- Email: [email protected]
Adsorption and decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) on Si(001) studied by XPS, HREELS, and TPD
applii surface science ELSEVIER
Applied Surface Science 113/l 14 (1997) 546-550
Adsorption and decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) on SiiOOl) studied by XPS, HREELS, and TPD G. Kaneda, J. Murata, T. Takeuchi, Y. Suzuki, N. Sanada, Y. Fukuda Research Institute
of Electronics,
Shizuoka
University.
Hamamatsu
*
432, Japan
Abstract Adsorption and decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) have been studied using XPS, HREELS, and TPD. TEP is adsorbed molecularly on the Si(OO1) surface at RT and some of it is desorbed as a molecule between about 50 and 300°C. The other is decomposed and C,H, is evolved between about 150 and 500°C. For TBP, it is suggested to be partially dissociated at RT and C,H, is evolved between about 70 and 450°C. No carbon left on the surfaces is detected within the detection limit of AES after the TPD measurement for TEP and TBP. The decomposition mechanisms of TEP and TBP on the surface are proposed. F’ACS:
81.15.Gh; 82.65.M~; 82.40.-g.
Keywords:
Triethylphosphine (TEP); Tertiarybutylphosphine (TBP); Si(OO1);XPS; HREELS; TPD
1. Introduction Strong interest has been shown in the heteroepitaxial growth of III-V compound semiconductor films on silicon since III-V/Si structures are promising for large area, low cost, and high quality optical and optoelectronic applications. They include solar cells (for example Ref. [l]), light emitting devices (for example Ref. [2]), and monolithic integration of III-V optical devices with silicon integrated circuits. Phosphine has been used as a precursor for growth of III-V compound semiconductor films by various techniques: metalorganic chemical vapor deposition
* Corresponding author. Tel.: + 81-53-4781305; fax: +81-534740630; e-mail: [email protected]. I7.00 Copyright SO169-4332(96)00867-7
0169-4332/97/$ PII
(MOCVD) (for example Ref. [3]), metalorganic molecular beam epitaxy (MOMBE) (for example Ref. [4]), chemical beam epitaxy (CBE) (for example Ref. [5]), and atomic layer epitaxy (ALE) [6]. Recently, much attention has been paid to alternatives (for example Ref. 171) such as alkyl-phosphine for the growth because phosphine is toxic, hazardous, and pyrolyzed at high temperature. Triethylphosphine (TEP) and tertiarybutylphosphine (TBP) are attractive and promising precursors as an alternative to phosphine. Their low pyrolysis temperature enables low growth temperature and a low V/III ratio as well as better compositional controllability. However, there is a possibility of carbon contamination in the films when using precursors with alkyl groups, which would influence the electrical characteristics of the films.
0 1997 Elsevier Science B.V. All rights reserved.
G. Kaneda et al. /Applied
Surface Science 113 / I14
The first step of fabrication of semiconductor thin films by MOCVD, CBE, and ALE is adsorption of metalorganic (MO) gases on substrates. Therefore, it is very important to study adsorption and decomposition of the MO gases on the surfaces because interfaces between the films and the substrates, which are controlled by adsorption and following decomposition of the gases, strongly affect electrical properties of devices. No detailed study has been carried out for adsorption and decomposition of the precursors on semiconductors. Therefore, we have studied adsorption and decomposition of TEP and TBP on a clean Si(OO1) surface using X-ray photoelectron spectroscopy (XPS). high-resolution electron energy loss spectroscopy (HREELS). and temperature programmed desorption (TPD) to elucidate the decomposition mechanism of the precursors on the Si(OO1) surface.
2. Experimental An n-Si(OOl) (0.025 0 cm) sample was chemically etched by acid for 1 min at RT. It was cleaned by repeated cycles of Ar ion sputtering and annealing in an ultra-high vacuum chamber (I X IO-” Torr). Cleanness of the surface was checked by Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). TPD spectra were measured for the sample exposed to TEP (60 L) and TBP (60 L) at RT with a heating rate of 4”C/s. A quadrupole mass spectrometer, with a small (2 mm) aperture, was placed close to the sample to detect only gases desorbed from the surface and surrounded with a liquid nitrogen shroud to suppress background signals. Measurements of the ion intensities were controlled by a computer which can simultaneously detect ten kinds of ions. XPS (Perkin-Elmer, hv = 1486.6 eV) and HREELS (built by ourselves) spectra were measured for the sample exposed to TEP and TBP at RT to elucidate the chemical and vibrational states of adsorbed species, respectively. HREELS used here consists of double monochromators and analyzers. The resolution was about below 6 meV for a direct beam and was typically 9-13 meV at an incident energy of 5 eV for this experiment. All spectra were
f 1997)
546-550
measured at a specular position angle of 60” to the normal.
