Multilayer Halftone Phase Shift Mask for Defect Inspection
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Solution Overview
Problem
Current halftone phase shift masks face challenges in achieving precise defect inspection and maintaining desired optical properties when exposed to shorter wavelengths, such as 157 nm, due to variations in transmittance and reflectance, which affect etching behavior, etching rate, conductivity, and chemical resistance.
Innovation Solution
A multilayer halftone phase shift mask structure is developed, featuring a light absorbing film with a higher concentration of Group 4A metal elements near the phase shift film and a substrate, and a phase shift film composed of silicon and multiple metal elements, ensuring precise control over transmittance and phase shift, and incorporating a second light absorbing film within the phase shift film for improved etching selectivity and chemical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer halftone phase shift mask is used, then the construction is simpler and manufacturing precision is improved, but the transmittance becomes highly dependent on wavelength which worsens defect inspection precision
Solution Approach 1:
The mask is divided into multiple functional layers: a first light-absorbing layer for controlling transmittance, a phase-shifting layer for inducing phase difference, and a second light-absorbing layer for improving inspection contrast. This segmentation allows each layer to optimize its specific function, resolving the contradiction between simple construction and inspection precision.
Solution Approach 2:
The patent uses composite material structures with specific compositions (e.g., MoSiON, MoSiOxNy) in each layer to achieve wavelength-insensitive transmittance characteristics while maintaining high inspection contrast. The composite nature of these materials allows simultaneous optimization of multiple optical properties.
2Manufacturing precision
If the exposure wavelength is reduced to achieve higher resolution, then the manufacturing precision is improved, but the equipment and material expenses increase
Solution Approach 1:
The patent changes the optical parameters of the mask layers (transmittance, phase shift, absorbance) to maintain effective pattern transfer at longer wavelengths (e.g., 248 nm KrF laser) without requiring shorter wavelengths. This parameter optimization allows using less expensive equipment while achieving the same manufacturing precision.
3Manufacturing precision
If the numerical aperture is increased to improve resolution, then the manufacturing precision is improved, but the focal depth decreases which worsens process stability
Solution Approach 1:
The patent changes the optical parameters of the mask (phase shift amount, transmittance ratio) to enhance the contrast of transferred images, which allows maintaining smaller numerical aperture values. This preserves sufficient focal depth and process stability while achieving the required resolution through optimized phase shift effects.
4Measurement precision
If the light transmittance of the phase shifter is increased to improve defect inspection, then the inspection precision is improved, but the phase shift effect is reduced which worsens the contrast of transferred image
Solution Approach 1:
The mask is divided into multiple functional layers: a first light-absorbing layer for controlling transmittance, a phase-shifting layer for inducing phase difference, and a second light-absorbing layer for improving inspection contrast. This segmentation allows each layer to optimize its specific function, resolving the contradiction between simple construction and inspection precision.
Solution Approach 2:
Different regions of the mask have different optical properties: the phase shifter region provides phase shift with controlled transmittance for image formation, while the light-absorbing layers provide high contrast for defect inspection. This local differentiation of optical quality allows simultaneous optimization of both inspection and image transfer functions.
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 enables precise processing and pattern transfer with minimal wavelength dependence, enhancing focal depth and inspection contrast, while maintaining optimal characteristics for shorter wavelength exposure, like F2 laser, and improving overall process stability.
Implementation Method 1
A phase difference of about 180° is set between the light transmitted by the uncovered substrate area 1a and the light transmitted by the phase shifter 2a. Due to light interference at the pattern boundary, the light intensity at the interfering boundary becomes zero
Implementation Method 2
In the halftone type phase shift masks, the light transmittance of the phase shifter section is several percents to several tens of percents of the light transmittance of uncovered substrate areas
Data Source
AI summary
In a halftone phase shift mask blank comprising a substrate, a light absorbing film, and a phase shifter film, the light absorbing film contains a metal element of Group 4A in a distribution having a higher metal element content in an upper region than in a lower region. Also provided is a halftone phase shift mask blank comprising a transparent substrate and a halftone phase shift film of a single layer or multiple layers having a preselected phase difference and transmittance, wherein at least one layer of the halftone phase shift film contains at least 90 atom % of silicon and a plurality of metal elements, typically Mo and Zr or Hf.