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Bosch Semiconductors for Automotive

DRIE (Deep reactive Ion etching)

High precision DRIE

Bosch’s trench performance is outstanding and is one key success factor for Bosch to be number 1 in silicon MEMS.

One of the key processes in MEMS is the vertical, anisotropic silicon etch, the so-called Bosch process.


Ideally, the trench is:

  • As vertical as possible
  • As narrow as possible the ratio of depth to width as high as possible
  • As deep as possible
  • As reliable as possible with minimum variation
DRIE
Precision Trench

Capabilities

  • Tunable etch profile (shape, angle, …) through process parameters
  • Minimal etch area possible
    - For square shapes down to 3 x 3 µm² @ etch depth up to 100 µm
    - For trenches: minimal gap possible: 400 nm (see picture)
  • Quick and reliable in-process control using optical non-destructive methods, resulting in extremely tight space width control
  • Aspect ratio depth / width 80:1 capability, 60:1 in development, 40:1 in mass production
  • Selectivity with mask is 150:1 for resist, 450:1 for oxide hard mask
  • Endpoint detection with stop layer (e.g. SiO2), open area down to 1%

High rate DRIE

Besides high precision trench, Bosch offers high rate trenching, for example to remove Si in a depth of several 100 microns.


Specific for high rate DRIE

  • Open area on wafer up to 60%
  • Etch depth currently up to 450µm (e.g. in 600 x 800), more possible
  • Negative taper sidewall, maximum 5°



Example 1: High rate without end-point-detection (suitable for cavity-trench)

  • Nominal depth 75 µm
  • Trench depth production data: 1σ < 4%
  • Open area 30%
  • Etch rate 6 µm/min


Example 2: High rate trench with End-point-detection and stop layer

  • Nominal depth 250 µm
  • Trench depth production data: 1σ < 6%
  • Open area 15%
  • Etch rate > 22 µm/min