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A comparison of polyatomic ion deposited, RF magnetron sputtered and plasma polymer organosilicon films
Thin Solid Films 502 (2006) 40 – 43 www.elsevier.com/locate/tsf
A comparison of polyatomic ion deposited, RF magnetron sputtered and plasma polymer organosilicon films A. Choukourov a, A. Grinevich a, J. Hanux a, J. Kousal a, D. Slavı´nska´ a, H. Biederman a,*, A. Bowers b, L. Hanley b a
Charles University, Faculty of Mathematics and Physics, Department of Macromolecular Physics, Czech Republic b Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA Available online 15 August 2005
Abstract In this work organosilicon films are prepared by plasma polymerization and mass-selected polyatomic ion deposition (MS-PID) of divinyltetramethyldisilazane, and by rf magnetron sputtering of polydimethylsiloxane. The composition of coatings is determined by XPS and FTIR. A chemical derivatization method is applied to detect amines in silazane films. Plasma polymers and ion deposited films are found to be more organic; whereas magnetron sputtered coatings are dominated by SiOx species. Plasma polymers are deficient of nitrogen with silicon bound in various Six Cy Oz species. Silicon in PID-films is bound mainly to nitrogen (Six N). The processes of aging in air or in water are also discussed. D 2005 Elsevier B.V. All rights reserved. Keywords: Plasma processing and plasma deposition; Ion bombardment; Organosilicon polymer
1. Introduction Silicon containing plasma polymers have been extensively studied as possible candidates for various application fields. Siloxanes, silazanes, silanes or their mixtures with O2, N2, N2O, NH3 have been used as precursors. Microelectronics require the films with good dielectric properties. Since polysiloxanes deposited by plasma polymerization possess excellent electrical and thermal properties, they are industrially used in electronic encapsulation applications or as passivation or insulation layers of integrated circuits and electronic devices [1]. Deposition of silicon containing thin films by plasma polymerization of organosilicon precursors is being increasingly used for the fabrication of transparent optical coatings. For example, SiOx coatings are known for their very low refractive index (n) and extinction coefficient (k). The addition of nitrogen in amount of several percent slightly
* Corresponding author. E-mail address: [email protected] (A. Choukourov). 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.07.231
increases n and k. On the other hand, the increase of hydrogen or in particular NH groups content results in a considerable decrease of refractive index. Thus, depending on the plasma conditions and type of monomer the optical properties can be varied to produce the films with desired intermediate n value or graded index optical films, in which the refractive index continuously varies as a function of depth [2,3]. As a result of their high chemical stability and low gas and water permeability, SiOx films are proposed as corrosion inhibitors [4,5]. SiCHN coatings have also a potential for use in high-power, high-frequency, and radiation-resistant applications [6].
2. Experimental 1,3-divinyltetramethyldisilazane, CH2_CH –Si(CH3)2 – NH – Si(CH3)2 – CH_CH2 (M = 185 g/mol), referred to below as silazane, was used as the monomer in the plasma polymerization and polyatomic ion deposition experiments. The plasma polymerization experiments were performed in a glass tubular reactor with external ring electrodes and
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
41
Table 1 The elemental content of organosilicon films determined by XPS Deposition method
Elemental composition, atomic percent C
Si
N
O
Plasma polymerization PID PID rf magnetron sputtering
61 72 65 33
14 17 15 19
– 8 5 –
25 7 17 48
standard excitation frequency of 13.56 MHz. The reactor was pumped by rotary and diffusion pumps, protected by a liquid nitrogen trap, to a base pressure of 1 10 3 Pa. The tank with liquid monomer was connected with the reactor via a needle valve, which controlled the flow rate of monomer vapors. All depositions were performed with a flow rate of 0.6 sccm and a pressure of 20 Pa. The power of 5 and 25 W was applied. In the case of polyatomic ion deposition (PID), the most abundant silazane ion formed by electron impact with m / z = 170 (C7Si2NH16+), corresponding to the molecular ion minus one methyl group or [CH2_CH – Si(CH3)2 –NH – Si(CH3) – CH_CH2]+was used. Films denoted as-deposited were analyzed by XPS immediately after deposition without exposure to air. A parallel-plate electrode system with rf (13.56 MHz) planar magnetron was used for magnetron sputtering. The sputtering was performed in Ar at 5 Pa pressure and 10 sccm flow rate. The substrates were positioned 5 cm above the target and rf power ranged from 20 to 80 W. Polydimethylsiloxane [– Si(CH3)2 –O– ]n was used as the target. The thickness of plasma polymerized and rf sputtered films was in a range of 100– 300 nm, whereas only several nanometers films were deposited by polyatomic ion deposition. Trifluoroacetic anhydride (TFAA) was used as derivatization agent to detect amines. TFAA is also sensitive to hydroxyl groups, a shortcoming which is discussed in the text where relevant.
