In the early 1990’s researchers at the Robert Bosch facility in Stuttgart invented a novel method of etching very deep features into silicon.  This led to a patent being granted in 1994.   Subsequently (and still) referred to as the ‘Bosch’ process it was first licensed to SPTS who shipped the first commercial systems in 1995.  Originally intended as a method of fabricating devices for the then emerging automotive MEMS sector, its use has since diversified to cover virtually all other MEMS markets. Most recently the use of the Bosch Process has expanded into through silicon via (TSV) etching in 3D packaging applications. In 2014 in Amsterdam the inventors (Franz Laermer and Andrea Urban) were awarded the IEEE Jun-Ichi Nishizawa Medal for revolutionising MEMS by enabling the proliferation of many of the everyday devices that surround us today (such as the inertial sensors in airbags and various chip-sets in smart phones, gaming consoles and laptop computers).

This paper will describe what is possible today using the Bosch process and will consider future applications and uses.  The diversity of the approach will be illustrated through various examples including cavities etched at high rates, features with aspect ratios of 90:1, profile tilt to <0.2°, TSVs for wafer stacking and the increasing demand for more precise control including end-point detection below 0.5% open area. The types of devices that require such performance will also be discussed – everything from inertial MEMS, integrated passives, microphones, power semiconductors, microphones, interposers and stacked memory die. The relevance of the Bosch process to newer application areas such as die singulation and BioMEMS will be discussed.  The developments in reactor designs necessary in achieving these advancements will also be reviewed.

The longevity of the Bosch approach is in part due to the lack of alternative methods able to achieve the same results in Si.  A brief comparison with the competing technologies of wet chemical etching, single step plasma etching, cryogenic etching and LASER drilling will be presented.

300mm wafers are in routine use for Bosch etching of TSVs as part of advanced wafer level packaging integration schemes.  However 300mm wafers are now also being considered for MEMS to maximise the die per wafer or to allow direct bonding and integration of MEMS functionality with the best available CMOS chip-sets.  The latest results for deep silicon etching of 300mm will also be presented.