EFFECT OF POWER OF ELECTRON SHOWER AND SUBSTRATE BIAS ON THE PREPARATION OF CEMENTITE FILM

S. J. Li, H. Yumoto, M. Shimotomai* and M. Ishihara**

Department of Materials Science and Technology, Science University of Tokyo Noda, Chiba 278-8510, Japan
a8297705@rs.noda.sut.ac.jp

*Super-Metal Consortium (steel group), Kawasaki Steel Corporation, Chiba, Chiba 260, Japan
**National Inst. of Materials & Chemical Res., 1-1 Higashi, Tsukuba, Ibaraki 305-0046, Japan

It is important to understand the mechanical properties of single-phase cementite in order to design the microstructure of advanced steels. Several papers have been published on mechanical properties of cementite embedded in steels or extracted from steels by electrolysis. However, single-phase cementite is not documented. The purpose of this study is to prepare cementite films by the PVD method and to characterize their properties.

The cementite films were prepared by electron-shower-assistant PVD method (1). Fig. 1 shows a schematic drawing of electron shower apparatus. Thermal electrons emitted from a heated Ta filament are accelerated by a potential between the tantalum filament and the ring shaped anode. Fe is evaporated from an Al2O3-coated tungsten basket. The Fe vapor and C2H2 gas are activated by passing through an electron shower, and formed cementite films on glass and silicon wafer substrates. The vacuum pressure was 7◊10-4 Torr (C2H2: 5 sccm).

The effect of power of electron shower and the substrate bias on preparation of cementite films were studied in this paper. XRD showed that at the lowest power (0.3A, 0.5kV) of electron shower, there were not only cementite peaks, but also a Fe peak. But at a higher power, there were only cementite peaks. As the substrate was heated by the irradiation from the filament, the temperature increased with increasing the power. FE-SEM revealed that the grain size became larger with the power. The grain size of the film was about 50nm at 0.3A, 0.5kV, and was about 400nm at 1.0A, 1.0kV. Oxide in the film was decreasing with increasing the power.

When the bias voltage (-500 ~ 0 V) were applied to the substrate, the intensity of cementite peaks was decreasing, and some of the peaks finally disappeared at -500V. In the other ways, a Fe5C2 peak was appeared with the bias. EPMA revealed that there is no oxide in the film above -300V.

REFERENCES
(1) H.Yumoto and et al. Thin Solid Films, 281-282 (1996) 311-313.