Development of self-aligned contact technology for 0.18 μm static random access memory devices

Abstract

A self-aligned contact (SAC) technology is developed for the application of electrical contacts between the local interconnect and the silicon diffusion regions for 0.18 μm static random access memory cells. The key components of this SAC technology include the deposition and gap fill of borophosphosilicate glass (BPSG) films, a selective oxide etch process, and metal-plug contact formation by Ti/TiN-liner silicidation and W filling. The BPSG film, deposited by plasma enhanced chemical vapor deposition, has exhibited an ability of filling 0.04 μm spaces with an aspect ratio (AR) of about 10:1 after reflow at 800 °C. Reduction of the reflow temperature without gap-fill deterioration by increasing the B incorporation in the BPSG film is not feasible due to an increase of BPSG defects. The oxide SAC etch performance is modulated by an oxide-to-nitride etch selectivity which has shown a strong dependence on the wafer temperature. The etch process window is improved by optimization of the process conditions including the wafer temperature uniformity. A novel SAC etch process was demonstrated for an ∼0.2 μm SAC opening. The electrical performance of a contact with an AR as high as 10:1 has met the design requirement, which has indicated sufficient liner silicidation and an excellent W plug process. Investigation of the contact resistance dependence on the contact AR has shown a reduction in contact resistance with increasing AR. All these findings are very instructive for our development projects.