541
with an incident
3. Results and discussion Fig. 1 shows XPS P 2p spectrum of the sample exposed to TEP (180 L) at RT. A broad and intense peak at about 133 eV with a shoulder at about 130 eV is seen in Fig. 1. Since the peak and shoulder correspond to the bulk plasmon loss of silicon and P 2p [8], respectively, the component of the loss was subtracted from the spectrum in Fig. 1 and the residual component was divided into P 2p3,z (129.5 eV) and 2p,,, (130.4 eV> with the spin-orbit splitting of 0.9 eV and the intensity ratio of 2:l [8]. Since the binding energy of P 2p3,? in Fig. 1 is higher than that (129.0 eV) of phosphorus bonded to Si [9] and lower than that (129.8 eV) bonded to hydrocarbon [lo], TEP is suggested to be adsorbed as a molecule. However, it is not clear from the XPS result whether TEP is partially decomposed, such as (C,H,),P (n < 3) or not. We will discuss this later using the HREELS results. Fig. 2 shows XPS P 2p spectrum of the sample exposed to TBP (180 L) at RT. We find the P 2p,,, line at 129.9 eV using the same analysis as in Fig. 1. Although TBP is also suggested to be molecularly adsorbed as well as TEP, the details will be discussed later. The C 1s lines were found at 285.7 and 285.4 eV for TEP and TBP on the surface, respectively. which are the typical binding energies for hydrocarbon. Atomic compositions of phosphorus in Figs. 1 and 2 were calculated using the relative sensitivity
Fig. 1. XPS P 2p (shoulder) spectrum of TEP(l80 L&adsorbed Si(OOl) at RT. A strong peak at about 133 eV is due to the bulk plasmon loss of silicon.
548
G. Kaneda et al./Applied
138
136
134
BIND I NO
132
130
128
Surface Science 113/ 114 Cl9971 546-550
126
ENERGY (eV)
Fig. 2. XPS P 2p (shoulder) spectrum of TBP(180 L&adsorbed Si(OO1) at RT. A strong peak at about 133 eV is due to the bulk plasmon loss of silicon.
factor: 0.05% for TEP and 2.0% for TBP. This would be due to the steric hindrance of TEP on the surface and partial decomposition of TBP which will be shown in Fig. 4. HREELS spectra of clean and TEP(lL)-adsorbed Si(OO1) surfaces at RT are displayed in Fig. 3. We find peaks at 2950, 1425, 1270, 1020, and 745 cm-‘. According to the results of diethylsilane on Si(OO1) [ll] and the P(C,H,), molecule [12], they are ascribed to y,(CH, > + v,,(CH,), S,,(CH & o(CH,) + T(CH?), v(CC> + y(CH,), and v(PC,H,), in which V, 6, w, 7, and y represent the stretching, deformation, wagging, twisting, and rocking vibrations. Since the peaks due to ethyl group bonded to silicon are at 2940, 1448, 1213, and 1008 cm-’ [ 111, Si-C, H, species are not on the surface studied here. This is consistent with the result that the Desks due to y(Si-P) are not found at about 800 and-400 cm-’ [13] in Fig. 3. Therefore, Fig. 3
IL TEP/SI(Wl)
Energy
s
Loss / cm”
Fig. 3. HREELS spectra of clean and TEP(lL)-adsorbed Si(OO1) at RT. The incident energy: 5 eV, resolution: 13 meV, and detection angle: 60” (specular position)
Energy Loss I cm”
Fig. 4. HREELS spectra of clean and TBP(SL)-adsorbed Si(OOi) at RT. The incident energy: 5 eV, resolution: 10 meV, and detection angle: 60” (specular position).
