REDUCTION OF CHARGE INJECTION INTO PECVD SINXHY BY CONTROL OF DEPOSITION CHEMISTRY

The high rate of charge trapping in thin-film silicon nitride causes its electrical properties to change with stressing level and time. The rate of shift of the high-frequency CV curves of Al/SiNxHy/cSi capacitors was used here to measure nitride charging rate and to compare PECVD nitrides deposited under various conditions of plasma power and gas mixture in the same parallel-plate reactor. By operating the plasma under high power to activate the NH3 or N2 and under low SiH4 flow to ensure that all of the SiH4 reacts with N, it is possible to deposit N-rich nitride that has no detectable Si-H bonding, which bonding others have correlated with charge trapping. Nitride deposited under these conditions using NH3 and 13 MHz rf power had charging rates for both gate polarities that were 20 times lower than those of nitride that had a "stoichiometric" N/Si ratio of 4/3 and that had its H distributed among Si-H and N-H bonds. MIS capacitors made with the latter nitride also had a high negative initial flat-bond voltage, indicating the presence of grown-in positive charge. This charge was large enough to invert the surface of p-Si substrates. N-rich nitride free of Si-H that was deposited either using N2 or using low-frequency rf power (≤400 kHz) had higher charging rates than did that deposited from NH3 at 13 MHz. Also, the low-frequency material contained grown-in positive charge that is attributed to H+ implanted by the high ion bombardment energy of the low-frequency plasma. © 1990 AIME.