Mask Blank Chromium Migration Suppression via Etching Stopper
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Solution Overview
Problem
In semiconductor device manufacturing, half tone phase shift masks experience chromium migration issues due to the movement of chromium atoms from the light shielding film into the phase shift film during exposure transfer, leading to reduced transmittance and phase shift effects, especially when using ArF excimer lasers.
Innovation Solution
A mask blank structure is developed with a phase shift film made from silicon and a light shielding film containing chromium, where the phase shift film has a specific refractive index and extinction coefficient profile, and the light shielding film is designed to minimize photoexcitation of chromium atoms, using a laminated structure with a lower and upper layer to enhance back-surface reflectance and reduce chromium migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shielding film containing chromium is used in a half tone phase shift mask, then light shielding performance is improved, but chromium atoms migrate into the phase shift film during exposure transfer, reducing transmittance and phase shift effects
Solution Approach 1:
An etching stopper film is introduced as an intermediary layer between the chromium-containing light shielding film and the silicon-based phase shift film. This intermediate layer prevents chromium atoms from migrating into the phase shift film during ArF laser exposure transfer, while maintaining the light shielding performance of the chromium film and the phase shift effects of the silicon film.
Solution Approach 2:
The mask structure is segmented into distinct functional layers: a light shielding film containing chromium, an etching stopper film as a barrier layer, and a phase shift film containing silicon. This segmentation isolates the chromium source from the phase shift film, preventing harmful atomic migration while preserving both light shielding and phase shift functions.
2Manufacturing precision
If different materials are used for phase shift film and light shielding film to achieve different dry etching characteristics, then patterning precision is improved, but chromium migration occurs during exposure transfer
Solution Approach 1:
The etching stopper film serves as a mediator that enables the use of different materials for the phase shift film and light shielding film while preventing chromium migration. This intermediate layer allows each film to be optimized for its specific function (etching characteristics and light shielding) without the harmful interaction between chromium and silicon.
3Use of energy by moving object
If the phase shift film transmits ArF exposure light at high transmittance, then phase shift effects are enhanced, but chromium migration reduces the transmittance over time
Solution Approach 1:
The etching stopper film is placed beforehand between the light shielding film and phase shift film to cushion against chromium migration. This preventive barrier protects the phase shift film from chromium contamination, ensuring that light transmittance remains stable and phase shift effects are maintained throughout the mask's operational life.
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 significantly suppresses chromium migration, maintaining the transmittance and phase shift effects of the phase shift film, ensuring precise exposure transfer and pattern accuracy in semiconductor devices.
Implementation Method 1
a phase shift film (2) formed from a material containing silicon and not substantially containing chromium... which has a function to generate a phase difference of not less than 150 degrees and not more than 200 degrees between the exposure light transmitted through the phase shift film (2) and the exposure light transmitted through air
Implementation Method 2
the lower layer (21)... has a refractive index n lower than the transparent substrate (1)... at a wavelength of the exposure light
Implementation Method 3
a layer of the light shielding film (3) at least in contact with the phase shift film (2)... formed from a material containing chromium... to minimize photoexcitation of chromium atoms
Data Source
AI summary
A mask blank having a phase shift film and a light shielding film laminated on a transparent substrate. The phase shift film transmits ArF exposure light at a transmittance of from 2% to 30% and generates a phase difference of from 150° to 200°, is formed from a material containing Si and not substantially containing Cr, and has a lower layer (L) and an upper layer (U) laminated from the transparent substrate side. A refractive index n for layer L is below that of the substrate while n for layer U is higher, and layer L has an extinction coefficient k higher than that of layer U. The light shielding film includes a layer in contact with the phase shift film that is formed from a material containing Cr, has a n lower than that of layer U, and has an extinction coefficient k higher than that of layer U.