Study on Improvement of FG Residue in NOR Flash by Etching Back

NOR Flash is a non-volatile semiconductor memory that can retain data for a long life when power is turned off. It is a form of electronically erasable programmed read-only memory that allows it to be erased or written multiple times during operation. erasing data of NOR flash is based on the F-N tunneling effect (Fowler-Nordheim), where electrons are tunneled through a dielectric layer to the silicon substrate, and the writing is injected into the Floating gate (FG) by hot electrons, which are released and captured to achieve 1/0 signal recognition. Therefore, FG related process is very important for NOR performance. At present, STI is the end point of FG CMP (Chemical Mechanical Polishing) process, and the general Oxide loss is 80~100 Å. However, due to insufficient filling capacity of STI loop, seams are easily generated in the center position, subsequently causing FG to be deposited in the void, and the CMP process cannot completely remove buried FG, resulting in Poly residue. Such defects will cause annular failure map, resulting in low yield. In this paper Most of the top FG poly was first removed by FG CMP, with OX loss 30~50 Å as the end point, and the poly residual was removed by the second dry etching, which overcomes the disadvantage that pure CMP process is difficult to completely grind FG residue on STI. At the same time, the thin thickness of FG caused by over-grinding can be avoided to ensure good cell performance. After improvement, the yield is improved by at least 2%