8:30 – 9:00 Research and Educational Objectives / Spanos

9:00 – 9:50 Plasma, Diffusion / 9:00 – 9:50 Plasma, Diffusion / Graves, Lieberman, Cheung, HallerGraves, Lieberman, Cheung, Haller

9:50 – 10:10 break10:10 – 11:00 Lithography / Spanos, Neureuther, Bokor 11:00 – 11:50 Sensors & Metrology / Aydil, Poolla, Smith, Dunn

12:00 – 1:00 lunch 1:00 – 1:50 CMP / Dornfeld, Talbot, Spanos

1:50 – 2:40 Integration and Control / Poolla, Spanos

2:40 – 4:30 Poster Session and Discussion, 411, 611, 651 Soda 3:30 – 4:30 Steering Committee Meeting in room 373 Soda 4:30 – 5:30 Feedback Session

3rd Annual SFR Workshop, November 8, 2000

11/08/2000

2

UC SMART Major Program AwardD. Graves, E. Haller, M. Lieberman, and N. Cheung

SFR Workshop11/8/00

Plasma and Diffusion Studies

11/08/2000

3

Outline

• Plasma-Surface Interactions and Modeling (Graves)• Diffusion in Isotopically Controlled Silicon (Haller)• Plasma Sources for SFR (Lieberman)• Plasma-Assisted Surface Modification: Low

Temperature Bonding and Layer Transfer (Cheung)

11/08/2000

4

Plasma-Surface Interactions and Plasma Modeling

David Graves, Frank Greer, Dave Humbird, John Coburn, and Dave Fraser

University of California Berkeley

SFR WorkshopNovember 8, 2000

Berkeley, CA

11/08/2000

5

Radical Enhanced Atomic Layer Chemical Vapor Deposition

(REALCVD)

Frank Greer, John Coburn, David Fraser, David Graves

SFR WorkshopNovember 8, 2000

11/08/2000

6

What is A.L.D.?• Atomic Layer Deposition

– A.K.A. – Sequential Deposition, Digital Deposition, …

– Usually a two step process• Chemisorption of a metallic precursor

• Reactive ligand stripping by reactive stable molecule

– Distinguishing feature Each step is self-limiting

– Film thickness controlled by number of cycles

M

~1 mL of M-Lx

~1 mL of M-Y

L

L

L

L

YS

S

S

S

L SL S

11/08/2000

7

Likely A.L.D. Applications

• High-k Gate Dielectrics– Highly uniform deposition

– Atomic layer control of interface

• Nitride Diffusion Barriers– Highly conformal deposition

• Theoretically 100% step coverage

11/08/2000

8

 

 

Barrier Layer Deposition by A.L.D.

Key Issues:Barrier Properties

ConductivityConformality

Thermal budget**

Current barrier/seed films deposited via i-PVDchallenged by high aspect ratios

Nitride diffusionbarrier

Low k ILD

11/08/2000

9

Radical Enhanced Atomic Layer CVD (REAL CVD)1

• Uses a volatile precursor and a radical

source to deposit a film

• Reactants introduced in separate steps to

achieve atomic layer control

• Products are nitride film and HCl

• Radical flux instead of heated substrate

catalyzes precursor decomposition

– Potentially lower processing temperatures

1A. Sherman U.S. Patent 1999.

Wafer

Heated (?) Pedestal

Precursor/RadicalInlet

Step 2: TiClx (ab) + XH*(g) + N*

(g) TiN (s) + HCl(g)

Step 1: TiCl4 (g)

11/08/2000

10

Surface Reaction Products

Atom Source

Schematic of the Beam Apparatus in Cross-section (Top View)

Quadrupole MassSpectrometer (QMS)

Main Chamber

Analysis SectionRotatable Carousel

+Experimental Diagnostics1. QCM - Measures mass change of film2. QMS

- Measures products formed on film- Characterize beams

Silicon-coatedQuartz Crystal

Microbalance (QCM)

Ion Source+

Chopper

X

TiCl4

Precursor Doser

X = O, N , D

Load Lock

Future in-vacuo Auger

Analysis

11/08/2000

11

Experimental Procedure

• Conventional ALD-like sequence– Each step in process monitored in-situ with QCM

– Cycle used multiple times to grow a film • Surface temp varied (32, 80, 135 oC)

TiCl4

~1 mL of TiClx

1. Adsorption

2. Pump down

D

~1 mL of Ti-Dx

3. Dechlorination

4. Pump down

5. Nitridation

N

~1 mL of Ti-Nx

11/08/2000

12

0

2E+14

4E+14

6E+14

8E+14

1E+15

1.2E+15

0 5000 10000 15000 20000

Precursor Adsorption QCM Results

• Two distinct uptake regimes– Initial rapid ads. followed by

significantly slower ads.