Experimental parameters
Silazane, 20 Pa, 25 W, 0.6 sccm; measured in 2 months after deposition Silazane, as-deposited, 15 eV, fluences are 1.4 to 6.8 1016 ions/cm2 Silazane, 7-day aged, 15 eV, fluences are 1.4 to 6.8 1016 ions/cm2 PDMS, 100 W, 5 Pa, 10 sccm; measured in 7 months after deposition
the substrate signal. Low energy ions form more organic polymer-like structures and higher energy ions deposit more inorganic SiCN coatings [8]. The PID-films are sensitive to aging in air, revealing a considerable increase of oxygen content within a 7-day period. The incorporation of oxygen proceeds via formation of surface hydroxyl groups, which is detected by the derivatization measurements [8]. Plasma polymers analyzed in 2 months after the deposition lack nitrogen and also exhibit an increased oxygen concentration. The deficiency of nitrogen in Si : C : N : O films due to high affinity of Si with O has been already reported [8,9]. No dependence of elemental composition of silazane plasma polymers on the discharge power is observed (Table 2). The plasma polymer samples were treated with TFAA immediately after the deposition without exposure to air, shipped to University of Illinois at Chicago and then analyzed by XPS. The fluorine concentration in amount of several percent proves the presence of secondary amines or hydroxyls in the as-deposited plasma polymers. However, their concentration is small. The lack of nitrogen in the aged samples can be explained either by the substitution with oxygen during plasma polymerization or by the hydrolysis reactions in air with elimination of volatile ammonia [8,10]. To solve this problem, the data on elemental content of as-deposited silazane plasma polymers are needed. The elemental composition of PDMS is 57% of C, 29% of Si and 14% of O. The rf magnetron sputtered films have lower carbon and silicon, and considerably higher oxygen content (Table 1).
3. Results and discussion The elemental content of organosilicon films deposited by various methods is given in Table 1. All XPS peaks are referenced to aliphatic C 1s (C– C, C –H) at 284.5 eV, chosen to take into account a considerable amount (¨15%) of silicon in the coatings, which shifts the carbon binding energy downwards slightly [7]. The peak positions vary with accuracy of 0.1 eV. The films deposited by PID are very close in composition to the precursor ion, which contains 70% of carbon, 20% of silicon and 10% of nitrogen. Several percent of oxygen in as-deposited films arise from the substrate’s SiO2 layer, as the films were thin enough to allow observation of
Table 2 The composition of silazane plasma polymers in dependence on discharge power Elemental composition, atomic percent C
Si
N
O
F
61
15
–
24
–
60
14
–
21
5
61
14
–
25
–
59
14
–
23
4
Experimental parameters
5 W, 0.6 sccm, 2 months after deposition As-deposited, after derivatization with TFAA 25 W, 0.6 sccm, 2 months after deposition As-deposited, after derivatization with TFAA
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
1.0
OH
Si 2p
Si 2s
C 1s
N 1s
O 1s
Plasma polymerization PID rf magnetron sputtering
102.5 102.7 103.0
153.5 153.6 153.9
284.5 284.5 284.5
– 396.9 –
530.5 530.0 532.5
