| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Plasma Chemistry and Plasma Surface Interactions |
| Presenter: | Christophe Cardinaud, CNRS - IMN, France |
| Authors: | C. Cardinaud, CNRS - IMN, France A. Pageau, CNRS - IMN, France L. Le Brizoual, IETR - Univ. Rennes, France F. Boulard, CEA, LETI, MINATEC Campus, France J. Baylet, CEA, LETI, MINATEC Campus, France |
| Correspondent: | Click to Email |
In the past 20 years, intrinsic properties of Hg(1-x)CdxTe have placed this semiconductor compound as the standard material for the fabrication of high performance infrared detection devices [1]. CH4-H2 based plasmas have proven to be efficient to etch HgCdTe [2]. In terms of mechanism, it is usually admitted that methyl radicals, coming from the dissociation of methane CH4, form volatile metal organic species, mainly Cd(CH3)2 and Te(CH3)2, while atomic hydrogen, coming from CH4 and H2 dissociation, forms volatile TeH2, and that Hg, due to its high vapor pressure, desorbs spontaneously from the surface. Strong Cd accumulation is always observed on the processed surface, underlining that Cd removal is the limiting step of HgCdTe plasma etching. In a previous study we have identified that the surface stoichiometry change appears as soon as the etching starts and that the etch rate is closely related to the incoming flux of methyl species [3]. Consequently, the Hg(1-x)CdxTe alloy removal takes place through a Cd-rich surface layer rather than through the bulk material itself. Low-pressure high-density plasma sources and independent control of sample bias enable operation of the process with more chemical than physical etching mechanisms. Such conditions should meet the main fabrication requirements: high anisotropy, smooth sidewalls, reasonable etch rate, and low level of surface damage. However they typically fall in the HgCdTe etching / hydrocarbon deposition borderline.
Plasma-surface interaction mechanisms are investigated when varying source power, sample bias, CH4 flow rate and total pressure. Mass spectrometry and electrostatic probes are respectively used to evaluate methyl and positive ion flux onto the surface. X-ray photoelectron spectroscopy provides surface composition. Results and etch rate measurements are discussed in the view of an ion-neutral species synergy model based on Langmuir adsorption kinetics [4] and taking into account the competition between hydrocarbon film formation and HgCdTe etching.
1 A. Rogalski, Infrared Phys. and Technol. (2011) 54, 136
2 R.C. Keller, M. Seelmann-Eggbert, and H.J. Richter, J. Electron. Mater. (1995) 24, 1155
3 F. Boulard, J. Baylet, and C. Cardinaud, J. Vac. Sci. Technol. A (2009) 27, 855
4 T.M. Mayer and R.A. Barker, J. Vac. Sci. Technol. (1982) 21, 757