Laser Condensing Point Detection Using Diffractive Mask
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Solution Overview
Problem
Current laser processing apparatuses face challenges in accurately and efficiently positioning the condensing point of a laser beam, leading to errors in wafer division and reduced productivity due to time-consuming measurement processes.
Innovation Solution
A method involving a mask with a slit portion and a condensing point forming portion to create irradiation marks on a substrate, allowing for accurate detection of the condensing point's position by forming linear and circular marks, which enables precise correction of the condensing point's position relative to the reticle projection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the condensing point position is adjusted using a reticle as reference, then the position can be aligned with the optical axis, but there is an error of approximately a few μm between the reticle projection position and the actual condensing point position
Solution Approach 1:
The patent introduces a mask with a specific pattern (including a central circular opening and concentric circular lines) as an intermediary object. This mask is irradiated by the laser beam to create irradiation marks that serve as a mediator for detecting the condensing point position. The pattern on the mask transforms the laser beam interaction into visible marks that clearly indicate when the condensing point is at the optimal position, thereby eliminating the alignment error between reticle projection and actual condensing point.
2Measurement precision
If the condensing point position is measured by forming a modified layer in a dummy wafer and measuring the length from the upper surface to the modified layer, then the error can be detected, but the measurement process takes a considerable time, resulting in poor productivity
Solution Approach 1:
The patent replaces the mechanical measurement system (forming modified layers and physically measuring lengths) with an optical detection system. The mask pattern, when irradiated by the laser beam, creates optical marks that can be immediately observed and measured using optical methods. This substitution eliminates the time-consuming process of forming and physically measuring modified layers, while still providing accurate detection of the condensing point position error.
3Measurement precision
If a mask with a slit portion is used to diffract the laser beam and form linear irradiation marks, then the condensing point position can be detected by observing when the linear mark divides a circular mark into two equal parts, but the system complexity increases
Solution Approach 1:
The patent applies local quality by designing specific regions on the mask with different functions. The mask includes a central circular opening for forming a reference circular irradiation mark, concentric circular lines for creating additional reference marks, and a slit portion for generating linear irradiation marks through diffraction. Each local region of the mask has a specialized structure optimized for its specific detection function, allowing the system to achieve high measurement precision while keeping the overall mask design systematic and manageable.
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 allows for rapid and accurate detection of the condensing point's position along the optical axis, improving productivity by simplifying the correction process and enhancing the precision of wafer division in laser processing.
Implementation Method 1
a part of the laser beam, the part reaching the slit portion formed in the mask, semicylindrically diffracts with the slit portion as an axis, is condensed by the condenser in a longitudinal direction of the slit portion
Implementation Method 2
detecting the position of the condensing point forming the proper irradiation mark as a position of an accurate condensing point
Data Source
AI summary
There is provided a condensing point position detecting method of detecting a position in an optical axis direction of a condensing point of a laser beam condensed by a condenser of a laser processing apparatus. The condensing point position detecting method includes: an irradiation mark forming step of forming a plurality of irradiation marks in a substrate by irradiating the substrate held by a chuck table with the laser beam while moving the condenser in the optical axis direction with respect to the substrate; and a condensing point position detecting step of detecting an irradiation mark having a proper shape from the plurality of irradiation marks formed in the substrate, and detecting the position of the condensing point forming the proper irradiation mark as a position of an accurate condensing point.