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RF sputtering of polymers and its potential application
Vacuum 59 (2000) 594}599
RF sputtering of polymers and its potential application H. Biederman* Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, V Holes\ ovicka& ch 2, 180 00 Prague 8, Czech Republic
Abstract Plasma polymerization processes are commonly used for the deposition of thin "lms of plasma polymers that have been proposed for a variety of applications ranging from surface modi"cations for biomedical purposes to optical coatings and variable and protective "lms in electronics. RF sputtering of polymeric materials in an inert gas (Ar) or in its own fragmented polymer vapours can be applied in order to avoid the conventional supply of gaseous monomer. Volatile fragments of polymeric target serve as plasma polymerization precursors in the case of RF sputtering. RF sputtering of polytetra#uoroethylene (PTFE), polyimide (PI), etc. are rewieved. Recent results from our laboratory on balanced and unbalanced magnetron RF sputtering of polytetra#uoroethylene and polyethylene (PE) are presented. The dependence of structure and morphology of RF sputtered plasma polymers on plasma parameters and substrate temperature is discussed. In conclusion potential applications are summarized. 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction In the 1970s the deposition of plasma polymers by means of radio frequency (RF) sputtering of targets made of conventional polymers received considerable attention. The interest was particularly focused on polytetra#uoroethylene (PTFE) [1}7]. The motivation was apparently to prepare good dielectric "lms [2] and low friction coatings [1,6]. Optical applications were also considered [6]. 2. Fluorocarbon plasma polymers Usually, PTFE was sputtered in argon. Also, the so called self-sputtering of PTFE was performed. In this case, argon was used only to initiate the discharge that continued in volatile * Fax: #42-02-688-5095. E-mail address: [email protected]!.cuni.cz (H. Biederman). 0042-207X/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 3 2 1 - 3
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fragments of PTFE when argon supply was shut o!. Because sputtered PTFE "lms were found de"cient in #uorine sputtering in a mixture of Ar and CF was performed that increased the ratio F/C in prepared "lms [8]. In a single case nitrogen was used as a working gas [9]. Later in addition to nitrogen, gases such as helium and neon were applied [10]. In recent years interest in RF sputtering of PTFE has been renewed [10}13] as the obtained plasma polymer "lms are again in demand as protective, low friction and non-wettable coatings.
3. Hydrocarbon plasma polymers compared to 6uorocarbons The second polymer that has been investigated for RF sputtering is polyimide (PI) known also by the trade name Kapton. Yamada et al. [14] sputtered PTFE and PI "lms in Ar at 6. 65;10\ Pa. At a constant power density 1.27 W cm\ the deposition rate for PTFE was 7;10\ lm/min while for PI it was only 2;10\ lm/min. Sputtering targets were polymer sheets 50 lm thick bonded to copper backed plates. The tribological performance was examined. The friction coe$cient (sliding steel ball) was found to be about 0.3 and 0.2 for both the "lms. Sputtered #uorocarbon "lms as well as polyimide "lms were worn away from the frictional tracks within a small number of passes. A very thin "lm was left on the track that served as a lubricant "lm. Lifetime of sputtered polyimide "lms was longer than that of #uorocarbon "lms. The tribological properties were further studied by Kitoh and Honda [15]. Comparing #uorocarbon and polyimide "lms sputtering, the deposition rates at 1 Pa of Ar and at RF power 240 W were found to be 25 nm/min and 3}4 nm/min, respectively. The FTIR spectra of sputtered "lms revealed no polyimide group. The ether, alkane and amine groups showed distinct peaks. The carbon concentration increased and nitrogen and oxygen concentrations decreased in comparison to the target material. The authors compared PI "lms to MoS , C, BN "lms prepared in the same way and found that the PI "lms had the lowest friction coe$cient and the highest abrasion resistance. RF sputtering of polyimide in argon was found to be slower than it was in case of polytetra#uoroethylene, also mentioned in Ref. [16]. The self-sputtering of polyimide was also attempted, however, it required power over 1 kW. The emission of polyimide fragments from the target was much lower in the case of PTFE. This resulted in low concentration of ions and electrons and overall current in the discharge. Neutral species observed by mass spectroscopy (QMS) are CO, CN, CNO, HCNO, etc., while in the case of PTFE more polymer building groups were found: CF, C F , CF , C F , CF . Using the infrared spectroscopy and ESCA analysis, it was concluded that PI sputtered "lms have no resemblance to their original parent PI (Kapton) material of the target. Both the imide group and the ether group of the original molecule are destroyed. Plasma polymers were also prepared by RF sputtering of EKONOL (trade name of Carborundum Co) which is an aromatic polyester based on p-hydroxybenzoic acid [17]. The target was a disc 80 mm in diameter 6 mm in thickness mounted on Al backed plate. Sputtering took place in Ar at a pressure 5;10\!7;10\ Torr and RF power 25}100 W. The deposition rate was 1}1.5 nm/min. When the "lms were deposited below 5;10\ Torr they peeled o!, probably because of compressive stress. The IR transmission spectra from the "lms deposited on NaCl showed the loss of ester groups. The X-ray di!raction spectra showed no sign of crystallinity. Prepared "lms appeared to be amorphous and disordered hydrocarbon plasma polymer.
