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XPS study of siloxane plasma polymer films
Surface and Coatings Technology 174 – 175 (2003) 1159–1163
XPS study of siloxane plasma polymer films R. Balkova*, J. Zemek, V. Cech, J. Vanek, R. Prikryl Institute of Materials Chemistry, Brno University of Technology, Purkynova 118, CZ-612 00 Brno, Czech Republic
Abstract Plasma polymer films were deposited from hexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO) on polished silicon wafers using a RF helical coupling deposition system. The composition of elements in the surface region (top 6–8 nm) of the deposited films was studied by X-ray-induced photoelectron spectroscopy (XPS) on an ADES 400 VG Scientific photoelectron spectrometer using MgKa (1253.6 eV) or AlKa (1486.6 eV) photon beams at the normal emission angle. Aging effects of plasma-polymerized (PP) HMDSO and DCMPS films stored under standard laboratory conditions were investigated by employing XPS. Post-deposition contamination and oxidation of pp-DCMPS and ppHMDSO film was carefully observed. An increase in oxygen atoms on the film surface over time is accompanied by changes in bulk atomic concentrations. Sequential sputtering with an Ar ion-beam, together with XPS analysis, was used to measure concentration depth profiles in pp-HMDSO and pp-DCMPS films. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Radio frequency (RF); X-Ray photoelectron spectroscopy (XPS); Electron spectroscopy for chemical analysis (ESCA)
1. Introduction Glow discharge polymerization w1x is a unique polymer-forming process, different from conventional polymerization. Starting materials introduced into the glow discharge are broken down into activated small molecules, and in the extreme to atoms, by the action of electrons, ions and radicals. These fragments then undergo stepwise recombination with accompanying rearrangements to form large molecules, and finally a polymer, with chemical composition, structure, chemical and physical properties, distinguished from those formed by conventional polymerization using the same monomer w2x. A wide range of plasma polymers is prepared from organosilanes w3,4x. Plasma polymer films based on siloxane bonds are very interesting materials for their electronic, optical, thermal and mechanical properties. In particular, plasma polymers prepared from organosilicone monomers are fascinating materials due to the
*Corresponding author. Tel.: q4205-4114-9350; fax: q4205-41149361. E-mail address: [email protected] (R. Balkova).
possibility of varying the degree of organicyinorganic character and the degree of cross-linking in the material. If such a plasma polymer needs to be joined to another material, the physical and chemical surface properties will determine the type of interfacial bonding between the two materials in contact. Therefore, the surface morphology, wettability, chemical composition and chemical structure at the film surface are of great importance. The process conditions (power, flow rate) and the sample position in the plasma chamber (plasma zone, remote plasma) can vary the physical and chemical properties of plasma polymers deposited with respect to the monomer used or a mixture with additional gas andy or gases. Three types of organosilicone monomer whexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO)x were used for glow-discharge polymerization to prepare thin films for use as glass-fiber surface sizing (HMDSO and VTEO) or photoelectronic material (DCMPS). The atomic composition of the surface region (top 6–8 nm) of the deposited films was studied by XPS, together with the influence of the plasma polymerization conditions and aging effects.
