Process for control of the shape of the etch front in the etching of polysilicon

Claim 1

A method for recess etchback of a polysilicon-filled trench formed in a substrate, wherein the method comprises the steps of: a) providing a trench formed in a semiconductor structure, wherein said structure includes a substrate, at least one gate dielectric layer overlying a surface of said substrate, and at least one etch barrier layer overlying said gate dielectric layer; b) forming a conformal dielectric film overlying said etch barrier layer and the sidewall and bottom of said trench; c) filling said trench with a layer of polysilicon which overlies said conformal dielectric film; and d) isotropically etching said polysilicon back to a depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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 the group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof.

Claim 2

A method for recess etchback of a polysilicon-filled trench formed in a substrate, wherein the method comprises the steps of: a) providing a trench formed in a semiconductor structure, wherein said structure includes a substrate, at least one gate dielectric layer overlying a surface of said substrate, and at least one etch barrier layer overlying said gate dielectric layer; b) forming a conformal dielectric film overlying said etch barrier layer and the sidewall and bottom of said trench; c) filling said trench with a layer of polysilicon which overlies said conformal dielectric film; and d) isotropically etching said polysilicon back to a depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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 the group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof.

Claim 16

A method of forming a trench capacitor in a single-crystal silicon substrate, wherein said trench capacitor includes a dielectric collar and a buried strap, the method comprising the steps of: a) providing a trench formed in a semiconductor structure, wherein said structure includes a single-crystal silicon substrate, at least one gate dielectric layer overlying a surface of said substrate, and at least one etch barrier layer overlying said gate dielectric layer; b) forming a conformal dielectric film overlying said etch barrier layer and the sidewall and bottom of said trench; c) filling said trench with a layer of polysilicon which overlies said conformal dielectric film; d) isotropically etching said polysilicon back to a first depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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 the group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof; e) forming a collar comprising a conformal layer of silicon oxide over said etch barrier layer, the sidewall of said trench, and the portion of said polysilicon which was exposed during the etching step (d); f) anisotropically etching said silicon oxide collar to expose said underlying polysilicon; g) refilling said trench with polysilicon; h) isotropically etching said polysilicon back to a second depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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; i) performing a wet etch step to remove the upper part of said silicon oxide collar to a third predetermined depth; j) refilling said trench with polysilicon; and k) isotropically etching said trench to remove said polysilicon to a fourth predetermined depth within said trench and to remove a portion of said single-crystal silicon substrate from the top portion of said sidewall above said silicon oxide collar, thereby forming a buried strap.

Claim 17

A method of forming a trench capacitor in a single-crystal silicon substrate, wherein said trench capacitor includes a dielectric collar and a buried strap, the method comprising the steps of: a) providing a trench formed in a semiconductor structure, wherein said structure includes a single-crystal silicon substrate, at least one gate dielectric layer overlying a surface of said substrate, and at least one etch barrier layer overlying said gate dielectric layer; b) forming a conformal dielectric film overlying said etch barrier layer and the sidewall and bottom of said trench; c) filling said trench with a layer of polysilicon which overlies said conformal dielectric film; d) isotropically etching said polysilicon back to a first depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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 the group consisting of a bromine-comprising gas, a chlorine-comprising gas, an iodine-comprising gas, or a combination thereof; e) forming a collar comprising a conformal layer of silicon oxide over said etch barrier layer, the sidewall of said trench, and the portion of said polysilicon which was exposed during the etching step (d); f) anisotropically etching said silicon oxide collar to expose said underlying polysilicon; g) refilling said trench with polysilicon; h) isotropically etching said polysilicon back to a second depth within said trench using a plasma produced from a plasma source gas comprising a reactive species which selectively etches polysilicon, wherein said 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; i) performing a wet etch step to remove the upper part of said silicon oxide collar to a third predetermined depth; j) refilling said trench with polysilicon; and k) isotropically etching said trench to remove said polysilicon to a fourth predetermined depth within said trench and to remove a portion of said single-crystal silicon substrate from the top portion of said sidewall above said silicon oxide collar, thereby forming a buried strap.