| abstract |
The present disclosure pertains to our discovery that the use of a particular combination of etchant gases results in the formation of a substantially flat etch front for polysilicon etching applications. In general, the process of the invention is useful for controlling the shape of the etch front during the etchback of polysilicon. Typically, the process comprises isotropically etching the polysilicon using a plasma produced from a plasma source gas comprising a particular combination of reactive species which selectively etch polysilicon. The plasma source gas comprises from about 80 % to about 95 % by volume of a fluorine-comprising gas, and from about 5 % to about 20 % by volume of an additive gas selected from a group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof. A preferred method of the invention, used to perform recess etchback of a polysilicon-filled trench in a substrate, comprises the following steps: a) providing a trench formed in a semiconductor structure, wherein the structure includes a substrate, at least one gate dielectric layer overlying a surface of the substrate, and at least one etch barrier layer overlying the gate dielectric layer; b) forming a conformal dielectric film overlying the etch barrier layer and the sidewall and bottom of the trench; c) filling the trench with a layer of polysilicon which overlies the conformal dielectric film; and d) isotropically etching the polysilicon back to a predetermined depth within the trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein the plasma source gas comprises from about 80 % to about 95 % by volume of a fluorine-comprising gas, and from about 5 % to about 20 % by volume of an additive gas selected from a group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof. Also disclosed herein is a method of forming a trench capacitor in a single-crystal silicon substrate, the trench capacitor including a dielectric collar and a buried strap. |