Characterising Backscattered Electrons in EBCMOS
Xuening Wang, Song De, Gangcheng Jiao, Ye Li, Weijun Chen
Abstract
The characteristics of backscattered electrons near the surface of a back-side bombarded CMOS (BSB-CMOS) within an electron bombarded CMOS (EBCMOS) were studied based on the principle of electron-solid interactions and Monte-Carlo simulation method. We mainly focused on the angular distributions of backscattered electrons, the ratio of backscattered electron number to incident electron number (RBI), and the distribution of the distance between backscattered electrons and incident electrons ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BI</sub> ). We studied how these characteristics were affected by the BSB-CMOS surface structure and incident electron energy. Firstly, RBI and the mean <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BI</sub> vary with the incident electron energy, the surface material type, and passivation layer thickness. Meanwhile, a lower RBI may reduce device noise originating from backscattered electrons ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE</sub> ) due to the smaller number of backscattered electrons. Besides, the lower mean <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BI</sub> may enhance the device resolution, because the backscattered electron beam is more concentrated. The distribution of backscattered azimuths ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\it \Phi}_{\rm B}$</tex-math></inline-formula> ) and the backscattered angle ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) follow uniform distribution and cosine angular distribution respectively, which are difficult to change. Finally, devices with the lowest RBI and a low mean value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BI</sub> were achieved when the BSB-CMOS surface was modified with 60 nm Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and the incident electrons were at 4 keV, which might improve the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE</sub> and resolution of the EBCMOS. This study will provide a theoretical foundation for the fabrication of high-resolution EBCMOS.