Angle Resolved x-ray Photoelectron Spectroscopy, ARXPS – Experience in the Wafer Processing Industry so far

- C.R. Brundle, C.R. Brundle & Associates, Soquel, CA

- G. Conti, Y. Uritsky – DTCL, Applied Materials, Santa Clara, CA

- J. Wolstenholme, Thermo Inc.

• Our practical experience using ARXPS for determining the following:

1. Thickness for nominally single overlayer films (0-40Å) – Characterization and Metrology

2. Composition depth distribution (0-40Å) – Characterization

Note: “Dose” is a sub-set of composition (Metrology?)

• Taken as a given that XPS is a powerful technique for elemental and chemical state identification for 0-40Å films.

Acknowledgements: - Charles Wang, Ghazal Peydaye-Saheli

at Applied Materials

ARXPS – Experience in the Wafer Processing Industry

• Will use our experience over a 3-4 year period with 10-30Å Si/O/N gate oxide material, as produced in development by Applied Materials wafer processing tools and processes for Semiconductor Industry customers.

• Will refer to a few other necessary “illustrative examples” along the way.

What does this industry want?

THICKNESS

• High Precision (better than 1% at 1σ repeatability / reproducibility for a 10Å film).

• For Metrology, fast (seconds per point), 5/9 point maps on 300mm wafers.

• Accuracy is of less concern. For metrology of no concern. Will be calibrated anyway, and a λeff (“effective attenuation length”).

Would like to be able to distinguish “apparent thickness variations” from what are really materials changes.

→ λeff changing with material change

→ λeff changing with t

What does this industry want?

DOSE (e.g. N in Si/O/N; As in Si(100))

• 1% precision at 10Å for 1x1015 atoms/cm2.

• Accuracy is again of less concern, BUT need to distinguish “apparent dose changes” from depth distribution changes.

DEPTH DISTRIBUTION

• A crude distribution is OK (layer model approach?).

• BUT it needs to be reproducible and correct.

• Would like to be able to detect small variations in a given distribution (e.g. wafer to wafer or point to point on a wafer).

Other Issues

• For the Si/O/N work described here we assume flat (low roughness), laterally homogenous (over analysis area) films. We know this to be true.

• For Hf based high k work the above is not always true.

• All the work is done using the Theta 300 Thermo Inc tool.

• All the “recipe development” for converting ARXPS data to depth profiling is done by P. Mack at Thermo Inc. We are merely users, though we do have the freedom to vary some parameters.

• We often have to make correlations with data from the ReVera tool (Gate group at Applied Materials), which is a single angle only tool designed specifically for metrology (t, N dose) in Si/O/N

Theta Probe avoids the disadvantages by collecting all angles in parallel.

Theta Probe – Parallel ARXPS (PARXPS)

Two Dimensional Detector

Measures Energy and Angle Simultaneously

The Theta Probe ARXPS Solution

Collection Conditions

• Angular Range– 20° to 80°

• Parallel collection– Up to 96 channels in angle

• Generally, 16 angles are used giving an angular resolution of 3.75°

– Up to 112 channels in energy • Parallel collection allows rapid ‘snapshot

acquisition’– Excellent for ARXPS maps– Thickness maps– Dose maps

How is Surface Sensitivity Achieved?

• Intensity as a function of depth– 65% of signal from <

– 85% from <2

– 95% from <3

• Information depth greater than thickness of gate dielectric = Inelastic Mean Free Path (0.4 - 4nm)

0

20000

40000

60000

80000

100000

120000

140000

160000

010020030040050060070080090010001100

Cou

nts

/ s

Binding Energy (eV)

N1s

O1s

Si2pC1s

Typical XPS Full Spectrum For Si/N/O

2

4

6

8

10

12

14

16

18

390392394396398400402404406

Binding Energy (eV)

N1s

5

10

15

9698100102104106108

Binding Energy (eV)

Si4+ Si2p

2

4

6

8

10

12

14

16

18

275280285290295

Binding Energy (eV)

C1s

0

1000

2000

3000

4000

526528530532534536538540

Cou

nts

/ s

Binding Energy (eV)

O1s

ARXPS data for each element present

What is Angle Resolved XPS (ARXPS)?

