metal-assisted chemical etching -...
TRANSCRIPT
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Metal-assisted Chemical Etching
(MacEtch)
Wet etch, Dry etch, and now MacEtch
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Outline
• What is MacEtch?
• Background and Mechanism
• Characteristics
• Device applications
• Inverse MacEtch (I-MacEtch)
• Magnetic-field MacEtch (h-MacEtch)
• Summary
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isotropic - • most wet etches are isotropic
i.e. they etch equally in all directions
• isotropic etches result in undercutting
for an isotropic etch, radius = depth
Wet Etchhttp://fabweb.ece.illinois.edu
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rate determining steps - diffusion of reactants to the surface
reaction rate at the surface
desorption of reaction products
reaction equation mA + nB reaction products
reaction rate
RT
Enm
A
eBAkr
material removed
Wet Etchhttp://fabweb.ece.illinois.edu
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Dry Etch
• Goal: – enhance anisotropy
• without losing selectivity
• without causing damage
• maintain controllable etch rate
• Mechanism:– Chemical:
• plasma etch - small degree of anisotropy
– Physical: • sputtering, directional but no selectivity
• Techniques:
https://www.crystec.com/trietche.htm
http://fabweb.ece.illinois.edu
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Dry Etching Issues
charging
++++
undercutting
sidewall residue
trenching
mask erosion
Surface damage
`
http://fabweb.ece.illinois.edu
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SiSi
• Process Flow
– Pattern metal
– Immerse in HF/H2O2
– Etching takes
place underneath
the metal
• Contrast with
– wet vs dry etch
– bottom-up growth
MacEtch: wet etch but directional
Metal-Assisted Chemical Etching (MacEtch)
Scalable, high throughput, low cost
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Metal-Assisted Chemical Etching (MacEtch)
Metal
• not stationary
• not a mask
• not consumed
Not limited to Au
• X. Li and P. W. Bohn, APL, 77, 2572 (2000).
• Patents: 4 issued and 3 pending
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MacEtch mechanism
– Mechanism: metal is a catalyst
– Rate determining step: charge or mass transport
– Simplicity: no bias, no high energy ions, no light
Local electrochemical reactions:
“Metal-assisted chemical etching in HF/H2O2 produces porous silicon", X. Li and
P.W. Bohn, Appl. Phys. Lett.77, 2572 (2000).
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CHARACTERISTICS
MacEtch
“Metal-assisted chemical etching of silicon: a review,” Huang Z, Geyer N,
Werner P, de Boor J, Gosele U. Adv Mater 2011; 23(2):285–308.
“Metal Assisted Chemical Etching for High Aspect Ratio Nanostructures: A
Review of Characteristics and Applications in Photovoltaics,” X. Li, Current
Opinion in Solid State & Materials Science, invited review article, 16, 71-81
(2012).
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Extremely High Aspect Ratio Si nanowire array: 550 nm diameter, 51 m height
produced by Au-MacEtch in 20 mins
Nanotechnology, 23, 305304 (2012).
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Scalability
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MacEtch of poly and amorphous
Jpn. J. Appl. Phys. 53, 02BE09 (2014)
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Metal Pattern Formation and resolution
MacEtch has been realized using metal
catalyst formed by the following techniques
• Electroless plating (e.g. from AgNO3 solution)
• Colloidal nanoparticles
• Optical lithography
• Electron beam lithography
• Nanoimprint/soft lithography
• Superionic solid state stamping
• Nanosphere lithography
• High aspect ratio shadow mask
• Tip-based lithography (AFM, STM)
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Applicability to different
semiconductors
• Si
• Ge
• GaAs
• InGaAs
• AlGaAs
• InP
• GaN
1 µm
GaAs p-i-n Pillar Array by MacEtch
Heterojunctions and p-n junctions
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Sidewall morphology
• No high energy ion induced sidewall
damage
• Sidewall smoothness is determined
entirely by the edge roughness of the
metal pattern
• No porosity in the pillars if the MacEtch
condition is tuned as a function of
semiconductor doping level
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3D patterns formed by MacEtch
1 µm
a) b)
by periodic variation of etchant concentration
DeJarld et al. Nano Lett. 11, 5259 (2011).
