Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO 2 Layers
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Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers Sabina Spiga1, Sandro Ferrari1, Marco Fanciulli1, Bernd Schmidt2, Karl-Heinz Heinig2, Rainer Grötzschel2, Arndt Mücklich2, Giuseppe Pavia3 1 Laboratorio MDM-INFM, via C. Olivetti 2, I-20041 Agrate Brianza, Italy 2 Research Center Rossendorf, Institute of Ion Beam Physics, P.O. Box 510 119, D-01314 Dresden, Germany 3 STMicroelectronics, via C. Olivetti 2, I-20041 Agrate Brianza, Italy
ABSTRACT In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (fluences of 0.1-1 x 1016 cm-2) Sn implantation in 85 nm thick SiO2, followed by annealing (800-1000°C for 30-300 sec under Ar or N2 dry ambient) in a rapid thermal processing (RTP) system, leads to the formation of two cluster bands, near the middle of the SiO2 layer and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed between the two bands. Cluster-size distribution and cluster-crystallinity are related to implantation fluence and annealing time. Low energy (10-12 keV) Sb and Sn implantation (fluences 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.
INTRODUCTION Metallic and semiconducting nanocrystals embedded in dielectric materials are attracting considerable interest due to their novel electrical and optical properties, such as single electron effects [1,2] and luminescence characteristics [3,4]. Memory devices [5] using nanocrystals as charge storage elements and single electron transistors based on metallic nanoparticles [6] have been demonstrated. The comprehension and control of the nanocrystal structural and electrical properties are fundamental steps towards technological applications. Ion beam synthesis of nanocrystals in SiO2 represents a promising technique compatible with present silicon technology and allows the control of size, density and depth distribution of nanocrystals by varying the implantation and annealing parameters. In addition, under appropriate conditions, a rather narrow cluster-size distribution can be obtained. The ion beam synthesis of clusters is based on the supersaturation of the matrix after ion implantation, precipitation of the impurity atoms and growth of the resulting clusters by Ostwald ripening during annealing. The formation of metallic clusters in SiO2 has often been studied in thick oxides (500 nm) [3]. In contrast, the cluster formation mechanism in oxides thinner than 100 nm, more suitable for the application of the clusters as charge storage elements in memory devices, is less investigated. Recently, the ion beam synthesis of Sn and Sb nanoclusters in thin SiO2 layers has been demonstrated and single electron effects have been observed at low temperatures [7,8]. However, several problems, mainly related to the control of the cluster-size distribution and cluster position in the oxide layer, remain to be solved. Moreover, small clusters are very reactive, due to the high
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