Comparison of Electrical Properties of Silicon-on-Insulator Structures Fabricated with Use of Hydrogen Slicing and BESOI

Abstract

The top silicon layers and the bonded Si/SiO 2 interfaces in silicon-on-insulator ͑SOI͒ structures fabricated by ͑i͒ wafer bonding and hydrogen slicing, and (ii) by wafer bonding and chemical mechanical thinning ͑back-etch SOI, BESOI͒ were investigated and compared by charge deep-level transient spectroscopy. The hydrogen slicing was provided by hydrogen implantation into one of the bonded wafers and led to the high hydrogen concentration during SOI fabrication. Hydrogen presented in SOI during the fabrication process partially neutralizes the traps at the Si/thermal SiO 2 interface, and completely neutralizes shallow acceptors and contamination with deep levels in the top silicon layer.The conventional Si/SiO 2 interface prepared by thermal oxidation of silicon has a transition SiO x layer 2 nm thick. 1 It is, namely, the transition SiO x layer that determines the spectrum of interface traps. 2 Recently, a new method to create the Si/SiO 2 interface was developed. It is bonding of a silicon wafer with an oxidized one. 3 Bonding technology is now a promising way to create new structures for microelectronics. 3,4 Particularly, different silicon -on-insulator ͑SOI͒ structures are fabricated with use of bonding technology ͓for example, Smart-Cut technology 5 and back-etch SOI ͑BESOI 6 ͔͒. Recently, we showed that the spectrum of traps at a bonded Si/SiO 2 interface substantially differs from that at an Si/SiO 2 interface prepared by thermal oxidation. 7,8 This difference was attributed to the absence of the transition SiO x layer at the bonded interface or/and intense neutralization of traps by hydrogen due to utilization of hydrogen slicing technology ͑hydrogen implantation in one of the bonded wafers͒. The concentration of hydrogen present in SOI during fabrication can be lowered if one uses BESOI technology. 6 In this case we did not use hydrogen implantation, and a thinning of the top silicon layer was performed with polishing and etching.The aim of this study was to compare interface traps and centers with deep and shallow levels in the top silicon layers of two different SOI types: ͑i͒ structures prepared by hydrogen slicing, 7,8 and (ii) BESOI structure. 6 The final heat-treatment of both SOI was annealing at high temperature ͑ϳ1100°C͒. The result was that hydrogen concentration was decreased dramatically and became lower than the sensitivity of secondary-ion mass spectroscopy ͑SIMS͒. 9 Introduction of shallow acceptors, centers with deep levels, and higher density of the interface traps was observed in BESOI structures. A high concentration of hydrogen in the first type of SOI leads to neutralization of all contamination and a decrease in interface density. Experimental and ResultsTo fabricate the SOI structures, Czochralski ͑Si-CZ͒ and float zone ͑Si-FZ͒ grown silicon wafers with n-type conductivity were used. SOI structures fabricated by hydrogen slicing were marked as SOI-A. The BESOI structures were marked as SOI-B. The type of initial silicon ͑FZ or CZ͒ was added to the SOI designation. Both SOI-A and S...