Phase-Shift Mask Endpoint Layer Design
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Solution Overview
Problem
In photolithography, the reduction of semiconductor device feature sizes to below the wavelength of light used leads to distorted pattern transfer due to optical fringing, and the use of phase-shift masks is hindered by over-etching issues caused by similar atomic numbers of the phase shifter and substrate, resulting in reduced image quality and increased light scattering.
Innovation Solution
A phase-shift mask is fabricated with an end-point layer having a distinct atomic number and transparency to specific wavelengths, combined with a phase shifter that shifts light by π, and an opaque layer to minimize undesired light leakage, along with specific deposition processes and etch techniques to enhance image contrast and prevent over-etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a phase-shift mask is used to improve pattern transfer precision, then resolution is improved, but over-etching occurs due to similar atomic numbers of phase shifter and substrate
Solution Approach 1:
The patent divides the mask structure into distinct functional layers: a substrate layer, a phase shifter layer deposited on the substrate, and an endpoint layer deposited on the phase shifter. This segmentation allows the endpoint layer to serve as a distinct etching reference point with a different atomic number from both the substrate and phase shifter, enabling reliable endpoint detection during etching while maintaining the phase-shifting function of the middle layer.
Solution Approach 2:
The endpoint layer acts as an intermediary between the substrate and the phase shifter during etching processes. It provides a distinct atomic number signature that serves as a reliable endpoint indicator for etching the phase shifter layer, preventing over-etching into the substrate while allowing the phase shifter to maintain its optical function.
2Productivity
If feature sizes are reduced below the wavelength of light used, then device density increases, but optical fringing causes distorted pattern transfer
Solution Approach 1:
The patent utilizes phase-shifting parameters to modify the optical properties of light passing through the mask. By introducing a phase shifter layer that shifts the phase of transmitted light by π (180 degrees), the patent creates destructive interference of optical fringing effects, thereby improving pattern transfer accuracy for sub-wavelength features while maintaining high device density.
3Ease of operation
If the atomic number of the phase shifter is similar to the substrate, then material compatibility is improved, but image contrast decreases and light scattering increases
Solution Approach 1:
The patent segments the mask structure into three distinct layers with different atomic numbers: the substrate, the phase shifter layer, and the endpoint layer. This segmentation ensures that the endpoint layer has a distinct atomic number from both the substrate and phase shifter, providing sufficient image contrast for etching while allowing the phase shifter to maintain material compatibility with the substrate for its optical function.
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 improves the precision of pattern transfer by reducing over-etching and light scattering, maintaining image quality and minimizing the risk of false end-point detection, thereby enhancing the resolution and accuracy of semiconductor device fabrication.
Implementation Method 1
a phase shifter over the end-point layer and configured to shift a phase of incident light by π
Implementation Method 2
the phase shifter is configured to shift a phase of incident light by π
Implementation Method 3
an end-point layer over the substrate, wherein a signal contrast between the end-point layer and each of the phase shifter and the opaque layer is greater than a signal contrast between the substrate and each of the phase shifter and the opaque layer
Data Source
AI summary
A method of manufacturing a mask includes depositing an end-point layer over a light transmitting substrate, depositing a phase shifter over the end-point layer, depositing a hard mask layer over the phase shifter, and removing a portion of the hard mask layer and a first portion of the phase shifter to expose a portion of the end-point layer. The end-point layer and the light transmitting substrate are transparent to a predetermined wavelength.