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Magnetic-Field Guidance (h-MacEtch)
• Use Au/Fe/Au Tri-Layer catalyst
• Guidance
• Programmability
• a – c: Increasing External magnetic field guidance
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Inverse MacEtch: InP
• Metal edge roughness no longer limits sidewall smoothness
• Limited aspect ratio (height/width) because of the inverse nature
“Inverse Metal-Assisted Chemical Etching Produces Smooth High Aspect Ratio InP Nanostructures,” S. H. Kim, P. K. Mohseni, Y. Song, T. Ishihara, and X. Li, Nano Lett. 15 (1), pp 641–648 (2015).
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Examples of semiconductor
nanostructures produced by MacEtch
d) e) f)Sub-15 nm InP Fins
100/1 aspect ratio Si NWs n-GaAs pillars
f)Curvy-linear Si Holey Si from SOI
GaAs p-i-n pillars
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MacEtch vs wet and dry etch
Wet Etch Dry Etch MacEtch
Directionality Isotropic Anisotropic Anisotropic
Aspect Ratio Low Medium High
Ion Induced Damage None Mild to Severe None
Crystal-Orientation
Dependence
Some Weak Weak
Etch Rate Fast Slow Fast
Sidewall Smoothness Smooth Not Smooth Smooth or Rough
Chemical Selectivity Good Poor Depends
Cost Low High Low
“Metal Assisted Chemical Etching for High Aspect Ratio Nanostructures: A
Review of Characteristics and Applications in Photovoltaics,” X. Li, Current
Opinion in Solid State & Materials Science, 16, 71-81 (2012).
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APPLICATIONS
MacEtch
• Solar cells
• LEDs
• Photonic Crystals
• Thermoelectrics
• Transistors
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GaAs p-i-n Pillar Based LED by MacEtch
“III-As pillar array-based light emitting diodes fabricated by metal-assisted chemical etching,”
P. K. Mohseni, S. H. Kim, X. Zhao, K. Balasundaram, J. D. Kim, L. Pan, J. A. Rogers, J. J. Coleman, and X. Li,
J. Appl. Phys. 114, 064909 (2013).
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GaAs p-i-n Pillar Based LED by MacEtchGaAs p-i-n Pillar Based LED by MacEtch
Mohseni et al. Appl. Phys. 114, 064909 (2013).
• Pillar showed stronger emission at all injection levels
• Enhancement is stronger at higher I
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MacEtched Si NW PV cell
Shin et al. IEEE J. Photovoltaics, 2, 129 (2012).
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Efficiency limited by surface area
Shin et al. IEEE J. Photovoltaics, 2, 129 (2012).
It is all about the surfaces!
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MacEtched Ph.C. Reflectors
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I-MacEtch of InP
• Aspect ratio > 40:1
• MOSFETs – excellent offstateperformance
Song et al. unpublished.
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Publications on MacEtch from Illinois
• “Inverse Metal-Assisted Chemical Etching Produces Smooth High Aspect Ratio InP Nanostructures,” S. H. Kim, P. K. Mohseni, Y. Song, T.
Ishihara, and X. Li, Nano Lett. 15 (1), pp 641–648 (2015).
• “Fabrication of Arbitrarily-Shaped Silicon and Silicon Oxide Nanostructures Using Tip-based Nanofabrication,” Huan Hu, Parsian K.
Mohseni, Lei Pan, Xiuling Li, Suhas Somnath, Jonathan Felts, Mark A Shannon, and William P. King, J. Vac. Sci. Tech. B, 31(6), 06FJ01
(2013).
• ''Photonic crystal membrane reflectors by magnetic field-guided metal-assisted chemical etching,' K. Balasundaram, P. K. Mohseni, Y-C
Shuai, D. Zhao, W. Zhou, and X. Li, Appl. Phys. Lett, 103, 214103 (2013).
• ''GaAs pillar array-based light emitting diode fabricated by metal-assisted chemical etching'', J. Appl. Phys, 114, 064909 (2013).
• "Silicon nanowires with controlled sidewall profile and roughness fabricated by thin-film dewetting and metal-assisted chemical etching,
"Bruno Azeredo, Jyothi Sadhu, Jun Ma, Kyle Jacobs, Junhwan Kim, KunHyuck Lee and James Eraker, Xiuling Li, Sanjiv Sinha, Nicholas
Fang, Placid Ferreira and Keng Hsu, Nanotechnology, 24, 225305 (2013).
• “Sub-100 nm Si nanowire and nano-sheet array formation by MacEtch using a non-lithographic InAs Nanowire Mask,” Jae Cheol Shin,
Chen Zhang and Xiuling Li, Nanotechnology, 23, 305305 (2012).
