Hydrogen Evolution and Interface Reaction of Cu Thin Film on a-Si:H
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HYDROGEN EVOLUTION AND INTERFACE REACTION OF Cu THIN FILM ON a-Si:H L. Bemardino*, Carlos Achete*, F. L. Freire Jr** *Programa de Metalurgia e Materiais, COPPE, Universidade Federal do Rio de Janeiro Caixa Postal 68505, Rio de Janeiro, Brasil,. * *PUC-Rio, Brasil. ABSTRACT The Cu/a-Si:H system has been studied by gas effusion method, elastic recoil detection analysis (ERDA), in situ sheet resistance measurements and scanning electron microscopy. Cu layers of 15 and 90 nm in thickness were deposited by e-beam evaporation onto 1 Am a-Si:H films produced by RF glow discharge on Si(100) substrates at 250 OC. The most important effects are observed in the effusion measurements, when pure a-Si:H samples and Cu/a-Si:H samples are compared. For the Cu/a-Si:H samples, one at very low three well-defined peaks are observed, temperature (T=200 °C), another at 380 °C and a high temperature peak at about. However, pure a-Si:H shows only one effusion maxima at 550 OC. The low temperature effusion peaks are directly correlated with steps increases in the sheet resistance measurements. The first one (T=200 oC) is due to the beginning of silicide formation. The H2 evolution at 380 °C is correlated to phase transition in the a-Si:H film. The hydrogen depth profiles obtained by ERDA and SEM observations are also used to describe the aspects of the Cu/a-Si:H interaction. 1. INTRODUCTION In the past few years interest has increased in studying the properties of copper silicon interface. Basically there are two different motivations for this interest. The first one is the demand of silicon technology for high performance devices [1] and the second is related with the basic studies on amorphous silicon crystallization induced by metal or silicide (2,3]. Crystallization of amorphous silicon (a-Si) when 0in contact with etal like gold, for example, occurs at about 130 C, which is an abnormally low temperature compared with a-Si crystallization temperature of 600-700 0 C (4]. In this concern much work has been published using metals like Au, Ag or Al as metalcontact. It is noteworthy to note that Au, Ag and Al do not form silicide compound with silicon. On the other hand there exist several Cu-Si compounds according to the phase diagram of Cu-Si. Many aspects of the reaction between Cu and Si have been recently investigated. It is relatively well established that the first phase to form is for Cu deposited on Si single crystal Cu3 Si at a temperature of about 200 0 C [5-7). Higher temperature annealing results in Si segregation to the surface (8]. In this situ sheet resistance work we report a study using in elastic recoil detection measurements, gas effusion method, analysis (ERDA), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). The structure of the surface, the hydrogen evolution process, reaction and interdiffusion at the interface of thin Cu films deposited onto a-Si:H have been investigated.
Mat. Res. Soc. Symp. Proc. Vol. 311. ©1993 Materials Research Society
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EXPERIMENTAL
Films of a-Si:H of about
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