The Story of Picosecond Ultrasonics

1 Christopher Morath, Ph.D.

From “Lab”… …to “Fab”

Rudolph MetaPULSE™

Outline

2

Technology Transfer – 1996 to 1998

MetaPULSE product innovations & development

Applications – Memory & Logic

Would MetaPULSE have succeeded today?

Summary

TECHNOLOGY TRANSFER 1996 - 1998

Timeline Overview

4

• 1984 – 1995: Brown University – Picosecond ultrasonics discovered & developed

by Maris & Tauc groups

• 1995: Rudolph licenses Brown IP

• Jan - Oct `96: “Alpha” prototype – Opto-mechanical: stability, packaging

– Electronics: signal processing, control systems

– Software: numerical algorithms, “recipes”

– Compact laser development: Coherent Vitesse

• Oct `96 - Dec `97: automated Beta tool – 200mm wafer handling, machine vision, multi-

site measurements, automated calibrations

– Tool shipped to Intel May ‘97

• Jan `98: Commercial introduction – 10 tools shipped in first year

– “Scientists in the Box” trained and included with 1st tool purchase to drive new applications

MEASUREMENT TIME

5 yrs (PhD) 2 yrs (MS)

5 min

30 sec

15 sec

5 sec

+

Work hard!

Picosecond Ultrasonics Benefits

5

• Non-contact, non-destructive technique

• Multi-layer metal film thickness capability

• Small spot for product wafer measurements – <10 mm spot fits in 30x30mm test sites

• Excellent throughput and repeatability

• Film/process characterization

– Density, roughness, phase

Picosecond Ultrasonic Laser Sonar E

t = 0

t = t1

Photocell

t = t2

PUMP

PROBE

Key success factors for MetaPULSE

6

Ultrafast Laser Technology Rapid Advances 1980’s – 90’s

Picosecond Ultrasonics Research & Applications

Semiconductor Industry Rapid Growth 1970’s – 90’s

Rob Stoner

More than breakthrough

technology was necessary!

Mira Ti:sapphire (1W, ~0.3% noise)

Innova Ar+ pump

+

Ultrafast Laser Breakthroughs of 1990s

7

Satori (100mW, ~0.5% noise) Sub-picosecond saturable absorber dye

1990 1994

Antares Modelocked YAG Flash lamp pumped

+

1997

Vitesse (300mW, 0.1% noise) Ti: sapphire + Nd:YV04 pump

Verdi pump laser

Semiconductor Industry: 1980s – present

8

$0.50 $3

2001 2009 2017

<5% growth Cost reductions Consolidations

1993 1985

$60

$35

$15

15-20% annual growth Large R&D investment High IPO rate Entrepreneurial culture

Novel SEMI equipment was a “hot” investment in the 1990s

Semiconductor Technology Drivers

9

Economies of

Scale Productivity

Interconnect speed

“RC delay”

SOURCE: INTEL

20 FinFET

Cu interconnect, low-k ILED, and 300mm wafer automation became requirements shortly after the introduction of MetaPULSE

METAPULSE PRODUCT EVOLUTION

MetaPULSE Development: 1997 - 2010

11

MP - XCu

(400nm l for

copper) MetaPULSE

(200mm &

300mm)

`98 `99 2004-07 2010

CA

PA

BIL

ITY

/ T

HR

OU

GH

PU

T

`97

MP Beta tool

(Intel 180nm

node)

MetaPULSE-II

MetaPULSE-III

(Cu CMP &

low-k ILD’s)

MetaPULSE-G

(green

wavelength)

SHG

>$300M total revenue, ~$50M total R&D spend

Optical Schematic - simplified

12

15 mm ® 1 psec

1psec ~ 30Å

Pulsed Laser (~100 fsec, 800nm

80 MHz)

Lens Splitter

photocell

Wafer

time (psec)

DR

0 10 20 30 40 50 60 70 80 90 100

SHG (option)

Recipe-based

wavelength selection

(use 400nm for Cu)

Servo Delay

< 0.1 mm repeatability

(<10 fsec or <0.03 Å)

13

System stability – time zero calibration

time (psec)

DR

-1.5e-05

-1e-05

-5e-06

0

5e-06

1e-05

1.5e-05

2e-05

2.5e-05

3e-05

0 10 20 30 40 50 60 70 80 90 100

Thickness determination: (vS x tECHO)/2 = (60Å/psec x 26.2 psec) / 2 = 786Å

techo 2techo

3techo

Thickness error estimate: D Thickness = 1/2 vS DtERROR Let DtERROR = 0.1 psec => D Thickness = (60 A/psec)(0.1 psec)/2 = 3Å

DtERROR 786 Å TiN

Si

786 Å film -> 0.4% 60 Å film -> 5.0% !!!