indicates that TEP is adsorbed as a molecule on the surface at RT. HREELS spectra of clean and TBP (5 L)-adsorbed Si(OO1) surfaces at RT are shown in Fig. 4. Two peaks at 2084 and 796 cm-’ are seen for the clean surface. They would be due to Si-OH and Si-H, respectively. We find peaks at 2936, 2344, 2 112, 17 12, 1456, 1192, 968 (shoulder), 824, and 6 16 cm- ’ for the sample exposed to TBP. The peaks at 2936, 1456, 1192, and 968 cm-’ can be assigned to v,(CH~) + v,,(CH,), 6,,(CH,), y(CH,), and v(CC>, in which the peak at 1192 cm-’ is a characteristic one (skeletal vibration) for the t-butyl group [14]. Since the peaks at 2112 and 616 cm-’ can be ascribed to v(SiH) and G(SiH) [13], respectively, one hydrogen, at least, in TBP is dissociated, leading to the formation of the Si-H bonds. This is consistent with finding the peak at 2344 cm-’ due to (PHI [ 131. The peak at 824 cm- ’ would be due to the vibration of Si-C shifted by superimposing with the shoulder at about 968 cm ’ . The peak at 17 12 cm _ ’ cannot be assigned to any vibrational mode. We believe that the P-C,H, bond is not broken on the surface because the binding energy of phosphorus in Fig. 2 is close to that of phosphorus bonded to hydrocarbon. TPD spectra of TEPf (m/e = 118), C,Hl (301, C,HT (28), and Hl (2) for the TEP-adsorbed Si(OO1) surface are shown in Fig. 5. We find peaks at about 150°C for TEP+, about 320°C for C, H4+, and about 320 and 490°C for Hl. No peak is found for C, Hi and PC (not shown here). The TPD spectra of C2 Hz
549
G. Kaneda et al. /Applied Surface Science 1 J3/ 114 (19971546-550
and Hl are divided into two and three components, respectively, because of their asymmetry: the peaks are at about 150 and 320°C for the former and at about 150, 320, and 490°C for the latter. Some of TEP on the surface is desorbed as a molecule between about 50 and 300°C. The weak peaks of C,H: and Hl at about 150°C would correspond to the fragmentation of TEP. The peak of Hl at about 320°C would include both the fragmentation of C,H,’ and the decomposition product of ethyl group. Since the HREELS result showed that no species containing hydrogen was left on the surface at about 500°C [ 151, the peak at about 500°C is concluded to be due to hydrogen evolved from the sample holder. No carbon left on the surface was detected by AES after the TPD measurement, although the detection limit in AES is about 0.1 at% of the detection volume. From the above results, we propose the following decomposition mechanism of TEP on Si(OO1 >. RT:
(C2H5)3P(g)
-+ (GH,),P(a)
about 50-300°C: (CzHs),P(a)
-+ (C,H,),P(g)
+ (C>H,),P(a)
about 150-500°C: (CZHS)G’(~)
-, C?H&)
+ H,(g)
+ PC (a)
TPD spectra of TBP+ (m/e = 901, C,Hc (57), C,Hi (561, and H: (2) are shown in Fig. 6. The peaks of C,Hxf at about 320°C with a shoulder at
0
200 SUBSTRATE
400
600
TEMPERATURE (“c)
Fig. 6. TPD spectra of TBP+ (m/e = 90). C,HG (571, C,Hi (56). and Hi (2) for TBP(60 Lhadsorbed Si(OOl) at RT.
about 150°C and Hl at about 570°C are found. No peaks for TBP+, C,Hl, PC (not shown here) are found up to 650°C. The evolution of hydrogen from the surface is observed between about 70 and 500°C. It would be due to the fragmentation of C,H, and the decomposition of the t-butyl group. Since the Si-H stretching vibration is observed in Fig. 4, the peak at about 570°C is due to decomposition of Si-H. Carbon left on the surface was not detected by AES after the TPD measurement. From the results of Figs. 4 and 6, we propose the following decomposition mechanism of TBP on the Si(OO1) surface. RT:
(C,H,)PH2(g)
about 70-450°C
+ (C,H,)PH(a)
+ H(a)
:
WWW) about 500-620°C:
+ C&(g)
+ W
+ H(a)
H(a) + H,(g)
Acknowledgements
0
200 400 ml SUBSTRATE TEMPERATURE 1.~)
800
Fig. 5. TPD spectra of TEP+ (m/e = 118). C,Hl (30). C?H: (28). and Hl (2) for TEP(60 L&adsorbed Si(OOl) at RT.
