A photothermal method of simultaneous determination of ultra-shallow junction depth and abruptness
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A photothermal method of simultaneous determination of ultra-shallow junction depth and abruptness Alex Salnick1, Lena Nicolaides1, Jon Opsal1, Amitabh Jain2, Duncan Rogers2, and Lance Robertson2 1 Therma-Wave, Inc., 1250 Reliance Way, Fremont, CA 94539 2 Texas Instruments, Inc., 125100 TI Boulevard, Dallas, Texas 75243 ABSTRACT Thermal wave (TW) studies of ultra-shallow junctions (USJ) formed by ion implantation into a semiconductor wafer followed by rapid thermal annealing (RTP) are described. It is shown that using the TW technique allows for a simultaneous determination of the most important USJ parameters – depth and profile abruptness. Experimental results for junction depth and abruptness obtained on a set of B+-implanted, RTP-annealed USJ samples show better than 0.99 correlations to the corresponding secondary ion mass spectroscopy (SIMS) data.
INTRODUCTION Surface modifications of semiconductor materials – ion implantation and thermal annealing – are key technological processes at the initial stages of microelectronics manufacturing. Thermal-wave (TW) technology [1-3] based on modulated optical reflectance (MOR), also known as photomodulated reflectance, (PMR) detection [4] has long been used for the characterization and control of the accuracy and uniformity of the ion implantation dose. Modern semiconductor technology uses low energy ion implantation process to achieve ultra-shallow (< 500 Å) implantation depths. Several types of thermal annealing methods have been found to avoid excessive enhanced diffusion of dopants, and to form effective ultra-shallow junctions (USJ). Low energy high doping concentration (~1020 cm-3) implantation of B+ combined with rapid thermal annealing (RTA) currently represents the leading solutions for obtaining the required ultra-shallow scaling. The process problems in forming USJ layers lie in both the implant and the anneal procedures. While it is relatively easy to create a shallow layer by implantation, keeping the USJ profile abrupt and close to the surface after anneal is a big challenge. Therefore, junction depth (Xj) and profile abruptness are among the most critical parameters in characterization of USJ. Non-uniformities associated with ion implantation and RTA or other types of anneal systems result in residual damage areas on the surface of a semiconductor wafer after anneal and require monitoring to ensure process control. Recently, there is an urgent need for a sensitive, rapid, and nondestructive technique capable of monitoring all key USJ profile parameters. In this paper, we show how conventional TW methodology coupled with a new signal-processing algorithm can be successfully applied for quantitative, simultaneous characterization of USJ depth and abruptness.
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RESULTS AND DISCUSSION Experimental Method The system hardware configuration for the present study was the same as found in commercially available Therma-ProbeTM ion implant monitoring devices [5]. The TW system is equipped with a module for varying the pump-probe beam offset distanc
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