A set of measurements over a range of provides composition information over a range of depths.

Information depth varies with collection angle

– I = I exp(-d/cos)

Spectra from thin films on substrates are affected by the collection angle

XPS as a function of the angle, , (w.r.t. the surface normal) that the photoelectrons leave the surface

Thickness Determination

• Based on the classical approach of determining the ratio of overlayer / substrate XPS intensities and using the Beer-Lambert equation and values for λ.

• For Si/O/N on Si(100) the overlayer signal is Si4+ and the substrate is Si0.

λSi SiO ~ λSi SiO (KE’s are nearly the same)

So reduces to:

ln [1+R/R∞] = d/(λSi, SiO cosθ)

4+ 2

0 2

2

………

………

………

0 2

R = R∞ [1-exp (-d/λSi , SiO )]4+ 2

exp(-d/λSi , SiO cosθ)

4+

0

ІSi

ІSi

4+

0

ІSi

ІSi

∞

∞

[1-exp (-d/λSi , SiO )]4+ 2

exp(-d/λSi , SiO cosθ)=

0 2

Thickness Determination

• Many sources for λSi , Si (and λ values in general – see C. Powell publications)

• Classical approach ignores elastic scattering, λe. We know (Powell et al) this can cause significant errors, so that a λeff should be used, and that the errors vary with thickness, so that λeff becomes a function of t.

• The effects of elastic scattering get greater at higher θ (more grazing angle), over representing the substrate, leading to a low estimate of t if a fit is made to equation 3 that includes data at high θ (see later).

• Our values of λ come from the Thermo Inc algorithm. They are calculated on the basis of formula, density, band gap, and KE.

4+ 4+

R∞σSi, SiO λSi, SiO DSiO FSi λSi, SiO

σSi, Si λSi, Si DSi FSiO λSi, Si

ІSiO∞

2

ІSi∞

2 2 2

2

x 2===

0

1

2

3

4

5

0 0.5 1 1.5 21/cos()

ln(1

+R

/R)

9.0 nm

6.4 nm

4.3 nm

3.6 nm

2.3 nm

1.9 nm

• Silicon Dioxide on Silicon

• Plot: ln[1+R/ R ] vs. 1/cos()

• Fitting: Fit through the origin

• Gradient: = d/

• NOMINAL THICKNESS VALUES FROM ELLIPSOMETRY

Thickness Measurement : Testing Model Validity

• SiO2 on Si

– Excellent linearity

– Ellipsometry included C layer in thickness

– The offset will change as a function of time as more contamination is picked up

y = 1.0114x - 0.8303

R2 = 0.9997

0

2

4

6

8

0 2 4 6 8Ellipsometry Measurements (nm)

AR

XP

S M

ea

su

rem

en

ts (

nm

)

Ellipsometry included C in layer thickness

Comparison of XPS Results To Ellipsometry

Thickness

• data considered for Si/O/N on Si(100)

1) 8 sample set with t ~ 10-30Å

N% age ~ 7-30%

- 4 from process A; 4 from process B

- Determine d, N dose, and Max. Ent. Derived depth profile

- Only one set of experimental data, but evolving treatment over a 3 year period.

Note: very large t and N% range – not typical for metrology

Thickness:

• Quality of Data?

• Manual Fits - Operator Influence?

- Repeatability by single operator?

• Effect of changing composition (N% age), which is large here?

• Effects of angular range used?

- Depends on thickness, material

- Consequence for single angle determination?

• Effect of composition variation with depth?

→ Automated 3-layer model (p. Mack, Thermo)

- No operator dependency

- Completely reproducible

- Iterative fit to 3-layer depth distribution model and t (i.e. value of N dose and it’s distribution effect, t)

Single Overlayer Model for Film Thickness:quality of data?; manual fits?

