Characterization of carbon nitride thin films deposited by reactive

W.T. Zheng *, N. Hellgren, H. Sjiistriim, J.-E. Sundgren
Thin Film Division, Department of’ Physics. Linkiiping Uttirersity, S-58183 Linkiipittg, Sweden
2. Experimental Deposition of CN, thin films on various substrates, amorphous SiO,, polycrystalline Si,N,, single crystalline TIN ( 111) and Ni( 100). and high-speed steel, was carried out in a d.c. magnetron sputtering system with a base pressure of 5.0 x 10d8Torr. The target and discharge gas were a high-purity 99.99% pyrolytic graphite disc and 99.9999% pure nitrogen, respectively. All substrates were cleaned ultrasonically in acetone and alcohol. The high-speed steel substrates were further cleaned by sputter-etching to remove any residual contaminants. In all experiments, P,, was kept at either 2.5 or 10 mTorr, and T, was varied from ambient (IV 100 “C) to 500 “C. The effects of plasma heating were accounted for in reported T, values. The film thickness was evaluated using a surface profilometer. Mass spectrometry measurements of the ionic specieswere performed using a quadrupole mass spectrometer in vacua and in N, (2.5 mTorr) discharge. To determine the composition, surface roughness,microstrucures, and mechanical properties of films, Auger electron spectroscopy (AES), Rutherford backscattering spectroscopy (RBS ), atomic
Keywords: Carbon nitride; Magnetron
sputterrates
1. Introduction CN, (~~57 at.%) films typically exhibit interesting properties such as fullerene-like or amorphous microstructures, high hardness and extreme elastic properties [ 11, and a good tribological performance [2-51. CN films may thus have some potential in such applications as overcoats on computer hard disks and sliders [2,6] as well as solid lubricants [4]. The substrate material is known as a very important parameter for determining the film structure and properties. The proper choice of substrate materials can stabilize not only certain crystal structures, but also improve adhesion and properties of the deposited coatings. In this paper, various substrate materials are used during reactive magnetron sputter deposition of CN, films in order to study their influence on the growth process, film microstructure, and mechanical properties of the films.
Abstract
The effects of substrate material on structure, composition and mechanical properties of carbon nitride thin films, deposited by reactive d.c. magnetron sputtering in N, discharge, have been studied. CN, films, with a nitrogen concentration between 15 and 30 at.%, were deposited at two different N2 partial pressures (2.5 mTorr and 10 mTorr) on to a number of different substrate materials, SiO,, Si,N,, TIN, Ni and high-speed steel, kept at temperatures between ambient and 500 C. The results show that the adhesion of CN, films to Ni and steel substrates was very poor, especially at elevated temperatures, whereas in the case of Si02, Si,N,, and TIN substrates, the adhesion was generally good. The variation in growth rate was also found to be different depending on which substrate was used. Atomic force microscopy (AFM ) revealed that the films grown at a lower pressure were very smooth with an rms roughness between 0.2 and 0.3 nm, whereas the roughness was more than one order of magnitude higher (2-10 nm) for films grown at 10 mTorr. Nanoindentation measurements showed that the films grown at the low pressure and above 200 “C were both hard and elastic as expected. based on previous results. The films grown at temperatures below 200 “C were much softer and less elastic. 0 1998 Elsevier Science S.A.
Surface and Coatings Technology 100~101 ( 1998) 287-290
Characterization of carbon nitride thin films deposited by reactive d.c. magnetron sputtering on various substrate materials
PII SO257-8972(97)00634-8
force microscopy (AFM ), high-resolution microscopy ( HREM ), and nanointentation ments were utilized. A detailed description measurements can be found elsewhere [7].
* Corresponding author. Dept. of Material Science, Jilin University, Chagchun 130023, P.R. China. e-mail: weizh@ifm.liu.se 0257~8972/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved.
electron measureof these
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100 0 0
3. Results and discussion Mass spectra were recorded during, and prior to, depositions. The presence of background components such as Hz0 and CO, with intensities of below 5 x 10-s Torr in vacua was observed. During the depositions of CN, films on various substrates, the dominant ions were Ni and N +, but in addition, (CN): and CN + ionic species were observed as well as ions due to the background components, as shown in Fig. 1. The ionic species (CN): and CN + result from chemical reactions on the carbon target surface during the sputter process. As expected, different substrate materials do not influence the intensities of individual ionic species. Both the growth rate R, and the N-content decreased as the growth temperature was increased at a constant PNz. For example, for films grown on SiO,, RD decreased from 28.5 to 185 nm h-‘, and C, from 30 to 20 at.% as T, (PNZ =2.5 mTorr) was increased from 100 “C to 500 “C. Since both R, and C, decrease as T, is increased, it can be concluded that film growth is precursormediated and/or simply controlled by desorption reactions on the growth surface. Fig. 2 shows the variation in R, versus T, for films deposited at PN2=2.5 mTorr on various substrates. It can be seen that the RD of films grown on the metal substrates [high-speed steel, single crystalline Ni(OOl)] decreases more rapidly as T, is increased than on non-metal substrates [amorphous SiO,, polycrystalline Si,N4, and TiN( 1 11 )]. This may be due to a weak chemical affinity between C or N and surface atoms in the metal substrates such as high-speed steel and Ni. Thus, the incoming species on the surface 1o-4