• “Porosity control in metal assisted chemical etching of degenerately doped silicon,” Karthik Balasundaram, Jyothi S. Sadhu, Jae Cheol
Shin, Bruno Azeredo, Debashis Chanda, Mohammad Malik, Keng Hsu, John A. Rogers, Placid Ferreira, Sanjiv Sinha, and Xiuling Li.,
Nanotechnology, 23, 305304 (2012).
• “Metal Assisted Chemical Etching for High Aspect Ratio Nanostructures: A Review of Characteristics and Applications in Photovoltaics,” X.
Li, Current Opinion in Solid State & Materials Science, invited review article, 16, 71-81 (2012).
• “Experimental Study of Design Parameters in Periodic Silicon Micropillar Array Solar Cells Produced by Soft Lithography and Metal
Assisted Chemical Etching,” J.C. Shin, D. Chanda, W. Chern, K.J. Yu, J.A. Rogers, and X. Li, IEEE J. Photovoltaics, 2, 129-133 (2012).
• “Formation of High Aspect Ratio GaAs Nanostructures with Metal Assisted Chemical Etching,” M. T. DeJarld, J. C. Shin, W. Chern, D.
Chanda, K. Balasundaram, J. A. Rogers, and X. Li, Nano Lett., 11, 5259-5263 (2011).
• “Nonlithographic Patterning and Metal-Assisted Chemical Etching for Manufacturing of Tunable Light-Emitting Silicon Nanowire Arrays,” W.
Chern, K. Xu, I. Chun, B. P. de Azeredo, N. Ahmed, K-H. Kim, J. Zuo, N. Fang, P. Ferreira, and X. Li, Nano Lett. 10 (5), pp 1582–1588
(2010).
• "Nanoscale three dimensional pattern formation in light emitting porous silicon," I.S. Chun, E. Chow, and X. Li, Appl. Phys. Lett. 92, 191113
(2008).
• "In-plane Bandgap Control in Porous GaN through Electroless Wet Chemical Etching," X. Li, Y.-W. Kim, P. W. Bohn, and I. Adesida, Appl.
Phys. Lett., 80 980-982 (2002).
• “Metal-assisted chemical etching in HF/H2O2 produces porous silicon", X. Li and P.W. Bohn, Appl. Phys. Lett.77, 2572 (2000).
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MacEtch Patent Portfolio
• TF00067 metal-assisted chemical etching to produce porous
silicon US 6790785
• TF00154 metal assisted chemical etch to produce group III-V
porous material and porous silicon US 6762134
• TF08145 method of forming nanoscale three-dimensional
patterns in a porous material US 8486843
• TF09098 method of forming an array of high aspect ratio
semiconductor nanostructures US2013/0052762
• TF11074 metal assisted chemical etching to produce III-V
semiconductor nanostructures US2013/0280908
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MacEtch: metal-assisted chemical etching
Defying text definition of wet etch, MacEtch is an anisotropic wet etching method that could potentially replace, improve dry etch for various electronics, photonics, and energy applications.
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Current group members:
• Dr. Parsian Mohseni
• Kevin Bassett
• Chen Zhang
• Jeong Dong Kim
• Kyooho Jung
• Yi Song
• Karthik Balasunderam
• Paul Froeter
• Wen Huang
• Kelson Chabak
• Ryan Kim
• Xiang Zhao
• Wonsik Choi
• Moyang Li
• Clarence Chan
Funding sources
• NSF ECCS
• NSF DMR
• DARPA
• DOE
• INTEL etc.
• ONR YIP
• I2CNER
Acknowledgement
Collaborators
http://mocvd.ece.illinois.edu
• P. Braun, J. J. Coleman, P. Ferreira, M.
Gillette, S. Gong, L. Lee, J. Lyding, J. A.
Rogers, P. Ye, K. J. Hsia, W. King, E. Pop,
J. Schutt-Aine, S. Sinha, D. Cahill, D. Ruzic,
J. Williams, W. Wilson, J. ZuoFormer group members:
• Dr. Ik Su Chun, Dr. Ryan Dowdy, Dr. Xin Miao, Dr. Jae Cheol Shin, Dr. Xin Yu, Lei Pan, Matt
Dejarld, Seth Fortuna, Winston Chern, Archana Challa, Mohammad Malik, Aiyin Liu