Experimentally, it is found out that the fixed positive charge density in LPCVD Si-nitride is very high, which can induce an inversion layer at the emitter surface of MIS/IL solar cell. The lower the temperature for depositing Si-nitride with LPCVD the higher the fixed positive charges will be. In order to realize charge storage in Si-nitride the negative pulse voltage height must be high enough to make the field intensity in Si-nitride reach 3-4 multiplied by 10**6 V/cm, and the pulse duration is only about 10 seconds. Due to the charge storage effect in Si-nitride the peak ramp voltage with high frequency C-V method to evaluate the fixed positive charges in Si-nitride should be chosen suitably, otherwise, false results about the fixed positive charges may be derived from the C-V measurement.