Unexpected Surface Implanted Layer in Static Random Access Memory Devices Observed by Microwave Impedance Microscope

TL;DR

This study uses microwave impedance microscopy to map doping in SRAM devices, revealing an unexpected dopant layer caused by heavy implantation, which could impact device performance.

Contribution

The paper demonstrates the use of MIM combined with SCM to detect unexpected dopant penetration in SRAM devices, providing new insights into implantation effects.

Findings

MIM reveals unexpected dopant layers in SRAM devices.

SCM images match the nominal device structure.

Heavy implantation causes dopant ions to penetrate protective layers.

Abstract

Real-space mapping of doping concentration in semiconductor devices is of great importance for the microelectronic industry. In this work, a scanning microwave impedance microscope (MIM) is employed to resolve the local conductivity distribution of a static random access memory (SRAM) sample. The MIM electronics can also be adjusted to the scanning capacitance microscopy (SCM) mode, allowing both measurements on the same region. Interestingly, while the conventional SCM images match the nominal device structure, the MIM results display certain unexpected features, which originate from a thin layer of the dopant ions penetrating through the protective layers during the heavy implantation steps.