Low-pressure microwave plasma nucleation and deposition of diamond films

Studies on nucleation process in diamond CVD: an overview of recent developments

“…Nucleation enhancement has also been achieved by covering substrate surfaces with graphite fibers/clusters [33,60,102], or films [70,101], and coating substrate surfaces with thin films of metals (Fe, Cu, Ti, Nb, Mo, Ni) [31,104], C 60 , C 70 [26,125], a-C [30], DLC [126], Y-ZrO 2 [103], a-BN and SiC [14,18,104], or hydrocarbon oil [127], etc. The efficacy of the overlaid materials on nucleation enhancement decreases in the order from C 70 , a-C, DLC, graphite fiber, graphite film, Fe, Cu, Ti, Ni, Mo, to Nb [26,30,[100][101][102]104].…”

“…The precursors are adsorbed on the substrate mainly by physical adsorption below 900 ˚C and predominantly by chemical adsorption above this temperature, resulting in an abrupt increase in the diffusion length of the precursors around 900 ˚C [96]. As a result, the capture rate of the precursors (sticking probability) on the substrate surface, and hence the nucleation rate and density, drastically increase when the substrate temperature approaches 860 C. [18] Suppresses nucleation [17] Decreases nucleation density, 33% O 2 [133] 0.75-0.9 O 2 /C 2 H 2 [21] The effect of filament temperature in HFCVD on nucleation is similar to that of substrate temperature, i.e., with increasing filament temperature, nucleation density initially increases, reaches a maximum at 2100 ˚C and decreases thereafter, with 2100 ˚C being a possible optimum value [43]. The drop-off for T > 2100 ˚C is explained by the observation that the etching of nucleation sites is enhanced with increasing filament temperature [47].…”

“…However, the addition of oxygen is also reported to suppress diamond nucleation by etching nucleation sites (graphite) on Ni and Pt substrates [17]. An optimum oxygen concentration is found to be about 33% in arc plasma jet CVD [133], 2-10% in low pressure low temperature MW PACVD [18], and 0.75-0.9 O 2 /C 2 H 2 in flame CVD [21].…”

“…These studies have led to a reasonable understanding of growth mechanisms and processing parameters. Recently, extensive work [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] on the nucleation and early growth stages has been performed in an effort to enhance diamond nucleation and to control film morphology. As a result, technology problems associated with the nucleation of polycrystalline diamond films have been adequately addressed.…”

“…Nucleation density has been increased from <10 5 cm -2 on untreated substrates up to 10 11 cm -2 on scratched or biased substrates [39,40]. The effects of surface conditions and deposition parameters on the nucleation process have been investigated [12,16,18,21,[41][42][43][44][45][46][47][48][49][50] to provide the guideline for the selection of optimum surface pretreatment methods and deposition parameters. Recent advances in experimental measurement methods make it possible to directly observe the nucleation stage, and in some cases in-situ and/or in vacuo measurements [23,40].…”