Control of nitrogen reactive species in helicon plasmas for III-N semiconductor growth

Summary form only given. Molecular beam epitaxy of III-N materials is potential alternative to MOVPE for fabrication of high quality wide band gap semiconductor devices. However, during the MBE film growth enhancement of nitrogen accommodation and sputtering damage minimization remain as technological hurdles. We report preliminary results on control of reactive nitrogen species performed in a steady state, high density, helicon plasma source CHEWIE (Compact HElicon Waves and Instabilities Experiment). The helicon vacuum chamber is a 12 cm long, Pyrex tube, 6 cm in diameter, connected to a stainless steel diffusion chamber. RF power of up to 1.0 kW over a frequency range of 6-18 MHz is used to create the steady state plasma. A 7 cm long, half wave, m=+1, helical antenna couples the rf energy into the plasma. By a proper selection of the helicon wave phase velocity and input power it is possible to modify the electron velocity distribution function. Thereby increasing the production of molecular excited species, which are favorable to the growth process, and decreasing the production of ionic species, which are detrimental to the epilayer. Further, the expansion of the helicon plasma into the diffusion chamber should permit, through spontaneous radiative relaxation, the different N/sub 2/ triplet excited states to cascade down to the metastable A/sup 3//spl Sigma//sub u//sup +/ state. With a sufficiently long transit time to the expansion chamber, the long lived A/sup 3//spl Sigma//sub u//sup +/ state will become the dominant reactive nitrogen specie in the plasma. Previous optical emission spectroscopy investigations have demonstrated that the N/sub 2/ (B/sup 3//spl Pi//sub g/, v\´=11 /spl rarr/A/sup 3//spl Sigma//sub u//sup +/, v"=7 at 580.4 nm) transition, which is a part of the 1st positive system, is the dominant transition in nitrogen helicon generated plasma.