Multicrystalline Silicon Wafer Gettering for Lifetime
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Solution Overview
Problem
Conventional multicrystalline silicon wafers experience reduced minority carrier lifetime and increased production costs due to high temperature phosphorous gettering, which does not effectively increase the lifetime of solar cells when compared to lower temperature processes.
Innovation Solution
Subjecting compensated p-type multicrystalline silicon wafers with specific boron and phosphorous content to phosphorous diffusion and gettering at temperatures of at least 950°C, resulting in increased minority carrier lifetime and enabling the production of solar cells with buried contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temperature phosphorous gettering (>900°C) is performed on conventional multicrystalline wafers, then phosphorous diffusion is enhanced, but minority carrier lifetime is reduced due to increased dissolved metal impurities
Solution Approach 1:
The patent changes the chemical composition parameters of the silicon wafer by introducing specific amounts of aluminum (0.01-1.0 ppma) and phosphorous (0.01-1.0 ppma) impurities before the gettering process. This parameter change modifies the wafer's response to high temperature treatment, enabling effective phosphorous diffusion at >900°C while preventing excessive dissolution of metal impurities that would otherwise reduce minority carrier lifetime.
Solution Approach 2:
The patent introduces aluminum and phosphorous as intermediary elements that mediate between the high temperature diffusion process and the metal impurity dissolution. These intermediaries form chemical interactions that control the solubility and precipitation behavior of metal impurities during the high temperature gettering process, allowing the system to achieve both deep phosphorous diffusion and acceptable lifetime.
2Productivity
If high temperature phosphorous gettering (>900°C) is performed, then processing time is reduced, but dissolved metal impurity concentration increases
Solution Approach 1:
The patent performs preliminary action by pre-introducing controlled amounts of aluminum and phosphorous impurities into the silicon wafer before the high temperature gettering process. This preliminary modification of the wafer composition enables the subsequent high temperature process to proceed faster while controlling metal impurity dissolution through the pre-established chemical environment.
Solution Approach 2:
The patent changes the initial composition parameters of the silicon wafer by adding specific concentrations of aluminum and phosphorous. This parameter change fundamentally alters the high temperature reaction kinetics, allowing faster processing times while maintaining control over metal impurity solubility and precipitation behavior during the gettering process.
3Reliability
If conventional multicrystalline wafers undergo high temperature diffusion, then phosphorous gettering efficiency is improved, but production cost increases due to reduced lifetime
Solution Approach 1:
The patent changes the compositional parameters of the silicon wafer by introducing controlled amounts of aluminum and phosphorous impurities. This parameter change enables high temperature gettering processes that achieve superior phosphorous diffusion and impurity removal efficiency, while the modified composition prevents excessive metal dissolution that would otherwise reduce cell lifetime and increase production costs.
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 significantly increases the minority carrier lifetime to 100-200 µs, reduces edge effects, and allows for faster processing without compromising quality, thereby reducing production costs and improving solar cell efficiency.
Implementation Method 1
an applied phosphorous source is forced a few micrometers into the surface of the wafer by diffusion in order to create a pn-junction
Implementation Method 2
the phosphorous gettering takes place where unwanted dissolved and mobile metallic impurity elements are transported to and captured by the phosphorous layer that has been diffused into the surface of the wafer
Implementation Method 3
said p-type multicrystalline silicon wafers are subjected to phosphorous diffusion and phosphorous gettering at a temperature of at least 950°C
Data Source
AI summary
The present invention relates to multicrystalline p-type silicon wafers with high lifetime. The silicon wafers contain 0.2-2.8 ppma boron and 0.06-2.8 ppma phosphorous and/or arsenic and have been subjected to phosphorous diffusion and phosphorous gettering at a temperature of above 925?C. The invention further relates to a method for production of such multicrystalline silicon wafers and to solar cells comprising such silicon wafers.