0257-8972/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972Ž03.00462-6
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R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163
2. Experimental 2.1. Preparation of plasma polymer films
Table 1 Atomic concentrations of pp-films and atomic ratios of monomers and deposited films Polymer
Three types of organosilicone monomers were used for plasma polymerization deposition: hexamethyldisiloxane (HMDSO; 99.5% purity, Aldrich), dichloro(methyl)phenylsilane (DCMPS; Aldrich), and vinyltriethoxysilane (VTEO; purity G98%, Aldrich). A dual capacitive coupling system (13.56 MHz), with only one part utilized for sample preparation, was used for DCMPS plasma polymerization. The electrode spacing was 2.5 cm and substrates were placed on the grounded electrode. The reactor was first evacuated to 0.5 Pa and purged with Ar plasma to eliminate water and contamination of the substrate and chamber wall. Gaseous hydrogen and DCMPS vapors were then introduced into the chamber at partial pressures of 43 and 12 Pa, respectively. The polymer films were deposited at a power density of 1 W cmy2 and the substrate temperature was maintained at 80 8C. Pp-DCMPS films were subjected to post-deposition annealing at 160 8C for 1 h in the reactor chamber filled with argon gas at pressure of 100 Pa to reduce free radicals. Deposited films were stored in a dark and dry place. After several days, some films were vacuum-heated at a rate of 20 8C miny1 up to the temperatures ranging from 450 to 700 8C to determine the high-temperature stability for practical use, and were then slowly cooled. Pp-HMDSO thin films were prepared using a helical coupling plasma system with an inductive coil wrapped around the outside of the glass tube (plasma chamber) connected to a RF generator, operating at a frequency of 40 MHz. The reactor was first evacuated to 1=10y3 Pa and together with Si wafers was purged with Ar plasma. Pp-films were deposited using continual plasma concentrated under the coil at pressure of 10 Pa. RF generator power was applied in the range of 10–90 W. The same helical coupling plasma system, but with the RF generator operating at a frequency of 13.56 MHz, was used for deposition of pp-VTEO thin films. Treatment procedures were carried out at a power level of 50 W and process pressure of approximately 3.5 Pa. The flow rate of the monomer was adjusted to 1 sccm. It should be noted that all deposited specimens have remained in the deposition chamber after the glow discharge was switched off. This meant that monomer molecules could react with a great number of free radicals and fragments on the freshly prepared material. 2.2. X-Ray photoelectron spectroscopy The composition of elements in the surface region (top 6–8 nm) of the deposited layers was studied by X-ray photoelectron spectroscopy (XPS) on an ADES
pp-HMDSO pp-DCPMS pp-VTEO
Concentration
Atomic ratio
(at.%)
Film
Monomers
C
O
Si
CySi
OySi
CySi
OySi
61 61 57
16 26 29
23 13 14
2.7 4.7 4.9
0.7 2.0 2.5
3 7 8
0.5 0 3
400 VG Scientific photoelectron spectrometer using MgKa (1253.6 eV) or AlKa (1486.6 eV) photon beams at the normal emission angle. Atomic concentrations were semi-quantitatively determined, assuming the model concerns a solid that is homogeneous in composition w5x. The Au 4f7y2 core level at 83.8 eV was used for calibration of the energy scale. Concentration depth profiles of pp-DCMPS and ppVTEO thin films were performed by sequential Ar ionbeam sputtering (4000 eV ion beam energy, 1=10y5 A cmy2 ion beam density, impact angle of 608 with respect to the surface normal) and XPS analysis. The elemental composition of pp-HMDSO films was also measured 9 months after deposition. During that time the specimens were stored in a dry and dark place. 3. Results and discussion Atomic concentrations of carbon, oxygen and silicon determined in the surface region (top 6–8 nm) of ppDCMPS, pp-HMDSO and pp-VTEO films, together with mean element ratios for the monomers and the films, are shown in Table 1. The theoretical composition of HMDSO monomer is two silicon atoms, one oxygen atom and six carbon atoms; that is, CySi and OySi ratios are of 3 and 0.5, respectively. If we assume that there is no reason for a change in concentration of Si atoms, we can also calculate atomic ratios from the XPS results. It is evident that there is a slightly higher amount of oxygen and a lower amount of carbon in pp-HMDSO. This is because of the formation of a cross-linked carbonsiloxane network and possible reaction of free radicals on the surface with air. In one step, films were deposited on substrates placed in different positions with respect to the plasma center (continuous plasma concentrated under the helical coil). Fig. 1 shows no atomic concentration change for these specimens (10 Pa, 50 W, 30 min). There is also no significant elemental composition change as a function of applied power, as can be observed from Fig. 2. Finally, specimens deposited in different positions were tested after 9 months (Fig. 3) to study the possibility of pp-HMDSO surface reactions with air components, and depth profiling (Fig. 4) was carried out to determine
R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163
Fig. 1. Element composition of pp-HMDSO film surface as a function of sample position with respect to the plasma center (Ls0 point on x-axis).
the possibility of oxygen diffusion into the film. It is evident that to a depth of 50 nm there is a different layer structure, probably due to post-deposition reaction with monomer in the reaction chamber. The composition of the surface itself could be modified by air components (the specimens were stored in the dark site in the laboratory). The XPS measurement 9 months after specimen preparation revealed a higher amount of oxygen, as well as carbon. This is probably due to oxygen and hydrocarbon diffusion and additional cross-linking. The theoretical composition of DCMPS monomer is one silicon atom, two chlorine atoms and seven carbon atoms; that is, the CySi ratio is 7. This value is in contrast to the pp-DCMPS film, where CySis4.7. This means that the monomer is highly fragmented in the discharge, some fragments are probably evacuated and a cross-linked carbonsiloxane network is formed. Because of the great amount of oxygen atoms found in the deposited films, we were interested in the depth
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Fig. 2. Element composition of pp-HMDSO film surface as a function of applied RF power.
