Photomask Blank Interface Defect Prevention
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Solution Overview
Problem
Photomask blanks with film structures containing chromium-containing and silicon-containing films tend to develop defects over time due to oxidation and volume changes at their interface, affecting the accuracy and longevity of semiconductor pattern transfer.
Innovation Solution
A method for preparing photomask blanks using a transparent substrate with a chromium-containing film (A) and a silicon-containing film (B), where the films are contacted using a sputtering method with controlled oxygen gas supply to adjust the intensity of secondary ions, ensuring that the intensity of Cr2O5 is lower than SiN at their interface, thereby reducing defect generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a chromium-containing film and a silicon-containing film are contacted in a photomask blank, then the photomask blank can be used for micropatterning with high integration density, but defects are generated due to oxidation and volume changes at the interface over time
Solution Approach 1:
An aluminum-containing film is introduced as an intermediary layer between the chromium-containing film and the silicon-containing film. This intermediate layer prevents direct contact between chromium and silicon, thereby eliminating the oxidation reaction and volume changes that occur at their interface. The aluminum-containing film serves as a buffer that resolves the harmful interaction while allowing both the chromium-containing film (for light shielding) and silicon-containing film (for etch resistance) to function properly in the photomask blank structure.
2Ease of manufacture
If chromium-containing film and silicon-containing film are used together, then light shielding and etch resistance are achieved, but oxidation at the interface causes volume changes and defects
Solution Approach 1:
The aluminum-containing film acts as a protective intermediary that physically separates the chromium-containing film and silicon-containing film. This prevents the oxidation of chromium by silicon dioxide at the interface, eliminating the harmful volume changes and defect generation. The intermediate layer maintains the functional benefits of both films while blocking the harmful chemical interaction.
3Measurement precision
If the photomask blank uses conventional film structure, then initial pattern formation is accurate, but defects develop with age due to interface oxidation
Solution Approach 1:
The aluminum-containing film is deposited in advance between the chromium-containing film and silicon-containing film during the manufacturing process. This preliminary protective action prevents oxidation and volume changes from occurring at the interface during subsequent storage and use. By preemptively introducing the intermediate layer, the photomask blank maintains its pattern accuracy and remains free of defects throughout its service life, extending its operational longevity.
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 approach significantly reduces the occurrence of defects at the interface between chromium and silicon-containing films, enhancing the durability and accuracy of photomask blanks and photomasks, particularly in the microfabrication of semiconductor integrated circuits.
Implementation Method 1
a method for preparing a photomask blank... by a sputtering method
Implementation Method 2
the film (B) is sputtered with supply of an oxygen-containing gas in an amount or flow rate which is reduced relative to a set value
Implementation Method 3
for a predetermined period of time at the initial stage of deposition, the film (B) is sputtered with supply of an oxygen-containing gas... thereby reducing defect generation
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A photomask blank including a transparent substrate, and at least one film (A) containing chromium and nitrogen and free of silicon and at least one film (B) containing silicon and oxygen, and free of a transition metal that are contacted to each other In the blank, when an intensity of secondary ions is measured along a thickness direction of the films by a time-of-flight secondary ion mass spectrometry (TOF-SIMS), an intensity of secondary ions derived from Cr2O5 is lower than an intensity of secondary ions derived from SiN, at a position located at the interface or its vicinity of the film (A) and film (B) and having a maximum intensity of secondary ions derived from SiCrOs.