Study of Electrical Properties of Defects in SOI Films by Wafer Bonding
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STUDY OF ELECTRICAL PROPERTIES OF DEFECTS IN SOI FILMS BY WAFER BONDING Akira USAMI, Taichi NATORI, TOKUDA.., and Takao WADA
Akira ITO, Shun-ichiro ISHIGAMI.,
Nagoya Institute of Technology, Nagoya 466, Japan *Mitsubishi Material Co.,Ltd., Omiya 330, Japan .. Aichi Institute of Technology, Yakusa, Toyota 470-03,
Yutaka
Japan.
ABSTRACT Silicon-on-insulator films fabricated by the wafer bonding technique were studied with capacitance-voltage (C-v) and deep-level transient spectroscopy (DLTS) measurements. For our experiments, two kinds of SOI wafers were prepared. Many voids were present in one sample (void sample), but few voids were in the other sample (no void sample). Before annealing, two DLTS peaks (Ec-0.48 eV and Ec-0.38 eV) were observed in the SOI layer of the void sample. For the no void sample, different two DLTS peaks (Ec-0.16 eV and Ec-O.12 eV) were observed. The trap with an activation energy of 0.48 eV was annealed out after 450 'C annealing for 24 h. On the other hand, other traps were annealed out after 450 'C annealing for several hours. During annealing at 450 'C, thermal donors (TDs) were formed simultaneously. In usual CZ silicon, a DLTS peak of TD was observed around 60 K. In the no void sample, however, a TD peak was observed at a temperature lower than 30 K. This TD was annihilated by rapid thermal annealing. This suggests that the TD with a shallower level was formed in the no void sample after annealing at 450 'C. 1. INTRODUCTION The structure of silicon-on-insulator (SOI) has been needed for highdensity, high-voltage or high-speed devices since the integrated circuit was developed. To form this structure, zone-melt recrystallization (ZMR) [11 and separation by implanted oxygen (SIMOX) [21 have been investigated for several years. Both of these methods, however, have a definite disadvantage in terms of crystal perfection. Recently, SOI made by wafer bonding has attracted much attention to its high crystallinity. In this technique, good quality bulk silicon can be utilized as an SOl active layer. One of the problems of this technique is formation of voids ,i.e.. the lack of local bonding after the bonding process. Because the void leads to delamination and subsequent loss of the device film in the unbonded region, their reduction is the most important subject for the wafer bonding technology. A comprehensive review on SOI with wafer bonding technique has been reported [3]. Oxygen is one of the impurities investigated most extensively in silicon materials. It is well-known that the Czochralski-grown (CZ) silicon is supersaturated with oxygen. Because SOI by wafer bonding is also fabricated by CZ silicon, the behavior of oxygen and of related defects in SOI layers cannot be ignored. Oxygen forms so-called thermal donor (TD) during heat treatments around 450 'C [4,5]. The TD affects the electrical properties of devices, e.g., resistivity and lifetime. Since the TDs grow into the oxygen precipitbtes by successive heat treatments and the precipitates strongly affect intrinsic gettering, the b
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