Characterization of amorphous metal films

Characterization of amorphous metal films

Thin Solid Films, 58 ( 1979) 325-326 0 Elsevier Sequoia S.A., Lausanne-Printed CHARACTERIZATION 325 in the Netherlands OF AMORPHOUS METAL FILMS* ...

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Thin Solid Films, 58 ( 1979) 325-326 0 Elsevier Sequoia S.A., Lausanne-Printed

CHARACTERIZATION

325

in the Netherlands

OF AMORPHOUS

METAL FILMS*

G. MENZEL Forschungslaborarorien der Siemens AG, 8000 Miinchen 83, Otto-Hahn-Ring 6 (F.R.G.)

In order to obtain non-crystalline phases thin metal films of thickness 50-80 nm were prepared by vapour quenching in ultrahigh vacuum onto liquid-nitrogencooled substrates (deposition temperature, - 160 “C). The electrical resistance of the films was measured in situ as a function of substrate temperature. The structure and the microstructure of all the films were investigated by electron microscopy. The purity of the films was checked by secondary ion mass spectrometry and Auger analysis. Non-crystalline phases were found in the alloyed and gas-doped metal films investigated (Table I). The non-crystalline films showed the same electron diffraction patterns as bulk metglasses, e.g. Metglas [email protected]“; four diffuse lines of decreasing intensity over a range of interplanar spacings from 0.5 to 0.08 nm were observed. The temperature coefficient of resistivity (TCR) u of the metglas films varied between positive and negative values (Table I). In spite of the variation in the TCR the electron diffraction patterns of the films did not change. TABLE I COMPOSITION

System

Taco Ta-Ni w-cu W-N Ta-N Ta-Ar

AND ELECTRICAL

PROPERTIES

OF THE INVESTIGATED

METGLAS

FILMS

Composition 8, partial pressure b

P20

a’

(NJ cm)

@pm K-‘1

10-90x co 20-55% Ni 40-70x cu 2~10-“dp~><3xlO-~ 8 x 10-e Q pNI < 3.5 x 10-s 5 x 10-4 < pAr G 3 x 10-a

120-250 120-200 180-190 260-350 320-380 230

-1OOto -250 to -5oto -180to -200to -300

’ Concentration in mole fraction. b Partial pressure (N me2) of nitrogen or argon during ’ Temperature range for a, - 160 to + 20 “C.

-

+250 +500 +120 -220 -300

film deposition.

Using a high resolution electron microscope with superconducting lenses it was shown that the metglas films consist mainly of coherent scattering regions with a diameter of about 2.5 nm. In Ta-Ni films with 20-30 mol.% nickel and in Ta-N thin films (4 x 10e5 N *Abstract of a paper presented at the Fourth International Ct. Britain, September 11-15, 1978: Paper 4Bll.

Congress

on Thin Films, Loughborough,

326

AUTHORS’

ABSTRACTS

me2 G pNI < 3 x 10m3 N me2) another non-crystalline phase was found which we have termed solid-amorphous. The electron diffraction patterns of solid-amorphous films showed only two intensity maxima over the same range of interplanar spacings as for the metglas films. However, in contrast with the metglas films the first electron diffraction maximum lay within a broad halo. No preferred atomic distance appeared in the halo. Thus the matrix of the solid-amorphous phase consists mainly of randomly distributed metal atoms. This was also proved from high resolution electron micrographs by optical light evaluation. In contrast with the metglas films the solid-amorphous films contained only some short-range-ordered regions which had a maximum’diameter of 1 nm and which lay isolated in the matrix. Thus these regions cannot affect the electrical properties of the films. The negative TCR which we found for the solid-amorphous Ta-Ni films (a = - 100 to -300 ppm K- ‘, - 180-220 uR cm, depending on composition) and for the Ta-N films go=--900 ppm K-r, p 20 = 950 &I cm) could therefore be a criterion for’ the existence of a solid-amorphous phase. The values for the resistivity show also that even in the solid-amorphous state the metallic conductivity of the thin films is maintained. 1

G. J. Sellers, European EMC Symp., Montreux, Switzerland, June 28-30,1977.