Specific Process Knowledge/Etch/KOH Etch: Difference between revisions
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[[Category: Equipment|Etch Wet KOH etch]] | [[index.php?title=Category:Equipment|Etch Wet KOH etch]] | ||
[[Category: Etch (Wet) bath|KOH etch]] | [[index.php?title=Category:Etch (Wet) bath|KOH etch]] | ||
==Si etch - ''Anisotropic silicon etch''== | ==Si etch - ''Anisotropic silicon etch''== | ||
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KOH belongs to the family of anisotropic Si-etchants based on aqueous alkaline solutions. The anisotropy stems from the different etch rates in different crystal directions. The {111}-planes are almost inert whereas the etch rates of e.g. {100}- and {110}-planes are several orders of magnitude faster. | KOH belongs to the family of anisotropic Si-etchants based on aqueous alkaline solutions. The anisotropy stems from the different etch rates in different crystal directions. The {111}-planes are almost inert whereas the etch rates of e.g. {100}- and {110}-planes are several orders of magnitude faster. | ||
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. we also recommend to rinse the wafers in a 5% HCL solution to remove metal ions from the KOH solution.''' | ||
At DTU Nanolab 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. Etching with IPA added to the KOH solution (250ml IPA/1000ml KOH) can be done in KOH fumehood. | At DTU Nanolab 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. Etching with IPA added to the KOH solution (250ml IPA/1000ml KOH) can be done in KOH fumehood. | ||
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*Mixing ratios giving 28 wt% KOH solutions | *Mixing ratios giving 28 wt% KOH solutions | ||
KOH:H<sub>2</sub>O - 1000 ml: 1200 ml, when using premixed 50% KOH solution | KOH:H<sub>2</sub>O - 1000 ml: 1200 ml, when using premixed 50% KOH solution | ||
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*Mixing ratios giving 28 wt% KOH solutions | *Mixing ratios giving 28 wt% KOH solutions | ||
KOH:H<sub>2</sub>O - 1000 ml: 1200 ml, when using premixed 50% KOH solution | KOH:H<sub>2</sub>O - 1000 ml: 1200 ml, when using premixed 50% KOH solution | ||
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