Deep germanium etching using time multiplexed plasma etching

Abstract

There is a growing need for patterning germanium for photonic and photovoltaics applications. In this paper, the authors use a time multiplexed plasma etch process (Bosch process) to deep etch a germanium substrate. They show that germanium etching presents a strong aspect ratio dependent etching and that patterns present scallops mostly on the upper part (aspect ratio below 0.8). Passivation layers are formed during the passivation step by neutrals' deposition and are reinforced during the etching step by the redeposition of sputtered fluorocarbon species from the etch front. When the sidewalls are passivated, reactive neutrals diffuse through Knudsen-like diffusion down to the bottom of the pattern to etch the germanium. The Knudsen-like diffusion is responsible for the aspect ratio dependent etching and makes difficult the etching of holes with aspect ratios above 10 while trenches with aspect ratio of 17 are still etched faster than 2 μm/min.

Three‐junction monolithic interconnected modules for concentrator photovoltaics

“…The cell singulation occurs by means of plasma etching through the 170‐μm active wafer (Figure 1F). The etching is performed using a Bosch process that consists in alternating etching steps (13 s, SF 6 /O 2 ) and passivation steps (7 s, C 4 F 8 ) for 45 min (average etch rate is >3.8 μm/min for 20‐μm‐wide trenches) 16 . The SiO x layer acts as an etch‐stop layer and can be removed by etching after the cell singulation occurs in case the front‐contacted cells are used as stand‐alone devices.…”

Towards miniaturization of concentrated photovoltaics (CPV): impact on fabrication, performance and robustness of solar cells

“…Then, an antireflective coating (ARC) made of SiNXHY/SiOXHY is deposited by plasmaenhanced chemical vapor deposition (PECVD). Besides increasing optical absorption of the cell, such ARC permits a passivation effect, which can limit perimeter recombination rate [9]. The ARC is then opened on metallization to access the electrical contacts.…”

Plasma etching applications in concentrated photovoltaic cell fabrication

“…The contact layer was etched using a NH 4 OH/H 2 O 2 /H 2 O solution and the samples were singulated either by full saw-dicing (reference samples, samples with holes, and one sample with isolation area etched by plasma) or plasma etching (one sample with isolation area etched by plasma). In the latter case, 125 µm of germanium is etched using a time multiplexed plasma etching process with 60 cycles of SF 6 /O 2 and C 4 F 8 plasmas to mimic a complete dicing by plasma etching while avoiding exposing the back side metal to the etching process [5]. To limit the surface recombination, a last step was done on the cells with via holes.…”