Analysis of Ion Implantation Damage in Silicon Wafers by a Contactless Microwave Diagnostic
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Analysis of Ion Implantation Damage in Silicon Wafers by a Contactless Microwave Diagnostic Richard K. Ahrenkiel Measurements and Characterization Division National Renewable Energy Laboratory 1617 Cole Blvd. Golden, CO 80401 B. Lojek ATMEL Corporation 1150 E. Cheyenne Mtn. Blvd. Colorado Springs, CO 80906 ABSTRACT Rapid thermal annealing (RTA) of lattice damage created by heavy ion implantation damage is required to maintain the integrity of semiconductor material used for submicron-integrated circuit devices. A quick, efficient, and contactless diagnostic of the implantation damage is highly desirable in both research and production environments. A contactless measurement technique has been recently applied to this problem that uses a deeply penetrating low-frequency microwave probe frequency operating at 420 MHz. Here, we will demonstrate the use of this high frequency resonance-coupled photoconductive decay (RCPCD) technique, which, when combined with a tunable optical excitation source, enables us to map the radiation damage in boron and arsenic-implanted silicon wafers. We quantify the damage by mapping the minoritycarrier lifetime as a function of optical penetration depth. In this work, we quickly and efficiently compared the effectiveness of various RTA processes by the RCPCD diagnostic. INTRODUCTION The fabrication of very high-density silicon-integrated circuits requires a combination of ion implantation followed by rapid thermal annealing. Ion implantation is necessary to produce the submicron device dimensions that are standard in current technology. Here we will discuss a new diagnostic used to analyze implantation damage and annealing used in 0.18-µm integrated circuit technology. The integrity of submicron structures can be maintained by ion implantation, but the implantation process produces damage to the near-surface region. The implantation damage is reduced by annealing, but the process must be rapid compared to ionic or atomic diffusion times. This precludes more conventional annealing as a processing tool. Thus, rapid thermal annealing is the standard method of damage removal for silicon wafers. The mechanisms of rapid thermal annealing processes and the effectiveness of alternative processes are the subject of the studies to be described here. Contactless measurement diagnostic We have found that contactless measurements of the surface minority-carrier lifetime is an excellent indicator of implantation damage removal. We have used a technique, developed at the R4.2.1
National Renewable Energy Laboratory (NREL), called resonance-coupled photoconductive decay (RCPCD) [1]. This technique can handle wafers of any finite size (up to 12-inch diameter) and is completely contactless. The sample lies on an insulating, moveable platform in an enclosed aluminum box that is resonant at a specific low-frequency microwave (or UHF) frequency. The sample is impedance coupled to a small antenna that is connected to a detection system by means of an unidirectional coupler. The conductance of the sample shifts
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