EUV-initiated surface changes in polymers

A. Bartnik, H. Fiedorowicz, R. Jarocki, J. Kostecki, M. Szczurek Institute of Optoelectronics, Military University of Technology,

Kaliskiego 2 ,00-908 Warsaw, Poland

A. Biliński, O. Chernyayeva, J.W. Sobczak Institute of Physical Chemistry Polish Academy of Sciences, 44-

52 Kasprzaka Street, 01-224 Warsaw, Poland

Outline

• motivations

• laser - plasma EUV source for surface modification

- the source description

- EUV parameters

• interaction with selected polymers

- surface morphology - SEM measurements

- chemical changes - XPS measurements

• summary

Motivations

• Surface processing- what for?

Change of some surface properties: wettability, roughness, optical and adhesive properties, biocompatibility

• How can be obtained?

Changing surface morphology and chemical structure

• Physical methods:

plasma treatment, ion implantation, UV irradiation

• Why EUV irradiation?

Additional method, very small penetration depth, applicable for any polymer

EUV source for surface processing

Laser-plasma EUV source,

Gas-puff target,Low vacuum

EUV collector,Efficient turbo pump,Differential pumping

Chamber for irradiation,Options:•High vacuum for mass spectrometry,•Reactive gas under low pressure• possible use for micromachining

EUVbeam

EUV source for surface processing

View of the EUV source for surface modification

Source section, low vacuum

Schematic view of the double stream gas puff target

Gas puff target area

Gas valve

Orifice for differential pumping

lenslaser

beam

low-Z gas(hydrogen, helium)

krypton

outer nozzle inner nozzle

LaserNd:YAG

0.8 J, 4 ns, 10 Hz

Spectra of Xe, Kr, Kr+10%Xe EUV direct radiation measured using a spectrograph withtransmission grating TG 5000 lines/mm (high resolution) and 250 lines/mm (low resolution)

EUV spectra of Kr, Kr+Xe, Xe plasmas

High resolution spectra of Xe, Kr, Kr+10%Xe EUV reflected from Au plated ellipsoidal collector,measured using a spectrograph with transmission grating TG 5000 lines/mm

EUV spectra of Kr, Kr+Xe, Xe plasmas (reflected)

Low resolution spectra of Xe, Kr, Kr+10%Xe EUV reflected from Au plated ellipsoidal collector,measured using a spectrograph with 250 lines/mm transmission grating

EUV spectra of Kr, Kr+Xe, Xe plasmas (reflected)

2,0 1,5 1,0 0,5 0,0 0,5 1,0

0

10

20

30

40

fluen

ce (

mJ/

cm2 )

distance from axis (mm)

Intensity distribution close to 10nm in the focal plane of the EUV collector

Intensity distribution in the wide wavelength range in the focal plane of the EUV collector

2 1 0 1 20

10

20

30

40

50

60

70

fluen

ce (

mJ/

cm2 )

distance (mm)

EUV fluence in the focal plane for Kr plasma

Poly (methyl methacrylate) PMMA 5 EUV pulsesa)no further treatmentb)soaked in PMMA developer (methyl isobutyl ketone + isopropyl alcohol)

Polyamide 6 (Nylon) 5 EUV pulsesa)no further treatmentb)soaked in isopropyl alcohol)

EUV induced structures on PMMA and PA surfaces

Two opposite processes are possible: crosslinking and fragmentation of polymer chains.

Evidences of fragmentation shown here and in next slides

SEM images of the microstructures formed under EUV irradiation with the fluence close to maximum, well above the ablation threshold, followed by acetone rinsing

Surface morphology of PET foil irradiated with different number of EUV pulses

with further acetone treatment:

a) 10 pulses,

b) 25 pulses,

without acetone treatment:

c) 10 pulses

d) 250 pulses

The acetone rinsing removes the light fractions revealing the nanostructures having the form of grains with the size of the order of tens nanometers. The general form of surface microstructures remains unchanged.

EUV induced structures on PET surface

Measurements of chemical changes

500 1000 1500 2000

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

not - irradiated EUV - irradiated

inte

nsity

(ar

b. u

nits

)wave number (cm-1)

•Raman scattering

•Infrared spectroscopy

•X-ray photoelectron spectroscopy

500 1000 1500 2000

EUV - irradiated not - irradiated

inte

nsity

wavenumber (cm-1)

Raman spectra Infrared spectraSignals come mainly from bulk with a very small contribution from the modified near surface layer. Hence the spectra before and afterirradiation are almost identical.

XPS spectra of PEN

1400 1200 1000 800 600 400 200 00

1x105

2x105

3x105

4x105 b)a)

C KL1

O KL1

C 1sO 1s

C KL1

O KL1C 1s

O 1s

inte

nsity

(ar

b. u

nits

)

binding energy (eV)

1400 1200 1000 800 600 400 200 00

1x1052x1053x1054x105

binding energy (eV)

inte

nsity

(ar

b. u

nits

)

290 288 286 284 2820

1x1042x1043x1044x1045x104

290 288 286 284 2820.0

2.0x104

4.0x104

6.0x104

C2

C3

C1

c)

a)

d)

b)

inte

nsity

(arb

. uni

ts)

binding energy (eV)536 534 532 530 528

1x1042x1043x1044x1045x104

O1O2

int

ensi

ty (a

rb. u

nits

)

binding energy (eV)

C1C

2C

3

inte

nsity

(arb

. uni

ts)

binding energy (eV)536 534 532 530 528

1x104

2x104

3x104

4x104

O1O2

inte

nsity

(arb

. uni

ts)

binding energy (eV)

• Concentration of C2 and C3remarkably decreased,• Concentration of oxygen decreased• O1/O2 ratio remained almost unchanged

• Broadening of the peaks• Shift of maxima of the peaks

oxygen is being removed as a whole O-C=O functional group

each peak comes from more than one unique specie

XPS spectra of PET, PEN and PI

• Carbon enrichment in the near surface layer in all cases

• Concentration of O and N decreased

Changes in ablation and surface modification

thresholds

polymer PET PEN PI

component C1s O1s C1s O1s C1s O1s N1s

non-treated 72,07 27,94 70,67 26,92 75,9 17,51 6,58

irradiated 80,23 19,77 82,16 17,85 82,92 12,31 4,77

40 30 20 10 0 -10

PEN not-irradiated PEN EUV-irradiated

inte

nsity

binding energy (eV)

40 30 20 10 0 -10

PI not-irradiated PI EUV-irradiated

inte

nsity

binding energy (eV)

30 20 10 0 -10

-C=C-(benzene)

O=C-O

C-CC=OC-O

PET not-irradiated

inte

nsity

binding energy (eV)

30 20 10 0 -10

PET EUV-irradiated

inte

nsity

binding energy (eV)

PET – valence XPS

not-irradiated

EUVirradiated

not-irradiated

EUV rradiated

not-irradiated

EUV irradiated

PEN – valence XPS

PI – valence XPS

XPS spectra of PET, PEN and PI

Conclusions

• EUV source for surface modification was presented

• Parameters of the EUV source were measured

• morphology changes in selected polymers were presented

• chemical changes were proved

• results and interpretation of XPS measurements were presented

The research was partially performed in the frame of the EUREKA project E! 3892 ModPolEUV

and under COST Action MP0601, funded by the Ministry of Science and Higher Education

(decision Nr 120/EUR/2007/02)

Acknowledgements