Surface cleaning aluminum foil with ozone gasTakashi Momose, Eisyuh Hayasaka, Katuhiro Saitou, Katuya Nagayama, and Sin’ya Abe Citation: Journal of Vacuum Science & Technology A 16, 961 (1998); doi: 10.1116/1.581220 View online: http://dx.doi.org/10.1116/1.581220 View Table of Contents: http://scitation.aip.org/content/avs/journal/jvsta/16/3?ver=pdfcov Published by the AVS: Science & Technology of Materials, Interfaces, and Processing Articles you may be interested in Surface cleaning and modification of Si(100) substrates by ethanol and water cluster ion beams Rev. Sci. Instrum. 77, 03B508 (2006); 10.1063/1.2172342 Surface chemical changes of aluminum during NF 3 -based plasma processing used for in situ chamber cleaning J. Vac. Sci. Technol. A 22, 158 (2004); 10.1116/1.1633566 Characterization of Al, Cu, and TiN surface cleaning following a low-K dielectric etch J. Vac. Sci. Technol. B 17, 1435 (1999); 10.1116/1.590772 Surface cleaning on aluminum for ultrahigh vacuum using supercritical fluid CO 2 with H 2 O and NaCl asadditives J. Vac. Sci. Technol. A 17, 1391 (1999); 10.1116/1.581825 Aluminum Foil by XPS Surf. Sci. Spectra 5, 4 (1998); 10.1116/1.1247850

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Surface cleaning aluminum foil with ozone gasTakashi Momose,a) Eisyuh Hayasaka, Katuhiro Saitou, Katuya Nagayama,and Sin’ya Abeb)

Miyagi National College of Technology, Natori Miyagi 981-12, Japan

~Received 9 October 1997; accepted 23 March 1998!

Residual oil on rolled aluminum foil prevents good adherence of print or paint. Ozone gas exposureshows promise of effectively reducing the surface hydrocarbons to acceptable levels for industrialcoatings~,10% surface carbon!. Ozone and thermal treatments performed on laboratory- andindustrial-scale samples which were surface analyzed using x-ray photoelectron spectroscopy andfurther characterized with H2O contact angle measurements. The samples were exposed to oxygengas including ozone 630 ppm at a flowing rate of 0.5l /min. Two treatments, heating treatment andozone treatment with heating, are compared at a heating temperature, 200 °C for 6 h exposure timefor laboratory-scale samples and 200 °C for 30 min and for 160 min at higher than 100 °C forindustrial-scale samples. The atomic concentration % of carbon~C! proportional to the quantity ofoil on the surface was determined to be 9.8% for the laboratory-scale sample and 7.4% for theindustrial-scale sample. ©1998 American Vacuum Society.@S0734-2101~98!08503-0#

I. INTRODUCTION

UV/ozone cleaning of surfaces has been done by Vig1 toremove contamination. However, UV light cannot penetrateinto the complicated structure in a vacuum chamber to becleaned. Therefore, simple ozone gas has been used to re-duce carbon contaminants on UHV surfaces which are sub-ject to synchrotron radiation.2–4 Rao made cleaning alumi-num foil and evaluation.5 Energy dispersive x ray~EDX!was used for the evaluation of the foil surfaces. The methodhas high sensitivity, but the elements inside surface can bedetected because of the deep penetration depth of x ray. Wewant to know mainly the coverage of carbon on the surface.Therefore we adopted x-ray photoelectron spectroscopy~XPS! for the surface evaluation. XPS was used byStroheimer6 to evaluate aluminum foil surfaces treated withO2 plasma treatment. The treatment was not so effective forthe contamination inside surfaces.7 XPS can help to specu-late the oxide, hydroxide or not. In our case, we wanted toestimate the concentration of the elements on the surface.The motivation for the current work was just to improve andspeed up the existing industrial process of cleaning alumi-num foil to remove residual oil, which normally involvesbaking for 50–100 h at 250 °C, and as a result, to save en-ergy by reducing treatment time and temperature. This articledescribes the results of ozone and thermal treatments per-formed on laboratory- and industrial-scale samples whichwere surface analyzed using XPS and further characterizedwith H2O contact angle measurements.

II. EXPERIMENTAL SETUP

The schematic drawing of the ozone treatment apparatusis shown in Fig. 1~a! and an industrial-scale aluminum foilcoil set in the treatment chamber in Fig. 1~b!. Pure oxygenwas transferred from the pressurized tank to the ozonizer

through a liquid nitrogen trap to remove water, and thenthrough a heater to return the gas to room temperature. Oxy-gen gas containing ozone about 630 parts per million~ppm!ozone was introduced into the treatment chamber at a flowrate of 0.5l /min. The small test samples were supported ona stainless-steel open screen to provide isotropic exposure.The small samples consisted of 10 stacked sheets of AlN30-H18 aluminum foil, each sheet 29mm thick, 30 mm wide,and 40 mm long. Exposure time was 6 h each for samplesheld at 19, 30, 50, 100, and 150 °C. Industrial aluminum foil

a!Electronic mail: momose@miyagi-ct.ac.jpb!Present address: Shouwa Aluminum Corp., Oyama Tochigi 480, Japan.

FIG. 1. ~a! Schematic drawing of the ozone treatment apparatus, and~b! anindustrial-scale aluminum foil coil set in the treatment chamber.