• Adsorption may not be confined to a single monolayer

• Data fairly well represented by assuming precursor adsorbs two monolayers of TiCl2 *

• Model fit allows estimation of:– Sticking probabilities

– Active site (*) densities*

TiClx

*

* Suntola, T. et al. 1996

Uptake Upon Exposure to TiCl4

TiC

l 2 M

olec

ules

/cm

2

TiCl4 Exposure (L)

TiCl4

Adsorption

1 L = 1015 Molecules

11/08/2000

13

Adsorption Model Results

• initial sticking ~ 100x self sticking– contributes to uniformity

• self sticking decreases with inc. T– coverage is more monolayer-like at higher

temperatures

TiCl4

5x10146x10-58x10-3135

5x10149x10-58x10-380

5x10141x10-48x10-332

Site Density (#/cm2)

s(TiClx)

self

sticking

s(TiN)

initial

sticking

Temperature

(oC)

0

2E+14

4E+14

6E+14

8E+14

1E+15

1.2E+15

0 2000 4000 6000 8000 10000

Exposure (L)

TiC

l2 m

ole

cule

s/cm

2 Raw Adsorption DataModel Fit to Data

11/08/2000

14

0.00E+00

4.00E+14

8.00E+14

1.20E+15

1.60E+15

2.00E+15

0 2000 4000 6000 8000 10000 12000

Raw DataModel Fit

Dechlorination Results

• Cl loss due to abstraction by D atoms• ex-situ XPS analysis shows ave. Cl conc. = 2.2% (0.6%-3.8%)*

D

Cl

Cl Lost Upon Exposure to DeuteriumQCM

Dechlorination

• Exponential decay in Cl/cm2

fit assuming replacement of Cl

with D

• kD+ClDCl = 3x10-4

• Fairly insensitive to T

• Calculated removed Cl

density within a few% of ads.

assumptions

• Suggests TiCl2 is appropriate

surface species

Cl A

tom

s/cm

2

D atom Exposure (L) * Process not optimized for chlorine removal

11/08/2000

15

0

2E+15

4E+15

6E+15

8E+15

1E+16

0 500 1000 1500

Raw DataModel Fit

Nitrogenation ResultsN

D

Uptake Upon Exposure to N atoms

QCM

Nitrogenation

N A

tom

s/cm

2

Nitrogen Atom Exposure (L)

• Nitrogen uptake does not

saturate!

• ex-situ XPS shows N/Ti > 3

• Initial uptake of nitrogen fit to

linear model

• sN = 8x10-3

• fairly insensitive to T

• uptake slows over time

suggesting diffusional

limitations into the film

11/08/2000

16

Summary and Implications

1. TiCl4 has two adsorption regimes at these temperatures:• Initial rapid uptake

(s1=8x10-3)• Slower continuing uptake

(s2~8x10-5)• Change likely coincides

with 1st monolayer coverage

2. D atoms remove Cl from surface:

= 3 x10-4

• ex-situ XPS shows not all Cl removed from surface

Summary of Results• Cl content of films

– TiCl4 overexposure

– Insufficient D exposure

0

2E+14

4E+14

6E+14

8E+14

1E+15

1.2E+15

0 5000 10000

Exposure (L)

TiC

l2 m

ole

cule

s/cm

2

Raw Adsorption DataModel Fit to Data

11/08/2000

17

Summary and Implications

3. N atoms react with surfaceInitial Reaction

Probability:s = 8x10-3

• Rate slows over time, but does not stop

• Likely becomes diffusion limited

Summary of Results

H N

• Low rxn. probabilities for all species• Correct comparison for processing is rate of transport of radicals to feature bottom with rate of

reaction on feature sides• Transport rate > Reaction rate for aspect ratio ~ 5

– uniform rxn. rates throughoutfeatures

• As aspect ratio increases, transport rate will slow– could lead to non-uniform deposition

