Technique to deposit sidewall passivation for high aspect ratio cylinder etch

A method of forming an etched feature in dielectric material on a semiconductor substrate, the method comprising:

• (a) generating an etching plasma comprising an etching reactant, exposing the substrate to the etching plasma, and partially etching the feature in the dielectric material, wherein the substrate comprises a mask layer;
• (b) after (a), depositing a protective film on sidewalls of the feature, wherein the protective film is deposited along substantially the entire depth of the feature, and wherein the mask layer is substantially preserved during (b), wherein depositing the protective film comprises the following steps performed in a cyclic manner:
• (i) flowing a first deposition reactant into a reaction chamber and allowing the first deposition reactant to adsorb onto the substrate surface, wherein the first deposition reactant is a silicon-containing reactant;
• and
• (ii) flowing a second deposition reactant into the reaction chamber, wherein the first and second deposition reactants react to form the protective film;
• and
• (c) repeating (a)-(b) until the feature is etched to a final depth, wherein the protective film deposited in (b) substantially prevents lateral etch of the feature during (a), and wherein the feature has an aspect ratio of about 5 or greater at its final depth.

A method of depositing a silicon-containing film on a substrate, the method comprising:

• (a) flowing a first reactant into a reaction chamber and exposing the substrate to plasma comprising the first reactant, wherein the first reactant comprises a silicon-containing reactant;
• (b) flowing a second reactant into the reaction chamber and exposing the substrate to plasma comprising the second reactant, wherein the second reactant comprises carbonyl sulfide (COS);
• (c) reacting the first and second reactant to thereby deposit the silicon-containing film on the substrate,
• wherein during (a)-(c), a composition of the plasma changes over time such that during a first stage during (a) the plasma comprises the first reactant but not the second reactant, during a second stage the plasma comprises inert gas and neither the first nor second reactant, and during a third stage during (b) the plasma comprises the second reactant but not the first reactant,
• wherein the first, second, and third stages occur in that order;
• and
• (d) cyclically repeating the first, second, and third stages until the silicon-containing film reaches a final thickness.

An apparatus for forming an etched feature in dielectric material on a semiconductor substrate, the apparatus comprising:

• one or more reaction chambers, wherein at least one reaction chamber is designed or configured to perform etching, and wherein at least one reaction chamber is designed or configured to perform deposition, each reaction chamber comprising:
• an inlet for introducing process gases to the reaction chamber,
• an outlet for removing material from the reaction chamber, and
• a plasma source;
• and
• a controller having instructions for:
• (a) generating a first plasma comprising an etching reactant, exposing the substrate to the first plasma, and partially etching the feature in the dielectric material, wherein (a) is performed in the reaction chamber designed or configured to perform etching;
• (b) after (a), depositing a protective film on sidewalls of the feature, wherein the protective film is deposited along substantially the entire depth of the feature, wherein (b) occurs while substantially preserving a mask layer on the substrate, wherein (b) is performed in the reaction chamber designed or configured to perform deposition, and wherein depositing the protective film comprises:
• (i) flowing a first deposition reactant into the reaction chamber designed or configured to perform deposition, generating a deposition plasma comprising the first deposition reactant, and exposing the substrate to the deposition plasma, wherein the first deposition reactant is a silicon-containing reactant,
• (ii) ceasing the flow of the first deposition reactant,
• (iii) flowing a second deposition reactant into the reaction chamber designed or configured to perform deposition and generating or maintaining the deposition plasma to thereby drive a surface reaction between the first and second deposition reactants to form the protective film, the deposition plasma in (iii) comprising the second deposition reactant, wherein a composition of the deposition plasma changes over the course of (i)-(iii),
• (iv) ceasing the flow of the second deposition reactant, and
• (v) repeating (i)-(iv) until the protective film reaches a final thickness;
• and
• (c) repeating (a)-(b) until the feature is etched to a final depth, wherein the protective film deposited in (b) substantially prevents lateral etch of the feature during (a), and wherein the feature has an aspect ratio of about 5 or greater at its final depth.