A case study in a 100/spl times/reduction in sodium ions in a 0.8 /spl mu/m BiCMOS process using triangular voltage sweep

This case study shows how to use Triangular Voltage Sweep (TVS) to reduce Na and K in the backend of a triple-metal BiCMOS process from 10/sup 12/ ions/cm/sup 2/ to 10/sup 10/ ions/cm/sup 2/. TVS is compared to Bias Temperature Stress (BTS) techniques. While Capacitance-Voltage plots are good monitors for bulk contamination (metal, deposited oxide, etc.), data is presented which shows that TVS is superior for detecting surface-introduced mobile ions (photoresist, solvent strip, etc.). Process integration techniques and issues in the reduction of mobile ions are discussed. When TVS structures are put on product-like wafers, the mobile ions can be measured accurately and repeatably within 10 minutes of completing the process step-no alloy is required! Finally, the use of Ammonium Fluoride solutions to reduce the surface mobile ions are discussed.