Anisotropic Etching

Local use only, see Ethanolamine results.

See also O. Tabata, R. Asahi, H. Funabashi, K. Shimaoka, and S. Sugiyama, Anisotropic etching of silicon in TMAH solutions, Sensors and Actuators, A34, 51-57, 1992

Etch rate and selectivity of TMAH vs EDP anisotorpic etching

Table from V. Temesvary, S. Wu, W. Hsieh, Y-C Tai, and D. Miu, Design, Fabrication and Testing of Silicon Microgimbals for Super-Compact Ridid Disk Drives, J. Microelectromechanical systems 4, 22.

(TMAH is 15% wt)		TMAH	TMAH	EDP
Temperature			80C	90C	95C
Etch rate (100) Si (&um/hr)	40	65	90
Si:LPCVD LTO oxide		1190:1	800:1	-
Si:2E20/cc B doped Si		27:1	20:1	>500:1
Si:1E21/cc B doped Si		100:1	92:1	>500:1

Ammonium Hydroxide etching

Author       SCHNAKENBERG, U.; Benecke, W.; Lochel, B.; Ullerich, S.; Lange,
             Fraunhofer-Inst. fur Mikrostrukturtech., Berlin, Germany
Title        NH/sub 4/OH-based etchants for silicon micromachining:
             influence of additives and stability of passivation layers
Source       Eurosensors IV '90; Part:  Karlsruhe, West Germany; Part:  1-3
             Oct. 1990;
             Sponsored by:  EPS; EUREL; IEEE; et al;
             Sensors and Actuators A (Physical);
             vol.A25, no.1-3;
             Oct. 1990-Jan. 1991 pp.; pp. 1-7 pp.
Abstract     Solutions based on ammonium hydroxide and water were
             investigated for anisotropic etching of monocrystalline
             silicon. In 2.65 M NH/sub 3/ solutions at 80 degrees C, the
             addition of H/sub 2/O/sub 2/ in a concentration between 0.
             65*10/sup -2/ M and 1.84*10/sup -2/ M increases the silicon
             etch rate in the (100) direction to 75 mu m/h, which is a
             factor of about 2.5 higher compared to pure etchants. In
             addition, when the pH value was adjusted above 11.3, silicon
             etching proceeds in H/sub 2/O/sub 2/-doped solutions without
             formation of pyramidal-shaped hillocks. The influence of the
             pH value and H/sub 2/O/sub 2/ concentration on the etching
             behaviour is discussed in detail. Passivation layers, like
             silicon oxides and silicon nitrides formed under various
             preparation conditions, and metals show excellent stability in
             AHW solutions. The temperature dependence of etch rates as
             well as the influence of post-treatments on the etching
             behaviour is discussed

Author       SCHNAKENBERG, U.; Benecke, W.; Lochel, B.;
             Fraunhofer-Inst. fur Mikrostrukturtech., Berlin, West Germany
Title        NH/sub 4/OH-based etchants for silicon micromachining
Source       5th International Conference on Solid-State Sensors and
             Actuators and Eurosensors III; Part:  Montreux, Switzerland; Pa
             rt:  25-30 June 1989;
             Sponsored by:  Swiss Soc. Sensor Technol.; IEEE;
             Sensors and Actuators A (Physical);
             vol.A23, no.1-3;
             April 1990 pp.; pp. 1031-5 pp.
Abstract     Wet chemical etchants based on ammonium hydroxide-water (AHW)
             solutions for micromachining monocrystalline silicon are
             described. The etchants can be applied under clean-room
             conditions within standard IC fabrication lines. The nature of
             AHW solutions is discussed with respect to anisotropy and
             selectivity. At 75 degrees C and 9 wt.% AHW, a maximum etch
             Si/sub 3/N/sub 4/ and highly boron-doped silicon. Aluminium
             will not be attacked by silicon-doped AHW etchants. Therefore,
             standard IC metallization techniques can be used for device
             fabrication. The application of AHW solutions to the
             fabrication of basic micromechanical structures is demonstrated