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

3

Silicon crystal structure

4

Dr. Pha

m Huy

Tuan

3/23/2014

3

Simplified schematic drawing of the Czochralski puller. Clockwise (CW), counterclockwise (CCW).

Czochralski crystal growth

5

http://www.fullman.com/

Crystal growing

6

Dr. Pha

m Huy

Tuan

3/23/2014

4

x

y

z

<100> plane

Silicon crystal plane <100>

7

x

y

z

<100> plane

<111> plane

x

y

z

<110> plane

8

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

10

❶ Physical Vapor Deposition

❷ Chemical Vapor Deposition

❸ Other Deposition Techniques

Dr. Pha

m Huy

Tuan

3/23/2014

6

11

• 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

12

• 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

13

• 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

14

• 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

15

• 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

16

Dr. Pha

m Huy

Tuan

3/23/2014

9

Sputter

17

Cooling system

Sputtering chamber

Controlling system

Sputter

18

Mechanical pump

Dr. Pha

m Huy

Tuan

3/23/2014

10

Sputter

19

Diffusion pump

20

• 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

21

• 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

22

Dr. Pha

m Huy

Tuan

3/23/2014

12

PECVD

23

• 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.

24

Electroless deposition

Electroplating

Spin coating

Sol-gel

Dr. Pha

m Huy

Tuan

3/23/2014

13

Electroplating system

25

• 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

26

• 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

27

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

3

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

4

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

7

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

9

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

11

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

13

The test setup

• The shaker and function generator were used to specify a base motion to excite the packaged accelerometer.

Nanotechnology

14

Dr. Pha

m Huy

Tuan

5/29/2013

8

Testing resultsNanotechnology

15

Output voltage vs. input accelerationNanotechnology

16

Dr. Pha

m Huy

Tuan

5/29/2013

9

ConclusionsNanotechnology

17

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

18

Dr. Pha

m Huy

Tuan