Oxide-Semiconductor Interface Characterization Using Kelvin Probe-AFM In Combination With Corona-Charge Deposition
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Oxide-Semiconductor Interface Characterization Using Kelvin Probe-AFM In Combination With Corona-Charge Deposition Bert Lägel, Maria D. Ayala*, Elena Oborina and Rudy Schlaf** Department of Electrical Engineering, University of South Florida, Tampa, Fl 33620 * Undergraduate Research Associate ** To whom correspondence should be addressed: email: [email protected]
ABSTRACT Corona charge deposition methods in combination with spatially resolved surface potential measurements have become a standard tool for Si oxide quality monitoring 1. Based on this technique oxide-semiconductor interface parameters such as surface barrier height, oxide thickness and oxide charge density can now be monitored in-line with commercially available devices. The ongoing downscaling of integrated circuits into the sub-100 nm regime makes the development of high resolution oxide screening methods increasingly important. However, currently available commercial devices are limited in their spatial resolution since they employ the traditional vibrating Kelvin probe technique, restricting their lateral resolution to several µm 2. In order to increase the lateral resolution of this measurement method we have combined the corona-charge deposition technique with Kelvin Probe AFM. We present initial results of this novel measurement technique and demonstrate its feasibility by measurements on lithographically prepared oxide patterns on Si wafers with different oxide thicknesses. INTRODUCTION According to the International Technology Roadmap for Semiconductors the standard “technology” node size will decrease to 100nm by 20053 . This corresponds to a gate length of about 65nm for metal oxide field effect transistors (MOS-FET) which are the main design features in integrated circuits. Therefore, the development of sub-100nm semiconductor characterization techniques is vital for the success of the envisaged progress in reducing the technology node size. One of the most powerful semiconductor characterization method is the surface voltage and surface photovoltage measurement technique1,2. In particular, via the addition of corona charge deposition, the range of material and device parameters that can be obtained is substantial 4 and has led to the development of commercial devices that are now widely used by the semiconductor industry. Instruments based on this technique, termed COCOS (Corona Oxide Characterization of Semiconductor)5, allow wafer-scale in-line monitoring e.g. of surface voltage, barrier height, oxide thickness, oxide integrity, mobile charge and interface trap density as well as generation and recombination lifetime and doping density. One of the major advantages is the non-contact and non-destructive nature of the measurement method using a Kelvin Probe (KP)1,6. However, employment of the traditional vibrating KP limits the spatial resolution of the measurement to typically several µm 2. In order to overcome this limitation we have investigated the feasibility of using a Kelvin Probe Atomic Force Microscope (KPAFM) to measure
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