C5-2(41-Plasma Etching Part 1)

8/10/2019 C5-2(41-Plasma Etching Part 1)

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Plasma etchingPlasma etching

K - JISTK - JISTMaterials Science & Engineering

Nanophotonic semiconductor Materials Lab.1

Bibliography

1. B. Chapman, Glow discharge processes, (Wiley, New York, 1980).

- Classical plasma processing of etching and sputtering

2. D. M. Manos and D. L. Flamm, Plasma etching; An introduction,

(Academic, Boston, 1989).

- Most helpful textbook for the researcher majoring the dry etching.

3. M. Sugawara, Plasma etching; Fundamentals and applications,

(Oxford Univ. Press, New York, 1998).

- Mostly dedicated to the high density plasma sources such as ICP and ECR

4. W. N. G. Hitchon, Plasma processes for semiconductor fabrication,

(Cambridge Univ. Press, Cambridge, 1999)

- Theoretical approach to the plasma etching and plasma deposition process

5. R. J. Shul and S. J. Pearton, Handbook of advanced plasma processing techniques,

(Springer, Heidelberg, 2000).

- Helpful textbook for the researcher in the field of compound semiconductor process

6. http://newton.hanyang.ac.kr/plasma/

- Dedicated to the plasma physics for graduate student in physics
http://newton.hanyang.ac.kr/plasma/http://newton.hanyang.ac.kr/plasma/


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7. 1. Introduction



Etch

removal of unwanted area during the fabrication of

semiconductor

Etching is the most important step in the fabrication ofsemiconductor devices along with a lithography technique.

InGaN mesa for LED

etched by ICPInP via-hole etched by RIE GaAs laser-facet etched by ICP


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Advantage of plasma etching



Etching can be anisotropic

Less consumption of chemicals; cost, environment impact

Clean process (vacuum)Compatible with automation

Precise pattern transfer

Deep silicon etching for sensor application


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Formation of sheath region



The fast-moving electrons hitthe wall before the ions do andsome stick to the wall.

The wall charges up negativelyand this negative charge pushesother electrons away at thesame time as attracting positiveions.

The field near the wall holds theelectrons away from the walland accelerates the positiveions toward the wall.

High energy ion bombardment

cf) Generally, the voltage drop couldnt be measured. In practice process

engineers usually monitor the dc potential (relative to ground) of the electrode

instead, which is called dc-bias.


7/29K - JISTK - JIST

Materials Science & Engineering


Processes in the sheath region


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7. 4. Mechanism of plasma etching



(a) Physical sputtering - purely

physical process by energetic ion

bombardment

(b) Chemical etching - purely chemical

process by forming volatile by-

product through chemical reaction

between substrate and active

radicals in plasma

(c) Accelerated ion-enhanced etching -

chemical etching + physical

etching: removal of volatile product

is accelerated by energetic ion

bombardment(d) Sidewall-protected (inhibitor driven)

ion-enhanced etching deposition

of etch-resistant layer with ion

bombardment isotropic etching

7. 4. 1. Etch mechanism


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7. 4. 2. Sequential steps in etching



Formation of active etchant byelectron collisions

Transport of active etchant to thewafer surface

Adsorption of etchant to wafer surface Reaction of etchant and wafer to form

etch-product

Desorption of etch-product form the

wafer surface

Acceleration of desorption of etch-product by ion bombardment

Transport of etch-product to the bulk

plasma

Redissociation of etch-product in theplasma or pumped out

Redeposited on the reactor wall or

pumped out

cf) If any of these steps fails to occur,

the overall etch cycle ceases and the step

failed is a rate-limiting step


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7. 4. 3. Radicals in plasma



Radicals are generated through dissociation and ionization

ex) e + O2 O+ + O* + 2e,

e + CF4

CF3+

+ F* + 2eRadicals are much more abundant than ions in plasma because;

(1) They are generated at a higher rate due to;

- lower threshold energy and ionization is often dissociative

(2) Radicals survive longer than ions

Although the concentration of radicals is much larger than that of

positive ions, the reactive fluxes incident on the surfaces can be

comparable, since ions are moving faster because they have

large energy obtained from the electric field in the sheath.