A-11

There is ambiguity in assigning intensitybetween the Si4+ and Si0 peaks

• ARXPS measurements– Effect of angular range upon

measured thickness– Minimum angle is 23° in all cases– Highest usable maximum angle

depends upon oxide thickness

• Comparison of ARXPS with fixed angle XPS– Good agreement except at

large thickness– Single angle measurement

samples large angular range.

0

2

4

6

8

10

20 30 40 50 60 70 80

Maximum Angle (°)

Ca

lcu

late

d T

hic

kn

es

s (

nm

)

0

2

4

6

8

10

0 2 4 6 8 10

Nominal Thickness (nm)

Mea

sure

d T

hic

knes

s

ARXPSInstrument 1 Single AngleInstrument 2 Single AngleInstrument 2, 2 AnglesLinear (ARXPS)

XPS Measurements of SiO2 Thickness:

Effect of angular range included?

J. Wolstenholme, Thermo, Inc.

Thickness• 8 SAMPLE SET of Si/O/N– One set of experimental data, but how it has

been processed has changed from 2003 to 2007. Note: Very large t and N% range

Process A Process B

Slot No. 1 3 11 10 15 3* 13 6

N%age 8.5 16.0 6.7 23.7 9.6 12.1 18.6 29.8

t(Å) June 2003 14.1 16.3 19.8 20.1 10.4 11.2 14.2 21.1

Jan 2007 1st 14.3 15.9 18.9 19.4 10.7 11.6 14.0 20.4

2nd 19.3

3rd 19.0

Angle Restriction January 2007

76° 1st 14.9 Underestimate

2nd 14.9

69° 1st 18.3

2nd 18.1

61° 1st 18.9

Identical, within statistics 2nd 18.8

54° 1st 18.8

2nd 18.6

3-layer model Jan 2007

1st 13.8 14.5 19.7 16.8 10.3 10.4 12.2 16.4

2nd 13.8 14.5 19.7 16.8 10.3 10.4 12.2 16.4

Single Overlayer Mod. for Film Thickness, slot 11

Thickness

Conclusions• Precision of data is no problem

• Validity of model should be tested (ie use angular data and fit to equation. not just a single angle determination)

• For Si4+ (overlayer) / Si° (substrate) fit to data, operator dependence for manual fit can be a problem

• Automated fit (3 layer model) can be completely reproducible

• Relative accuracy depends on validity of parameters input – λ(f(t)?), density (f(N%age)), depth distribution (f(N%age)?)

(e.g. 14.1Å for a 8.5%N film going to 20.1Å for a 23.7%N film, found using the manual non-iterative model, is a very different %age change compared to 13.8Å going to 16.8A in the 3 layer model)

N Dose

• So far have been only listing “N%age”; i.e. the usual XPS approach of peak intensities corrected for photoionization cross-section. This assumes homogenous composition.

• Dose is the total amount of N in the film.

• If uniform distribution Dose = N%.t.C

• If non-uniform, N%.t.C becomes an “Apparent Dose”

- The “Apparent Dose” can be greater or less than true dose, depending on depth distribution

- ReVera single angle approach?

∙ Initially – assumed a depth distribution???

∙ Now – determines a depth distribution from a Tougaard background approach.

• Theta 300/Thermo : N dose by integrating N depth profile distribution from (a) Full Max Ent approach or

(b) 3-layer model (automated).

CN

d

CN

d

So, we need to know N distribution to get true N dose

• True dose < Apparent Dose

• True dose >Apparent Dose

CN = N Concentration

d = depth

Effect of Distribution on Dose Calculation

N Dose (x e15 atoms/cm2): 8 sample set

(from integrating N depth distribution; discussed later)

Process A Process B

Slot No. 1 3 11 10 15 3* 13 6

N%age 8.5 16.0 6.7 23.7 9.6 12.1 18.6 29.8

t(Å) 14.1 16.3 19.8 20.1 10.4 11.2 14.2 21.1

June 2003 dose 7.61 17.0 8.57 31.9 6.33 8.41 17.2 40.5

June 2004 dose 7.25 17.8 7.35 32.3 6.00 8.50 19.0 47.8

3-layer model t(Å) 13.8 14.5 19.7 16.8 10.3 10.4 12.2 16.4

dose 7.6 16.0 8.2 30.1 6.7 8.6 16.6 35.3

(ratio to June 2003) 1.00 1.06 1.05 1.06 0.95 0.98 1.04 1.15

N%∙t VS N Dose

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60

N Dose

N.t

June 2003

June 2004

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45

N Dose June 2003

N D

ose

3-l

ayer

June 2003 vs 3-layer

Linear (June 2003 vs 3-layer)

N Dose 3 layer Jan 2007 versus N Dose June 2003.

