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New precursors for chemical vapour deposition of platinum and the hydrogen effect on cvd
IWyhedron Vol. 8, No. 4, pp. Printed in Great Britain
551-553,
1989 0
0277-5387/89 $3.00 + 03 1989 Pergamon Press plc
COMMUNICATION NEW PRECURSORS FOR CHEMICAL VAPOUR DEPOSITION OF PLATINUM AND THE HYDROGEN EFFECT ON CVD R. KUMAR, S. ROY, M. RASHIDI
and R. J. PUDDEPHATT*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7 (Received 14 August 1988 ; accepted 24 October 1988)
Abstract-Volatile organoplatimun(I1) complexes have been studied as precursors for low temperature chemical vapour deposition (CVD) of platinum films. The temperature of CVD and the carbon contamination of the films can both be decreased by conducting the CVD process in the presence of hydrogen. Good adherence of the films to a silicon semiconductor is obtained.
gen, reduces both the pyrolysis temperature and the amount of carbon contamination. Some results for CVD of platinum are shown in Table 1. The major new class of organoplatinum precursors comprises the alkylplatinum(I1) complexes, such as cis-[PtMe2(MeNC)z] and ptMe2 (COD)] (COD = 1,5-cyclooctadiene) and some known precursors are included for comparison. In all cases, when CVD was carried out at 25O”C, with the precursor warmed to 40-120°C so as to give reasonably rapid deposition, the platinum films which were formed contained carbon impurities, as found in previous studies. l-3 Analysis of platinum films deposited on silicon wafers was carried out by XPS ; films were cleaned before analysis by argon sputtering since much of the surface carbofi impurity was formed after CVD by adsorption of atmospheric carbon. Now, since platinum is an excellent hydrogenation catalyst, CVD experiments in the presence of hydrogen (10e3 torr) were carried out (Table 1). In nearly all cases, the carbon impurities were reduced in the presence of hydrogen and in some cases the effect was dramatic. We presume that organic carbon is hydrogenated and hence the surface is continuously cleaned. Another useful effect of H2 is to decrease the temperature required for CVD. For example, with [PtMe2(COD)], [PtMe(q’C,H,)(COD)] and ptMe($-&H,)(CO)], CVD was observed at 135°C and was efficient at 180°C in the presence of hydrogen, but the onset of CVD *Author to whom correspondence should be addressed. occurred at 235°C in the absence of hydrogen.
The noble metals, particularly gold, palladium and platinum, are used extensively in semiconductor device processing and are usually deposited by sputtering or electron-beam evaporation. Platinum is particularly difficult to filament-evaporate because it rapidly forms an alloy with tungsten and because its vapour pressure is low, yet it is valuable in forming platinum silicide ohmic and Schottky diode contacts to silicon and also to gallium arsenide. ’ The evaporation methods can lead to degradation of the semiconductor devices and there would therefore be advantages in using a milder deposition method, such as CVD. 2*4This technique, operating at low temperature and pressure, has recently been the subject of intense research with special emphasis on CVD of gold lilms,5-‘2 but with some renewed interest in platinum.‘-3,‘s’5 For the noble metals, a major problem has been to find organometallic precursors for CVD which have sufficient volatility and which decompose to the pure metal under mild thermal or photochemical conditions. ‘-I 5 Platinum precursors have been [PtCl,(CO)d,‘y3 bis(diketonato)platinum(II) complexes, l-39I 3*I 5 trimethyl@diketonato)platinum(IV)3 and trimethyl(q-cyclopentadienyl)platinum(IV). 3*14The platinum films usually contain much carbon, chlorine or other impurities. I-3 This paper describes new alkylplatinum(II) precursors and shows that CVD, in the presence of hydro-
551
552
Communication Table 1. Analytical
data for platinum films formed by chemical vapour deposition at 250°C”*b
Complex
H 2 present
[PtMe2WNCLl [PtMe,(COD)ld FtMe(rl ‘-W-LKOW [PtMeCl(COD)] ptMe(rl ‘-C sH #-WI [PtMe3(v5-GW [Pt(~3-Wb)(tlZGHd [PtMe3(acac)l z
No Yes No Yes No Yes No Yes No No No No
XPS analysis’ (Element %) Pt c 0 88 95 86 94 77 95 70 88 71 74 60 66
11 5 10 4 19 5 25 9 27 25 38 30
4 2 4 5 3 2 1 2 4
“CVD carried out in a vertical reactor. Adherence tested by the scratch test. bKnown complexes were prepared according to ref. 16. ‘After argon sputtering for 30 s. d Sample purified by sublimation. ’ 13CNMR (CDCl,) : 6 = 26.8 [‘J(l?tC) = 383, CHJ; 70.2 [‘J(PtC) = 75, CH]; 90.7 [‘J(PtC) = 32, &H,].
