LabAdviser/Technology Research/Fabrication of Hyperbolic Metamaterials using Atomic Layer Deposition/TiO2 Q plates: Difference between revisions

A 500 μm thick wafer of silica (SiO₂) goes through RCA clean and low-pressure chemical vapor deposition (LPCVD) (furnace from Tempress) based on SiH₄ (silane) at 560^◦C to form a layer of 300 nm of amorphous silicon (Si) [Fig. 1]. The back side of deposited Si was etched using KOH wet etch. In order to remove residues from the etching process, it was performed oxygen plasma cleaning. A CSAR resist was spin-coated to the thickness of 150 nm, followed by exposure of Electron Beam Lithography (EBL) (JEOL JBX-9500 Electron-beam) generating a mask with concentric ring patterns. After development, the wafer was submitted to advanced silicon etch (ASE). To form the trenches of the TiO₂ structures, a thin film of TiO₂ was deposited using the ALD technique in a hot-wall system (Picosun R200), working with 2000 cycles at 150^◦C [Fig.1]. The precursors used were titanium tetrachloride (TiCl₄) and H₂O (supplied by Strem Chemicals Equipment). The process was followed by Ar⁺ ion beam etching (IBE) on both sides of the wafer to remove excess of ALD deposited material. At the top most TiO₂ layer the physical sputtering of the sample using Ar⁺ ions was performed in order to get access to Si core. On the backside, the Ar⁺ ions were used to remove the deposited TiO₂. Finally, we performed a reactive ion etch on silicon, leaving only the TiO₂ structures. The final system comprehends a base of SiO₂ with nano-structures of TiO₂ on it. Figure 2 shows the image of the system taken using scanning electron microscope (SEM) and conventional optical microscope. Figure 3 illustrates SEM cross-sectional image of the prepared Q-plate .

image:Q_plates_fab_sheme_new.jpg| Figure 1. Scheme of fabrication flow.

image:TiO2nanorings.jpg| Figure 2. TiO₂ concentric nanorings acting as a Q-plate. Insets show optical and SEM images of the whole plate.

image:Q_plates_cross_section.jpg| Figure 3. Cross-sectional SEM image of the TiO₂ Q-plate. a) The low magnification image shows the whole plate b) High magnification allows to inspect individual rings cross-sections.

Description of steps for fabrication of Q-plates.

|RCA clean.

|Before Si deposition in LPCVD furnace, the quartz (fused silica) wafers need to be cleaned

|[[Specific_Process_Knowledge/Wafer_cleaning/RCA| RCA]]

|[[image:Zero1.jpg|250x350px|center|]]

|Low-Pressure Chemical Vapour Deposition (LPCVD) of Si.

|LPCVD deposition of 300 nm amorphous Si

|[[Specific_Process_Knowledge/Thin_film_deposition/Furnace_LPCVD_PolySilicon| 6" LPCVD polysilicon furnace (E2)]].  

|[[image:Zero2.jpg|250x350px|center|]]

|Si anisotropic wet etch.

|Removal of the Si from the back side of the wafer.

| [[Specific_Process_Knowledge/Etch/KOH_Etch|KOH]].

|[[image:Image1_Si_on_SiO2.jpg|250x350px|center|]]

|Plasma surface treatment.

|To ensure that all organic remainings are gone, wafer is treated by O₂/N₂ plasma. (Optional step)

|

[[Specific_Process_Knowledge/Lithography/Strip#Plasma_Asher_2| Plasma Asher 2]]

|E-Beam Lithography (EBL).

|Spin-coating of CSAR resist to the thickness of 150 nm, followed by e-beam exposure.

[[Specific_Process_Knowledge/Lithography/EBeamLithography/JEOL_9500_User_Guide|JEOL JBX-9500 Electron-beam]]  

|[[image:Image2_ebeam_on_Si.jpg|250x350px|center]]

|Advanced Silicon Etching.

|Creating sacrificial silicon template.

|

[[Specific_Process_Knowledge/Etch/ASE_(Advanced_Silicon_Etch)|ASE]]  

<br clear="all" />

|[[image:Image3_ASE_of_SI.jpg|250x350px|center]]

|Scanning Electron Microscopy inspection.

|The fabricated template inspects by SEM

|[[image:Si_template_q_plates.jpg|250x350px|center]]  

|Plasma surface treatment.

|To ensure that all organic remainings are gone, template is treated by O₂/N₂ plasma. (Optional step)

|

[[Specific_Process_Knowledge/Lithography/Strip#Plasma_Asher_2| Plasma Asher 2]]

<br clear="all" />

[[Specific_Process_Knowledge/Lithography/Strip#Plasma_asher| Plasma Asher 1]]

|

 

 

 

 

|Scanning Electron Microscopy inspection.

|SEM inspection of ALD deposition and IBE etching.

|[[image:top_removal_q_plates.jpg|250x350px|center]]  

!1.12

|Selective etch of Si between ALD TiO₂ coatings. (Reactive Ion Etching)

|Si etching proceeds using Reactive Ion Etching (RIE) with isotropic process based on SF₆ process gas.

||Equipment used: [[Specific_Process_Knowledge/Etch/RIE_(Reactive_Ion_Etch)|RIE2]].  

|[[image:Image6_ALD_Final_structure.jpg|250x350px|center]]

!1.13

|Scanning Electron Microscopy inspection.

|[[image:Si_removal_q_plates.jpg|250x350px|center]]