11/08/2000

18

Milestones

• 2001

– Design and test precursor doser, conduct preliminary film deposition studies

– Test self-limiting film formation kinetics

• 2002

– study effects of surface type, preparation and temperature on film properties

– measure radical-surface kinetics

• 2003

– apply method for patterned barrier film application

– Explore DRAM capacitor applications

11/08/2000

19

Damage Profiles of Low-Energy Ion Bombardment:

Application to Ion Milling

Dave Humbird, David GravesSFR Workshop

November 8, 2000Berkeley, CA

11/08/2000

20

Motivation

• Theory suggests that ion energy deposition is closely related to surface roughening and rippling: possible LER impact

• MD studies show energy deposited by low-energy (eg. 200 eV) ion impact is localized to a very narrow region near the surface

• Motivates question: how small a feature can be etched or milled by very tightly focused ion beam?

11/08/2000

21

Molecular Dynamics (MD) Simulation

Interatomic Potential Interatomic Forces

rjk

typical MD time step:

initialconfiguration

update positions

update velocities

evaluateforces• Simulation is non-

equilibrium!

• Kinetic + potential energy is always conserved

11/08/2000

22

Ion-Induced Displacement Simulations• Simulation cell size is 20 x 20 x 20 ų

(512 atoms)

• Introduce energetic Ar with velocity normal to surface

• Follow motion of all Si atoms until collision cascade subsides

• Repeat x 2000 for statistics

• Formulate a distribution (in r and z, relative to the point of impact) of atoms’ displacements 1

Expense: 100 impacts = 40 min (PIII-700)

1 in the spirit of Winterbon, Sigmund, and Sanders, Mat. Fys. Medd. Dan. Vid. Selsk. 37 (14) (1970)

11/08/2000

23

Ion Energy Deposition (Displacement) ProfileAtomic Displacement Distribution

200 eV Ar Impacts, Normal Incidence• Si atoms are displaced from their

origins by a distance proportional to the color temperature. (red → ~6 Å, blue → 0 Å)

ion trajectory

Relative coordinate system:

Ar

r

z

projected pointof impact

vacuumsolid

axisymmetric

20Å

11/08/2000

24

Ion “Milling” Simulation

• Simulation cell is substantially larger (60 x 60 x 40 ų, 9200 atoms)

• Introduce energetic Ar ion above surface, confined to a “beam” of radius 12 Å about the center

• Follow collision cascade

• Delete sputtered Si atoms

• Cool cell to room temperature

• Accumulate impacts on the same cell

Expense: 100 impacts = 20 hours (PIII-700)

11/08/2000

25

Feature EvolutionRepresentations of the surface after 330 impacts (200 eV Ar, normal incidence)

Stereograph top view

Tissue-paper plot

• side view, +y direction25 Å

11/08/2000

26

Milestones2001 Milestone

Write and test MD code to study energy deposition profiles. Conduct preliminary sputtering studies. Compare to

phenomenological theory.

2002 Milestone

Write and test code to study ion-induced surface diffusion. Compare results to phenomenological theory and experiment.

2003 Milestone

Simulate energy deposition and surface diffusion andcompare to LER experiments.

11/08/2000

27

Diffusion in Isotopically Controlled Silicon

Eugene E. Haller

University of California at Berkeley

and

Lawrence Berkeley National Laboratory

SFR-UCB SMART, November 8, 2000

11/08/2000

28

Collaborators

• C. B. Nelson, GSRA in MSE Dept., UCB

• Dr. H. Bracht, Univ. of Münster, Germany

• Dr. S. Burden, ISONICS Corp., Golden, CO

11/08/2000

29

Diffusion, Native Defects and Impurities

– Major experimental observation: Substitutional

impurities diffuse assisted by native defects

– The major native defects are vacancies and self-

interstitials in monatomic crystals

– Many native defects exist in more than one charge state:

Fermi level effects

11/08/2000

30

11/08/2000

31

Dopant and Self-Diffusion in Crystalline Solids

interstitialcy- vacancy - Exchange (ring) mechanism

I V

DSD = VCVeqDV + ICI

eqDI + Dex

11/08/2000

32

Self-Diffusion in Crystalline Solids

• Self-diffusion studied with radioactive isotopes:

