Advanced Optical Inspection TechniquesSeptember 9, 2010

Andrei Brunfeld

2

Contents

• Introduction

• Current Challenges

• Xyratex solution

• Main defect categories images

• Summary

Areal Density and Critical Defect Size - Expected Evolution

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0.500

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2010 2011 2012 2013 2014 2015

Year

Area

l Den

sity

(Tb/

in2)

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Criti

cal p

artic

le s

ize

(um

)

Areal Density - Low Estimate (Tb/in²) Areal Density - High Estimate (Tb/in²) Critical Particle Size (µm)

200nm 100nm 50nm

Laser beam

Detector Surface under test

Cells region

Diffracted field(from every cell)

U0Propagation region

U 1U 2

Πsurf R 2z

In-Line Testing Challenges

Brief Review

4

Areal Density and Bit Dimension

• Bit aspect ratio continues to decline

• Required critical defect detectability more stringent

• Current in-line inspection is limited– Detectability vs. Speed– Classification– Special requirements

5

Key Production Concerns: Substrate Media Drive

• Drive reliability (at fly-height sub 3 nm range)– Thermal Asperities & Head damage

• Embedded particles• Buried defect• Fly height variations

– Bumps– Shallow defects – (slider wavelength based)– Raised scratches

– Soft defects (parametric thresholds)• Fly height variations

– Shallow defects –parametric variations• Scratches

– Shallow pass then fail when head changes slightly– Grown defects

• Presputter contamination

• Yield – Requirements vary from Drive Company to Drive Company– Defect counts

• Presputter Scratches• Sputter voids• Surface roughness

– Thermal Asperities• (see above)

– Servo failures• PES failures – most likely due to scratches

• Drive reliability and yield requirements ARE conflicting!

6

Main Defect Categories

• Shallow defects– Pits (short, long)– Bumps – Craters– Large waviness – slider wavelength

related– Stains – film/coating

• Shallow defects– Scratches– Ridges (raised scratches)

• Particles/Protrusions– Grown defects

– Voids

– Handling damages

– Thermal asperities

– Particulates

AreaH= -8nm

W= 30000nm

H= -1.3nm

W= 50nm

Line

Point

7

Drive sensitivity to spacing loss (scratches/shallow defects)

25% signal loss critical for servo, 50% critical for drive error rate

Spacing Loss vs. Year

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3.00

2009 2010 2011 2012 2013 2014 2015

Year

Dept

h (n

m)

A = A010-2πd/λ

25% Signal Loss

50% Signal Loss

• Required spacing variation currently at around 2 nm

• Future challenge heading toward 1nm

8

Particle Size Detectability Estimation

Areal Density and Critical Defect Size - Expected Evolution

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0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

2010 2011 2012 2013 2014 2015

Year

Area

l Den

sity

(Tb/

in2)

0

0.05

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Cri

tical

par

ticle

siz

e (u

m)

Areal Density - Low Estimate (Tb/in²) Areal Density - High Estimate (Tb/in²) Critical Particle Size (µm)

200nm 100nm 50nm

• Current production requirements about 100nm PSL equivalent

• Future requirements toward 50nm PSL equivalent or less

9

Main Reasons for/against Optical Testing

But…

– Similar optical defects have different effects in singular applications

– Optical ≠ Mechanical ≠ Magnetic

– Only optical information available

– Thorough classification is required

– Within limits…

For Optical

– Defect concerns are similar for substrate, media, drive

– Sensitive, fast and repeatable

– Possible 100% surface inspection

– Can be used at any step in process

– Simple, well-known, traceable

10

Critical Requirements for Optical Detection

• Shallow defects:– 1 – 2 nm depths– 10,000-50,000nm diameter – Up/Down discrimination

• Scratch sensitivity:– 1- 2nm depths – <100nm width– Side discrimination (transparent

substrates)

• Particles:– 100nm PSL detection (less in the near

future)– Potential for separating removable

from non removable– Side discrimination (transparent

substrates)

Optical SignalsScattering Phase/Height/Polarization

• All requirements to match production line throughput, approx 2000pph

11

Current optical inspection systems concepts

• Monolithic: Single inspection head, single spindle– High sensitivity– Multiple signal channels: dark-field, bright-field, polarization, etc.– Small spot size– High classification level– Limited speed

