Rotating Transparent Plate for Photomask Exposure Uniformity
Solution Overview
Problem
Existing Talbot-effect-based photolithographic methods require high-collimation and monochromatic light, making them sensitive to small imperfections in optical components, which leads to localized intensity inhomogeneities and degradation of pattern resolution.
Innovation Solution
A method and apparatus that use a transparent plate with parallel surfaces to illuminate a photomask at an initial angle, then rotate the plate during exposure to displace the beam translationally across the mask, reducing the contrast of local inhomogeneities caused by optical defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-collimation and monochromatic light are used in Talbot-effect-based photolithography, then the Talbot effect can be effectively utilized for periodic pattern printing, but the system becomes sensitive to small imperfections in optical components, causing localized intensity inhomogeneities
Solution Approach 1:
The patent introduces dynamic movement of the photomask relative to the illumination beam during exposure. The mask is moved through a range of positions such that any localized intensity inhomogeneity (such as shadows from optical defects) is displaced across different regions of the mask during the exposure process. This dynamic displacement causes the inhomogeneities to be averaged out over time, reducing their contrast and improving uniformity of exposure while maintaining the ability to print high-resolution periodic patterns.
2Device complexity
If a stationary beam is used to illuminate the photomask, then the exposure process is simple, but localized inhomogeneities in the beam intensity distribution produce corresponding inhomogeneities in the printed pattern
Solution Approach 1:
The patent employs dynamic movement of the photomask during exposure to transform a static beam illumination problem into a dynamic one. By moving the mask through a range of positions, the system converts localized intensity inhomogeneities into time-dependent variations that average out during exposure, thereby improving pattern uniformity without significantly increasing process complexity.
Solution Approach 2:
The mask movement is performed in a periodic or systematic manner through a defined range of positions. This periodic action ensures that any given point on the mask receives illumination from different parts of the beam profile over time, causing inhomogeneities to be distributed and averaged out, thereby improving overall uniformity of exposure.
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 method effectively reduces the contrast of localized inhomogeneities in the energy density distribution, improving the uniformity of exposure and maintaining the resolution of the printed pattern.
Implementation Method 1
a) providing a plate that is composed of a material transparent to the beam and that has parallel opposing surfaces separated by a thickness; b) arranging said plate in the photolithographic system such that the beam illuminates the plate at an initial angle of incidence and the beam transmitted by the plate illuminates the photomask
Implementation Method 2
The periodic pattern in the mask diffracts the beam and at certain, periodic distances from the mask, which are separated by a so-called Talbot distance, the diffracted orders interfere to reproduce the pattern in the mask
Implementation Method 3
Photolithographic exposure of periodic patterns using the Talbot effect, or Talbot imaging, is well-known in the prior art
Data Source
AI summary
A method and an apparatus for improving the uniformity of exposure of a first periodic pattern in a photomask by a collimated beam of monochromatic light in a photolithographic system that prints a second periodic pattern into a photosensitive layer on a substrate that is in proximity to the photomask, include providing a plate that is composed of a material transparent to the beam and that has opposing surfaces that are parallel and separated by a thickness. The plate is arranged in the photolithographic system such that the beam illuminates the plate at an initial angle of incidence and the beam transmitted by the plate illuminates the photomask. The plate is rotated by at least one angle about at least one axis of rotation during the exposure such that the transmitted beam displaces translationally across the photomask.