– often limited by low activity and short half-life of the radiotracer (e.g. T1/2 of 31Si is 2.6 hrs)

– deposition alters the near-surface crystal quality of the material under study

– special safety requirements

• Self-diffusion studied with stable isotopes:

– at least two stable isotopes must exist (28Si, 29Si, 30Si)

– growth of epitaxial layers by VPE or MBE

– self-diffusion can be observed at several buried interfaces

11/08/2000

33

Isotope Heterostructures

The Isotope Superlattice

1017

1018

1019

1020

1021

1022

0 0.2 0.4 0.6 0.8 1 1.2 1.4

natSi -28Si-Superlattice: as-grown

30S

i-C

ON

CE

NT

RA

TIO

N (

cm-3

)

DEPTH (microns)

28Si

30Si

11/08/2000

34

Undoped Silicon Isotope Heterostructure

1017

1021

1019

1018

1020

1022

Con

cen

trat

ion

(cm

-3)

29Si

30Si

Depth (micron)

1 20 3 4 5 6

11/08/2000

35

Self-Diffusion in Pure Silicon

1017

1018

1019

1020

1021

1022

4 63 5

1322C; 30 min

1045C; 12 d

x (m)

30S

i con

cent

rati

on (

cm-3

)

Profiles:

H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett 81 (1998) 393

as-grown

11/08/2000

36

Self-Diffusion in Pure Silicon

10-19

10-17

10-15

10-13

10-11

0.6 0.7 0.8 0.9

1400 1200 1000 800

103/T (K

-1)

DS

i (cm

2 s-1)

T (oC)

Temperature dependence:

120 scm530

eV75.4

D

Q

H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett 81 (1998) 393

11/08/2000

37

Thermodynamic Properties

defect H f+H m S f+S m H f S f H m S m

I 4.95 eV 13.2 k 3.2 to 3.5 4 to 6 (1.4 to 1.8) (7 to 9)

V 4.24 eV 6.6 k 2.0 to 4.0 1 to 16 (0.2 to 2.2) (-9 to 6)

exp exp ,,,,,,

kT

HH

k

SSDC

mVI

fVI

mVI

fVI

VIeq

VI

• I-related data consistent with theoretical results

• reliable data for V are still lacking (controversy: low T high T)

Results:

Transport coefficients:

11/08/2000

38

Boron and Si Self-Diffusion

• Boron diffusion mechanism

• Considering charge states:

and

IS BIB

IBB SI0

hIBB SI 00

11/08/2000

39

Boron and Si Self-Diffusion• Boron and Si self-diffusion are coupled via the Si

interstitial population

• System of four coupled differential equations has to be solved numerically

kf,b = forward/backward rate constants

.0

0

0

0

0

0

0

2

2

x

CD

xt

C

CCkCCkx

p

p

C

x

C

xD

t

C

CCkCCkx

CD

t

C

CCkCCkt

C

SiSi

Si

IBboBfII

II

IBboBfB

B

B

IBboBfB

si

si

I

I

I

sI

S

11/08/2000

40

Boron and Si Self-Diffusion

• Modification of the Si self-diffusion coefficient through the presence of B

• Extraction of as function of the temperature and EF

• Determination of donor level position of I0/+

• In case CI ~ Cboron, compensation of boron acceptors will accrue, allowing the determination of CI

oeqVVV

eqV

eqIII

eqII CCCDCfCCDCfSiD V /]//[

IeqI DC

11/08/2000

41

Boron and Si Self-Diffusion

B in Si Superlattice Simulation

1.0E+17

1.0E+18

1.0E+19

1.0E+20

1.0E+21

1.0E+22

0 400 800 1200 1600

Depth (nm)

Co

nc

en

tra

tio

n (

cm

-3)

30Si

BAs-Grown

11/08/2000

42

Conclusions and Outlook

• Boron doped Si isotope heterostructures hold promise for the first determination of the interstitial transport coefficient CIVI as a function of EF and temperature.

• In case CI ~ CB , we can determine CI

• Accurate knowledge of CIVI is crucial for modeling B diffusion

• Analogous experiments will be conducted with P. High P concentrations will induce the formation of vacancies

11/08/2000

43

SFR WorkshopNovember 8, 2000

Berkeley, CAM. A. Lieberman, A. J. Lichtenberg, A. M. Marakhtanov,

K. Takechi, and P. Chabert Berkeley, CA

Plasma Sources for Small Feature Reproducibility

11/08/2000

44

Milestones• September 30, 2001 - Etch resist in LAPS to examine uniformity. - Characterize instability using OES/actinometry and planar probe.

