layer 214 the first photoresist layer 216 has a trench opening 217 by using conventional lithographic technology then the first bottom anti reflective coating barc layer 214 is etch by using the first photoresist layer 216 as a mask referring to fig2 b the first hardmask layer 212 has a trench opening 217 a by using conventional lithographic technology then the second cap layer 210 is etch by using the first hardmask layer 212 as a mask then the trench opening 217 a is formed by anisotropically etching method a first photoresist layer 216 is then removed then the bottom anti reflective coating barc layer 214 is also removed at the same time referring to fig2 c a dielectric layer 218 is formed on the second dielectric layer 208 and filled in the trench opening 217 a by spin on the dielectric layer 218 is a low k dielectric material a second hardmask layer 220 is formed over the silk layer 218 the second hardmask layer 220 comprises tin then a second bottom anti reflective coating barc layer 222 is formed on the second hardmask layer 220 a second photoresist layer 224 is deposited on the second bottom anti reflective coating barc layer 222 the second photoresist layer 224 has a via opening 225 a by using conventional lithographic technology then the bottom anti reflective coating barc layer 222 the second hardmask layer 220 the dielectric layer 218 the second dielectric layer 208 and the first dielectric layer 206 are.