Phase Shift Mask Haze Prevention via Alkaline Neutralization
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Solution Overview
Problem
Conventional phase shift masks suffer from haze defects due to residual sulfuric acid and damage from alkaline cleaning solutions, which hinder the formation of high-resolution patterns in semiconductor devices.
Innovation Solution
A phase shift mask design incorporating a transparent layer, a transmittance control layer, and a shading layer, with a hard mask layer, that utilizes an alkaline cleaning solution to completely remove sulfuric acid ions without damaging the phase shift pattern, ensuring effective light transmittance and phase control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulfuric acid cleaning solution is used to remove contaminants from the phase shift mask, then cleaning effectiveness is improved, but haze defects are generated due to residual sulfuric acid
Solution Approach 1:
The patent applies neutralization chemistry to convert the harmful residual sulfuric acid into beneficial soluble salts. By using alkaline cleaning solutions (ammonium hydroxide or potassium hydroxide), the sulfuric acid residues are chemically neutralized to form ammonium sulfate or potassium sulfate salts, which are highly soluble in water and can be completely removed by rinsing, thereby eliminating haze defects while maintaining effective contaminant removal
Solution Approach 2:
The patent changes the chemical parameters of the cleaning solution by introducing alkaline substances (ammonium hydroxide or potassium hydroxide) to neutralize the acidic cleaning solution. This parameter change transforms the cleaning mechanism from purely acidic dissolution to a neutralization reaction, enabling complete removal of sulfuric acid residues and prevention of haze defects
2Object-affected harmful factors
If alkaline cleaning solution is used to remove sulfuric acid residues, then haze defects are prevented, but the phase shift layer is damaged by hydroxyl groups
Solution Approach 1:
The patent applies local quality by using different cleaning solutions for different regions of the mask. The alkaline cleaning solution (ammonium hydroxide or potassium hydroxide) is specifically applied to areas with sulfuric acid residues for neutralization, while the phase shift layer is protected through selective exposure and controlled cleaning procedures, ensuring that only the necessary regions undergo alkaline treatment
Solution Approach 2:
The patent introduces an intermediary rinsing step using deionized water between the sulfuric acid cleaning and alkaline cleaning processes. This intermediary rinsing removes excess sulfuric acid before alkaline solution application, reducing the risk of phase shift layer damage while maintaining effective neutralization of residues
3Ease of manufacture
If conventional cleaning process is used, then manufacturing simplicity is maintained, but complete removal of sulfuric acid is not achieved
Solution Approach 1:
The patent applies preliminary action by performing a first cleaning with sulfuric acid to remove organic contaminants, followed by a second cleaning with alkaline solution to neutralize and remove sulfuric acid residues. This two-stage preliminary cleaning sequence ensures complete removal of both organic contaminants and acid residues, achieving high manufacturing precision while maintaining reasonable process simplicity
Solution Approach 2:
The patent ensures continuity of useful action by implementing a continuous multi-stage cleaning process: sulfuric acid cleaning → rinsing → alkaline cleaning → final rinsing. This continuous process eliminates idle time between cleaning stages and ensures uninterrupted removal of contaminants and residues, maintaining both manufacturing efficiency and cleaning effectiveness
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 prevents haze defects and maintains the integrity of the phase shift pattern, enabling the formation of high-resolution, precise patterns in semiconductor devices by effectively removing sulfuric acid ions and ensuring the phase shift mask's endurance to alkaline cleaning.
Implementation Method 1
the phase shift mask is rinsed using a solution including diluted ammonium hydroxide reacting with sulfuric acid
Implementation Method 2
The light transmitted through one passage may have a phase difference of about 180° from light passing through adjacent openings of the phase shift mask. The light having the phase difference of about 180° may cause destructive interference, so that the intensity of the lights may be diminished or reduced substantially to zero.
Data Source
AI summary
A phase shift mask having a first region and a second region in a transverse direction includes a transparent layer, a phase shift pattern disposed in the first region, a transmittance control layer pattern disposed in the second region, and a shading layer pattern disposed on the transmittance control layer pattern. The phase shift pattern has a first pattern including a transparent material and a second pattern including metal. The phase shift mask may prevent haze effects through a cleaning process using an alkaline cleaning solution.