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Oriented growth of A1N films on oriented A1 films
Journal of Crystal Growth 29 (1975) 127—129 © North-HollandPublishing Co.
ORIENTED GROWTH OF MN FILMS ON ORIENTED M FILMS YOICHIRO UEMURA and MINORU IWATA National Institute for Researches in Inorganic Materials, Kurakake, Sakura-Mura, Niihari-Gun, Ibaraki, 300—31, Japan Received 10 December 1974; revised manuscript received 31 December 1974 It has been found that oriented AIN films can be grown at relatively low substrate temperature on thin oriented aluminum films. A1N films have been prepared by dc glow discharge in pure N 2 gas in the temperature range from room temperature to about 400 °C.Aluminum films, which had been deposited on NaCI single crystals at several temperatures and annealed at the growth temperature of AIN in vacuum, have been used as substrates. The structure and orientation of the films have been studied by transmission electron diffraction.
Recently, the epitaxial growth of A1N films has been actively studied. Various preparative methods have been reported: chemical vapor deposition’~),reactive 5) and reactive sputtering6’7). A1N films evaporation have been prepared on a number of substrates such as Si’—3), SiC2’3’6), ~s-Al 2~’ 7), quartz2) and spinel3). 2O3 The epitaxial temperatures reported were above 1000 °C in all cases. In this study, we used thin aluminum metal films as substrates. The films were evaporated from a W-coil heater under vacuum conditions in the low 10 8 torr range onto NaCl single crystals (cleaved in air) at several substrate temperatures. The thickness of aluminum films ranged between 150 A and 200 A. AiM films were formed on these aluminum films (not exposed to the air) by dc glow discharge in pure N2 gas at about 6 x 10-2 torr (the water vapor concentration was less than 0.5 ppm by volume). An aluminum plate was placed as cathode about 1 cm from the substrates and biased —1000 V with respect to ground. There are two possible formation mechanisms of AIN using this method. One is a reactive sputtering of aluminum cathode, and the other is direct reaction between substrate aluminum and active nitrogen. 8). The former is dominant in ratherrate thickofA1N The deposition A1Nfilms was determined from measurements ofAl—AIM—Au type capacitors assuming the dielectric constant of A1N to be 8.5. The capacitors were fabricated in the following manner. Aluminum was evaporated in vacuum onto pyrex-glass to form the base electrode of about 1000 A thick, A1N was
then formed by the above technique at room temperature, and finally gold was evaporated as the top electrode the was baseabout aluminum The thickness of the across Au films 500 A.stripes. The effective area of these electrodes was about 1 mm2. The deposition rate was calculated to be 4.8 A/mm from the relationship between A1N film thickness and glow discharge time. The deposition rate, however, was strongly dependent upon growth conditions such as the N 2 pressure, the distance from the cathode to the substrate, and the discharge voltage. In the preparation of A1N films for transmission electron diffraction, the deposition rates
127
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Fig. 1. An electron diffraction pattern taken from an Al film deposited at about 200 °C.
128
YOICHIRO LTEMURA AND MINORU IWATA
_________
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________ ______ -
~ -
-
-
-:
- -
~
~
-
-—
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Fig. 2. An clc~trondiffraction pattern taken from an oriented AIN turn on oriented Al film.
were not allowed to exceed the above value and discharge times ranged between an hour and two hours. The ifim structure was examined by means of transmission electron diffraction (in the direction normal to the film surface). Samples of each film were removed from the substrate by dissolving the NaC1 in water, and were supported on copper screens for observation, The diffraction pattern of the aluminum metal deposited at about 200 °Cconsisted of rings and spots (fig. 1). The spots having 4-fold symmetry superposed
oriented (111) Al which exhibits the following orientation relationship: (111) Al 11(001) NaCl and [110]Al I [110]NaC1 or [110]Al I [110]NaCl9). A typical diffraction pattern and the indices of A1N film formed on such oriented aluminum substrates are shown in fig. 2. on continuous line with (220) index are due to the The A1N and Al were deposited at about 340 °Cand 290 Thefig.lines having (hkl) (1that ~ 0)A1N indices°C,respectively. do not appear in 2. This indicates exhibits an orientation such as (001) A1N 11(111) Al. This result seems to be plausible, because the A1N crystal possesses the wurzite type structure, and the (001) surface is close-packed, as is the (111) surface of the fcc Al crystal structure. We could not distinguish, however, between the [1001A1N I [1101Al and [110]A1N I [110]Al orientation relationships. For such a determination, it would be necessary to form a single crystal AIN film on a single crystal Al film substrate. In the case of A1N films formed at 400 °Con aluminum substrates deposited at room temperature, the spotty diffraction pattern was not observed in spite of the elevated growth temperature of the AIN (fig. 3). Noreika Ct al.’ 0) reported that the A1N films deposited by reactive sputtering at 600 °Con single crystal Si substrates showed only a strong (001)-fiber texture and diffraction pattern consisted only of continuous rings. Gold films, about 200 A thick, were also used as sub-
inertness to nitrogen. The films deposited at about 180 °Con NaCl single crystals showed (001) orientation accompanied by (111) orientation. The AIN films formed on the oriented gold substrates showed the same diffraction pattern as that for A1N formed on orientedfor strates Al the films.sake Thisofresult comparison shows thebecause possibility of their that oriented AiM films can be formed on oriented metal films other than on aluminum films. According to these experimental results, it may be concluded that, in a dc glow discharge, oriented A1N ~ may be formed on thin oriented Al films at a substrate temperature as low as 340 °C,and that the degree of orientation of the A1N is strongly affected by the crystalline state of substrate metals. It is expected that the crystalline quality of AIN films improves by using Al metal film substrates which have the better (111) epi-
•
~ ~ ____ _____ ________
-
______ _______
____________
________
Fig. 3. An electron diffraction pattern taken from an AIN film deposited at 400 °Con Al film deposited at room temperature.
