Ultrahigh aspect ratio etching of silicon in SF6-O2 plasma: The clear-oxidize-remove-etch (CORE) sequence and chromium mask

Abstract

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OES diagnostics as a universal technique to control the Si etching structures profile in ICP

“…As the gas pressure increases, the mean free path of the particles decreases and, therefore, the energy of the ions bombarding the surface will also decrease. At the same time, the width of the angular distribution of ions will increase 19 , 21 , 39 – 41 . In addition, at fixed values of gas mixture flow rate, increasing the pressure leads to increasing the dwell time of CAP at the processing surface, hence, the number of chemical reactions of CAP with Si will increase.…”

“…The advantage of this technique is the replacement of C x F y gases with oxygen. Oxygen passivation, unlike C x F y , is a self-limiting process and, therefore, the oxide thickness at the bottom of the etching window will be approximately the same for structures with different aspect ratios 19 – 21 . The key to the realization of such a process is to carry it out in a system that uses flat electrodes for plasma generation (capacitive coupling).…”

Silicon Nanowires: A Breakthrough for Thermoelectric Applications

“…The large side is perpendicular to the surface, therefore this design allows the packing of a large number of nanostructures, limited only by the width and the pitch between the nano-lamellae. Thicker SOI wafer can be considered: the limit of the width/height ratio is determined by the aspect ratio of the selective plasma etching process, which could reach 100:1 [ 67 , 68 , 69 , 70 , 71 ] (10 m for a width of 100 nm) if deep reactive etching is used.…”

Cr and CrOx etching using SF6 and O2 plasma

“…25 In our previous publications, we introduced a new plasma etch sequence-called CORE-able to structure high aspect ratio (AR) features into silicon. [26][27][28] CORE stands for Clear, Oxidize, Remove, and Etch and is a room temperature process dedicated for ultrahigh AR fabrication that uses a cycle of SF 6 plasma to etch Si and O 2 to protect the sidewalls of the etching features. Cr is of particular interest in the CORE sequence as it serves as a durable hard mask in the quest to go beyond an AR of 100 in Si etching.…”

“…In our latest publication, we have used the liftoff procedure to pattern Cr. 28 However, with the continuous downscaling of the requested nanoscale devices, the control of the feature size of patterned Cr becomes increasingly more important, and the liftoff is neither sufficiently accurate nor reliable at the nanoscale. This is why plasma etching has become the standard technique, already for many decades, in mainstream nanofabrication.…”