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Communication Dans Un Congrès Année : 2021

SiOxFy layer deposition for cryogenic nanoscale etching

Résumé

Cryogenic deep etching of Silicon is a well-known process. It consists in using SF6 / O2 plasma in order to etch Si anisotropically. A pure SF6 plasma etches isotropically Si by creating SiF4 etch by-products. The addition of O2 enables the creation of a silicon oxyfluoride passivation layer, which is only stable at low temperature and sensitive to ion bombardment. Hence, this layer only builds up on the trench sidewalls, preventing lateral etching [1]. This passivation layer has been the subject of several studies. It inspired the development of the STiGer process, which consists in alternating a passivation step of SiF4 / O2 plasma and a SF6 plasma for Si deep etching [2]. However, new characterizations have brought a new insight. In the results presented in this paper, the SiOxFy layer is deposited by using SiF4 / O2 plasma at different temperatures and for different gas ratios. Then, the layer composition, the deposited amount, the layer desorption and finally the robustness to etching are investigated. A cryogenic ICP reactor was used to deposit the SiOxFy layer on Si coupons. The thickness evolution during the deposition was monitored using an in-situ Spectroscopic Ellipsometer (SE) in kinetic mode. A Quadrupole Mass Spectrometry (QMS) coupled to this reactor has also been used to detect the desorbed species when the sample is brought back to room temperature. For the layer composition, another ICP reactor coupled to an X-Ray Photoelectron Spectroscopy (XPS) was used. A moving sample rod, that can be cooled, is used to transfer the sample from the ICP reactor to the XPS chamber to perform quasi in-situ measurements. These different characterizations offered a better understanding on the formation of the SiOxFy layer and its dependence towards the temperature. In particular, it was shown that the process can switch from deposition to etching regime just by changing the temperature, keeping the same process parameters. This study has also inspired the development of new cryogenic processes that can be applied at the nanoscale. Thanks/Acknowledgement The authors thank S. Tahara for all the helpful discussions. This work was supported by CERTeM 2020 platform, which provides most of the equipment; the CNRS-Réseau des Plasmas Froids is also acknowledged for giving access to the Optimist platform. References [1] X. Mellhaoui et al., J. Appl. Phys, vol. 98, no. 10, p. 104901, 2005 [2] T. Tillocher et al., J. Electrochem. Soc., vol. 155, no. 3, p. D187, 2008
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Dates et versions

hal-03539368 , version 1 (21-01-2022)

Identifiants

  • HAL Id : hal-03539368 , version 1

Citer

Gaelle Antoun, Thomas Tillocher, Philippe Lefaucheux, Jack Nos, Aurélie Girard, et al.. SiOxFy layer deposition for cryogenic nanoscale etching. PLATHINIUM (Plasma Thin film International Union Meeting) 2021, Sep 2021, Antibes, France. ⟨hal-03539368⟩
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