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Evaporation source for 57Fe thin film deposition
NUCLEAR INSTRUMENTS AND METHODS 116 (1974) 59 1- 59 2:
© NORTH-HOLLAND PUBLISHING CO .
EVAPORATION SOURCE FOR "Fe THIN FILM DEPOSITION W. KEUNE Fachbereich Angewandte Physik, Universität des Saarlandes, 66 Saarbrücken, Gern-y Received 14 January 1914 Asimple electron-beam heated furnace is described hich allows the controlled evaporation of small quantities of isotopes, particularly of 5717e, forthin film deposition.
For vapor deposition of thin films special furnaces have to be used if expensive isotopes are to be evaporated at lowcosts. In this case the evaporation source should allow the reproducible evaporation of small quantities (in the mg region) of the isotope without large losses due to divergence of the vapor beam or
evaporation source with constant deposition rate for nearly constant electron-beam current during deposition. With controlled deposition rates of 0.5®I Als
diffusion of the isotope into the crucible. During the course of "Fe thin film investigations by Mdssbauer spectroscopy a convenient electron-beam heated source for "Feevaporation hasbeen developed which has the required properties (fig. 1). The furnace
consists of a 17 mm x 13 mm diam . tantalum cylinder fixed vertically on a small central Ta rod and held on ground potential. Metallic "Fe is evaporated from a cylindrical A1203 crucible of 15 mm x 10 mm diam . which fits into the Ta cell. The electron source is a concentric ring-shaped 0.2 mm diam . tungsten wire, about 5 mm apart from the Ta cell and held by two small electrically insulated Ta rods which servo as electrodes for the ac resistance heated Wfilament . The furnace is surrounded by a 40 mm diam. insulated Ta tube and atop cover whichhas a 5 mm collimating hole for the vapor beam. "Fe deposited on this shield can easily be regained by chemical treatment . An accelerating do voltage of -4 kV is applied to the Wfilament and the Ta shield . The furnace temperature is regulated by changing the current :n the tungsten filament. A Varian 4kV/500 mA power supply which normally serves as supply for a commercial 2 kW electron gun has been used . It is advisable to watercool the outer wall of the vacuum system in the vicinity of the furnace support. A vacuum of better than 10"s torr is necessary for furnace operation.
The insert in fig. I shows the iron deposition'rateas function of do electron-beam current as measured with aquartz crystal thicknessandrate monitor 30 cm above the Ta cell, with a 100 mg "Fe pellet in thealuminum crucible. This quantity was sufficient to produce an 1000 !k thick film on a substrate 30 cm above the
0 z 10
10
60
SO
r00
mA
Fig. 1. Cross section through furnace . (1) s7 Fe pellet, (2) AI_03 crucible, (3) Ta cell, (4) W filament, (5) Ta rods, (6) Ta shield, {7) Ta collimator, (8) A1203 insulation, (9) stainless-steel support; insert : iron deposition rate as a function of electron-beam current for a source-to-substrate distance of 30 cm .
591
592
W. KELNE
and vacua < 10 -' torr during evaporation iron films with nominal thickness of one to several monolayers . could be prepared with goal reproducibilityby chosing; the appropriate (vapor beam) shutter opening-time, as has been tested by measuringthe Mdssbauer spectra. of several films prepared under the same conditions'). Thelarge temperature sensitivity of thefurnace with respect to small electron-beam current changes is an advantage which is useful forautomatically controlling
deposition rates . Automatic, control has been achieved by using commercial quartz crystal deposition rate monitors and rate controllers . This work was supported by the Deutsche Forschungsgemeinschaft . Reference 1)
W. Keune, D. L. Williamson and J. Lauer ; in preparation .
© NORTH-HOLLAND PUBLISHING CO .
EVAPORATION SOURCE FOR "Fe THIN FILM DEPOSITION W. KEUNE Fachbereich Angewandte Physik, Universität des Saarlandes, 66 Saarbrücken, Gern-y Received 14 January 1914 Asimple electron-beam heated furnace is described hich allows the controlled evaporation of small quantities of isotopes, particularly of 5717e, forthin film deposition.
For vapor deposition of thin films special furnaces have to be used if expensive isotopes are to be evaporated at lowcosts. In this case the evaporation source should allow the reproducible evaporation of small quantities (in the mg region) of the isotope without large losses due to divergence of the vapor beam or
evaporation source with constant deposition rate for nearly constant electron-beam current during deposition. With controlled deposition rates of 0.5®I Als
diffusion of the isotope into the crucible. During the course of "Fe thin film investigations by Mdssbauer spectroscopy a convenient electron-beam heated source for "Feevaporation hasbeen developed which has the required properties (fig. 1). The furnace
consists of a 17 mm x 13 mm diam . tantalum cylinder fixed vertically on a small central Ta rod and held on ground potential. Metallic "Fe is evaporated from a cylindrical A1203 crucible of 15 mm x 10 mm diam . which fits into the Ta cell. The electron source is a concentric ring-shaped 0.2 mm diam . tungsten wire, about 5 mm apart from the Ta cell and held by two small electrically insulated Ta rods which servo as electrodes for the ac resistance heated Wfilament . The furnace is surrounded by a 40 mm diam. insulated Ta tube and atop cover whichhas a 5 mm collimating hole for the vapor beam. "Fe deposited on this shield can easily be regained by chemical treatment . An accelerating do voltage of -4 kV is applied to the Wfilament and the Ta shield . The furnace temperature is regulated by changing the current :n the tungsten filament. A Varian 4kV/500 mA power supply which normally serves as supply for a commercial 2 kW electron gun has been used . It is advisable to watercool the outer wall of the vacuum system in the vicinity of the furnace support. A vacuum of better than 10"s torr is necessary for furnace operation.
The insert in fig. I shows the iron deposition'rateas function of do electron-beam current as measured with aquartz crystal thicknessandrate monitor 30 cm above the Ta cell, with a 100 mg "Fe pellet in thealuminum crucible. This quantity was sufficient to produce an 1000 !k thick film on a substrate 30 cm above the
0 z 10
10
60
SO
r00
mA
Fig. 1. Cross section through furnace . (1) s7 Fe pellet, (2) AI_03 crucible, (3) Ta cell, (4) W filament, (5) Ta rods, (6) Ta shield, {7) Ta collimator, (8) A1203 insulation, (9) stainless-steel support; insert : iron deposition rate as a function of electron-beam current for a source-to-substrate distance of 30 cm .
591
592
W. KELNE
and vacua < 10 -' torr during evaporation iron films with nominal thickness of one to several monolayers . could be prepared with goal reproducibilityby chosing; the appropriate (vapor beam) shutter opening-time, as has been tested by measuringthe Mdssbauer spectra. of several films prepared under the same conditions'). Thelarge temperature sensitivity of thefurnace with respect to small electron-beam current changes is an advantage which is useful forautomatically controlling
deposition rates . Automatic, control has been achieved by using commercial quartz crystal deposition rate monitors and rate controllers . This work was supported by the Deutsche Forschungsgemeinschaft . Reference 1)
W. Keune, D. L. Williamson and J. Lauer ; in preparation .