Abstract
The use of pulsed dc-sputtering sources for reactive magnetron
sputtering with oxygen offers a possibility to suppress negative effects
of target poisoning (such as arcing). This results in a wide process
range for the selection of a desired operating point. The control of
target poisoning plays a major role in maintaining constant coating
properties and affects the stoichiometry of the reactive coating, as
well as the coating rate and the economic impact of the coating process.
The target poisoning during the reactive sputtering of titanium under
oxygen addition proceeds nonlinear in a hysteresis. Without the use of a
suited target poisoning control technique the sputtering process can
abruptly change to an unstable state. As a result, variations of the
stoichiometry can occur during the deposition process. A proven method
for maintaining a stable reactive sputtering process is the control of
oxygen flow with the input variable target voltage. By determining the
typical oxygen hysteresis at constant target power and constant argon
flow, an operating point for the control loop is determined. The desired
target voltage then serves as the input variable for the control loop of
the target poisoning. The controlling technique for target poisoning is
a basic requirement for the production of the photolytic active anatase
phase of titanium dioxide by means of reactive magnetron sputtering. The
photocatalytic equipment of surfaces with a titanium dioxide coating in
the anatase phase can be realized with the reactive pulsed dc magnetron
sputter ion plating process (MSIP). The pulsed dc MSIP process provides
the ability to coat a variety of surfaces at temperatures below 200 °C
in an environmentally friendly manner.