effects on both the purity of the films and the temperature of CVD could be obtained at higher hydrogen pressures, but decreased volatility of the precursors is a problem under these conditions. Low temperature CVD is particularly important for metallization of the thermally sensitive III-V semiconductors. In summary, this work has shown that alkylplatinum(I1) complexes are useful precursors for CVD of platinum, and that lower temperature CVD and a reduction in the carbon impurities in the platinum films can be accomplished by carrying out the CVD in the presence of hydrogen. Such CVD processes may have applications not only in the metalhzation of electronic devices but also in the preparation of heterogeneous platinum catalysts. Studies of the mechanistic basis for the CVD are in progress. It is likely that greater
thank NSERC (Canada) and the province of Ontario for funding through the strategic grant programme and centres of excellence (OCMR) programme, respectively. XPS analyses were carried out by Surface Science Western.
Acknowle&ements-We
REFERENCES 1. M. J. Rand, J. Electrochem. Sot. 1973, 120, 686. 2. C. F. Powell, J. H. Oxley and J. M. Blocher, Jr, Vapor Deposition, pp. 310-314. John Wiley, New York (1966). 3. W. Westwood, Gmelin Handbook of Inorganic Chemistry--Supplement Vol. Al, Technology of PlatinumGroup Metals, 8th edn, pp. 43-50 (1986). 4. D. C. Bradley, New Scientist 1988,38. 5. T. T. Kodas, T. H. Baum and P. B. Comita, J. Cryst. Growth 1988,87,378. 6. C. E. Larson, T. H. Baum and R. L. Jackson, Mater. Res. Sot. Symp. Proc. 1987, 75, 721; C. E. Larson, T. H. Baum and R. L. Jackson, J. Electrochem. Sot. 1987,134,266. 7. T. H. Baum, J. Zdec~rochem. Sot. 1987, 134,2616. 8. M. R. Aylett, Chemtronics 1986, 1, 146. 9. G. M. Shedd, H. Lezec, A. D. Dubner and J. Melngailis, Appl. Phys. L&t. 1986, 49, 1584. 10. T. H. Baum and C. R. Jones, Appl. Phys. Lett. 1985, 47, 538. 11. T. T. Kodas, T. H. Baum and P. B. Comita, J. Appl. Phys. 1987,62,281. 12. R. J. Puddephatt and I. Treumicht, J. Organomet. Chem. 1987,319, 129. 13. D. Braichotte and H. van den Bergh, Laser Process Diagn 1986,2, 95.
Communication 14. J. E. Gozum, D. M. Pollina, J. A. Jensen and G. S. Girolami, J. Am. Chem. Sot. 1988,110,2688. 15. H. H. Gilgen, R. Cacouris, P. S. Shaw, R. R. Krchnavek and R. M. Osgood, Appl. Phys. 1987, 42B, 55. 16. H. C. Clark and L. E. Manzer, J. Orgunomet. Chem.
1973, 59,411;
553 H. C. Clark and A. Shaver, Can. J.
Chem. 1976, 54, 2068 ; S. D. Robinson and B. L. Shaw, J. Chem. Sot. 1965,1529 ; R. C. Menzies and H. Overton, J. Chem. Sot. 1933, 1290; B. E. Mann, B. L. Shaw and G. Shaw, J. Chem. Sot. A 1971, 3536.
