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====Procces flow description====
'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/LabAdviser/Technology_Research/Fabrication_of_Hyperbolic_Metamaterials_using_Atomic_Layer_Deposition/AZO_gratings click here]'''
 
<i>This page is written by <b>Evgeniy Shkondin @DTU Nanolab</b> if nothing else is stated. <br>
All images and photos on this page belongs to <b>DTU Nanolab</b> and <b>DTU Electro</b> (previous DTU Fotonik).<br></i>
 
 
=Fabrication of Hyperbolic Metamaterials by ALD: AZO Gratings=
 
The fabrication and characterization described below were conducted in <b>2013-2016 by Evgeniy Shkondin, DTU Nanolab</b>.<br>
 
== Procces flow description ==


=====Si template fabrication=====
=====Si template fabrication=====
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=====Atomic Layer Deposition=====
=====Atomic Layer Deposition=====
The AZO coatings were made in a thermal, hot-wall ALD system (Picosun R200). The precursors were obtained from Strem Chemicals. ZnO was deposited using diethylzinc (Zn (C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>, DEZ) and deionized water (H<sub>2</sub>O), whereas Al doping of the ZnO was introduced by a single cycle of trimethylaluminium (Al(CH<sub>3</sub>)<sub>3</sub>, TMA) and H<sub>2</sub>O into a ZnO matrix made by 20 cycles of “DEZ +H<sub>2</sub>O”. This defines an AZO macrocycle: 20 cycles of “DEZ+H<sub>2</sub>O” and one cycle of “TMA+H<sub>2</sub>O”. The deposition temperature was kept constant at 200°C. Approximately 55 AZO macrocycles need to be deposited in order to fill the Si trench template entirely.
The AZO coatings were made in a thermal, hot-wall ALD system (Picosun R200). The precursors were obtained from Strem Chemicals. ZnO was deposited using diethylzinc (Zn (C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>, DEZ) and deionized water (H<sub>2</sub>O), whereas Al doping of the ZnO was introduced by a single cycle of trimethylaluminium (Al(CH<sub>3</sub>)<sub>3</sub>, TMA) and H<sub>2</sub>O into a ZnO matrix made by 20 cycles of “DEZ +H<sub>2</sub>O”. This defines an AZO macrocycle: 20 cycles of “DEZ+H<sub>2</sub>O” and one cycle of “TMA+H<sub>2</sub>O”. The deposition temperature was kept constant at 200°C. Approximately, 55 AZO macrocycles need to be deposited in order to fill the Si trench template entirely.


=====Top layer removal and selective etch of the Si template=====
=====Top layer removal and selective etch of the Si template=====
In order to get rid of the deposited top layer of AZO and to gain access to the Si template core, a pure physical etching with Ar<sub>+</sub> ions (Ionfab 300 plus from Oxford Instruments) was used. Here, the process was tuned to an etch rate of 20 nm/min which provided a well-controlled top layer breakthrough. Following this, the subsequent selective silicon etching (template removal) proceeded using a continuous isotropic etch in a reactive ion etching tool (RIE, from SPTS) based on SF<sub>6</sub> at a substrate temperature of 20°C. The SF<sub>6</sub> gas flow was kept constant at 35 sccm at a process pressure of 80 mTorr. The coil power was set to 30W. This process proceeds with an extreme selectivity towards the deposited AZO without any observable harm on the prepared AZO grating structure. Controlling the etch time is crucial, since prolongation of the etching will result in a collapse of the AZO gratings. 18 min of Si etching was required to fabricate a free standing, separated AZO grating with a minimal amount of the Si core between the AZO lamellas needed to support the grating skeleton.  
In order to get rid of the deposited top layer of AZO and to gain access to the Si template core, a pure physical etching with Ar<sup>+</sup> ions (Ionfab 300 plus from Oxford Instruments) was used. Here, the process was tuned to an etch rate of 20 nm/min which provided a well-controlled top layer breakthrough. Following this, the subsequent selective silicon etching (template removal) proceeded using a continuous isotropic etch in a reactive ion etching tool (RIE, from SPTS) based on SF<sub>6</sub> at a substrate temperature of 20°C. The SF<sub>6</sub> gas flow was kept constant at 35 sccm at a process pressure of 80 mTorr. The coil power was set to 30W. This process proceeds with an extreme selectivity towards the deposited AZO without any observable harm on the prepared AZO grating structure. Controlling the etch time is crucial, since prolongation of the etching will result in a collapse of the AZO gratings. 18 min of Si etching was required to fabricate a free standing, separated AZO grating with a minimal amount of the Si core between the AZO lamellas needed to support the grating skeleton.  




