Si O x F y passivation layer in silicon cryoetching

Abstract

The SiOxFy passivation layer created on structure sidewalls during silicon cryoetching is investigated. This SiOxFy passivation layer formation strongly depends on O2 content, temperature and bias. It is a fragile layer, which mostly disappears when the wafer is warmed up to ambient temperature. A mass spectrometer was used to analyze the desorbed species during the warm-up and using this instrument allowed us to find a large signal increase in SiF3+ between −80°C and −50°C. SiF4 etching products can participate in the formation of the passivation layer as it is shown by a series of test experiments. SiF4∕O2 plasmas are used to form a thin SiOxFy layer on a cooled silicon wafer. Thickness and optical index of this thin film can be determined by in situ spectroscopic ellipsometry. It is shown that the passivation layer spontaneously desorbs when the silicon wafer temperature increases in good agreement with the mass spectrometry analysis. Two physical mechanisms are proposed to explain the SiOxFy passivation layer buildup involving either the etching products or the SiFx sites created during etching. In both cases, oxygen radicals react at the surface to form the SiOxFy layer.

The structural and optical properties of black silicon by inductively coupled plasma reactive ion etching

“…However, the layer is not very stable and dissociates when heated 24 or under ion bombardment from the plasma. 25 Thus, the actual formation of a passivation layer is strongly influenced by the substrate temperature, the ion energy (i.e., the substrate self-bias) and the oxygen flow.…”

“…Figure 1 gives a comprehensive morphology overview (30 elevation, cross-section and top-view) of the structures evolving after 2 min, 3 min, 5 min, and 10 min. In the discussion of the evolution of the Black Silicon structures, we will rely on the extensive studies of SF 6 -O 2 etching process by Dussart and co-workers 15,[24][25][26] as well as the pioneering work of Jansen, de Boer and co-workers who first described the Black Silicon process. 14,27 Generally two reactions occur in the presence of the SF 6 -O 2 plasma.…”

“…Second, ionized etch products SiF þ y react with oxygen radicals O* and form a silicon oxyfluoride layer 14,24 SiF…”

Properties of deep etched trenches in silicon: Role of the angular dependence of the sputtering yield and the etched species redeposition

“…We use the industrial equipment 601 E of Alcatel company (the reader will find more information about it in Ref. [1]) which works under a cryogenic process: the silicon substrate is cooled to induce the formation of a passivation layer on the trench sidewalls [19], blocking the isotropic processes and thus enhancing the anisotropy. A series of in situ plasma diagnostics (Langmuir probe, optical spectroscopy) and surface characterizations (SEM, XPS and ellipsometry) allow the characterization of the whole process equipment, understanding the implicated mechanisms and improving the results [18,19].…”

Advanced Plasma Processing: Etching, Deposition, and Wafer Bonding Techniques for Semiconductor Applications

“…The current understanding of the chemical process is that oxygen ions combine with the fluorine bonded to the silicon surface prior to the silicon's removal and forms a SiO x F y layer. The exact composition of this layer is a topic of current research (Mellhaoui et al, 2005). In a manner similar to the chopping Bosch passivation, the SiO x F y passivation layer protects the exposed vertical silicon while the unmasked horizontal silicon is etched way.…”