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4. Composites metal/plasma polymer Au and Pt}10%Rh metals were RF co-sputtered with EKONOL from the composite target. Most of the attention was paid to Au/EKONOL sputtering. Composite "lms with an Au concentration from 1 to 40 vol % of Au were prepared and their DC and AC resistivities measured. The same composites were attempted using RF co-sputtering of the above-mentioned metals and Cu with PTFE. However, in this case, cross-contamination e!ects of the target occurred resulting in a low deposition rate and re-sputtering e!ects at the substrate. Composite Au/#uorocarbon plasma polymer "lms were successfully prepared by RF planar magnetron sputtering from composite PTFE/Au target in CF gas [18] (for review see, e.g. [19]).
5. Recent results in PTFE sputtering In our laboratory we attempted to prepare #uorocarbon and hydrocarbon plasma polymers by means of RF (13.56 MHz) self-sputtering of PTFE and PE (polyethylene) targets (78 mm in diameter) [12,13]. A parallel plate electrode system with the magnetron facing down the substrate positioned 100 mm away from the substrate was applied (Fig. 1). The pumping system consisted of di!usion and rotary pumps. First, we determined conditions for self-sputtering mode for our deposition apparatus in the case of balanced magnetron. When one gradually increases the power and relates to its each value the extinguishing pressure (i.e. pressure value at which the discharge switches o! after the cut o! of Ar supply), one can "nd for a given target size (geometrical con"guration) and e!ective pumping speed in the deposition chamber, the threshold power for self-sputtering. In our case, it was 220 W and a deposition rate related to the power unit was
Fig. 1. The deposition arrangement (PT * polymer target, M * magnetron, Sh * shutter, W * window, Ar * gas inlet, P-to pumps).
H. Biederman / Vacuum 59 (2000) 594 }599
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0.15 nm/minW. During sputtering the deposition rate decreases (by 30% within 40 min) due to the build up of an altered layer on the target surface enriched by carbon. F/C ratio in the erosion track is 0.7 while in the center of the target it is 1.3 as measured by ESCA. The SEM micrographs of the cross-section of the "lms deposited at various substrate temperature show columnar structure at low temperature while amorphous structure is apparent at high temperatures [20] as may be seen from Fig. 2. The morphology of the "lm changes from amorphous-continuous at higher positive temperatures, while below the room temperature a closely packed "brilar structure appears. Columnar structures are clearly apparent at negative temperatures (Fig. 2a). The generalized structure zone models can be applied. Polarized specular re#ectivity spectra of the "lms deposited on glass substrates precoated with Al layer were measured with FTIR spectrometer. A shift of the band wavenumber with polarization is observed: 1250$5 cm\ for the radiation electric "eld, this being perpendicular to the sample plane (re#ectivity p-polarization); 1215$10 cm\ for the electric vector in the sample plane (s-polarization in re#ectivity and transmissivity measurements). This anisotropy could be caused by an orientation of C}C bonds (predominantly perpendicular to the sample plane) and C}F bonds
Fig. 2. The cross section of the "lm deposited on Si at a) !153C and at #383C. Self-sputtering, 85 W.
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Fig. 3. Model of a #uorocarbon plasma polymer obtained by PTFE sputtering (* * #uorine, 䢇 * carbon).
