Evaluation of extrinsic gettering techniques

Nitride (N-EG); poly-nitride (PN-EG), and poly (P-EG) extrinsic gettering techniques were evaluated using a 3.0 micron P-well CMOS process with N/N+ substrates. The devices used for this evaluation were a 2K SRAM and a N+ to P-well test diode. All gettering was applied as a post-epitaxial process except the P-EG material. Results showed that the N-EG material had lower defect surface densities and superior diode characteristics when compared to the P-EG and epitaxial control Epi-C without gettering. Test diode characteristics showed the PN-EG and the N-EG samples having very low leakage currents compared to the P-EG and EPI-C samples. Similar findings also were obtained for the leakage current of the 2K SRAM. A graphical correlation between the leakage currents of the 2K SRAM and the test diode is established. This demonstrates how effective the N-EG and PN-EG gettering ability is for COMS processing. All devices receiving the nitride or the polynitride gettering showed improved device performance.