INSPECTING METHOD OF INSULATOR FILM

PURPOSE:To reject a product having a secular deterioration of insulator thin film in the initial stage after its manufacture and improve the reliability of products by measuring temperature dependency at a prescribed voltage and calculating a temperature coefficient. CONSTITUTION:A thermochuck is set at a prescribed temperature, and then a polysilicone electrode 3-3' on the insulator film 2 of silicon dioxide is applied with a voltage such a polarity that an electric field is applied forward to a semiconductor element substrate 1 and a voltmeter 7 measures the voltage of the film 2 at a rated current value. The temperature of the thermochuck 4 is varied and reaches to a prescribed temperature, and the voltage of the film 2 is measured similarly. The temperature dependency of the dielectric strength is calculated on the basis of the measured voltages at the respective temperatures. The secular deterioration is larger and larger as the coefficient of the temperature dependency larger and larger, and the secular deterioration is estimated, thereby removing a secular deteriorating product in its initial stage.