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Spectroscopic ellipsometry as sensor for hard-coating and steel nitriding


Plasma nitriding of steel and plasma assisted chemical vapour deposition (PACVD) of titanium nitride and related binary or ternary compounds are essential industrial processes for surface hardening/coating and increase the life time, the corrosion resistance and decrease the wear of tools. This process is widely used in SMEs working in coating and hardening technology. However, neither the e.g. TiN deposition process nor the FexNy diffusion process is monitorable nor controllable due to a lack of in process monitoring techniques. A new sensor technology (Spectroscopic Ellipsometry SE), up to now used only in the semiconductor technology industry will be investigated as in situ sensor for the steel coating/hardening industry. Within a Research Feasibility Study it was shown, that spectroscopic ellipsometry provides an opportunity for distinguishing ex situ (with the samples measured at an optical bench) the most important hard coatings as e.g. TiN, TiB2, TiCN, TiBN, TiAIN and FexNy and can also be used for monitoring the stoichiometry and the thickness of optically thin layers. The first R&D work will be the design and layout of the in situ SE setup; i.e. combining the PACVD process reactor with the optical monitoring. The major task is to perform the in situ measurements and to interpret the measured data in terms of roughness, voids at the steel/coating layer interface, growth rate and stoichiometry for titanium nitride (TIN) and iron nitride (FexNy) layers. Furthermore we will use Auger electron spectroscopy (AES) and electron microprobe analysis in order to correlate the SE data on an absolute scale to their composition. Also additional titanium based hard coatings, TiB2:, TiBN, TiAIN, TiCN, will be investigated with SE and AES. There are two processes, where spectroscopic ellipsometry can be applied in hardening/coating shops, namely a) the coating process of serial parts and b) the deposition process parameter determination. - We expect that the percentage of parts rejected in permanent processes can be reduced from currently 5 10% to virtually none. Ellipsometry also provides a tool to measure (ex situ) and non destructively the homogeneity of the coatings produced at different points in the reactor. Furthermore, sometimes due to failures occurring in the reactor or with the sources or the control, the whole lot is rubbish. Although these processes are in general occurring in only 5 10% of all lots, we expect, that with in line monitoring this number can be reduced to virtually zero, or failure corrective actions can be set without the need of having to open the reactor. - It is ultimately expected that the proposed online monitoring (and closed loop control) tool will cut the cost and time required for the determination of process parameters by at least 50%, reducing the current average 1,5 man month per new/ changed coating to less than 0,75 MM. Summing up these numbers, the typical profitability of the additional optical equipment estimated from the current knowledge would be between 3 month and 2 years Working conditions will only slightly change with optical monitoring. The worker will perform more supervising and controlling tasks and less manual operations, but the workers need better training to be able to use the powerful device. The main environmental impact is the avoidance of rejected material, as well as the avoidance of non usable test products, and so a reduced consumption of raw materials and power and less waste will be obtained.

Funding Scheme

CRS - Cooperative research contracts


Rübig GmbH & Co KG
Schafwiesenstrasse 56
4600 Wels

Participants (5)

Im Stadtgut A2
4407 Steyr
Carl-scheele-strasse, 16
12489 Berlin
Viale I Maggio 30
20014 Nerviano
Thermi-lyon Sarl
Rue De Gerland 195
69353 Lyon
8-10,Wiedner Hauptstrasse 8-10
1040 Wien