N Dose

Conclusions

NEED CALIBRATION/VERIFICATION BY MEIS!

• Striking agreement between 3-layer model and the June 2003 Max Ent results, except for very high N content (even though large differences in estimated t!).

• June 2003 – About 8% spread from pure N%·t approach.

• 3-layer – About 15% spread from pure N%·t approach, but linear

• Limiting angular range (66°-55°) produces up to 10% variation (because Max Ent derived depth profile is different).

• Note: very large dose variations are being considered here. Not usual for metrology.

• Because of the short mean free path lengths, λ, of the photoelectrons generated and used in XPS, non-destructive depth profiling is limited in the depth it can effectively go to

– 65% from < 1 λ; 85% from < 2 λ; 95% from 3 λ

– λ ranges from 0.5nm to 4nm (material and electron energy dependant)

• How limited depends on level of detail wanted

– ARXPS quite capable of detecting a substrate > 3 λ down, but not profiling the 3 λ overlayer or giving a precise thickness

– Detailed profiling possible up to ~ 2 λ thickness

– Reliability of profile obtained by ARXPS?

• Relative Depth Plot, RDP - QUALITATIVE but simple, fast, model independent

• Maximum Entropy Method - QUANTITATIVE, but modelled and requires experience or a ‘recipe’

Ultra-Thin Film Depth Profiling by ARXPS Status

Processing the data– RDP

A relative depth index can be calculated using:

An indication of the layer order can then be achieved by plotting out the relative depth index for each species.

Peak Area (Surface)

Peak Area (Bulk)ln{ }= RDP ratio

• Construction:

– Collect ARXPS spectra

– For each element, calculate:

Si

SiO2

HfO2/Al2O3

C

• Information

– Reveals the ordering of the chemical species

RDP

C1s

O1s (Low BE)

Al 2pHf 4f

O 1s (High BE) Si 2p

(Ox)

Si 2p (El)

Surface

Bulk

RDP

BulkAngle

leSurfaceAng

I

Iln le

ALD TaN Film: chemical state RDP

Angle Resolved Spectra from TaN Sample

TaNt

TaOx

• Advantages

– Fast

– Model independent, no assumptions

• Limitation

– No depth scale

– No concentration profile structures

– In my opinion an RDP is the most generally useful approach in ARXPS for characterization of unknown film structures seen during process development.

Relative Depth Profile, RPD

SampleGenerate Random

Profile

0

10

20

30

40

50

60

304050607080

Ato

mic

pe

rce

nt

(%)

Angle (°)

Calculate Expected ARXPS Data (Beer

Lambert Law)

Tj() = exp(-t/cos)

Al2O3

C

SiO2

Si

O

Si4+

C

Sio

Surface sensitive More bulk sensitive

Al

Max. Ent. : Depth Profile Generation

k k

obsk

calck II

2

2

2

Determine error between observed and calculated data:

• The MaxEnt solution is derived by minimising 2 while maximising the entropy

• Maximise the joint probability function

• Repeat process to obtain most likely profile

0

i,j

i,ji,j

0i,j

j ii,j c

clogcccS 25.0 SQ

Depth Profile Generation (cont.)

• Calculate the entropy associated with a particular profile (the probability of finding the sample in that particular state)

• cj,i is the concentration of element i in layer j

• Simple model fit to the data can never be unique! The Max Ent approach (balance with Entropy) is a “regularization” approach. Detail of results are nearly always over-interpreted.