profile of atomic concentrations. Depth profiles across the whole film are shown in Fig. 5. The concentration of oxygen atoms slowly decreases with the depth, while the concentrations of carbon and silicon atoms are almost constant in the bulk, except for at interfaces. The great amount of oxygen in pp-DCMPS can originate from oxygen-contaminated monomer, the presence of oxygen or, more likely, water in the reaction chamber, but also from subsequent post-deposition oxidation w6x. The atomic concentrations of several annealed samples are plotted as a function of annealing temperature in Fig. 6. It is evident that the concentration of carbon atoms decreases, whereas that of oxygen atoms increases with temperature and n(Si) is approximately constant, except for the value at a temperature of 700 8C. This can be explained by the release of weakly bonded methyl and phenyl groups from the heated material. The increase in oxygen atoms with increasing temperature can be explained by additional cross-linking of the polymer material with new siloxane bonds, whereby
Fig. 3. 9-month aging effect of pp-HMDSO film surface as a function of sample position with respect to the center of plasma (Ls0 point on xaxis).
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Fig. 4. Depth profiles of atomic concentrations across the pp-HMDSO film, together with element ratios. Interfaces of the film are marked out.
multifunctional silicones replaced most of the monofunctional groups. A very interesting question arises from the XPS results: why is there no chlorine detected in the surface layer as well as in the depth profile? This issue can be explained on the basis of the intensive fragmentation of DCMPS molecules, resulting in reactive chlorine atom production. Chlorine reacts with the introduced hydrogen, forming hydrogen chlorine (HCl), which is evacuated (a small amount of chlorine, decreasing with aging time, has been detected in several samples). Thus, as can be observed, the great disadvantage of using DCMPS is the HCl production, because it is highly corrosive and deleterious for the plasma system. The theoretical composition of VTEO monomer is one silicon atom, three oxygen atoms and eight carbon atoms; that is, the CySi and OySi ratios are 8 and 3,
Fig. 6. Atomic concentrations of pp-DCMPS film surface as a function of annealing temperature.
respectively. Results for pp-VTEO films revealed the formation of a highly cross-linked carbonsiloxane network with no oxygen and hydrocarbon contamination of the surface. 4. Conclusion Plasma-polymerized thin films were deposited from HMDSO, DCMPS and VTEO vapors on polished silicon substrates using the RF glow discharge technique. Each of the prepared films seems to be highly cross-linked. A great amount of oxygen, which slightly decreased with the film depth, was found in pp-DCMPS due to the presence of water molecules in the reaction chamber during deposition. Chlorine atoms produced during the fragmentation process reacted with the present hydrogen, forming hydrogen chlorine, which was evacuated. Weakly bonded methyl and phenyl groups were released from annealed pp-DCMPS films and additional cross-linking of the polymer material resulted. The different composition of pp-HMDSO to a depth of 50 nm is probably caused by the post-deposition reaction of freshly prepared film with the remaining unfragmented monomer in the reaction chamber; the increase in oxygen and carbon atoms after 9 months is probably caused by oxygen and hydrocarbon diffusion into the film from the air. Acknowledgments This work was supported by the contracts GACR 104y00y0708 (Grant Agency of the Czech Republic) and COST 527.110 (Ministry of Education). References
Fig. 5. Depth profiles of atomic concentrations across the pp-DCMPS film, together with element ratios. Interfaces of the film are marked out.
w1x N. Inagaki, S. Kondo, T. Murakami, J. Appl. Polym. Sci. 29 (1984) 3595–3605.
R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163 w2x H. Yasuda, Plasma Polymerization, Academic Press, New York, 1985. w3x A.M. Wrobel, M.R. Wertheimer, in: R. D’Agostino (Ed.), Plasma Deposition, Treatment, and Etching of Polymers, Academic, New York, 1990, Chapter 3. w4x Y. Segui, in: R. D’Agostino, P. Favia, F. Fracassi (Eds.), Plasma Processing of Polymers, Kluwer, Dordrecht, 1997, p. 305.
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w5x J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray Photoelectron Spectroscopy, Perkin Elmer Co, Eden Prairie, MN, 1992. w6x T.R. Gengenbach, H.J. Griesser, J. Polym. Sci. A: Polym. Chem. 36 (1998) 985.
