Specific Process Knowledge/Etch/KOH Etch: Difference between revisions
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==KOH etch - ''Anisotropic silicon etch''== | ==KOH etch - ''Anisotropic silicon etch''== | ||
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. | ||
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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. | ||
<gallery caption="Different places to do wet silicon oxide etch" widths="300px" heights="300px" perrow="3"> | |||
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:Stinkskab RR2.jpg|PP-bath: positioned in the upper right corner of the fumehood in cleanroom 2. </gallery> | |||
Key facts for the different etch baths available at Danchip are resumed in the table: | Key facts for the different etch baths available at Danchip are resumed in the table: | ||