August_EDFA_Digital

edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 3 24 ELECTRICAL CHARACTERIZATIONS BASED ON AFM: SCM AND SSRMMEASUREMENTS WITH A MULTIDIMENSIONAL APPROACH R. Coq Germanicus and U. Lüders University of Caen Normandy - UNICAEN, France rosine.germanicus@unicaen.fr EDFAAO (2022) 3:24-31 1537-0755/$19.00 ©ASM International ® INTRODUCTION In front end of line (FEOL) process control, the detec- tion, quantification, and spatial distribution of the local electrical properties with high spatial resolution are keys to optimizingmicroelectronic processes. For dopant con- centration andmapping, several techniques are available based on chemical detection and probing characteriza- tion. For the chemical dopant distribution, the most accurate quantitative analysis method is secondary ion mass spectrometry (SIMS). For 3D tomography, time of flight secondary ion mass spectrometry (TOF-SIMS) can be deployed. Atom probe tomography (APT or 3D atom probe) alsoprovides chemical compositionwithhighmass resolution and ppmsensitivity. Due to the specific sample preparation, this powerful technique provides localized information. However, for complexmicroelectronic struc- tures, these techniques are somewhat limited to render the full view of the structure. Both techniques are based on the chemical presence of the dopant element, and not its electrical effects, and exclude the in-depth investiga- tion of the interfaces. Thus, complementary techniques to determine the electrical structure of complex devices have to be identified to allow for a complete view. Based on an atomic force microscope (AFM), electri- cal probing techniques [1] such as scanning capacitance microscopy (SCM) and scanning spreading-resistance microscopy (SSRM) are widely used to determine semi- conductor local electrical properties. SCM probes local dopant properties in terms of the doping type (n- or p-type) and doping levels. [2] In SSRM, a conductive AFM tip probes the local resistance between the tip and AFM chuck contact when a DC voltage is applied. These two modes can be used in spectroscopy mode to achieve local bias dependence and 2D scans to achieve electrical maps, but also in a multidimensional mode [3] (also called DataCube (DCUBE)) where the spectroscopy is combined with 2D-mapping. All acquisitions are obtained with the spatial resolution of the AFM. Thus, these AFM-based modes allow investigation of the dopant activities, both their type and levels, local resistivity, and gain comple- mentary informationwith respect to the techniques based on the chemical detection. Here, the value of the AFM-based electrical modes for the characterization of a complex microelectronic struc- ture will be demonstrated. With the integration of more and more functionalities onto the same semiconductor die, many RF circuits are developed by incorporating several functions in a single module. In this context, mul- tiple devices with different functionalities such as digital, analog and radio frequency (RF) blocks are co-designed in the same monolithic substrate. However, the main challenge is increasing the semiconductor integration by miniaturization while preserving the functionality and efficiency of each block. Especially for RF applications, the integration of several components on the same chip asks for stringent requirements for low loss, high gain, and excellent isolation. For high RF performance, deep trench isolation (DTI) structures are added to limit the contribu- tion of the substrate noise and decrease parasitic capaci- tances. These structures, designed into a silicon wafer, surrounding the device provide parasitic and crosstalk reductions for RF components. This article describes the SCM and SSRM analysis of the DTI structure designed for an analog, digital, RF inte- grated circuits. The goal is to expose themultidimensional methodology for a comprehensive analysis and also high- light the difference and complementarity of the two AFM