Photomask Blank With Segmented Hardmask And Frame Layer
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Solution Overview
Problem
Conventional phase shift masks require a thick opaque material layer for both the frame and the mask pattern, leading to suboptimal thickness for image resolution and increased risk of stray light distortion, as the same layer is used for both functions.
Innovation Solution
A method where a mask blank is coated with a layer stack including a frame layer, a first hardmask layer, and a phase-shift layer, where the frame layer is patterned separately from the hardmask layer to form a thicker frame that blocks stray light, allowing the hardmask layer to be thinner and optimized for pattern formation, and the phase-shift layer for improved image resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick opaque material layer is used for both the frame and mask pattern, then the frame can effectively block stray light, but the thickness is suboptimal for image resolution and requires a thick resist layer
Solution Approach 1:
The patent divides the originally unified opaque material layer into two separate layers: a thick frame layer (50-100 nm) dedicated to blocking stray light, and a thin hardmask layer (3-10 nm) optimized for pattern formation. This segmentation allows each layer to be optimized for its specific function without compromise.
Solution Approach 2:
Different regions of the mask structure are assigned different thicknesses and material properties. The frame region uses a thick opaque layer for maximum light blocking, while the chip area uses a thin hardmask layer for precise patterning and optimal image resolution. This local differentiation resolves the contradiction between stray light blocking and manufacturing precision.
2Device complexity
If the same opaque material layer is used for both frame and mask pattern, then the structure is simpler, but a thick resist layer is required and processing becomes more complex
Solution Approach 1:
By segmenting the functional layers, the patent enables different etching processes to be applied to different regions. The frame can be formed first using the thick frame layer, then the chip area can be processed with the thin hardmask layer, allowing for optimized processing sequences and reduced resist thickness requirements.
Solution Approach 2:
The frame layer is patterned and formed as a preliminary structure before the hardmask layer is processed. This preliminary action allows the frame to serve as a reference and protective structure during subsequent chip area processing, simplifying the overall manufacturing sequence despite the increased layer count.
3Illumination intensity
If a thick opaque material layer is used, then sufficient optical density is achieved, but the hardmask layer thickness is not optimized for pattern formation
Solution Approach 1:
The patent applies different material thicknesses to different functional regions: the frame layer achieves high optical density (50-100 nm) for stray light blocking, while the hardmask layer uses optimal thin thickness (3-10 nm) for precise pattern formation. This local quality differentiation resolves the contradiction between optical density and pattern formation quality.
Solution Approach 2:
By separating the opaque material into distinct frame and hardmask layers, each layer can be independently optimized for its specific requirement. The frame layer thickness is optimized for optical blocking, while the hardmask layer thickness is optimized for etching precision and pattern fidelity.
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 approach reduces the need for a thick resist layer, improves image resolution, linearity, and critical dimension uniformity by allowing for thinner hardmask layers and asynchronous formation of the frame and mask features, minimizing damage to sub-resolution assist features and reducing processing steps.
Implementation Method 1
The frame is configured to block light from entering from outside of the chip area when the photomask is used in a lithography tool
Implementation Method 2
Phase shift masks are photomasks that leverage the interference generated by phase differences to thereby improve image resolution
Data Source
AI summary
Methods for manufacturing a photomask, photomask blanks, and photomasks used in chip fabrication. A phase-shift layer is formed on a mask blank, a hardmask layer is formed on the phase-shift layer, and a layer stack is formed on the hardmask layer to make a photomask blank. The layer stack includes a first layer comprised of a first material and a second layer comprised of a second material that can be etched selective to the first material. The first layer is thicker than the second layer, and the first layer is also thicker than the hardmask layer. The photomask blank may be used to make a photomask in which, during manufacture, the hardmask layer is used to pattern mask features in a chip area of the photomask and the thicker of the first layer or the second layer is used to pattern a frame of the photomask.