Lithography Source Optimization and Assist Features
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Solution Overview
Problem
Lithographic processes face challenges in reducing pattern displacement errors, contrast loss, and best focus shift, which affect the process window and overall accuracy of feature transfer onto substrates, particularly due to non-zero angles of incidence and reflective patterning devices.
Innovation Solution
The method involves adjusting the characteristics of the illumination source and placing assist features on the patterning device to optimize the illumination source and compensate for these issues, using a computer-implemented approach that calculates a continuous transmission map and determines the positions, shapes, and numbers of assist features to minimize pattern displacement errors and enhance exposure latitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-zero angles of incidence are used in lithographic apparatus, then productivity and scanning capability are improved, but pattern displacement errors and contrast loss increase
Solution Approach 1:
The patent applies asymmetry by using non-zero angles of incidence for illumination, creating an asymmetric illumination pattern that enables scanning capability and improved productivity. This asymmetric illumination geometry allows the beam to scan across the patterning device while maintaining efficient light utilization, directly addressing the productivity improvement while accepting the resulting pattern displacement errors that the patent then seeks to correct through other means.
2Productivity
If non-zero angles of incidence are used in lithographic apparatus, then productivity and scanning capability are improved, but contrast loss increases
Solution Approach 1:
The patent employs asymmetric non-zero angles of incidence to enable scanning operation and improve productivity. This asymmetric illumination geometry is fundamental to the scanning capability, allowing the illumination beam to efficiently scan across the patterning device while accepting the trade-off of contrast loss that occurs with oblique incidence angles.
3Manufacturing precision
If assist features are added to the patterning device, then pattern displacement errors and contrast loss are reduced, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-positioning assist features on the patterning device based on continuous transmission maps. These assist features are designed in advance to compensate for pattern displacement errors and contrast loss that will occur during illumination, allowing the main features to be printed with higher precision without requiring real-time correction mechanisms.
Solution Approach 2:
The patent implements local quality by placing assist features at specific locations around main features based on local transmission requirements. The continuous transmission map analysis identifies where assist features are most needed, and they are positioned accordingly to provide localized correction for pattern displacement and contrast issues, rather than uniformly increasing complexity across the entire patterning device.
4Manufacturing precision
If continuous transmission map calculation is performed, then assist feature optimization is improved, but computation time and processing complexity increase
Solution Approach 1:
The patent applies preliminary action by performing continuous transmission map calculations and assist feature optimization in advance, before actual lithographic production. This pre-computation approach allows complex calculations to be done when computational resources are available, and the results are stored for use during production, avoiding time losses during actual manufacturing operations.
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 improves the lithographic process by reducing pattern displacement errors, contrast loss, and best focus shift, thereby enlarging the depth of focus and process window, leading to more accurate and reliable feature transfer on substrates.
Implementation Method 1
a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (e.g., a mask) may contain or provide a circuit pattern corresponding to an individual layer of the IC, and this circuit pattern can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material
Implementation Method 2
the circuit pattern can be transferred onto a target portion by methods such as irradiating the target portion through the circuit pattern on the patterning device
Data Source
AI summary
Disclosed herein are several methods of reducing one or more pattern displacement errors, contrast loss, best focus shift , tilt of a Bossung curve of a portion of a design layout used in a lithographic process for imaging that portion onto a substrate using a lithographic apparatus. The methods include adjusting an illumination source of the lithographic apparatus, placing assist features onto or adjusting positions and/or shapes existing assist features in the portion. Adjusting the illumination source and/or the assist features may be by an optimization algorithm.