Diamond film nucleation and interface characterization
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F. Hillion CAMECA Courbevoie 92400, France (Received 5 December 1991; accepted 23 March 1992)
A powerful micro SIMS technique coupled to a computer driven acquisition system has allowed the simultaneous recording of C~, MoO~, and Si" images of the sample surfaces, or of the transverse cross sections of the Mo-diamond interface. Diamond deposition has been shown to take place on a Mo 2 C layer, and the influence on the nucleation process of Si contamination, coming from the quartz tube etched by H atoms, has been investigated. Contamination can in fact occur during the shutdown procedures or during the whole experiment. This last contamination can be avoided by using suitable pressure ranges or gas combinations. Moreover, the deposition time necessary to obtain well-crystallized diamond films and the nucleation density could be optimized by an in situ pretreatment stage. This treatment reduces the delay observed before nucleation (which would correspond to the carbide formation), and increases the carbon activity at the sample surface.
I. INTRODUCTION
II. EXPERIMENTAL
Diamond films have been obtained by various deposition techniques: filament assisted CVD, 1-4 microwaves, R.F. or D.C. discharges,5"10 plasma jets,11 or oxyacetylenic torches... 12 ' 13 These different methods have already been classified into two families owing to their ability in dissociating hydrogen molecules into H atoms,14 which mostly depends on the amount of power density injected in the reactor. A classification of the various methods of diamond growth has also been proposed by Angus et aV5 The nucleation, growth, and quality of diamond layers can be correlated to the CHX/H (0 =£ x =£ 3) ratio; thus for given H, concentrations correspond to typical values of the methane (or other carbon carrier) percentage, thus leading to the determination of deposit qualities.16 The nucleation and deposition rates are all the more important when the CHX concentrations are high, but it must be kept in mind that high CH 4 % deteriorates the diamond quality if the amount of H atoms is not correspondingly raised. So, a study of the influence of parameters that could act on the nucleation process would give a better understanding of this critical stage. The nucleation could then be either enhanced to obtain dense layers, or inhibited to reach selective deposition. Secondary Ion Mass Spectrometry (SIMS) is a well-known technique for obtaining information about the chemical nature of the first atomic layers of a sample, but a new powerful instrument with a high sensitivity and a high spatial resolution ion probe, performs parallel mapping of several elements on the sample surface.
The deposits have been obtained in a microwave reactor with a classical configuration that has already been previously reported.16 A quartz tube of 3.2 cm in internal diameter crosses a waveguide connected to a 1.2 kW generator (2.45 GHz). A mixture composed of CH4 and H2 with or without additional O2 and (or) Ar was used to grow diamond on molybdenum samples which were cylinders of
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