We compared the anisotropic etching properties of KOH and TMAH solutions. We used hemispherical specimens of single-crystal silicon whose surface exhibited every crystallographic orientation, in order to evaluate the etching properties as a function of the orientation. We carried out a series of experiments using different etchant concentrations and etching temperatures. The orientation dependence in the etching rates of the surface crystals significantly differed between the two etchants, especially for the (111) and (221) planes. We conclude that the two etchants have different etching mechanisms at least in an area including these two planes. The etching rates varied with etchant concentration and etching temperature. The concentrations that maximized the etching rate were 25 wt.% for KOH and 20 wt.% for TMAH. The activation energies in KOH and TMAH were almost the same for the (100), (110), and (320) planes but not for the (221) and (111) planes. Etchant circulation had a significant effect on the etching rates in diluted TMAH solution but not in KOH solution. The roughness of the (100) plane in KOH was one order smaller than that in TMAH.

Differences in anisotropic etching properties of KOH and TMAH solutions

The etching process of (1 0 0) silicon wafers in KOH and TMAH solutions with isopropyl alcohol (IPA) has been studied. The etching rates of different crystallographic planes in the wide range of solutions concentration have been estimated. The mutual relations of the etching rates of these planes have been analysed. Special emphasis was put on the roughness of silicon surface obtained in effect of etching. It was proved that IPA added to the solution improves the morphology of resulted surface. Detailed indications about the solution composition, ensuring satisfactory surface quality have been given. On the basis of experimental results and theoretical considerations, some attempts were made to explain the etching behaviour of silicon in KOH and TMAH solutions with IPA addition. It was suggested that TMA+ ions play similar role in the solution to IPA particles and participate in smoothening of the etched surface.

The effect of isopropyl alcohol on etching rate and roughness of (1 0 0) Si surface etched in KOH and TMAH solutions

We evaluated orientation dependence in the etching rate of single-crystal silicon for tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including TMAH concentrations of 10–25% and temperatures of 70–90°C. We found significantly different characteristics from those for KOH water solutions. Firstly, different types of orientation dependence in etching rate were found around (111) between TMAH and KOH. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms for the two etchants. Secondly, effects of the circulation of etchants on the etching rates were not negligible in TMAH in contrast to KOH system.

Anisotropic etching rates of single-crystal silicon for TMAH water solution as a function of crystallographic orientation

Silicon wafers with (1 1 0), (3 3 1), (3 1 1) and (2 1 1) crystallographic orientations etched in KOH and KOH saturated with isopropyl alcohol solutions have been studied. Etch rates of selected (h k l) planes were estimated by direct etch depth measurements. The effects of IPA additive on etch rates, hillocks formation and surface roughness of considered planes were analysed. It was shown that IPA affects the planes of (h h l)-type, causing both their etch rate reduction and surface quality improvement. IPA addition to KOH solution does not reduce etch rates of (h l l)-type planes but results in bulky hillocks formation on the whole etched area. The type of IPA interaction with different crystallographic planes probably depends on bond configuration on a particular plane.

Etch rates and morphology of silicon (h k l) surfaces etched in KOH and KOH saturated with isopropanol solutions

Macroscopic etch anisotropies and microscopic reaction mechanisms: a micromachined structure for the rapid assay of etchant anisotropy

We have evaluated the orientation dependence in chemical anisotropic etching of single-crystal silicon. Etch rates for a number of crystallographic orientations have been measured for a wide range of etching conditions, including KOH concentrations of 30 to 50% and temperatures of 40 to 90 °C. Though the etchants all consist of the same components KOH and water, the orientation dependence varies considerably with change in etchant temperature and concentration. The resulting etch-rate database allows numerical prediction of etch profiles of silicon, necessary for the process design of microstructures. Changing the KOH concentration yields different etch profiles both analytically and experimentally.

Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration

We have evaluated the orientation dependence in chemical anisotropic etching of single-crystal silicon. Etch rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including KOH concentrations of 30 to 50% and temperatures of 40 to 90°C. Though the etchants all consisted of the same components KOH and water, the orientation dependence varied considerably with change in etchant temperature and concentration. The resulting etch rate database allows numerical prediction of etch profiles of silicon, necessary for the process design of microstructures. Changing the KOH concentration yielded different etch profiles both analytically and experimentally.

http://ieeexplore.ieee.org/iel3/4441/12601/00581871.pdf

Yoshihiro Matsushima

Papers

Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration

Characterization of anisotropic etching effects of koh concentration on etching profiles properties of single-crystal silicon: