High-pressure RHEED for deposition systems
Refection High-Energy Electron Difraction (RHEED) is a very widely used technique for the study of surfaces of materials. By virtue of the intensity variation of the difraction spots, caused by roughness of the surface, RHEED can be used to study in-situ the growth mode of thin flms.
Furthermore, by studying the difraction pattern itself, surface reconstructions can be identifed. Up to about 20 years ago, it was not possible to use RHEED in combination with deposition techniques that require relatively high background pressures, such as Pulsed Laser Deposition (PLD). The increased scattering of the electrons would fade out the difraction pattern before it could be detected.
In 1997, the Low Temperature Division at the University of Twente developed a system, which allows RHEED operation also in higher pressure environments. [A.J.H.M. Rijnders et al., Appl.Phys. Lett., 70(14), 1888-1890 (1997)].
The scattering losses are decreased to such a level that good RHEED-patterns can be obtained in pressures up to 60 Pa (500 mTorr).
Twente Solid State Technology offers custom solutions to your requirements. The specifications mentioned here are not stringent and can always be adapted to meet your specific needs.
The system consists of an extension tube, typically attached to a 30keV RHEED-gun. This tube is kept at a low pressure. At the end of the tube is a pinhole, through which the electron beam enters the deposition chamber, close to the substrate.
The entire RHEED-gun and extension can be mounted on an XY-stage to allow for electron beam adjustment with respect to the substrate.
At the other end of the tube a valve can be included to allow atmospheric pressure annealing.
The phosphor screen is mounted on a flange that extends into the chamber to place the screen as close as possible to the substrate. A metal shield is attached to the phosphor screen to avoid as much deposition as possible on the screen itself. Data acquisition for the software is realized with a camera capturing the image on the screen.
An optional shutter can be mounted to protect the phosphor screen during depositions without RHEED.
The system requires little maintenance. Only some deposition on the phosphor screen cannot be avoided, despite the placement of a shield. This means that the phosphor screen has to be replaced once every few years, depending on how much the system is used.
Filament exchange is only required occasionally and can be done by the customer.
There are some requirement to properly integrate high pressure RHEED into a deposition system. The system requires one port for the electron gun and one port for the phosphor screen, in-line with the substrate surface. Substrate tilting and azimuthal rotation is required to get the optimal orientation and angle of incidence. Finally the system must allow for a differential pumping connection.