Structural Investigation of Cr(Al)N/SiO_x Films Prepared on Si Substrates by Differential Pumping Cosputtering

Abstract

Analytical electron microscopy revealed the structure and growth of hard coating Cr(Al)N/SiOx nanocomposite films prepared in a differential pumping cosputtering (DPCS) system, which has two chambers to sputter different materials and a rotating substrate holder. The substrate holder was heated at 250 °C and rotated at a speed as low as 1 rpm. In order to promote the adhesion between the substrate and composite film, transition layers were deposited on a (001) Si substrate by sputtering from the CrAl target with an Ar flow and a mixture flow of Ar and N2 (Ar/N2) gases, subsequently, prior to the composite film deposition. Then, the Cr(Al)N/SiOx nanocomposite film was fabricated on the transition layers by cosputtering from the CrAl target with the Ar/N2 gas flow and from the SiO2 target with the Ar gas flow. The film had a multilayer structure of ∼1.6 nm thick crystallite layers of Cr(Al)N similar to NaCl-type CrN and ∼1 nm thick amorphous silicon oxide layers. The structure of the transition layers was also elucidated. These results can help with the fabrication of new hard nanocomposite films by DPCS.

Structure of multilayered Cr(Al)N/SiOx nanocomposite coatings fabricated by differential pumping co-sputtering

“…5 To elucidate the process and mechanism of film growth in the DPCS system, we prepared a hard coating Cr(Al)N/SiO x nanocomposite layer on the under buffer layers that were grown on a Si substrate, and examined the structure of these layers by means of analytical electron microscopy. 6 In the present paper, we show details of the structure of the multilayered Cr(Al)N/38 vol. % SiO x nanocomposite coating and discuss its growth and hardness, indicating a new superhard coating of Cr(Al)N/17 vol.…”

“…The preparation conditions for these transition layers were the same as that used for the previous Cr(Al)N/SiO x nanocomposite coating. 6 Next, the main deposition was carried out for 660 min by operating both the CrAl chamber A and the SiO 2 chamber B, on the transition layers rotated at the same speed. The CrAl sputtering and the SiO 2 sputtering were performed with flows of Ar (10 sccm) þ N 2 (20 sccm) and Ar (20 sccm) at RF powers of 200 and 75 W, respectively, so as to obtain a nominal composition of Cr(Al)N/38 vol.…”

“…The Cr(Al)N is a NaCl-typed CrN crystal containing some amounts of Al atoms, having a lattice parameter of 0.402 nm as small as 3% compared with the pure CrN crystal. 6 In our previous paper, 6 we described that amorphous silicon oxide (a-SiO x ) grew as separated island particles rather than continuous cover layer on the surface of the Cr(Al)N crystal layer in the columnar grains, which were extended from the under transition layers. During the following CrAl deposition in chamber A, Cr(Al)N crystals could grow directly on surface areas of the under Cr(Al)N crystal where no a-SiO x particles were deposited, keeping the coherent lattice relation.…”

“…From these observations, we can conclude that the deposited SiO 2 did not cover over the surface of the under Cr(Al)N crystalline layer with a smooth layer but grew as island particles (with 1 nm or less in size) on its surface, which supports our previous description. 6 The next deposition of Cr(Al)N can continue the growth on the under Cr(Al) crystal, enclosing the SiO x particles. Therefore, the growth of the present Cr(Al)N/SiO x film is different from that of AlN/SiO 2 , 4 VN/SiO 2 , 11 or TiAlN/SiO 2 multilayer film 12 where the SiO 2 took the same or pseudo structure as the nitride under the so-called template effect.…”

“…Furthermore, when the substrate holder rotated at 1 rpm, it took about 15 s from deposition of CrAlN layer to the next deposition of SiO x layer. 6 During such a long interval, a copious amount of gas atoms are absorbed on the CrAlN surface before the deposition of SiO x , and prevent the heteroepitaxial growth of SiO x , accordingly. Hence SiO x deposit can coagulate to form a-SiO x particles on the surfaces of the under Cr(Al)N layers.…”