Reticle Pattern Area Topography Measurement for Photolithography
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Solution Overview
Problem
Conventional photolithographic processes face challenges in accurately focusing patterns on wafers due to non-uniformities in reticles, as existing methods rely on estimating topography from perimeter alignment marks, which may not provide sufficient data for small feature sizes, and require expensive lithographic tools, leading to reduced throughput.
Innovation Solution
Obtaining qualitative data from within the pattern area of the reticle using a measurement tool located remotely from the photolithography tool, allowing for the determination of a correction model to adjust the wafer stage and optics, thereby improving accuracy and productivity by eliminating the need for on-line reticle calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods use perimeter alignment marks to estimate reticle topography, then measurement process is simple, but measurement precision is insufficient for small feature sizes
Solution Approach 1:
The reticle measurement is segmented into two distinct phases: (1) perimeter region measurement using alignment marks to obtain initial topography data, and (2) pattern area measurement using the same alignment marks to obtain precise topography data. This segmentation allows combining simple perimeter measurement with precise pattern area measurement, resolving the contradiction between measurement simplicity and precision.
Solution Approach 2:
The alignment marks are pre-positioned in both the perimeter region and pattern area of the reticle before measurement. This preliminary placement enables the measurement system to first capture perimeter data for initial compensation, then use the same marks for detailed pattern area measurement, achieving high precision without adding measurement complexity.
2Measurement precision
If lithographic tools are used to measure reticle non-uniformities, then measurement accuracy is high, but productivity decreases due to downtime
Solution Approach 1:
The measurement function is extracted from the production lithographic tool and performed separately using the tool's existing alignment mark infrastructure. By measuring reticle topography in the pattern area using alignment marks that are already part of the reticle structure, the system obtains precise measurement data without requiring dedicated measurement equipment or taking the lithographic tool offline, thus maintaining high productivity.
Solution Approach 2:
The alignment marks serve dual purposes: (1) as reference features for photolithographic pattern transfer, and (2) as measurement targets for reticle topography characterization. This multi-functionality eliminates the need for separate measurement markings or procedures, allowing accurate reticle measurement to be integrated into the existing photolithography workflow without reducing wafer processing throughput.
3Quantity of substance
If feature sizes are decreased to increase density, then device complexity increases, but measurement accuracy of reticle topography becomes insufficient
Solution Approach 1:
The measurement approach applies local quality by focusing measurement resources on the pattern area where actual features are located. By using alignment marks within the pattern area to measure local topography variations, the system obtains precise measurement data specifically where it is needed for small feature fabrication, rather than relying on average perimeter measurements that cannot capture local variations.
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 provides more accurate data for compensating reticle variances, enhancing the precision and efficiency of photolithography processes by allowing production wafers to be processed without downtime for reticle calibration, thus improving the overall productivity of photolithographic tools.
Implementation Method 1
The topography of the reticles is conventionally measured by detecting light that passes through alignment marks in a perimeter region outside of the pattern area of the reticle
Implementation Method 2
passing an imaging radiation through the reticle to expose the photoresist in the configuration of the mask pattern
Data Source
AI summary
Methods, systems, and tool sets involving reticles and photolithography processing. Several embodiments of the invention are directed toward obtaining qualitative data from within the pattern area of a reticle that is indicative of the physical characteristics of the pattern area. Additional embodiments of the invention are directed toward obtaining qualitative data indicative of the physical characteristics of the reticle remotely from a photolithography tool. These two aspects of the invention can be combined in further embodiments in which qualitative data is obtained from within the pattern area of a reticle in a tool that is located remotely from the photolithography tool. As a result, several embodiments of methods and systems in accordance with the invention provide data taken from within the pattern area to more accurately reflect the contour of the pattern area of the reticle without using the photolithography tool to obtain such measurements. This is expected to provide more accurate data for correcting the photolithography tool to compensate for variances in the pattern area, and it is expected to increase throughput because the photolithography tool is not taken away from processing production wafers to measure the reticle.