Dual Laser Beam Device for Silicon Wafer Ablation
Solution Overview
Problem
The existing laser machining processes for silicon wafers in solar cell production are limited by the speed at which deflection mirrors can be guided relative to the wafer, affecting the efficiency and cost-effectiveness of the backside opening process for passivation layers.
Innovation Solution
A device that generates two linearly polarized laser beams at an oblique angle, using a deflection and focusing unit with adjustable mirrors and a partially transparent end mirror, allowing for simultaneous processing and automatic compensation of positioning errors and thermal drifts to achieve faster and more precise ablation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single laser beam is used with a deflection and focusing unit, then the manufacturing precision is maintained, but the productivity is limited by the speed of the deflection mirrors
Solution Approach 1:
The single laser beam is divided into two separate laser beams that propagate at oblique angles to each other. Each beam is independently focused to create two separate processing lines on the workpiece, effectively doubling the material removal rate while using the same deflection and focusing unit.
Solution Approach 2:
Two laser beams are combined into a single processing system sharing the deflection and focusing unit. The beams are directed through the same optical path and focused onto the workpiece, merging the complexity of two separate systems into one while achieving doubled productivity.
2Productivity
If the spacing between laser lines is reduced to increase contact area, then the productivity increases, but the manufacturing precision decreases due to thermal-induced drift
Solution Approach 1:
A beam position detector continuously monitors the positions of the two laser beams and provides feedback signals to the control device. The control device adjusts the deflection mirrors in real-time to compensate for thermal drift and positioning errors, maintaining precise line spacing even when processing closely spaced lines.
Solution Approach 2:
The deflection and focusing unit is designed to handle two laser beams simultaneously with independent focus points. The system can dynamically adjust the spacing and positioning of both beams using shared optical components, providing universal control over multiple processing parameters.
3Productivity
If the deflection mirrors are moved faster to increase process speed, then the productivity increases, but the manufacturing precision deteriorates due to positioning errors
Solution Approach 1:
The beam position detector measures the actual positions of the laser beams and sends correction signals to the control device, which adjusts the deflection mirrors to compensate for positioning errors caused by high-speed movement, maintaining precision at increased speeds.
Solution Approach 2:
The feedback control system acts as an counteracting force against positioning errors. By continuously measuring and compensating for deviations, the system counterbalances the negative effects of high-speed mirror movement, maintaining manufacturing precision despite increased process speed.
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 doubles the process speed and ensures uniform, reproducible results by allowing closer spacing of laser beams and automatic adjustment of beam intersection points, reducing thermal-induced errors and maintaining precise line spacing on the wafer.
Implementation Method 1
The passivation layers on the back of the wafer are locally opened, i.e. locally removed, by means of laser ablation
Implementation Method 2
a deflection and focusing unit for guiding and focusing the laser beams over or onto the workpiece
Implementation Method 3
the transmitted partial beams being fed to a polarization beam splitter which separates the transmitted partial beams
Data Source
AI summary
The invention relates to a device for the laser processing of a workpiece (14), containing an apparatus (6) for producing a first and a second laser beam (L1, L2), which propagate obliquely to each other at an angle (a), and a refracting and focusing unit (10) for guiding and focusing the laser beams (L1, L2) over or onto the workpiece (14), wherein the laser beams (L1, L2) are linearly polarized in directions that are perpendicular to each other.