a semiconductor device and a method of manufacturing the same according to the first embodiment of the present invention will be described with reference to the accompanying drawings . [ 0032 ] fig2 a to 2 k show a process of manufacturing a semiconductor device according to the present invention in the order of its steps . first , as shown in fig2 a , an sio 2 insulating film 6 is formed on a silicon substrate 4 with a device element to a thickness of 500 nm by plasma cvd . subsequently , a photoresist 8 is applied to the sio 2 insulating film 6 , and a trench interconnection pattern is formed by photolithography . as shown in fig2 b , the insulating film 6 is etched by dry etching to form a trench , and the photoresist 8 is removed by o 2 dry ashing and wet etching . after that , ta 10 is formed as a barrier metal to a thickness of 50 nm , and a cu film is formed by sputtering to a thickness of 100 nm as a seed layer for cu plating on the entire surface of the silicon substrate 4 ( see fig2 c ). the trench is filled with cu 14 by electrolytic plating , and cu is annealed at 400 ° c . then , as shown in fig2 d , the cu 14 and barrier metal 10 on the insulating film 6 are removed by cmp , thus forming the cu interconnection 12 . as shown in fig2 e , by using a single - wafer type parallel - plate cvd apparatus , a diffusion preventive insulating layer sin as a first insulating film 16 is formed to a thickness of 20 nm by low - temperature film formation with a film formation temperature of 300 ° c , an sih 4 flow rate of 50 sccm , an nh 3 flow rate of 30 sccm , an n 2 flow rate of 2 , 000 sccm , a film formation pressure of 4 torr , and an rf power of 400 w . after that , by using another film formation chamber , a diffusion preventive insulating layer sin as a second insulating film 18 is formed to a thickness of 30 nm by high - temperature film formation with a film formation temperature of 400 ° c ., an sih 4 flow rate of 50 sccm , an nh 3 flow rate of 30 sccm , an n 2 flow rate of 2 , 000 sccm , a film formation pressure of 4 torr , and an rf power of 400 w . as shown in fig2 f , a 500 - nm thick sio 2 film is formed as an insulating film 20 by plasma cvd . the first and second insulating films 16 and 18 and the insulating film 20 make up the interlevel insulating film . how to form a via hole in the interlevel insulating film comprised of the insulating film 20 and the like will be described . as shown in fig2 g , a pattern for forming a via hole is formed with a photoresist 22 by photolithography , and the sio 2 film as the insulating film 20 is etched by dry etching using c 4 f 8 , ar , and o 2 ( see fig2 h ). in this case , the etching conditions are determined such that the etching selectivity of the cu diffusion preventive insulating film of the insulating film 20 to that of the second insulating film 18 is 10 or more , so the cu diffusion preventive insulating film of the second insulating film 18 serves as the etching stop layer when etching the insulating film 20 . as shown in fig2 i , the photoresist 22 is removed by o 2 ashing and resist peeling technique using a wet etchant . at this time , oxidation and etching of the first and second insulating films 16 and 18 , which occur when the surface of a cu interconnection 12 is exposed to an o 2 plasma and the like , are prevented . as shown in fig2 j , the cu diffusion preventive insulating layer comprised of the first and second insulating layers 16 and 18 is etched by dry etching using c 4 f 8 and ar , to form a via hole 30 . as shown in fig2 k , a tin film 11 is formed to a thickness of 50 nm , and thereafter a w ( tungsten ) film 32 is formed to a thickness of 700 nm . the w film 32 fills the via hole 30 , and the excessive w film 32 and tin film 11 on the interlevel insulating film 20 are removed by cmp , thus forming a via contact with respect to the cu interconnection 12 . in the above case , sin is used to form the diffusion preventive insulating layer comprised of the first and second insulating films 16 and 18 . alternatively , an insulating film such as a sic , sicn , or organic film which does not react with cu and thus serves to prevent diffusion of cu may be employed . to form the insulating film 20 , sio 2 is used . alternatively , an insulating layer , e . g ., a porous silica , organic , hsq , or msq film , with a lower relative dielectric constant than that of sio 2 may be used . in the second embodiment of the present invention , a cu interconnection 12 is formed in accordance with the same method as that of the first embodiment . subsequently , by using a parallel - plate cvd apparatus , a plasma pre - process is performed with a process temperature of 300 ° c ., an n 2 flow rate of 500 sccm , an nh 3 flow rate of 500 sccm , a pressure of 4 torr , and an rf power of 200 w in order to reduce the oxide layer on the cu surface . after that , a diffusion preventive insulating layer sin as a first insulating film 16 is formed to a thickness of 20 nm with the same conditions as those of the first embodiment . subsequently , by using another cvd apparatus , a diffusion preventive insulating layer sic as a second insulating film 18 is formed to a thickness of 30 nm with a film formation temperature of 400 ° c . an sio 2 layer is formed to a thickness of 500 nm by the parallel - plate plasma cvd apparatus , and an insulating film 20 is formed on the cu interconnection 12 . in this case , the pre - process for reducing the cu oxide layer is performed at 300 ° c . it suffices as far as aggregation of cu is suppressed at less than 300 ° c . although a plasma pre - process is performed , annealing in a reducing gas atmosphere of nh 3 or h 2 may be performed instead . although n 2 and nh 3 are used as gases for the pre - process , a single - gas atmosphere of h 2 or nh 3 , or a gas mixture atmosphere of n 2 , h 2 and nh 3 may be used instead . the gas type is not particularly specified as far as it can reduce the oxide layer on the cu surface . a process chamber for performing the plasma pre - process may be provided independently of the sin film formation chamber . in the above embodiments , sin is used to form the cu diffusion preventive insulating layer of the first insulating film 16 , and sic is used to form the cu diffusion preventive insulating layer of the second insulating film 18 . alternatively , an sicn , organic , or sion film may be used as each insulating film . the diffusion preventive layers formed of the first and second insulating films 16 and 18 need not have the same film composition , and are not particularly specified as far as they have an etching selectivity of a predetermined value or more with respect to the insulating film 20 . in the above embodiments , a cu diffusion preventive insulating layer with a double - layer structure is formed . alternatively , a multilayered structure of three or more layers - may be employed . the present invention is not particularly specified in this respect as well . as the manufacturing apparatus , the cvd apparatus is used to form the first insulating film 16 at a temperature of about 300 ° c . and the second insulating film 18 at a temperature of about 400 ° c . except for that , the arrangement of the manufacturing apparatus can be the same as that of a conventional apparatus .