Spectral Analysis During MPCVD Diamond Deposition

Compared with other diagnostic methods for plasma, plasma spectroscopy has adistinct advantage that it can measure plasma parameters and related radicals’distribution real time and on line during diamond deposition. In this paper, OES hasbeen used to measure the process of diamond deposition by microwave plasmachemical vapor deposition in-situ and online,which combined the process parameterand plasma parameters with the deposition mechanism organically, and supply thefoundation for further understanding the mechanism of diamond growth.（1） When the power、the pressure and the total gas flow was set constant, theinfluence of the methane concentration on active species’ spatial distribution andradicals’ intensities has been investigated during the experiment. The results show thatthere were many spectral lines during the deposition process, which included H_α（656.19nm）、H_β（486.71nm）、H_γ（434.56nm）ofhydrogenBalmerseries,mainlyFulcher-α（d³Î _u—a³Î£_g） series of hydrogen molecule, the radical CH A²Î”→X²Î ï¼ˆ431.31nm）、B²Î”→X²Î ï¼ˆ388.08nm）andC²Î£â†’X²Î ï¼ˆ314.99nm）,theradicalC₂mainly Swan band （d³Î _g→a³Î _u） series Δv=+1（470.14nm）,Δv=0（515.63nm）,Δv=1（563.10nm）andC¹Î _g→A¹Î _useries Δv=1（359.3nm）,Δv=-1（410.89nm）.The intensity of these spectral lines became stronger when themeasuring position near the reaction cavity,and became weaker when far way from it.With the methane concentration increasing, the intensities of active species increase,in which the radical C₂is the most obvious. It was inferred that the radical CH maybethe precursor of the diamond phase, and the radical C₂was likely to be the precursorof non-diamond phase.（2）The spectral lines were measured at different spatial positions of the cavityand the influence of the process parameters on the spatial distribution of importantradicals C₂、CH and hydrogen spectral line H_β, with different pressures and methaneconcentration have been studied. The results show that the intensities of radical C₂、CH and hydrogen spectral line H_βincrease obviously,but the uniformity of spatial distribution become worse rapidly, in which the radical C₂and hydrogen spectral lineH_βare more obvious than the radical CH. What’s more, the temperature of thesubstrate increase rapidly, but the electron temperature and the mean energy ofelectron in plasma decrease. The appropriate low pressure was necessary, when givenconsideration to the deposition rate、the uniformity of plasma and the quality ofdiamond. The intensities of the radicals C₂and CH increase but the uniformity of theirspatial distribution become worse, in which the uniformity of the radical C₂becomeworse than the radical CH. However，the temperature of the substrate is essentiallyunchanged, and the electron temperature increase slightly. The appropriate lowmethane concentration was necessary, when given consideration to the depositionrate、the uniformity of plasma and the quality of diamond.（3）The influence of noble gases on the intensities of important radicals during thediamond deposition, as well as the morphology and quality of diamond,has beenfurther researched in the experiment, with low concentration of argon and helium. Theresults show that with the argon concentration increasing, the intensities of radical C₂、CH and hydrogen spectral line H_α、H_β、H_γincrease, in which the radical C₂is moreobvious than CH, and the intensity of hydrogen spectral line H_αincreases mostobviously. When the argon concentration increases, the dissociation of hydrogen andmethane is accelerated, and the lifetime of active species become longer, so theintensities of active species and the deposition rate increase, whereas the electrontemperature, the mean electron energy and the quality of diamond decrease slightly.Meanwhile, the morphology and quality of diamond are improved effectively, duringthe diamond deposition with low argon concentration. With the helium concentrationincreasing, the changes of intensities of radical C₂、CHandhydrogenspectrallineH_βare small, only the intensity of hydrogen spectral line H_αincrease rapidly, whichillustrate that small amount of helium can improve the intensities of hydrogen spectralline,and achieve the aim of etching enhancement.