Phase Shift Mask Repair Using Plasma Passivation
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Solution Overview
Problem
Phase shift masks used in photolithography suffer from reduced light transmittance due to etching during cleaning processes, limiting their useful life and requiring frequent replacement, which increases manufacturing costs for semiconductor devices.
Innovation Solution
The method involves forming passivation layers on the phase shift pattern using plasma treatment with gases like oxygen, ozone, or nitrogen to protect the pattern during cleaning, allowing for repeated use without significant reduction in transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the phase shift mask is cleaned to remove cohered impurities, then the light blocking performance is improved, but the phase shift pattern thickness is reduced and light transmittance increases
Solution Approach 1:
A pellicle is attached to the phase shift mask before use to prevent impurities from adhering to the mask surface during exposure. This preliminary protective action eliminates the need for cleaning operations that would otherwise damage the phase shift pattern thickness
Solution Approach 2:
The pellicle is a disposable protective film that is replaced periodically rather than cleaning the expensive phase shift mask itself. This sacrifices a low-cost consumable item to preserve the high-value mask's phase shift pattern integrity
2Productivity
If the phase shift mask is used repeatedly for exposure, then productivity is improved, but the phase shift pattern thickness decreases due to cumulative etching during cleaning
Solution Approach 1:
The pellicle is installed in advance to prevent impurity adhesion, eliminating the need for periodic cleaning that causes etching damage. This allows the mask to maintain its phase shift pattern thickness throughout extended use
Solution Approach 2:
The disposable pellicle absorbs the wear and replacement costs, allowing the expensive phase shift mask to be used continuously without cleaning-induced degradation, thereby extending its operational life
3Manufacturing precision
If cleaning frequency is increased to maintain light blocking performance, then light transmittance control is improved, but manufacturing cost increases due to frequent mask replacement
Solution Approach 1:
The pellicle prevents impurity accumulation that would require frequent cleaning, allowing masks to be used until the pellicle itself degrades. This reduces the frequency of mask replacement while maintaining optical performance
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 method extends the useful life of phase shift masks by maintaining light transmittance within acceptable limits for up to 33 cleaning processes, reducing manufacturing costs and preventing unnecessary photomask discarding.
Implementation Method 1
forming passivation layers on the phase shift pattern using plasma treatment with gases like oxygen
Implementation Method 2
plasma treatment with gases like oxygen, ozone, or nitrogen to protect the pattern during cleaning
Data Source
AI summary
A method of repairing a phase shift mask includes exposing upper and side surfaces of the phase shift pattern of the mask, selectively forming a passivation layer on the surfaces of the exposed phase shift patterns, and then cleaning the phase shift mask on which the passivation layers are formed. The repairing of the phase shift mask is carried out in the midst of a series of photolithographic exposure processes in which the phase shift mask is used to transfer an image to a photoresist layer or layers. After the photomask is cleaned, a determination is made as to whether the transmittance of the phase shift pattern is above a threshold value.