Paper PS1-WeM11
Development of High Density Radical Source and the Behaviors of Radicals in N₂-H₂ Mixture Plasma

Wednesday, November 11, 2009, 11:20 am, Room A1

Dry processes using nitrogen atoms are essential to nitride semiconductor device fabrications such as nitridation, etching damage restoration or nitrogen doping technologies. To reduce the processing time and improve the film quality, the high density radical source with high efficiency and stability is strongly required. So far, some kinds of radical sources have been evaluated and characterized qualitatively using optical emission spectroscopy (OES). However, the absolute density could not be measured by the OES. In this study, we have developed a new high density radical source (HDRS) and measured the absolute density of atomic radicals by using vuacuum ultraviolet absorption spectroscopy (VUVAS).

The HDRS was designed by optimize the number of antenna coil turns in ICP. The ICP with 4 turns coil antenna enabled us to obtain the highest N atomic radical density. It was found that the radical density was significantly dependent on the power density, plasma density and gas temperature. N radical density was increasing from 7.3x10¹¹ to 3.6x10¹²cm^-3 with pressure increases from 0.025 to 0.5Pa. These results show the N radical density was one order magnitude higher than traditional source. In the power dependence of radical density, the radical density was increased with increase the powers up to 400W and saturated.

The HDRS was also characterized using N₂-H₂ gas mixture. Relative changes of N, H and NH₃ densities were measured as a function of the N₂ flow rate ratio. NH₃ was measured by Quadrupole Mass Spectroscopy (QMS). In this experiment, the total pressure N₂/H₂ was fixed at 0.5Pa. When N₂/H₂ ratio increased from 10% to 33.3%, the absolute density of H radical was increased from 2.3x10¹² to 4.1x10¹²cm^-3. Absolute density of N radical increased from 2.3x10¹¹ to 1.7 x10¹²cm^-3. At the N₂/H₂ ratios beyond 33.3%, the N radical density increased to 2.1x10¹²cm^-3, but H density decreased to 3.2x10¹¹cm^-3. In this experiment, the behaviors of NH₃ relative density agreed with those of H radical. When the N₂ flow rate ratio of 33% was fixed and the pressure was varied from 0.025 to 0.35Pa, it was found that the H radical density was higher than N radical density, but at pressures of above 0.35Pa the N radical density increased rapidly to 5.1x10¹¹cm^-3 and H radical density increased to 3.4x10¹¹cm^-3 . As a result, the behaviors of radicals in N₂-H₂ mixture plasma were investigated and the mechanism of radical kinetics in HDRS was discussed.