CMP Scratches; Their Detection and Analysis on … LEVITRONIX CMP and Ultrapure Conference 2 Nano-Bio Electronic Materials and Processing Lab. Outline Introduction Issues of CMP Defects(Scratch)

CMP Scratches; Their Detection and

Analysis on Root Causes

6th LEVITRONIX CMP and Ultrapure Conference The Westin Park Central, Dallas, Texas

May 11-12, 2011

May 11, 2011

Jin-Goo Park

Department of Materials Engineering, Hanyang University, Ansan, 426-791, Korea

2 Nano-Bio Electronic Materials and Processing Lab. 6th LEVITRONIX CMP and Ultrapure Conference

Outline

Introduction

Issues of CMP Defects(Scratch)

Motivation

Experimental

Results

Summary

Lab. capability

Experiment tools & procedure

Post-CMP cleaning

Detection method of scratches

Scratch source & scratch shape (pad debris, dry particle, diamond particle)

Effect of Large Particle concentration

Effect of conditioner diamond


ICPT 2011 in Seoul, Korea

• http://www.icpt2011.com/

• November 9 – 11, 2011

• Abstract due online July 4, 2011

http://www.icpt2011.com/


Scratch Sources in Oxide CMP

Polishing table

Polishing pad

Head

Pressure

Slurry

Conditioner Wafer

Slurry

Conditioner Surface

Pad Surface

CMP consumables : Pad, Slurry, Conditioner

These consumables should be controlled to achieve better performance


The Migration of CMP Technology

CMP Tool

Polishing recipe

Pattern design

Slurry

Consumable part

Pressure control & table speed tuning

Chosen the tool equipped the head of retainer ring

and membrane

Applied optional slurry for

each process

Compounding the

consumable parts

AMAT MIRRA tool

CMP simulation & dummy

pattern insert

Removal profile & selectivity, dishing control

The alterative application of

consumable parts

Removal profile control


The Type of defects Produced after oxide CMP

Surface

Void

Residual

Slurry Embedded

Particle

Scratch

Surface Particle

Common

CMP Defects

Scratch is the most deleterious defect compared to other type of defects.


ITRS Roadmap

Micro-scratches and defects can lead to severe circuit failure, low yield and

potential reliability issue.

It is important to evaluate defects and their sources for CMP sustainability.

Among defects, scratch is still not well understood in CMP process


The Factors that Play Key Role in the Scratch formation

Slurry

Pad

Conditioner

Wafer Surface

Wafer hardness : TEOS, HDP, BPSG

Abrasive size and Distribution

Large particle concentration

Abrasive type (Colloidal, Fumed, New type) and Agglomeration

Particle morphology

Diamond size & density

Diamond shape

Diamond patterns

Role of Active diamond

Diamond wearing or breaking

Pad asperity& contact area

Pad profile

Pad debris

Film Material : Cu, STI, ILD

Pad cutting rate

Design (asperities, pore and groove) Hardness


Motivation

Detection of scratches formed on oxide wafer

Effect of CMP process and consumables

• CMP Process (pressure, velocity of head/platen)

• CMP Slurry

• CMP pad & conditioner

• Thin film materials

Study on Scratch

formation CMP

performance

To evaluate the post CMP cleaning process to detect the scratches

easily by a new technique


Experimental (Modification of Polisher Head)

DOOPLA310 (300 mm) 12” Head 8” Head (scratch test)

• Modification and Installation of 8” polisher head for scratch

formation and detection

11 6th LEVITRONIX CMP and Ultrapure Conference Nano-Bio Electronic Materials and Processing Lab.

