Our Dry Etching Cluster consists of the Oxford RIE Plasmalab System 100 with ICP 380 source and the Oxford RIBE Ionfab 300. (RIE: Reactive Ion Etching, ICP: Inductively Coupled Plasma, RIBE: Reactive Ion Beam Etching). The Dry Etching Cluster is an advanced tool for micro- and nanomachining of various materials. The basic feature is a high frequency generator (RF) working at 13.56 Mhz, combined with a high vacuum chamber for wafers with a diameter of 4”. The power varies in the range of 1-2500 W. Available process gases are SF₆ and O₂ for silicon etching; Cl₂, He, Ar and O₂ for chromium and other metals.

Features

• Silicon etching via the cryo process (process temperatures are between -80 and -150 °C)
• Production of highly vertical, highly parallel and smooth sidewalls
• Critical lateral dimensions down to the range of 100 nm
• Aspect ratios (ARs) up to 6 are possible.
• Laser end point detection
• Metal etching via RIBE

Limitations/constraints

Silicon:

• Min. lateral dimensions: 100 nm
• Min. depth: 50 nm
• Max. aspect ratio at critical dimensions: 4
• Total max. depth: 40 µm

Chromium:

• Min. dimensions in lateral: 100 nm
• Selectivity over resist: 1:1
• Etch rate: 25…35 nm/min

Materials

• Mask material: PMMA, SiO₂, ma-N 2401
• Structures on Si fragments or complete 4” Si wafers

Notice: Only silicon and chromium substrates can be processed reproducibly with standard processes at the moment.

Design rules

• Explicit and unambiguous layout according to the mentioned limitations.
• Markers for the better localization of the structures, e.g. in the SEM
• If the micro/nano structure is already written onto the substrate, the mask material has to be PMMA, SiO₂ or ma-N 2401
• If combined with the KNMF e-beam, specific limitations concerning the e-beam design rules have to be considered

Typical structures and designs

Fig. 1: Deep etched silicon gratings

Fig. 2: Silicon nanopillars with high aspect ratio

Fig. 3: Freestanding cantilevers in silicon

Fig. 4: Cantilever structures in chromium