Measurements of Ultra-Shallow Junction (USJ) Sheet Resistance with a Non-Penetrating Four Point Probe
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Measurements of Ultra-Shallow Junction (USJ) Sheet Resistance with a Non-Penetrating Four Point Probe Robert J. Hillard, Robert G. Mazur, William J. Alexander, C. Win Ye, Mark C. Benjamin, and John O. Borland1 Solid State Measurements, Inc. 110 Technology Drive, Pittsburgh, PA 15275 1 J.O.B Technologies, 5 Farrington Lane, South Hamilton, MA 01982 [email protected] ABSTRACT An accurate method to measure the four point probe (4PP) sheet resistance (Rs) of USJ Source-Drain structures is described. The new method utilizes Elastic Material probes (EMprobe) to form non-penetrating contacts to the silicon surface. The probe design is kinematic and the force is controlled to ensure elastic deformation of the probe material. The probe material is selected so that large direct tunneling currents can flow through the native oxide thereby forming a low impedance contact. Sheet resistance measurements on USJ implanted P+/N structures with SIMS junction depths as shallow as 15 nm have been measured. The sheet resistance values obtained with the new EM-probe 4PP method were found to be consistent with expectations. In this paper, the method will be demonstrated on a variety of implanted USJ structures. INTRODUCTION Source-Drain(S/D) engineering is an important area in existing and future device development. Critical device parameters such as on-state drive current (IDS, ON) are highly dependent on the S/D series resistance (RDS). It is therefore desirable to have S/D structures that have low sheet resistances. This requires S/D structures with high carrier densities. At the same time, Threshold Voltage (VT) roll-off due to Short Channel Effects (SCE) increases as the channel length is decreased [1]. These effects need to be minimized. This requires producing a rectangular overall device structure [2] where the gate dielectric thickness, S/D junction depths and channel carrier profile are thin. Highly abrupt, steep gradient carrier density profiles are also necessary in order to reduce SCE via channel charge sharing [3]. Careful consideration of all of these device performance issues leads to the fact that the S/D carrier density profiles must be highly abrupt “Box” type profiles with a high peak carrier density and a shallow junction depth (xj). As an example, S/D structures with activated dopant densities at or near solid solubility with xj’s less than 20 nm are under development for the 65 nm technology node To produce these Ultra-Shallow Junction (USJ) structures careful process design of the Preamorphization implant (PAI), S/D implant and the dopant activation and implant anneal are required. The USJ junction depths and level of dopant activation depend heavily on processing [3]. A suitable method for characterizing these USJ structures is the Conventional Four Point Probe (4PP) Sheet Resistance (RS) technique [4]. The measured RS is highly sensitive to the activated carrier density and xj. This is a highly accurate, absolute method that has been used successfully on structures with deeper junction depths and laye
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