Effect of Statistical Dopant Fluctuations on Threshold Voltage of Emerging Devices

Abstract

This paper presents a comparative study on the effect of statistical dopant fluctuations on threshold voltage ( $V_{th}$ ) of emerging and conventional metal-oxide-semiconductor (MOS) field-effect (FET) transistors (MOSFETs). In this context, three ${n}$ -channel MOSFET structures representing three different complementary MOS (CMOS) technologies at the 20 nm node are considered. The structures represent a conventional device with symmetric halo or pocket regions around the $n^{+}$ source-drain formed by a single ${p}$ -type dopant implantation; a second conventional device with symmetric ${p}$ -type halo regions around the $n^{+}$ source-drain formed by multiple ${p}$ -type dopant implantations; and an emerging epitaxial-channel device with symmetric ${p}$ -type halo regions around the $n^{+}$ source-drain where the halo regions are formed by up-diffusion of multiple ${p}$ -type buried layers from the bulk-substrate during epitaxy. For these devices, the values of $V_{th}$ variance and mismatch are computed as a function of device dimensions. The results show that the multiple-halo devices, in general, offer significantly lower $V_{th}$ variance and mismatch compared to the conventional single-halo devices whereas, the emerging epitaxial-channel multiple-halo MOSFETs offer the lowest $V_{th}$ variability compared to the conventional devices at the same technology node. And, the value of the mismatch coefficient for the emerging technology is about 0.68 mV $\times \mu \text{m}$ compared to that of 1.33 and 1.07 mV $\times \mu \text{m}$ for the conventional single-halo and multiple-halo technologies, respectively. This study, clearly, demonstrates the benefit of the emerging epitaxial-channel buried-halo MOSFETs in significantly reducing the effect of statistical dopant fluctuations on $V_{th}$ at the advanced planar CMOS technology nodes.

Keywords

• Buried-halo
• discrete-dopants
• emerging transistors
• field-effect transistors
• threshold voltage
• mismatch