taxial quality [notcontaining @01) oriented Al]. Further experiments are being carried out on A1N film growth
ORIENTED GROWTH OF
A1N
at higher temperatures after carefully reducing the contamination by out-gassing at an elevated temperature. The authors wish to thank Dr. S. Horiuchi and Mr. K. Sakaguchi for the electron diffraction photographs and Mr. K. Tanaka for the preparation of A1N films. References 1) A. I. Noreika and D. W. Ing, J. AppI. Phys. 39 (1968) 5578. 2) A. J. Noreika, M. H. Francombe and S. A. Zeitman, I. Vacuum Sci. Technol. 6 (1968) 194. 3) H. M. Manasevit, F. M. Erdmann and W. I. Simpson, J. Electrochem. Soc. 118 (1971) 1864.
FILMS ON ORIENTED
Al
FILMS
129
4) W. M. Yim, E. I. Stolko, P. J. Zanzucchi, J. I. Pankove, M. Ettenberg and S. L. Gilbert, J. Appi. Phys. 44 (1973) 292. 5) M. T. Wauk and D. K. Winslow, AppI. Phys. Letters 13 (1968) 286. 6) T. L. Chu, D. W. Ing and A. J. Noreika, Solid-State Electron. 10 (1967) 1023. 7) A. J. Shuskus, T. M. Reeder and E. L. Paradis, AppI. Phys. Letters 24 (1974) 155. 8) Y. Uemura, K. Tanaka and M. Iwata, Thin Solid Films 20 (1974) 11. 9) S. mo, D. Watanabe and S. Obawa, I. Phys. Soc. Japan 19 (1964) 881. 10) A. J. Noreika, M. H. Francombe and S. A. Zeitman, NASA contract report, CR-86395 (1969).
ORIENTED GROWTH OF MN FILMS ON ORIENTED M FILMS YOICHIRO UEMURA and MINORU IWATA National Institute for Researches in Inorganic Materials, Kurakake, Sakura-Mura, Niihari-Gun, Ibaraki, 300—31, Japan Received 10 December 1974; revised manuscript received 31 December 1974 It has been found that oriented AIN films can be grown at relatively low substrate temperature on thin oriented aluminum films. A1N films have been prepared by dc glow discharge in pure N 2 gas in the temperature range from room temperature to about 400 °C.Aluminum films, which had been deposited on NaCI single crystals at several temperatures and annealed at the growth temperature of AIN in vacuum, have been used as substrates. The structure and orientation of the films have been studied by transmission electron diffraction.
Recently, the epitaxial growth of A1N films has been actively studied. Various preparative methods have been reported: chemical vapor deposition’~),reactive 5) and reactive sputtering6’7). A1N films evaporation have been prepared on a number of substrates such as Si’—3), SiC2’3’6), ~s-Al 2~’ 7), quartz2) and spinel3). 2O3 The epitaxial temperatures reported were above 1000 °C in all cases. In this study, we used thin aluminum metal films as substrates. The films were evaporated from a W-coil heater under vacuum conditions in the low 10 8 torr range onto NaCl single crystals (cleaved in air) at several substrate temperatures. The thickness of aluminum films ranged between 150 A and 200 A. AiM films were formed on these aluminum films (not exposed to the air) by dc glow discharge in pure N2 gas at about 6 x 10-2 torr (the water vapor concentration was less than 0.5 ppm by volume). An aluminum plate was placed as cathode about 1 cm from the substrates and biased —1000 V with respect to ground. There are two possible formation mechanisms of AIN using this method. One is a reactive sputtering of aluminum cathode, and the other is direct reaction between substrate aluminum and active nitrogen. 8). The former is dominant in ratherrate thickofA1N The deposition A1Nfilms was determined from measurements ofAl—AIM—Au type capacitors assuming the dielectric constant of A1N to be 8.5. The capacitors were fabricated in the following manner. Aluminum was evaporated in vacuum onto pyrex-glass to form the base electrode of about 1000 A thick, A1N was
then formed by the above technique at room temperature, and finally gold was evaporated as the top electrode the was baseabout aluminum The thickness of the across Au films 500 A.stripes. The effective area of these electrodes was about 1 mm2. The deposition rate was calculated to be 4.8 A/mm from the relationship between A1N film thickness and glow discharge time. The deposition rate, however, was strongly dependent upon growth conditions such as the N 2 pressure, the distance from the cathode to the substrate, and the discharge voltage. In the preparation of A1N films for transmission electron diffraction, the deposition rates
127
___________________________________________
Fig. 1. An electron diffraction pattern taken from an Al film deposited at about 200 °C.
