IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 53, NO. 7, JULY 2006 1583 On the Generation and Recovery of Interface Traps in MOSFETs Subjected to NBTI, FN, and HCI Stress Souvik Mahapatra, Member,IEEE, Dipankar Saha, Dhanoop Varghese, StudentMember,IEEE, and P. Bharath Kumar, StudentMember,IEEE Abstract—A common framework for interface-trap (N IT ) generation involving broken ≡ Si-H and ≡ Si-O bonds is developed for negative bias temperature instability (NBTI), Fowler–Nordheim (FN), and hot-carrier injection (HCI) stress. Holes (from inversion layer for pMOSFET NBTI, from channel due to impact ionization, and from gate poly due to anode–hole injection or valence-band hole tunneling for nMOSFET HCI) break ≡ Si-H bonds, whose time evolution is governed by ei- ther one-dimensional (NBTI or FN) or two-dimensional (HCI) reaction–diffusion models. Hot holes break ≡ Si-O bonds during both FN and HCI stress. Power-law time exponent of N IT during stress and recovery of N IT after stress are governed by relative contribution of broken ≡ Si-H and ≡ Si-O bonds (determined by cold- and hot-hole densities) and have important implications for lifetime prediction under NBTI, FN, and HCI stress conditions. Index Terms—Anode–hole injection (AHI), charge pumping (CP), Fowler–Nordheim (FN), hot-carrier injection (HCI), inter- face traps (N IT ), negative bias temperature instability (NBTI), reaction–diffusion (R–D) model, stress-induced leakage current (SILC), valence-band hole tunneling (VBHT). I. INTRODUCTION I NTERFACE-TRAP (N IT ) generation is an important reliability concern in MOSFETs subjected to negative bias temperature instability (NBTI), Fowler–Nordheim (FN), and hot-carrier injection (HCI) stress [1]–[12]. It is generally be- lieved that N IT generation is due to breaking of ≡ Si-H bonds at the Si-SiO 2 interface and the resultant production of ≡ Si-(N IT ), which show up as P b centers in electron spin resonance (ESR) studies [13]. The time evolution of N IT shows power-law dependence, with larger value of exponent n for FN and HCI compared with NBTI stress. On the other hand, unlike HCI and FN stress, significant N IT recovery has been observed after NBTI stress [14], [15]. The mechanism of N IT generation during stress and any recovery of N IT after stress must be prop- erly understood and modeled for accurate prediction of device lifetime under actual operating conditions. It is now believed that inversion-layer (cold) holes are re- sponsible for the breaking of ≡ Si-H bonds during NBTI stress in pMOSFETs [4]. Classical one-dimensional (1-D) reaction– diffusion (R–D) model [16] can successfully explain N IT gen- eration and recovery characteristics for NBTI stress [17], [18]. R–D model suggests that N IT generation is due to the break- Manuscript received October 20, 2005; revised February 21, 2006. The review of this paper was arranged by Editor G. Groeseneken. The authors are with the Department of Electrical Engineering, Indian Institute of Technology, Bombay, Mumbai 400076, India (e-mail: souvik@ ee.iitb.ac.in). Digital Object Identifier 10.1109/TED.2006.876041 ing of interfacial ≡ Si-H bonds and subsequent diffusion of released H species into the oxide bulk. N IT recovery is due to back diffusion of H species toward the Si-SiO 2 interface and repassivation of ≡ Si-. R–D model can explain the (relatively) lower n of N IT generation during NBTI stress as due to release and diffusion of either or both neutral H O and H 2 species [18]. Note that the crucial difference between NBTI and HCI or FN is the presence of hot electrons (HE) and hot holes (HH) for the latter stress conditions [4], [7], [10]. Significant efforts were made in the past to understand whether only electrons, or only holes, or both electrons and holes are responsible for breaking of ≡ Si-H bonds during HCI and FN stress [5]–[10], [12], [19], [20]. The higher n of N IT generation during uniform FN stress can be explained within the 1-D R–D framework by assuming possible release and subsequent drift of H + species [18]. A two-dimensional (2-D) extension of the classical R–D model, which considers localized (near drain junction) breaking of interfacial ≡ Si-H bonds and subsequent 2-D diffusion of released H O species, has been proposed to model HCI [21]. 1 The model suggests that the spread of HCI degraded region (due to broken ≡ Si-H bonds) determines n during stress and recovery after stress. However, the above models need experi- mental validation, and much work is needed to develop a unified model for N IT generation under all stress conditions. Furthermore, whereas NBTI stress (negligible hot carriers) produce only N IT [4], HCI and FN stress (hot carriers present) also produce bulk traps (N OT ) [7], [10]–[12], [23]–[26]. N OT generation is believed to be due to broken ≡ Si-O bonds at the oxide bulk [24]–[26]. There has been significant debate on whether HH or H + diffusion (following breaking of ≡ Si-H bonds) break ≡ Si-O bonds during FN and HCI stress [24], [25], [27], [28]. Broken ≡ Si-O bonds at oxide bulk give rise to stress-induced leakage current (SILC) [7], [12], [24]–[26], [29], [30], 2 whereas those at (or near) Si-SiO 2 interface can contribute to overall measured N IT [32]. However, unlike ≡ Si-H bonds, broken ≡ Si-O bonds are not known to recover at room temperature after the stress is removed. It is important to understand and quantify the nature and composition of N IT buildup due to broken ≡ Si-H and ≡ Si-O bonds [33], [34] (and check for the release of H + , if any), as these scenarios lead to substantially different lifetime projections for NBTI, FN, and HCI stress. We know of no effort so far that has 1 Alternatively, the stretched-exponent model [22] also explains power-law dependence of N IT generation. 2 An alternative viewpoint [31] for the origin of SILC is the bridging of H + into an existing oxygen vacancy. 0018-9383/$20.00 © 2006 IEEE