Abstract

Recently, the demand of a high resolution complementary metal-oxide semiconductor (CMOS) image sensor is dramatically increasing. As the pixel size reduces to submicron, however, the quality of the sensor image decreases. In particular, the dark current can act as a large noise source resulting in reduction of the quality of the sensor image. Fluorine ion implantation was commonly used to improve the dark current by reducing the trap state density. However, the implanted fluorine diffused to the outside of the silicon surface and disappeared after annealing process. In this paper, we analyzed the effects of carbon implantation on the fluorine diffusion and the dark current characteristics of the CMOS image sensor. As the carbon was implanted with dose of 5.0 × 1014 and 1 × 1015 ions/cm2 in N+ area of FD region, the retained dose of fluorine was improved by more than 131% and 242%, respectively than no carbon implantation indicating that the higher concentration of the carbon implantation, the higher the retained dose of fluorine after annealing. As the retained fluorine concentration increased, the minority carriers of electrons or holes decreased by more Si-F bond formation, resulting in increasing the sheet resistance. When carbon was implanted with 1.0 × 1015 ions/cm2, the defective pixel, dark current, transient noise, and flicker were much improved by 25%, 9.4%, 1%, and 28%, respectively compared to no carbon implantation. Therefore, the diffusion of fluorine after annealing could be improved by the carbon implantation leading to improvement of the dark current characteristics.

Highlights

  • Demand for complementary metal-oxide semiconductor (CMOS) image sensors is rapidly increasing due to broad application of multi-cameras and 3D cameras in smartphones and the expansion of 5G technology

  • Ha et al [13] reported that the dark current properties could be improved as a result of selective application of the fluorine implantation to the NMOS transistor of a CMOS image sensor

  • The SIMS analysis was performed to analyze the changes in concentration of carbon, fluorine, and arsenic ion according to the depth into the wafer before and after the annealing process

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Summary

Introduction

Demand for CMOS (complementary metal-oxide semiconductor) image sensors is rapidly increasing due to broad application of multi-cameras and 3D cameras in smartphones and the expansion of 5G technology. Ha et al [13] reported that the dark current properties could be improved as a result of selective application of the fluorine implantation to the NMOS transistor of a CMOS image sensor. If we can control or prevent the diffusion of the implanted fluorine after annealing process, the dark characteristics such as dark current can be much improved.

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