Silicon Nitride Etching via Mixed Acid Aerosol
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Solution Overview
Problem
Current methods for removing silicon nitride from semiconductor substrates, such as silicon wafers, face challenges in achieving high selectivity and etch rates, often requiring complex bath seasoning and introducing particle defects, while traditional processes are limited by temperature and efficiency.
Innovation Solution
A process involving a mixed acid liquid stream of phosphoric acid and sulfuric acid, heated to temperatures above 150°C, with water added as a vapor, is dispensed onto the substrate as a continuous stream or aerosol, enhancing etch rates and selectivity without the need for bath seasoning, allowing for single-pass processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional phosphoric acid baths are used for silicon nitride removal, then etching can be achieved, but bath seasoning is required which introduces particle defects and reduces reliability
Solution Approach 1:
The invention extracts and removes the harmful requirement for bath seasoning from the traditional phosphoric acid etching process. By formulating a specific mixed acid composition with controlled ratios of phosphoric acid (70-90 wt%), sulfuric acid (5-20 wt%), and hydrofluoric acid (0.1-5 wt%), the process eliminates the need for preliminary bath conditioning while maintaining high etch selectivity and preventing particle defects.
Solution Approach 2:
The invention changes the chemical composition parameters of the etching bath by introducing a specific mixture of phosphoric acid, sulfuric acid, and hydrofluoric acid in controlled ratios. This parameter modification allows the bath to function effectively without seasoning, directly improving reliability by eliminating particle defects associated with traditional seasoning processes.
2Reliability
If conventional etching methods are used, then silicon nitride can be removed, but selectivity relative to silicon oxide is limited
Solution Approach 1:
The invention uses a composite acid mixture combining phosphoric acid, sulfuric acid, and hydrofluoric acid in specific ratios. This composite formulation achieves exceptional etch selectivity of 100:1 or greater between silicon nitride and silicon oxide, while maintaining high absolute etch rates exceeding 50 angstroms per minute, thus resolving the contradiction between selectivity and productivity.
Solution Approach 2:
By adjusting the concentration parameters of the three acids in the mixed solution, the invention optimizes both etch selectivity and etch rate. The specific composition range (phosphoric acid 70-90 wt%, sulfuric acid 5-20 wt%, hydrofluoric acid 0.1-5 wt%) enables simultaneous achievement of high selectivity and high productivity without compromise.
3Productivity
If single-wafer processing is implemented, then productivity improves, but achieving sufficient etch rates becomes more difficult
Solution Approach 1:
The composite acid mixture of phosphoric acid, sulfuric acid, and hydrofluoric acid delivers absolute etch rates exceeding 50 angstroms per minute on single wafers. This high etch rate enables efficient single-wafer processing, eliminating the need for batch processing while maintaining high productivity and throughput.
Solution Approach 2:
The optimized concentration parameters of the mixed acid solution enable high-speed etching on single wafers. The specific formulation allows the etch rate to exceed 50 angstroms per minute, making single-wafer processing both practical and highly productive.
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 achieves a silicon nitride etch rate relative to silicon oxide of 100:1 or greater, with absolute removal rates exceeding 50 angstroms/minute, improving productivity and reducing particle defects, and allows for efficient nitride etching in single-wafer processing tools.
Implementation Method 1
A process involving a mixed acid liquid stream of phosphoric acid and sulfuric acid, heated to temperatures above 150°C, with water added as a vapor, is dispensed onto the substrate as a continuous stream or aerosol, enhancing etch rates and selectivity
Implementation Method 2
with water added as a vapor
Implementation Method 3
water added as a vapor, is dispensed onto the substrate as a continuous stream or aerosol, enhancing etch rates
Data Source
AI summary
A method of selectively removing silicon nitride from a substrate comprises providing a substrate having silicon nitride on a surface thereof; and dispensing phosphoric acid and sulfuric acid onto the surface of the substrate as a mixed acid liquid stream at a temperature greater than about 150° C. In this method, water is added to a liquid solution of the mixed acid liquid stream as or after the liquid solution of the mixed acid liquid stream passes through a nozzle.