Fluonitric Acid Etching for Flat SOI Backside Substrates
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Solution Overview
Problem
The existing methods for etching the backside of SOI substrates using fluonitric acid result in an infinite number of projections and recesses on the surface, causing light scattering and diffuse reflection, which hinders efficient light entry into photoelectric conversion elements in backside illumination image sensors, and increasing production time and cost.
Innovation Solution
A method involving the use of a fluonitric acid composition with a concentration ratio of hydrofluoric acid and nitric acid of 50 wt% or more, along with water, to selectively etch the Si substrate while minimizing the etching of the SiO2 layer, ensuring a flat and efficient light entrance surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMP or wet etching is used to remove the Si substrate to reduce light absorption, then light sensitivity is improved, but production time increases and manufacturing efficiency decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the etching solution by using a mixed acid solution containing hydrofluoric acid and nitric acid in specific proportions (1:1 to 4:1 volume ratio), which dramatically increases the etching rate of the Si substrate while maintaining selective etching capability to preserve the SiO2 layer, thereby reducing processing time without compromising light sensitivity
2Productivity
If conventional wet etching with fluonitric acid is used to etch the Si substrate, then etching speed is improved, but the surface becomes rough with projections and recesses causing light scattering
Solution Approach 1:
The invention optimizes the concentration ratios of hydrofluoric acid and nitric acid in the etching solution, specifically maintaining a volume ratio between 1:1 and 4:1, which controls the etching mechanism to produce a flat surface without projections and recesses while maintaining high etching speed, thereby resolving the contradiction between productivity and manufacturing precision
3Reliability
If the Si substrate thickness is reduced by CMP or wet etching to improve light transmission, then light absorption is reduced, but production time and cost increase
Solution Approach 1:
The invention uses a mixed acid etching solution with optimized hydrofluoric acid and nitric acid ratios that achieves rapid etching of the Si substrate (removing several micrometers in minutes), significantly reducing processing time compared to conventional methods, while the selective etching preserves the SiO2 layer to maintain light transmission efficiency
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 allows for rapid and flat wet etching of the Si substrate, reducing light absorption by the Si substrate and enhancing the flatness of the light entrance surface, thereby improving the efficiency and cost-effectiveness of producing backside illumination type photoelectric conversion modules.
Implementation Method 1
a method involving the use of a fluonitric acid composition with a concentration ratio of hydrofluoric acid and nitric acid of 50 wt% or more, along with water, to selectively etch the Si substrate while minimizing the etching of the SiO2 layer
Data Source
AI summary
A method of etching capable of rapidly and flatly performing wet etching on a Si substrate using fluonitric acid represented by HF(a)HNO3(b)H2O(c) (where the unit of a, b and c is wt % and a+b+c=100). The etching rate of an SiO2 layer with the highly concentrated fluonitric acid is significantly lowered by the appropriate selection of its composition as compared with the etching rate of the Si substrate, and etch the Si substrate until the SiO2 layer is exposed. In this way, it is possible to rapidly etch the Si substrate and significantly enhance the flatness of the etched surface.