Optimization of Structure and Electrical Characteristics for Four-Layer Vertically-Stacked Horizontal Gate-All-Around Si Nanosheets Devices

• Published in: Nanomaterials (Basel, Switzerland) Vol. 11; no. 3; p. 646
• Main Authors: Zhang, Qingzhu, Gu, Jie, Xu, Renren, Cao, Lei, Li, Junjie, Wu, Zhenhua, Wang, Guilei, Yao, Jiaxin, Zhang, Zhaohao, Xiang, Jinjuan, He, Xiaobin, Kong, Zhenzhen, Yang, Hong, Tian, Jiajia, Xu, Gaobo, Mao, Shujuan, Radamson, Henry H., Yin, Huaxiang, Luo, Jun
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI 05.03.2021; MDPI AG
• Subjects: channel release; gate-all-around (GAA); nanosheet (NS); parasitic channel; suppression; channel release; suppression; nanosheet (NS); gate-all-around (GAA); parasitic channel
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano11030646

In this paper, the optimizations of vertically-stacked horizontal gate-all-around (GAA) Si nanosheet (NS) transistors on bulk Si substrate are systemically investigated. The release process of NS channels was firstly optimized to achieve uniform device structures. An over 100:1 selective wet-etch ratio of GeSi to Si layer was achieved for GeSi/Si stacks samples with different GeSi thickness (5 nm, 10 nm, and 20 nm) or annealing temperatures (≤900 °C). Furthermore, the influence of ground-plane (GP) doping in Si sub-fin region to improve electrical characteristics of devices was carefully investigated by experiment and simulations. The subthreshold characteristics of n-type devices were greatly improved with the increase of GP doping doses. However, the p-type devices initially were improved and then deteriorated with the increase of GP doping doses, and they demonstrated the best electrical characteristics with the GP doping concentrations of about 1 × 1018 cm−3, which was also confirmed by technical computer aided design (TCAD) simulation results. Finally, 4 stacked GAA Si NS channels with 6 nm in thickness and 30 nm in width were firstly fabricated on bulk substrate, and the performance of the stacked GAA Si NS devices achieved a larger ION/IOFF ratio (3.15 × 105) and smaller values of Subthreshold swings (SSs) (71.2 (N)/78.7 (P) mV/dec) and drain-induced barrier lowering (DIBLs) (9 (N)/22 (P) mV/V) by the optimization of suppression of parasitic channels and device’s structure.