(predominantly parallel to the sample plane). Based on these measurements, a hypothetical model of our #uorocarbon "lms is presented in Fig. 3. This is in accord with the structure schemes for plasma polymers prepared by plasma polymerization processes from #uorocarbon gaseous feeds [21]. In the unbalanced magnetron deposition, we found by Langmuir probe measurements that the #oating substrate can be bombarded with positive ions which in the central region may have maximum energy 10}30 eV (radial distance from the axis of the magnetron up to 20 mm) while further from the axis (20}40 mm) the maximum energy is less * about 5}20 eV. Therefore, the deposition rate is very low or even negative (etching) in the central region than in longer radial distances. The C/F ratio as measured by ESCA is low (2) in the center; however, it is high (4) between 20}40 mm of the radial distance from the axis. The "lms deposited here are rather hard and therefore may be called as hard plasma #uorocarbon polymers (C:F).
6. Sputtering of polyethylene In polyethylene sputtering, an unbalanced magnetron RF of the same dimensions as described above was used [12]. The deposition rate was 0.04 nm/minW which is low in comparison to the PTFE case. FTIR absorption spectra show that the obtained "lm is very di!erent from the polyethylene target material. At low power (10 W) a carbonaceous "lm was deposited. At an increased power up to 300 and 400 W a "lm corresponding to the usual hydrocarbon plasma polymer was obtained as shown by the FTIR absorption spectra [12].
7. Conclusions Deposition of plasma polymers using RF sputtering of polymer targets is a promising process. Gaseous organic fragments as precursors for plasma polymerization process are emitted and
H. Biederman / Vacuum 59 (2000) 594 }599
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fragmented from the conventional polymer target. No gaseous or liquid precursors are needed. Especially, in the case of #uorocarbon "lms various applications were proposed. These included a low friction coating, protective and non-wettable "lms and barrier coatings. Optical properties of the "lms were considered, e.g. to use "lms as a quarter wavelength antire#ective coating on glass. Electrical properties of the "lms were also investigated with the aim of using them as a dielectric "lm. Polyimide "lms were considered for mechanical applications as low friction and wear resistant coatings.
Acknowledgements This work was supported by Grant COST OC NA 100, and partly by Grant ME 177 and GACR 80116. Part of this contribution has been published in the IEEE (London) Colloquium Digest No. 026 (1999). The author is indebted to Prof. SlavmH nskaH and Prof. HlmH dek for stimulating discussions.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Harrop R, Harrop PJ. Thin Solid Films 1969;3:109. Morrison DJ, Robertson T. Thin Solid Films 1973;15:87. Pratt IH, Lausmann TC. Thin Solid Films 1972;10:151. Tibbitt JM, Sten M, Bell T. Thin Solid Films 1975;39:L43. Holland L, Biederman H, Ojha SM. Thin Solid Films 197;35:19. Biederman H, Ojha SM, Holland L. Thin Solid Films 1977;41:329. Biederman H. Thin Solid Films 1978;55:L11. Lehmann HW, Frick K, Widmer R, Vossen JL, James E. Thin Solid Films 1978;52:231. Biederman H. Vacuum 1981;31:285. Ryan ME, Fonseca JLC, Tasker S, Badyal JPS. J Phys Chem 1995;99:7060. MareH chal N, Pauleau Y. J Vac Sci Technol A 1992;10:477. Biederman H, BmH lkovaH P, Jecek J, HlmH dek P, SlavmH nskaH D. J Non-Cryst Solids 1997;218:44. Biederman H, Jecek J, BmH lkovaH P, HlmH dek P, SlavmH nskaH D, Zemek J. In: Wu CK, editor. Proceedings of the ISPC 13, vol. III. Beijing: Peking University Press, 1997. p. 1264}8. Yamada Y, Tanaka K, Saito K. Surf Coat Technol 1990;43/44:618. Kitoh M, Honda Y. Thin Solid Films 1995;271:92. Hismeh GA, Barr TL, Sklyarov A, Hardcastle S. J Vac Sci Technol A 1996;14:1330. Roy RA, Messier R, Krishnaswamy SV. Thin Solid Films 1983;109:27. Biederman H, Holland L. Nucl Instr and Meth 1983;212:497. Biederman H, Osada Y. Plama polymerisation processes. Amsterdam: Elsevier, 1992. Biederman H, Jecek J, BmH lkovaH P, HlmH dek P, SlavmH nskaH D. In: Schauer F, editor. Third Conference Proceedings Physics and Chemistry of Molecular Systems, Faculty of Chemistry, TU Brno, Brno, 1998. p. 35}8. Favia P, d'Agostino R. Surf Coat Technol 1998;98:1102.
