also the polycrystalline silicon deposition is carried out at a temperature in the range of 350 u02dc 450 u00b0 c under pressure below 5 mtorr the polycrystalline silicon is plasma processed so as to remove the hydrogen h and carbon c the plasma process is carried out with any of he ar and ne gas as the plasma gas after removing the hydrogen and carbon the polycrystalline silicon is oxidized using n 2 o or o 2 gas as shown in fig2 c a second a third and a fourth polysilicon layers 132 133 and 134 are sequentially deposited until the spaces between the adjacent metal wirings are completely filled so as to form an inter metal dielectric 130 having plural polysilicon layer 131 132 133 and 134 each of the second third and fourth polysilicon layers 132 133 and 134 are formed in the same manner for forming the first polysilicon layer 131 in this embodiment the polysilicon layer is formed with four polysilicon layers 131 132 133 and 134 however the number of polysilicon layers can be changed according to the pitches of and widths between the metal wirings in case of forming the inter metal dielectric 130 by repeatedly depositing multiple thin layers unlike the conventional one which is formed thickly at a time the stepped coating degree is improved even when.