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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<gallery caption="Different places to do anisotropic wet silicon etch" widths="350px" heights="250px" perrow="3"> | <gallery caption="Different places to do anisotropic wet silicon etch" widths="350px" heights="250px" perrow="3"> | ||
image:KOH_BHF.JPG|Wetbench 01: Si etch, for Si etch of 4" and 6" wafers using KOH. Positioned in cleanroom D-3. | image:KOH_BHF.JPG|Wetbench 01: Si etch, for Si etch of 4" and 6" wafers using KOH. Positioned in cleanroom D-3. | ||
image:KOH_fumehood.JPG|Fume hood 06: Si etch, for Si etch of 4" and 6" wafers using KOH. Positioned in cleanroom D-3. This is used for wafers that are considered dirty.</gallery> | image:KOH_fumehood.JPG|Fume hood 06: Si etch, for Si etch of 4" and 6" wafers using KOH. Positioned in cleanroom D-3. This is used for wafers that are considered dirty. The workspace in the fume hood can also be booked and used for beaker etch of Si and in some cases Chromium etch.</gallery> | ||
'''The user manuals, quality control procedures and results, user APVs, technical information and contact information can be found in LabManager:''' | '''The user manuals, quality control procedures and results, user APVs, technical information and contact information can be found in LabManager:''' | ||
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Key facts for the different etch baths available at DTU Nanolab are resumed in the table: | Key facts for the different etch baths available at DTU Nanolab are resumed in the table: | ||
<br clear="all" /> | <br clear="all" /> | ||
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*Etch of Silicon in 28 wt% KOH | *Etch of Silicon in 28 wt% KOH | ||
The bath is dedicated | The bath is dedicated wafers with metal or otherwise dirty wafers | ||
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|style="background:LightGrey; color:black"|Link to safety APV and SDS | |style="background:LightGrey; color:black"|Link to safety APV and SDS | ||
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*:[http://kemibrug.dk/KBA/CAS/106882/?show_KBA=1&portaldesign=1 see SDS here] | *:[http://kemibrug.dk/KBA/CAS/106882/?show_KBA=1&portaldesign=1 see SDS here] | ||
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!style="background:silver; color:black" align="center" valign="center | ! rowspan="8" style="background:silver; color:black" align="center" valign="center" |Performance | ||
|style="background:LightGrey; color:black"|Etch rates in crystalline silicon (100) | |style="background:LightGrey; color:black"|Etch rates in crystalline silicon (100) | ||
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*Theoretical values: | *Theoretical values: | ||
*1.2 nm/min (60 °C) | *1.2 nm/min (60 °C) | ||
* | *7.5 nm/min (80 °C) | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
*Theoretical values: | *Theoretical values: | ||
*1.2 nm/min (60 °C) | *1.2 nm/min (60 °C) | ||
* | *7.5 nm/min (80 °C) | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
*Theoretical values: | *Theoretical values: | ||
*1.2 nm/min (60 °C) | *1.2 nm/min (60 °C) | ||
* | *7.5 nm/min (80 °C) | ||
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|style="background:LightGrey; color:black"|Etch rates in other oxides | |style="background:LightGrey; color:black"|Etch rates in other oxides | ||
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*TEOS oxide from furnace: 300nm etched in 11 min | *TEOS oxide from furnace: 300nm etched in 11 min | ||
jemafh@nilt 2019-Marts: | jemafh@nilt 2019-Marts: | ||
*Standard from PECVD3: selectivity 1:100 to Si | *Standard from PECVD3: selectivity 1:100 to Si(100) | ||
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. | . | ||
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|style="background:LightGrey; color:black"|Etch rates in PECVD SiN | |style="background:LightGrey; color:black"|Etch rates in PECVD SiN | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
|style="background:WhiteSmoke; color:black"|See etchrates for PECVD SiN [https://labadviser.nanolab.dtu.dk/index.php?title=Specific_Process_Knowledge/Thin_film_deposition/Deposition_of_Silicon_Nitride/Deposition_of_Silicon_Nitride_using_PECVD/PECVD3:_Low_stress_nitride_testing#DOE_made_to_find_a_good_QC_nitride_recipe_with_low_stress_and_low_KOH_etch_rate_(by_Berit_Herstrøm_@_DTU_Nanolab_2016_Marts) here] | |||
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|style="background:LightGrey; color:black"|Etch rates in LPCVD Si3N4 and SiN | |||
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*Etch rates in LPCVD nitrides is very low. Etch selectivities to Si(100) is higher than 1:10.000 | |||
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*Etch rates in LPCVD nitrides is very low. Etch selectivities to Si(100) is higher than 1:10.000 | |||
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*Etch rates in LPCVD nitrides is very low. Etch selectivities to Si(100) is higher than 1:10.000 | |||
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|style="background:LightGrey; color:black"|Roughness | |style="background:LightGrey; color:black"|Roughness | ||
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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 | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
* | *Mixing ratios giving 28 wt% KOH solutions | ||
KOH:H<sub>2</sub>O - 1000 ml: 1200 ml, when using premixed 50% KOH solution | |||
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|style="background:LightGrey; color:black"|Temperature | |style="background:LightGrey; color:black"|Temperature | ||