The XPS peak positions are summarized in Table 3. Silicon XPS peaks appear at the nearly identical positions in plasma polymerized and PID-films. The broad 102.7 eV peak is attributed to silicon bound to carbon, nitrogen, and oxygen within the silazane film. The exact assignment of the silicon peak is often problematic. SiC and SiN binding energies for the Si 2p peak range from 101.3 to 102.8 eV. As typically is the case, the difference between the nitrogen and oxygen chemical shifts in Si 2p cannot be resolved due to a diversity of bonding environments with close binding energies, which overlap into a broad final envelope. The broad Si 2p peak of the film deposited from siloxane ions appears at 103.2 eV (Fig. 1), at 0.5 eV higher binding energy than that of the silazane film. The oxygen –nitrogen shift in Si 2p indicates that SiN is a major component of the PID-silazane film, with smaller contributions from SiO and SiC environments. The N 1s peak is centered at a binding energy of 396.9 eV, lower than it is typical for nitrogen bound to carbon [7]. This lower N 1s binding energy is attributed to the predominance of nitrogen bound to silicon (i.e., as Six N). A slightly lower position of Si peak in plasma polymer and deficiency of nitrogen indicate that the peak is dominated by SiC and SiCO species. The Si 2p XPS peak of rf magnetron sputtered PDMS films locates at 103.0 eV binding energy, indicating the predominance of SiO bonding environments. This is confirmed by FTIR measurements. Fig. 2 shows the
0.9
Si-O-C, Si-O-Si
Elemental content, atomic percent
Transmittance, %
Deposition method
C=O
Table 3 XPS peak positions of organosilicon films
CHx
42
0.8
0.7 3600
4000
3500
3200
2800
3000
2500
2000
1500
Wavelength, cm
1000
Fig. 2. FTIR spectrum of a rf magnetron sputtered PDMS film (60 W).
presence of a very intensive band in a region 1000– 1500 cm 1, which can be assigned to the various SiOC or SiOSi stretching vibrations. Compared to these, hydrocarbon component appearing at ¨2900 cm 1 is much lower. Another weak band at ¨1600 cm 1 is assigned to C_O based functionalities. The deposition rate of PID-films is several nanometers per hour. This results in the XPS signal from substrate silicon even after several hours of deposition. Silazane plasma polymers deposit with much higher rates. The deposition at 5 W power proceeds with 20 nm/ min rate, whereas 30 W power increases the deposition rate to 42 nm/min. The deposition rate of rf magnetron sputtered PDMS films is of the order of several nanometers per minute, increasing with power (Fig. 3). The static contact angle of water (WCA) on the fresh samples is ¨75 –85- for the lower powers with a trend to increase to 95- for the higher power (Fig. 4). The samples were soaked in distilled water for 24 h, dried and WCA was measured again. The values of
100 10.0
silazane (Si-NH-Si) Deposition rate, nm/min
Intensity, a. u.
80 60
siloxane (Si-O-Si) 40 20 0 110
108
106
104
102
100
98
Binding energy, eV Fig. 1. Si 2p XPS peaks of polyatomic ion deposited silazane and siloxane films.
500
-1
9.5 9.0 8.5 8.0 7.5 7.0 50
55
60
65
70
75
80
Power, W Fig. 3. The deposition rate of rf magnetron sputtered PDMS.
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
Water contact angle, deg.
95
probably because of the hydrolysis reactions with formation of the surface hydroxyl groups.
before soaking in water after 24 hours soaking in water
90
43
85
Acknowledgements
80 75
This work is a part of the research plan MSM 0021620834 that is financed by the Ministry of Education of the Czech Republic and partly was supported by the projects Kontakt ME553 and Kontakt ME554 both also from the Ministry of Education of the Czech Republic.
70 65 60 55 30
40
50
60
70
80
Power, W Fig. 4. Static contact angle of water on rf magnetron sputtered PDMS films.
WCA decrease significantly compared to the fresh samples, which assumes that water molecules react with the radicals present in the film to produce surface polar groups such as hydroxyls.
