Minimizing CD Bias in Plasma Etching via Segmented Chemistry
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Solution Overview
Problem
Plasma etching processes for photolithographic substrates often result in critical dimension (CD) bias due to the anisotropic etching of chrome-containing films, leading to inaccuracies in replicating the initial mask image, which is exacerbated by the presence of oxygen in Cl2/O2 chemistries and the inefficiencies of polymer-based passivants.
Innovation Solution
A method that involves depositing a passivation film using specific process conditions, followed by a breakthrough step to clear passivation from horizontal surfaces, and then performing an anisotropic etch to minimize CD bias, with the process conditions optimized to maintain etch efficiency and passivation benefits by separating etch and passivation steps in time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If oxygen is added to Cl2-based etch chemistry to improve anisotropy, then etch anisotropy is improved, but photoresist lateral etching increases and CD bias worsens
Solution Approach 1:
The etch process is divided into multiple sequential steps with different gas chemistries: a first etch step using Cl2-based chemistry for initial material removal, followed by a second etch step using CF4-based chemistry for precise profile definition. This segmentation allows each step to optimize for its specific function, preventing the CD bias that would result from using oxygen-containing chemistry throughout the entire process.
Solution Approach 2:
The patent employs periodic switching between different etch chemistries in a cyclical manner, alternating between Cl2-based chemistry (which provides good etch rate) and CF4-based chemistry (which provides superior anisotropy and minimal lateral etching). This periodic action allows the process to benefit from the strengths of each chemistry at appropriate stages, maintaining both anisotropy and CD accuracy.
2Reliability
If polymer-based passivants are used to protect photoresist during etching, then photoresist protection is improved, but etch efficiency decreases due to oxygen consumption
Solution Approach 1:
The process separates the protection function from the etching function by using different chemistries for each. CF4-based chemistry is used specifically for steps requiring photoresist protection, while Cl2-based chemistry is used for steps prioritizing etch rate. This segmentation eliminates the trade-off by assigning each chemistry to its optimal application.
Solution Approach 2:
The patent introduces a third chemistry (CF4-based) as an intermediary that provides the passivation function without the harmful side effect of oxygen consumption. This intermediary chemistry acts as a mediator between the conflicting requirements of photoresist protection and etch efficiency, satisfying both needs without compromise.
3Reliability
If Cl2/O2 chemistry is used for chrome etching, then etch selectivity is improved, but CD bias increases due to photoresist undercutting
Solution Approach 1:
The etch process is segmented into multiple steps with different selectivity profiles. Early steps use Cl2-based chemistry for high selectivity chrome etching, while later steps use CF4-based chemistry for precise profile definition with minimal lateral etching. This segmentation allows the process to achieve both high selectivity and CD uniformity that cannot be obtained with a single chemistry.
Solution Approach 2:
The patent changes the chemical parameters of the etch process by switching between different gas compositions. By adjusting the chemistry from oxygen-containing to fluorocarbon-based, the process dynamically changes the etch characteristics to match the requirements at each stage, achieving both selectivity and CD control through parameter optimization.
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
This approach significantly reduces CD bias, ensuring accurate replication of critical dimensions by compensating for expected CD losses during the etching process, thereby improving the overall critical dimension performance and feature uniformity.
Implementation Method 1
depositing a passivation film on the photolithographic substrate in a plasma process
Implementation Method 2
etching the deposited film from the photolithographic substrate and etching an exposed surface of the photolithographic substrate
Data Source
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AI summary
The present invention provides a method for improving the critical dimension performance during a plasma etching process of a photolithographic substrate having a thin film. A passivation film is deposited onto the photolithographic substrate using a first set of process conditions. The deposited film is etched from the photolithographic substrate using a second set of process conditions. An exposed surface of the photolithographic substrate is etched using a third set of process conditions. During the plasma processing of the photolithographic substrate, the critical dimension performance of the photolithographic substrate is monitored to insure that the target uniformity and feature widths are obtained by adjusting the deposition and etch plasma processing of the photolithographic substrate.