Standard Operating Procedure
Bendix High Vacuum Thermal Evaporator

Introduction

Located in the cleanroom (V113C), this basic thermal deposition unit is configured for four sources and is primarily intended for optical thin-film coatings. The filaments would normally be loaded with both metals (such as aluminum) and dielectric materials such as magnesium fluoride (in a crucible) and sodium hexafluoroaluminate (cryolite) allowing fabrication of dielectric mirrors and filters. Unlike most of our other systems this is a completely manual system optimally suited for student laboratories.

Front View
This front view of the Bendix high-vacuum thermal evaporator system shows the major components including the vacuum chamber, controls stack (with gauges), and vacuum valves on the front panel.

The vacuum system

Filaments
The filament deck holds four filaments separated by shields to prevent cross-contamination. Atop these is a shutter which covers the filament in use during outgassing as well as to stop deposition. The substrate deck holds twenty substrates up to 1.5" diameter or 1" square. In the center of this deck is the crystal holder for the XTM monitor.

Bendix Diffusion Pump
This rare view of the system with all covers removed shows the diffusion pump and cold trap above it. The cold trap is filled with extremely cold liquid nitrogen (at a temperature of 77K) when the pump has been switched on but before the high-vacuum valve is opened.

Electrical Controls and Valves

Electrical Controls
The electrical control panel showing switches for both pumps (roughing and diffusion), filament power, and bell jar lift controls. The roughing pump must be energized and water flow must be present before the diffusion pump can be energized or filaments can be powered.

Current Control The active filament is selected via the rotary switch on the control stack just below the gauges. Filament current is controlled via a variable autotransformer on the top deck of the unit and is monitored via an ammeter on the front of the unit. Short, straight filaments require control settings in the 20A-35A range while larger helical filaments require higher settings. Crucibles heated with helical filaments can require control settings of over 100A for high melting point, low vapour pressure materials.

Valves
Basic manual controls allow the user to first rough pump the chamber via the ROUGHING valve then pump the chamber to high vacuum using the High-Vacuum valve. The Foreline valve is open whenever the diffusion pump is used. The vent valve allows the chamber to be brought back to atmospheric pressure to raise it and load/unoad substrates.

Gauges

Gauges
The control stack features two Varian Multigauges. The one on the left indicates chamber pressure via both a thermocouple (TC) gauges and an ion gauge and the one on the right indicates foreline pressure via a TC gauge. Pressing the "CHANNEL" button (upper left on each gauge) allows the user to configure the display on each gauge - this button selects each function cyclically - when an unused channel (TC2, 3, or 4) is selected an "E03" error is displayed. For the chamber gauge (the left one), the only two valid options are to display the chamber pressure (from TC1) both on the bargraph and numerically on the main display or to display the TC1 pressure on the bargraph and the ion gauge pressure numerically on the main display (as shown above). The foreline gauge always displays the foreline pressure the the TC gauge on both the bargraph and numerically on the main display.

Varian MultiGauge
During chamber roughing, the chamber pressure is monitored using the TC alone: the user may use the bargraph or may select to have the pressure displayed numerically on the main display. When the chamber pressure is low enough (after rough-pumping) the high vacuum valve is opened and the chamber is pumped through the diffusion pump. ONLY after the high vacuum valve is opened, and the chamber TC1 bargraph has 'bottomed out' can the ion gauge be used by pressing the EMIS button on the chamber gauge. Only the chamber gauge features a BA (Bayert-Alpert ion) gauge. DO NOT turn the ion gauge filament ON until the chamber TC gauge 'bottoms out' to 1.0E-3 torr and the high-vacuum valve is open.

This stack also includes an Inficon XTM quartz-crystal deposition monitor allowing in-process monitoring of depositions, a filament selector (one of four filaments plus an OFF position) and a lamp indicating water failure to the diffusion pump. Filament #1 is on the LEFT side of the chamber, filament #4 is on the RIGHT side of the chamber.

Inficon XTM Monitor
The Inficon XTM Monitor allows the user to determine the rate of deposition (in Angstroms/second) as well as the total thickness of the deposit (in kilo-Angstroms) simultaneously. Before use the unit must be programmed with the density of the material being deposited (in grams/cm3) and a tooling factor. When first switched on the unit enters programming mode automatically (as evident by the PROGRAM lamp being lit). When materials are switched the unit must also be reprogrammed by pressing the PROGRAM button.

To set the density of the material, press the PROGRAM key (if not already in program mode) and then press the DENSITY button. Enter the density and press the ENTER key to store it. There is no decimal point key so the density of aluminum would be entered as '2', '7', '0', then enter. The decimal place is implied at two places. Next, enter the Z-ratio (a number ranging from 0.000 to 1.000) followed by the tooling factor. Tooling factors ranging from 10 to 200 percent are entered in a similar manner by pressing the TOOLING key beside the DENSITY key. This factor defaults to 100% at power-up, begin with a value of 120.0% with the crystal monitor located at the center of the substrate deck.

When a deposition is started (i.e. just before the shutter is opened), press the ZERO button to reset the display. It is also important to ensure the crystal is oscillating before the chamber is pumped. The XTAL lamp will blink if there is a problem with the crystal or the oscillator package.

PROCEDURES

Start-Up Procedures

Pump-Down Procedures

Evaporation Procedures

Opening Procedures

Shutdown Procedures

Filament Loading Procedures

PDF Document outlining the basic procedures required to operate the Bendix System.

Filament Configuration:

Filament # Material Index of Refraction Deposition Rate (Angstroms/sec)
1 Cryolite 1.33 15 - 25 typical, 35 Max
2 Aluminum 5 - 10 typical, 50 Max
3 Aluminum (backup)
4 Cryolite (backup) 1.33


Updated 2018/05/23 by M. Csele

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