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7. 4. 4. Volatility and evaporation



Volatility of etch-products is a key distinction between plasma

etching and sputtering.

In general, desorption is a rate-limiting steps in the plasma

etching Highly volatile by-product formation is important.

Evaporation rate of material (a) of molecular weight Ma is

proportional to its vapor pressure, pa, (refer to Chap. II)

The evaporation rate is increased with increasing temperature.

However, plasma etching generally done at room temperature.

formation of volatile product at RT is most important.

RTHa

aa

RTH

aaaa

a

eRT

M

C

eCppRT

M

=

=

=

2

1

2

1

2

,2


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Boiling point of etch product (Si and metal)



Etch product Boiling point() Comment

Si

(SiO2, Si

3N

4)

SiH4

-111.6 Gas at RT

SiF4

-95.7 Gas at RT

Si2H

6-15 Gas at RT

SiHCl3

31.7

SiCl4

56.7

Si2OCl6 135.5Si

2Cl

6147

Metal

(Ag, Al, Ti, Au, Co, Cr, Cu, Ni,

Pb, Pt, Ta, W, Zn)

AgCl 1550

AlCl3

182.7 Sublimation

TiCl4

136.45

TiF4

284 Sublimation

Au2Cl3 - Non volatileAu

2Br

3- Non volatile

CoCl2

1050

CrO2Cl

2117

Cr(CO)6

151

CuCl2

655 Non volatile

CuBr2 900 Non volatileNi(CO)

4-25

PbCl2

954

PtF6

69.1

TaF5

229.5

WF6

17 Sublimation

(CH3)2Zn 46ZnCl2

756 Non volatile


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Boiling point of etch product (III-V semiconductor)



Etch product Boiling point() Comment

III-V semiconductor

(GaAs, InP, GaN)

Ga2H

6-63 Gas at RT

GaCl3

201.3

GaCl2

535

GaF3

~ 1000

GaBr3

279

GaI3 < 345(CH

3)

3Ga 55.7

(C2H

5)3In -32 Gas at RT

(CH3)3In 88

InCl3

418 Sublimation

InBr3

371 Sublimation

AsH3 -54.8 Gas at RTAsF

5-52.9 Gas at RT

AsF3

63

AsCl3

130.4

AsBr3

221

PF3

-101 Gas at RT

PH3

-88 Gas at RT

PF5 -75 Gas at RTPCl

562

NCl3

< 71

NF3

-129 Gas at RT

NI3

- Explode

NH3

-33 Gas at RT

N2 -196 Gas at RT(CH3)

3N -33 Gas at RT


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Typical gases used for plasma etching



Feed gas Mechanism Selective to

n type Si

Cl2

Chemical

SiO2

Cl2/C

2F

6Ion-inhibitor

SiCl4

Si

Cl2

Ion-energetic SiO2CCl4/O2

SiCl4/O

2

Al

Sl2/SiCl

4

Ion inhibitor

/energetic

SiO2, some resist,

Si3N4

Cl2/CCl

4

Cl2/CHCl

3

Cl2/BCl

3

III-V semiconductor

Cl2

Chemical

SiO2, resist

Cl2/BCl

3

Ion-inhibitor

Cl2/CH4

Cl2/CCl

4

CCl4/ O

2

SiCl4/O

2

III-V semiconductor

Without Al

Cl2/O

2Chemical Al-containing alloy,

SiO2CF2Cl2 Ion-inhibitor


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7. 5. Dry etch method and reactor type



7.5.1. Dry etch method

Plasma method

(a) Plasma etching (PE)(b) Reactivel ion etching (RIE)

(c) High density plasma etching: Electron cyclotron resonance

etching (ECR) and inductively coupled plasma etching (ICP)

