Reflective Photomask Compensatory Portion for Shadow Effect Reduction
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Solution Overview
Problem
Reflective photomasks used in photolithography for semiconductor fabrication face structural defects that lead to light loss and pattern distortion due to the absorption pattern's thickness variations, causing shadow effects and focus shifts, which are not adequately addressed by material improvements or process enhancements.
Innovation Solution
A reflective photomask design incorporating a compensatory portion adjacent to the absorption pattern, formed thinner than the absorption pattern, with a substrate of quartz and a reflective layer of molybdenum and silicon, and a capping layer of silicon or metal compounds, to compensate for light reflection and absorption, thereby reducing shadow effects and maintaining pattern uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reflective photomask uses an absorption pattern on the reflective layer, then pattern information can be transferred to the wafer, but light loss occurs and shadow effects are generated due to thickness variations
Solution Approach 1:
The patent applies local quality by creating a compensatory portion with different thickness characteristics than the absorption pattern. The compensatory portion has a gradient thickness structure that is thinner at the incident light side and thicker at the reflected light side, providing localized optical compensation exactly where needed to balance the light path differences caused by the absorption pattern's thickness variations.
Solution Approach 2:
The compensatory portion is designed to preemptively counteract the shadow effects and light loss caused by the absorption pattern. By positioning the compensatory portion adjacent to the absorption pattern and giving it a thickness profile that opposes the light loss mechanism, the patent prevents shadow effects before they can significantly degrade pattern transfer accuracy.
2Ease of manufacture
If the absorption pattern has uniform thickness, then manufacturing is simpler, but shadow effects and focus shifts occur due to the inherent structure of reflective photomasks
Solution Approach 1:
Instead of making the entire absorption pattern non-uniform, the patent applies non-uniformity locally to the compensatory portion. The absorption pattern maintains its uniform thickness for ease of manufacture, while the adjacent compensatory portion introduces the necessary thickness variation to correct optical path differences, achieving both manufacturing simplicity and pattern uniformity.
Solution Approach 2:
The patent segments the photomask structure into functionally distinct regions: the absorption pattern for light blocking and the compensatory portion for optical path compensation. This segmentation allows each component to be optimized independently - the absorption pattern for manufacturing ease and the compensatory portion for optical performance.
3Use of energy by moving object
If light enters diagonally at the reflective layer, then reflection occurs, but light not arriving at the reflective layer due to absorption pattern sidewalls causes focus shifts
Solution Approach 1:
The compensatory portion acts as an intermediary element between the absorption pattern and the incident/reflected light paths. It mediates the optical interaction by providing a thickness profile that compensates for the path differences caused by diagonal light entry and absorption pattern sidewalls, maintaining focus consistency without interfering with the primary reflection function.
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 compensatory portion effectively minimizes light loss and maintains consistent focus, ensuring uniform line widths and improved pattern fidelity on the wafer, enhancing the fine pattern forming ability in photolithography.
Implementation Method 1
The reflective layer 20 may be formed on the substrate 10 and may reflect incident light
Implementation Method 2
The absorption pattern 30 may keep pattern information to be transferred onto a wafer, and may absorb rather than reflect incident light
Data Source
AI summary
The reflective photomask may include a substrate, a reflective layer formed on the substrate, an absorption pattern formed on the reflective layer and over a first portion of the substrate. A compensatory portion may be formed over at least a second portion of the substrate. The second portion is adjacent to the first portion, and the compensatory portion is thinner than the absorption pattern.