4. Conclusion Organosilicon thin films were deposited by plasma polymerization, polyatomic ion deposition and rf magnetron sputtering. Plasma polymerization and PID of silazane produce organic-like coatings with ¨14– 17 at.% of silicon and ¨60 – 70 at.% of carbon. Silicon in PID-films is bound mainly to nitrogen (Six N). Plasma polymers are deficient in nitrogen. Silicon in plasma polymers is bound in various SiCO species. The films age in the open air with incorporation of oxygen. Magnetron sputtering of PDMS produces more inorganic films with ¨20 at.% of Si and ¨33 at.% of C. Presence of considerable amount of SiO species is established. The films age in water with considerable increase of surface energy,
References [1] A. Hiratsuka, I. Karube, Electroanalysis 12/9 (2000) 695. [2] L. Martinu, D. Poitras, J. Vac. Sci. Technol., A 18/6 (2000) 2619. [3] S. Larouche, R. Vernhes, A. Amassian, O. Zabeida, J.E. KlembergSapieha, L. Martinu, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 405. [4] E. Angelini, F. Fracassi, S. Grassini, F. Palumbo, F. Rosalbino, F. Spada, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 385. [5] G. Moretti, F. Guidi, R. Canton, M. Battagliarin, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 406. [6] J. Huran, I. Hotovy, A.P. Kobzev, N.I. Balalykin, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 401. [7] G. Beamson, D. Briggs, High Resolution X-Ray Photoelectron Spectra of Organic Polymers: The Scienta ESCA300 Database, John Wiley, New York (1992). [8] A. Choukourov, J. Kousal, D. Slavı´nska´, H. Biederman, E. Fuoco, S. Tepavcevic, J. Saucedo, L. Hanley, Vacuum 75 (2004) 195. [9] L. Martinu, D. Poitras, J. Vac. Sci. Technol., A 18/6 (2000) 2619. [10] A.M. Wrobel, M.R. Wertheimer, in: R. d’Agostino (Ed.), Plasma Deposition, Treatment and Etching of Polymers, Academic Press, San Diego, 1990, p. 163.
A comparison of polyatomic ion deposited, RF magnetron sputtered and plasma polymer organosilicon films A. Choukourov a, A. Grinevich a, J. Hanux a, J. Kousal a, D. Slavı´nska´ a, H. Biederman a,*, A. Bowers b, L. Hanley b a
Charles University, Faculty of Mathematics and Physics, Department of Macromolecular Physics, Czech Republic b Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA Available online 15 August 2005
Abstract In this work organosilicon films are prepared by plasma polymerization and mass-selected polyatomic ion deposition (MS-PID) of divinyltetramethyldisilazane, and by rf magnetron sputtering of polydimethylsiloxane. The composition of coatings is determined by XPS and FTIR. A chemical derivatization method is applied to detect amines in silazane films. Plasma polymers and ion deposited films are found to be more organic; whereas magnetron sputtered coatings are dominated by SiOx species. Plasma polymers are deficient of nitrogen with silicon bound in various Six Cy Oz species. Silicon in PID-films is bound mainly to nitrogen (Six N). The processes of aging in air or in water are also discussed. D 2005 Elsevier B.V. All rights reserved. Keywords: Plasma processing and plasma deposition; Ion bombardment; Organosilicon polymer
1. Introduction Silicon containing plasma polymers have been extensively studied as possible candidates for various application fields. Siloxanes, silazanes, silanes or their mixtures with O2, N2, N2O, NH3 have been used as precursors. Microelectronics require the films with good dielectric properties. Since polysiloxanes deposited by plasma polymerization possess excellent electrical and thermal properties, they are industrially used in electronic encapsulation applications or as passivation or insulation layers of integrated circuits and electronic devices [1]. Deposition of silicon containing thin films by plasma polymerization of organosilicon precursors is being increasingly used for the fabrication of transparent optical coatings. For example, SiOx coatings are known for their very low refractive index (n) and extinction coefficient (k). The addition of nitrogen in amount of several percent slightly
* Corresponding author. E-mail address: [email protected] (A. Choukourov). 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.07.231
increases n and k. On the other hand, the increase of hydrogen or in particular NH groups content results in a considerable decrease of refractive index. Thus, depending on the plasma conditions and type of monomer the optical properties can be varied to produce the films with desired intermediate n value or graded index optical films, in which the refractive index continuously varies as a function of depth [2,3]. As a result of their high chemical stability and low gas and water permeability, SiOx films are proposed as corrosion inhibitors [4,5]. SiCHN coatings have also a potential for use in high-power, high-frequency, and radiation-resistant applications [6].
