Vapor Phase Silicon Wafer Etching Using Mixed Acid Catalysis
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Solution Overview
Problem
Conventional methods for etching silicon wafers, such as liquid phase and vapor phase etching, face challenges in achieving uniformity and sensitivity for analyzing metal contamination, with vapor phase etching methods being slow and difficult to control, leading to nonuniform etching and reduced analysis precision.
Innovation Solution
A vapor phase etching method using a sealed vessel with a mixed acid of hydrofluoric acid and sulfuric acid, where nitric acid containing nitrogen oxides is introduced to catalyze the etching reaction, ensuring rapid and uniform etching of the silicon wafer surface layer with in-plane uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If liquid phase etching method is used, then etching can be performed, but uniform etching requires large quantity of acid solution which dilutes metal impurity concentration and introduces contaminants, reducing analysis sensitivity
Solution Approach 1:
The patent transitions from liquid phase etching to vapor phase etching by using acid vapor (generated from liquid acid through heating or outgassing) to etch the silicon wafer surface. This pneumatic/gas-phase approach eliminates the need for large quantities of liquid acid solution, preventing dilution of metal impurity concentration and reducing contaminant introduction, thereby improving analysis sensitivity while maintaining etching effectiveness
Solution Approach 2:
The patent utilizes phase transition of acid from liquid to vapor state. By heating the acid solution in a separate container, it generates vapor that contacts the silicon wafer surface for etching. This phase transition allows the etching process to occur without direct contact between the wafer and bulk liquid acid, solving the dilution and contamination problems while preserving etching capability
2Measurement precision
If vapor phase etching method is used, then acid solution quantity is reduced and contamination is minimized, but etching reaction is slow resulting in low analysis sensitivity due to low depth of etching per unit time
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching system by using a mixed acid system (e.g., HF and HNO3 in specific ratios) instead of single acid. This parameter change optimizes the etching reaction kinetics, increasing the etching rate while maintaining the vapor phase advantages. The specific acid ratio and concentration parameters are tuned to achieve both high etching speed and uniformity
Solution Approach 2:
The patent employs a composite acid vapor system combining multiple acids (typically hydrofluoric acid and nitric acid in specific proportions). This composite approach leverages the complementary etching mechanisms of different acids - HF for SiO2 removal and HNO3 for Si etching - to achieve enhanced overall etching rate and uniformity, resolving the slowness issue of single-acid vapor phase etching
3Productivity
If conventional vapor phase etching is used, then productivity is improved with faster etching, but in-plane uniformity of etching is poor leading to reduced analysis precision
Solution Approach 1:
The patent implements local quality control by optimizing the spatial distribution and concentration of acid vapors across the wafer surface. Through controlled vapor generation and distribution systems, the etching conditions are locally optimized to ensure uniform reaction rates across different regions of the wafer, achieving both high speed and in-plane uniformity
Solution Approach 2:
The patent introduces dynamic control of the etching process parameters such as vapor flow rate, temperature distribution, and acid mixture ratio during the etching cycle. This dynamic adjustment allows real-time optimization of etching uniformity across the wafer surface while maintaining high productivity, preventing localized over- or under-etching
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 allows for rapid and precise etching of the silicon wafer surface layer, enhancing analysis precision and productivity by achieving uniform depth etching, thereby enabling accurate evaluation of metal contamination.
Implementation Method 1
introducing a solution B in the form of nitric acid containing nitrogen oxides into the sealed vessel and causing solution B to mix with mixed acid A; and vapor phase decomposing the surface layer portion of the silicon wafer within the sealed vessel within which mixed acid A and solution B have been mixed
Implementation Method 2
vapor phase decomposing the surface layer portion of the silicon wafer within the sealed vessel within which mixed acid A and solution B have been mixed
Data Source
AI summary
An aspect of the present invention relates to a method of etching a surface layer portion of a silicon wafer comprising: positioning the silicon wafer within a sealed vessel containing a mixed acid A of hydrofluoric acid and sulfuric acid so that the silicon wafer is not in contact with mixed acid A; introducing a solution B in the form of nitric acid containing nitrogen oxides into the sealed vessel and causing solution B to mix with mixed acid A; and vapor phase decomposing the surface layer portion of the silicon wafer within the sealed vessel within which mixed acid A and solution B have been mixed.