• Balance of 2 and is operator (or recipe) chosen– Requires experience with sample at that thickness– Requires assumptions about ‘unrealistic solutions’

• e.g. Too spiky a distribution? 2 weighting too high (or too small)

• e.g. Too smooth, substrate never reaches 100%, film elements never go to 0%? too big

• For a ‘simple’ film of < 2λ; with good statistics data; a substrate with no species common to the film; zero or small surface contamination

– Develop reliable recipe (2, , …verification?)– Possible to obtain a reliable profile for system appropriate to that ‘recipe’

(see examples following)

– Is it for Si/O/N with t, N dose variations?

Reliability of Max Ent Modeling

HfSiON Reconstructed Profile

0

20

40

60

80

100

0 1 2 3 4 5

Depth / nm

At

%

O N

HfSi4+

Si0

Si

HfSiON

Comparison of ARXPS with MEIS

O

N

Hf

Si4+

Si0

Total Si (MEIS)

0

20

40

60

80

100

0 1 2 3 4

Depth / nm

At

%

PEO-thiol SAM on Silver

Depth Profile

C1s (O)O1s

C1s

S2p

Ag3d

Relative Depth Plot

C 1s (Ether)

C 1s (H/C) Ag 3d

S 2pO 1s

QuartzTiWAgSAM

SAM = -S-(CH2)11-(O-CH2-CH2-)3-OH

Reliability?

• Need high quality angular data – good S/N

• Need “constraints” and a “recipe” for term

Example of Max Ent Derived Depth Profile on an

Ultra-Thin Si/O/N Film

0.4

0.6

0.8

1

1.2

20 40 60 80

Angle (°)

Re

lati

ve

N/O

In

ten

sit

y R

ati

o

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3Depth (nm)

Co

nc

en

tra

tio

n (

Ato

mic

%) C1s

N1s

O1s

Si2pO

Si2p

Effect of Depth Distribution on Peak Intensity Ratios

Extreme Example: answer qualitatively obvious from raw data or RDP, but cannot know whether detailed Max Ent distribution is valid without verification/calibration by some other method.

Repeatability of ARXPS Concentration Profiles

• Three ARXPS datasets acquired dynamically from point on a Si oxynitride sample (sample repositioned each time).

• Concentration profiles reconstructed from each dataset

• Good reproducibility of reconstructed profiles.

Relative Depth Plot for 8 sample set: process A

Set A

Relative Depth Plot for 8 sample set: process B

Set B

Process 11At = 19.8ÅN% = 6.7%N Dose = 8.57 x 1014 atoms/cm2

Process 1At = 14.1ÅN% = 8.5%N Dose = 7.61 x 1014 atoms/cm2

Process 3At = 16.3ÅN% = 16%N Dose = 1.70 x 1015 atoms/cm2

Process 3Bt = 11.2ÅN= 12.1%N Dose = 8.41 x 1014 atoms/cm2

Process 15Bt = 10.4ÅN= 9.6%N Dose = 6.33 x 1014 atoms/cm2

Process 13Bt = 14.2ÅN= 18.6%N Dose = 1.72 x 1015 atoms/cm2

Process A

Process B

June 2003. Max. Ent. α=2e-4

09498102106110

Binding Energy (eV)

Si0

SiO2

Si/O/N

• Different Si 2p binding energy for Si4+ in SiO2 and Si/O/N allows separation in profile

• t = 21.1 Å N = 29.8%

Example of Chemical Depth Profiling, June 2003: Distinction of Si-O Using Si Chemical Shifts

0

20

40

60

80

100

0 1 2 3 4

Depth (nm)

Ato

mic

Co

ncen

trato

n (

%)

C1s

Si2pO

Si2pN

O1s

N1s

Si2p

Post Oxidation? Film is actually more like this:

SiO2

Si/O/NSi (100)

Graded Region

SET 10A

t = 20.1Å

N = 23.7%

SET 6B

SiO4 SiO3N

Slot 10Slot 3Slot 1Slot 11

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3 3.5

Normalised Depth / nm

N C

on

ce

ntr

ati

on

/ %

Interface

0

5

10

15

20

25

30

35

40

0 0.5 1 1.5 2 2.5 3 3.5

Normalised Depth / nm

N C

on

ce

ntr

ati

on

/ %

Slot 15Slot 6Slot 3*

Slot 13

Interface

Set 1

Set 2

• Set A and set B are very similar (not expected)• N distribution does not change much with N total dose• Hard to get more than 10%

N absolute at surface (air oxidation and HC pickup

will reduce N content)• No evidence for a nitrogen spike at the surface, cf.TOF SIMS.

