J.H. Song

Large area high quality diamond film deposition by high power DC arc plasma jet operating at gas recycling mode

Abstract Principles of a high power DC arc plasma torch with rotating arc roots and the semi-closed gas recycling system are presented. Recent results on large area high quality free standing diamond film deposition by a high power DC arc plasma jet CVD system operating at gas recycling mode is discussed. It was shown that the uniformity of diamond film deposition over a large substrate area was closely dependent on the uniformity and symmetry of the plasma, which can be adjusted by proper manipulation of the magnetic field and the effects of fluid dynamics. Effect of gas recycling on the quality of diamond films is discussed. By proper design of the whole system and process optimization, thick uniform diamond wafers of Φ60–110 mm in diameter with a thickness up to 2 mm and transparent diamond wafers of Φ30–60 mm in diameter has been deposited successfully. It is demonstrated that gas recycling can be used even for high quality diamond film synthesis. This is of technical and economical importance in the development of high power DC arc plasma jet CVD systems for economical fabrication of high quality diamond wafers.

Factors Affecting the Fracture Strength of Freestanding Diamond Films

As an emerging brand new type of engineering material for a variety of important high technology applications, the deep understanding of the mechanical behavior of freestanding diamond films has become an emergent task of vital importance. Unfortunately the mechanical behavior of this brand new material is not fully understood. Effects that affect the fracture strength are still not very clear except that the fracture strength of freestanding diamond films is only depended on the grain size (film thickness), and is insensitive to the microscopic defects, and the strength is considerably higher when the nucleation side is in tension than that when the growth side is in tension. However, this is not the full story. Based on the experimental date accumulated in USTB (University of Science and Technology Beijing) for high power dc arcjet diamond films, other factors that may affect the fracture strength of freestanding diamond films are discussed in detail. Effects of the quality of the diamond films, impurities (nitrogen, hydrogen, non-diamond carbon etc.), film morphology and texture, on fracture strength are discussed. Effects of the deposition parameters are explained. Advantages for small amount of nitrogen addition, and for the use of higher substrate temperatures in the increase in fracture strength are demonstrated, which have already been applied in the mass production of tool grade freestanding diamond films. It is hoped that the present paper will be helpful for those who wish to understand and use this brand new type of engineering material

Thermal Stress in Free-standing Diamond Films with Cr Interlayer Destroyed

Thermal stress in large area free-standing diamond films was remarkable during the post-deposition cooling of direct current (DC) arc plasma jet chemical vapor deposition (CVD) process. In this research, the stress release caused by delamination of Cr interlayer was of great importance to ensure the integrity of free-standing diamond film. The effects of Cr interlayer on Mo substrate, namely composite substrate, on thermal stress were investigated. Thermo-mechanical coupling analysis of the thermal stress was applied by finite element analysis (FEA) using ANSYS code. It was found that the interlayer could be destroyed first by the large thermal stress, and then the stress could be released and the probability of diamond film crack initiation would be reduced. The stress concentration at the bent edge of diamond film was also discussed. In addition, diamond films deposited on Mo substrates with and without Cr interlayer were prepared by DC arc plasma jet CVD system and experimental measurements were used to characterize these films. It was found that composite substrate could be an effective method of growing free-standing crack-free diamond films by DC arc plasma jet CVD system when there is no special requirement to the film strength.