HF etching mechanisms of advanced low-k films

Scaling of the Cu interconnect structures requires low-k materials which also have an adequate Young´s modulus (e.g. E > 6 GPa) and good chemical resistance. This last characteristic can be determined through HF wet etching tests. In this paper, different types of low-k films (k-value range: 2.0-2.3; E range: 2 - 9 GPa) were immersed in a 0.5 volume % HF solution. The HF etching behaviour proved to be very dependent on the wetting properties of the film: even with lower Si-CH₃ content, the film with highest water contact angle (i.e. most hydrophobic surface) was the most resistant against the HF etching.