14

Finetune Calibration

Short Time Fit

-2.00E-06

0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

1.00E-05

1.20E-05

1.40E-05

1.60E-05

-2 -1 0 1 2 3 4 5 6

Time (psec)

Ch

ang

e in

Ref

lect

ed P

rob

e (m

W)

Time Zero “Finetune” Calibration

Reference Data Curve

System Measurement Curve

RESULTS: T_offset = 3.7e-2 psec

A_effective = 6.71e-6 cm2

TOFFSET

Pump / probe overlap

15

Self check results - time zero stability (5 days)

System Time Offset [ps]

0.00

0.05

0.10

1/5 1/6 1/7 1/8 1/9 1/10 1/11

Trend: temperature & alignment drift (selfcheck corrects)

Scatter: Algorithm repeatability ~ 0.005 psec => 0.015 A

Same “golden” reference file on all tools for thickness matching

Tool Matching Example

16

tool average wiw std dev 1 2 3 4 5

Tool 1 Mean 43.9696 1.81956 47.0686 42.6183 43.8191 43.3486 42.9933

Tool 1 Sdt Dev 0.24 0.18 0.29 0.43 0.39 0.42 0.55

Tool 1 P/T 0.072 0.055 0.088 0.128 0.117 0.127 0.164

PASS PASS PASS PASS PASS PASS

Tool 2 Mean 44.0882 1.93826 47.3170 42.5546 44.1080 43.4429 43.0182

Tool 2 Sdt Dev 0.16 0.28 0.39 0.45 0.45 0.39 0.68

Tool 2 P/T 0.047 0.083 0.116 0.134 0.135 0.116 0.204

-0.12 -0.25 0.06 -0.29 -0.09 -0.02

UCI -0.01 0.00 -0.07 0.29 -0.07 0.12 0.30

LCI -0.23 -0.24 -0.43 -0.17 -0.51 -0.31 -0.35

30 < N, T-statistic > 2.042 PASS PASS PASS PASS PASS PASS

2X30 Ti

tool average wiw std dev 1 2 3 4 5

Tool 2 Mean 59.1365 3.94404 52.6965 59.6553 59.3786 60.5675 63.3847

Tool 2 Sdt Dev 0.18 0.14 0.29 0.46 0.25 0.28 0.38

Tool 2 P/T 0.053 0.042 0.086 0.138 0.074 0.083 0.115

PASS PASS PASS PASS PASS PASS

Tool 1 Mean 58.5981 3.88157 52.2590 59.1085 58.7302 60.1849 62.7079

Tool 1 Sdt Dev 0.19 0.17 0.25 0.48 0.34 0.32 0.44

Tool 1 P/T 0.056 0.050 0.074 0.145 0.103 0.095 0.133

0.54 0.44 0.55 0.65 0.38 0.68

UCI 0.63 0.14 0.58 0.80 0.81 0.54 0.90

LCI 0.44 -0.02 0.30 0.30 0.49 0.23 0.46

30 < N, T-statistic > 2.042 PASS PASS PASS PASS PASS PASS

2X30 TiN

LAYER 1: 40 Angstroms Ti

LAYER 2: 60 Angstroms TiN

10-20 tools matched at each process node (Intel)

0.12 Å mean matching

0.54 Å mean matching

Automation Platform Overview

17

System Computer

Power Box

Electronics Box

X- Lower Axis

Chuck

FAN FILTER UNIT

Load Port

FOUP

Robot

Vibration Isolation

Y- Upper Axis

Metrology Head

Metrology Electronics

Robot Controller

Automation Computer

Front End Module Metrology Platform

Airflow

SEMICONDUCTOR APPLICATIONS

Memory Application Examples: MetaPULSE-I (800nm wavelength)

