method of changing the composition ratio of si to n in the above nitride film the flow of sih 4 is made constant and the total flow of nh 3 and n 2 is gradually decreased with the flow ratio of nh 3 to n 2 being kept 1 5 although in the above described embodiment the graded layer has a multilayer deposited structure the content of nitrogen n in the graded layer may be continuously changed by continuously changing the flow ratio of nh 3 to n 2 an embodiment in which the present invention is applied to a multilayer structure of a static ram will be described with reference to fig5 fig5 is a cross sectional view showing a static ram as shown in fig5 a source electrode 23 and a drain electrode 24 are formed on the surface of a p type silicon si substrate 21 using a poly si gate 22 as a mask by self alignment and a sio 2 insulator film 25 is formed so as to surround the poly si gate 22 a first graded layer 26 having an oxygen density sequentially decreased in the direction of the thickness is formed on the insulator film 25 and a poly si resistor 27 is formed thereon a sio 2 insulator film 29 is formed on the poly si resister 27 through a second graded layer 28 having an oxygen density sequentially increased in the direction of the thickness a line 30 made of al is formed on the insulator film 29.