The 4PP: Obsolete or Timeless

Walt Johnson

KLA-Tencor

7/18/20092

Short History of the 4PP

1978 Tencor introduces the M-gage

• Replaced my +/- 10% Veeco 4PP with an M-Gage (4PP obsolete?)

1983 Prometrix Introduces dual configuration +/-1%

• Bought an OmniMap

1985 Prometrix reviews future

• Management decides 4PP has 2 yrs life

1994 Prometrix merges with Tencor

Tencor management drops M-Gage, decides 4PP has 2 more yrs

1997 Tencor merges with KLA

KLA management decides the 4PP has 2 more years

7/18/20093

The Status of the 4PP

So where do we stand today?

7/18/20094

Markets addressed by the 4PP

Metals

Metal sheet resistance

Metal thickness assuming a given resistivity

Metal resistivity assuming a given thickness

Ion Implant

Dose monitoring (post anneal assuming a given anneal level)

Ion activation (post anneal assuming a given dose level)

7/18/20095

NCRs (eddy current) Replaces 4PP for metals(at least for thick metals on high resistance substrates)

Pre and Post Polish Diameter Scans With RS300 4PP and RS300 NCRs

10,000

11,000

12,000

13,000

14,000

15,000

16,000

17,000

18,000

1 9 17 25 33 41 49

Position across wafer (L-R)

Co

pp

er

Fil T

hic

kn

ess (

Å)

Rs200 4PP 1585B PRE Rs200 E.C. 1585B PRE

Rs200 4PP 1585B PST Rs200 E.C. 1585B PST

Pre-Polish

Post-Polish

7/18/20096

Copper Removal Correlation

Overall correlation between

4PP and NCRs (on multiple

wafer sets)

y = 0.9874x

R2 = 0.9987

-2000

0

2000

4000

6000

8000

10000

12000

14000

0 5000 10000 15000

4PP Removal Rate(A)

NC

Rs

Re

mo

va

l R

ate

(A)

7/18/20097

New Eddy Current Probe Development (Patent pending)

The direction of eddy current by current probe is parallel to film surface and less sensitive to via sidewall coverage

The direction of eddy current by new probe is perpendicular to film surface which should have better sensitivity

Standard

EC probeNew EC

probe

TSV

Eddy

current

Metal film

Metal film

Eddy

current

Coil Coil

7/18/20098

Eddy Current Signal on Unfilled & Filled Via

Filled and unfilled via shall show difference in eddy current signal

TSV

Eddy

current

Metal film

Unfilled TSV Filled TSV

7/18/20099

3.83E-02

3.85E-02

3.87E-02

3.89E-02

3.91E-02

3.93E-02

3.95E-02

3.97E-02

-150 -100 -50 0 50 100 150

Y (mm)

Rs

(o

hm

/sq

)

Slot1

Slot2

Y-direction Diameter Scan (in arrow direction)

Peak area correlates to via coverage

Repeated via peaks super-imposed on the global Rs non-uniform distribution

7/18/200910

Rs Peak Area Calculation Algorithm

Rs peak area correlates to via coverage

0.0388

0.0389

0.0390

0.0391

0.0392

0.0393

0.0394

0.0395

-50 -40 -30 -20 -10 0 10 20 30 40 50

Radius (mm)

Rs (

oh

m/s

q)

Rs

Baseline

0.00000

0.00002

0.00004

0.00006

0.00008

0.00010

0.00012

0.00014

0.00016

0.00018

0.00020

-50 -40 -30 -20 -10 0 10 20 30 40 50

Radius (mm)

Delt

a R

s (

oh

m/s

q)

Original

Rs

Eliminate

Baseline

Curve

Calculate

Peak Area

Area

7/18/200911

Hi Density Rs Measurement in Die (Slot 4)

0.0

15

0.0

16

0.0

17

0.0

18

0.0

19

0.0

2

0.0

21

0.0

22

0.0

23

0.0

24

-10

01

02

03

04

05

06

0Y

(m

m)

Rs (ohms/sq)

Depending on

if Rs variations

are of interest,

recipe set up

will need to be

used to either

measure

those areas or

avoid them.

7/18/200912

Improved USJ Measurements with Hx probes

7/18/200913

Activation Development & Control

Conventional Four-Point Probe results on 0.5 keV Boron USJ

0

500

1000

1500

2000

2500

0˚C 1300˚C 1350˚C

Laser anneal Temperature

Sh

eet

resis

tan

ce (

Oh

m/s

q.)

