AVS 60th International Symposium and Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP1
Dry Deep Etching of GaN Wide Band-gap Semiconductor

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Session: Plasma Science and Technology Poster Session
Presenter: N. Gosset, GREMI CNRS/Université d'Orléans, France
Authors: N. Gosset, GREMI CNRS/Université d'Orléans, France
J. Ladroue, STMicroelectronics Tours SAS, France
T. Tillocher, GREMI CNRS/Université d'Orléans, France
P. Lefaucheux, GREMI CNRS/Université d'Orléans, France
M. Boufnichel, STMicroelectronics Tours SAS, France
R. Dussart, GREMI CNRS/Université d'Orléans, France
Correspondent: Click to Email
Gallium nitride (GaN) is a III-V semiconductor with a large and direct band-gap (3,4 eV). Furthermore, GaN has a high electron mobility and strong chemicals bonds. These physical properties make GaN very interesting and open new prospects for microelectronics power devices. Indeed, GaN-based devices, compared to silicon devices, can operate under high temperature, high power and high frequency. For GaN-based power devices, an etched depth as high as 6 to 10 μm is typically required. This is considered as deep etching compared to the etch depth necessary for light emitter devices (a few hundred nanometers). It was shown that wet etching of GaN c-plan (plan where etching is generally needed) is limited due to its chemical inertness. Therefore GaN deep etching is achieved by plasma etching. Chlorine-based chemistries are commonly used because GaCl3 is the most volatile Ga etching product. We studied GaN etching (7 μm thick epilayer grown on Si) in Cl2/Ar plasma using two industrial Inductively Coupled Plasma (ICP) reactors (Corial 200IL and Alcatel 601 E) and by Ion Beam Etching (IBE) (Plassys MU450). After etching, three regimes of defects were observed: columns, pits and “White GaN”. It was shown that both columns and pits are linked to nanopipes and dislocations created during epitaxial growth of GaN. In addition, oxygen based species, coming from either the SiO2 coverplate or the alumina/quartz tube, play an important role in the columnar regime. They preferentially oxidize dislocations, leading to the observed columns. “White GaN” is a very high roughness coming from surface over-oxidation. For industrial applications, all these defects and roughness must be limited. Plasma investigations, using Langmuir probe, mass spectrometry and optical emission spectroscopy, revealed that SiCl4 can scavenge oxygen. This subsequently results in elimination of defects. Consequently, using Si coverplate or injection of SiCl4 leads to defect free surfaces. An optimized IBE process appears to be also a way to reduce defects. The addition of other gases (like BCl3, CHF3 and SF6) will be also investigated to evaluate the impact on both GaN etch rate and selectivity in Cl2/Ar chemistry. XPS and AFM surface analysis will be performed to better understand the formation mechanism of defects. Finally, regardless of defects, etch rate as high as 1 μm.min−1 and a selectivity of 6 can be obtained.