Lithographic Projection Apparatus Iso-Dense Bias Control
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Solution Overview
Problem
Conventional lithographic apparatuses fail to directly address the issue of iso-dense bias, where features with the same critical dimensions print differently due to pitch-dependent diffraction effects, leading to variations in critical dimension (CD) and limited process latitude, especially when printing both isolated and dense features simultaneously.
Innovation Solution
The method involves modifying the iso-dense bias characteristic by inducing a loss of contrast during exposure, achieved by displacing the substrate table perpendicular to the notional image surface or tilting the scanning direction, allowing independent manipulation of contrast and through-pitch effects to match different lithographic apparatuses' characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional lithographic techniques are used with fixed optical parameters, then the apparatus can operate with standard settings, but iso-dense bias causes pitch-dependent variation in printed critical dimensions
Solution Approach 1:
The patent applies dynamics by making the illumination system adjustable during operation. The σ-outer and σ-inner settings of the illumination system can be dynamically changed to match different iso-dense bias characteristics of various lithographic apparatus. This allows the system to adapt to different pitch configurations and apparatus-specific variations, resolving the contradiction between fixed operational settings and the need to compensate for pitch-dependent CD variations.
Solution Approach 2:
The patent utilizes parameter changes by modifying the illumination system's σ-outer and σ-inner parameters to alter the iso-dense bias characteristic. By changing these illumination parameters, the system can compensate for apparatus-specific variations and achieve consistent critical dimension control across different pitch configurations, thereby improving manufacturing precision while maintaining adaptability.
2Productivity
If different lithographic apparatus are used for the same manufacturing process, then production capacity is increased, but machine-to-machine differences cause variance in iso-dense bias characteristics
Solution Approach 1:
The patent applies universality by creating a standardized method to match iso-dense bias characteristics across different lithographic apparatus. By adjusting the illumination system parameters (σ-outer and σ-inner) on each machine to match a target iso-dense bias characteristic, the system achieves consistent critical dimension control across multiple apparatus. This allows different machines to be used interchangeably for the same manufacturing process while maintaining precision and consistency.
Solution Approach 2:
The patent utilizes feedback by measuring the actual iso-dense bias characteristic of each lithographic apparatus and using this information to adjust the illumination system parameters. The measured characteristic serves as feedback to determine the appropriate σ-outer and σ-inner settings, ensuring that each machine is optimized to match the target characteristic. This feedback mechanism enables consistent critical dimension control across multiple apparatus while maintaining high production capacity.
3Manufacturing precision
If Optical Proximity Correction (OPC) is applied to compensate for iso-dense bias, then critical dimension uniformity is improved, but reticle manufacturing cost and complexity increase
Solution Approach 1:
The patent applies copying by creating a matched iso-dense bias characteristic through illumination system adjustment rather than modifying the reticle pattern. Instead of creating complex OPC-reticles with pre-compensated patterns, the system copies the desired critical dimension uniformity by adjusting the illumination parameters to match the target iso-dense bias characteristic. This approach achieves the same result as OPC but without the increased reticle complexity and manufacturing cost.
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 reduces residual inter-machine iso-dense bias differences by about a factor of three, enabling the use of identical reticles on various machines and reducing the need for expensive Optical Proximity Correction (OPC)-reticles, while maintaining process latitude.
Implementation Method 1
pitch dependent diffraction effects
Data Source
AI summary
A method for exposing a resist layer on a substrate to an image of a pattern on a mask is disclosed whereby, after starting exposure and before completing exposure, a controlled amount of contrast loss is introduced by a controller in the image at the resist layer by changing during exposure the position of the substrate holder. The contrast loss affects the pitch dependency of the resolution of a lithographic projection apparatus, and its control is used to match pitch dependency of resolution between different lithographic projection apparatus.