Electrical And Emission Properties Of Slow Doped Copper Films, Prepared By Vacuum Deposition
ELECTRICAL AND EMISSION PROPERTIES OF SLOW DOPED COPPER FILMS, PREPARED BY VACUUM DEPOSITION
A.I. Kostrjitskiy
Odessa State Academy of Food Industry,
Kanatnaya st. 112, 65039 Odessa, Ukraine, e-mail: profAIK@ipss.net
The electrical and emission properties of slow doped copper alloy films, namely Cu-Cr-Ti and Cu-Cr-Ni, containing about 10 wt.% of doping elements, produced by finite charge evaporation in vacuum, have been studied. These films are widely used in radio engineering and electronics. The choice of doping elements is based on physics-chemical properties of alloy systems, analysis of alloy constitutional diagrams and composition-properties diagram. It’s well known fact, that doping elements Ni, Cr and Ti are used to impart thermostability of high conductive copper based films with low secondary electron emission. These metals have low electron affinity, so the elevated concentration of these elements in final layers of multicomponent films must assure low secondary emission and increase film stability to heat treatment.
Bulk and surface resistivities of multicomponent films were determined with 4-zond compensation technique. Secondary electron emission coefficient were measured with a single impulse method at normal incidence of primary electron. Structure and phase distribution were studied with X-ray spectroscopy, electron microscopy and electron diffraction analysis.
Using the method of mathematical planning of experiment with doping element concentration variations at two levels with zero point, we received the next regression equations for characteristic of effect on multicomponent films resistivity:
(Cu-Cr-Ti) R = 8,02 + 2,45XCr - 1,2Xti +0,18XCrXTi (1)
(Cu-Cr-Ni) R = 6,80 + 0,92XCr + 4,71XNi - 1,86XCrXNi (2)
Analysis of there equations and experimental results showed, that films of following compositions: Cu – (2,0…3,5)Cr – (0,5…4,5)Ti and Cu – (3,5…4,0)Cr – (4,0…6,0)Ni have minimum resistivities. It was shown, that short-term annealing stabilizes the film resistivity and further prolonged annealing doesn’t effect on it.
Secondary electron emission coefficient d characterizes emission properties of materials. The main results of secondary electron emission coefficient values of Cu-Cr-Ti and Cu-Cr-Ni before and after annealing (640…670 K, 3 h) are given in table.
Composition
Values of d at Ep, eV:
before annealing
200
300
400
500
600
2000
Cu-3,5Cr-1,5Ti
2,88
3,25
3,43
3,17
3,13
2,52
Cu-4,3Cr-2,4Ti
2,94
3,30
3,17
2,88
2,72
2,43
Cu-7,8Cr-0,8Ti
1,66
2,31
2,74
2,62
2,58
2,35
Cu-2,5Cr-4,3Ni
3,24
3,38
3,57
3,41
3,25
2,67
Cu-5,5Cr-7,8Ni
2,88
3,50
2,85
2,75
2,73
2,40
after annealing
Cu-3,5Cr-1,5Ti
2,25
2,25
2,65
2,57
2,54
2,40
Cu-4,3Cr-2,4Ti
2,68
2,71
2,99
2,85
2,65
2,38
Cu-7,8Cr-0,8Ti
2,11
2,29
2,40
2,40
2,26
2,12
Cu-2,5Cr-4,3Ni
6,75
7,84
9,35
11,02
10,87
8,48
Cu-5,5Cr-7,8Ni
9,34
9,42
10,25
11,75
11,05
9,54
Apparently, maximum values of d (3,2…3,5) of annealed films correspond to primary electron energies Ep = 300…400 eV. The presence of maximum d at this energy interval is in a good agreement with theoretically predicted one.
We have also found, that chromium concentration doesn’t influence the secondary electron emission properties of multicomponent films (Cu-Cr-Ti and Cu-Cr-Ni), because chromium concentrates in initial layers of condensate and is respon-sible for high adhesion strength of these films to glass substrates. Moreover, emission properties of unannealed Cu-Cr-Ti and Cu-Cr-Ni films are analogous and after annealing they are essentially different.
Present results may be successfully used, when stable high conductive layers with low secondary electron emission are developing.
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