Fast and Accurate in-Line Monitor of Boron Implantation Energy and Dose by Spectroscopic Ellipsometry

Abstract

Ion implantation is a key process for front end of line semiconductor manufacturing and directly correlates to device performance. Inability to rework mandates precise control. As of today, there is still limited production worthy solution for in-line boron implanted energy and dose monitor on product wafer. This paper describes a fast and accurate in-line method for monitoring Boron (B) implantation energy and dose measurement, simultaneously, in a production environment using spectroscopic ellipsometry (SE) after the source-drain PMOS implant process step. The implanted species damage the silicon substrate lattice, producing amorphous-Si like characteristics and a different refractive and absorption indexes compared to crystalline silicon substrate. Furthermore, the damaged depth is a function of implant energy. SE spectra are very sensitive to measure the optical properties variation of these materials (Figure 1). In this work, a single look-up optical model is created to monitor the damaged layer. The look-up components relate to implanted dose behavior, the thickness of the damage layer to the implanted depth (energy) behavior. Secondary Ion Mass Spectrometer (SIMS) is used as a reference tool. Excellent correlation (R2> 0.99) can be achieved between SE results and SIMS (Figure 2). The damaged layer thickness correlates to SIMS depth (Rp); and the look-up model components correlate to SIMS dose. Q-time limitation must be considered to achieve stable implantation monitoring before annealing. The implanted surface is unstable and damaged depth and implanted dose decay rapidly within a few hours. Q-time correlation formula is used to compensate the implanted decay behavior (Figure 3). As a result, 1.64% depth and 0.43% dose range variation can be achieved after Q-time correlation is applied. This research also shows that SE metrology is sensitive to other species used for source-drain implantation and can be extended to control NMOS implant process using Arsenic (As) species.