Plasma damage effects on low-fr porous organosilicate glass

摘要

Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si-(CH_3)_x bonds. It was found that both charged-particle bombardment and radiation from the ECR plasma damage these bonds. Ellipsometric measurements showed that both the dielectric thickness and the dielectric constant changed during plasma exposure. In addition, both plasma-induced swelling and UV-exposure shrinking effects were observed. The plasma-induced swelling occurs at the surface of the dielectric without changing the porosity of the dielectric, while UV-induced shrinking changes the porosity significantly.