Specific Process Knowledge/Etch/KOH Etch: Difference between revisions
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KOH-etching is a highly versatile and cheap way to realize micro mechanical structures if you can live with the necessary Si<sub>3</sub>N<sub>4</sub>- or SiO<sub>2</sub>-masking materials and the potassium contamination of the surface. '''The latter necessitates in most cases a wet post-clean ([[Specific Process Knowledge/Wafer cleaning/7-up & Piranha|'7-up']] or [[Specific Process Knowledge/Wafer cleaning/RCA|RCA-clean]]) if the wafer is to be processed further.''' | KOH-etching is a highly versatile and cheap way to realize micro mechanical structures if you can live with the necessary Si<sub>3</sub>N<sub>4</sub>- or SiO<sub>2</sub>-masking materials and the potassium contamination of the surface. '''The latter necessitates in most cases a wet post-clean ([[Specific Process Knowledge/Wafer cleaning/7-up & Piranha|'7-up']] or [[Specific Process Knowledge/Wafer cleaning/RCA|RCA-clean]]) if the wafer is to be processed further.''' | ||
At Danchip we use as a standard a 28 wt% KOH. The etch rate - and the selectivity towards a SiO<sub>2</sub>-mask - is depending on the temperature. We normally use T=80 <sup>o</sup>C but may choose to reduce this to e.g. 60 <sup>o</sup>C or 70 <sup>o</sup>C in case of a high-precision timed etch (e.g. defining a thin membrane). In some cases we recommend to saturate the standard 28 wt% KOH with IPA with an etch temperature at T=70 <sup>o</sup>C (reduce evaporation of IPA). One example is for boron etch-stop, where the selectivity towards the boron-doped silicon is improved compared to the standard etch. | At Danchip we use as a standard a 28 wt% KOH. The etch rate - and the selectivity towards a SiO<sub>2</sub>-mask - is depending on the temperature. We normally use T=80 <sup>o</sup>C but may choose to reduce this to e.g. 60 <sup>o</sup>C or 70 <sup>o</sup>C in case of a high-precision timed etch (e.g. defining a thin membrane). In some cases we recommend to saturate the standard 28 wt% KOH with IPA with an etch temperature at T=70 <sup>o</sup>C (reduce evaporation of IPA). One example is for boron etch-stop, where the selectivity towards the boron-doped silicon is improved compared to the standard etch. | ||
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<gallery caption="Different places to do wet silicon | <gallery caption="Different places to do anisotropic wet silicon etch" widths="399px" heights="300px" perrow="3"> | ||
image:KOH3_RR4_1.JPG|KOH etch for 4" and 6" wafers. Positioned in cleanroom 4. | image:KOH3_RR4_1.JPG|KOH etch for 4" and 6" wafers. Positioned in cleanroom 4. | ||
image:KOH_4tommer.jpg|KOH etch for 4" wafers. KOH1 to the left and KOH2 to the right, in between you find the BHF tank. Positioned in cleanroom 3. | image:KOH_4tommer.jpg|KOH etch for 4" wafers. KOH1 to the left and KOH2 to the right, in between you find the BHF tank. Positioned in cleanroom 3. | ||