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3/23/2014
1
Course: Nanotechnology
Pham Huy Tuan (Ph.D)
MARCH 23, 2014
2
❶ Introduction
❷ Silicon
❸ Optical lithography
❹ Deposition
❺Thermal oxidation, diffusion, ion implantation
Dr. Pha
m Huy
Tuan
3/23/2014
2
Figure. Three cubic-crystal unit cells. (a) Simple cubic. (b) Body-centered cubic. (c) Face-centered cubic.
1. Cubic-crystal unit cells
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Silicon crystal structure
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Dr. Pha
m Huy
Tuan
3/23/2014
3
Simplified schematic drawing of the Czochralski puller. Clockwise (CW), counterclockwise (CCW).
Czochralski crystal growth
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http://www.fullman.com/
Crystal growing
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Dr. Pha
m Huy
Tuan
3/23/2014
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x
y
z
<100> plane
Silicon crystal plane <100>
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x
y
z
<100> plane
<111> plane
x
y
z
<110> plane
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2. Manufacturing process for IC
Mask/Reticle Manufacture
Package & Test Test & Dice
Electronic Grade Polysilicon Single Crystal
Silicon (Boule and Wafers)
Melt Crystal Growth
Pattern (Photolithography)
Film Deposition (CVD, PECVD, etc) Etch
(RIE,Plasma,etc)
Repeat Cycle for Each Layer
Circuit Design Database
Dr. Pha
m Huy
Tuan
3/23/2014
5
9
Other processes after lithography
Etching
Deposition
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❶ Physical Vapor Deposition
❷ Chemical Vapor Deposition
❸ Other Deposition Techniques
Dr. Pha
m Huy
Tuan
3/23/2014
6
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• PVD is the method for metallic thin-film deposition.
• Material is injected from a solid target material and transport in vacuum to the substrate surface.
Physical Vapor Deposition
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• Atoms can be ejected from the target by:
Open source resistive heating Thermal evaporation
Electron beam heating E-beam evaporation
Equilibrium source heating Molecular beam epitaxy
Argon ion bombardment Sputtering
Laser beam bombardment Ablation
Dr. Pha
m Huy
Tuan
3/23/2014
7
Evaporation and Molecular beam epitaxy
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• Heated metals have high vapor pressure and in high vacuum.
• The evaporated atoms will be transported to the substrate.
• There is no bombardment.
• Uniformity is fixed.
• Low melting-point metal (Au, Al, ..) can easily be evaporated.
• Refractory metals require more sophisticated heating methods.
• The molten metal reacts with the crucible (Mo, Ta, W, graphite, BN, SiO2, ZrO2).
Evaporation
Evaporation and Molecular beam epitaxy
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• The source material is heated in an equilibrium source (Knudsen cell).
• An atomic beam exits the cell through an orifice.
• More stable than open sources.
• Compound evaporation is difficult
Molecular beam epitaxy
Dr. Pha
m Huy
Tuan
3/23/2014
8
Sputtering
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• Atoms are ejected from a solid target material due to bombardment of the target by energetic particles like atoms or ions.
• Adhesion to a substrate is high
• The only film deposition method that an alloy film can form
• The high melting point raw materials which are difficult with vacuum deposition method can form a film
• It is easy to control attributions of a film
• A clean film formation method
Sputter system
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Dr. Pha
m Huy
Tuan
3/23/2014
9
Sputter
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Cooling system
Sputtering chamber
Controlling system
Sputter
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Mechanical pump
Dr. Pha
m Huy
Tuan
3/23/2014
10
Sputter
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Diffusion pump
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• The source materials are brought in gas phase into the vicinity of the substrate.
• They decompose and react to deposit film.
• Gaseous by-products are pumped away.
Dr. Pha
m Huy
Tuan
3/23/2014
11
Chemical Vapor Deposition
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• Decomposition of source gas is induced either by
� Temperature (thermal CVD)
� Plasma (Plasma-enhanced CVD, PECVD)
• Thermal CVD: 300 to 900oC
• PECVD: 100 to 400oC.
CVD Variants
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Dr. Pha
m Huy
Tuan
3/23/2014
12
PECVD
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• Wafers are placed on a heated bottom electrode.
• Source gases are introduced from the top, and pumped away around the bottom electrode.
• In thermal CVD, pressure, temperature, flow rate and flow rate ratio are main variables.
• In PECVD, additional variable is RF power.
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Electroless deposition
Electroplating
Spin coating
Sol-gel
Dr. Pha
m Huy
Tuan
3/23/2014
13
Electroplating system
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• Wafer is connected to a cathode in metal-ion containing electrolyte solution.
