lecture 16 pvd

7/27/2019 Lecture 16 PVD

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Copyright A.J. StecklJ.C. Heikenfeld

All rights reserved2007

Lecture 16

Physical Vapor Deposition I

Definition for Physical Vapor Deposition (PVD)

-molecules are removed from a source, transported in vacuum, anddeposited on substrate (physi-sorption)

- in contrast chemical vapor deposition (CVD) involves chemical reaction

- need vacuum: the pressure usually < 10-2 Torr. (760 Torr = 1 atm)

At 1 atm : P = 760Torr Lm=

5 103

760 6.6 10

6cm 66nm

At 1 mTorr : Lm=

5 103

103

= 5cm

At 10-5Torr : L

m=

5 103

105

= 500cm = 5 meters!

Lmcm( ) =

5 103

P,

P = Pressure in Torr

Need vacuum in order to:

- prevent incorporation of background molecules (oxygen, etc.)

- minimize intermolecular collision (mean free path, Lm) so that moleculescombine only when they reach the substrate

moleculeor atom

source

d < Lm substrate


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Lecture 16

Physical Vapor Deposition I

How is low pressure achieved?

1 atm = 760 Torr.

Mechanical pump (~10-3 Torr)

TurboMolecular Pump (~10-6 Torr)

Cryogenic Pump (~10-9 Torr)

>50,000 rpm!

liquid He cooled

down to ~ 10K!


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Lecture 16PVD Techniques

A.Evaporation

- evaporation (from solid) or sublimation (solid)

- material held in a boat or crucible

- heat: direct electric current through resistor

indirect high current e-beam

local heating by e-beam less contamination

B.Molecular Beam Epitaxy (MBE)

- specially designed effusion cell (thermal evap)

- can also use plasma and low-pressure gases

- deposit material with atomic control (layer-by-layer)

C.Plasma-Assisted Deposition

- DC or RF sputtering

reactive sputtering

magnetron sputtering


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Lecture 16Vapor Pressure

Fig. 12-1 Vapor pressure curves for selected materials.

W

Ta

MoNi

Cr

Au

Melting Pt.

typical requiredvapor pressure

Al

use

evaporation

usesputtering


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Lecture 16Thermal Evaporation

Crucible Basket Coated Boat

Conical BasketCoils

Note angulardependence ofevaporated material fromvarious sources

/s

90 1800

material material

0

90

180

substratebad designnon-uniform film better approach


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Lecture 16e-Beam Evaporation

Bent Beam Approaches:Bent Beam Approaches:

-no back-deposition from crucible to e-gun minimize contamination

- also more compact

Indirectly Heated:Indirectly Heated:local heating by electron beam less contamination

- e-beam current (usually in hundred mA), electron energy ~1-3 keV

InlineInline ApproachApproach

Target material


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Lecture 16Molecular Beam Epitaxy

Fig. 12-6

A basic MBE

deposition system.

Dinger [13].

Molecular beam epitaxy (MBE) uses evaporation but

- low pressure (


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Lecture 16MBE Systems

Veeco MBE Systems

thermally isolatedeffusion cell

(allow high temperature)

Crucibles - conical evap. profile

production: 4x4 wafersR&D machine


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Lecture 16Sputter Deposition

Physical bombardment of heavy and inert atoms (Ar) causes atoms or

molecules at target to be removed

example:RFsputtering Ar Ar+ e-

substrate

target

chamberwall

~

C

1) RF voltage creates a plasma ofAr+ and e-

2) target:plasma capacitance has less

area that wall:plasma capacitance

3) therefore plasma (voltage drop)

occurs near the target

~10 mTorr

substrate

target

chamberwall

~

C

4) e- smaller mass than Ar+ move quicklyenough in RF (MHz) field to reach the target

5) these electrons build up -DC voltage on

target (~100s V)

6) negative voltage causes Ar+ acceleration

toward target and sputtering of material

deposited material


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Lecture 16Sputter Deposition Equipment

3 sputtertargets

RF matching network

Loadlock

power/controls


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Lecture 16Sputtering Techniques

(A) Sputter Deposition Ar gas: easy to achieve plasma (i.e. breakdown) & high mass (~40

AMU)

DC or RF power can generate plasma

DC only for conductive target, RF for both conductive & insulatingtargets

Efficient: no major differences for conductive target material

(B) Reactive Sputtering

If compound or alloy not available, it can be formed by chemical reaction

Examples: Si target + reactive gas N* (N2) Si3N4

(C) Planar Magnetron Sputtering (electron cyclotron)

Permanent magnet increases the plasma density

100 to 500 gauss

High deposition rate (> sputtering or evaporation)


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Lecture 16Sputtering Techniques

N

S

N

S

N

S

N

S

S

N

S

N

S

N

material

e-

e-

magnetic field increases path length for electron- increased ionization of ArAr++ e-

-increasedflux of Ar+and sputter rate


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Lecture 16

Calendar

Dec. 7Dec. 6

Final Exam

8:00AM

Dec. 5

WEEK

Dec. 4

FINALS

Dec. 3

Nov. 29

Q & A

899 Rhodes Hall

Nov. 27

Physical VaporDeposition

Lecture 16

Nov. 22

No School

Thanksgiving

Nov. 20

Lithography/

Resist

Lecture 15

Nov. 15

Etching

Lecture 14

Nov. 13

QUIZ #2

Nov. 8

Ion Implantation:Dose/Damage

Lecture 13

Nov. 6

Ion Implantation:Mechanisms

Lecture 12

Nov. 1

Diffusion:

npn BJT

Lecture 11

Oct. 30

Diffusion in Si

Lecture 10

FRIDAYTHURSDAYWEDNESDAYTUESDAYMONDAY

lecture 16 pvd

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