cBN Thin Film Deposition
Figure 1: IBAD with simultaneous ion irradiation
Figure 2: Magnetron sputtering with complex bipolar pulsed bias.
Cubic boron nitride (cBN) is a promising material for hard-coatings applications having a number of useful properties:
- Very high hardness (second to diamond)
- Resistant against oxidation even at high temperatures
- Inertness with respect to ferrous materials
- Wide band gap
- p- and n- type doping
Problem: The synthesis of cBN requires low energy ion bombardment (100 - 500 eV) which results in excessive intrinsic stress and delamination.
Solution: Medium-energy ion implantation (2 - 30 keV) induces atomic rearrangements beneath the surface leading to defect annealing and stress relaxation.
A combined process of cBN thin film deposition and medium energy ion implantation has been developed at FZD.
- Time and cost-effective continuous processing without breaking the vacuum
- No post-deposition treatment
The technique can be applied in ion beam assisted deposition by using an additional 35 keV nitrogen ion beam.
With the aim of increasing the deposition rate and the process efficiency, the technique has been further developed to include magnetron sputtering. The improved processing is characterised by:
- High rate cBN thin film deposition
- Complex bipolar pulsed bias with high voltage (HV) pulses resulting in simultaneous stress relaxation
- Bias voltages as low as -2.5 kV are necessary for stress relaxation!
In situ stress measurement
Stress relaxation is measured in situ and in real time using the so-called substrate bending principle. Laser deflectometry in conjunction with in situ ellipsometry are employed to monitor the instantaneous stress.
|Fig. 3: Force per unit width (FPUW) as a function of film thickness recorded during deposition of cBN using high voltage pulses for stress relaxation. The open squares represent the FPUW data points; the solid lines indicate linear regression while their slope gives the instantaneous stress for the respective film thickness.|
Ullmann et al., J.Appl.Phys. 83 (1998) 2980Boyen et al., APL 76 (2000) 709Fitz et al., APL 80 (2002) 55
Abendorth et al. Thin Solid Films 447-448 (2004) 131
"Vergleich verschiedener Abscheideverfahren zur Herstellung von kubischem Bornitrid" (SMWK 7541.83-fzr/405)
"Super hard coatings c-BN and CNx" (PROCOPE/EU)
"Dicke c-BN-Schichten" (DFG SPP463/ Mo 297/6-1)
"Spannungen in c-BN-Schichten" (DFG)
"BN-Technologietransfer " (Industrie)
Contact: Prof. Dr. Kolitsch, Andreas