Hexagonal Light-Homogenizing Rod for Exposure Field Uniformity
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Solution Overview
Problem
Photolithographic tools face challenges in achieving a high useful depth of focus and adaptability when imaging dense patterns on patterned sapphire substrates, leading to inhomogeneous pattern images and low yield due to focal plane control errors and substrate warpage.
Innovation Solution
The exposure apparatus employs a light-homogenizing quartz rod with a regular hexagonal cross section and matching hexagonal masks, along with a flood exposure unit, to reduce the impact of projection objective depth of focus and increase the useful field of view, allowing for more accurate and consistent pattern imaging on substrates like sapphire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional quadrilateral light-homogenizing rod and masks are used, then the illumination system is simple and easy to manufacture, but the useful depth of focus is reduced and pattern inhomogeneity occurs
Solution Approach 1:
The patent applies asymmetry by changing the light-homogenizing rod from a conventional quadrilateral cross-section to a regular hexagonal cross-section. This asymmetric geometric change optimizes the light distribution path, reducing the impact of projection objective depth of focus limitations and eliminating pattern inhomogeneity while maintaining manufacturability.
2Area of stationary object
If the field of exposure size is increased, then more substrate area is covered, but the impact of projection objective depth of focus increases causing greater pattern inhomogeneity
Solution Approach 1:
The hexagonal cross-section of the light-homogenizing rod creates an optimized light distribution pattern that maintains uniformity across a larger exposure field. The geometric properties of the hexagon allow for better light homogenization compared to quadrilateral designs, enabling increased field area without sacrificing pattern uniformity.
3Manufacturing precision
If multiple measure and exposure cycles are used, then focal plane accuracy is improved, but exposure time increases and productivity decreases
Solution Approach 1:
The patent implements preliminary action by performing comprehensive focal plane measurement and tilt calculation before the actual exposure process. The system measures the substrate surface profile, calculates the tilt for each field of view, and stores this data for use during exposure. This pre-processing eliminates the need for multiple iterative cycles during exposure, achieving high focal plane accuracy in a single pass and significantly improving productivity.
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 configuration enhances the steepness of pattern side faces, improves pattern regularity, increases yield, and reduces manufacturing costs by enabling exposure in one pass with improved focal plane control and adaptability to substrates with high hardness or warpage.
Implementation Method 1
a light-homogenizing quartz rod in a light-homogenizing unit of the illumination system has a regular hexagonal cross section
Implementation Method 2
The light-homogenizing unit includes a light-homogenizing quartz rod
Implementation Method 3
a projection objective for projecting a pattern onto a substrate
Implementation Method 4
the imaging of dense holes or circular pillars is much more difficult and tends to suffer from a much reduced depth of focus
Data Source
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AI summary
An exposure apparatus includes an exposure unit (100) for exposing a wafer (200). The exposure unit (100) includes an illumination system (110) and masks (120). The illumination system (110) includes a light-homogenizing unit (113). The light-homogenizing unit (113) includes a light-homogenizing quartz rod (1131) having a regular hexagonal cross section. Each of the masks (120) has a regular hexagonal shape matching with the cross section of the light-homogenizing quartz rod (1131). A field of exposure resulting from this arrangement is less affected by objective field of view distortion and allows a higher useful depth of focus (UDoF) when compared to other fields of exposure of the same size. In addition, with the same projection objective DoF, a greater field of exposure can be obtained.