The authors gratefully acknowledge partial support from the Ministry of Education, Science and Culture, Japan and the Tokai Foundation for Technology. We are grateful to Benkan Corp., especially the late Mr. Noriyuki Seo, for making a ultra-high vacuum chamber for HREELS to us.
550
G. Kaneda et al./Applied
Surface Science 113/ 114 (1997) 546-550
References [9] [1] Y. Itoh, T. Nishioka, A. Yamamoto and M. Yamaguchi, Appl. Phys. Lett. 52 (1988) 1617. [2] S. Kondou, S. Matsumoto and K. Nagai, Appl. Phys. Lett. 53 (19881 279. [3] H.M. Manasevit and W.I. Simpson, J. Electrochem. Sot. 116 (19691 1723. [4] N. Putz, E. Veuhoff, H. Heinecke, M. Heyen, H. Luth and P. Balk, J. Vat. Sci. Technol. B 3 (19851 671. [5] W.T. Tsang, Appl. Phys. Lett. 45 (1984) 1234. [6] T. Suntola, in: Proc. 16th Conf. on Solid State Devices and Materials (Japan Society of Applied Physics, Kobe, 1984) p. 647. [7] G.B. Stringfellow, J. Electron. Mater. 17 (1988) 327. [8] J.F. Moulder, W.F. Stickle, P.E. Sobol and K.D. Bomben.
[lo] [11]
[12]
[13] [14] [15]
Handbook of X-Ray Photoelectron Spectroscopy (PerkinElmer, MN, 1992). M.L. Yu. D.J. Vitkavage and B.S. Meyerson. J. Appl. Phys. 59 (1985) 4032. C. Battistoni, G. Mattogno, E. Paparazzo and L. Naldini, Inorg. Chem. Acta 102 (19851 1. A. Mahajan, B.K. Kellerman, N.M. Russell, S. Banerjee, A. Campion, J.G. Ekerdt, A. Tasch, J.M. White and D.J. Bonser, J. Vat. Sci. Technol. A 12 (1994) 2265. C.P. Pouchert, The Aldrich Library of FT-IR, Vol. 1, No. 1 (Aldrich Chemical Company, Inc.. Milwaukee, 19851 p. 907c. M.L. Colaianni, P.J. Chen and J.T. Yates, Jr., J. Vat. Sci. Technol. A 12 (1994) 2995. L.J. Bellamy. The Infra-red Spectra of Complex Molecules (John Wiley & Sons, NY, 19661. Cl. Kaneda, N. Sanada and Y. Fukuda, to be published.
Applied Surface Science 113/l 14 (1997) 546-550
Adsorption and decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) on SiiOOl) studied by XPS, HREELS, and TPD G. Kaneda, J. Murata, T. Takeuchi, Y. Suzuki, N. Sanada, Y. Fukuda Research Institute
of Electronics,
Shizuoka
University.
Hamamatsu
*
432, Japan
Abstract Adsorption and decomposition of triethylphosphine (TEP) and tertiarybutylphosphine (TBP) have been studied using XPS, HREELS, and TPD. TEP is adsorbed molecularly on the Si(OO1) surface at RT and some of it is desorbed as a molecule between about 50 and 300°C. The other is decomposed and C,H, is evolved between about 150 and 500°C. For TBP, it is suggested to be partially dissociated at RT and C,H, is evolved between about 70 and 450°C. No carbon left on the surfaces is detected within the detection limit of AES after the TPD measurement for TEP and TBP. The decomposition mechanisms of TEP and TBP on the surface are proposed. F’ACS:
81.15.Gh; 82.65.M~; 82.40.-g.
