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}} | ||
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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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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-cutting behavior around but not at the <110>-directions, was described by Vangbo and Bäcklund | 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) --> | ||