Optimizing MIM Device Electrical Properties. Impact of Bottom Electrodes and High K Materials
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1108-A09-03
Optimizing MIM Device Electrical Properties: Impact of Bottom Electrodes and High k Materials
M. Bonvalot, C. Vallée, E. Gourvest, C. Jorel, P. Gonon.
ABSTRACT M/HfO2/Au (M = Pt, TiN) MIM structures have been characterized by X-ray Photoelectron Spectroscopy and electrical C(V) measurements. It is shown that the bottom electrode material strongly affects the linear behaviour of C(V) curves. To account for this result, it is proposed that oxygen vacancies accumulate at the metallic electrode-dielectric interface and act as a double layer capacitance upon applied voltage. The use of high work function materials can improve the MIM linearity thanks to the formation of a reduced interfacial oxygen trap layer.
INTRODUCTION High quality MIM capacitors with improved capacitance density, low leakage currents and linear C(V) behaviour are the object of active research, with potential applications in CMOS, BICMOS and bipolar technologies as filters, analog to digital converters and related radiofrequency operating devices. Several high-k materials (Ta2O5, Y2O3, HfO2, ZrO2, Al2O3HfTiO, HfON-SiO2) have been put on trial as possible candidates for SiO2 substitution which is required by the aggressive downscaling of electronic devices [1-6]. Among those, HfO2based materials seem to offer promising properties, combining a high chemical stability with Si and a high k value. However, HfO2 shows a strong ability to favour charge defects such as oxygen vacancies, which in turn affect the intrinsic properties of devices such as threshold voltage or leakage currents [7]. These oxygen vacancies are actually thought to accumulate in the vicinity of the electrode, thus forming an oxidized interfacial layer and inducing a significant voltage linearity degradation of MIM capacitors [8, 9]. Moreover, it is widely accepted that this voltage linearity is also affected by the small thickness of the dielectric required to maximize the overall capacitance value [10-11]. The voltage linearity behaviour of a MIM device can be expressed by the following formula [12]:
∆C C (V ) − C0 = = αV ² + β V C0 C0
with: C0: minimum capacitance at zero bias, α and β: quadratic and linear coefficients. The linear voltage coefficient β can be regulated by appropriate conception and design rules [13]. Thus, the quadratic coefficient α is the key contribution to voltage non linearity [11, 14]. In this work, we show that in the case of identical insulating material, the α coefficient is also strongly influenced by the bottom electrode material itself. For this purpose, we have investigated the behaviour of two MIM capacitor stacks having the same HfO2 dielectric layer and top electrode Au material, but with two different bottom electrode materials, namely Pt and TiN. Standard physico-chemical characterization techniques (X-ray Photoelectron Spectroscopy XPS, Attenuated Total Reflexion spectroscopy ATR and Spectroscopic Ellipsometry SE) have been used. The obtained results have been correlated to C(V) electrical characterization measurements.
EXPERI
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