Wafer Laser Focal Control for Uniform Modified Layer Depth
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Solution Overview
Problem
The existing laser processing methods for wafer division often result in non-uniform modified layers due to variations in wafer thickness, chuck table height, and protective tape thickness, leading to non-straight side edges of chips.
Innovation Solution
A laser processing method that involves measuring the upper and lower surface heights of the wafer, calculating a correction value to adjust the focal point position of the laser beam, and continuously adjusting the focusing means to maintain a uniform modified layer height from the lower surface of the wafer along division lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the focal point of the laser beam is set at a fixed height to form each modified layer, then the processing speed is maintained, but the modified layer is not formed at a uniform height from the lower surface of the wafer due to variations in wafer thickness, chuck table height, and protective tape thickness
Solution Approach 1:
The patent dynamically adjusts the vertical position of the focal point based on measured variations in wafer thickness, chuck table height, and protective tape thickness. By changing the focal position parameter in response to measured deviations, the system maintains uniform modified layer height from the lower surface while preserving processing speed.
Solution Approach 2:
The patent implements a feedback mechanism where the actual positions of the wafer upper surface, lower surface, and protective tape are measured, and these measurements are used to calculate and adjust the focal point position. This closed-loop control ensures that despite variations in input parameters, the modified layer is consistently formed at the desired height.
2Ease of manufacture
If the modified layer is not formed at a uniform height from the lower surface of the wafer, then the external force applied to each modified layer becomes nonuniform, but this results in side edges of chips being less straight
Solution Approach 1:
By dynamically adjusting the focal point position based on measured variations, the patent ensures that the modified layer is formed at a uniform height from the lower surface. This uniformity allows external force to be applied consistently across all modified layers, resulting in straight chip side edges.
3Manufacturing precision
If measurements and corrections are performed for each position along the division line, then the modified layer is formed at constant height from the lower surface, but the device complexity increases
Solution Approach 1:
The patent replaces complex mechanical adjustment mechanisms with optical measurement systems (laser displacement meters) and computational correction. Instead of using complex mechanical means to physically adjust the focal point position throughout the processing, the system uses optical measurements and calculates the required adjustments, simplifying the mechanical complexity while achieving high precision.
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 ensures the formation of a modified layer at a consistent vertical position from the lower surface of the wafer, enhancing the straightness of chip edges and reducing damage during division.
Implementation Method 1
applying a laser beam having a transmission wavelength to the workpiece in the condition where the focal point of the laser beam is set inside the workpiece
Implementation Method 2
dividing the distance calculated above by a value obtained by adding a predetermined coefficient to the refractive index of the workpiece, thereby calculating a correction value
Data Source
AI summary
In a laser processing apparatus, a height of a focusing lens in a processing unit can be changed according to a change in height of an upper surface of a wafer, thereby changing a vertical position of a focal point of a laser beam inside the wafer. Accordingly, the laser beam can be applied to the wafer as feeding the wafer in a condition where the focal point is set at a vertical position spaced a fixed distance from the lower surface of the wafer. As a result, a modified layer can be formed inside the wafer at a uniform height from the lower surface of the wafer.