19

DRAM Cell and Metallization

20

Word line – Access transistor gate control(on/off)

Bit line

– Data transfer line. Read/write

Transistor – NMOS transistor as a switch

Capacitor – Data storage

Plug, Metal1, Metal2, … – Metal interconnect to external world

1 Transistor 1 Capacitor cell (1X, 1Y)

CAP

DRAM structure & applications (circa 2000)

21

W Bit Line W / CVD-TiN / Ti

BEOL Metalization Al stack: TiN/Ti/AlCu/Ti

Word Line WSix / poly-Si

W plug W/ TiN/ Ti W-deposition, W CMP

Al Bond Pad Al/TiAlx/TiN/Ti ILD & TiN etch

W Bit Line

22

W deposition process

100Å Pulsed nucleation seed

400Å CVD W

MetaPULSE measurement

Total W thickness ~ 500Å

Occasionally W thickness becomes too thin causing chip malfunction

W Barrier Metal (Ti/TiN)

23

Barrier for both Bit Line and Blanket W

TiCl4 CVD process

TiCl4 + 2H2 Ti + 4HCl

6TiCl4 + 8NH3 6TiN + 24HCl + N2

Better step coverage than PVD

Total Thickness and density are monitored

High density result is predictive of high electrical resistance

Electrical Test Data MP Density Data

Barrier Metal – TiSix Thickness

24

Application: Monitor TiSix thickness at the bottom of W plug

Measurement on test site whose substrate is Si

MP measures TiN and TiSix thickness

0 . 3 ㎛

0 7 5

Si

BPSG

TiSix

Plug-W

25

Via fill process for Metal 1 or Metal 2

Good step coverage but high electrical resistivity

Typically 3 - 4kÅ CVD W is deposited

W(CVD) has adhesion problem with SiO2.

– Barrier as glue layer

– At the edge where there is no barrier, W film lifts up causing particle problem

– Edge profile monitoring is important

0 . 3 ㎛

0 7 5

0 . 3 ㎛

0 7 5

0 . 3 ㎛

0 7 5

W Plug depth

This thickness is measured

Barrier Depo W Depo W Etch/CMP

W Edge Thickness Monitoring

26

3mm Si Si

Optimized film edge profile

W W

W film at wafer edge may break off

Tungsten

Edge Scan

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

96 96.5 97 97.5 98 98.5 99 99.5

Radial distance (mm)

W t

hic

kn

ess (

An

g)

Aluminum “CAP” layers – TiN / Ti

27

Anti-Reflection Layer for metal 1 Semi-transparent layers => reflectance depends on thickness

Measure individual TiN and Ti thickness

Reflective surface below PR causes notches at the side profile.

Metal 2: 5000 Å Al/ 800 Å TiAlx

28

TiAlx is used to prevent electro-migration failures (voiding)

Deposition sequence: Ti(PVD)400 Al(CVD)500 Al(PVD)5500 Re-flow.

Re-flow (RTP) to fill up the voids in metal 2 plug.

During RTP, Ti turns into TiAlx with very rough interface.

Modeling “EASy” script categorizes various case of TiAlx formation, and model it appropriately.

Monitoring TiAlx Thickness

29

Unreacted Ti TiAlx formed

Metal Bond Pad

30

Passivation layer etch monitoring

Wire bond failure scenarios

Thin Al pad (over-etched)

Residual CAP2 or ILD above Al

Al

ETCH

Metal Pad Etch – Misprocessing detection

31

Modeling “script” used to identify filmstack and seed forward model

Copper Application Examples - MetaPULSE-III

32

Copper applications overview

33

Previous metallization levels

Low-k ILD

Cu liner/ barrier

Seed Cu ECD Cu

Electoplate Copper • Pre-CMP Cu thickness • Cu overburden

Low-k dielectric • Elastic Modulus

Post-CMP Residual barrier

Post-CMP dishing structure - Cu pad thickness

Seed Cu (PVD) • Cu thickness • Ta/TaN barrier

Post-CMP erosion structure - Cu Line Thickness

Seed Cu/Ta(N) measurements

34

Cu Thickness Map Ta(N) Thickness Map

PULSE Signal

DR

ILD

Underlying levels (Level N-1)

Cu seed

Ta(N) 400nm wavelength (Cu piezo-reflectance is zero at 800nm!)