XPS study of siloxane plasma polymer films R. Balkova*, J. Zemek, V. Cech, J. Vanek, R. Prikryl Institute of Materials Chemistry, Brno University of Technology, Purkynova 118, CZ-612 00 Brno, Czech Republic
Abstract Plasma polymer films were deposited from hexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO) on polished silicon wafers using a RF helical coupling deposition system. The composition of elements in the surface region (top 6–8 nm) of the deposited films was studied by X-ray-induced photoelectron spectroscopy (XPS) on an ADES 400 VG Scientific photoelectron spectrometer using MgKa (1253.6 eV) or AlKa (1486.6 eV) photon beams at the normal emission angle. Aging effects of plasma-polymerized (PP) HMDSO and DCMPS films stored under standard laboratory conditions were investigated by employing XPS. Post-deposition contamination and oxidation of pp-DCMPS and ppHMDSO film was carefully observed. An increase in oxygen atoms on the film surface over time is accompanied by changes in bulk atomic concentrations. Sequential sputtering with an Ar ion-beam, together with XPS analysis, was used to measure concentration depth profiles in pp-HMDSO and pp-DCMPS films. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Radio frequency (RF); X-Ray photoelectron spectroscopy (XPS); Electron spectroscopy for chemical analysis (ESCA)
1. Introduction Glow discharge polymerization w1x is a unique polymer-forming process, different from conventional polymerization. Starting materials introduced into the glow discharge are broken down into activated small molecules, and in the extreme to atoms, by the action of electrons, ions and radicals. These fragments then undergo stepwise recombination with accompanying rearrangements to form large molecules, and finally a polymer, with chemical composition, structure, chemical and physical properties, distinguished from those formed by conventional polymerization using the same monomer w2x. A wide range of plasma polymers is prepared from organosilanes w3,4x. Plasma polymer films based on siloxane bonds are very interesting materials for their electronic, optical, thermal and mechanical properties. In particular, plasma polymers prepared from organosilicone monomers are fascinating materials due to the
*Corresponding author. Tel.: q4205-4114-9350; fax: q4205-41149361. E-mail address: [email protected] (R. Balkova).
possibility of varying the degree of organicyinorganic character and the degree of cross-linking in the material. If such a plasma polymer needs to be joined to another material, the physical and chemical surface properties will determine the type of interfacial bonding between the two materials in contact. Therefore, the surface morphology, wettability, chemical composition and chemical structure at the film surface are of great importance. The process conditions (power, flow rate) and the sample position in the plasma chamber (plasma zone, remote plasma) can vary the physical and chemical properties of plasma polymers deposited with respect to the monomer used or a mixture with additional gas andy or gases. Three types of organosilicone monomer whexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO)x were used for glow-discharge polymerization to prepare thin films for use as glass-fiber surface sizing (HMDSO and VTEO) or photoelectronic material (DCMPS). The atomic composition of the surface region (top 6–8 nm) of the deposited films was studied by XPS, together with the influence of the plasma polymerization conditions and aging effects.
0257-8972/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972Ž03.00462-6
1160
R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163
2. Experimental 2.1. Preparation of plasma polymer films
Table 1 Atomic concentrations of pp-films and atomic ratios of monomers and deposited films Polymer
Three types of organosilicone monomers were used for plasma polymerization deposition: hexamethyldisiloxane (HMDSO; 99.5% purity, Aldrich), dichloro(methyl)phenylsilane (DCMPS; Aldrich), and vinyltriethoxysilane (VTEO; purity G98%, Aldrich). A dual capacitive coupling system (13.56 MHz), with only one part utilized for sample preparation, was used for DCMPS plasma polymerization. The electrode spacing was 2.5 cm and substrates were placed on the grounded electrode. The reactor was first evacuated to 0.5 Pa and purged with Ar plasma to eliminate water and contamination of the substrate and chamber wall. Gaseous hydrogen and DCMPS vapors were then introduced into the chamber at partial pressures of 43 and 12 Pa, respectively. The polymer films were deposited at a power density of 1 W cmy2 and the substrate temperature was maintained at 80 8C. Pp-DCMPS films were subjected to post-deposition annealing at 160 8C for 1 h in the reactor chamber filled with argon gas at pressure of 100 Pa to reduce free radicals. Deposited films were stored in a dark and dry place. After several days, some films were vacuum-heated at a rate of 20 8C miny1 