Improvement of AlTiN and AlCrN coatings with multicathode configuration

Multicathode configuration

is becoming very popular, and gains increased attention among the researchers and process engineers working in high power impulse magnetron sputtering in the Physical Vapour Deposition (PVD) coating industries.

in courtesy of Gencoa Ltd.

➡️Sequential operation of four or six cathodes (at least two) is showing evident improvement in the quality of deposited composite coatings like AlTiN or AlCrN, in particular.

in courtesy of Gencoa Ltd.

In this article, multiple cathodes refer to applying the power to pulse the discharge sequentially at the cathodes of same material composition one-after-the-other by giving a small-time interval of 20 - 50µs between each discharge pulses.

Of course,

co-sputtering increases the deposition rate as the coatings thickness increases with the number of cathodes engaged in the deposition process.

However, more than the coating thicknesses the quality of material has wear resistance, negation of argon incorporation and maintaining metastable cubic phase also improve depend on how the transition from argon-rich plasma to metal-rich plasma is controlled.

In high power impulse magnetron sputtering repetitive pulses of voltage and current are applied either with long or small duration between the pulses.

The current pulse usually lags the voltage applied to the cathode by a significant time ranging from 20 µs to many 10s of microseconds depending on many parameters but crucially on the power supply and the target cathode material. For a reliable industrial quality power supply, the current time lag is almost constant jitters less than 0.5% of the delay time.

❓Why does this delay occur

The delay depends on the minimum breakdown voltage to the product of gas pressure and electrode distance.

Based on this basic concept, the delay in origin of current with respect to the voltage depends on two important factors:

1. Generation of seed electrons to appear in the electric field between electrodes and

2. the time required to develop a complete stable discharge from those initial electrons

Using multi-cathode HiPIMS with a shorter time gap between the pulses triggering the adjacent cathodes sequentially allows to utilize the left-over electrons from the previous discharge to use as seed electrons to develop the discharge for the subsequent pulse.

In this case, the discharge on the cathode is developed too quickly and the argon-rich to metal-rich transition takes place within 20 µs.

The shortened argon rich regime helps to minimize the argon content in the HiPIMS deposited coatings while the process being operated at much higher pressure (4-5 µbar). Owing to the decreased argon ion peening, the energy window of impacting ions narrows, and the elastic property of the coatings increases (becomes less brittle).

More importantly,

the success of multi-cathode HiPIMS technology has been proven evidently in the coating process of AlTiN and AlCrN.

➡️Higher number of cathodes result in higher wear resistance (H/E).

This is a very interesting result.

HiPIMS community know that how much benefits the coatings of composite material such as AlTiN or AlCrN are improved when the bias pulses are synchronized with respect to the cathode pulses to minimize the energetic impact of argon ions on the substrate material.

Aluminum Chromium AlCr 80:20 at%

Aluminum Titanium AlTi 70:30 at%

Swift transition from argon-rich plasma to the metal-rich plasma is also one of the best ways to the energetic impact of argon ions on the substrate.

Conclusion in one sentence:

➡️Using a multi-cathode is the best way to achieve high quality nitrides of AlTi and AlCr while circumventing the use of bias voltage applied with synchronized delay.