Silicon Oxide Passivation for Dual-Dopant Activation Control
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Solution Overview
Problem
The existing photovoltaic cell manufacturing process faces challenges in simultaneously achieving the electrical activation of phosphorus and boron atoms without excessive diffusion of phosphorus atoms, which can degrade the performance of the photovoltaic cell.
Innovation Solution
A passivation process involving the application of ultraviolet radiation under an ozone atmosphere to form oxide films with specific thickness and composition, followed by the deposition of polysilicon layers with phosphorus and boron atoms, and a subsequent heat treatment at a temperature greater than or equal to the boron activation temperature to activate both phosphorus and boron atoms simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single heat treatment is applied at a temperature greater than or equal to the boron activation temperature to simultaneously activate both phosphorus and boron atoms, then the electrical activation of both dopants is achieved, but excessive diffusion of phosphorus atoms occurs which degrades photovoltaic cell performance
Solution Approach 1:
The patent applies a preliminary heat treatment step before the final high-temperature activation to pre-diffuse phosphorus atoms into the silicon substrate. This preliminary action creates a phosphorus gradient that prevents excessive out-diffusion during the subsequent high-temperature boron activation, thus resolving the contradiction between achieving full electrical activation and controlling phosphorus diffusion.
Solution Approach 2:
The patent divides the heat treatment process into multiple steps with different temperature parameters and durations. By changing temperature parameters sequentially (first at a lower temperature for phosphorus diffusion, then at higher temperature for boron activation), the process achieves simultaneous activation while controlling phosphorus diffusion through parameter optimization.
2Reliability
If two successive heat treatments are applied to electrically activate phosphorus and boron atoms separately at their respective optimum temperatures, then the electrical activation of each dopant is optimized, but the operating time is significantly increased
Solution Approach 1:
The patent merges the phosphorus activation and boron activation processes into a single integrated heat treatment step. By combining these two previously separate processes into one simultaneous operation at optimized temperature and duration, the patent achieves full electrical activation of both dopants while significantly reducing the total processing time.
Solution Approach 2:
The patent optimizes the temperature and time parameters of the heat treatment to enable simultaneous activation of both phosphorus and boron atoms. By carefully selecting parameters that satisfy both dopants' activation requirements, the process eliminates the need for separate treatment steps while maintaining activation 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 process effectively prevents excessive diffusion of phosphorus atoms while achieving simultaneous electrical activation of both phosphorus and boron atoms, thereby enhancing the efficiency and performance of the photovoltaic cell.
Implementation Method 1
applying ultraviolet radiation to the structure, under an ozone atmosphere, in such a way that the first oxide film has: a thickness strictly greater than the thickness of the second oxide film
Implementation Method 2
applying a heat treatment to the assembly comprising the structure and the first and second polysilicon layers, the heat treatment being applied at a temperature greater than or equal to the second electrical activation temperature so as to electrically activate the phosphorus atoms and the boron atoms concomitantly
Implementation Method 3
The oxide films also act as a barrier against diffusion of phosphorus atoms and boron atoms from the corresponding polysilicon layer into the substrate
Data Source
AI summary
A passivation process, including the following successive steps: a) providing a structure including a crystalline silicon-based substrate having opposite first and second surfaces; first and second oxide films; b) applying ultraviolet radiation to the structure, under an ozone atmosphere, in such a way that the first oxide film has: a thickness strictly greater than the thickness of the second oxide film, and/or a composition closer to the stoichiometric compound; c) forming first and second polysilicon layers on the first and second oxide films, respectively, these first and second polysilicon layers comprising phosphorus atoms and boron atoms, respectively; d) applying a heat treatment at a temperature greater than or equal to the electrical activation temperature of the boron atoms so as to electrically activate the phosphorus atoms and the boron atoms concomitantly.