The Effect of Substrate Bias on the Properties of Reactively Sputtered Silicon Nitride

Abstract

FLATBAND VOLTAGES OF MOS CAPACITORS 303hr and fields up to 6 • 106 V/cm. For a 15 min bias stress of 106 V/cm. no flatband voltage shifts could be detected except for the sample corresponding to 105 cma/min of TCE/He, in which a positive shift of 0.55V was observed. It would be consistent with the initial flatband measurements if this shift were due to the motion of mobile charge acquired in the sample oxidized with the high TCE/He flow rate. The ions H + or H30 + which are mobile at room temperature (7) are possible candidates. The actual role and fate of the hYdrogen contained in the TCE has not been established.Van der Meulen et aI. (4) have indicated that some sodium may be mobile at room temperature. For extremely high fields (6 • 106 V/cm) and negative gate bias, the samples oxidized with 105 craB/rain of TCE/He exhibited a transient flatband instability similar to that observed by Van der Meulen et al. (4) for C12-grown oxides, although the instability was less pronounced. The flatband voltage first shifted in the positive direction and then for long times (on the order of 10 hr) shifted slightly in the negative direction, the flatband voltage never changing sign, however. A positive bias stress of 106 V/cm inhibited this negative bias instability completely. At field strengths normally encountered in device operation, the oxides were more stable.Next the effects of positive bias stress were investigated. The resulting shift in flatband voltage is shown in Fig sites for electrons in the oxide will not account for this behavior. A flatband shift of 0.062V corresponds to a mobile charge density of about 5 • 109 charges/cm a.For higher flow rates of TCE/He the flatband shift increases. At a concentration of 105 cm~/min of TCE/ He, not shown in Fig. 2, the shift was about 2.5V (corresponding to a mobile charge concentration of 2.85 • 10n/cm2), and substantial hysteresis appears in the C-V characteristics. Figure 2 shows the recovery of this shift with time and the observed hysteresis.(No hysteresis was observed for samples oxidized with low concentrations of TCE.) The dramatic increase in VFB and AVFB implies high concentrations of mobile oxide charges or donor-like oxide traps, either of which could also cause the observed hysteresis.In summary we have shown that TCE can be effectively used to lower oxide charge mobile at room temperature (mostly H + or HsO + and perhaps some alkali ions) to values as small as 5 • 109/cm ~. Because of ease of handling, TCE may be a good substitute for HC1 in growing high quality oxides. For extremely high fields (larger than those normally encountered in device operation) the TCE-grown oxides exhibited a room-temperature instability similar to that observed in C12-grown oxides. For high quality oxides there is an optimum flow rate of TCE during oxidation of about 4-5%. Above this point, the introduction of additional positive mobile charge or donor-like traps in the oxide degrade the C-V characteristics. The incidence of low frequency behavior for large TCE flow rates indic...

Low Dielectric Constant Materials

“…Radio frequency (RF) bias sputtering of silica, which when done properly produces almost stoichimetric SiO 2 films with little SiOH, is quite slow and prone to particulate contamination. − Other sputtering techniques such as reactive sputtering, dual-ion sputtering, deposition by etching-enhanced reactive sputtering, etc. have been described but are not in common use in the BEOL for similar reasons as described above.…”