Interface trap density and doping density of grounded body SO1 (GBSOI) nMOSFET were analysed by charge pumping current and subthreshold swing measurements. Especially, measurements for Dit and NA of the sidewall channel inducing current leakage were managed. If the subthreshold regions of the main and sidewall channels are separated, Dit and NA of the sidewall channel may be extracted by the differential subthreshold slope measurement with varing SO1 body potential. D& and NA of the sidewall channel were about 1.6 X 10" eV'cm-2 and 7 X lox4 ~m -~, respectively. These values are order of magnitude larger and smaller than those of the main channel.
I . IntroductionAlthough various advantages of SO1 devices were suggested, their applications are not widely accepted due to substrate-or bodyfloating effect. To solve this probem, there were many tries to connect the SO1 body to a certain potential [1]-[SI. For grounded-body SO1 (GBSOI) n-MOSFET, the SO1 body is connected to ground potential through polysilicon [5]. GBSOI device fabricated using bonding and etch-back technology elliminated the body-floating effect completely, however, leakage current of the sidewall channel 'wits confirmed to exist [5]. This leakage was originated from low doping density near the LOCOS edge due to out-diffusion of boron atoms from their initial positions during the local oxidation of silicon and followed thermal treatments [6]. Depletion of dopants were only reasoned by simulation or nominal ID-Vi curves, but direct measurement has not been performed yet, possibly due to the facts that ID characteristics of the sidewall channel were not separated from those of the main channel or analyses of related measured results are d3icult. In this paper, i f & -V~ characteristics of the sidewall channel is separated form those of the main channel, interface trap density (Dit) and dopant concentration ( N ' are shown to be extracted using the recently developed differential subthreshold Swing measurement [7], [SI. I I . Structure of GBSOI MOSFET may be referred to the reference [SI. I II . Methods for Nn and Dit measurements A method to extract DIt and NA simultmouly was devised [7], [SI. Referring to this method, S is not a mean vahe in the subthreshold region. Measuring S for each VG and obtaining corresponding & are performed with varing V B~.Assuming that the same current flows at the same ry, for different VSS's, we can plot S and VBs relationship. Fig. 1 shows a cross section of GBSOI n-MOSFET. Fabrication sequence and processing methods for GBSOI nwhere CD is the depletion capacitance and Ca = qDa. In a w e that VBS approaches infinity, CD becomes zero (S becomes S,). From eq. (1) and S, measurement, D;t can be obtained.We can obtain a slope LS from S vs (ly, -VBSl/B-* graph as following [7], [SI.Therefore, NA can be extracted using eq. (2) and Ls measurement.
IV. Measurement and AnalvsesFig. 2 shows the ID-VG characteristics of GBSOI n-MOSFET. Dimension of the device is W L = 5 p / 4 p, and the gate oxide thickness is 230 A. Drain current o...