2. Experimental 1,3-divinyltetramethyldisilazane, CH2_CH –Si(CH3)2 – NH – Si(CH3)2 – CH_CH2 (M = 185 g/mol), referred to below as silazane, was used as the monomer in the plasma polymerization and polyatomic ion deposition experiments. The plasma polymerization experiments were performed in a glass tubular reactor with external ring electrodes and
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
41
Table 1 The elemental content of organosilicon films determined by XPS Deposition method
Elemental composition, atomic percent C
Si
N
O
Plasma polymerization PID PID rf magnetron sputtering
61 72 65 33
14 17 15 19
– 8 5 –
25 7 17 48
standard excitation frequency of 13.56 MHz. The reactor was pumped by rotary and diffusion pumps, protected by a liquid nitrogen trap, to a base pressure of 1 10 3 Pa. The tank with liquid monomer was connected with the reactor via a needle valve, which controlled the flow rate of monomer vapors. All depositions were performed with a flow rate of 0.6 sccm and a pressure of 20 Pa. The power of 5 and 25 W was applied. In the case of polyatomic ion deposition (PID), the most abundant silazane ion formed by electron impact with m / z = 170 (C7Si2NH16+), corresponding to the molecular ion minus one methyl group or [CH2_CH – Si(CH3)2 –NH – Si(CH3) – CH_CH2]+was used. Films denoted as-deposited were analyzed by XPS immediately after deposition without exposure to air. A parallel-plate electrode system with rf (13.56 MHz) planar magnetron was used for magnetron sputtering. The sputtering was performed in Ar at 5 Pa pressure and 10 sccm flow rate. The substrates were positioned 5 cm above the target and rf power ranged from 20 to 80 W. Polydimethylsiloxane [– Si(CH3)2 –O– ]n was used as the target. The thickness of plasma polymerized and rf sputtered films was in a range of 100– 300 nm, whereas only several nanometers films were deposited by polyatomic ion deposition. Trifluoroacetic anhydride (TFAA) was used as derivatization agent to detect amines. TFAA is also sensitive to hydroxyl groups, a shortcoming which is discussed in the text where relevant.
Experimental parameters
Silazane, 20 Pa, 25 W, 0.6 sccm; measured in 2 months after deposition Silazane, as-deposited, 15 eV, fluences are 1.4 to 6.8 1016 ions/cm2 Silazane, 7-day aged, 15 eV, fluences are 1.4 to 6.8 1016 ions/cm2 PDMS, 100 W, 5 Pa, 10 sccm; measured in 7 months after deposition
the substrate signal. Low energy ions form more organic polymer-like structures and higher energy ions deposit more inorganic SiCN coatings [8]. The PID-films are sensitive to aging in air, revealing a considerable increase of oxygen content within a 7-day period. The incorporation of oxygen proceeds via formation of surface hydroxyl groups, which is detected by the derivatization measurements [8]. Plasma polymers analyzed in 2 months after the deposition lack nitrogen and also exhibit an increased oxygen concentration. The deficiency of nitrogen in Si : C : N : O films due to high affinity of Si with O has been already reported [8,9]. No dependence of elemental composition of silazane plasma polymers on the discharge power is observed (Table 2). The plasma polymer samples were treated with TFAA immediately after the deposition without exposure to air, shipped to University of Illinois at Chicago and then analyzed by XPS. The fluorine concentration in amount of several percent proves the presence of secondary amines or hydroxyls in the as-deposited plasma polymers. However, their concentration is small. The lack of nitrogen in the aged samples can be explained either by the substitution with oxygen during plasma polymerization or by the hydrolysis reactions in air with elimination of volatile ammonia [8,10]. To solve this problem, the data on elemental content of as-deposited silazane plasma polymers are needed. The elemental composition of PDMS is 57% of C, 29% of Si and 14% of O. The rf magnetron sputtered films have lower carbon and silicon, and considerably higher oxygen content (Table 1).