Ion beam method

(a) Ion beam etching (IBE)

(b) Reactive ion beam etching (RIBE)

(c) Chemically-assisted ion beam etching (CAIBE)


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Detailed characteristics of dry etching technique



Parameter PE RIE MERIE ICP ECR IBE

(sputter)

frequency 13.56MHz 13.56MHz 13.56MHz 13.56MHz 2.45GHz -

Pressure

(torr)

0.1 ~ 10 0.01 ~ 0.1 0.010.001

~ 0.01

0.001

~ 0.01

0.001 ~ 0.1

Te (eV) ~ 8 ~ 8 ~ 5 ~ 4 ~ 4

Plasma

density~ 3e8-3 ~ 1e10-3 ~5e10-3 ~5e11-3 ~5e11-3 -

Wafer

location

Grounded

electrode

Powered

electrode

Powered

electrode

Powered

electrode

Powered

electrode

Powered

electrode

Ion voltage25 ~

100 V

250 ~

500 V

400 ~

1000 V

0 ~

1000 V

0 ~

1000 V

500 ~

2000 V

Ion energyNot

Controllable

Not

Controllable

Not

controllableControllable Controllable Controllable

Chemical

reaction

Yes Yes Yes Yes Yes No

Physical

reactionNo Yes Yes Yes Yes Yes

Selectivity Excellent Good Good Good Good Poor

Anisotropy poor Good Good Good Good Excellent


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Comparison of dry etching technique



advantage disadvantage

RIE economicalslow etch rate,

plasma damage

CAIBE

Relatively fast etch

rate low versatility

ECR fast etch ratehigh price,

low scalability

ICP fast etch rate,low plasma damage


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7. 5. 2. Reactor types of dry etch



(a) Plasma etching (PE) and Reactive ion etch (RIE)


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Plasma etching (PE) Same reactor geometry as PECVD system

Low ion bombardment energy due to the low sheath voltagedrop sample was loaded on the grounded electrode (anode)

Mainly chemical reactions and negligible physical etching

Isotropic etch profile

At relatively high pressure: 0.1 ~ 10 TorrReactive ion etch (RIE) Combination of chemical activity of reactive radicals with

physical effects due to high sheath drop sample was loaded

on the powered electrode (cathode) Ion bombardment strongly enhances the chemical process

Anisotropic etch profile due to ion bombardment

Lower operation pressure of 0.01 ~ 0.1 Torr


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(b) Magnetically enhanced reactive ion etching (MERIE)



Reduce the plasma loss on the chamber wall using magnetic field byelectromagnet bucket

Electron collisional efficiency increase by interaction of E and B field

Substrate rotation for uniformity increase


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(d) Inductively coupled plasma



13.56 MHz currents pass through ICP coil

RF magnetic field formation along z axis

Induction of vortex electric field

Electrons oscillation

Increase of electron collision efficiency

More effective plasma generation than

conventional RIE high radical density

Electrostatic shield configuration eliminates

capacitive coupling

Independent ion energy control by table

power

Z


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Types of Inductively coupled plasma



Cylindrical type ICP

Contamination-free geometry

Planar type ICP

Contamination of wafer by

sputtering of window material.


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Laser interferometer on chamber-top

Optical emission spectroscopy throughsidewall window

Electrostatic shield btw quartz and coil

ICP/PECVD cluster tool in K-JIST

Inductively Coupled Plasma in K-JIST


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(e) Ion beam-based reactor



IBE inert gas ion (Ar+) formation in

external RF ion source and extracted

to the reaction chamber by

acceleration electrode (grid).RIBE reactive gas besides inert gas

ions are extracted from the external

source to the reaction chamber. Etch

rate is increased by the additionalchemical reaction

CAIBE inert gas ion (Ar+) are

extracted from the external sourceand the reactive gas are

independently supplied to the wafer

surface through shower-ring just

above the wafer.

C5-2(41-Plasma Etching Part 1)

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