Formation of aluminum nitride on aluminum surfaces by ECR nitrogen plasmas

In order to overcome the difficulty in thermally nitriding aluminum, plasma nitriding was attempted by means of electron cyclotron resonance (ECR) nitrogen plasma combined with negative bias to aluminum substrates. Aluminum nitride (AlN) was formed on the substrate surface only when the vacuum chamber was evacuated to 2.3x10(-4) Pa or under, however, the formation rate was as high as 15 mu m thick AlN layer was formed in 900 s without any pretreatments. Vickers hardness (Hv) of AIN was about 1400. Also, this AIN layer showed an electrical conductivity. Scanning electron microscopy (SEM) on the cross-section of AIN layer revealed its bi-layer structure consisting of porous granular and dense columnar structure. It is speculated, from the SEM observations, that the AlN was formed through melting of the aluminum surface by ion bombardment.