Direct Laser Interference Patterning of Thin Films
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Solution Overview
Problem
Existing methods for forming periodic structures in thin films require intermediate photoresist layers and chemical etching, which are complex, slow, and limited in pattern diversity, and cannot change the shape of the formed structures.
Innovation Solution
Directly forming periodic structures in thin films using interfering laser beams without photoresist and chemical etching, by controlling the phase difference and intensity of multiple laser beams to achieve diverse symmetrical patterns, including hexagonal, square, and rectangular symmetries, and modifying the interference distribution with a central beam and varying the distance between the film and beam intersection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If interfering laser beams are used to form periodic structures directly in thin films, then manufacturing complexity and process time are reduced, but control over structure shape and pattern diversity is limited
Solution Approach 1:
The patent applies dynamics by making the laser beam parameters adjustable and variable during the formation process. The phase difference between interfering beams can be dynamically changed to produce different interference patterns, and the laser intensity can be adjusted to control the ablation depth and structure shape. This dynamic control enables the same laser system to produce multiple pattern types (circular holes, rectangular structures, triangular patterns) without changing the fundamental direct-write approach, thus maintaining high productivity while achieving pattern diversity.
Solution Approach 2:
The patent utilizes parameter changes by varying key laser parameters including phase difference between interfering beams, laser intensity, pulse duration, and beam convergence angle. By changing the phase difference from 0 to π/2 to π, different interference maxima positions are created, resulting in different structural patterns. The laser intensity is adjusted to control whether material is ablated or merely modified, enabling both hole formation and surface structuring. These parameter changes allow a single direct laser writing method to achieve multiple pattern types and structures.
2Manufacturing precision
If intermediate photoresist layers and chemical etching are used, then pattern precision and control are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the intermediate photoresist layer and chemical etching steps from the traditional multi-stage process. By using direct laser ablation and modification of the thin film material itself, the method removes the need for separate patterning and etching processes. The laser directly writes the desired pattern into the functional film, combining what were previously separate steps (patterning + etching + cleaning) into a single direct-write operation, thus reducing process complexity while maintaining precision through direct digital control of the laser.
Solution Approach 2:
The patent applies self-service by using the laser beam itself to both define the pattern and directly modify/ablate the material to create the final structure. The interfering laser beams create an interference pattern that directly correlates to the desired structure locations, and the same laser energy that defines the pattern also performs the material removal or modification. This self-service approach eliminates the need for separate photoresist coating, exposure, development, and chemical etching processes, reducing both complexity and the number of process steps while maintaining manufacturing precision through direct optical control.
3Productivity
If laser intensity is increased above ablation threshold, then structure formation speed is improved, but control over structure shape and size is reduced
Solution Approach 1:
The patent applies periodic action by using pulsed laser radiation with controlled pulse duration and repetition frequency. The pulsed nature allows the material to respond differently at different stages: during each pulse, high intensity creates rapid ablation for efficient material removal, while the intervals between pulses allow heat dissipation and prevent excessive melting or deformation. This periodic application of energy enables both fast structure formation and good shape control, as the cumulative effect of multiple controlled pulses builds the desired structure progressively with precision.
Solution Approach 2:
The patent utilizes partial action by adjusting the laser intensity to be just above the ablation threshold for minimal material removal, or significantly above for rapid ablation, depending on the desired outcome. By using interfering beams, the energy is distributed in a periodic pattern where only specific regions (interference maxima) receive sufficient intensity for ablation, while other regions receive sub-threshold energy for minimal effect. This partial application of excessive energy at specific locations enables fast structure formation at targeted positions without affecting the entire film uniformly, thus maintaining shape control while improving formation speed.
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
Enables the direct and efficient creation of various periodic structures without intermediate steps, allowing for control over shape and size, extending the application to spectral filters, frequency selective coatings, and thin-film electronic contacts, with improved manufacturing efficiency and diversity of patterns.
Implementation Method 1
when the pulse laser beam is split into two beams that are focused on the metal film, by forming there an interference field, where at the intensity maxima of the interference field the metal is ablated
Implementation Method 2
The said interfering beams form a periodic radiation intensity distribution in the photoresist
Data Source
Figure 1~2(b)
Figure 3~4f
Figure 5~6b
AI summary
The invention relates to the field of laser technology and provides for the direct formation methods of periodic structures in thin films, and can be used to produce periodic structures (arrays) for spectral and other optical devices, as well as shielding of electromagnetic field. This invention seeks to form periodic structures directly without using intermediate films (photoresist) and without using additional operations (placing photoresist, developing, chemical etching), and to control the formation of periodic structures with different shapes. Three or four, or six interfering laser beams get directed into the thin material film, in such a way that by interfering they would form a periodic laser radiation intensity distribution. At the high intensity zones of the interference pattern, the film material is ablated, while the remaining film material forms the periodic structure, which corresponds to the layout of low-intensity interference image. The shape of the formed periodic structures can be changed, by modifying the overall level of intensity of the interfering laser beams directed into the said film, by satisfying the condition the condition that the said total intensity at the maxima of the formed intensity distribution should be greater than the evaporation intensity threshold of the said film.