850 Spike

950 Spike

1000 Spike

1020 Spike

1040 Spike

1050 Spike

Laser anneal improving activation

and lowering Rs.

(Junction depth not changed due to laser.)

4PP provides sensitivity for process

development & monitoring to detect small

temperature fluctuations

No

activation

increase

Increased

activation

& junction

depth

Customer “A” data

7/18/200914

Discovering Annealer Problems on a 0.5 keV B+ implant

High variations toward upper left edge of wafer 14 points in area show measurement error or data outside sigma filter

Center ring possibly due to thermocouple from annealer

Three higher Rs regions around center possibly due to pedestal in annealer

Excellent matching between probe heads, and results repeatability

Probe head 2 Probe head 3Probe head 1

Customer “C” data

Yield-limiting detail analysis of Anneal process equipment

7/18/200915

Long-Term Repeatability

BF2 1.5E14, 8

KEV

25 repeats

BF2 1E14, 5

KEV

25 repeats

As 1E14, 5 KEV

25 repeats

As 1E14, 3

KEV

25 repeats

Mean 1451 2508 1252 1613

% Stdev 0.16% 0.21% 0.14% 0.12%

Repeatability on BF2 and Arsenic

USJ implant maps is excellent

Customer “C” data

Repeatability of Contour Map Results:

7/18/200916

Alternate Implant Monitoring Techniques

IonScan

Metrix e-beam

TW

SemiLab / FSM / Quantox (KLA-Tencor)

Microwave ?

7/18/200917

TP to Rs Comparison

Another example of laser anneal optimization with TP including comparison with Rs

7/18/200918

Junction Leakage Limits 4PP Usage

Hx Four-point Probe Data

0

1000

2000

3000

4000

5000

6000

14 15 16 17 18 19 20 21 22 23 24 25

Slot #

Sh

eet

Resis

tan

ce (

Oh

m/s

q.)

1175C

1225C

1275C

1325C

1E15 B, 100 eV 1E15 BF2, 500 eV

No PAI No PAI

Ge PAI

Xe PAI

Ge PAI

Xe PAI

7/18/200919

SPV, JPV or LPV

Correlation of RsL & QTX Lifetime

0.70

0.90

1.10

1.30

1.50

1.70

1.90

2.10

2.30

55.00 56.00 57.00 58.00 59.00 60.00 61.00 62.00 63.00 64.00

Lifetime (uS)

Rs

L L

ea

ka

ge

Quantox SPV Decay

0

0.1

0.2

0.3

0.4

0.5

0.6

1.00E-04 1.00E-03 1.00E-02

Time (s)

Vs(V

)

Wafer 3

Wafer 2

Wafer 1

7/18/200920

4PP Method

The 4PP leakage through substrate can be modeled by following

equivalent circuit

When Ileakage

7/18/200921

4PP Method (for leakage)

Measured Rs is a function of applied current for a fixed diode leakage density

7/18/200922

Increased Leakage below 1275˚ Anneal

Slot 20

0.995

0.996

0.997

0.998

0.999

1

1.001

1.002

1.003

1.004

1.005

0 50 100 150 200 250

MicroAmps

Re

lati

ve

Sh

ee

r R

es

ista

nc

e

1175°C

1225°C

1275°C

1325°C

7/18/200923

Current Ramp Comparison to SPV

Correlation of RsL & QTX Lifetime

0.70

0.90

1.10

1.30

1.50

1.70

1.90

2.10

2.30

55.00 56.00 57.00 58.00 59.00 60.00 61.00 62.00 63.00 64.00

Lifetime (uS)

Rs

L L

ea

ka

ge

Correlation of Rs slope & Lifetime

-1.E-03

-8.E-04

-6.E-04

-4.E-04

-2.E-04

0.E+00

55.00 56.00 57.00 58.00 59.00 60.00 61.00 62.00 63.00 64.00

Lifetime (uS)

Slo

pe o

f R

s (

1u

A-5

00u

A)

Quantox SPV Decay

0

0.1

0.2

0.3

0.4

0.5

0.6

1.00E-04 1.00E-03 1.00E-02

Time (s)

Vs(V

)

Wafer 3

Wafer 2

Wafer 1

7/18/200924

Present Status of the 4PP

New (and older) technologies eddy current, TW, SPV etc. adding information on traditional 4PP

applications

BUT!!!

4PP

Still not ready to give up