• Monolithic: Single inspection head, multiple spindles– High speed – Dark-field and bright-field– Large spot size– Limited classification

• Modular: Multiple inspection heads, multiple spindles– Miniature optical head– High sensitivity and high speed– Dark-field and bright-field– Medium spot size– High classification versatility– Distributed test recipes available for each head+spindle system– Special tests (e.g. for glass: side discrimination, cracked disk)

Xyratex Sensor

13

Concept

• Mathematical model for actual electromagnetic field propagation– Surface roughness considered in the model– Accurate evaluation of signal for each detector– Good optimization possibilities– Proven results consistent with experiments

• Single source - dual detection– Simple and efficient, “dark field” and “bright field” channels– Scattering and non-scattering defects– Correlation between two channels for classification– Side discrimination

• Miniature sensor– Complete separation between “dark” and “bright” field channels– Modular construction

• Sensor• Tester• Production cell

14

Diffraction and Propagation

Laser beam

Detector Surface under test

Cells region

Diffracted field(from every cell)

U0Propagation region

U 1U 2

Πsurf R 2z

R – propagation operator

U – Complex amplitude

Π – Phase (height) function

Define surface in optical terms: cells

Define cells interaction with the laser beamIntroduce defect function as an “abnormal” cell

Propagate through the optical system

Calculate the optical amplitude and the signal

[ ]z z surface z 0R == ΠU U

( ) ( ) ( )surface m nm,n

2i h x, y 2ix, y e xp 1 h x , y⎛ ⎞π π

Π = = +⎜ ⎟λ λ⎝ ⎠∑

[ ] 2z 2 2

exp(ikz) iR U ( ) exp ( ) U( )di z z

π⎧ ⎫= −⎨ ⎬λ λ⎩ ⎭∫r r r r r

ideal 2z z mn 2

m,n m,n

exp(ikz) 2i ih exp ( ) U( )di z z∈

π π⎧ ⎫= + −⎨ ⎬λ λ λ⎩ ⎭

∑ ∫r

U U r r r r

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Area Shallow Defects – Modeling Results

Shallow Defects - Estimated Differential Signal

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Defect depth (nanometers)

Opt

ical

sig

nal f

or 1

00%

ref

lect

ivity

(%

)

25µm width 50µm width 100µm width

• Note the decrease of the signal with increased defect size

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Particle Defects Detection – Modeling Results (PSL)

Summary of Expected PSL SensitivityVarious Substrates and Spot Sizes

0

5

10

15

20

25

50 70 90 110 130 150 170 190

PSL Size (nm)

Exp

ecte

d G

auss

ian

Inte

rrac

tion

(um

)

Al 9 x 4.5 Al 13 x 6.5 Glass 9 x 4.5 Glass 13 x 6.5

• Note the non-linear relation with the particle diameter

Main Defect Categories - Images

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Area Shallow Defect – Crater (glass substrate)

HRV 2 Amplitude (mV)

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-400

-300

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-100

0

100

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300

400

0 1000 2000 3000 4000 5000 6000 7000 8000

Microns

HRV

2 A

mpl

itude

(mV

)

19

Linear Shallow Defect - Light Scratch (Al substrate)

Depth x Width ≈ 1.5nm x 50nm

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Particle Sensitivity (glass substrate)

90nm PSL

100nm PSL

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Side Discrimination – Glass Substrates

Medium Scratch

-1000

100200300400500600700800900

1000

0 50 100 150

Distance (um)

Sign

al (m

V)

Defect on Side A Defect on Side B

Backside detection <0.2%

• The current head has less than 0.2% cross talk

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Advanced Algorithm for Side Discrimination

• Most defects easily detected and side definedScratch Shallow-Disk 5 Defect On Bottom

Ghost Elimination

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Summary

• Focus on optical testing– Bit density vs. defect size– Production concerns– Optical testing – pro and contra– Detection requirements/challenges– Throughput

• Xyratex sensor– Concept– Modularity– Maps of main detector categories

• Contributors– Andrei Brunfeld– Bryan Clark– Gregory Toker– Morey Roscrow– Peter Goglia

• Entire Titan project team