Specific Process Knowledge/Etch/KOH Etch/ProcessInfo: Difference between revisions
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==QC== | ==QC== | ||
===Quality Control (QC) for the KOH Si etching baths.=== | ===Quality Control (QC) for the KOH Si etching baths.=== | ||
'''All links in the table below reguire login to labmanager''' | |||
{| border="1" cellspacing="2" cellpadding="2" colspan="3" | {| border="1" cellspacing="2" cellpadding="2" colspan="3" | ||
|bgcolor="#98FB98" |'''Quality Control (QC) for Si Etch 01, and Si Etch 02''' | |bgcolor="#98FB98" |'''Quality Control (QC) for Si Etch 01, and Si Etch 02''' | ||
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*[http://labmanager.dtu.dk/d4Show.php?id=5476&mach=407 The QC procedure for Si Etch: 03]<br> | *[http://labmanager.dtu.dk/d4Show.php?id=5476&mach=407 The QC procedure for Si Etch: 03]<br> | ||
{| {{table}} | {| {{table}} | ||
| align="center" | | | align="center" | | ||
{| border="1" cellspacing="1" cellpadding="2" align="center" style="width:200px" | {| border="1" cellspacing="1" cellpadding="2" align="center" style="width:200px" | ||
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|Time | |Time | ||
|90 min | |90 min | ||
|- | |- | ||
|Substrate | |Substrate | ||
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<math>X=\frac{(Y\cdot 1000g)}{(1.509g/ml\cdot(0.5-Y))}</math> | <math>X=\frac{(Y\cdot 1000g)}{(1.509g/ml\cdot(0.5-Y))}</math> | ||
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Nanolab has backside protection holders for the two baths KOH 2 and KOH 3 for 4” wafer, and it is possible to mount two wafers in one holder. The material is PEEK, which is suitable for nearly all etchants and you will find the holders by the KOH baths. The recommended space from the wafer edge to your pattern is 7 mm. The thickness of the wafer would typically be 350 μm and the wafer would typically be polished on both sides, however with the right gasket (contact wet chemistry) the holders can accommodate 500-525 μm wafers. In order to avoid differences in pressure between the backside of the wafer and the surrounding environment, the venting tubes should be filled with water. The holder is clamped around the wafers by screws, if these screws are tightened too much or too little, it will affect the etching result. For the KOH 2 bath we have another type of holder which is clamped around the wafer with clamps (it cannot be adjusted to another wafer thickness). | Nanolab has backside protection holders for the two baths KOH 2 and KOH 3 for 4” wafer, and it is possible to mount two wafers in one holder. The material is PEEK, which is suitable for nearly all etchants and you will find the holders by the KOH baths. The recommended space from the wafer edge to your pattern is 7 mm. The thickness of the wafer would typically be 350 μm and the wafer would typically be polished on both sides, however with the right gasket (contact wet chemistry) the holders can accommodate 500-525 μm wafers. In order to avoid differences in pressure between the backside of the wafer and the surrounding environment, the venting tubes should be filled with water. The holder is clamped around the wafers by screws, if these screws are tightened too much or too little, it will affect the etching result. For the KOH 2 bath we have another type of holder which is clamped around the wafer with clamps (it cannot be adjusted to another wafer thickness). | ||
See more specific details about the screwed holders here, the holders we have at Nanolab is the Tandem4 type. | See more specific details about the screwed holders [https://ammt.com/support/files/AMMT_PI_WETandem.pdf here], the holders we have at Nanolab is the Tandem4 type. | ||
==Theory== | ==Theory== | ||
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Due to the almost inert (111)-planes it is possible by KOH etching to realize high aspect ratio structures in sigle crytalline silicon using the (111)-planes as sidewalls. In Si(100) these sidewalls are inclined - 54.7<sup>o</sup> with respect to the (100) surface - whereas in Si(110) the sidewalls are vertical (see figures below). | Due to the almost inert (111)-planes it is possible by KOH etching to realize high aspect ratio structures in sigle crytalline silicon using the (111)-planes as sidewalls. In Si(100) these sidewalls are inclined - 54.7<sup>o</sup> with respect to the (100) surface - whereas in Si(110) the sidewalls are vertical (see figures below). | ||
<gallery caption="Anisotropic wet silicon etch: dependency on crystal orientation" widths=" | <gallery caption="Anisotropic wet silicon etch: dependency on crystal orientation" widths="760px" heights="150px" perrow="1"> | ||
Image:KOH_Anisotropy.jpg|Etched profile when etching Si(100). | |||
Image:KOH_Anisotropy(110).jpg|Etched profile when etching Si(110). | Image:KOH-etch.JPG|Etched profile when etching Si(100) and when etching Si(110) respectively | ||
<!-- Image:KOH_Anisotropy.jpg|Etched profile when etching Si(100).--> | |||
<!-- Image:KOH_Anisotropy(110).jpg|Etched profile when etching Si(110).--> | |||
</gallery> | </gallery> | ||
<br clear="all"/> | <br clear="all"/> | ||
For Si(100), the relation between the width of the bottom of the etched groove (W<sub>b</sub>) and the width of the opening (W<sub>o</sub>) at the wafer surface in a groove etched to the depth | For Si(100), the relation between the width of the bottom of the etched groove (W<sub>b</sub>) and the width of the opening (W<sub>o</sub>) at the wafer surface in a groove etched to the depth d is given by: | ||
<math>W_b = W_o - 2d cot(54.7^o) = W_o - \sqrt{2} d</math> | |||
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===Definition of <110> alignment structures=== | ===Definition of <110> alignment structures=== | ||
The etch rate dependence on the crystallographic planes can be used to determine the <110> crystal directions with high precision (better than +/- 0.05 <sup>o</sup>). A fast method for doing this, using the symmetric under- | The etch rate dependence on the crystallographic planes can be used to determine the <110> crystal directions with high precision (better than +/- 0.05 <sup>o</sup>). A fast method for doing this, using the symmetric under-cutting behavior around but not at the <110>-directions, was described by [https://iopscience.iop.org/article/10.1088/0960-1317/6/2/011/meta Mattias Vangbo and Ylva Bäcklund 1996 J. Micromech. Microeng. '''6''', 279-284]. High-precision control of the <110>-direction during alignment can be necessary in order to control the dimensions of KOH-etched structures (e.g. precise control of V-groove dimensions). | ||
<br clear="all" /> | <br clear="all" /> | ||
===Etch rates: Empirical formula (Seidl et al)=== | <!-- ===Etch rates: Empirical formula (Seidl et al)=== | ||
The following empirical formula can be used for concentrations in the range of 10-60 wt%: | The following empirical formula can be used for concentrations in the range of 10-60 wt%: | ||
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where k<sub>0</sub> = 2480 µm/hr (mol/l)<sup>-4.25</sup>, E<sub>a</sub> = 0.595 eV for Si(100) | where k<sub>0</sub> = 2480 µm/hr (mol/l)<sup>-4.25</sup>, E<sub>a</sub> = 0.595 eV for Si(100) | ||
and k<sub>0</sub> = 4500 µm/hr (mol/l)<sup>-4.25</sup>, E<sub>a</sub> = 0.60 eV for Si(110) | and k<sub>0</sub> = 4500 µm/hr (mol/l)<sup>-4.25</sup>, E<sub>a</sub> = 0.60 eV for Si(110) --> | ||