up to the temperatures ranging from 450 to 700 8C to determine the high-temperature stability for practical use, and were then slowly cooled. Pp-HMDSO thin films were prepared using a helical coupling plasma system with an inductive coil wrapped around the outside of the glass tube (plasma chamber) connected to a RF generator, operating at a frequency of 40 MHz. The reactor was first evacuated to 1=10y3 Pa and together with Si wafers was purged with Ar plasma. Pp-films were deposited using continual plasma concentrated under the coil at pressure of 10 Pa. RF generator power was applied in the range of 10–90 W. The same helical coupling plasma system, but with the RF generator operating at a frequency of 13.56 MHz, was used for deposition of pp-VTEO thin films. Treatment procedures were carried out at a power level of 50 W and process pressure of approximately 3.5 Pa. The flow rate of the monomer was adjusted to 1 sccm. It should be noted that all deposited specimens have remained in the deposition chamber after the glow discharge was switched off. This meant that monomer molecules could react with a great number of free radicals and fragments on the freshly prepared material. 2.2. X-Ray photoelectron spectroscopy The composition of elements in the surface region (top 6–8 nm) of the deposited layers was studied by X-ray photoelectron spectroscopy (XPS) on an ADES
pp-HMDSO pp-DCPMS pp-VTEO
Concentration
Atomic ratio
(at.%)
Film
Monomers
C
O
Si
CySi
OySi
CySi
OySi
61 61 57
16 26 29
23 13 14
2.7 4.7 4.9
0.7 2.0 2.5
3 7 8
0.5 0 3
400 VG Scientific photoelectron spectrometer using MgKa (1253.6 eV) or AlKa (1486.6 eV) photon beams at the normal emission angle. Atomic concentrations were semi-quantitatively determined, assuming the model concerns a solid that is homogeneous in composition w5x. The Au 4f7y2 core level at 83.8 eV was used for calibration of the energy scale. Concentration depth profiles of pp-DCMPS and ppVTEO thin films were performed by sequential Ar ionbeam sputtering (4000 eV ion beam energy, 1=10y5 A cmy2 ion beam density, impact angle of 608 with respect to the surface normal) and XPS analysis. The elemental composition of pp-HMDSO films was also measured 9 months after deposition. During that time the specimens were stored in a dry and dark place. 3. Results and discussion Atomic concentrations of carbon, oxygen and silicon determined in the surface region (top 6–8 nm) of ppDCMPS, pp-HMDSO and pp-VTEO films, together with mean element ratios for the monomers and the films, are shown in Table 1. The theoretical composition of HMDSO monomer is two silicon atoms, one oxygen atom and six carbon atoms; that is, CySi and OySi ratios are of 3 and 0.5, respectively. If we assume that there is no reason for a change in concentration of Si atoms, we can also calculate atomic ratios from the XPS results. It is evident that there is a slightly higher amount of oxygen and a lower amount of carbon in pp-HMDSO. This is because of the formation of a cross-linked carbonsiloxane network and possible reaction of free radicals on the surface with air. In one step, films were deposited on substrates placed in different positions with respect to the plasma center (continuous plasma concentrated under the helical coil). Fig. 1 shows no atomic concentration change for these specimens (10 Pa, 50 W, 30 min). There is also no significant elemental composition change as a function of applied power, as can be observed from Fig. 2. Finally, specimens deposited in different positions were tested after 9 months (Fig. 3) to study the possibility of pp-HMDSO surface reactions with air components, and depth profiling (Fig. 4) was carried out to determine
R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163
Fig. 1. Element composition of pp-HMDSO film surface as a function of sample position with respect to the plasma center (Ls0 point on x-axis).
the possibility of oxygen diffusion into the film. It is evident that to a depth of 50 nm there is a different layer structure, probably due to post-deposition reaction with monomer in the reaction chamber. The composition of the surface itself could be modified by air components (the specimens were stored in the dark site in the laboratory). The XPS measurement 9 months after specimen preparation revealed a higher amount of oxygen, as well as carbon. This is probably due to oxygen and hydrocarbon diffusion and additional cross-linking. The theoretical composition of DCMPS monomer is one silicon atom, two chlorine atoms and seven carbon atoms; that is, the CySi ratio is 7. This value is in contrast to the pp-DCMPS film, where CySis4.7. This means that the monomer is highly fragmented in the discharge, some fragments are probably evacuated and a cross-linked carbonsiloxane network is formed. Because of the great amount of oxygen atoms found in the deposited films, we were interested in the depth
1161
Fig. 2. Element composition of pp-HMDSO film surface as a function of applied RF power.
