Reflective Photomask Border Annealing With Shaped Laser Spots
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Solution Overview
Problem
Conventional laser annealing methods for reflective photomasks result in an unnecessarily wide forbidden area due to a gentle slope in the edge area of the border, potentially damaging the reflection and absorption layers with steep slopes or cracks when using short pulsed lasers.
Innovation Solution
A method and apparatus for laser annealing that split-irradiate laser beam spots onto the border area of reflective photomasks, using a beam shaper with a blind area, transparent center, and semitransparent area to create a uniform energy profile at the center and an inclined profile at the edge, allowing for precise control of the energy distribution to recess the border area without damaging the layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a very short pulsed laser is used to create a steep slope in the edge area, then the reflectance of the border area is reduced, but the reflection layer and absorption layer are physically damaged (cracked)
Solution Approach 1:
The laser beam is divided into multiple discrete spots arranged in a matrix pattern across the border area. Each spot creates a localized modification, and the collective effect of all spots achieves the desired reflectance reduction without concentrating excessive energy in one location, thereby preventing layer damage.
Solution Approach 2:
The laser spots are strategically positioned to create different modification intensities in different regions. The edge areas receive controlled energy to form appropriate slopes, while the center areas receive different energy levels, achieving locally optimized properties that prevent both over-modification (damage) and under-modification (insufficient reflectance reduction).
2Illumination intensity
If a general laser annealing method is used, then the border area reflectance is reduced, but a very gentle slope occurs in the edge area causing the forbidden area to be unnecessarily widened
Solution Approach 1:
The laser processing parameters are dynamically adjusted based on the spatial position within the border area. By varying the spot size, energy density, and scanning speed across different regions, the method achieves a controlled slope profile that reduces reflectance effectively while maintaining precise control over the forbidden area dimensions.
Solution Approach 2:
Different laser parameters (power, pulse duration, spot size, scanning speed) are changed across different regions of the border area. The edge areas use parameters that create gentle slopes for reflectance reduction, while the center areas use parameters that maintain sharp boundaries, thus controlling the forbidden area width precisely.
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 effectively reduces the width of the edge area to be equal to or less than 1/20 of the border area, preventing physical damage and ensuring a sufficiently low reflectance in the border area while maintaining the integrity of the reflection and absorption layers.
Implementation Method 1
irradiating a laser beam onto the border area of the reflective photomask
Implementation Method 2
Method of annealing reflective photomask by using laser
Implementation Method 3
Each of the plurality of laser beam spots may be shaped using a beam shaper
Data Source
AI summary
A laser annealing method performed on a reflective photomask may include preparing a reflective photomask including a pattern area and a border area surrounding the pattern area and irradiating a laser beam onto the border area of the reflective photomask. The irradiating of the laser beam may include split-irradiating a plurality of laser beam spots onto the border area. Each of the plurality of laser beam spots may be shaped using a beam shaper. The beam shaper may include a blind area, a transparent area at a center of the blind area, and a semitransparent area between the blind area and the transparent area. Each of the plurality of laser beam spots may include a center portion passing through the transparent area and having a uniform energy profile and an edge portion passing through the semitransparent area and having an inclined energy profile.