Keywords:
Triethylphosphine (TEP); Tertiarybutylphosphine (TBP); Si(OO1);XPS; HREELS; TPD
1. Introduction Strong interest has been shown in the heteroepitaxial growth of III-V compound semiconductor films on silicon since III-V/Si structures are promising for large area, low cost, and high quality optical and optoelectronic applications. They include solar cells (for example Ref. [l]), light emitting devices (for example Ref. [2]), and monolithic integration of III-V optical devices with silicon integrated circuits. Phosphine has been used as a precursor for growth of III-V compound semiconductor films by various techniques: metalorganic chemical vapor deposition
* Corresponding author. Tel.: + 81-53-4781305; fax: +81-534740630; e-mail: [email protected]. I7.00 Copyright SO169-4332(96)00867-7
0169-4332/97/$ PII
(MOCVD) (for example Ref. [3]), metalorganic molecular beam epitaxy (MOMBE) (for example Ref. [4]), chemical beam epitaxy (CBE) (for example Ref. [5]), and atomic layer epitaxy (ALE) [6]. Recently, much attention has been paid to alternatives (for example Ref. 171) such as alkyl-phosphine for the growth because phosphine is toxic, hazardous, and pyrolyzed at high temperature. Triethylphosphine (TEP) and tertiarybutylphosphine (TBP) are attractive and promising precursors as an alternative to phosphine. Their low pyrolysis temperature enables low growth temperature and a low V/III ratio as well as better compositional controllability. However, there is a possibility of carbon contamination in the films when using precursors with alkyl groups, which would influence the electrical characteristics of the films.
0 1997 Elsevier Science B.V. All rights reserved.
G. Kaneda et al. /Applied
Surface Science 113 / I14
The first step of fabrication of semiconductor thin films by MOCVD, CBE, and ALE is adsorption of metalorganic (MO) gases on substrates. Therefore, it is very important to study adsorption and decomposition of the MO gases on the surfaces because interfaces between the films and the substrates, which are controlled by adsorption and following decomposition of the gases, strongly affect electrical properties of devices. No detailed study has been carried out for adsorption and decomposition of the precursors on semiconductors. Therefore, we have studied adsorption and decomposition of TEP and TBP on a clean Si(OO1) surface using X-ray photoelectron spectroscopy (XPS). high-resolution electron energy loss spectroscopy (HREELS). and temperature programmed desorption (TPD) to elucidate the decomposition mechanism of the precursors on the Si(OO1) surface.
2. Experimental An n-Si(OOl) (0.025 0 cm) sample was chemically etched by acid for 1 min at RT. It was cleaned by repeated cycles of Ar ion sputtering and annealing in an ultra-high vacuum chamber (I X IO-” Torr). Cleanness of the surface was checked by Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). TPD spectra were measured for the sample exposed to TEP (60 L) and TBP (60 L) at RT with a heating rate of 4”C/s. A quadrupole mass spectrometer, with a small (2 mm) aperture, was placed close to the sample to detect only gases desorbed from the surface and surrounded with a liquid nitrogen shroud to suppress background signals. Measurements of the ion intensities were controlled by a computer which can simultaneously detect ten kinds of ions. XPS (Perkin-Elmer, hv = 1486.6 eV) and HREELS (built by ourselves) spectra were measured for the sample exposed to TEP and TBP at RT to elucidate the chemical and vibrational states of adsorbed species, respectively. HREELS used here consists of double monochromators and analyzers. The resolution was about below 6 meV for a direct beam and was typically 9-13 meV at an incident energy of 5 eV for this experiment. All spectra were
f 1997)
546-550
measured at a specular position angle of 60” to the normal.
541
with an incident
3. Results and discussion Fig. 1 shows XPS P 2p spectrum of the sample exposed to TEP (180 L) at RT. A broad and intense peak at about 133 eV with a shoulder at about 130 eV is seen in Fig. 1. Since the peak and shoulder correspond to the bulk plasmon loss of silicon and P 2p [8], respectively, the component of the loss was subtracted from the spectrum in Fig. 1 and the residual component was divided into P 2p3,z (129.5 eV) and 2p,,, (130.4 eV> with the spin-orbit splitting of 0.9 eV and the intensity ratio of 2:l [8]. Since the binding energy of P 2p3,? in Fig. 1 is higher than that (129.0 eV) of phosphorus bonded to Si [9] and lower than that (129.8 eV) bonded to hydrocarbon [lo], TEP is suggested to be adsorbed as a molecule. However, it is not clear from the XPS result whether TEP is partially decomposed, such as (C,H,),P (n < 3) or not. We will discuss this later using the HREELS results. Fig. 2 shows XPS P 2p spectrum of the sample exposed to TBP (180 L) at RT. We find the P 2p,,, line at 129.9 eV using the same analysis as in Fig. 1. Although TBP is also suggested to be molecularly adsorbed as well as TEP, the details will be discussed later. The C 1s lines were found at 285.7 and 285.4 eV for TEP and TBP on the surface, respectively. which are the typical binding energies for hydrocarbon. Atomic compositions of phosphorus in Figs. 1 and 2 were calculated using the relative sensitivity
Fig. 1. XPS P 2p (shoulder) spectrum of TEP(l80 L&adsorbed Si(OOl) at RT. A strong peak at about 133 eV is due to the bulk plasmon loss of silicon.
