Laser Processing Apparatus Condensing Lens Vertical Position Calculation

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Solution Overview

Problem

Conventional laser processing methods require time-consuming and tedious adjustments to position the condensing lens accurately for forming modified layers in workpieces, especially when there are slight variations in workpiece thickness, due to the assumption that the focused laser beam moves four times the distance the condensing lens moves, which may not always be accurate.

Innovation Solution

A laser processing apparatus with a control unit that calculates the appropriate vertical position for the condensing lens using the equation Defocus=(thickness of the workpiece−height value−b)/a, determining constants 'a' and 'b' from multiple measurements to accurately position the lens for forming modified layers at a predetermined height from the workpiece's lower surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the conventional process of moving the condensing lens by one quarter of the determined distance is used, then the focused point can be positioned in the workpiece, but the vertical position of the formed modified layers shifts when workpiece thickness varies

Engineering Contradiction:

Improvevertical position precision of modified layersVSAvoidposition accuracy under thickness variation

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the control parameter from a fixed lens movement distance (one quarter of the determined distance) to a variable distance calculated using the equation Defocus=(thickness−height value−b)/a. This allows the lens movement to be precisely adjusted according to actual workpiece thickness, eliminating position shifts caused by thickness variations.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If experimental fine adjustment of the condensing lens position is conducted, then accurate positioning of the focused point can be achieved, but the processing time increases significantly

Engineering Contradiction:

Improvefocused point positioning accuracyVSAvoidtime for lens position adjustment

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent replaces the mechanical experimental adjustment process with a mathematical calculation system. The calculating section uses the equation Defocus=(thickness−height value−b)/a to directly compute the required lens position, eliminating the need for time-consuming experimental fine-tuning while maintaining positioning accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent performs preliminary calculation of the lens position using the established equation before actual processing begins. By pre-calculating the Defocus value based on measured thickness and predetermined parameters, the system avoids time-consuming adjustments during the processing stage.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If the assumption that the focused point moves four times the lens movement distance is used, then the calculation is simple, but the positioning accuracy is insufficient when the ratio deviates from 4

Engineering Contradiction:

Improvecalculation simplicityVSAvoidfocused point position accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent transitions from a static fixed ratio (4:1) to a dynamic adjustable ratio through the equation Defocus=(thickness−height value−b)/a. The calculating section determines the actual ratio based on real-time thickness measurements and predetermined parameters, allowing the system to adapt to different workpiece conditions while maintaining both calculation efficiency and positioning accuracy.

Inventive Principle:

Principle #15Dynamics

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 eliminates the need for two-stage adjustments and reduces the time required for fine-tuning the lens position, allowing for more precise and efficient formation of modified layers by accurately calculating the vertical position of the condensing lens.

Implementation Method 1

a laser beam having a wavelength that is transmittable through a plate-shaped workpiece is applied to an upper surface of the workpiece, with its focused point positioned in the workpiece

Methodology Applied

Scientific EffectFocusing: Focusing

Implementation Method 2

since the ratio of the refractive index of silicon to the refractive index of air is approximately 4, or actually 3.7 to be more precise, it is known that the focused point of a laser beam that has traveled through a condensing lens moves in the workpiece by a distance that is approximately four times the distance that the condensing lens moves

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS11351631B2Laser processing apparatus with calculating section

Publication Date: 2022.06.07 DISCO CORP

AI summary

A calculating section of a control unit calculates a vertical position Defocus for a condensing lens using a height value H1 of a modified layer in a wafer that is set by a setting section according to the equation (1) below.Defocus=(thickness T1 of wafer−height value H1−b)/a (1)The calculating section calculates an appropriate vertical position for the condensing lens according to the equation (1) depending on the height value H1 of the modified layer that is set by the setting section. Therefore, the vertical position of the condensing lens in laser processing operation can be determined more easily, and a time-consuming and tedious experiment for fine adjustment of the vertical position of the condensing lens does not need to be conducted.