RF sputtering of polymers and its potential application H. Biederman* Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, V Holes\ ovicka& ch 2, 180 00 Prague 8, Czech Republic
Abstract Plasma polymerization processes are commonly used for the deposition of thin "lms of plasma polymers that have been proposed for a variety of applications ranging from surface modi"cations for biomedical purposes to optical coatings and variable and protective "lms in electronics. RF sputtering of polymeric materials in an inert gas (Ar) or in its own fragmented polymer vapours can be applied in order to avoid the conventional supply of gaseous monomer. Volatile fragments of polymeric target serve as plasma polymerization precursors in the case of RF sputtering. RF sputtering of polytetra#uoroethylene (PTFE), polyimide (PI), etc. are rewieved. Recent results from our laboratory on balanced and unbalanced magnetron RF sputtering of polytetra#uoroethylene and polyethylene (PE) are presented. The dependence of structure and morphology of RF sputtered plasma polymers on plasma parameters and substrate temperature is discussed. In conclusion potential applications are summarized. 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction In the 1970s the deposition of plasma polymers by means of radio frequency (RF) sputtering of targets made of conventional polymers received considerable attention. The interest was particularly focused on polytetra#uoroethylene (PTFE) [1}7]. The motivation was apparently to prepare good dielectric "lms [2] and low friction coatings [1,6]. Optical applications were also considered [6]. 2. Fluorocarbon plasma polymers Usually, PTFE was sputtered in argon. Also, the so called self-sputtering of PTFE was performed. In this case, argon was used only to initiate the discharge that continued in volatile * Fax: #42-02-688-5095. E-mail address: [email protected]!.cuni.cz (H. Biederman). 0042-207X/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 3 2 1 - 3
H. Biederman / Vacuum 59 (2000) 594 }599
595
fragments of PTFE when argon supply was shut o!. Because sputtered PTFE "lms were found de"cient in #uorine sputtering in a mixture of Ar and CF was performed that increased the ratio F/C in prepared "lms [8]. In a single case nitrogen was used as a working gas [9]. Later in addition to nitrogen, gases such as helium and neon were applied [10]. In recent years interest in RF sputtering of PTFE has been renewed [10}13] as the obtained plasma polymer "lms are again in demand as protective, low friction and non-wettable coatings.
3. Hydrocarbon plasma polymers compared to 6uorocarbons The second polymer that has been investigated for RF sputtering is polyimide (PI) known also by the trade name Kapton. Yamada et al. [14] sputtered PTFE and PI "lms in Ar at 6. 65;10\ Pa. At a constant power density 1.27 W cm\ the deposition rate for PTFE was 7;10\ lm/min while for PI it was only 2;10\ lm/min. Sputtering targets were polymer sheets 50 lm thick bonded to copper backed plates. The tribological performance was examined. The friction coe$cient (sliding steel ball) was found to be about 0.3 and 0.2 for both the "lms. Sputtered #uorocarbon "lms as well as polyimide "lms were worn away from the frictional tracks within a small number of passes. A very thin "lm was left on the track that served as a lubricant "lm. Lifetime of sputtered polyimide "lms was longer than that of #uorocarbon "lms. The tribological properties were further studied by Kitoh and Honda [15]. Comparing #uorocarbon and polyimide "lms sputtering, the deposition rates at 1 Pa of Ar and at RF power 240 W were found to be 25 nm/min and 3}4 nm/min, respectively. The FTIR spectra of sputtered "lms revealed no polyimide group. The ether, alkane and amine groups showed distinct peaks. The carbon concentration increased and nitrogen and oxygen concentrations decreased in comparison to the target material. The authors compared PI "lms to MoS , C, BN "lms prepared in the same way and found that the PI "lms had the lowest friction coe$cient and the highest abrasion resistance. RF sputtering of polyimide in argon was found to be slower than it was in case of polytetra#uoroethylene, also mentioned in Ref. [16]. The self-sputtering of polyimide was also attempted, however, it required power over 1 kW. The emission of polyimide fragments from the target was much lower in the case of PTFE. This resulted in low concentration of ions and electrons and overall current in the discharge. Neutral species observed by mass spectroscopy (QMS) are CO, CN, CNO, HCNO, etc., while in the case of PTFE more polymer building groups were found: CF, C F , CF , C F , CF . Using the infrared spectroscopy and ESCA analysis, it was concluded that PI sputtered "lms have no resemblance to their original parent PI (Kapton) material of the target. Both the imide group and the ether group of the original molecule are destroyed. Plasma polymers were also prepared by RF sputtering of EKONOL (trade name of Carborundum Co) which is an aromatic polyester based on p-hydroxybenzoic acid [17]. The target was a disc 80 mm in diameter 6 mm in thickness mounted on Al backed plate. Sputtering took place in Ar at a pressure 5;10\!7;10\ Torr and RF power 25}100 W. The deposition rate was 1}1.5 nm/min. When the "lms were deposited below 5;10\ Torr they peeled o!, probably because of compressive stress. The IR transmission spectra from the "lms deposited on NaCl showed the loss of ester groups. The X-ray di!raction spectra showed no sign of crystallinity. Prepared "lms appeared to be amorphous and disordered hydrocarbon plasma polymer.