548
G. Kaneda et al./Applied
138
136
134
BIND I NO
132
130
128
Surface Science 113/ 114 Cl9971 546-550
126
ENERGY (eV)
Fig. 2. XPS P 2p (shoulder) spectrum of TBP(180 L&adsorbed Si(OO1) at RT. A strong peak at about 133 eV is due to the bulk plasmon loss of silicon.
factor: 0.05% for TEP and 2.0% for TBP. This would be due to the steric hindrance of TEP on the surface and partial decomposition of TBP which will be shown in Fig. 4. HREELS spectra of clean and TEP(lL)-adsorbed Si(OO1) surfaces at RT are displayed in Fig. 3. We find peaks at 2950, 1425, 1270, 1020, and 745 cm-‘. According to the results of diethylsilane on Si(OO1) [ll] and the P(C,H,), molecule [12], they are ascribed to y,(CH, > + v,,(CH,), S,,(CH & o(CH,) + T(CH?), v(CC> + y(CH,), and v(PC,H,), in which V, 6, w, 7, and y represent the stretching, deformation, wagging, twisting, and rocking vibrations. Since the peaks due to ethyl group bonded to silicon are at 2940, 1448, 1213, and 1008 cm-’ [ 111, Si-C, H, species are not on the surface studied here. This is consistent with the result that the Desks due to y(Si-P) are not found at about 800 and-400 cm-’ [13] in Fig. 3. Therefore, Fig. 3
IL TEP/SI(Wl)
Energy
s
Loss / cm”
Fig. 3. HREELS spectra of clean and TEP(lL)-adsorbed Si(OO1) at RT. The incident energy: 5 eV, resolution: 13 meV, and detection angle: 60” (specular position)
Energy Loss I cm”
Fig. 4. HREELS spectra of clean and TBP(SL)-adsorbed Si(OOi) at RT. The incident energy: 5 eV, resolution: 10 meV, and detection angle: 60” (specular position).
indicates that TEP is adsorbed as a molecule on the surface at RT. HREELS spectra of clean and TBP (5 L)-adsorbed Si(OO1) surfaces at RT are shown in Fig. 4. Two peaks at 2084 and 796 cm-’ are seen for the clean surface. They would be due to Si-OH and Si-H, respectively. We find peaks at 2936, 2344, 2 112, 17 12, 1456, 1192, 968 (shoulder), 824, and 6 16 cm- ’ for the sample exposed to TBP. The peaks at 2936, 1456, 1192, and 968 cm-’ can be assigned to v,(CH~) + v,,(CH,), 6,,(CH,), y(CH,), and v(CC>, in which the peak at 1192 cm-’ is a characteristic one (skeletal vibration) for the t-butyl group [14]. Since the peaks at 2112 and 616 cm-’ can be ascribed to v(SiH) and G(SiH) [13], respectively, one hydrogen, at least, in TBP is dissociated, leading to the formation of the Si-H bonds. This is consistent with finding the peak at 2344 cm-’ due to (PHI [ 131. The peak at 824 cm- ’ would be due to the vibration of Si-C shifted by superimposing with the shoulder at about 968 cm ’ . The peak at 17 12 cm _ ’ cannot be assigned to any vibrational mode. We believe that the P-C,H, bond is not broken on the surface because the binding energy of phosphorus in Fig. 2 is close to that of phosphorus bonded to hydrocarbon. TPD spectra of TEPf (m/e = 118), C,Hl (301, C,HT (28), and Hl (2) for the TEP-adsorbed Si(OO1) surface are shown in Fig. 5. We find peaks at about 150°C for TEP+, about 320°C for C, H4+, and about 320 and 490°C for Hl. No peak is found for C, Hi and PC (not shown here). The TPD spectra of C2 Hz
549
G. Kaneda et al. /Applied Surface Science 1 J3/ 114 (19971546-550