3. Results and discussion The elemental content of organosilicon films deposited by various methods is given in Table 1. All XPS peaks are referenced to aliphatic C 1s (C– C, C –H) at 284.5 eV, chosen to take into account a considerable amount (¨15%) of silicon in the coatings, which shifts the carbon binding energy downwards slightly [7]. The peak positions vary with accuracy of 0.1 eV. The films deposited by PID are very close in composition to the precursor ion, which contains 70% of carbon, 20% of silicon and 10% of nitrogen. Several percent of oxygen in as-deposited films arise from the substrate’s SiO2 layer, as the films were thin enough to allow observation of
Table 2 The composition of silazane plasma polymers in dependence on discharge power Elemental composition, atomic percent C
Si
N
O
F
61
15
–
24
–
60
14
–
21
5
61
14
–
25
–
59
14
–
23
4
Experimental parameters
5 W, 0.6 sccm, 2 months after deposition As-deposited, after derivatization with TFAA 25 W, 0.6 sccm, 2 months after deposition As-deposited, after derivatization with TFAA
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
1.0
OH
Si 2p
Si 2s
C 1s
N 1s
O 1s
Plasma polymerization PID rf magnetron sputtering
102.5 102.7 103.0
153.5 153.6 153.9
284.5 284.5 284.5
– 396.9 –
530.5 530.0 532.5
The XPS peak positions are summarized in Table 3. Silicon XPS peaks appear at the nearly identical positions in plasma polymerized and PID-films. The broad 102.7 eV peak is attributed to silicon bound to carbon, nitrogen, and oxygen within the silazane film. The exact assignment of the silicon peak is often problematic. SiC and SiN binding energies for the Si 2p peak range from 101.3 to 102.8 eV. As typically is the case, the difference between the nitrogen and oxygen chemical shifts in Si 2p cannot be resolved due to a diversity of bonding environments with close binding energies, which overlap into a broad final envelope. The broad Si 2p peak of the film deposited from siloxane ions appears at 103.2 eV (Fig. 1), at 0.5 eV higher binding energy than that of the silazane film. The oxygen –nitrogen shift in Si 2p indicates that SiN is a major component of the PID-silazane film, with smaller contributions from SiO and SiC environments. The N 1s peak is centered at a binding energy of 396.9 eV, lower than it is typical for nitrogen bound to carbon [7]. This lower N 1s binding energy is attributed to the predominance of nitrogen bound to silicon (i.e., as Six N). A slightly lower position of Si peak in plasma polymer and deficiency of nitrogen indicate that the peak is dominated by SiC and SiCO species. The Si 2p XPS peak of rf magnetron sputtered PDMS films locates at 103.0 eV binding energy, indicating the predominance of SiO bonding environments. This is confirmed by FTIR measurements. Fig. 2 shows the
0.9
Si-O-C, Si-O-Si
Elemental content, atomic percent
Transmittance, %
Deposition method
C=O
Table 3 XPS peak positions of organosilicon films
CHx
42
0.8
0.7 3600
4000
3500
3200
2800
3000
2500
2000
1500
Wavelength, cm
1000
Fig. 2. FTIR spectrum of a rf magnetron sputtered PDMS film (60 W).
presence of a very intensive band in a region 1000– 1500 cm 1, which can be assigned to the various SiOC or SiOSi stretching vibrations. Compared to these, hydrocarbon component appearing at ¨2900 cm 1 is much lower. Another weak band at ¨1600 cm 1 is assigned to C_O based functionalities. The deposition rate of PID-films is several nanometers per hour. This results in the XPS signal from substrate silicon even after several hours of deposition. Silazane plasma polymers deposit with much higher rates. The deposition at 5 W power proceeds with 20 nm/ min rate, whereas 30 W power increases the deposition rate to 42 nm/min. The deposition rate of rf magnetron sputtered PDMS films is of the order of several nanometers per minute, increasing with power (Fig. 3). The static contact angle of water (WCA) on the fresh samples is ¨75 –85- for the lower powers with a trend to increase to 95- for the higher power (Fig. 4). The samples were soaked in distilled water for 24 h, dried and WCA was measured again. The values of
100 10.0
silazane (Si-NH-Si) Deposition rate, nm/min
Intensity, a. u.
