Studies of post-implant ash induced ring-pattern defects after gate poly and Wsix etch

摘要

In this paper, one type of heavy ring-pattern poly spike defect was studied, which detects after gate poly and Wsix etch. The implant effects on the ring pattern defects were studied. Our experimental results show clearly that the ion implant can only cause the poly surface change to an amorphous layer, and the degree of amorphousness will depend on the type, weight, and size of the implant ion. The root cause of ring pattern defect is found to be related to the post-Vt implant ash and clean-up. These include three main steps: the first step was the post-implant photo resistor ash. Here two kinds of ash methods were used and compared, one was Radio Frequency (RF) plasma ash and the other was remote microwave ash. The second step was post-ash clean-up. Here also two methods were used and compared, one was piranha clean followed by SCI clean, and the other was piranha clean only. The third step was pre-Wsix deposition clean-up. Again two methods were used and compared. One was wet HF clean, and the other was vapor HF clean. It was found that the original ring-pattern was from plasma ash as well as remote microwave ash, but RF plasma pits poly Si more than remote microwave, resulting in a ring dent on the poly surface. SCI in the second step is not the root cause for ring-pattern, but SCI will decorate the ring-pattern to make it worse. During step 3, the dissolved SiO{sub}2 residuals can be removed by the wet HF method but not by vapor HF method. The ring-pattern defects form mechanism is also discussed in detail in this paper.