EUV Mirror Coating Compaction for Stable Surface Shape
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Solution Overview
Problem
Existing methods for manufacturing mirrors for semiconductor lithography systems, particularly EUV lithography systems, face challenges in maintaining the mirror's surface geometry and reflectivity specifications due to unpredictable changes in substrate compaction and reflective coating thickness during and after coating processes, leading to wavefront errors and stray light issues.
Innovation Solution
A method that optimizes the local compaction of the substrate and reflective coating jointly, considering factors like surface shape, reflectivity changes, and temperature distribution, using a combination of electron beam and laser-induced annealing to correct and stabilize these properties over the mirror's lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reflective coating is applied to the substrate surface, then the mirror achieves the required reflectivity for EUV radiation, but the coating process causes unpredictable changes in surface shape and compaction, leading to wavefront errors and stray light
Solution Approach 1:
The patent applies preliminary electron beam irradiation to compact the substrate surface before applying the reflective coating. This pre-compaction action anticipates and compensates for the unpredictable compaction that would otherwise occur during the coating process, thereby maintaining surface shape precision while achieving the required reflectivity.
Solution Approach 2:
The patent changes the physical state and properties of the substrate through controlled electron beam irradiation, inducing compaction and densification of the substrate material. By adjusting irradiation parameters (dose, energy distribution), the substrate's mechanical properties are modified to compensate for subsequent coating-induced deformations, resolving the contradiction between achieving reflectivity and maintaining surface precision.
2Manufacturing precision
If local electron beam irradiation is used to compact the substrate and correct surface shape, then the surface geometry is improved, but the reflective coating becomes detuned due to compaction, affecting reflection behavior
Solution Approach 1:
The patent applies local electron beam irradiation with spatially varying energy distribution to compact different regions of the substrate to different degrees. By tailoring the irradiation dose and energy locally, the substrate compaction is optimized for each region to maintain surface geometry, while the reflective coating's compaction is simultaneously managed to preserve its optical properties and reflection behavior.
3Duration of action of stationary object
If tempering is applied to accelerate decompacting and stabilize the substrate, then the lifetime stability is improved, but the reflective coating undergoes additional compaction, requiring further detuning compensation
Solution Approach 1:
The patent incorporates tempering as a preliminary stabilization step before final coating optimization. By applying controlled thermal tempering to accelerate decompacting and stabilize the substrate's long-term behavior, the substrate reaches a more stable equilibrium state. This preliminary stabilization reduces lifetime drift, and subsequent coating parameter adjustments compensate for the predictable coating compaction that occurs during tempering, maintaining both stability and precision.
4Manufacturing precision
If multiple sequential processes (coating, electron beam compaction, annealing, laser-induced annealing) are used to optimize mirror properties, then the manufacturing precision is improved, but the processing time and development effort increase significantly
Solution Approach 1:
The patent merges the electron beam compaction process with the reflective coating application process, and integrates annealing steps into a unified thermal processing sequence. By combining these previously sequential operations into integrated process steps, the patent reduces the total number of separate processing stages while maintaining the necessary precision for surface geometry and coating quality, thereby reducing overall processing time and development effort.
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 reduces processing time and development effort while ensuring precise control over mirror performance, minimizing wavefront errors and stray light by optimizing the interaction between substrate compaction and coating compaction processes.
Implementation Method 1
locally compacting the substrate, preferably by electron beam processing
Implementation Method 2
with subsequent annealing, especially with homogeneous annealing
Implementation Method 3
locally compacting the reflective coating by local, preferably radiation-induced, annealing of the mirror
Implementation Method 4
a reflective coating for reflecting light from a light source in the EUV range
Data Source
Figure 1
Figure 2a~4b
AI summary
The invention relates to a method for producing a mirror (Mi) for a semiconductor lithography system, in particular for an EUV lithography system, comprising: applying a reflective coating (26) to a surface (25a) of a substrate (25) of the mirror (Mi), locally compacting the substrate (25), preferably by electron beam processing, in particular with subsequent annealing, in particular homogeneous annealing, and locally compacting the reflective coating (26) by local, preferably radiation-induced annealing of the mirror (Mi).During the fabrication of the mirror (Mi), the local compaction of the substrate (25) and the local compaction of the coating (26) are jointly optimized, taking into account the following influencing factors: a local surface shape (PA, PB) during the fabrication of the mirror (Mi), a change in the local surface shape (PA, PB) due to decompacting the substrate (25) over the lifetime of the mirror (Mi), a local reflectivity (RA, RB) of the mirror (Mi), a change in the local reflectivity (RA, RB) due to compaction of the reflective coating (26) over the lifetime of the mirror (Mi), and an expected temperature distribution on the surface (25a) of the substrate (25) during operation of the mirror (Mi) in the semiconductor lithography system.