Non-destructive Characterization of Activated Shallow B and as Implants in full NMOS and PMOS Process Flows
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Non-destructive characterization of activated shallow B and As implants in full NMOS and PMOS process flows Peter G. Bordena, Laurie Bechtlera, Lawrence Larsonb, Bob Murtob, Billy Covingtonc, Clarence Fergusonb and Billy Nguyenb (aBoxer Cross Inc, 978 Hamilton Court, Menlo Park, CA 94025; bInternational Sematech, 2706 Montopolis Drive, Austin, TX 78741; c presently at Southwest Texas State University, 601 University Dr., San Marcos, TX 78666) ABSTRACT A new method for non-destructive, small area characterization of ultra-shallow junctions, called Carrier Illumination™ (CI) has recently been developed1. This work validates the CI measurement in full CMOS and NMOS process flows, with the aim of demonstrating its capability to provide in-line characterization of junction depth and uniformity on product wafers. Measurements have been carried out on both unpatterned and patterned wafers at various steps in the SEMATECH standard process flow. CI was used to characterize annealed 800 eV B11 PLDD implants into n-wells and annealed As75 NLDD source/drain (S/D) implants into p-wells. This work demonstrates correlation to dose, junction depth as measured with SIMS and SRP, and electrical properties of test structures. (1) Proceedings of the Fifth International Workshop on Measurement, Characterization and Modeling of Ultra-Shallow Doping Profiles in Semiconductors, usj-99, Research Triangle Park, NC, March 1999, pp. 314-18. INTRODUCTION Deep sub-micron transistor source-drain structures demand a challenging combination of ultra-shallow depth and low series resistance. Because these factors affect both off-state leakage and circuit speed, it is important to maintain tight control of depth, active doping and uniformity over the full wafer diameter. Conventional methods for measuring junction depth and active doping include a mix of four point probing (4PP), which measures active dose, and secondary ion mass spectroscopy (SIMS), which measures total dopant profile. The limitation of 4PP is that it is a large area contact measurement, not readily used on patterned wafers. The limitation of SIMS is primarily throughput. Consequently, SIMS is used for process qualification, but generally not for measurement of junction depth uniformity or in-line process control. A new method for characterizing annealed ultra-shallow implants, called Carrier Illumination™, was developed to overcome these limitations. CI uses a slowly modulated laser with a photon energy above the silicon bandgap to generate a quasi-static distribution of excess carriers. The excess carrier concentration rises steeply at the edge of a doped region, creating a sharp index of refraction gradient at a depth equal to the edge of the doped profile. Light from a second laser reflected from this structure yields a signal that may be analyzed to determine the depth of the profile, typically defined as the depth at which the concentration reaches 1018/cm3.
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With a spot diameter under 2 µm, this non-destructive measurement has the potential to provide in-line charact
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