Experimental Procedure (Scratch Formation)

New Pad

Break-In

Conditioning

CMP

-Dummy (2)

- RR&N.U (2)

- Gathering (2)

-- Scratch (3)

Cleaning

Detection

Pad – IC1010

Break In

- Conditioning with DIW (30min)

- Conditioning with Slurry (10min)

Conditioning

- Conditioning with DIW (10min),

- Conditioning with Slurry (5min)

CMP

- Dummy CMP 2times

- CMP for CMP performance 2 times

- Dummy CMP for slurry gathering 2times

- CMP for scratch 3times

Cleaning

- SC-1 (10min)→Over Flower (3min) → DHF (3min)

→ Over Flower (210 Sec) → SC-1 (10min) → IPA Dry

Repeating


Optimization of Post-CMP Cleaning for Scratch Detection

Contact Angle Analyzer

Wet Station Ozone

Generator

Aaron Single Tool

Particle Scanner

(Surfscan6200)

Laser Shock Wave Cleaning Tool

Fluorescent Microscope

AFM

H2-DIW

Generator

FPD Cleaning

Tool

table

Main Table PIV

Work Table

Particle deposit

ion OM

Air Shower Akrion

Single Tool

7,2

00 5

,750

1,4

50

• Lab. capability : Clean Room (class 10) - Post-CMP Cleaning & Scratch detection

Sample Room

Dress Room

Clean Area

Entrance


Analysis Tools for Scratch detection

Particle scanner

(Surfscan 6200, KLA-Tencor, USA)

• Surfscan6200 (KLA-Tencor)

: Detection of Scratch number

• Control the Gain value & Threshold value

Optical Microscope

(Nikon, LV-100D)

1000X 20μm

• Analysis of Scratch shape

• Counting the non-removed particle after cleaning

Defect number Scratch shape


Post-CMP Cleaning (Role of Scrubber Cleaning)

Wet Send

Indexer Brush

Module

DIW

1 min

Schematic of removal of particle

from surface by scrubber

A standard, hollow cylindrical

sponge with nodules

PVA Scrubber

• Scrubber Cleaning after slurry dipping during 1min

• PRE is increased by scrubber cleaning

0

5000

10000

15000

20000

No scrubber

LP

D (

ea)

Scrubber

Gain(4), Threshold(0.18)

: 0.18 um ~ 1.6 um

Gain(4), Threshold(0.36)

: 0.36 um ~ 1.6 um

Effect of Scrubber Cleaning


Optimization of RCA Cleaning (Wet station for 200/300mm wafer cleaning)

0

1000

2000

3000

4000

5000

6000

7000

Particle Size Range

SC-1 => HFSC-1

LP

D (

ea.)

Initial

0.18 ~ 0.6 um

0.21 ~ 7.7 um

0.32 ~ 28 um

2 ~ 63 um

Sequence : 1. SC1 – 2. HF

SC-1 SPM HF Sink IPA

vapor dryer

Quartz heater

1 MHz Megasonic

SC-1 Quartz bath • Optimization of SC1 process

- NH4OH : H2O2 : DIW = 1 : 2 : 50 @ 50°C with 1MHz megasonic

• Optimization of HF Cleaning and Etching (HF 0.5%)

- HF cleaning (30s) : Particle removal

- Scratch etching (180s) : Magnification of Scratch

• Optimization of IPA vapor dryer


Effect of HF etching for Scratch Detection

• Treatment of HF solution (30s) - Surface cleaning

• Treatment of HF solution (180s) – Extension of generated scratches

• Scratches were extended to defect easiliy by HF solution after CMP

Before HF etching After HF etching


PRE of cleaning process and optimization of surfscan recipe

Gain(1)

Threshold

(2 ㎛)

• At threshold 2㎛ almost all the particle were removed (Efficiency 99%)

• Hence any particle appear at this range after CMP process, that might be related to the scratch directly.


CMP Performance & Scratch Number (Reference)

Removal Rate & Non-uniformity

• Evaluation of Reference process during 360 times CMP

- Process Condition : 4.5 psi, head 67rpm/ platen 73 rpm, 30s

- RR : Avg. 460 nm/min, WIWNU : below 5%

• Evaluation of Reference Scratch formation during 360 times CMP

- Reference scratch formation : below 15EA

0 50 100 150 200 250 300 350 4000

100

200

300

400

500

600

0 50 100 150 200 250 300 350 4000

5

10

15

20

Rem

oval

Rate

(n

m/m

in)

The time of CMP

Removal Rate

No

n-U

nifo

rmity

(%)

Non-uniformity

-50 0 50 100 150 200 250 300 350 400

0

30

60

90

120

150

Th

e n

um

ber

of

scra

tch

(E

A)

The time of CMP

2 ~ 63 m

Scratch Number (reference)