596
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4. Composites metal/plasma polymer Au and Pt}10%Rh metals were RF co-sputtered with EKONOL from the composite target. Most of the attention was paid to Au/EKONOL sputtering. Composite "lms with an Au concentration from 1 to 40 vol % of Au were prepared and their DC and AC resistivities measured. The same composites were attempted using RF co-sputtering of the above-mentioned metals and Cu with PTFE. However, in this case, cross-contamination e!ects of the target occurred resulting in a low deposition rate and re-sputtering e!ects at the substrate. Composite Au/#uorocarbon plasma polymer "lms were successfully prepared by RF planar magnetron sputtering from composite PTFE/Au target in CF gas [18] (for review see, e.g. [19]).
5. Recent results in PTFE sputtering In our laboratory we attempted to prepare #uorocarbon and hydrocarbon plasma polymers by means of RF (13.56 MHz) self-sputtering of PTFE and PE (polyethylene) targets (78 mm in diameter) [12,13]. A parallel plate electrode system with the magnetron facing down the substrate positioned 100 mm away from the substrate was applied (Fig. 1). The pumping system consisted of di!usion and rotary pumps. First, we determined conditions for self-sputtering mode for our deposition apparatus in the case of balanced magnetron. When one gradually increases the power and relates to its each value the extinguishing pressure (i.e. pressure value at which the discharge switches o! after the cut o! of Ar supply), one can "nd for a given target size (geometrical con"guration) and e!ective pumping speed in the deposition chamber, the threshold power for self-sputtering. In our case, it was 220 W and a deposition rate related to the power unit was
Fig. 1. The deposition arrangement (PT * polymer target, M * magnetron, Sh * shutter, W * window, Ar * gas inlet, P-to pumps).
H. Biederman / Vacuum 59 (2000) 594 }599
597
0.15 nm/minW. During sputtering the deposition rate decreases (by 30% within 40 min) due to the build up of an altered layer on the target surface enriched by carbon. F/C ratio in the erosion track is 0.7 while in the center of the target it is 1.3 as measured by ESCA. The SEM micrographs of the cross-section of the "lms deposited at various substrate temperature show columnar structure at low temperature while amorphous structure is apparent at high temperatures [20] as may be seen from Fig. 2. The morphology of the "lm changes from amorphous-continuous at higher positive temperatures, while below the room temperature a closely packed "brilar structure appears. Columnar structures are clearly apparent at negative temperatures (Fig. 2a). The generalized structure zone models can be applied. Polarized specular re#ectivity spectra of the "lms deposited on glass substrates precoated with Al layer were measured with FTIR spectrometer. A shift of the band wavenumber with polarization is observed: 1250$5 cm\ for the radiation electric "eld, this being perpendicular to the sample plane (re#ectivity p-polarization); 1215$10 cm\ for the electric vector in the sample plane (s-polarization in re#ectivity and transmissivity measurements). This anisotropy could be caused by an orientation of C}C bonds (predominantly perpendicular to the sample plane) and C}F bonds
Fig. 2. The cross section of the "lm deposited on Si at a) !153C and at #383C. Self-sputtering, 85 W.
598
H. Biederman / Vacuum 59 (2000) 594 }599
Fig. 3. Model of a #uorocarbon plasma polymer obtained by PTFE sputtering (* * #uorine, 䢇 * carbon).