profile of atomic concentrations. Depth profiles across the whole film are shown in Fig. 5. The concentration of oxygen atoms slowly decreases with the depth, while the concentrations of carbon and silicon atoms are almost constant in the bulk, except for at interfaces. The great amount of oxygen in pp-DCMPS can originate from oxygen-contaminated monomer, the presence of oxygen or, more likely, water in the reaction chamber, but also from subsequent post-deposition oxidation w6x. The atomic concentrations of several annealed samples are plotted as a function of annealing temperature in Fig. 6. It is evident that the concentration of carbon atoms decreases, whereas that of oxygen atoms increases with temperature and n(Si) is approximately constant, except for the value at a temperature of 700 8C. This can be explained by the release of weakly bonded methyl and phenyl groups from the heated material. The increase in oxygen atoms with increasing temperature can be explained by additional cross-linking of the polymer material with new siloxane bonds, whereby
Fig. 3. 9-month aging effect of pp-HMDSO film surface as a function of sample position with respect to the center of plasma (Ls0 point on xaxis).
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R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163
Fig. 4. Depth profiles of atomic concentrations across the pp-HMDSO film, together with element ratios. Interfaces of the film are marked out.
multifunctional silicones replaced most of the monofunctional groups. A very interesting question arises from the XPS results: why is there no chlorine detected in the surface layer as well as in the depth profile? This issue can be explained on the basis of the intensive fragmentation of DCMPS molecules, resulting in reactive chlorine atom production. Chlorine reacts with the introduced hydrogen, forming hydrogen chlorine (HCl), which is evacuated (a small amount of chlorine, decreasing with aging time, has been detected in several samples). Thus, as can be observed, the great disadvantage of using DCMPS is the HCl production, because it is highly corrosive and deleterious for the plasma system. The theoretical composition of VTEO monomer is one silicon atom, three oxygen atoms and eight carbon atoms; that is, the CySi and OySi ratios are 8 and 3,
Fig. 6. Atomic concentrations of pp-DCMPS film surface as a function of annealing temperature.
respectively. Results for pp-VTEO films revealed the formation of a highly cross-linked carbonsiloxane network with no oxygen and hydrocarbon contamination of the surface. 4. Conclusion Plasma-polymerized thin films were deposited from HMDSO, DCMPS and VTEO vapors on polished silicon substrates using the RF glow discharge technique. Each of the prepared films seems to be highly cross-linked. A great amount of oxygen, which slightly decreased with the film depth, was found in pp-DCMPS due to the presence of water molecules in the reaction chamber during deposition. Chlorine atoms produced during the fragmentation process reacted with the present hydrogen, forming hydrogen chlorine, which was evacuated. Weakly bonded methyl and phenyl groups were released from annealed pp-DCMPS films and additional cross-linking of the polymer material resulted. The different composition of pp-HMDSO to a depth of 50 nm is probably caused by the post-deposition reaction of freshly prepared film with the remaining unfragmented monomer in the reaction chamber; the increase in oxygen and carbon atoms after 9 months is probably caused by oxygen and hydrocarbon diffusion into the film from the air. Acknowledgments This work was supported by the contracts GACR 104y00y0708 (Grant Agency of the Czech Republic) and COST 527.110 (Ministry of Education). References
Fig. 5. Depth profiles of atomic concentrations across the pp-DCMPS film, together with element ratios. Interfaces of the film are marked out.
w1x N. Inagaki, S. Kondo, T. Murakami, J. Appl. Polym. Sci. 29 (1984) 3595–3605.
R. Balkova et al. / Surface and Coatings Technology 174 – 175 (2003) 1159–1163 w2x H. Yasuda, Plasma Polymerization, Academic Press, New York, 1985. w3x A.M. Wrobel, M.R. Wertheimer, in: R. D’Agostino (Ed.), Plasma Deposition, Treatment, and Etching of Polymers, Academic, New York, 1990, Chapter 3. w4x Y. Segui, in: R. D’Agostino, P. Favia, F. Fracassi (Eds.), Plasma Processing of Polymers, Kluwer, Dordrecht, 1997, p. 305.
1163
w5x J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-Ray Photoelectron Spectroscopy, Perkin Elmer Co, Eden Prairie, MN, 1992. w6x T.R. Gengenbach, H.J. Griesser, J. Polym. Sci. A: Polym. Chem. 36 (1998) 985.