Hans Lydtin

Towards a general concept of diamond chemical vapour deposition

Abstract A C H O phase diagram is introduced providing a common scheme for all major diamond chemical vapour deposition (CVD) methods used to date. It reveals that low pressure diamond synthesis is only feasible within a well-defined field of the phase diagram, a diamond domain that allows general predictions of gas phase compositions and starting materials suitable for diamond synthesis. It gives an explanation for the quality variations of diamonds deposited from different gas mixtures. The concept originates from the thorough analysis of experiments by thermal CVD, hot filament CVD, various plasma deposition techniques and combustion flames. This analysis also shows that the large deposition rate differences between the various methods correlate well with the coirresponding gas temperatures, indicating that a hot spot in the gas phase fosters high rate diamond growth.

Thermodynamische Betrachtungen zur Kohlenstoffabscheidung bei der pyrolyse Gasförmiger Kohlenstoffverbindungen

Zusammenfassung Zur Beurteilung der Eignung eines Gases fur die pyrolytische Abscheidung von Kohlenstoff ist die Kenntnis seiner Gleichgewichtszusammensetzung uber festem Kohlenstoff wichtig. Das Abscheidungsverhalten eines Gases ist namlich unmittelbar mit dieser Zusammensetzung, der Temperatur und dem Gesamtdruck verknupft. Die mit festem Kohlenstoff koexistierende Gasphase wurde fur die Systeme C-O, C-H, C-S, C-H-N und C-O-S zum Teil berechnet, wahrend einige Angaben der Literatur entnommen werden konnten. Ein modifiziertes Ergebnis solcher Berechnungen ist die “Loslichkeit” des Kohlenstoffs in der Gasphase. Besonders bemerkenswert sind das ausgepragte Minimum der Kohlenstoffloslichkeit im System C-H und die bislang nicht diskutierten gunstigen Abscheidungsbedingungen im System C-S. In den Systemen C-H und C-S wurden die thermodynamischen Ergebnisse mit Hilfe einer einfachen experimentellen Anordnung uberpruft und qualitativ bestatigt.

Diamond Forming Discharges

Methods to prepare diamond thin films by means plasma chemical vapor deposition are reviewed. The various techniques available to date are compared with respect to their deposition rates, deposition area, quality and homogeneity of the material produced, and their specific advantages and drawbacks. The deposition rates of both thermally induced and plasma induced CVD methods correlate well with the gas temperature in the reaction zone supporting the hypothesis that the large quantities of diamond precursor species necessary for high deposition rates are formed in a hot spot of the deposition system.

High Rate Versus Low Rate Diamond CVD Methods

A wide variety of methods to deposit diamond films and particles from the vapor phase emerged from different laboratories since the breakthrough publications of diamond deposition onto non-diamond substrates by B.V. Spitsyn et al [1], B.V. Derjaguin et al [2] of the USSR Academy of Science in Moscow as well as M. Kamo [3] and his colleagues at the Japanese National Institute for Research in Inorganic Materials (NIRIM). All of these methods have in common that diamond is deposited from a carbon carrier gas that is decomposed and the formation of non-diamond carbon is prevented by the presence of a selective etchant such as atomic hydrogen or oxygen.