Multi-Phase Shift Photomask for Non-Uniform Wafer Focusing
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Solution Overview
Problem
Conventional photomasks fail to accurately focus light on semiconductor wafers with non-uniform focal planes, leading to distorted patterns due to differences in layer heights across various areas, resulting in blurry or inaccurate etching.
Innovation Solution
A multi-shifting photomask with adjustable protrusions and absorber portions on its light-exit surface, allowing for customized phase shifts to align focal planes with varying heights on the wafer, ensuring focused exposure across all areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photomasks with uniform phase-shifting are used, then the manufacturing process is simple, but the focusing accuracy deteriorates on wafers with non-uniform focal planes
Solution Approach 1:
The photomask applies different phase-shifting properties to different regions corresponding to different focal planes. Specifically, a first phase-shifting amount is applied to a first region and a second phase-shifting amount is applied to a second region, allowing each region to be optimized for its specific focal plane requirements.
Solution Approach 2:
The photomask is divided into multiple regions, each with distinct phase-shifting characteristics. The mask structure includes a substrate with multiple absorber layers or phase-shifting layers that create different optical path differences for different regions, enabling simultaneous focus compensation for multiple focal planes.
2Manufacturing precision
If phase-shifting photomasks are used to improve pattern sharpness, then the etching accuracy is improved, but the photomask design and manufacturing complexity increases
Solution Approach 1:
The invention controls the optical path difference parameter to achieve specific phase-shifting amounts (e.g., 180 degrees or pi radians) for different regions. By precisely controlling the thickness and refractive index of layers, the desired phase shifts are achieved to enhance etching accuracy while maintaining manufacturability through standardized layer deposition processes.
3Manufacturing precision
If multiple phase-shifting amounts are applied to different regions, then the focal plane alignment is improved across varying wafer heights, but the photomask manufacturing complexity increases
Solution Approach 1:
The invention introduces an optical dimension (phase shift) to compensate for physical height variations in the wafer. By manipulating the optical path length through different phase-shifting layers rather than physically adjusting the wafer or mask position, focal plane alignment is achieved across multiple height levels.
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 photomask ensures sharp and accurate patterns are etched across semiconductor devices with different focal planes, enhancing manufacturing yield and reducing defects, while being compatible with existing photolithography apparatuses.
Implementation Method 1
phase-shifting photomasks are specifically designed only to allow for passing light to exit the photomask with either a zero degree phase shift (in exposure areas) or a 180 degree phase shift (in non-exposure areas)
Implementation Method 2
a first optical path difference different from a second optical path difference between a first region and a second region
Data Source
AI summary
Manufacturing of semiconductor devices often involves performed photolithography to pattern and etch the various features of those devices. Such photolithography involves masking and focusing light onto a surface of the semiconductor device for exposing and etching the features of the semiconductor devices. However, due to design specifications and other causes, the semiconductor devices may not have a perfectly flat light-incident surface. Rather, some areas of the semiconductor device may be raised or lowered relative to other areas of the semiconductor device. Therefore, focusing the light on one area causes another to become unfocused. By carefully designing a photomask to cause phase shifts of the light transmitted therethrough, focus across all areas of the semiconductor device can be achieved during photolithography, which results in sharp and accurate patterns formed on the semiconductor device.