A novel process for narrow, ca. 100 nm wide, airgap formation based on chemical selectivity is presented. First, chemically modified sites are induced at the Ta(N)/SiC interface during patterning operations. Then, the SiO 2 material lying between copper lines is locally removed by vapor HF exposure, leading to air cavity formation between closely packed interconnects. Based on simulations this sidewall airgap concept has a promising potential for very narrow interline dielectrics in future interconnect generations.