Phosphoric Acid Etching Control for Stable Nitride Selectivity
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Solution Overview
Problem
Conventional substrate etching techniques using phosphoric acid aqueous solutions face challenges in maintaining uniform selectivity between silicon oxide and silicon nitride films due to varying silicon concentrations, leading to unstable etching processes when the solution is reused, and result in inefficient use of the etching solution.
Innovation Solution
A substrate processing method that involves preparing a phosphoric acid processing liquid with a precipitation inhibitor, which is initially added to inhibit silicon oxide precipitation, and the inhibitor's concentration is increased when a threshold number of substrates or silicon concentration is reached, allowing for multiple etching processes while maintaining selectivity by adjusting the etching rate of the silicon oxide film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the phosphoric acid processing liquid is reused for multiple etching processes, then productivity is improved, but the selectivity between silicon oxide and silicon nitride films deteriorates due to varying silicon concentrations
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the concentration of precipitation inhibitor in the phosphoric acid processing liquid based on the silicon concentration. As the silicon concentration increases during reuse, the precipitation inhibitor concentration is increased accordingly to maintain constant selectivity, transforming the processing liquid from a static to a dynamically adjusted composition
Solution Approach 2:
The patent implements feedback control by monitoring the silicon concentration in the processing liquid and adjusting the precipitation inhibitor concentration in response. The controller increases the precipitation inhibitor concentration when silicon concentration reaches a predetermined threshold, creating a closed-loop control system that maintains stable etching selectivity throughout the reuse period
2Manufacturing precision
If the concentration of precipitation inhibitor is increased to maintain selectivity, then manufacturing precision is improved, but the complexity of the processing system increases
Solution Approach 1:
The patent applies self-service by having the processing liquid automatically adjust its own composition. The system circulates the processing liquid through a reservoir where precipitation inhibitor is added based on silicon concentration thresholds, allowing the liquid to self-regulate its chemical composition without manual intervention
Solution Approach 2:
The phosphoric acid processing liquid serves multiple functions: it etches silicon nitride films, suppresses silicon oxide precipitation through dynamic adjustment of inhibitor concentration, and maintains stable selectivity throughout extended reuse periods. The single processing liquid system replaces what would traditionally require multiple separate etching solutions
3Reliability
If the precipitation inhibitor concentration is dynamically adjusted, then reliability of etching process is improved, but the difficulty of detecting and measuring increases
Solution Approach 1:
The patent replaces complex continuous monitoring systems with a simplified threshold-based electronic control system. Instead of continuously measuring and adjusting inhibitor concentration, the system uses sensors to detect when silicon concentration reaches predetermined thresholds, triggering automatic inhibitor addition only when needed
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 method enables efficient reuse of the phosphoric acid solution by stabilizing the selectivity between silicon nitride and silicon oxide films, ensuring consistent etching performance and reducing the need for frequent solution disposal.
Implementation Method 1
supplying a precipitation inhibitor which suppresses a precipitation of silicon oxide into a phosphoric acid aqueous solution
Implementation Method 2
etching a substrate by immersing the substrate in a processing tub in which the phosphoric acid processing liquid is stored
Data Source
AI summary
A substrate processing method includes preparing a phosphoric acid processing liquid, etching a substrate and increasing a concentration of the precipitation inhibitor. The phosphoric acid processing liquid is prepared by supplying a precipitation inhibitor into a phosphoric acid aqueous solution. The substrate having a silicon oxide film and a silicon nitride film is etched by immersing the substrate in a processing tub. The concentration of the precipitation inhibitor is increased by additionally supplying the precipitation inhibitor into the phosphoric acid processing liquid when a number of substrates etched has reached a first threshold value or when a silicon concentration in the phosphoric acid processing liquid has reached a second threshold value. The etching of the substrate comprises etching a new substrate by immersing the new substrate in the processing tub in which the phosphoric acid processing liquid with the increased concentration of the precipitation inhibitor is stored.