down to the surface and be deposited. This resulting gunk is called contamination and usually looks like a black deposit. The hydrocarbon vapor came from vacuum pump oil, lubricants, O-ring grease, finger prints and skin oil, dirty specimens, and any number of minor sources in the vacuum chambers. Ronald Vane working as SEM service support engineer started working on the commination problem in 1990. After finding a technique that worked and testing it he was laid off in the recession of 1991. But he created a similar product he could sell to sell to users and started his business XEI Scientific to sell and install cleaning devices for SEMs.
In 1995 Argonne National Laboratory was granted a patent to use plasma cleaning for cleaning Analytical Electron microscope, specimens, and electron microscope specimen support stages. Argonne modified an inductively Coupled Plasma (ICP) device found in a surplus at the lab. Mr. Vane was trying to sell his slower device for cleaning SEMs and decided he had to develop a commerical plasma device small enough to mount on SEMs. But not all plasmas are not created equal, and among the various plasma-based cleaning methods ICP was large, used too much power, and needed impedance matching adjustment to strike and stay on. With the help of a short course on RF plasmas and an RF plasma match manufacturer he designed a plasma cleaner small enough to be mounted on most SEMs and bought a patent licence from Arrgonne. He named it “Evactron®”. It used an unique hollow cathode plasma plasma source in the shape of a bird cage that could plasma clean at just 10 Watts of power. And he sold sold the first ones in 1999. This was the first comercial plasma cleaner designed to mounted on a SEM or vacuum chamber to clean the interior. A new product class was created. With the support of an RF third party manufacturer he worked a selling and installing the Evactron and creating a market for plasma cleaning SEMs. In late 2003 he made the leap of expanding the business and manufacturing the Evactron with his own staff.
He led XEI to do its own engineering to create a more reliable product that was easier to assemble. This lead to a to succession of new products with computer control and faster cleaning.
For the Evactron plasma cleaning, the change from oil filled rotary vane pumps and oil diffussion to dry pumps on SEMs was an impotant step in improving plasma cleaning speeds.
Dry pumping allowed Evactron plasma operation down to the lower High Vacuum pressures. The reactive plasma radicals are lost by collision processes at higher pressures and cleaning speed increases down to about 5mTorr and then decreases due to the loss of density. This has lead to a new series of Evactron models for pristine cleaning. The latest inovation has moved the Cathode outside a plasma chamber made of Macor ceramic in a smaller model that has no ignition problems and operates at low power to surpress any sputtering. No adjustment of the impedence match is needed in contrast to ICP plasma. Another recent Evactron model with the Macor plasma chamber is compatable with Ultra high vacuum chambers. Plasma cleaning of UHV systems can remove all hydrocarbons to make them pristine and speed pump down to UHV levels and can easily add a day of uptime to the operating schedules of these tools.
Evactron devices are smaller than other modern plasma cleaning systems. It typically operates in the range of 10 to 50 watts RF power, depending on the size of the vacuum chamber of the targeted device. Evactron units uses a hollow cathode-type RF-excited plasma to make flowing afterglows that carry neutral radicals to the cleaning sites. Away from the plasma source there is ion or electron bombardment to cause sputter damage or dust as it does a better cleaning job than ICP at a molecular and ion level. Using such plasma flowing afterglow, XEI makes low-energy plasmas that run cooler, waste less energy, clean more efficiently, and create less sputter damage on the things to be cleaned.
Since XEI Scientific builds Evactron systems to last for years, it provides its clients with a five-year warranty. Ronald says, “Because we build it to last, we get very few returns for service repairs. As a result, we don’t have a service department.”
Instead, the people involved in the device production are the ones that fix them by replacing modules. The cleaning system is designed so that removing it from operation for a few days to fix it will not hamper the functions of the target instrument in any way.
XEI Scientific now primarily sells Evactron E50 Series plasma cleaning devices for SEM. This year, the company released the similar U50 model for use on UHV or ultrahigh vacuum systems that can be pumped to 10-11 millitorr. The U50 provides ultra-high vacuum technologists with a way to clean the chambers of the microscope without having to bake them for cleaning. As a result, where baking the chamber required a microscope to be down for 2-3 days, the cleaning process now only takes a single afternoon. This ability to bring UHV chambers to pristine conditions fast will increase the productivity of these tools. Additionally, XEI has launched the smaller E16 Model this year to clean small chambers, to mount in tight spaces, or to use in low power applications where one needs to avoid sensitivity to higher voltage ions.
Moving ahead, XEI plans to apply Evactron units to clean instruments that don’t use plasma-based cleaning yet and present their device to their manufacturers as a viable alternative. The company also believes that clients can use its cleaning equipment more extensively in other high vacuum applications like cleaning laser mirrors. Hence, XEI, with the help of its different versions of Evactron systems, continues to present its clients with pristine vacuum environments so that they can use their tools at maximum performance.