Stresses in UHV Planar Magnetron Sputtered Films
- PDF / 407,718 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 35 Downloads / 216 Views
STRESSES IN UHV PLANAR MAGNETRON SPUTTERED FILMS
C. HUDSON AND R. E. SOMEKH
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street,Cambridge CB2 3QZ, United Kingdom
ABSTRACT A method has been developed to measure the stress in films which have been sputtered using a planar magnetron in a small-scale UI-IV chamber. The stress has been measured for different materials as a function of the sputtering gas pressure P and the substrate-target distance d. It is found that the stress in films of the same material deposited at different values of d is dependent only on the pressure-distance product (Pd), except at short (less than about 30mm) distances. The value of Pd required to produce a stress-free film is found to increase with the more extreme ratios between the atomic masses of the film material and the sputtering gas for the case of metals. However, the required Pd product is higher for the case of amorphous semiconductors. The stress in alloy films is also investigated. Introduction Sputtering is being used for depositing films of an increasing number of materials, and the stress in the film is important for several reasons. A film under tension will tend to crack, and a compressive film can form whiskers. Both of these stress states will cause the film to debond from the substrate if the strain energy in the film is greater than the interfacial energy between it and the substrate. In the case of superconducting devices, stresses in the film will cause it to deform after it is fabricated and can have a considerable effect on the device performance [1]. Magnetic films under stress will exhibit magnetostriction and stress-induced anisotropy which may have a considerable effect on their performance, which may or may not be desirable. Whatever the actual stress in a film, it is clear that it needs to be controlled in a systematic way. An early literature exists in which the general problem of stress in films was described by Thornton and Hoffman [2]. Most of this work was performed in sputter deposition systems in which the target-substrate distance was fixed, thus the sputtering pressure was the key parameter used to describe the variation of stress in the film. These early studies were also aimed at understanding the general growth morphology of films besides the stress state, and it has been reported [3] that various structure zones are possible by varying the sputtering gas pressure, and a transition between zone T and zone I (using the terminology in ref. 3) corresponds to a change from a dense, compressive film to a tensile film with a columnar structure, producing a transition pressure as described in [4]. The pressure of the sputtering gas was said to affect the degree to which the energy of the sputtered atoms and reflected neutrals is reduced, and the energy with which the atoms bombard the substrate therefore decreases with increasing pressure. Hence the stress in a sputtered film appears to be related to the energy of substrate bombardment. Various models were developed
Data Loading...