- Install the Z-scan sensor and explore the spectral RF signature of plasma instabilities.

• September 30, 2002 - Characterize plasma instability using V-I-phase probe. - Model for reduced electron temperature and density.

• September 30, 2003 - Develop and test instabilities control. Reduce electron

temperature and density in discharges.

11/08/2000 Y. Moon, K. Bevans, and D. A. Dornfeld

Experimental LAPS Setup

A

Xm(0.5uH)

X1

X2

Rs

Vrf

Plasma

900 pF(fixed)

12-1000 pF

12-500 pF

Bm1

Voltage sensorD

C B

Bm2

Antenna coil embedded in the plasma

Eight quartz tubes threaded by copper

antenna tubes

36.0 cm x 46.5 cm processing area

New series-parallel

system configuration

11/08/2000

46

Oxygen Discharge Model

0exp8

1

2

2

k iz

kO

a

izii

rRn

D

Knn

r1 r2 r8…..

Substrate holder metal

Side metal

Calculation area

RQuartz-5

5

-15 15 (cm)

B.C. Vn=0

Chamber geometry used in the model

(Center of the chamber)(cm)

222

OidissOO nnKnD

Particle balance :

Power balance :

walls iTabs dSEeP iecT EEEE

11/08/2000

47

0 5 10 15 20 25 3010

13

1014

1015

1016

Pabs

=500 W

O2 gas pressure

1 mTorr 5 mTorr 20 mTorr 50 mTorr 100 mTorr

Flu

x of

ions

inci

dent

on

subs

trat

e ho

lder

(cm

-2s-1

)

Distance from the center (cm)

Ion flux profiles at substrate surface for various gas pressures (simulation results)

11/08/2000

48

Photoresist Etch Model

O

ref

biasiref

BpkVk

jAkRE

1)(

1

..

1

E.R. : Etch rateji : Ion current density at substrate surfacepO : O-atom pressure at substrate surfacekref : Ion-induced desorption rate constant at

Vbias= 0 V

1 10 1000

50

100

150

200

Data (500 W) Fit (500 W) Data (1000 W) Fit (1000 W) Data (1500 W) Fit (1500 W)

Etc

h R

ate

(nm

/min

)

Gas Pressure (mTorr)

Plots of etch rate vs.

pressure for various rf

powers. The fits are from

the above equation

with simulation results.

11/08/2000

49

Etch rate profiles at a gas pressure of 5 mTorr at Vbias= 0 V and Vbias= -80 V

-30 -20 -10 0 10 20 30

100

40

200

5 mTorr, Vbias=0 V 5 mTorr, Vbias=0 V 5 mTorr, Vbias=-80 V 5 mTorr, Vbias=-80 V

Etc

h R

ate

(nm

/min

)

Vertical Position (cm)

Applying a Vbias leads to

increase in both etch rate

and uniformity over the

processing area.

Effect of applying a substrate bias on

etch rate and uniformity

11/08/2000 Y. Moon, K. Bevans, and D. A. Dornfeld

Experimental TCP Setup

Mass Spectrometer

PlasmaPlasmaInductive CoilInductive Coil

Langmuir ProbeLangmuir ProbeOES (PMT)OES (PMT)

30

cm

19 cm

Planar Probe

Monochromator

11/08/2000

51

Instability Windows

0 20 40 60 80 1000

200

400

600

800

SF6/Ar (1:1)

Pressure (mTorr)

0 20 40 60 80 1000

200

400

600

800

INSTABILITY

Pure SF6

Pressure (mTorr)

Po

we

r (W

)

• Unstable in most of discharge conditions used in etching

• Instability linked to average attachment rate

Capacitive

Capacitive

Inductive

11/08/2000

52

Effect of Matching Network

0,0 0,4 0,8 1,2 1,6 2,00,0

0,2

0,4

0,6

0,8

Lig

ht in

ten

sity

(a.u

.)

time (ms)

• In Ar/SF6 discharges the frequency depends on the settings of the matching

network

Ar / SF6 (1:1)

p = 5 mTorr

Prf = 500 W

f1 = 1.0 kHz

f2 = 8.5 kHz

SETTING 1 (LOW FREQ.) SETTING 2 (HIGH FREQ.)

