Pellicle Agglutinant Layer for Mask Flatness Control
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Solution Overview
Problem
The existing pellicle systems for lithography cause deformation and flatness changes in masks due to the mismatch in flatness between the pellicle frame and the mask, leading to pattern deformation and poor overlay alignment accuracy, especially with the increasing demand for sub-quarter-micron resolutions.
Innovation Solution
A pellicle with an agglutinant layer having a Young's modulus of 0.01 to 0.1 MPa, a tensile strength of 0.02 to 0.1 N/mm², and a surface flatness of 0 to 15 micrometers, which allows for an adhesion-assist load of 0.008 to 5 kgf to minimize deformation and prevent air pass creation when attached to the exposure original plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pellicle is attached to the mask to prevent dust adhesion, then dust protection is improved, but mask flatness deteriorates due to pellicle frame deformation
Solution Approach 1:
A buffer layer is introduced between the pellicle frame and the mask to act as an intermediary that absorbs deformation. The buffer layer has different mechanical properties than both the rigid pellicle frame and the delicate mask, allowing it to cushion the frame's deformation and prevent direct transmission to the mask surface.
Solution Approach 2:
The mechanical parameters of the buffer layer are specifically designed to match or bridge the gap between the pellicle frame and mask properties. By controlling the buffer layer's elasticity, thickness, and material composition, the system transforms the rigid connection into a compliant interface that accommodates frame deformation without compromising mask flatness.
2Manufacturing precision
If the pellicle frame flatness is increased to match mask flatness, then mask deformation is reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The pellicle system is segmented into three distinct functional layers: the pellicle frame, the buffer layer, and the mask. This segmentation allows each component to be optimized independently - the frame provides structural support and dust protection, the buffer layer absorbs deformation, and the mask maintains pattern precision, avoiding the need to over-engineer the frame's flatness.
Solution Approach 2:
The buffer layer serves as a mediator that decouples the mechanical relationship between the pellicle frame and mask. This allows the frame to have lower, more manufacturable flatness specifications while still protecting the mask, as the buffer absorbs the dimensional mismatches and deformation differences.
3Strength
If a rigid connection is used between pellicle frame and mask, then attachment strength is improved, but pattern positioning accuracy deteriorates due to stress transmission
Solution Approach 1:
The buffer layer is implemented as a flexible thin film that provides compliant attachment between the frame and mask. This flexible interface maintains sufficient mechanical strength for attachment while allowing stress relaxation, preventing rigid stress transmission that would deform the mask pattern and compromise positioning accuracy.
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 solution effectively minimizes mask deformation and maintains accurate pattern positioning by absorbing unevenness of the pellicle frame, ensuring air pass-free adhesion and reducing the risk of pellicle detachment, thus enhancing the flatness and alignment accuracy of the mask.
Implementation Method 1
an agglutinant layer, which is characterized in that the material for the agglutinant layer is selected from such that when an adhesion-assist load of 0.008 to 5 kgf including a weight of the pellicle is added on the exposure original plate, no air pass is created
Data Source
AI summary
A pellicle for lithography, in which an agglutinant layer is so controlled that the deformation of the pellicle frame is prevented from transferring to an exposure original plate to which the pellicle is attached so that pattern transferred scarcely undergoes deformation; in particular the agglutinant layer has a Young's modulus of 0.02 to 0.08 MPa and a tensile bond strength of 0.04 to 0.08 N/mm2.