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https://doi.org/10.1007/s11664-020-08236-1 Ó 2020 The Minerals, Metals & Materials Society

INTERNATIONAL ELECTRON DEVICES AND MATERIALS SYMPOSIUM 2019

Reduction of Contact Resistivity by Nano-Textured Contact BING-YUE TSUI

,1,2 YA-HSIN LEE,1 and CHEN-YI LEE1

1.—Institute of Electronics, National Chiao Tung University, Hsinchu City, Taiwan, ROC. 2.—e-mail: [email protected]

The feasibility of reducing contact resistance by adding nano-textures on the contact surface is evaluated by three-dimensional simulation. Upward and downward pyramids and hemispheres are considered, and the effects of contact area and electric field are discussed. The downward nano-texture has a stronger electric field than the upward nano-texture; thus the increasing contact area will be more effectively used and lead to a greater improvement effect. On the other hand, the electric field of the hemisphere nano-texture is lower than that of the pyramid nano-texture. With proper design, the nanotextured contact can effectively reduce contact resistance up to 30–50%. Therefore, the proposed nano-textured contact is a promising approach with contact resistivity approaching physical limits. Key words: Contact resistance, contact resistivity, contact area, Schottky barrier, nano-texture

INTRODUCTION Moore’s law has long served as an important indicator of the progress of semiconductor technology. The number of transistors on integrated circuits (ICs) has doubled every 1.5 to 2 years, and this law has held true for more than 50 years.1 Today, the channel length of advanced MOSFETs is approaching 10 nm, and the area of the contact window for the transistor contact with metal is drastically reduced to less than 1000 nm2, so that the contact resistance of the metal–semiconductor interface increases exponentially. Total resistance is a key factor in the operating speed of MOSFETs. Figure 1 compares the components of external resistance (Rext) of advanced FinFETs.2 Among the components of Rext, contact resistance (RC) is the major portion beyond the 7 nm technology node. With scaling, the continuous increase in contact resistance due to the reduction in contact area (AC) will result in the obstacle of total resistance reduction, which may significantly affect the operating speed of the MOSFETs and

(Received January 3, 2020; accepted May 26, 2020)

ICs.2,3 Thus, reducing RC is critical in order to reduce Rext. Contact resistance arises from the Schottky barrier between the metal and semiconductor, making it difficult for the carrier to pass through the contact interface.  From  the thermionic field emission model, ; bn qc / exp pffiffiffiffiffi , where qc is the specific contact ND

resistivity in X-cm2, /bn is the Schottky barrier height in eV, and ND is the carrier concentration in cm3,4,5 it is clear that to reduce the contact resistivity (qc), two common strategies can be employed. The first is to minimize the Schottky barrier height.6 We can choose a material to form the contact with a lower barrier height, such as metal silicide.7,8 The other i