551-553,
1989 0
0277-5387/89 $3.00 + 03 1989 Pergamon Press plc
COMMUNICATION NEW PRECURSORS FOR CHEMICAL VAPOUR DEPOSITION OF PLATINUM AND THE HYDROGEN EFFECT ON CVD R. KUMAR, S. ROY, M. RASHIDI
and R. J. PUDDEPHATT*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7 (Received 14 August 1988 ; accepted 24 October 1988)
Abstract-Volatile organoplatimun(I1) complexes have been studied as precursors for low temperature chemical vapour deposition (CVD) of platinum films. The temperature of CVD and the carbon contamination of the films can both be decreased by conducting the CVD process in the presence of hydrogen. Good adherence of the films to a silicon semiconductor is obtained.
gen, reduces both the pyrolysis temperature and the amount of carbon contamination. Some results for CVD of platinum are shown in Table 1. The major new class of organoplatinum precursors comprises the alkylplatinum(I1) complexes, such as cis-[PtMe2(MeNC)z] and ptMe2 (COD)] (COD = 1,5-cyclooctadiene) and some known precursors are included for comparison. In all cases, when CVD was carried out at 25O”C, with the precursor warmed to 40-120°C so as to give reasonably rapid deposition, the platinum films which were formed contained carbon impurities, as found in previous studies. l-3 Analysis of platinum films deposited on silicon wafers was carried out by XPS ; films were cleaned before analysis by argon sputtering since much of the surface carbofi impurity was formed after CVD by adsorption of atmospheric carbon. Now, since platinum is an excellent hydrogenation catalyst, CVD experiments in the presence of hydrogen (10e3 torr) were carried out (Table 1). In nearly all cases, the carbon impurities were reduced in the presence of hydrogen and in some cases the effect was dramatic. We presume that organic carbon is hydrogenated and hence the surface is continuously cleaned. Another useful effect of H2 is to decrease the temperature required for CVD. For example, with [PtMe2(COD)], [PtMe(q’C,H,)(COD)] and ptMe($-&H,)(CO)], CVD was observed at 135°C and was efficient at 180°C in the presence of hydrogen, but the onset of CVD *Author to whom correspondence should be addressed. occurred at 235°C in the absence of hydrogen.
The noble metals, particularly gold, palladium and platinum, are used extensively in semiconductor device processing and are usually deposited by sputtering or electron-beam evaporation. Platinum is particularly difficult to filament-evaporate because it rapidly forms an alloy with tungsten and because its vapour pressure is low, yet it is valuable in forming platinum silicide ohmic and Schottky diode contacts to silicon and also to gallium arsenide. ’ The evaporation methods can lead to degradation of the semiconductor devices and there would therefore be advantages in using a milder deposition method, such as CVD. 2*4This technique, operating at low temperature and pressure, has recently been the subject of intense research with special emphasis on CVD of gold lilms,5-‘2 but with some renewed interest in platinum.‘-3,‘s’5 For the noble metals, a major problem has been to find organometallic precursors for CVD which have sufficient volatility and which decompose to the pure metal under mild thermal or photochemical conditions. ‘-I 5 Platinum precursors have been [PtCl,(CO)d,‘y3 bis(diketonato)platinum(II) complexes, l-39I 3*I 5 trimethyl@diketonato)platinum(IV)3 and trimethyl(q-cyclopentadienyl)platinum(IV). 3*14The platinum films usually contain much carbon, chlorine or other impurities. I-3 This paper describes new alkylplatinum(II) precursors and shows that CVD, in the presence of hydro-
551
552
Communication Table 1. Analytical
data for platinum films formed by chemical vapour deposition at 250°C”*b
Complex
H 2 present
[PtMe2WNCLl [PtMe,(COD)ld FtMe(rl ‘-W-LKOW [PtMeCl(COD)] ptMe(rl ‘-C sH #-WI [PtMe3(v5-GW [Pt(~3-Wb)(tlZGHd [PtMe3(acac)l z
No Yes No Yes No Yes No Yes No No No No
XPS analysis’ (Element %) Pt c 0 88 95 86 94 77 95 70 88 71 74 60 66
11 5 10 4 19 5 25 9 27 25 38 30
4 2 4 5 3 2 1 2 4
“CVD carried out in a vertical reactor. Adherence tested by the scratch test. bKnown complexes were prepared according to ref. 16. ‘After argon sputtering for 30 s. d Sample purified by sublimation. ’ 13CNMR (CDCl,) : 6 = 26.8 [‘J(l?tC) = 383, CHJ; 70.2 [‘J(PtC) = 75, CH]; 90.7 [‘J(PtC) = 32, &H,].
