Photomask Auxiliary Pattern for CD Uniformity
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Solution Overview
Problem
The optical proximity effect limits the resolution of optical exposure equipment in photomask manufacturing for microelectronic devices, causing variations in critical dimensions (CDs) of patterns transferred to substrates, which existing correction methods, such as etching the back side of photomasks or ion beam repair, cannot fully address.
Innovation Solution
A photomask with a substrate transparent to light, featuring a mask pattern and an auxiliary pattern of recesses or holes on the front side that adjust the light beam intensity by inducing phase differences, allowing for precise control of CD uniformity through varying recess sizes and densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the scale of mask patterns is reduced to achieve higher integration, then device integration increases, but optical proximity effect worsens and limits resolution
Solution Approach 1:
An auxiliary pattern is introduced as an intermediary element between the mask pattern and the substrate. This auxiliary pattern modulates the light beam intensity to compensate for optical proximity effects, enabling precise pattern formation at reduced scales without sacrificing resolution
Solution Approach 2:
The invention changes the physical parameters of the light beam by introducing an auxiliary pattern that modifies light intensity distribution. By varying the density and configuration of the auxiliary pattern, the optical parameters are adjusted to maintain manufacturing precision at smaller feature sizes
2Manufacturing precision
If etching is applied to the back side of photomask to correct global CD variations, then global CD uniformity improves, but local CD non-uniformity cannot be corrected
Solution Approach 1:
The auxiliary pattern is designed with spatially varying properties where different regions have different densities and configurations tailored to correct local CD variations. This local quality variation enables both global and local correction capabilities simultaneously
Solution Approach 2:
The correction function is segmented into multiple zones corresponding to different regions of the mask pattern. Each zone's auxiliary pattern is optimized independently to address specific local CD non-uniformities while contributing to overall global uniformity
3Manufacturing precision
If ion beam repair is used to correct mask patterns, then local CD correction is possible, but global correction capability is limited and applications are restricted
Solution Approach 1:
The auxiliary pattern provides a universal correction mechanism that can address both local and global CD variations within a single integrated structure. This multi-functional approach eliminates the need for separate repair processes and expands applicability to various pattern types
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 auxiliary pattern ensures high shot uniformity and accurate CD transfer by adjusting light beam intensity, effectively correcting both local and global CD variations, thereby improving pattern formation on substrates.
Implementation Method 1
an auxiliary pattern on the front side of the substrate for adjusting the intensity of a light beam entering the substrate at the back side thereof and passing through the substrate
Data Source
AI summary
A photomask ensures the transfer of a pattern having a uniform and desired CD onto a substrate from which an electronic device or the like is made. The photomask includes a transparent substrate, a light-shielding film on the front side of the substrate and defining a mask pattern of transmission regions dedicated for pattern formation, and an auxiliary pattern on the front side of the substrate that alters the intensity of the light beam passing through the substrate. After the mask pattern is formed, the photomask is tested to determine variations between the desired (target) CD and the CDs of the features of a pattern transcribed onto a test wafer using the photomask. A density function in which characteristics of the auxiliary pattern to be formed, e.g., the size, depth and/or pitch of recesses, is developed as a prediction of the intensity distribution of the light beam transmitted through the substrate once the auxiliary pattern is present at the front side of the substrate. The photomask is then repaired/corrected by designing and forming the auxiliary pattern according to the density function so as to prevent local or global variations between the desired CD and the actual CD from occurring.