Chemical Vapor Deposition of Diamond from Alcohol Precursors at 1.0 Torr
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ABSTRACT Typically, diamond chemical vapor deposition (CVD) is conducted at pressures of 10 to 100 Torr and temperatures of 700 - 1000 'C. Both thermally activated (hot-filament) and plasma enhanced (DC, microwave) systems are used to deposit diamond from mixtures of hydrogen and some carbon-containing monomer, most typically methane. These systems may produce films of high phase purity which typically exhibit tensile intrinsic (non-thermal) growth stresses. We have used an electron cyclotron resonance (ECR) enhanced plasma system to deposit diamond films at a pressure of 1 Torr over a temperature range of 550 - 700 'C using methyl alcohol as the carbon source. Optical emission spectroscopy (OES) was used to analyze the plasma discharge for the determination of active species present during diamond growth. Correlations of emission variations with film characteristics were made to evaluate their importance in the diamond formation process. Particular emphasis was placed on the nature of the intrinsic growth stresses developed in this process, which appeared to be consistently compressive in nature based on Raman analysis. INTRODUCTION It is well known that diamond is a material possessing many extreme properties that make it very attractive for many engineering applications. High hardness, thermal conductivity, chemical
inertness, resistivity and optical transparency all lend themselves to various types of thin film coating applications such as wear-resistant tool or optical coatings, heat-spreading electronic packaging, and protective coatings for measurement probes. For most applications, depositing the diamond film directly on the appropriate substrate is highly desirable. However, the typical conditions used for diamond chemical vapor deposition can be quite harsh, involving substrate temperatures greater than 700 'C in an atmosphere with high concentrations of atomic hydrogen, therefore limiting the number and type of prospective substrate materials. Beyond limitations of material degradation, other considerations can limit the utility of a diamond film in a particular application. Nucleation of diamond on non-diamond materials is an energetically unfavorable process, requiring some kind of enhancement to enable sufficient nucleation for uniform coating. Common processes used for nucleation enhancement include abrading the substrate with diamond particles [1, 2], applying a negative bias during the nucleation stage of deposition [3-6], and seeding of the substrate surface with diamond particles [7-10]. Once nucleation is accounted for, there may further be issues related to residual stress, which may cause failure of the coating through cracking or debonding. Residual stresses due to differences in the thermal expansion coefficients of the deposited film and substrate generally account for the majority of the measured stress in diamond films. We have used a modified electron cyclotron resonance (ECR) enhanced plasma system to deposit diamond films over a range of relatively low deposition temperatures. Plasma
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