INFICON TM-400 Thin Film Deposition Monitor - Manual (Page 15)

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TM-350/400 Operating Manual
Chapter 2
General Description
2.1 Introduction
The Thickness Monitor allows improved manual control of the vacuum film
deposition process by providing a direct display of film thickness and deposition
rate during deposition.
Semiautomatic control of film thickness can be accomplished by utilization of the
shutter control relay in the Monitor. The shutter control relay allows for direct
operator control of the systems shutter and will also automatically close the shutter
when the deposition thickness equals a pre programmed value.
The Monitor requires 4 (6 in a TM-400 using crystal switching) operator-supplied
parameters in order to provide direct readout and shutter control. Entry,
modification and display of these parameters are easy and straightforward.
Parameter storage is not dependent on continuous AC power. An internal,
self-charging, lithium battery provides parameter storage for a minimum of five
years without external power.
2.2 Features
2.2.1 Independent Film Density and Tooling Factor Parameters
The tooling factor parameter allows the Monitor to compensate for deposition
geometry effects such as different source to sensor and source to substrate
distances, which result in proportional but not equal film thicknesses at the sensor
and the substrates. By utilizing the tooling factor, the Monitor can calculate and
display film thickness and rate at the substrate rather than at the sensor.
2.2.2 Acoustic Impedance Correction
The Monitor corrects the thickness reading for acoustic impedance mismatch
between the crystal and film material by taking into account the operator supplied
Acoustic Impedance Parameter for the film. If not corrected for, errors result as the
film thickness builds up on the sensor crystal. The sensitivity of quartz crystals to
material buildup changes with the amount of material on the crystal if the deposited
material's acoustic impedance is significantly different than that of quartz. With
some materials this effect can lead to differences between indicated and actual
thickness of up to 20% as material builds up on the sensor crystal.