Excimer Light Source Phase Modulation for Speckle Reduction
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Solution Overview
Problem
In semiconductor lithography, deep ultraviolet (DUV) light sources experience speckle patterns due to high temporal and spatial coherence, leading to reduced critical dimension uniformity and blurring of microelectronic features on wafers.
Innovation Solution
A method and apparatus that modulate the optical phase of pulses in a DUV light source to reduce temporal coherence, using a phase modulator system to convert pulses with high initial coherence into modified pulses with lower coherence, thereby reducing speckle patterns by adjusting the optical phase over the pulse duration and increasing the pulse duration through temporal stretching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temporal coherence is maintained in the DUV light source, then the light beam quality is improved, but speckle patterns occur leading to reduced critical dimension uniformity
Solution Approach 1:
The patent applies dynamic phase modulation to the light pulses, where the optical phase is continuously varied over the pulse duration. This dynamic change in phase causes the speckle pattern to fluctuate and average out over time, reducing the harmful speckle contrast while preserving the beneficial temporal coherence for light beam quality
Solution Approach 2:
The patent modifies the temporal coherence parameter by controlling the spectral bandwidth of the light pulses. By adjusting the bandwidth within acceptable ranges, the temporal coherence is optimized to reduce speckle patterns while maintaining the necessary coherence for high-quality lithography illumination
2Object-affected harmful factors
If temporal coherence is reduced to decrease speckle, then speckle patterns are reduced, but critical dimension uniformity may be affected
Solution Approach 1:
The dynamic phase modulation technique allows temporary reduction of temporal coherence during the pulse to reduce speckle, while the overall pulse structure maintains sufficient coherence. The phase is modulated only over a portion of the pulse duration, preserving the core coherence properties needed for critical dimension uniformity
Solution Approach 2:
The patent carefully controls the bandwidth parameter to achieve the right balance. By adjusting the bandwidth to remain within acceptable ranges, the temporal coherence is reduced enough to decrease speckle but not so much that it degrades critical dimension uniformity
3Object-affected harmful factors
If pulse duration is increased through temporal stretching, then speckle reduction is enhanced, but the pulse energy distribution is altered
Solution Approach 1:
The patent applies dynamic phase modulation during the pulse duration, which effectively increases the temporal coherence length and reduces speckle. This dynamic process allows energy redistribution in the time domain while maintaining the total pulse energy, achieving speckle reduction without significant energy loss
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 approach effectively reduces speckle patterns by decreasing temporal coherence, leading to improved critical dimension uniformity and clearer microelectronic features on wafers, with the coherence reduction limited by maintaining the slit-averaged bandwidth within acceptable ranges.
Implementation Method 1
the optical phase is modulated over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length
Data Source
AI summary
A method includes: producing a light beam made up of pulses having a wavelength in the deep ultraviolet range, each pulse having a first temporal coherence defined by a first temporal coherence length and each pulse being defined by a pulse duration; for one or more pulses, modulating the optical phase over the pulse duration of the pulse to produce a modified pulse having a second temporal coherence defined by a second temporal coherence length that is less than the first temporal coherence length of the pulse; forming a light beam of pulses at least from the modified pulses; and directing the formed light beam of pulses toward a substrate within a lithography exposure apparatus.