Xing Sheng, EE@Tsinghua Principles of Micro-and ... ---- Etching… · Xing Sheng, EE@Tsinghua 1 Xing Sheng盛兴 Department of Electronic Engineering Tsinghua University [email protected]

Xing Sheng, EE@Tsinghua

1

Xing Sheng盛兴

Department of Electronic EngineeringTsinghua University

[email protected]

Etching 刻蚀

Principles of Micro- and Nanofabrication for Electronic and Photonic Devices


Pattern Formation

3


Etching vs. Corrosion

4

Etching (刻蚀) Corrosion (腐蚀)

wanted unwanted


Wet vs. Dry

5

liquid source gas source


Chemical vs. Physical

6


Etching

7

Process Parameters Time

Temperature

Etchant type

Etchant concentration

Mask type

...

Control Parameters Etch rate

Selectivity

Anisotropy

Uniformity

...

diffusion - reaction - diffusion

- chemical reactions occur- products should be disposable


Selectivity

8

1 2 1 2 2

112

R

RS


SiO2 / Si wet etch by HF solution very large selectivity SSiO2/Si ~ infinity

SiO2 / Si dry etch by CF4 plasma selectivity SSiO2/Si ~ 10

Selectivity - Example

9

SiO2

Si


Anisotropy (各向异性)

10

vertical

lateral

R

RA 1degree of anisotropy

isotropicA = 0

fully anisotropicA = 1

anisotropic0 < A < 1


11

Isotropic vs. Anisotropic

chemical physical


Uniformity

12


13

Trends of Etching


Etching Methods

14

Wet Etching 湿法刻蚀

Dry Etching 干法刻蚀

CMP and other methods


References

15

Wet Etching Recipes

Guide to references on III-V semiconductor chemical etching

http://ieeexplore.ieee.org/iel4/84/11954/00546406.pdfhttp://ieeexplore.ieee.org/iel4/84/11954/01257354.pdf

http://www.sciencedirect.com/science/article/pii/S0927796X00000279

https://cleanroom.byu.edu/chemical_etching.html


Metal Dissolution in Acids

16

hydrogen

easy

hard


17

Metal Dissolution in Acids

Strong Acids + Strong Oxidants

Aqua Regia (王水) HCl : HNO3 = 3:1even dissolves Au, Pt

Piranha H2SO4 : H2O2 = 3:1dissolves most metals and organics

However, difficult to obtain ideal selectivity ...


18

SiO2 etching

Alkali (NaOH, etc) slowly etches SiO2

SiO2 + 2NaOH = Na2SiO3 + H2O

HF strongly etches SiO2

SiO2 + 6HF = H2SiF6 + 2H2O

Buffered HF (BHF/BOE) HF + NH4F

lower etch rate

safer for use

glass art by HF etch


19

Cu etching

Cu + 2FeCl3 = CuCl2 + 2FeCl2


20

Selectivity for Wet Etch

mask

mask SiO2KOH + K3[Fe(CN)6]

GaP

PRFeCl3Cu

PRKI + I2Au

PRH3PO4 + H2O2

GaAs

Si3N4

PR

MaskEtchantFilms

KOHSi

HFSiO2

most wet etch recipes are isotropic, except KOH etch for Si


Isotropy for Wet Etch

21

isotropicA = 0

Wet etch is usually isotropic

Exceptions some etching for single crystals

KOH etch Si


22

Si etching

HNO3 + HF isotropic etch


23

Si etching

KOH anisotropic etch

etch rate (111):(110):(100) ~ 1:600:400

mask: SiO2, Si3N4, Cr/Au, ...

Other chemistries TMAH: Tetramethyl ammonium hydroxide

EDP: Ethylene diamine pyrochatecol

Q: why?


24

Si etching

Single Crystalline Si Solar Cells KOH anisotropic etch

optical trapping and antireflection

world record efficiency: 26%


25

Si etching

Si cantilever beam KOH anisotropic etch


26

Si etching

Micro-Electro-Mechanical Systems (MEMS)


27

III-V etching

GaAs, AlGaAs, InGaAs H3PO4 + H2O2

NH4OH + H2O2

AlGaAs when Al > 70%, HF and HCl etch

InP, InGaP, InAlP HCl

GaN, InGaN no reliable wet etchants ...


28

Etch Stops

InGaP / GaAs lattice matched epitaxy

H3PO4 + H2O2 only etches GaAs

HCl only etches InGaP


29

Etch Stops

highly p-dope Si is resistant to KOH


30

Etch Stops

Silicon based 'Michigan Probe' for neuroscience


31

Electrochemical Etch


32

Anodization (阳极氧化) - Porous Si


33

Anodization - Porous Al2O3

H. Masuda and K. Fukuda, Science 268, 1466 (1995)


Thin-Film Si from SOI wafers

34H. C. Ho, et al., Nature 454, 748 (2008)

human eyes compound eyes

Y. M. Song, et al., Nature 497, 95 (2013)

'epidermal' electronics

D. Kim, et al., Science 333, 838 (2011)


Thin-Film Si from Si (111)

35J. Yoon, et al., Nature Mater. 7, 907 (2008)

KOH etches faster for Si (100) than (111)

Thin-film Si solar cells

High efficiency (Single Crystal)

Flexible

Low cost (wafer reuse)


GaN on Si (111)

36H. Kim, et al., Proc. Natl. Acad. Sci. 108, 10023 (2011)

KOH etches faster for Si (100) than (111)


