Silicon Tunnel Oxide Layering for Stable Passivated Contacts
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Solution Overview
Problem
Existing processes for manufacturing silicon solar cells with passivated contacts face challenges in the thermal stability and control of silicon oxide tunnel layers, leading to instability and contamination issues that affect the passivation and barrier properties.
Innovation Solution
A process involving the application of a second silicon oxide layer by physical or chemical vapor deposition, optionally after in-situ plasma treatment, to enhance the thermal stability and adjust the thickness and dopant concentration of the overall silicon oxide layer, ensuring precise control over the tunnel oxide layer's properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet chemical oxidation is used to generate silicon oxide tunnel layers, then the process is cost-effective and can be performed in one system without reloading, but the resulting layers are not sufficiently stable to withstand subsequent high-temperature thermal processes
Solution Approach 1:
The patent creates a composite oxide layer structure combining wet-chemically generated silicon oxide (first layer) with thermally grown silicon oxide (second layer). The wet-chemical process provides cost-effectiveness and integration, while the thermal oxidation layer provides thermal stability. The combined structure achieves both low cost and high reliability by leveraging the strengths of both oxidation methods.
Solution Approach 2:
The wet chemical oxidation is performed first to create the initial tunnel oxide layer with the desired thickness (1.4-1.8 nm), followed by thermal oxidation to reinforce it. This preliminary action of creating the base layer chemically before thermal processing allows the subsequent thermal step to focus solely on stabilization without compromising the tunneling properties.
2Reliability
If the tunnel oxide layer thickness is reduced to improve passivation, then the passivation quality improves, but the layer becomes more susceptible to contamination and uncontrolled oxidation
Solution Approach 1:
The patent applies a protective measure by growing an additional thermal oxide layer over the thin wet-chemical tunnel oxide. This thermal layer acts as a protective cushion that prevents contamination and uncontrolled oxidation of the underlying thin tunnel layer, while the tunnel layer itself maintains its optimized thickness for passivation.
Solution Approach 2:
The structure combines a thin wet-chemical oxide layer (optimized for passivation) with a thicker thermal oxide layer (optimized for protection). This composite structure allows the tunnel layer to remain thin for excellent passivation while the thermal layer provides the necessary protection against contaminants.
3Reliability
If thermal oxidation is used to generate silicon oxide layers, then the layers have good thermal stability, but the process requires elevated temperatures and cannot be performed in the same system as surface cleaning
Solution Approach 1:
The patent divides the oxide layer generation into two distinct segments: wet chemical oxidation performed in the cleaning system, and thermal oxidation performed in a separate thermal processing system. This segmentation allows each process to be optimized for its specific requirements without compromising the other.
Solution Approach 2:
The wet-chemically generated oxide layer serves as an intermediary that enables subsequent thermal processing. It provides a stable base layer that can withstand the thermal oxidation process, allowing the thermal system to focus on stability enhancement without needing to perform the initial surface preparation.
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
The enhanced process improves the thermal stability and control of the silicon oxide layer, maintaining passivation properties and allowing precise adjustment of dopant diffusion, thereby improving the efficiency and reliability of silicon solar cells.
Implementation Method 1
Said first silicon oxide layer on the first side of the silicon wafer is then coated with a second silicon oxide layer by means of physical or chemical vapor deposition
Implementation Method 2
Said first silicon oxide layer on the first side of the silicon wafer is then coated with a second silicon oxide layer by means of physical or chemical vapor deposition
Implementation Method 3
optionally after an additional in-situ plasma intermediate treatment
Data Source
AI summary
The present invention is directed to a process for manufacturing a starting material for a silicon solar cell having passivated contacts, a system for carrying out the process, and an intermediate product resulting from the process.