Method for ion-assisted self-limited conformal etch

A method for forming a semiconductor device, the method comprising:

• providing a substrate having a patterned film stack including alternating first and second films that are vertically stacked, wherein the first films have a first outer dimension, wherein the second films have a second outer dimension, wherein the second films have indentations so that the second outer dimension of the second films is smaller than the first outer dimension of the first films, wherein a spacer layer is conformally deposited over the patterned film stack and within the indentations in the second films, and wherein the spacer layer comprises a silicon-carbon-containing material, a silicon-nitrogen-containing material, a silicon-oxygen-containing material, or a silicon-carbon-oxygen-containing material;
• reacting a surface of the spacer layer with a plasma-excited first etch gas to form a reacted layer on the spacer layer, wherein the plasma-excited first etch gas includes fluorine, hydrogen, and nitrogen, wherein the reacted layer comprises ammonium fluorosilicate (AFS);
• removing at least part of the reacted layer by ion bombardment from exposure to a plasma-excited second etch gas;
• and
• sequentially repeating the reacting of the surface of the spacer layer and the removing of at least part of the reacted layer at least once to expose side surfaces of the first films while retaining at least part of the spacer layer in the indentations of the second films.

A method for forming a semiconductor device, the method comprising:

• providing a substrate having a patterned film stack including alternating first and second films that are vertically stacked, wherein the first films have a first outer dimension, wherein the second films have a second outer dimension, wherein the second films have indentations so that the second outer dimension of the second films is smaller than the first outer dimension of the first films, wherein a spacer layer is conformally deposited over the patterned film stack and within the indentations in the second films, and wherein the spacer layer comprising SiOCN;
• reacting a surface of the spacer layer with a plasma-excited first etch gas to form a reacted layer on the spacer layer, wherein the plasma-excited first etch gas includes fluorine, hydrogen, and nitrogen, wherein the reacted layer comprises ammonium fluorosilicate (AFS);
• removing at least part of the reacted layer by ion bombardment from exposure to a plasma-excited second etch gas;
• and
• sequentially repeating the reacting of the surface of the spacer layer and the removing of at least part of the reacted layer at least once to expose side surfaces of the first films while retaining at least part of the spacer layer in the indentations of the second films, wherein the reacting of the surface of the spacer layer and the removing at least part of the reacted layer are performed in a same chamber of a same plasma processing system using isotropic plasma exposures, wherein the reacting of the surface of the spacer layer and the removing at least part of the reacted layer are performed within a same substrate temperature range from 8 to 28 degrees Celsius.