(predominantly parallel to the sample plane). Based on these measurements, a hypothetical model of our #uorocarbon "lms is presented in Fig. 3. This is in accord with the structure schemes for plasma polymers prepared by plasma polymerization processes from #uorocarbon gaseous feeds [21]. In the unbalanced magnetron deposition, we found by Langmuir probe measurements that the #oating substrate can be bombarded with positive ions which in the central region may have maximum energy 10}30 eV (radial distance from the axis of the magnetron up to 20 mm) while further from the axis (20}40 mm) the maximum energy is less * about 5}20 eV. Therefore, the deposition rate is very low or even negative (etching) in the central region than in longer radial distances. The C/F ratio as measured by ESCA is low (2) in the center; however, it is high (4) between 20}40 mm of the radial distance from the axis. The "lms deposited here are rather hard and therefore may be called as hard plasma #uorocarbon polymers (C:F).
6. Sputtering of polyethylene In polyethylene sputtering, an unbalanced magnetron RF of the same dimensions as described above was used [12]. The deposition rate was 0.04 nm/minW which is low in comparison to the PTFE case. FTIR absorption spectra show that the obtained "lm is very di!erent from the polyethylene target material. At low power (10 W) a carbonaceous "lm was deposited. At an increased power up to 300 and 400 W a "lm corresponding to the usual hydrocarbon plasma polymer was obtained as shown by the FTIR absorption spectra [12].
7. Conclusions Deposition of plasma polymers using RF sputtering of polymer targets is a promising process. Gaseous organic fragments as precursors for plasma polymerization process are emitted and
H. Biederman / Vacuum 59 (2000) 594 }599
599
fragmented from the conventional polymer target. No gaseous or liquid precursors are needed. Especially, in the case of #uorocarbon "lms various applications were proposed. These included a low friction coating, protective and non-wettable "lms and barrier coatings. Optical properties of the "lms were considered, e.g. to use "lms as a quarter wavelength antire#ective coating on glass. Electrical properties of the "lms were also investigated with the aim of using them as a dielectric "lm. Polyimide "lms were considered for mechanical applications as low friction and wear resistant coatings.
Acknowledgements This work was supported by Grant COST OC NA 100, and partly by Grant ME 177 and GACR 80116. Part of this contribution has been published in the IEEE (London) Colloquium Digest No. 026 (1999). The author is indebted to Prof. SlavmH nskaH and Prof. HlmH dek for stimulating discussions.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Harrop R, Harrop PJ. Thin Solid Films 1969;3:109. Morrison DJ, Robertson T. Thin Solid Films 1973;15:87. Pratt IH, Lausmann TC. Thin Solid Films 1972;10:151. Tibbitt JM, Sten M, Bell T. Thin Solid Films 1975;39:L43. Holland L, Biederman H, Ojha SM. Thin Solid Films 197;35:19. Biederman H, Ojha SM, Holland L. Thin Solid Films 1977;41:329. Biederman H. Thin Solid Films 1978;55:L11. Lehmann HW, Frick K, Widmer R, Vossen JL, James E. Thin Solid Films 1978;52:231. Biederman H. Vacuum 1981;31:285. Ryan ME, Fonseca JLC, Tasker S, Badyal JPS. J Phys Chem 1995;99:7060. MareH chal N, Pauleau Y. J Vac Sci Technol A 1992;10:477. Biederman H, BmH lkovaH P, Jecek J, HlmH dek P, SlavmH nskaH D. J Non-Cryst Solids 1997;218:44. Biederman H, Jecek J, BmH lkovaH P, HlmH dek P, SlavmH nskaH D, Zemek J. In: Wu CK, editor. Proceedings of the ISPC 13, vol. III. Beijing: Peking University Press, 1997. p. 1264}8. Yamada Y, Tanaka K, Saito K. Surf Coat Technol 1990;43/44:618. Kitoh M, Honda Y. Thin Solid Films 1995;271:92. Hismeh GA, Barr TL, Sklyarov A, Hardcastle S. J Vac Sci Technol A 1996;14:1330. Roy RA, Messier R, Krishnaswamy SV. Thin Solid Films 1983;109:27. Biederman H, Holland L. Nucl Instr and Meth 1983;212:497. Biederman H, Osada Y. Plama polymerisation processes. Amsterdam: Elsevier, 1992. Biederman H, Jecek J, BmH lkovaH P, HlmH dek P, SlavmH nskaH D. In: Schauer F, editor. Third Conference Proceedings Physics and Chemistry of Molecular Systems, Faculty of Chemistry, TU Brno, Brno, 1998. p. 35}8. Favia P, d'Agostino R. Surf Coat Technol 1998;98:1102.