GaAs and AlAs lattice matched growth

AlAs is selectively etched by HF

flexible III-V devices

GaAs Device Liftoff

37S. I. Park, et al., Science 325, 977 (2009)J. Yoon, et al., Nature 465, 329 (2010)

solar cells LED


Epitaxy Liftoff

38

NH4OH wet etch

KOH wet etch

HCl wet etch

FeCl3 wet etch

HCl wet etch

HF / HCl wet etch

HF wet etch

HF wet etch

KOH wet etch

HF wet etch

Release methods

sapphireZnOGaN

InPInGaAsInGaAs / InP

SiSiO2SiC

Si (111)-GaN

SiSiO2Ge

GaAsAlAsGaAs / InGaP

GaSb

GaAs

Si (111)

Si

SubstratesSacrificial layersMaterials

InAlPGaAs / InGaP

InGaSbInAs

-Si (111)

SiO2Si

H. Xu, et al., Adv. Mater. 30, 1800156 (2018)


Bio-degradable Materials

39

Materials that can be dissolved in the body.

Biodegradable Suture Cardiovascular Stent Bone Scaffold

Biocompatible and Degradable Materials Organic: PLGA, PLA, silk, ...

Metals: Mg, Ca, Zn, Fe, ...

Semiconductors: Si, Ge, ...


Bio-degradable Electronics

40

Si devices that can be dissolved by body fluids.

S. Hwang, et al., Science 337, 1640 (2012) Video


Etching Methods

41





Challenges for Wet Etching

42

Most wet etching processes are chemical, isotropic

For features < 3 m, dry etching has much better resolution


Dry Etching

43

plasma etch


2XeF2 (g) + Si (g) = 2Xe (g) + SiF4 (g) very isotropic and selective

Dry Etch without Plasma

44

SiF4 boiling point 4 oC


Heavy ions (e.g. Ar)

Highly anisotropic

Poor selectivity for Au, Pt, ...

Ion Milling

45


Heavy ions (e.g. Ar)

Highly anisotropic

Poor selectivity

Ion Milling

46


Chemically reactive ions improved selectivity

lower power

Example: Si etch CF4 gas does not react with Si

energized F- plasma can react with Si

SiF4 is volatile (boiling point 4 oC)

Very isotropic no direction

Plasma Etch

47Si


Improved directionality by applied fields more anisotropic

Reactive Ion Etching (RIE)

48


Si SF6 plasma

SiO2

CF4 / CHF3 plasma

Photoresists can be used as masks F ions etch PR very slowly

RIE - Si and SiO2

49


Si SF6 plasma

SiO2

CF4 / CHF3 plasma

Photoresists can be used as masks F ions etch PR very slowly

RIE - Si and SiO2

50

SF6 is heavier than air


O2 plasma C-H-O + O- = CO2 + H2O

O2 plasma does not etch Si, SiO2, or metals SiO2 / metal oxides are non-volatile

RIE - Organics

51


Cl2 / BCl3 / SiCl4 plasma GaAs/AlGaAs, InP, GaN/InGaN, ...

RIE - III-Vs

52

130AsCl3

200GaCl3

180AlCl3

> 1000lnF3

boiling point (oC)product

> 1000AlF3

1000GaF3

Q: why?

GaAs trenches


RIE - Recipes

53


Inductively Coupled Plasma (ICP) higher power

mostly for III-Vs

ICP-RIE

54


alternative etch / passivation

Deep RIE for Si

55

'Bosch process'


Atomic Layer Etching (ALE)

56

1. Si + 2Cl2 = SiCl42. SiCl4 removed by plasma3. Repeat 1 and 2

K. J. Kanarik, et al., J. Vac. Sci. Tech. A 33, 020802 (2015)


Issues in Dry Etch

57


Summary of Dry Etch

58


Etching Methods

59





Pattern Formation

60


Planar Layers are Desirable

61non-planarized IC planarized IC


62

Issues with Depth of Focus (DOF)

smaller , larger NA ----> smaller DOF

depth of focus(DOF)


Damascene Process

63P. C. Andricacos, et al., IBM J. Res. Develop. 42, 567 (1998)

Cu

SiO2

ancient art work


CMP: Chemical Mechanical Polishing

64

Chemical selectivity + Mechanical Planarization

applied for Cu, W, SiO2, ...

Video


3D IC

65

Electroplating + CMPdirtiest process for the most advanced IC


Other Methods for Etching

66

Laser Lift-Off

FIB: Focused Ion Beam

Laser Milling

...


GaN devices grown on sapphire low cost

low thermal conductivity

electrically insulating

sapphire is very difficult to etch

Release by laser liftoff KrF excimer UV laser (248 nm)

GaN = Ga + N2 (gas)

bonding onto new substrates

GaN Laser Liftoff

67W. S. Wong, et al., Appl. Phys. Lett. 72, 599 (1998)


Flexible GaN blue LEDs

68T. Kim, et al., Science 340, 211 (2003)


69

FIB: Focused Ion Beam

Etch: GaDeposition: Pt

- nanostructures- SEM/TEM sample

preparation- doping


Types

CO2 laser 10 m

Near-IR laser 1064 nm

UV laser 365 nm

Excimer laser 248 nm, 193 nm

ps/fs laser ...

Applications die cut, PCB cut, ...

Laser Milling

70

shorter wavelengthshorter pulse

better resolution

Documents

Xing Sheng, EE@Tsinghua Principles of Micro-and ... ---- Etching… · Xing Sheng, EE@Tsinghua 1 Xing Sheng盛兴 Department of Electronic Engineering Tsinghua University [email protected]