On the Contacts Formed in Ni-Al-Si System Due to Localized Melting by Means of Rapid Thermal Processing
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ON THE CONTACTS FORMED IN Ni-Al-Si SYSTEM DUE TO LOCALIZED MELTING BY MEANS OF RAPID THERMAL PROCESSING A. KATZ AND Y. KOMEM Department of Materials Engineering, of Technology, Haifa 32000, Israel
Technion-Israel
Institute
ABSTRACT Localized rapid melting of an intermediate Al film in the Ni(30nm)/Al(10nm)/n-Si system was successfully carried out by means of rapid thermal processing at temperatures higher than 580°C. This rapid melting resulted in the formation of a unique metal-silicon contact composed of three separated layers and has the following structure: Ni(Alo.,Sio. 5 )/Al 3 Ni/NiSi / n-Si. It was found on the basis of quenching treatments after subsequent rapid thermal processings that an eutectic melting initiated at the Al-Si interface at 580°C, propagated towards the Ni layer and then formed a localized melt zone confined mainly to the region of the intermediate Al layer. The formation of the nickel silicides took place at the silicon surface after Ni diffusion through the melt zone, while the Al compounds were formed during a solidification process of the eutectic liquid. The eutectic melting at 580°C led to the decrease of the sheet resistance of the formed films from 3.2 to 2.6 / and to the increase of the Schottky barrier height of the contact from 0.6 to 0.76 eV. INTRODUCTION The application of the rapid thermal processing (RTP) in carrying out controlled localized melt reaction in the Ni/Al/Si system at temperatures higher than 580'C was first reported by us (1-31. As a result of this melting a unique contact was formed with the following polycrystalline layer structure: Ni(Alo. 5 Sio.s)/Al 3 Ni/Ni-Si•/Si. This contact, obtained already after 2 seconds of RTP, is characterized by an "inversed" structure, in which the nickel and aluminum are changing locations. The nickel is in contact with the silicon in the form of silicides, while the aluminum is in the outer region in the form of Al-compounds as a result of the melt reaction. In this work we bring further results based on quenching treatments after subsequent RTP and electrical measurements which give more evidence for the microstructure evolution due to RTP at temperatures higher than 580'C. EXPERIMENTAL PROCEDURE Substrates of Si n-type with resistivity of 2 -cm, were used for preparing the Ni/Al/Si specimens. The Ni and Al layers were deposited by E-beam gun either directly onto the substrate for the metallurgical studies, or throughout circular openings (22pm in diameter), made by photolithography in a SiO2 film of thermally oxidized Si substrates, for the electrical studies. The RTP were carried out by means of a
Mat. Res. Soc. Symp. Proc. Vol. 100. 01988 Materials Research Society
720
HeatpulseTM annealer at temperatures between 300 to 900°C under . The accuracy of the temperature nitrogen atmosphere measurement was ±2'C"-' for RTP of 2 seconds . In order to study the sequence of reactions during the melting some samples were quenched subsequently after the RTP by removing them rapidly from the heating chamber and immersing them di
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