Control the high scratch using the break-in process

- 30min with DIW - 10 min with slurry


Scratch Detection Mathods

(0,0)

Surface Analyzer Image Section Paper

• The surface analyzer image exactly overlapped with section paper to detect the location of the defects

• Each individual defect was inspected by Optical Microscope using the above approach

(0,0)

Both surface analyzer image and

section paper exactly overlapped


CMP

Clean

Oxide Wafer

Post-CMP Cleaning

Scratch Image

By Optical Microscope ( LV-

100D, Nikon, Japan)

• Lap Scale (micron)

• Specific Scratch

at Specific Area

• Scratch Characterization

( Dimension, Shape)

≤ 15000 ea

≤ 20 ea

SC-1

(600C, 10min)

DHF

(0.5vol%,

210s)

Marangoni

IPA Dry

Removal of Slurry Reside

Extension of Scratch

Removal of Water Mark

By Surface Particle Scanner

(surfscan 6200 KLA, Tencor, USA)

Summary of Scratch Detection Method

SC-1

(600C, 10min)

Removal of

Re-contamination particle


Capturing the image of a scratch by the new method

• The specific scratch at specific region could be observed by a microscope using wafer matching method.

• Over 95% accuracy was observed in detecting the scratches

• And also, the scratch analysis was done by AFM

Wafer Matching Test after CMP

5.664 um

5.317 um

OM image

AFM image


Classification of Scratches Formed on Oxide Surface

Line chatter Broken chatter Group chatter

• The Major type of scratch shapes are Chatter on oxide surface : Chatter type occupies more than 70%

Continuous Line Broken Line Random

•Sliding of embedded large particle • Indentation depth determine the scratch shape

• Irregular scratch source and it’s behavior may generate the random type


Scratch Formation Theory (Chatter Scratch Formation)

* H-J Kim, et al., “Modeling on the CMP Scratch”, 43th Technical Meeting of Korea CMPUGM (2009)

• Stick-Slip phenomena

- Stick friction is increased by the stress concentration,

which induce the Scratch formation

- Slip friction is generated after surface fracture, which

decide the distance between chatter scratch

Most probable mechanism


Vacuum

Pump

Slurry Delivery Atomizer

Head

Conditioner

After CMP

• To investigate the scratch sources generated during polishing, a gathering system was developed to collect the byproducts directly during the CMP process. • After examining the several locations , to gather byproducts, it was found that gathering of byproducts at the back position of the wafer would be the better position .

Gathering of CMP byproducts

Schematic diagram of slurry gathering system


• The comparison was performed among fresh pad and byproducts collected during just conditioning and actual polishing

• SEM images shows the presence of some large matter in byproducts

• EDX analysis confirms that the large matters related to pad debris. The byproducts of polishing also contains Si composition,

which is due to the slurry

• It could be concluded that generation of pad debris is significant during CMP process and their effect should be studied.

SEM and EDX analysis of gathered CMP byproducts


The number of Byproduct after CMP

5 10 15 20 25 30

0

500

1000

1500

2000

2500

3000

3500

4000

Slurry 100L

Nu

mb

er

of

Part

icle

Particle Size (m)

Fresh slurry

In-situ conditioning

• After CMP process, large particle number is increased in byproduct (byproduct 100 uL) • During in-situ conditioning, Pad debris is generated which affect to scratch formation

Number of Byproduct


0

20

40

60

80

100

Sc

ratc

h N

um

be

r (%

)

Addition of Pad Debris

Rolli

ng type

Total L

ine

Bro

ken L

ine

Contin

uous Lin

e

Total C

hatte

r

Gro

up Chat

ter

Dot C

hatte

r

Bro

ken C

hatte

r

Line

Chat

ter

Correlation between scratch source and scratch shape

0

20

40

60

80

100

Rolli

ng type

Total L

ine

Bro

ken L

ine

Contin

uous Lin

e

Total C

hatte

r

Gro

up Chat

ter

Dot C

hatte

r

Bro

ken C

hatte

r

Line

Chat

ter

Scra

tch

Nu

mb

er

(%) Reference Wafer

0

20

40

60

80

100

Sc

ratc

h N

um

be

r (%

)

