Silicon Substrate Resistivity Measurement for Ion Implantation
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Solution Overview
Problem
Variations in the resistivity of bulk silicon substrates used in solar cells lead to inefficiencies in solar cell performance due to non-uniform ion implantation processes, as high resistivity can decrease carrier mobility and increase series resistance, while existing techniques lack effective methods to counteract these variations.
Innovation Solution
A system and method that measures the resistivity of silicon substrates and adjusts the ion implantation process accordingly, using a resistivity measurement system, controller, and ion implanter to achieve a desired sheet resistance by varying the dose for the back surface field (BSF) based on measured resistivity values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform ion implantation process is used on bulk silicon substrates with varying resistivity, then the manufacturing process is simple, but the solar cell efficiency deteriorates due to non-optimal processing for high resistivity substrates
Solution Approach 1:
The patent applies parameter changes by adjusting ion implantation parameters (dose, energy, or timing) based on the measured resistivity values of individual substrates. The system measures resistivity and dynamically modifies implantation parameters to optimize performance for each substrate, resolving the contradiction between process simplicity and efficiency by automating parameter adjustment.
Solution Approach 2:
The patent implements feedback control by measuring the resistivity of each substrate before ion implantation and using this measurement to determine the appropriate implantation parameters. This closed-loop feedback system ensures that high resistivity substrates receive optimized processing while maintaining overall system simplicity through automated control.
2Quantity of substance
If high resistivity bulk silicon is used, then material cost may be reduced, but carrier mobility decreases and series resistance increases
Solution Approach 1:
The patent compensates for the adverse effects of high resistivity by changing the ion implantation parameters specifically for high resistivity substrates. By measuring resistivity and adjusting implantation dose or energy accordingly, the system restores optimal carrier mobility and series resistance characteristics without requiring expensive low-resistivity material.
3Reliability
If resistivity measurement and adaptive processing is implemented, then solar cell performance is optimized, but device complexity increases
Solution Approach 1:
The patent manages complexity by implementing a straightforward feedback loop: measure resistivity, compare to setpoints, and adjust implantation parameters accordingly. The controller system automates this process, hiding the complexity from manual operation while delivering optimized performance. The complexity is centralized in the control system rather than distributed across multiple manual processes.
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 ensures consistent series resistance across solar cells by tailoring the ion implantation process to the substrate's resistivity, improving solar cell performance by optimizing carrier mobility and reducing series resistance.
Implementation Method 1
measuring a resistivity of a first substrate
Implementation Method 2
implanting ions into the substrate using the selected dose to create the BSF
Data Source
AI summary
The resistivity of a silicon boule may vary along its length, thereby making a uniform ion implantation process sub-optimal. A system and method for measuring a resistivity of a substrate, and processing the substrate based on that measured resistivity is disclosed. The system includes a resistivity measurement system, a controller and an ion implanting system, where the controller configures the ion implantation process based on the measured resistivity of the substrate.