| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+AS-MoM |
| Session: | Plasma Processing of Challenging Materials |
| Presenter: | Frédéric Le Roux, CEA-Leti, France |
| Authors: | F. Le Roux, CEA-Leti, France P. Burtin, CEA-Leti, France N. Possémé, CEA-Leti, France A. Torres, CEA-Leti, France S. Barnola, CEA-Leti, France |
| Correspondent: | Click to Email |
Formation of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructrures is the key-point for successful development of GaN-based power-electronics such as High Electron Mobility Transistors and diodes.
Today, plasma-etching are considered as one of the most critical step in fabrication of such devices. Indeed plasma etching can lead to charge generation (depleting the channel)1,2, AlGaN amorphisation (modifying the structure and the polarisations of the AlGaN)3,4 or element implantation inducing charges or traps5.
In this study, we propose to evaluate the impact of several plasma parameters (chemical, physical and physico-chemical) on 2DEG degradation occurring during silicon nitride etching (selectively to AlGaN). Experiments have been carried out on 200mm wafers using the following stack: 10nm Si3N4/24nm Al0,22Ga0,78N/AlN spacer/2µm GaN/buffer layers. The AlGaN degradation has been determine thanks to Rsheet and Hall measurements.
First the impact of a conventional fluorocarbon etch chemistry (CF4/CH2F2/O2/He) on 2DEG degradation will be presented as an ion-energy function. It will be demonstrated that Rsheet is degraded with the ion energy increase and confirmed by the evolution of career- density and mobility.
Then the pure-chemical etching effects (using wet and downstream-plasma etching process) as well as physical etching effects, with ion bombardment, (using Ion Beam Etching process (IBE)) will be discussed in term of Rsheet.
Finally, the benefit of new silicon nitride etching process, which has already been tested and validated for silicon nitride spacer application6, has been evaluated for diode contact application. This process is based on two steps. In a first step, the film is modified in volume by a He plasma performed in a conventional etch tool (ICP) followed by a second step of selective removal (HF dip) of the modified layer (Si3N4) with respect to the non-modified material (AlGaN).
Thanks to this study, the plasma-etching’s role in the channel characteristics degradation have been highlighted and linked to the plasma parameter through the Rsheet and Hall measurement evolutions. In order to increase the degradation mechanism understanding engendered by etching steps, physico-chemical characterisations will be developed to determine the degradation sources.
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