EUV Exposure Apparatus Mask Defocus Measurement
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Solution Overview
Problem
In EUV exposure technology, measuring mask defocus and distortion is challenging due to the short wavelength of the exposure light and the electrostatic chuck system, leading to difficulties in accurately transferring patterns to semiconductor wafers.
Innovation Solution
An exposure apparatus with a variable light blocking slit that adjusts its aperture shape and position to measure light intensity, allowing for the calculation of mask defocus and distortion by maximizing light intensity, thereby correcting focus and alignment issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrostatic chuck system is used to hold the mask under vacuum, then the mask can be securely held for EUV exposure, but mask defocus occurs due to particles attached on the absorbing unit or variation of absorption force
Solution Approach 1:
The system performs preliminary measurement of mask defocus and distortion using ArF exposure light before the actual EUV exposure. This allows the mask position and shape to be measured in advance, and correction data to be obtained before the main manufacturing process begins
Solution Approach 2:
The system uses detection units to measure the mask's actual position and shape, then feeds this information back to a control unit that calculates correction values. These corrections are applied to compensate for the defocus caused by the electrostatic chuck system, creating a closed-loop control mechanism
2Measurement precision
If ArF lithography measurement methods are used, then mask defocus can be measured in conventional systems, but it is difficult to measure mask defocus and distortion in EUV exposure technology apparatus
Solution Approach 1:
The system employs a multi-functional measurement approach that can measure both mask defocus and distortion using the same apparatus. It uses ArF exposure light for measuring mask defocus and shape, while the same system is adapted to measure distortion through specific detection unit configurations, making the EUV apparatus versatile for multiple measurement types
Solution Approach 2:
The system introduces an intermediary measurement process using ArF light as a mediator to indirectly measure mask properties that would be difficult to measure directly with EUV light. The ArF light serves as an intermediate tool to obtain measurement data that is then used to correct the actual EUV exposure process
3Productivity
If mask defocus and distortion are not measured and corrected, then the EUV exposure process can proceed without additional measurement steps, but defocus and distortion occur in the transfer pattern on the wafer
Solution Approach 1:
The system performs mask measurement and correction calculations before the actual EUV exposure of production patterns. By measuring mask defocus and distortion in advance using measurement marks and performing corrections beforehand, the system ensures high transfer pattern accuracy without slowing down the main production exposure process
Solution Approach 2:
The system separates the measurement and correction functions from the main exposure process. Measurement marks are placed in specific regions of the mask, allowing measurement to be performed on these dedicated marks while the rest of the mask contains the production patterns. This segmentation allows measurement and production to occur efficiently without interfering with each other
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 accurate measurement and correction of mask defocus and distortion, improving the transfer characteristics of patterns onto semiconductor wafers, enhancing the precision of EUV lithography processes.
Implementation Method 1
a light blocking unit that passes an exposure light reflected on a reflective mask through an aperture and that blocks the exposure light at a part other than the aperture
Implementation Method 2
a detection unit that measures the light intensity of the exposure light passed through the light blocking unit
Data Source
AI summary
According to one embodiment, an exposure apparatus includes a light blocking unit that blocks an exposure light reflected on a reflective mask at a part other than an aperture; a detection unit that measures a light intensity of the exposure light passed through the light blocking unit; and a calculation unit that calculates, based on the light intensity, a transfer characteristic when a pattern on the reflective mask is transferred to a substrate. In the light blocking unit, a position on an aperture plane and a position in an optical axis direction of the exposure light are adjusted. The calculation unit calculates the transfer characteristic based on the position in the optical axis direction in which the light intensity is maximized.