Technique to deposit sidewall passivation for high aspect ratio cylinder etch

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

• (a) generating a first plasma comprising an etching reactant, exposing the substrate to the first plasma, and partially etching the feature in the substrate;
• (b) after (a), depositing a protective film on sidewalls of the feature, wherein the protective film is deposited as a self-assembled monolayer film that is substantially free of silicon;
• (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,
• wherein the dielectric material is provided in a stack comprising one or more layers of a first material and one or more layers of a second material, and wherein a precursor used to form the protective film reacts with the first material at a first surface density and reacts with the second material at a second surface density, the first surface density being at least twice the second surface density such that the protective film preferentially forms on sidewalls of the one or more layers of the first material compared with sidewalls of the one or more layers of the second material.

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

• one or more reaction chambers, wherein at least one reaction chamber is configured to perform etching, and wherein at least one reaction chamber is 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 configured to cause:
• (a) generating a first plasma comprising an etching reactant, exposing the substrate to the first plasma, and partially etching the feature in the substrate;
• (b) after (a), pre-treating the substrate to form activated surface groups on sidewalls of the feature;
• (c) after (b) begins, depositing a protective film on sidewalls of the feature, wherein the protective film is deposited as a self-assembled monolayer film;
• and
• (d) repeating (a)-(c) until the feature is etched to a final depth, wherein the protective film deposited in (c) 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.

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

• one or more reaction chambers, wherein at least one reaction chamber is configured to perform etching, and wherein at least one reaction chamber is 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 configured to cause:
• (a) generating a first plasma comprising an etching reactant, exposing the substrate to the first plasma, and partially etching the feature in the substrate;
• (b) after (a), depositing a protective film on sidewalls of the feature, wherein the protective film is deposited as a self-assembled monolayer film that is substantially free of silicon;
• (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,
• wherein the dielectric material is provided in a stack comprising one or more layers of a first material and one or more layers of a second material, and wherein a precursor used to form the protective film reacts with the first material at a first surface density and reacts with the second material at a second surface density, the first surface density being at least twice the second surface density such that the protective film preferentially forms on sidewalls of the one or more layers of the first material compared with sidewalls of the one or more layers of the second material.