(this was the original reason for studying these

sets of samples)

Normalized Overlays of N Distribution, June 2003

Slot-1

0

1020

3040

50

6070

8090

100

0 0.5 1 1.5 2 2.5

Si2p-ox

N1s

O1s

Si2p

Slot_3

0

20

40

60

80

100

0 1 2 3

depth (nm)

ato

mic

%

Si2p-ox

O1s

N1s

Si2p

Slot_11

0

20

40

60

80

100

0 1 2 3 4

depth (nm)

ato

mic

%

Si2p-ox

O1s

N1s

Si2p

Slot_10

0

20

40

60

80

100

0 1 2 3 4

depth ( nm)

atom

ic %

Si2p-ox

O1s

N1s

Si2p

0ctober 2003. Max. Ent. α=5e-007. Set A

Slot-15

0

20

40

60

80

100

0 0.5 1 1.5 2

depth (nm)

ato

mic

%

Si2p-ox

O1s

N1s

Si2p

Slot3 *

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

depth (nm)

ato

mic

%

Series1

Series2

Series3

Series4

Slot_13

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

depth (nm)

ato

mic

%

Si2p-ox

O1s

N1s

Si2p

Slot_6

0

20

40

60

80

100

0 1 2 3 4

depth (nm)

ato

mic

%

Si2p-ox

O1s

N1s

Si2p

0ctober 2003. Max. Ent. α=5e-007. Set B

Slot 1 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

Si (ox)

N

O

Si (el)

Slot 10 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 11 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 3 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3

Si (ox)

N

O

Si (el)

June 2004. Max. Ent. α=5e-07. Process A

Slot 15 B

0

20

40

60

80

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Si (ox)

N

O

Si (el)

Slot 3* B

0

20

40

60

80

100

0 0.5 1 1.5 2

Si (ox)

N

O

Si (el)

Slot 6 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 13 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

Si (ox)

N

O

Si (el)

June 2004. Max. Ent. α=5e-07. Process B

3 Layer Model for Silicon Oxynitride

• Assume 2 layers of SiO2, 1 layer SiOxNy, substrate

• Total d value is fixed from Si2p spectrum• Adjust d1, d3 and N concentration to get best

fit to ARXPS data• Advantages

– Fast• Only needs to fit 3 parameters (by

least squares fitting)• Easily automated

– Accurate• Attenuation lengths can be calculated

for each layer– Precise

• Only needs to fit 3 parameters

SiO2

Si3N4 + SiO2

SiO2

Si

d1

d2

d3

0%

20%

40%

60%

80%

100%

0 1 2 3 4

Depth / nm

At %

Silicon Oxynitride

Automated N distribution correction

0

20

40

60

80

100

0 1 2 3 4

Depth (nm)

At

%

0%

20%

40%

60%

80%

100%

0 1 2 3 4

Depth / nm

At %

N

O

Sin+

Si0

N

O

Sin+

Si0

N

O

Sin+

Si0

N

O

Sin+

Si0

Maximum Entropy Results

Automated N

distribution

0

20

40

60

80

100

0 1 2 3

Depth (nm)

At

%

slot 1 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 3 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 10 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

slot 11 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

3-layer model Jan 2007 (Can’t sell this to a process engineer!)

slot 3 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 6 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

slot 13 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 15 B

0

10

2030

40

50

60

7080

90

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

3-layer model Jan 2007

A1

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

angle=55

A1 angle=66 alfa=510-7

0102030405060708090

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

A3 angle=55 alfa=510-7

0102030405060708090

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

A3 alfa=51o-7 angle=66

010

2030

4050

6070

8090

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

Effect of varying angular range. Jan 2007. α=5e007

A10 angle-55 a=510-7

0

20

40

60

80

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

A10 alfa-510-7 angle=66

0

20

40

60

80

100

0 5 10 15 20 25

depth(A)

