Paper PS-TuA11
Ar Ion Sputtering of GaAs Studied by Molecular Dynamics Simulation and Laser Spectroscopy of Ga Atoms in the Gas Phase

Tuesday, October 21, 2008, 5:00 pm, Room 304

III-V compounds such as GaAs or GaN-based materials are increasingly important for their use in optoelectronic applications, especially in the telecommunications industry. Photonic devices including lasers, photodetectors or LEDs, require reliable dry etching processes characterized by high etch rate, profile control and low damage. Recently, inductively coupled plasma-reactive ion etching (ICP-RIE) has been used to etch GaAs and its alloys.¹ Due to its high plasma density, ICP-RIE generally results in a high ion flux with moderate ion energies. However, ion bombardment during the etching process can damage the material and lead to amorphisation at high doses. Molecular dynamics (MD) simulations of GaAs sputtering under low-energy Ar ion bombardment were recently developed by Despiau-Pujo et al.² This study showed that a significant fraction of Ga products leave the surface with more than 10% of the incident ion energy. The aim of the present work is to verify the simulation predictions and measure the velocity distribution function of Ga sputtered atoms. We describe the operation of a GaN laser diode at 403.3 nm for the spectroscopy of Ga atoms in an ICP argon discharge. To obtain both perpendicular and longitudinal velocity components, LIF measurements are performed in z direction and atomic absorption spectroscopy in x direction. Ga atoms are sputtered from the wafer surface by energetic ions produced in the Ar buffer gas of an industrial ICP etch reactor (LAM 9400). The external cavity diode laser is tested and tuned on resonance with Ga transition. For various pressure and ion energy conditions, we perform a systematic study of the Doppler-broadened LIF and absorption spectra to extract perpendicular and longitudinal velocity distributions of sputtered Ga atoms. At very low pressure, these distributions are compared to sputtering theory and MD results. We observe a good agreement between MD predictions and experiment, even if simulations tend to overestimate the perpendicular velocities of sputtered atoms. These results confirm the existence of products sputtered from the surface with significant energies, which constitutes a key point since these atoms could alter passivation layers on sidewalls during etching, and be responsible for defects observed in nanodevices.

¹Y. Matsukura et al, J. Vac. Sci. Technol. B 18, 864 (2000)
²E. Despiau-Pujo et al, J. Vac. Sci. Technol. A 26, 274 (2008).