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
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