Photomask Blank Reflective Layer Heat Absorption
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Solution Overview
Problem
During the photolithography process, heat absorption by the light shielding pattern in photomasks leads to temperature increases in the light transmitting substrate, causing positional errors in pattern formation due to substrate expansion, which affects the precision of the overlay between the wafer and the photomask.
Innovation Solution
The development of photomasks with a highly reflective material layer and a light shielding layer on a light transmitting substrate, where the highly reflective material layer reflects 20% to 90% of the incident light, reducing heat absorption and temperature rise by distributing light energy differently across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shielding layer is used in the photomask to block light, then light blocking performance is improved, but heat absorption increases causing substrate temperature rise
Solution Approach 1:
A reflective layer is introduced as an intermediary between the light shielding layer and the substrate. This reflective layer reflects incident light before it reaches the substrate, preventing heat absorption by the substrate while maintaining the light blocking function of the photomask.
Solution Approach 2:
The patent converts the harmful effect of light absorption (heat generation) into a beneficial effect by using the reflective layer to redirect light. The light that would otherwise be absorbed and converted to heat is now reflected, preventing substrate heating while still achieving the desired light blocking performance.
2Object-affected harmful factors
If the photomask substrate absorbs heat from incident light, then light shielding is achieved, but positional precision deteriorates due to substrate expansion
Solution Approach 1:
The reflective layer serves as a mediator that intercepts incident light and reflects it away from the substrate. This prevents the substrate from absorbing heat and expanding, thereby maintaining the positional precision of the pattern during photolithography exposure.
3Temperature
If a highly reflective material layer is added to the photomask structure, then heat absorption is reduced, but device complexity increases
Solution Approach 1:
The patent changes the optical parameters of the photomask by introducing a layer with high reflectivity. This parameter change (from light-absorbing to light-reflecting) fundamentally alters how the photomask interacts with incident light, reducing heat absorption while accepting the trade-off of increased structural complexity.
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 solution effectively suppresses heat absorption and temperature rise in the photomask, enhancing the precision of pattern formation and overlay accuracy by managing light energy distribution, thereby improving the photolithography process.
Implementation Method 1
a highly reflective material layer disposed on the light transmitting substrate... formed of a material which reflects 20% to 90% of light is irradiated
Data Source
AI summary
A photomask blank and/or photomask includes a light transmitting substrate, a highly reflective material layer disposed on the light transmitting substrate, and a transfer pattern layer disposed on the highly reflective material layer. The highly reflective material layer reflects light to be transmitted through the light transmitting substrate, with a predetermined reflectivity.