128
YOICHIRO LTEMURA AND MINORU IWATA
_________
-
________ ______ -
~ -
-
-
-:
- -
~
~
-
-—
-
Fig. 2. An clc~trondiffraction pattern taken from an oriented AIN turn on oriented Al film.
were not allowed to exceed the above value and discharge times ranged between an hour and two hours. The ifim structure was examined by means of transmission electron diffraction (in the direction normal to the film surface). Samples of each film were removed from the substrate by dissolving the NaC1 in water, and were supported on copper screens for observation, The diffraction pattern of the aluminum metal deposited at about 200 °Cconsisted of rings and spots (fig. 1). The spots having 4-fold symmetry superposed
oriented (111) Al which exhibits the following orientation relationship: (111) Al 11(001) NaCl and [110]Al I [110]NaC1 or [110]Al I [110]NaCl9). A typical diffraction pattern and the indices of A1N film formed on such oriented aluminum substrates are shown in fig. 2. on continuous line with (220) index are due to the The A1N and Al were deposited at about 340 °Cand 290 Thefig.lines having (hkl) (1that ~ 0)A1N indices°C,respectively. do not appear in 2. This indicates exhibits an orientation such as (001) A1N 11(111) Al. This result seems to be plausible, because the A1N crystal possesses the wurzite type structure, and the (001) surface is close-packed, as is the (111) surface of the fcc Al crystal structure. We could not distinguish, however, between the [1001A1N I [1101Al and [110]A1N I [110]Al orientation relationships. For such a determination, it would be necessary to form a single crystal AIN film on a single crystal Al film substrate. In the case of A1N films formed at 400 °Con aluminum substrates deposited at room temperature, the spotty diffraction pattern was not observed in spite of the elevated growth temperature of the AIN (fig. 3). Noreika Ct al.’ 0) reported that the A1N films deposited by reactive sputtering at 600 °Con single crystal Si substrates showed only a strong (001)-fiber texture and diffraction pattern consisted only of continuous rings. Gold films, about 200 A thick, were also used as sub-
inertness to nitrogen. The films deposited at about 180 °Con NaCl single crystals showed (001) orientation accompanied by (111) orientation. The AIN films formed on the oriented gold substrates showed the same diffraction pattern as that for A1N formed on orientedfor strates Al the films.sake Thisofresult comparison shows thebecause possibility of their that oriented AiM films can be formed on oriented metal films other than on aluminum films. According to these experimental results, it may be concluded that, in a dc glow discharge, oriented A1N ~ may be formed on thin oriented Al films at a substrate temperature as low as 340 °C,and that the degree of orientation of the A1N is strongly affected by the crystalline state of substrate metals. It is expected that the crystalline quality of AIN films improves by using Al metal film substrates which have the better (111) epi-
•
~ ~ ____ _____ ________
-
______ _______
____________
________
Fig. 3. An electron diffraction pattern taken from an AIN film deposited at 400 °Con Al film deposited at room temperature.
taxial quality [notcontaining @01) oriented Al]. Further experiments are being carried out on A1N film growth
ORIENTED GROWTH OF
A1N
at higher temperatures after carefully reducing the contamination by out-gassing at an elevated temperature. The authors wish to thank Dr. S. Horiuchi and Mr. K. Sakaguchi for the electron diffraction photographs and Mr. K. Tanaka for the preparation of A1N films. References 1) A. I. Noreika and D. W. Ing, J. AppI. Phys. 39 (1968) 5578. 2) A. J. Noreika, M. H. Francombe and S. A. Zeitman, I. Vacuum Sci. Technol. 6 (1968) 194. 3) H. M. Manasevit, F. M. Erdmann and W. I. Simpson, J. Electrochem. Soc. 118 (1971) 1864.
FILMS ON ORIENTED
Al
FILMS
129
4) W. M. Yim, E. I. Stolko, P. J. Zanzucchi, J. I. Pankove, M. Ettenberg and S. L. Gilbert, J. Appi. Phys. 44 (1973) 292. 5) M. T. Wauk and D. K. Winslow, AppI. Phys. Letters 13 (1968) 286. 6) T. L. Chu, D. W. Ing and A. J. Noreika, Solid-State Electron. 10 (1967) 1023. 7) A. J. Shuskus, T. M. Reeder and E. L. Paradis, AppI. Phys. Letters 24 (1974) 155. 8) Y. Uemura, K. Tanaka and M. Iwata, Thin Solid Films 20 (1974) 11. 9) S. mo, D. Watanabe and S. Obawa, I. Phys. Soc. Japan 19 (1964) 881. 10) A. J. Noreika, M. H. Francombe and S. A. Zeitman, NASA contract report, CR-86395 (1969).