Application of three-step epitaxial process to dual trench epitaxial diode array.

The application of three-step Epitaxial (EPI) process to dual trench epitaxial diode array for high density phase change random access memory (PCRAM) was reported in this paper. With three-step EPI process condition, both vertical and lateral Arsenic auto-doping were suppressed effectively from Arsenic heavily-doped substrate. It was found that EPI layer (similar to 300 nm) with high-quality single crystalline and good thickness uniformity within 200 mm diameter wafer could be achieved. It was also found that both lateral and vertical Arsenic auto-doping concentration could be reduced by 2 similar to 3 orders by adding high temperature and low deposition rate EPI step before main EPI process, as compared to the conventional CVD EPI process. As a result, diode breakdown voltage was improved above 11 V and the On/Off current ratio of diode is greater than 9 orders of magnitude.