Addition of Dried Slurry Particles

Rolli

ng type

Total L

ine

Bro

ken L

ine

Contin

uous Lin

e

Total C

hatte

r

Gro

up Chat

ter

Dot C

hatte

r

Bro

ken C

hatte

r

Line

Chat

ter 0

20

40

60

80

100

Sc

ratc

h N

um

be

r (%

)

Addition of Diamond Particles

Rol

ling

type

Tota

l Lin

e

Bro

ken

Line

Con

tinuo

us L

ine

Tota

l Cha

tter

Gro

up C

hatter

Dot

Cha

tter

Bro

ken

Cha

tter

Line

Cha

tter

• Different scratch sources added individually to the CMP process and then their effect on scratch shapes was studied


δ

α

Pad

F

Wafer

Hertzian Indentation

Schematic of Scratch Generation

Hard Surface (HDP) Soft Surface (BPSG)

- In oxide film, scratch is generated by particle’s indentation depth and stick-slip phenomenon

- In lower hardness films, assume that longer and wider chatter type was generated due to deeper indentation depth and rotation of particles.

HDP TEOS BPSG


Conditioner #1 - Low density diamond

Conditioner #2 - Mid density diamond

(Std. conditioner)

Conditioner #3 - High density diamond

Effect of Conditioner Diamond Density On Scratch Formation

Conditioner Images as a function of Diamond Density


• In high density conditioner case, Lower RR (450 nm/min) is measured than that of other conditioners

• Conditioning with DIW

- Larger pad particle is generated during high density diamond conditioning

0

1

2

3

4

5

300

350

400

450

500

550

No

n-u

nifo

rmity

(%)

Rem

oval R

ate

(n

m/m

in)

Removal Rate

HighMidLow

Diamond Density

Non-uniformity

Removal Rate & Non-uniformity

CMP Performance as a function of Diamond Density

After conditioning with DIW

10 100 1000 10000 100000 10000000

10

20

30

40

50

60

Low

Mid

High

Dif

fere

nti

al n

um

be

r %

Diameter (nm)

Diamond Density


- Pad height probability is measured after conditioning - (Wyco-NT9100, VEECO, USA)

row

mid

high

• After conditioning using the High density diamond conditioning, Pad height probability is generated at high pad height • It means that conditioning is provided to only pad asperity area. Also, enough conditioning isn’t provided at the pore area • Because the pressure on each diamond of high density is lower than that of standard or low density conditioner

Pad height probability(Data for *Dow chemical Company)

Polishing Pad

Diamond conditioner

Pad Surface Analysis after conditioning


- The scratch number is measured after HF 0.5 vol% etching (210s)

- The highest number of scratch is generated during polishing with high density diamond

conditioner

- The scratch number may be affected by conditioner performance and generated Pad particle size

Scratch Number as a function of Diamond Density

0

10

20

30

40

50

60

70

3

3

3

2

2

2

1

1

HF 0.5% etching (210s)

1

High DensityMid Density

Th

e N

um

be

r o

f S

cra

tch

(E

A)

Low Density


Summary

Optimized Post CMP Cleaning Process

- Cleaning sequence : SC1 (10min) HF Cleaning (210s) SC1 (10min) wafer Dry

SC1 Cleaning : Removal of particles

HF Cleaning : Removal of particles and extension of scratches

Classification and sub classification of scratch shapes on oxide after CMP

- The major type of scratch shapes are Chatter on oxide surface

- Also, unstable friction between pad and wafer may generate the Broken/Group chatter scratches

Scratch Source Vs Scratch Shape

- Three different scratch sources were tested on the shape of scratch formation.

- It was found that specific scratch source has specific effect on scratch shape and size.

- The dried and diamond particles showed severe effect on scratch formation due to their hard nature

Characterization of Process Consumables

- Surface hardness : Indentation depth by abrasive particle affect to scratch number and shape

- LPC : Large particle of slurry can cause the unstable scratch formation

- Conditioner : Conditioner performance may affect to the pad debris generation and scratch formation


Documents

CMP Scratches; Their Detection and Analysis on … LEVITRONIX CMP and Ultrapure Conference 2 Nano-Bio Electronic Materials and Processing Lab. Outline Introduction Issues of CMP Defects(Scratch)