Self-aligned contact etch with high sensitivity to nitride shoulder

A method for etching a substrate, comprising the steps of:

• positioning in a chamber a structure comprising a first layer disposed on a substrate, the first layer being selected from the group consisting of dielectric layers and semiconductor layers;
• supplying a reactive gas mixture to the chamber, the gas mixture comprising a first gas having the formula CaFb and a second gas having the formula CxHyFz, wherein a/b≧⅔ and x/z≧½, and wherein a, b, x, y, and z are all greater than 0;
• applying sufficient RF energy to the chamber to establish an etching plasma and an associated electric field perpendicular to the surface of the substrate;
• applying a magnetic field to the chamber substantially perpendicular to the electric field and substantially parallel to the surface of the substrate;
• and
• allowing the plasma to etch at least a portion of the first layer.

A method for etching a substrate, comprising the steps of:

• providing a substrate selected from the group consisting of semiconductor and dielectric substrates;
• and
• etching the substrate through a magnetically enhanced reactive ion etch process, the process including the addition of a source of hydrogen radicals to a gas mixture in an amount sufficient to increase the value of at least one parameter selected from the group consisting of etch rate and selectivity of the reactive gas mixture for the substrate;
• wherein the gas mixture comprises a first gas having the formula CaFb and a second gas having the formula CxHyFz, and wherein a/b≧⅔ and x/z≧½, and wherein a, b, x, y, and z are all greater than 0.

A method for etching a substrate, comprising the steps of:

• providing a substrate selected from the group consisting of semiconductor and dielectric substrates;
• etching the substrate through the use of a plasma based on a gaseous mixture comprising C4F6, O2, and Ar, thereby forming a modified substrate;
• and
• further etching the modified substrate through the use of a plasma based on a gaseous mixture comprising C4F6, O2, Ar, and C2H2F4.

A method for etching a substrate, comprising the steps of:

• providing a substrate comprising (a) a first layer comprising a doped oxide, and (b) a second layer, comprising an undoped oxide;
• etching the substrate through the use of a plasma based on a first gaseous mixture comprising C4F6, O2 and Ar so as to form a depression that extends at least partially through the second layer, but does not extend substantially into the first layer, thereby forming a modified substrate;
• and
• etching the modified substrate through the use of a plasma based on a second gaseous mixture comprising C4F6, O2, C2H2F4, and Ar so as to extend the depression substantially into the first layer.

An article, comprising:

• a substrate;
• first and second gate structures disposed on said substrate, said first and second gate structures being separated by a gap of less than about 0.25 microns;
• a layer of silicon nitride disposed over said gate structures and said gap;
• a layer of doped oxide disposed over said layer of silicon nitride;
• and
• a layer of undoped oxide disposed over said layer of doped oxide.