and Hl are divided into two and three components, respectively, because of their asymmetry: the peaks are at about 150 and 320°C for the former and at about 150, 320, and 490°C for the latter. Some of TEP on the surface is desorbed as a molecule between about 50 and 300°C. The weak peaks of C,H: and Hl at about 150°C would correspond to the fragmentation of TEP. The peak of Hl at about 320°C would include both the fragmentation of C,H,’ and the decomposition product of ethyl group. Since the HREELS result showed that no species containing hydrogen was left on the surface at about 500°C [ 151, the peak at about 500°C is concluded to be due to hydrogen evolved from the sample holder. No carbon left on the surface was detected by AES after the TPD measurement, although the detection limit in AES is about 0.1 at% of the detection volume. From the above results, we propose the following decomposition mechanism of TEP on Si(OO1 >. RT:
(C2H5)3P(g)
-+ (GH,),P(a)
about 50-300°C: (CzHs),P(a)
-+ (C,H,),P(g)
+ (C>H,),P(a)
about 150-500°C: (CZHS)G’(~)
-, C?H&)
+ H,(g)
+ PC (a)
TPD spectra of TBP+ (m/e = 901, C,Hc (57), C,Hi (561, and H: (2) are shown in Fig. 6. The peaks of C,Hxf at about 320°C with a shoulder at
0
200 SUBSTRATE
400
600
TEMPERATURE (“c)
Fig. 6. TPD spectra of TBP+ (m/e = 90). C,HG (571, C,Hi (56). and Hi (2) for TBP(60 Lhadsorbed Si(OOl) at RT.
about 150°C and Hl at about 570°C are found. No peaks for TBP+, C,Hl, PC (not shown here) are found up to 650°C. The evolution of hydrogen from the surface is observed between about 70 and 500°C. It would be due to the fragmentation of C,H, and the decomposition of the t-butyl group. Since the Si-H stretching vibration is observed in Fig. 4, the peak at about 570°C is due to decomposition of Si-H. Carbon left on the surface was not detected by AES after the TPD measurement. From the results of Figs. 4 and 6, we propose the following decomposition mechanism of TBP on the Si(OO1) surface. RT:
(C,H,)PH2(g)
about 70-450°C
+ (C,H,)PH(a)
+ H(a)
:
WWW) about 500-620°C:
+ C&(g)
+ W
+ H(a)
H(a) + H,(g)
Acknowledgements
0
200 400 ml SUBSTRATE TEMPERATURE 1.~)
800
Fig. 5. TPD spectra of TEP+ (m/e = 118). C,Hl (30). C?H: (28). and Hl (2) for TEP(60 L&adsorbed Si(OOl) at RT.
The authors gratefully acknowledge partial support from the Ministry of Education, Science and Culture, Japan and the Tokai Foundation for Technology. We are grateful to Benkan Corp., especially the late Mr. Noriyuki Seo, for making a ultra-high vacuum chamber for HREELS to us.
550
G. Kaneda et al./Applied
Surface Science 113/ 114 (1997) 546-550
References [9] [1] Y. Itoh, T. Nishioka, A. Yamamoto and M. Yamaguchi, Appl. Phys. Lett. 52 (1988) 1617. [2] S. Kondou, S. Matsumoto and K. Nagai, Appl. Phys. Lett. 53 (19881 279. [3] H.M. Manasevit and W.I. Simpson, J. Electrochem. Sot. 116 (19691 1723. [4] N. Putz, E. Veuhoff, H. Heinecke, M. Heyen, H. Luth and P. Balk, J. Vat. Sci. Technol. B 3 (19851 671. [5] W.T. Tsang, Appl. Phys. Lett. 45 (1984) 1234. [6] T. Suntola, in: Proc. 16th Conf. on Solid State Devices and Materials (Japan Society of Applied Physics, Kobe, 1984) p. 647. [7] G.B. Stringfellow, J. Electron. Mater. 17 (1988) 327. [8] J.F. Moulder, W.F. Stickle, P.E. Sobol and K.D. Bomben.
[lo] [11]
[12]
[13] [14] [15]
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