AU

Si2pO

O1s

N1s

Si2p

A11 alfa=510-7 angle-55

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

A11 angle-66 a=510-7

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

depth(A)

A.U

Si2pO

O1s

N1s

Si2p

Effect of varying angular range. Jan 2007. α=5e007

B15 a=510-7 angle=55

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

AU

Si2pO

O1s

N1s

Si2p

B15 angle=66 a=510-7

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

AU

Si2pO

O1s

N1s

Si2p

Effect of varying angular range. Jan 2007. α=5e007

B3 a=510-7 angle=55

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

depth(A)

AU

Si2pO

O1s

N1s

Si2p

B3 angle=66 a=510-7

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

A.U

Si2pO

O1s

N1s

Si2p

B6 angle=55 a=510-7

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

A.U

Si2pO

O1s

N1s

Si2p

B6 angle=66 a=510-7

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

A.U

Si2pO

O1s

N1s

Si2p

Effect of varying angular range. Jan 2007. α=5e007

B13 a=510-7 angle=55

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Depth(A)

A.U

Si2pO

O1s

N1s

Si2p

B13 a=510-7 angle=66

0

20

40

60

80

100

0 5 10 15 20 25

Depth(A)

AU

Si2pO

O1s

N1s

Si2p

Slot 1 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

Si (ox)

N

O

Si (el)

slot 1 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 3 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

Slot 3 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3

Si (ox)

N

O

Si (el)

Comparison of 3-layer model to full Max. Ent June 2004

slot 11 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

slot 10 A

0102030405060708090

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

Slot 10 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 11 A

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 15 B

0

20

40

60

80

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Si (ox)

N

O

Si (el)

Slot 3* B

0

20

40

60

80

100

0 0.5 1 1.5 2

Si (ox)

N

O

Si (el)

slot 3 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

slot 15 B

0

10

2030

40

50

60

7080

90

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

Comparison of 3-layer model to full Max. Ent June 2004

slot 6 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

nm

[N]

[O]

[Si]

slot 13 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

nm

[N]

[O]

[Si]

Slot 6 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Si (ox)

N

O

Si (el)

Slot 13 B

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

Si (ox)

N

O

Si (el)

Comparison of 3-layer model to full Max. Ent June 2004

Thickness Dose

Nitrogen Dose and Thickness• 300 mm wafer• Single measurement• 49-point maps (after initial depth distribution determination at the

wafer center)

conclusions• Thickness can be obtained to the required precision for 10 to 40A homogeneous

composition (lateral and in depth) films. The accuracy, or even relative accuracy depends on how much effort is put into calibration and what range of thickness or materials changes are occurring. For inhomogeneous films (lateral or depth) errors will occur, which will depend on the specifics. OK for thickness metrology. Comparison to ellipsometry?

• At one extreme, for a first time analysis of a new film composition, with little or no constraints on what could be the situation, do not go beyond a dimensionless qualitative Relative Depth Profile approach (which can, nevertheless be extremely useful)

• At the other extreme, where a very constrained system is involved (ie you either already nearly know the answer, or the depth distribution is so extreme it is basically obvious from the raw data), ARXPS, plus appropriate data modeling, can give depth distributions to some degree, but never, in real situations, a unique highly precise profile.

• The quality of the data needed and the intellectual effort required to write (and verify) a “recipe” for fitting/modeling the data, which then only works within a narrow confine of constraints and, even then, only provides imprecise and not highly depth resolved information, means, in our opinion, that though ARXPS has its uses for characterization within the wafer industry, it is not suitable for rapid metrology intended to provide detailed information on depth distributions and related parameters which may rely on knowing the depth distribution (like dose for instance).

– May be OK for dose metrology for a small dose change range, using automated 3 layer model. Will be precise and reproducible, but only as accurate as the 3 layer model is accurate