Lifting Defect Improvement of Plasma Enhanced Nitride
Plasma enhanced nitride (PESiN) has been applied for various layers in semiconductor device such as spacer, etch stopping layer, strain layer, hard mask. In order to match with each function of PESiN, process condition should be well optimized in terms of etch rate, stress, uniformity. In addition, defects which might be caused during process should be controlled for manufacturability. In this paper, Bubble shaped lifting defects that were observed open by PESiN were investigated. According to study for various cases of PESiN lifting defect, methods to control lifting defect were defined.
Lifting defects were observed after compressive PESiN deposition which is one of the strain technologies  that tensile PESiN is applied for nMOS and compressive PESiN is for pMOS as a contact etch stop layer to improve device performance in figure 1. Lifting defects were detected in wide pattern and wafer edge region on nickel silicide by compressive stress of PESiN and low adhesion between PESiN and nickel silicide. Buffer oxide, tensile SiN and compressive stress were split to reduce lifting defect, which led to lifting defect free in the sum condition of buffer oxide 150°Ê, tensile SiN 100°Ê and 2.5GPa compressive stress in figure 2. However, since buffer layer caused degradation of stress effect, bevel etch was processed before compressive PESiN. It showed lifting defect free due to adhesion increase between PESiN and nickel silicide in figure 3. The other lifting defects were observed after processing high density plasma inter layer dielectric (HDPILD) on stopper PESiN. Hydrogen radicals were generated during HDPILD process and these hydrogen radicals could be captured between SiN and silicon, which caused lifting defect. According to split of SiN thickness, lifting defects were shown in the range of 30°Ê~40°Ê SiN thickness. In the other hands, thicker SiN than this range prevented hydrogen trapping to SiN sub and thinner SiN than this led to hydrogen passing out through SiN in figure 4. According to study of HDPILD dependency, high deposition rate without hydrogen condition showed lifting defect reduction in figure 5. Since initial HDPILD layer was thicker in high deposition rate, hydrogen trapping could be prevented more.
In this paper, lifting defects by compressive stress and hydrogen trapping were introduced. According to analysis of lifting defect mechanism, several reduction methods were investigated such as buffer layer, pre bevel etch, SiN thickness dependency, post hydrogen effect. These various methods will be helpful to solve this kind of lifting defect for manufacturability.