Microelectronic Engineering 59 (2001) 271–275 www.elsevier.com / locate / mee Extraction of gate oxide thickness from C –V measurements * Frans P. Widdershoven Philips Research Leuven, Kapeldreef 75, B-3001 Leuven, Belgium Abstract A new empirical method is described to extract the oxide thickness from C –V curves of MOS capacitors in accumulation. An analytical expression is derived for the oxide capacitance. The method is applied to MOS capacitors with metal or poly-Si gates, and with varying oxide thickness.  2001 Elsevier Science B.V. All rights reserved. Keywords: MOS capacitor; Oxide capacitance; Oxide thickness; Capacitance–voltage measurement; Accumulation layer; Poly depletion; Gate depletion; Metal gate; High-K dielectric; Process control monitor 1. Introduction Several methods have been proposed to extract the oxide capacitance from C –V curves [1–7,9]. Most are based on semiclassical (SC) models of the accumulation layer charge [1,2,4,5,7,9], and therefore are not applicable to thin oxides where quantum mechanical (QM) effects are important. The flat-band method of [3] is claimed to be insensitive to QM effects. However, it is easily disturbed by interface states and impurity deionisation [8]. In [6] a method based on an empirical QM model of the accumulation layer charge is proposed. Although quite accurate, it is rather complicated because it uses numerical integration within an iteration loop to extract the oxide thickness. Here an alternative empirical QM model is presented for the accumulation layer charge. An analytical expression is derived for the oxide capacitance C . It is applied to measured C –V curves. ox 2. New method The asymptotic SC expression for the accumulation layer charge in an n-type semiconductor is 1/2 Q 52 2e k TN exp[ q Dc /(2kT )], where N is the donor concentration and Dc is the s d s,SC S B D s B D s semiconductor potential drop [10]. To take QM effects into account approximately this expression is modified empirically into Q 5 Q 1 Q exp[2DE /(2kT )], where DE is an effective shift of s,QM 0 s,SC C B C *Tel.: 132-16-281-941; fax: 132-16-281-844. E-mail address: frans.widdershoven@philips.com (F.P. Widdershoven). 0167-9317 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0167-9317(01)00609-8