Exposure Apparatus Field Stop Aperture Edge Positioning
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Solution Overview
Problem
High numerical aperture in projection optical systems leads to stray light reflections from the reticle back surface, causing critical dimension abnormalities in adjacent areas due to the conventional positioning of the masking blade's aperture edge at the center of the light shielding area, which increases manufacturing costs and reduces imaging precision.
Innovation Solution
The aperture edge of the field stop in the illumination optical system is positioned closer to the patterned area than the center of the light shielding area, effectively restricting stray light reflections and maintaining imaging precision while reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the masking blade aperture edge is positioned at the center of the light shielding area, then the imaging precision is maintained, but stray light reflects off the reticle back surface causing critical dimension abnormalities in adjacent areas
Solution Approach 1:
The patent applies asymmetry by positioning the masking blade aperture edge asymmetrically relative to the light shielding area. Specifically, the aperture edge is positioned closer to the patterned area than to the center of the light shielding area, creating an asymmetric configuration that prevents stray light from reflecting off the reticle back surface and entering the projection optical system, thereby eliminating CD abnormalities in adjacent areas while maintaining imaging precision.
Solution Approach 2:
The masking blade aperture edge serves as an intermediary element that controls the path of illumination light. By strategically positioning this aperture edge, the patent mediates between the illumination light source and the reticle, blocking the specific angular range of light that would otherwise reflect off the reticle back surface and cause harmful stray light effects, thus preventing CD abnormalities.
2Object-affected harmful factors
If an antireflection film is applied to the reticle back plane to prevent stray light, then CD abnormality is avoided, but the manufacturing cost increases
Solution Approach 1:
The patent extracts the stray light control function from the reticle structure itself (by removing the need for antireflection films) and relocates it to the illumination optical system through the masking blade configuration. By positioning the aperture edge of the masking blade closer to the patterned area than to the center of the light shielding area, the system prevents stray light generation at its source, eliminating the need for expensive antireflection film applications on the reticle back plane.
Solution Approach 2:
The patent replaces the expensive and complex solution of applying antireflection films to the reticle with a simpler, more economical approach using the masking blade configuration. The masking blade, which is a standard component of the illumination optical system, is repositioned to achieve stray light control, avoiding the need for additional costly reticle modifications while effectively preventing CD abnormalities.
3Object-affected harmful factors
If the light shielding area is sufficiently widened to prevent stray light leakage, then CD abnormality is prevented, but the exposure area widens and device arrangement efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the effective light shielding configuration adjustable through the positioning of the masking blade aperture edge. Rather than requiring a fixed, excessively wide light shielding area, the system dynamically controls the illumination angle and light path by positioning the aperture edge closer to the patterned area, allowing the light shielding area to maintain its original size while still preventing stray light leakage that causes CD abnormalities.
Solution Approach 2:
The patent changes the critical parameter of the masking blade aperture edge position relative to the light shielding area. By adjusting this position to be closer to the patterned area than to the center of the light shielding area, the system alters the angular range of illumination light, effectively preventing stray light from reflecting off the reticle back surface. This parameter change allows the light shielding area to remain compact while still achieving stray light control, thereby maintaining device arrangement efficiency.
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 prevents critical dimension abnormalities by minimizing unnecessary light exposure on the wafer, enhancing imaging precision, and reducing manufacturing costs by optimizing the light shielding area without widening the exposure area.
Implementation Method 1
an illumination optical system for illuminating the patterned area of the reticle 20, including a field stop 18 having an aperture 18a which defines a region for illuminating the reticle 20
Implementation Method 2
a projection optical system 30 for projecting an image of the patterned area 22 of the reticle 20 onto a wafer 40
Implementation Method 3
the light can be reflected on the light shielding area, then on the reticle back surface that opposes to the patterned surface, and finally return to the reticle patterned surface
Data Source
AI summary
An exposure method for exposing a pattern of a reticle which has a patterned area that has the pattern, and a light shielding area provided around the patterned area, said exposure method includes the step of illuminating the reticle via an illumination optical system that includes a field stop, wherein a position corresponding to an edge of an aperture in the field stop is closer to the patterned area than a center of a width of the light shielding area on the reticle, the aperture defining a region for illuminating the reticle.