effects on both the purity of the films and the temperature of CVD could be obtained at higher hydrogen pressures, but decreased volatility of the precursors is a problem under these conditions. Low temperature CVD is particularly important for metallization of the thermally sensitive III-V semiconductors. In summary, this work has shown that alkylplatinum(I1) complexes are useful precursors for CVD of platinum, and that lower temperature CVD and a reduction in the carbon impurities in the platinum films can be accomplished by carrying out the CVD in the presence of hydrogen. Such CVD processes may have applications not only in the metalhzation of electronic devices but also in the preparation of heterogeneous platinum catalysts. Studies of the mechanistic basis for the CVD are in progress. It is likely that greater
thank NSERC (Canada) and the province of Ontario for funding through the strategic grant programme and centres of excellence (OCMR) programme, respectively. XPS analyses were carried out by Surface Science Western.
Acknowle&ements-We
REFERENCES 1. M. J. Rand, J. Electrochem. Sot. 1973, 120, 686. 2. C. F. Powell, J. H. Oxley and J. M. Blocher, Jr, Vapor Deposition, pp. 310-314. John Wiley, New York (1966). 3. W. Westwood, Gmelin Handbook of Inorganic Chemistry--Supplement Vol. Al, Technology of PlatinumGroup Metals, 8th edn, pp. 43-50 (1986). 4. D. C. Bradley, New Scientist 1988,38. 5. T. T. Kodas, T. H. Baum and P. B. Comita, J. Cryst. Growth 1988,87,378. 6. C. E. Larson, T. H. Baum and R. L. Jackson, Mater. Res. Sot. Symp. Proc. 1987, 75, 721; C. E. Larson, T. H. Baum and R. L. Jackson, J. Electrochem. Sot. 1987,134,266. 7. T. H. Baum, J. Zdec~rochem. Sot. 1987, 134,2616. 8. M. R. Aylett, Chemtronics 1986, 1, 146. 9. G. M. Shedd, H. Lezec, A. D. Dubner and J. Melngailis, Appl. Phys. L&t. 1986, 49, 1584. 10. T. H. Baum and C. R. Jones, Appl. Phys. Lett. 1985, 47, 538. 11. T. T. Kodas, T. H. Baum and P. B. Comita, J. Appl. Phys. 1987,62,281. 12. R. J. Puddephatt and I. Treumicht, J. Organomet. Chem. 1987,319, 129. 13. D. Braichotte and H. van den Bergh, Laser Process Diagn 1986,2, 95.
Communication 14. J. E. Gozum, D. M. Pollina, J. A. Jensen and G. S. Girolami, J. Am. Chem. Sot. 1988,110,2688. 15. H. H. Gilgen, R. Cacouris, P. S. Shaw, R. R. Krchnavek and R. M. Osgood, Appl. Phys. 1987, 42B, 55. 16. H. C. Clark and L. E. Manzer, J. Orgunomet. Chem.
1973, 59,411;
553 H. C. Clark and A. Shaver, Can. J.
Chem. 1976, 54, 2068 ; S. D. Robinson and B. L. Shaw, J. Chem. Sot. 1965,1529 ; R. C. Menzies and H. Overton, J. Chem. Sot. 1933, 1290; B. E. Mann, B. L. Shaw and G. Shaw, J. Chem. Sot. A 1971, 3536.