Low-Frequency Noise in Triple-Gate n-Channel Bulk FinFETs E. Simoen, M. Aoulaiche, N. Collaert and C. Claeys* Imec Kapeldreef 75, B-3001 Leuven, Belgium Eddy.Simoen@imec.be *also at ESAT-INSYS Department, Katholieke Universiteit Leuven, 3001 Leuven, Belgium Abstract—The noise in n-channel bulk MuGFETs with 2.5 nm SiON gate dielectric is reported. It is shown that besides number fluctuations-related 1/f noise often Generation-Recombination (GR) noise is observed. From a detailed study of the fin length and width dependence it is concluded that the GR noise preferentially occurs for short and wide transistors. The latter observation points to traps in the gate oxide edges as a possible source of the excess noise. Keywords-bulk MuGFETs; 1/f noise; GR noise I. INTRODUCTION Multiple-gate transistors (MuGFETs) hold great promise for integration at the 22-nm CMOS node or below. This is related to the good electrostatic integrity which controls the Short-Channel Effects (SCEs) [1], especially for narrow fin structures. While FinFETs were originally developed on Silicon-on-Insulator (SOI) substrates, the concept has also been adapted to bulk silicon wafers [2]. Figure 1 gives a cross- section and plan view of a triple-gate bulk FinFET fabricated at imec, whereby the fin is defined by Shallow Trench Isolation (STI) regions. Over the years, the low-frequency (LF) noise has been studied in detail for SOI FinFETs (for a recent overview see, e.g., Ref. [3]), but so far, only little is known about the noise behavior of their bulk counterparts. A recent study on p- channel bulk MuGFETs demonstrated that the observed 1/f noise tends to be governed by so-called mobility fluctuations (Δµ model) rather than by trapping of charge carriers in the gate dielectric [4]. It is the aim here to report on the LF noise of bulk nMuGFETs and discuss the underlying mechanisms. Fig. 1. Cross-sectional (a), top view (b) and schematic cross section (c) of a bulk triple-gate FinFET. II. EXPERIMENTAL The studied devices have been processed on 300 mm Cz Si wafers. Both p-well and ground-plane implantations have been performed prior to the gate stack processing. The gate stack consists of 2.5 nm SiON and 5 nm TiN, capped with a polysilicon gate. The devices have 5 parallel fins with height H~60 nm and a fin width W fin of 20, 30 or 250 nm. The effective width is then 5×(2H+W fin ). N-channel transistors with mask lengths ranging from 70 nm to 1 µm have been characterized. Extension, halo and HDD implantations were activated by a 1050 o C spike anneal in He. These transistors have been developed for capacitor-less 1-transistor bulk FinFET Random Access Memory cell applications [5]. The noise measurements have been executed at wafer level using the BTA hardware controlled by the NoisePro software of ProPlusSolutions. Measurements were in linear operation, applying a drain bias V DS =50 mV and varying the gate bias V GS from weak to strong inversion in steps of 50 mV. The input characteristics in the ohmic regime for an array of W fin =20 nm bulk nMuGFETs is represented in Fig. 2a, showing good subthreshold behavior of the drain current I D . III. RESULTS The normalized current noise spectral density S I /I D 2 at a frequency f=25 Hz and corresponding with the devices of Fig. 2a is represented in Fig. 2b versus I D . The usual plateau in weak inversion, followed by a roll-off with drain current above threshold, is observed, pointing towards a number- fluctuations origin of the 1/f-like noise. This is supported by the comparison with (g m /I D ) 2 in Fig. 3 for the L=1 µm nMuGFET, with g m the transconductance, showing that both characteristics run parallel over most of the drain current range investigated. The trap density derived from the input-referred flat-band voltage noise spectral density (S VG in weak inversion) equals N T =1.65x10 17 cm -3 eV -1 , which is a good value for nitrided-oxide based gate oxide transistors [6,7]. One issue in Fig. 2b is the non-scaling of the normalized noise with the device length, suggesting significant device-to-device variations. 2011 21st International Conference on Noise and Fluctuations 978-1-4577-0192-4/11/$26.00 ©2011 IEEE 127