11/08/2000

53

Determination of time varying densities from planar and cylindrical probes currents

The negative ion fraction a can be deduced from the saturation current ratio:

en

n fI

VIR

sat

p

time (ms)

, where

Ar / SF6 (1:1)

p = 5 mTorr

Prf = 550 W

f = 0.8 kHz

11/08/2000

54

Results in (1:1) Ar/SF6 discharge

Ar / SF6 (1:1)

p = 5 mTorr

Prf = 500 W

f = 0.8 kHz

• The electron density changes by a factor of 20 with fast rise and decay times

• Positive and negative ion densities decay at the same rate

11/08/2000

55

Results in pure SF6 discharge

SF6

p = 5 mTorr

Prf = 500 W

f = 12.9 kHz

5

400

• The electron density exhibit sharp peaks; the ion density is slightly modulated

• The discharge spends a long time in low-density regime with 400

11/08/2000

56

Future Work

• Modeling silane deposition processes in LAPS

• Modeling reduced electron temperature and density processing plasmas in LAPS or TCP

• Upgrading TCP with higher power, Z-scan, and new matching network

• Instability measurements in upgraded TCP

11/08/2000

57

Plasma Assisted Surface Modification:Low Temperature Bonding

SFR WorkshopNovember 8, 2000

Yonah Cho, Adam Wengrow, Changhan Yun, Nathan Cheung

UC-Berkeley, CA

2001 GOAL: Establish plasma recipes and bonding data for Si, oxide and metal surfaces

11/08/2000

58

Motivation : Heterogeneous Integration by Bonding

SiO2

SOI

Si

Si

SOI

Photonics on Si Silicon-On-Insulators

Microfludic Transport

200 m

Dual Gate MOS

11/08/2000

59

Bonding Methods & Temperature Dependence

• Anodic BondingAnodic Bonding

• Direct BondingDirect Bonding• Metal BondingMetal Bonding

• Adhesive BondingAdhesive Bonding

Choice of bonding methoddepends on thermal budget & materials systems

Hydrophobic Si

Hydrophilic Si

3000

2500

2000

1500

1000

500

0100 200 300 400 500 600 700 800 900

Bon

din

g E

ner

gy (

mJ/

m2 )

Annealing Temperature (oC)

Bonding Energy vs. Temperature

11/08/2000

60

*Plasma Treatment*Gases Used:

O2, He, N2, Ar

Pressure 200mTorr

Power50W-300W

Time15-30 seconds

+

O2

Thermal Annealing

Room Temp Bonding

Chemical Cleaning:Piranha + RCA

-

Plasma Assisted Bonding

11/08/2000

61

Bonding Kinetics

2.0 2.5 3.0 3.5

10

100

1000

B

ondi

ng E

nerg

y (m

J/m

2 )

Temperature (oC)

50100200

1000/Temperature (K)

Si-SiO2 Plasma-treated

Si-Si

Chemically cleanedSi-Si

Chemically cleaned SiO2-SiO2

Ea ~ 0.07 eV

Ea ~ 0.2 eV

Ea > 0. 7 eV

Plasma treated Si surfaces achieve covalent bonding as low as 105oC

O2 Plasma-treated Si-SiO2

11/08/2000

62

Surface Chemistry: XPS

90 95 100 105 110 115100

200

300

400

500

600

In

tena

sity

(A

.U.)

90 95 100 105 110 115

90 95 100 105 110 115100

200

300

400

500

600

Inte

nasi

ty (

A.U

.)

Binding energy (eV)90 95 100 105 110 115

Binding energy (eV)

SiO2Si

HydrophobicSi

HydrophilicSi

O2 plasma treated

Si

Thermal SiO2

SiO2Si

11/08/2000

63

Plasma Effect Over Time

0 1 2 3 4

100

2000

Room Temperature

Annealed at 167 oC

Bo

nd

ing

Str

en

gth

(m

J/c

m2)

Time between plasma treatment and bonding (days)

11/08/2000

64

Surface Morphology

Chemically cleaned SiO2 plasma

150W-300W30 seconds

No Change in Surface Roughness

RMS < 0.5 nm

RMS < 0.5 nm

11/08/2000

65

Surface Modification by Concomitant/Sequential Plasma Treatment

• Mechanical and chemical properties of surface can be effected.

