Micro Unetched Oxide Defects during Buffered Oxide Etchant Process

摘要

There are two oxide regions for high and low voltages in NAND flash memory devices, in order to improve their program speed and reliability. Generally, the two regions are created by pattern blocking using photoresists followed by etching of the low voltage oxide with BOE(Buffered Oxide Etchant). However, as the 10nm scale NAND flash devices are massively manufactured, 0.2um size defects after oxide etching with BOE are newly detected. Partially unetched oxide defects in the low voltage oxide region causes the thicker tunnel oxide and influences abnormal electron's tunneling. As a result, program and erase speeds are declined on the relevant transistor, and it causes a yield drop by the degradation of electrical characteristics. As possible sources of the defects, the micro impurities in the chemical or the micro bubbles from surfactant are suspected, but real root cause has not yet been known. In this study, the effects of filter pore size and nozzle movement of cleaning equipment on oxide etching are examined in other to reduce the defects.