80 60
siloxane (Si-O-Si) 40 20 0 110
108
106
104
102
100
98
Binding energy, eV Fig. 1. Si 2p XPS peaks of polyatomic ion deposited silazane and siloxane films.
500
-1
9.5 9.0 8.5 8.0 7.5 7.0 50
55
60
65
70
75
80
Power, W Fig. 3. The deposition rate of rf magnetron sputtered PDMS.
A. Choukourov et al. / Thin Solid Films 502 (2006) 40 – 43
Water contact angle, deg.
95
probably because of the hydrolysis reactions with formation of the surface hydroxyl groups.
before soaking in water after 24 hours soaking in water
90
43
85
Acknowledgements
80 75
This work is a part of the research plan MSM 0021620834 that is financed by the Ministry of Education of the Czech Republic and partly was supported by the projects Kontakt ME553 and Kontakt ME554 both also from the Ministry of Education of the Czech Republic.
70 65 60 55 30
40
50
60
70
80
Power, W Fig. 4. Static contact angle of water on rf magnetron sputtered PDMS films.
WCA decrease significantly compared to the fresh samples, which assumes that water molecules react with the radicals present in the film to produce surface polar groups such as hydroxyls.
4. Conclusion Organosilicon thin films were deposited by plasma polymerization, polyatomic ion deposition and rf magnetron sputtering. Plasma polymerization and PID of silazane produce organic-like coatings with ¨14– 17 at.% of silicon and ¨60 – 70 at.% of carbon. Silicon in PID-films is bound mainly to nitrogen (Six N). Plasma polymers are deficient in nitrogen. Silicon in plasma polymers is bound in various SiCO species. The films age in the open air with incorporation of oxygen. Magnetron sputtering of PDMS produces more inorganic films with ¨20 at.% of Si and ¨33 at.% of C. Presence of considerable amount of SiO species is established. The films age in water with considerable increase of surface energy,
References [1] A. Hiratsuka, I. Karube, Electroanalysis 12/9 (2000) 695. [2] L. Martinu, D. Poitras, J. Vac. Sci. Technol., A 18/6 (2000) 2619. [3] S. Larouche, R. Vernhes, A. Amassian, O. Zabeida, J.E. KlembergSapieha, L. Martinu, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 405. [4] E. Angelini, F. Fracassi, S. Grassini, F. Palumbo, F. Rosalbino, F. Spada, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 385. [5] G. Moretti, F. Guidi, R. Canton, M. Battagliarin, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 406. [6] J. Huran, I. Hotovy, A.P. Kobzev, N.I. Balalykin, in: R. d’Agostino, P. Favia, F. Fracassi, F. Palumbo (Eds.), 16th International Symposium on Plasma Chemistry, Taormina, Italy, June 22 – 27, 2003, Symposium Proceeding, 2003, p. 401. [7] G. Beamson, D. Briggs, High Resolution X-Ray Photoelectron Spectra of Organic Polymers: The Scienta ESCA300 Database, John Wiley, New York (1992). [8] A. Choukourov, J. Kousal, D. Slavı´nska´, H. Biederman, E. Fuoco, S. Tepavcevic, J. Saucedo, L. Hanley, Vacuum 75 (2004) 195. [9] L. Martinu, D. Poitras, J. Vac. Sci. Technol., A 18/6 (2000) 2619. [10] A.M. Wrobel, M.R. Wertheimer, in: R. d’Agostino (Ed.), Plasma Deposition, Treatment and Etching of Polymers, Academic Press, San Diego, 1990, p. 163.