• Modified surface layer can be from substrate or grown / deposited / transferred layer.

• Physical and/or chemical changes of surface possible by altering chemical composition of plasma and ion energies.

Surface Layer

Si Substrate

PlasmaTreatment

ModifiedSurface

*By simply varying the potential of the PIII reactor, it can serve as surface modifier to implanter.

11/08/2000

66

2002 and 2003 Goals

•Demonstrate concomitant plasma treated deposition layer as effective diffusion layer.

•Demonstrate polymer surface modification with plasma implantation

11/08/2000

67

Layer Transfer for System Integration

SFR WorkshopNovember 8, 2000

Adam Wengrow ,Changhan Yun,, Yonah Cho,and Nathan Cheung

Berkeley, CA

2001 GOAL: Establish new layer transfer methods for integration of photonics ,IC, and MEMS

11/08/2000

68

Motivation

CPU

UV-Blue laser

Micro mirrors

1m

Micro pump

100 m

200 m

Micro-fluidic channels

x-y Detector Arrays

LED display

Paste-and-Cut Approach for Integration of Si IC, Photonics, and MEMSPaste-and-Cut Approach for Integration of Si IC, Photonics, and MEMS

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Substrate A

Substrate AProcessing A

Substrate A

MaterialGrowth A

Substrate A

Cut

Receptor Wafer

Substrate B

Substrate BProcessing B

Substrate B

MaterialGrowth B

Substrate BCut

Paste Paste

Paste-and-Cut for Materials IntegrationPaste-and-Cut for Materials Integration* Bypass material compatibility limitations* Flexible process flow for integration

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Mechanical Transfer of Pattern-Implanted Si

Implantation Masks

Si donor wafer

Si handle wafer

H+

SiO2

DeviceRegion

Hydrogenpeak

TransferredSi Layer

1. H+ Implantation through mask pattern

2. Wafer Bonding at low temperature

3. Mechanical pulling for layer transfer

Localized can exceed the fracture strength of silicon, overcoming the limitation of the thermal cut method

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Thermal-cut versus Mechanical-cut

0 20 36 50 75 100100

101

102

103

104

105

FIA(%)

t(se

c)

No

laye

r tr

ansf

er

>1day

550C

600C650C

700C

FIA =Total area

Implanted area

Hydrogen implantation: 51016 H+/cm2 at 150keV

No thermal-cut for FIA20%

1m

Mechanical-cut shown possiblefor FIA~20%

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Poly-Silicon Layer Transfer Using Ion-cutH+

Si donor

Handle wafer

Bondinginterface

Hydrogenpeak SiO2

Transferred poly-Si layer

Poly-Si

Poly dep. & H+ implant

Low-temperature wafer bonding Thermal or mechanical layer cleavage

Si donor

Si donor

Oxygen plasma

Si donor Handle wafer

CMP poly-Si

Handle wafer

Plasma surface activation for bonding

Rough surface for CVD Si.

Smooth after CMP

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Poly-Silicon CMP for Direct Bonding

2m

2m

0nm76nm

0m

0m

2m

7.6nm

0m 0m

2m

0nm

As-deposited:RMS roughness ~10.2nmNOT BONDABLE

After CMP:RMS roughness ~0.93nmBONDABLE

10 times smoother after CMP!

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Poly-Si Layer Transfer Time vs. Temperature

13 14 15 16 17 18 19 20

-8

-7

-6

-5

-4

-3

-2

-1

ln[1

/t(s

ec)]

1/kT(eV-1)

Ea~1.3eV

Ea~0.17eV

400500600 300

5 sec.10 sec.

20 sec.

1 min.2 min.

5 min.10 min.

20 min.

50 min.

T(C)

t

Poly-Sic-Si

Poly-Si has 10 times smaller Ea thansingle-crystal Si !

RMS roughness of cut surface ~ 4.2nm, same as single-crystal cleavage

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2002 and 2003 Goals

Demonstrate integration vehicle with microfluidic flows, photonic source and photonic detection

Establish low-temperature layer transfer methodologies for Si-based, III-V based, and polymer- based thin-film devices