• Counterelectrode is either passive, like platinum, or made of the metal to be deposited.
• Reduction reaction:
Cu2+ + 2e- � Cu (s), electrolyte solution CuSO4.
Spin coating
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• The main parameters for film thickness control are viscosity, solvent evaporation rate and spin speed control.
(b) Slow rotation of ca. 300rpm.
(c) Acceleration to ca. 5000rpm spreads the liquid towards the edges.
Dr. Pha
m Huy
Tuan
3/23/2014
14
References
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1. Sami Franssila, “Introduction to Micro Fabrication” Wiley, 2004.
2. http://www.memsnet.org/about/fabrication.html
3. http://www.judylab.org/doku.php?id=academics:classes:ee_cm150l:week_0
4. Y.H. L i n and W. Hsu, “Polymer as the protecting passivaton layer in fabricating suspended SCS structures in both,” J. Micromech. Microeng., Vol. 22 (2012), p.045015.
5. Shin, S.J. et al., “Firing frequency improvement of back shooting ink-jet print head by thermal management,” Transducers’03 (2003), p. 380.
Dr. Pha
m Huy
Tuan
5/29/2013
1
CHUANWEI WANG ET AL.,JOURNAL OF MICROMECHANICS AND MICROENGINEERING.
VOL. 17 (2007) 1275-1280
A novel CMOS out-of-plane accelerometer
OUTLINENanotechnology
2
Introduction
Schematic of devices
Sensing principle
Fabrication process
Testing
Conclusions
Dr. Pha
m Huy
Tuan
5/29/2013
2
J. Micromech. Microeng.Nanotechnology
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Introduction• An accelerometer is a device that measures proper
acceleration.• It is the acceleration associated with the phenomenon of
weight experienced by any test mass at rest in the frame of reference of the accelerometer device.
Nanotechnology
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Gap-closing sensing electrodes
Parallel vertical comb sensing electrodes
Dr. Pha
m Huy
Tuan
5/29/2013
3
IntroductionNanotechnology
5
• Accelerometer applications:
Automotive industry.
Cell phone.
Digital still camera (DSC)
Laptops and video games.
Introduction
• Previous accelerometers: sensing circuits and mechanical devices are separated.
• The use of standard CMOS process to fabricate MEMS devices to have the monolithic integration of IC and MEMS components
Nanotechnology
6
Dr. Pha
m Huy
Tuan
5/29/2013
4
CIC CMOS MEMS SCHEMATICNanotechnology
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Schematic of the CMOS accelerometer
• The sensing electrodes attached to
Proof mass act as moving electrodes
Supporting frame act as stationary electrodes.
Nanotechnology
8
Dr. Pha
m Huy
Tuan
5/29/2013
5
Sensing principleNanotechnology
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Gap-closing sensing electrodes
Parallel vertical comb sensing electrodes
Design concept• Critical design
considerations:
Sensing area is increased.
Sub-micron gap of 0.65mm.
Fully differential sensing electrodes.
Nanotechnology
10
Dr. Pha
m Huy
Tuan
5/29/2013
6
Fabrication process steps
After the TSMC 0.35mm 2P4M CMOS process
Nanotechnology
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Metal wet etching for a sub-micron gap
Remove silicon oxide by RIE, M4 is mask.
Release structure by XeF2 isotropic etching
Details of metal wet etchingNanotechnology
12
Dr. Pha
m Huy
Tuan
5/29/2013
7
SEM image of fabricated accelerometer
• The SEM (scanning electron microscopy) photos.
• The reinforced rib is exploited to prevent the sensing electrodes from bending by residual stress.
Nanotechnology
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The test setup
• The shaker and function generator were used to specify a base motion to excite the packaged accelerometer.
Nanotechnology
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Dr. Pha
m Huy
Tuan
5/29/2013
8
Testing resultsNanotechnology
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Output voltage vs. input accelerationNanotechnology
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Dr. Pha
m Huy
Tuan
5/29/2013
9
ConclusionsNanotechnology
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The CMOS accelerometer has been demonstrated using the standard TSMC CMOS-MEMS 2P4M process plus the post-release technique.
A post-CMOS wet-etching process has been established to realize a sub-micron sensing gap.
The present design is ready to integrate with the existing in-plane CMOS accelerometers, a monolithic three-axis CMOS accelerometer can be realized.
Thank you!
Nanotechnology
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Dr. Pha
m Huy
Tuan