CO2/CO Plasma Ashing for Dielectric Sidewall Roughness Control
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Solution Overview
Problem
Conventional ashing processes using oxygen plasma often damage dielectric layers and worsen feature roughness during the removal of mask layers in semiconductor fabrication, particularly affecting low-k dielectric films and leading to pitting and increased dielectric constant.
Innovation Solution
A method involving a plasma processing system that uses a combination of CO2 and CO process gases, where the flow rate of CO relative to CO2 is selectively controlled to minimize damage and improve profile control, reducing sidewall roughness and pitting while maintaining critical dimension integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen plasma is used for ashing to remove mask layers, then the mask layer removal efficiency is improved, but the dielectric layer is damaged and feature roughness increases
Solution Approach 1:
The patent changes the chemical composition parameters of the plasma gas from conventional oxygen (O2) to a carbon dioxide (CO2) and carbon monoxide (CO) mixture. This parameter change fundamentally alters the plasma chemistry to reduce damage to dielectric layers while maintaining effective mask layer removal, directly resolving the technical contradiction between removal efficiency and damage prevention
Solution Approach 2:
The patent employs a composite gas mixture of CO2 and CO instead of a single oxygen gas. This composite approach creates a plasma environment that combines the benefits of both gases: CO2 provides effective oxidation for mask removal while CO acts as a reducing agent that minimizes damage to dielectric materials, thereby solving the contradiction between removal efficiency and damage control
2Speed
If conventional ashing processes are used, then the processing speed is maintained, but sidewall roughness and pitting increase
Solution Approach 1:
By changing the gas composition from oxygen to CO2/CO mixture, the patent modifies the plasma reaction kinetics and byproducts. This parameter change enables faster processing speeds while simultaneously improving sidewall roughness and profile control, as the CO component reduces etch byproducts that cause pitting and roughness
Solution Approach 2:
The patent converts the typically harmful carbon-containing plasma byproducts into beneficial effects. The CO component in the plasma acts as a reducing agent that removes carbon deposits from sidewalls, preventing pitting and roughness while maintaining high processing speed, thus turning a potential harm into a benefit
3Device complexity
If oxygen plasma is used for mask removal, then the etch chemistry is simple, but the critical dimension uniformity deteriorates
Solution Approach 1:
The patent uses a composite CO2/CO gas mixture that creates a more complex but controllable plasma chemistry. This composite approach provides multiple reaction pathways that improve critical dimension uniformity by reducing sidewall damage and pitting, while the process complexity remains manageable through established plasma processing equipment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The CO2/CO ashing process effectively reduces sidewall damage, pitting, and profile bowing, improving profile control and critical dimension uniformity, thereby enhancing the integrity of dielectric layers and reducing feature roughness.
Implementation Method 1
A process gas comprising CO2 and CO is introduced into the plasma processing system, and plasma is formed
Data Source
AI summary
A method for removing a mask layer and reducing damage to a patterned dielectric layer is described. The method comprises disposing a substrate in a plasma processing system, wherein the substrate has a dielectric layer formed thereon and a mask layer overlying the dielectric layer. A pattern is formed in the mask layer and a feature formed in the dielectric layer corresponding to the pattern as a result of an etching process used to transfer the pattern in the mask layer to the dielectric layer. The feature includes a sidewall with a first roughness resulting from the etching process. A process gas comprising CO2 and CO is introduced into the plasma processing system, and plasma is formed. The mask layer is removed, and a second roughness, less than the first roughness, is produced by selecting a flow rate of the CO relative to a flow rate of the CO2.