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|-
|-
!1.1
!1.1
|Plasma surface treatment
|Plasma surface treatment.
|To ensure clean surface, the 100 mm Si wafer is treated by O<sub>2</sub>/N<sub>2</sub> plasma. (Optional step)
|To ensure clean surface, the 100 mm Si wafer is treated by O<sub>2</sub>/N<sub>2</sub> plasma. (Optional step)
|
|
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|- style="background:#BCD4E6; color:black"
|- style="background:#BCD4E6; color:black"
!1.2
!1.2
|DUV Resist patterning
|DUV Resist patterning.
|DUV
|DUV
|[[Specific_Process_Knowledge/Lithography/DUVStepperLithography|DUV Stepper Lithography]].  
|[[Specific_Process_Knowledge/Lithography/DUVStepperLithography|DUV Stepper Lithography]].  
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|-
|-
!1.3
!1.3
|Deep reactive ion etching (DRIE)
|Deep reactive ion etching (DRIE).
|DRIE; [[Specific_Process_Knowledge/Etch/DRIE-Pegasus/DUVetch|Recipe: PolySOI10]] Recipe needs to be tuned. Adjusted parameters: temperature, etching and passivation times.
|DRIE; [[Specific_Process_Knowledge/Etch/DRIE-Pegasus/DUVetch|Recipe: PolySOI10]] Recipe needs to be tuned. Adjusted parameters: temperature, etching and passivation times.
| [[Specific_Process_Knowledge/Etch/DRIE-Pegasus|DRIE Pegasus]].
| [[Specific_Process_Knowledge/Etch/DRIE-Pegasus|DRIE Pegasus]].
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|- style="background:#BCD4E6; color:black"
|- style="background:#BCD4E6; color:black"
!1.4
!1.4
|Plasma surface treatment
|Plasma surface treatment.
|To ensure that remainings of DUV resist are gone, samples are treated by O<sub>2</sub>/N<sub>2</sub> plasma. (Optional step)
|To ensure that remainings of DUV resist are gone, samples are treated by O<sub>2</sub>/N<sub>2</sub> plasma. (Optional step)
|
|
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|-
|-
!1.5
!1.5
|Scanning Electron Microscopy inspection  
|Scanning Electron Microscopy inspection.
|By cleaving the sample it is possible to inspect DRIE etched Si trenches in cross-sectional mode
|By cleaving the sample it is possible to inspect DRIE etched Si trenches in cross-sectional mode.
|
|
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
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|- style="background:#BCD4E6; color:black"
|- style="background:#BCD4E6; color:black"
!1.6
!1.6
|Atomic Layer Deposition of Al-doped ZnO (AZO)
|Atomic Layer Deposition of Al-doped ZnO (AZO).
|Deposition carried at 200<sup>o</sup>C. Thickness is above 100 nm.
|Deposition carried at 200<sup>o</sup>C. Thickness is above 100 nm.
||Equipment used: [[Specific_Process_Knowledge/Thin_film_deposition/ALD_Picosun_R200|ALD Picosun R200]]. Standard recipe used: [[Specific_Process_Knowledge/Thin_film_deposition/ALD_Picosun_R200/AZO_deposition_using_ALD| AZO 20T]].
||Equipment used: [[Specific_Process_Knowledge/Thin_film_deposition/ALD_Picosun_R200|ALD Picosun R200]]. Standard recipe used: [[Specific_Process_Knowledge/Thin_film_deposition/ALD_Picosun_R200/AZO_deposition_using_ALD| AZO 20T]].
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|-
|-
!1.7
!1.7
|Scanning Electron Microscopy inspection
|Scanning Electron Microscopy inspection.
|By cleaving the sample it is possible to inspect ALD coatings deposited on Si trenches in cross-sectional mode
|By cleaving the sample it is possible to inspect ALD coatings deposited on Si trenches in cross-sectional mode.
|
|
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
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|-
|-
!1.9
!1.9
|Scanning Electron Microscopy inspection
|Scanning Electron Microscopy inspection.
|By cleaving the sample it is possible to inspect IBE etching results in cross-sectional mode
|By cleaving the sample it is possible to inspect IBE etching results in cross-sectional mode.
|
|
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
[[Specific_Process_Knowledge/Characterization/SEM_Supra_1|SEM Supra 1]]  
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