Influence of nitrogen doping on growth rate and texture evolution of chemical vapor deposition diamond films

Abstract

Chemical vapor deposition ͑CVD͒ diamond films were prepared using a variation in nitrogen addition into the gas source admixture by a direct current CVD method. The influence of nitrogen addition on the crystallographic texture and grain shape evolution in heteroepitaxial polycrystalline diamond films was investigated using high-resolution electron backscattering diffraction and x-ray diffraction. The analysis reveals that an addition of 1.5% N 2 to the CH 4 gas flow leads to a strong enhancement in a ͕110͖ fiber texture. The phenomenon is discussed in terms of a competitive growth selection mechanism. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3072601͔ Studies on diamond films are of high relevance as they are increasingly used as semiconductor in electronic devices such as ultraviolet light emitting diode, high-speed switches, and high-power transistors. Nitrogen-doped diamond is a n-type semiconductor while boron-doped diamond is p-type. Usually, it is more practical to synthesize n-type semiconducting chemical vapor deposition ͑CVD͒ diamond because the high boiling point of boron prevents its incorporation into diamond. Nitrogen incorporation into the deposition atmosphere has drawbacks and benefits. Concerning the disadvantages, the existence of nitrogen reduces the thermal conductivity and the optical transparency.1,2 In addition, nitrogen has a high solubility in diamond and is found to be either concentrated in small precipitates ͑type Ia͒ or dispersed on substitutional atomic sites ͑type Ib͒.3 Nitrogen addition gives diamond a yellow tarnish and increases the defect content, resulting in a negative influence on various physical properties. 4 Regarding the advantages, a small amount of nitrogen favors a ͗100͘ growth texture, 3,5 which has lower roughness, 6 higher wear resistance, and higher heat conductivity 7,8 than other crystallographic directions. Also, a limited incorporation of nitrogen seems to promote the deposition rate.9-11 Thus, it is important to understand the influence of nitrogen additions in order to take advantage of the benefits and avoid the disadvantages during diamond film synthesis. Corresponding studies have been conducted using characterization by secondary ion mass spectroscopy, 2 Raman spectroscopy, 3,4 and x-ray diffraction ͑XRD͒. 3This paper presents an investigation on the growth rate and the crystallographic texture of diamond as a function of nitrogen additions. We used a high-power direct current arc plasma jet method, operated in gas recycling mode to prepare large-scale freestanding CVD diamond films.11-13 Sets of films were deposited using variations in nitrogen addition ranging from 0.5% to 3.5% N 2 / CH 4 . The molybdenum ͑Mo͒ substrates were kept at 1050°C ͑Ϯ20 K͒ during deposition. The ratio of methane to hydrogen in the feeding flow was 1.6%. The N 2 / CH 4 ratios in the feeding flow were set to 0.5%, 1.5%, 2.5%, and 3.5%, respectively. Since the roughness of the substrate promotes nucleation, 14,15 the substrates were polished using diamond powder and ...

Development of Crystallographic Texture and In‐Grain Misorientation in CVD‐Produced Single and Polycrystalline Diamond

“…[33][34][35] It is difficult to avoid incorporation of such impurities in CVD-produced diamond layers. An exhaustive range of very interesting literature, [19,[28][29][30][31][32][33][34] including TEM Full Paper (transmission electron microscopy) studies, [28,29,32] exists on the subject of defects in diamond thin films. Typical EBSD scans are not sensitive, directly, to many such defects.…”

“…[19,[28][29][30][31][32] Many of such defects exist in the HPHT substrate, [33][34][35] and hence may affect the defect evolution of the homo-epitaxially grown diamond thin films. For example, the HPHT substrates typically contain different types of impurities (H, O, and N).…”

“…electron backscattered diffraction (EBSD) is the most potent microtexture tool and it has been used successfully, in particular, for CVD diamond thin films. [16,19,20] Defects in diamond films may exist as dislocations, grain boundaries, and various other imperfections. [21][22][23][24] Typically, geometrically necessary boundaries (GNBs) and dislocations may accommodate lattice misorientations in a crystalline material.…”

“…It has gained significant importance in the studies of thin films, particularly relevant for diamond films. [12][13][14][15][16] In all such studies, X-ray texture data have been appropriately represented [17][18][19] to show preferred orientations. There have also been attempts to relate such bulk crystallographic texture with the processing and/or properties, [12][13][14] however such representations are/were qualitative at best.…”

Surface Chemistry of Diamond

“…N doping will enhance the diamond growth rate, and thereby reduce the production costs. The influence of nitrogen on the deposition rate has already been reported for both poly-and mono-crystalline diamond [39][40][41][42]. Recently, the catalytic effect by N on the CVD diamond growth rate enhancement has been studied using laser reflection interferometry [43].…”