“Fast Deflector” Technology for Low-k processes

35

• Challenge: Low-k Dielectrics have low thermal conductivity

• Solution: AOD rapid beam dithering

No fast deflector (P ~2 mW)

Fast Deflector (P ~20 mW)

EFFECTIVE “THERMAL” SPOT SIZE

Range: ~10 spots

F (t) = F0 + F1 cos(wt)

LASER SPOT SIZE

w / 2p ~ 1 MHz

~30 mm

AOD

Cu Seed/Barrier Measurements with Low-k ILD

36

65nm node

Ta+TaN

Cu seed

45nm node

32nm node

Ta+TaN thickness 220A 150A 70A

Av.Cu thickness 600A 470A 200A

Electroplate Cu: Superfilling of narrow lines

37

1

2

1

2

1

2

On narrow line structures, MetaPULSE measures both the Cu in the trench and ECP Cu over the trench

MetaPULSE Vs SEM Correlation

38

Superfill Profile Impacts CMP Results

+450

Avg

-450

+150

Avg

-150

Overburden

Thickness (Å)

Pre-CMP Array

Thickness (Å)Post-CMP Thickness

Thickness (Å)

+170

Avg

-170

Normal

Non uniform as-deposited film affects Post-CMP line thickness

Position Sensitive Detector Enables Erosion Measurements

39

PSD benefit: surface displacement signals are less sensitive to submicron line patterning

50 mm test site

Spot covers ~50 Cu Line & space pairs

Correlation to device performance (65nm process)

40

M. H. Hsieha, J. H. Yeha, M. S. Tsaia, C. L. Yanga, J. Tanb, S. P. Learyb

aUnited Microelectronics Corporation, Science-Based Park, Hsinchu, Taiwan bRudolph Technologies, Flanders, NJ 07836 Presented at SPIE Conference, Feb 2006

CMP polishing profiles for

thickness and 1/R are

highly correlated

PULSE offers inline

measurement with

excellent correlation to

final performance

Correlation to E-Test and TEM Results

41

Very good correlation with TEM thickness results

Excellent correlation with 1/R electrical test results

42

PULSE Modulus Measurement Principle

Time [ps]

DR

/R [

norm

aliz

ed]

Air/Dielectric

interface

Dielectric/Si interface

Amplitude decreases after Dielectric/Si interface

Interference oscillation

Period of interference oscillation speed of sound

Reflection(s) at interface(s) ＆ speed of sound thickness

Amplitude change ＆ speed of sound density

Speed of sound ＆ density elastic modulus

Modulus Measurements of Different ILD Films

43

Poisson’s ratio: Fixed input

MetaPULSE Trends – 2011 to present

44

WOULD METAPULSE HAVE SUCCEEDED TODAY?

Semiconductor Industry Investment Trends M. Noonen et al, Solid State Technology Magazine – July 2014

Semiconductor investments have moved to higher ROI industries

Investment challenges today for the next MetaPULSE

Ultrafast Laser Technology

Picosecond Ultrasonics Research & Applications

Semiconductor Industry Slow Growth

More than breakthrough technology is

necessary!

Summary

Picosecond ultrasonics was a highly successful transfer from “lab to fab”

The 1990s offered a prime opportunity for commercialization and funding

Semiconductor investments have slowed but there are is still opportunity!

Biotech & medical devices remain attractive for VC funding and may be a better target market

Acknowledgements…

Rudolph Acknowledgments

• Rudolph Research – Greg Wolf, Rob Loiterman, Richard Spanier

• Development / Engineering team – Guray Tas*, Mike Colgan, Jim Onderko, Mike

Kotelyanskii, Andrei Vertikov*

• Applications Scientists (in a box) – Jonathan Cohen (US accounts including Intel)

– Cheolkyu Kim* (Korea)

– Joerg Schmal (Germany)

– Niall McCusker (Seagate)

* Brown University Physics graduates