Single-Side Emitter Removal Using Two-Step Silicon Etching
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Solution Overview
Problem
Conventional methods for selectively removing emitter layers from silicon substrates in semiconductor manufacturing, particularly in solar cell production, face challenges such as the use of hazardous etching solutions, uneven surface processing, and increased safety and disposal costs due to the need for combined etching steps using hydrofluoric and nitric acids.
Innovation Solution
A two-step etching process is introduced, where a first etching solution selectively removes the silicate glass layer without etching silicon, followed by a second etching solution that removes the emitter layer without affecting the silicate glass, using hydrofluoric acid and an alkaline base respectively, to improve selectivity and safety, and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a combined etching solution of hydrofluoric acid and nitric acid is used to remove both silicate glass layer and emitter layer in a single step, then the etching process is simplified and productivity is improved, but the toxicity and operational hazards increase significantly
Solution Approach 1:
The patent divides the etching process into two separate steps: first removing the silicate glass layer with hydrofluoric acid, then removing the emitter layer with an alkaline solution. This segmentation eliminates the need for hazardous combined etching solutions while maintaining process efficiency.
Solution Approach 2:
The patent replaces expensive and hazardous nitric acid with a cheaper, safer alkaline solution (such as KOH or NaOH) for the second etching step. The alkaline solution can be easily disposed of or neutralized, reducing environmental and safety concerns.
2Device complexity
If a combined etching solution is used to etch both silicate glass and silicon, then the number of processing steps is reduced, but the surface uniformity and manufacturing precision deteriorate
Solution Approach 1:
By separating the etching process into two distinct steps with different chemicals, each step can be optimized for its specific purpose: the first step cleanly removes glass without attacking silicon, and the second step removes the emitter layer with controlled etching, resulting in superior surface uniformity.
Solution Approach 2:
The patent applies different etching solutions with different properties to different stages of the process. The first etching solution (HF) is specifically tailored for glass removal, while the second etching solution (alkaline) is optimized for silicon etching, ensuring each material is removed with the appropriate chemical properties.
3Productivity
If hydrofluoric acid and nitric acid are used together for etching, then both silicate glass and emitter layer can be removed in one step, but the safety costs and disposal costs increase
Solution Approach 1:
The patent replaces the expensive and hazardous nitric acid with a cheaper, safer alkaline solution that can be easily handled and disposed of. The alkaline solution does not require special safety infrastructure or expensive disposal procedures, significantly reducing manufacturing costs.
Solution Approach 2:
The first etching step using hydrofluoric acid acts as an intermediary step that removes the protective silicate glass layer, exposing the emitter layer for subsequent removal. This intermediate step enables the use of safer chemicals in the second step while achieving the same overall result.
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 more controlled and efficient emitter layer removal with reduced toxicity and operational hazards, resulting in a smoother surface and lower production costs, while minimizing the use of hazardous chemicals and byproducts.
Implementation Method 1
selectively removing the silicate glass layer exclusively on a first side of a silicon substrate by contacting the silicate glass layer exclusively on the first side with a first etching solution, the first etching solution etching silicate glass and not substantially etching silicon
Implementation Method 2
removing the emitter layer on the first side of a silicon substrate by contacting the emitter layer on the first side with a second etching solution, the second etching solution etching silicon and not substantially etching silicate glass
Implementation Method 3
The nitric acid oxidises the silicon of the emitter layer in order to form silicon oxides which may then be etched by the hydrofluoric acid
Data Source
Figure 1~1(d)
Figure 2
AI summary
A method for selectively removing an emitter layer (5) on a single side (13) of a silicon substrate (3) and a wet bench (1) for implementing such method are described. Therein, the silicon substrate (3) initially comprises an emitter layer (5) at both opposing sides (13, 15) and the silicon substrate (3) initially comprises a silicate glass layer (7) covering the emitter layer (5) at both opposing sides (13, 15). The method comprises at least the following two steps: - selectively removing the silicate glass layer (7) exclusively on a first side (13) of a silicon substrate (3) by contacting the silicate glass layer (7) exclusively on the first side (13) with a first etching solution (17), the first etching solution (17) etching silicate glass and not substantially etching silicon; and - removing the emitter layer (5) on the first side (13) of a silicon substrate (3) by contacting the emitter layer (5) on the first side (13) with a second etching solution (19), the second etching solution (19) etching silicon and not substantially etching silicate glass. By replacing, in an emitter removal process, a conventional single step etching procedure based on an etching composition comprising HF and HNO3 by a two- step sequence using e.g. a HNO3-free and/or NOx-free HF-based first etching solution (17) and e.g. an alkaline base as the second etching solution (19), various benefits may be (realised. )