Quantitative characterization of pore stuffing and unstuffing for postporosity plasma protection of low-k materials

Abstract

The problem of k-value degradation (plasma damage) is a key issue for the integration, and it is becoming more challenging as the dielectric constant of low-k materials scales down. One way to circumvent this issue is temporarily conversion of low-k material from a porous to a dense state by filling the pores with a sacrificial polymer after the deposition and curing of the low-k material. A detailed process scheme for the pore stuffing and postetch polymer removal of PMMA is described in this work. The filling temperature was optimized according to the molecular weight of the PMMA. To remove the polymer after plasma-etching in a purely thermal environment, a temperature of at least 430 °C had to be applied. Annealing assisted by variable frequency microwaves could remove the polymer already at 380 °C and with a He–H2 afterglow plasma the polymer could be removed at 280 °C. Laser annealing allowed the removal at a stage temperature of 200 °C with an only surface-limited heating of about 500 °C and higher to prevent the FEOL structures from damage. This work presents the results of the detailed study of stuffing and unstuffing processes, discusses mechanisms, and provides background for a robust stuffing and polymer removal process for the plasma damage reduction in porous low-k dielectrics.