Paper PS-ThM4
Deep Inductively Coupled Plasma Etching of GaN

Thursday, October 21, 2010, 9:00 am, Room Aztec

III-Nitride semiconductors such as gallium nitride are widely used in light emitter device manufacturing¹. GaN physical properties also open new prospects in microelectronics developments². Combining a wide bandgap (3.4eV), strong chemical bonds and high electron mobility, GaN based devices should operate under higher temperature, higher power and higher frequency than typical silicon devices. Due to inert chemical nature of GaN, wet etching is limited³. As a consequence, it is necessary to use dry etching method⁴ to obtain a reliable MESA structure. Chlorine based plasmas are commonly used because GaCl₃ is the most volatile etching product. Etch rate is also found to strongly depend on physical sputtering. GaN etching requirements for power device applications are different from those concerning photonic devices. Due to the power density supplied to the next generation of power devices, deep structures as high as 10µm should be build. As a comparison, the etched depth needed for light emitter are of the order of a few hundreds of nanometers. Deep GaN etching implies etch rate issues as well as surface roughness defects. We showed that these etching defects are linked with dislocations and nanopipes inherent to the substrates and revealed during etching⁵. Experiments were mainly performed in two Inductively Coupled Plasma (ICP) reactors: an industrial Alcatel 601E, composed of an ICP source and a diffusion chamber and an ICP-RIE Corial 200IL without diffusion chamber. For a better understanding of the etching mechanisms, different diagnostics are used to characterize the plasma. Optical emission spectroscopy, Langmuir probe and mass spectrometry are performed as a function of process parameters. We observe that etching behaviour depends on cover plate material. An optimum etch rate as a function of source power is measured by using a silicon cover plate. OES and Langmuir probe measurements suggest that silicon cover plate, which is etched by chlorine radicals, can be a limitation in the etching performance of the process. Different chemistries are studied as source of active species, sputtering ions or molecule scavenging impurities. We have shown that oxygen impurities are responsible for the columnar defects. We also show that adding a small amount of nitrogen in the chemistry could increase the selectivity with SiO₂ mask.

¹S. Nakamura & al., Appl. Phys. Lett., 67, 1868 (1995)

²G.T. Dang & al., IEEE Trans. On Elec. Dev., 47, 692-696 (2000)

³D. Zhuang and J.H. Edgar, Mat. Sci. and Eng., 48, 1–46 (2005)

⁴S.J. Pearton & al., J. Appl. Phys., 86 (1999)

⁵J. Ladroue, A. Meritan, M. Boufnichel, P. Lefaucheux, P. Ranson and R. Dussart, JVST A submitted (2010)