SiO2 films deposited on silicon at low temperature by plasma-enhanced decomposition of hexamethyldisilazane: Defect characterization

Silicon dioxide films have been deposited by plasma-enhanced chemical vapor deposition at low substrate temperature (50 degreesC) in a parallel-plate reactor using hexamethyldisilazane (HMDS), diluted in He, and O-2 as Si and O precursors. The effect of the O-2/(HMDS+He) flow rate ratio on the oxide properties has been investigated in the range of 0.05-1.25 by means of dep osition rate, wet etching rate, secondary ion mass spectrometry, thermally stimulated luminescence, and high frequency capacitance-voltage measurement s. Both the deposition rate and the etching rate increase by increasing the O-2/(HMDS+He) flow rate ratio and reach a constant value at flow rate rati os higher than 0.6. The strong increase and saturation in the deposition ra te can be attributed to the impinging oxide atoms flux and to the consumpti on of silyl radicals at the deposition surface, respectively. The Si/SiO2 i nterface state density and the positive fixed charge density are in the ran ge 1X10(11)-1X10(12)eV(-1)cm(-2) and 6X10(11)-1.5X10(12)Ccm(-2), respective ly. These concentrations are comparable with literature data concerning SiO 2 films obtained by plasma enhanced chemical vapor deposition at temperatur es higher than 200 degreesC using other Si precursors. Moreover, the interf ace state density decreases while the fixed oxide charge increases by incre asing the O-2/(HMDS+He) flow rate ratio. A correlation has been found betwe en defects monitored by thermally stimulated luminescence and fixed oxide c harges. From a comparison with secondary ion mass spectrometry results, the fixed oxide charges can be preliminarily attributed to intrinsic defects. (C) 2001 American Vacuum Society.