Edwards Auto 306 Cryo Evaporator Technical Specification

This evaporator is configured for evaporation of Chromium (from a rod source) and Gold (from a boat). It also has a plasmaglo accessory installed (for cleaning substrates such as glass with an oxygen plasma prior to deposition) and a radiant heater (to enable the substrate temperature to be raised to a maximum of 350 oC). The heating can be applied at high vacuum before, during or after the deposition. This enables the film to be annealed as it is deposited. The cryo vacuum pumping system enables high vacuum to be reached to enable contaminant free deposition.

Substrate Mounting

The substrates are mounted inverted above the source. For small substrates (up to 10 cm in diameter) a rotating support is available, this enables the sample to be continuously rotated during the deposition enabling a uniform deposition across the sample surface (this rotating sample holder cannot be heated above the temperature induced by the evaporation sources). For larger sample and those that need to be heated up to 350 oC a larger diameter sample holder (which can support samples up to 20 cm in diameter) is available which has thermocouple mounted in it to enable precise control of the substrate temperature.

Film Thickness Monitor

Positioned close to the sample is a 6 MHz quartz crystal microbalance. Connected to this is a control unit which reads out the film thickness (between 0 and 0.999 mm with a resolution of 0.1nm) and deposition rate (between 0 and 999.9 nms-1 with a resolution of 0.1nm).

Vacuum Pumping System

BOC Edwards' RV8 rotary roughing pump with oil trap and Coolstar cryopump provides very high speed pumping (25 min pump down time to 10-6 mbar) and an ultimate vacuum of 2 x 10-7 mbar. This option provides a contaminant-free, ultra-clean vacuum for the optimum deposition environment, with a tested leak rate less than or equal to 10-5 mbar ls-1.

Pressure monitors

To monitor the pressure in the chamber and in the backing line two Pirani gauges (Chamber - PRL10K and backing - PRM10K) and a Penning gauge are incorporated into the evaporator to cover the range of 5 x 10-8 to 1000 mbar.

Automatic Vacuum Control System

The Auto 306 microprocessor vacuum controller provides easy pump down without operator errors. Pump down times are automatically kept to a minimum, saving process time. Fully reproducible parameters give consistent deposition conditions. A digital display provides vacuum and system status information.
The Auto 306 is designed to maintain clean high vacuum conditions and to protect substrates from contamination at all times. An intelligent high vacuum valve opening sequence ensures a gradual equalisation of the different vacuum pressures in the chamber and below the valve during the pump down cycle. Once the chamber has been rough pumped, the microprocessor controller slowly opens the high vacuum valve. If the backing pressure rises above minimum limits then the valve is closed again. Once the backing vacuum has recovered, the high vacuum valve is again opened. This cycle is repeated until the valve is fully open. To further protect the vacuum environment and substrate from oil contamination, an internal 12 volt battery closes the high vacuum valve in the event of an electrical supply failure.

Process Costs

For an oxygen plasma clean and then an ambient temperature deposition of 5 nm of Chromium followed by 100 nm of gold the cost is 25, for other depositions the cost can be obtained by emailing the SAF with the details of the process required.