Laser Fluence Control for Recessed Workpiece Processing
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Solution Overview
Problem
In semiconductor exposure apparatuses, the large spectral line width of KrF and ArF excimer laser devices leads to chromatic aberration and decreased resolution, necessitating a line narrowing module to reduce spectral line width, but this can result in film formation on workpiece surfaces due to varying fluence, affecting processing accuracy.
Innovation Solution
A laser processing method and system that concentrate laser light on a workpiece's front and bottom surfaces with specific fluence conditions (Fin < Ffth < Fmth) to prevent film formation and ensure effective processing, using an optical system with an fθ lens to control fluence and prevent chemical reactions at the upper end of recessed portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module is provided in the laser resonator to narrow the spectral line width, then chromatic aberration is reduced and resolution is improved, but film formation occurs on the workpiece surface due to varying fluence
Solution Approach 1:
The patent divides the laser processing into two distinct processes: a first process that concentrates laser light on the front surface to form a recessed portion, and a second process that concentrates laser light on the bottom surface of the recessed portion. This segmentation allows different fluence conditions to be applied to different regions, preventing film formation while maintaining resolution improvements from line narrowing
Solution Approach 2:
The patent applies different fluence conditions to different locations: in the first process, the fluence at the front surface is controlled to be below the film formation threshold, while in the second process, the fluence at the bottom surface is controlled to be above the film formation threshold. This local quality approach allows film formation to be prevented where needed while enabling effective processing where required
2Manufacturing precision
If laser light is concentrated on the front surface to form a recessed portion, then processing is initiated, but film formation occurs on the wall surface due to insufficient fluence control
Solution Approach 1:
The patent performs preliminary action by first forming a recessed portion through the first process with controlled fluence below the film formation threshold, creating a structure that directs subsequent laser light to the bottom surface. This preliminary recessed portion formation prevents film formation on the wall surfaces during the subsequent second process
Solution Approach 2:
The patent uses periodic pulsed laser action with different fluence levels: the first process uses lower fluence pulses to form the recessed portion without causing film formation, while the second process uses higher fluence pulses to process the bottom surface. This periodic alternation between different fluence conditions prevents film formation while maintaining processing effectiveness
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
The method effectively suppresses film formation and unnecessary processing, maintaining high precision and accuracy in forming recessed features like through holes by controlling fluence within specific limits, thereby enhancing the resolution and reliability of laser processing.
Implementation Method 1
concentrate laser light on a front surface of a workpiece to form a recessed portion, and a second process to concentrate the laser light on a bottom surface of the recessed portion
Implementation Method 2
an fθ lens which concentrates the laser light traveling from the optical system on a front surface of a workpiece
Implementation Method 3
there is a case in which a film is formed on a wall surface on an upper end side of the recessed portion
Data Source
AI summary
A laser processing method includes a first process to concentrate laser light on a front surface of a workpiece to form a recessed portion, and a second process to concentrate the laser light on a bottom surface of the recessed portion. In the second process, a fluence Fin satisfies an expression of Ffth<Fin<Fmth, where Fin represents a fluence of the laser light at an upper end of the recessed portion, Ffth represents a fluence being an upper limit with which a film is formed by a chemical reaction between the workpiece and the atmosphere due to irradiation with the laser light, and Fmth represents a fluence being a lower limit with which the laser light is capable of processing the workpiece.