961 961J. Vac. Sci. Technol. A 16 „3…, May/Jun 1998 0734-2101/98/16 „3…/961/3/$15.00 ©1998 American Vacuum Society

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coil samples are 145 mm in outer diameter, 75 mm in innerdiameter, and 250 mm long with a thickness of 20mm. Thefoil treatment tests were made at a maximum temperature of200 °C for 30 min and for 160 min at higher than 100 °C.The oxygen gas was supplied for 140 min.

Following the ozone exposure, the sample surface wereexamined by XPS looking for intensity changes in the Al 2s~74 eV!, C 1s ~284 eV!, O 1s ~532 eV! transitions. Theseintensities were used to calculate the surface atomic concen-tration. The C 1s spectrum was further deconvoluted to yieldratios of CH, CO, and COO. Measurements of H2O contactangles were also made in an attempt to establish a correlationwith the level of surface cleanliness.

III. RESULTS

Figure 2 compares the surface carbon levels versus expo-sure temperatures for the 6 h exposure with flowing oxygenand with oxygen plus 630 ppm ozone. It is clear that addingozone enhances the carbon removal rate and achieves thedesired 10% level after 6 h at 150 °C.Variations in surfaceconcentrations of oxygen, aluminum and carbon versus tem-perature for the 6 h ozone exposures are shown in Fig. 3.Most of the carbon reduction and surface oxygen increaseoccurs when the temperature is raised to 50 °C. Further in-creases in temperature show less dramatic changes. Figure 4shows the relative amounts of the deconvoluted CH, COO,and CO signals versus temperature. It appears that the mea-sured carbon reduction is from hydrocarbon removal propor-tional to temperature up to 50 °C. Normally mineral oil withseveral additives is used to decrease friction during rolling.Therefore the oil is the residual. The decrease in CH andincrease in COO of oil suggested that hydrocarbons consist-

FIG. 2. Surface carbon levels on small aluminum foil following 6 h expo-sures to flowing oxygen and to oxygen plus 630 ppm ozone at varioustemperatures.

FIG. 3. Surface concentrations of O, Al, and C on the ozone treated smallsamples.

FIG. 4. Surface concentrations of CH, COO, and CO on the ozone treatedsmall samples.

FIG. 5. H2O contact angle versus concentration of CH, COO, and CO on theozone treated small samples.

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J. Vac. Sci. Technol. A, Vol. 16, No. 3, May/Jun 1998

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ing of the oil was decomposed with ozone. Further changesat the highest temperature~150 °C! suggest oxide growthconversion from COO. Figure 5 compares H2O contact anglechanges with the deconvoluted surface carbon levels andconfirms that hydrocarbon reduction has the most pro-nounced effect on H2O contact angle, compared to the re-moval of CO and COO. Figure 6 shows that the variation inaluminum oxide thickness with treatment temperature foroxygen and for oxygen plus 630 ppm ozone flowing over thefoil for 6 h. There appears to be enhanced oxidation with theozone mixture at temperatures greater than 100 °C. Table Ishows carbon concentration, oxide thickness at central (c)part and edges, and H2O contact angle for original, bakedand ozone treated industrial-scale aluminum coils. The ozonetreated sample satisfied the industrial requirement for mini-mal C concentrations.

IV. CONCLUSION

Experiments on small sections of stacked aluminum foiland on full-scale rolls of industrial aluminum foil have dem-onstrated that temperature and times required to clean thesurfaces enough for acceptable adhesion of paint or print~,10% carbon! was reduced by about one order in treatmenttime at reduced temperature with flowing oxygen gas includ-ing 630 ppm ozone.

ACKNOWLEDGMENT

The authors would like to thank Mr. E. W. Hoyt at Sur-face & Material Science in the USA for his helpful discus-sions.

1J. R. Vig, J. Vac. Sci. Technol. A3, 1027~1995!.2T. Momose, K. Asano, N. Ohta, Y. Kanda, and H. Ishimaru, J. Vac. Sci.Technol. A13, 486 ~1995!.

3T. Momose, Y. Maeda, K. Asano, and H. Ishimaru, J. Vac. Sci. Technol.A 13, 515 ~1995!.

4T. Momose, K. Asano, Y. Katoh, and H. Ishimaru, Vacuum47, 319~1996!.

5V. Rao, J. Vac. Sci. Technol. A11, 1714~1993!.6B. R. Stroheimer, J. Vac. Sci. Technol. A7, 3238~1989!.7M. Saitoh, K. Kanazawa, T. Momose, H. Ishimaru, N. Ohta, and J. Ura-moto, J. Vac. Sci. Technol. A11, 2518~1993!.

FIG. 6. Oxide thickness versus treatment temperature for small samplestreated with oxygen and with oxygen plus 630 ppm ozone following 6 hexposures.

TABLE I. Carbon concentration, oxide thickness at central (c) part and edges(e), and water contact angle for original, baked, and ozone treatedindustrial-scale aluminum foil coils.

SamplesOxide~nm!

Atomic conc.~%!Cont. angl.~degrees!

C convol.~AC%!

C Alox Almet 0 CH CO COO

Original 4.7(e) 24(e) 20 5.1 50 90–100 19 22 3.6Baked 5.8(e) 13(e) 26 4.8 56 42 8.6 1.3 3.6

5.4(c) 19(c) 25 4.3 51 78 15 1.4 2.5Ozone 7.6(e) 7.4(e) 30 2.6 60 ,2 5.6 0.7 1.5Treated 7.5(c) 7.9(c) 30 2.3 60 ,2 6.0 0.8 1.4

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