CML Annual Sponsors’ Meeting

Deposition of Ultra‐thin Amorphous Carbon Films by Filtered Cathodic Vacuum Arc for the Head‐Disk Interface

‐ A Study of the Duty Cycle Effect

Jun XieAdvisor: Prof. K. Komvopoulos

Surface Sciences and Engineering Laboratory (SSEL)

Introduction

• Objective– Synthesize ultrathin (<2 nm), smooth and durable

amorphous carbon (a-C) overcoats• Higher storage level with high-quality protective

overcoats

• Method– Control of deposition parameters

• Competition between deposition, implantation and re-sputtering processes results in the modification of film properties

Deposition Method• Filtered Cathodic Vacuum Arc (FCVA)

– Energetic C+ ion bombardment– Substrate bias voltage controls the ion energy

Substrate pulse bias

Ion fluence(deposition time or arc current)

Ion energy (substrate bias voltage)

Incidence angle

Duty cycle of pulse bias

Duty cycle of substrate bias

• Controls the contributions of high- and low-energy FCVA deposition processes. – high C+ ion energy during negative biasing, low C+ ion energy during

off bias

• Defined as the ratio of the pulse-on Tontime to the pulse period T

T

Ton

λ = Ton / T 0 50 100 150 200

-150

-100

-50

0

Subs

trate

vol

tage

(V)

0 50 100 150 200

-150

-100

-50

0

0 50 100 150 200

-150

-100

-50

0

Duty cycle (%)0 50 100 150 200

-150

-100

-50

0

50 %

95 %

65 %

75 % Time (s)

Negative bias

Off bias

Film PropertiesT‐DYN (transport range of ions in matter) simulations

• Monte Carlo simulations of binary atom collisions• Computation conditions

– Target: silicon & incoming C+ ions– Ion energy: -173 eV for pulse-on time and 0 eV for pulse-off time, producing an average

ion energy between 86 eV and 146 eV for duty cycles in the range of 50% to 95%

0 2 4 6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

Atom

ic c

arbo

n fra

ctio

n

Depth (nm)

0% 50% 65% 75% 95% 100%

Film PropertiesThickness dependence on duty cycle

• Total thickness: thickness of all channels containing C atoms (0-100 at%)• Carbon layer: C atom fraction > 85 at%• Thickness of intermixing layer: C atom fraction 5-85 at%• More C+ implantation and less deposition with the increase of the duty cycle

0 20 40 60 80 1000

2

4

6

8

10

12

14

Thic

knes

s (n

m)

Duty cycle (%)

Total film thickness Carbon layer thickness Intermixing layer thickness

Film PropertiesSurface topography

• The film surface roughness was determined from 2×2 μm2 surface area images obtained with the AFM

• Roughness is influenced by deposition and sputtering process effects

50 60 70 80 90 100

0.120

0.125

0.130

0.135

0.140

R

ough

ness

(nm

)

Duty cycle (%)

Ion sputter etching dominated

Deposition dominated

Balance between deposition and sputtering

G peak - Stretching modeD peak - Breathing mode

Film PropertiesRaman measurement

• Methods– Gaussian fit of D and

G peaks

• Shape features – G peak FWHM– G peak position– I(D) / I(G) ratio

• Dependent factors– sp2 cluster size– Bond length/angle

disorder– sp2/sp3 ratio

1200 1400 1600 1800

Inte

nsity

(a.u

.)

Wavenumber (cm-1)

50%

65%

75%

95%

Duty cycleD G

Film PropertiesRaman measurement

50 60 70 80 90 100

180

190

200

210

220

230

G p

eak

FWH

M(c

m-1)

Duty cycle (%)

• Decrease of I(D)/I(G)- shows a decrease in• sp2 cluster size• sp2 ordering

• Increase of G peak FWHM- shows a decrease in• sp2 cluster size

50 60 70 80 90 1000.2

0.4

0.6

0.8

1.0

1.2

D-to

-G p

eak

inte

nsity

ratio

Duty cycle (%)

Film PropertiesRaman measurement VS stress relation

• Downward shift of G peak position – shows a decrease in

• sp2 cluster size and ordering• linear chain length• sp2 fraction

– shows an increase in• sp3 fraction• internal compressive

stress

50 60 70 80 90 1001550

1555

1560

1565

1570

1575

1580 G peak position Internal stress

Duty cycle (%)

G p

eak

posi

tion

(cm

-1)

-12

-11

-10

-9

-8

-7

Inte

rnal

stre

ss (G

Pa)

Increased ion Increased ion implantation

Excessive sputtering and thermal spikes 

• The internal stress σf is measured by curvature method

Film PropertiesTEM cross‐sectional sample

CM200 Tecnai

• HRTEM images • STEM• EELS

• Cross-sectional specimen

Film PropertiesTEM image

• intermixing layer thickness: 4.4 nm• a-C film thickness: 14.9 nm• total thickness: 19.3 nm

• Deposition condition• 95% duty cycle• 30 s deposition time

Conclusions• The duty cycle has a significant effect on the film properties

(controls the competing effects of deposition and sputtering).• The thickness of the a-C film and the intermixing layer increase

with the increase of the duty cycle• A 65% duty cycle yields the lowest roughness, whereas a 75% duty

cycle yields the highest compressive stress and sp3 fraction, smallest sp2 cluster size, less bond ordering, and lowest sp2 fraction

• Investigation of cross-sectional EELS spectra of a-C films for different duty cycles aimed at further reducing the thickness while preserving the protective film properties (e.g., high sp3 fraction)

• Comparison of sp2and sp3 hybridizations of a-C films obtained from cross-sectional EELS analysis with the overall film composition obtained by XPS

• Investigation of the duty cycle effect on the thermal stability of FCVA-deposited a-C films

Future Work

Thanks!