Deposition of Ultra thin Amorphous Carbon Films by Filtered Cathodic - - PowerPoint PPT Presentation

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 Xie Advisor: 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
• vercoats
• 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

• r 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

• ff bias
• Defined as the ratio
• f the pulse-on Ton

time to the pulse period T

T Ton

λ = Ton / T

50 100 150 200

• 150
• 100
• 50

Substrate voltage (V)

50 100 150 200

• 150
• 100
• 50

50 100 150 200

• 150
• 100
• 50

Duty cycle (%)

50 100 150 200

• 150
• 100
• 50

50 % 95 % 65 % 75 %

Time (s)

Negative bias Off bias

Film Properties T‐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%

2 4 6 8 10 12 14 0.0 0.2 0.4 0.6 0.8 1.0

Atomic carbon fraction Depth (nm)

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

Film Properties Thickness 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

20 40 60 80 100 2 4 6 8 10 12 14

Thickness (nm) Duty cycle (%)

Total film thickness Carbon layer thickness Intermixing layer thickness

Film Properties Surface 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

Roughness (nm) Duty cycle (%)

Ion sputter etching dominated Deposition dominated Balance between deposition and sputtering

G peak - Stretching mode D peak - Breathing mode

Film Properties Raman 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

Intensity (a.u.) Wavenumber (cm

• 1)

50% 65% 75% 95% Duty cycle D G

Film Properties Raman measurement

50 60 70 80 90 100 180 190 200 210 220 230

G peak FWHM(cm

• 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 90 100 0.2 0.4 0.6 0.8 1.0 1.2

D-to-G peak intensity ratio Duty cycle (%)

Film Properties Raman 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 90 100 1550 1555 1560 1565 1570 1575 1580

G peak position Internal stress

Duty cycle (%) G peak position (cm

• 1)
• 12
• 11
• 10
• 9
• 8
• 7

Internal stress (GPa)

Increased ion Increased ion implantation Excessive sputtering and thermal spikes

• The internal stress σf is measured by curvature method

Film Properties TEM cross‐sectional sample

CM200 Tecnai

• HRTEM images
• STEM
• EELS
• Cross-sectional

specimen

Film Properties TEM 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

• btained by XPS
• Investigation of the duty cycle effect on the thermal stability of

FCVA-deposited a-C films

Future Work

Thanks!