Nitride etching with hydrofluorocarbons. I. Selective etching of nitride over silicon and oxide materials by gas discharge optimization and selective deposition of fluorocarbon polymer
Selective etching of silicon nitride over silicon and silicon oxide is one of the most critical processes in the fabrication of complementary metal-oxide-semiconductor devices. In a typical spacer process, the gate is electrically isolated from the source and drain region by the deposition of thin nitride. A plasma etch is employed to remove the nitride from the source/drain regions without or with minimal damage to the exposed surfaces. The authors show that the typical plasma process that enables this process is based on the oxidation rate of silicon and has many limitations when applying this process to devices of 30 nm critical dimension (CD) or lower. The authors show novel gas discharges with which nitride can be etched differently, in particular, because the etch rates are controlled by selective polymer deposition. The novel etch mechanism is explained in detail and advantages and challenges are discussed, in particular. Selected studies of the feedgas chemistry lead to optimized dissociation as evidenced by the respective etch selectivities. The authors demonstrate that the novel etch mechanism is able to reduce nitride thinning and substrate damage significantly, enabling further pitch and CD scaling of spacer etch when employing this novel chemistry C4H9F. The authors also show that because of these advantages, the novel chemistry is a very promising candidate to enlarge the process window for spacer processes of nonplanar devices.