Spatial Light Modulator Pupil Shape Stability Feedback Control
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Solution Overview
Problem
Conventional spatial light modulators in illumination optical systems for lithography experience fluctuations in light intensity distribution due to changes in the rigidity of their driving mechanisms caused by exposure to illumination light, leading to unstable pupil shapes.
Innovation Solution
An illumination method and apparatus that utilize a spatial light modulator with multiple optical elements, where the state of incident light is controlled and monitored, and the control amounts are adjusted based on integrated energy measurements to maintain stable light intensity distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a spatial light modulator with multiple mirror elements is used to control light intensity distribution, then the pupil shape can be optimized for various illumination conditions, but the rigidity of the driving mechanism changes due to radiation from the illumination light beam, causing fluctuation in the light intensity distribution
Solution Approach 1:
The patent implements a feedback control mechanism where a monitor unit continuously measures the actual light intensity distribution on the pupil plane, and the control system adjusts the control amounts for each mirror element based on the difference between the target and actual distributions. This closed-loop feedback compensates for rigidity changes in the driving mechanism caused by radiation, maintaining stable light intensity distribution despite thermal effects during prolonged exposure
Solution Approach 2:
The patent dynamically changes the control parameters (control amounts) for each mirror element based on monitored light intensity measurements. By adjusting these parameters in real-time according to the actual state of the system, the patent compensates for drift in the driving mechanism rigidity and maintains the desired pupil shape throughout the exposure process
2Productivity
If exposure is continued for prolonged periods, then productivity increases, but the accumulated radiation causes gradual variation and fluctuation in the pupil shape
Solution Approach 1:
The patent maintains continuous monitoring and correction of the light intensity distribution throughout the prolonged exposure process. The monitor unit continuously measures the pupil plane intensity, and the control system continuously adjusts mirror element positions, ensuring uninterrupted compensation for thermal drift. This continuous action allows prolonged exposure operations while maintaining pupil shape consistency
Solution Approach 2:
The feedback mechanism operates continuously during prolonged exposure, detecting accumulated thermal effects on the driving mechanism rigidity and compensating in real-time. This enables extended productivity without sacrificing pupil shape stability, as the system adaptively corrects for cumulative radiation effects
Data Source
AI summary
There is provided an illumination method for illuminating an illumination objective surface by using a light from a light source. The illumination method includes setting control amount for controlling a plurality of optical elements, to control a state of an incident light coming into each of the plurality of optical elements, the plurality of optical elements being arranged in parallel and being capable of controlling the state of the incident light; illuminating the illumination objective surface with the light from the light source via the plurality of optical elements; monitoring integrated energy of the light from the light source; and correcting the control amount for the plurality of optical elements on the basis of a result of the monitoring of the integrated energy.