Tungsten plug formation by an optimized tungsten etch back process in non-fully planarized topology

Abstract

Reliable metallizations in contacts and vias with excellent filling properties for aspect ratios 1, can be achieved with a conformal blanket CVD tungsten deposition on top of a TiN barrier layer. The subsequent tungsten etch back has been investigated using a magnetically enhanced RIE process with pure SF 6 chemistry and He backside cooling. Highly uniform etch rates of up to 600 nm/min with 30% lateral component have been achieved at high RF power (400 W) and high pressure (200 m Torr). A low microloading effect of 1.1 — which is important for low tungsten recess in the plugs - together with sufficiently high W: TiN selectivity (10) can be established by operating at low pressure (< 50 mTorr), low RF power (< 150 W), and low temperature (< 40°C). A two-step process was found to be most suitable for complete removal of residues in topology without significantly effecting the other objectives. It consists of a fast, highly isotropic bulk etch and a slower, anisotropic clearing etch with minimized microloading effect. Tungsten residues can be completely removed on topology with flow angles of up to 30°. Simultaneously, the tungsten recess can be kept to less than 200 nm and the TiN loss to less than 30 nm. This process sequence enables perfect control of both bulk and overetch by emission spectroscopy. Thus, the TiN barrier, which has been used as tungsten adhesion layer and as etchstop, can also act as a nucleation layer for the subsequent Al metallization.