Wafer Backside Alignment via Dark-Field Scattering
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Solution Overview
Problem
Current semiconductor manufacturing processes face challenges in aligning structures on the backside of a wafer with those on the frontside, particularly in three-dimensional structures, due to limitations in existing alignment technologies that require specialized and costly equipment and may not achieve precision below 10 μm when using infra-red light.
Innovation Solution
A method and apparatus for aligning structures of a wafer's backside to its frontside using electromagnetic radiation in a dark-field configuration, where the wafer is illuminated with specific wavelength radiation that scatters at three-dimensional alignment targets on the frontside, allowing for precise alignment without the need for new equipment, by using existing steppers designed for front-to-front alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing alignment technologies using infra-red light are employed, then alignment can be performed, but alignment precision is limited to above 10 μm and specialized expensive equipment is required
Solution Approach 1:
The patent makes existing steppers designed for front-to-front alignment capable of performing front-to-backside alignment by using the wafer's transparency to electromagnetic radiation. The alignment target on the frontside is illuminated through the transparent wafer from the backside, allowing the same equipment to serve multiple alignment functions without requiring specialized equipment.
Solution Approach 2:
The patent changes the illumination approach from frontside to backside illumination through the transparent wafer. By using electromagnetic radiation that the wafer material is transparent to, and illuminating from the backside, the system achieves higher alignment precision while using existing equipment.
2Measurement precision
If front-to-backside alignment is performed with conventional methods, then alignment is achieved, but precision below 10 μm cannot be reached
Solution Approach 1:
The patent changes the illumination wavelength to electromagnetic radiation that the wafer material is transparent to, and changes the illumination direction to backside illumination. This parameter change enables the detection of three-dimensional alignment targets with higher precision, achieving alignment accuracy below 10 μm while maintaining reliability.
Solution Approach 2:
The patent replaces conventional optical reflection-based alignment with a transmission-based alignment system. By using the wafer's transparency and detecting scattered electromagnetic radiation from three-dimensional alignment targets, the system achieves higher precision without mechanical contact or complex positioning mechanisms.
3Measurement precision
If specialized alignment equipment is used for front-to-backside alignment, then alignment precision can be improved, but manufacturing cost increases
Solution Approach 1:
The patent enables existing steppers to perform front-to-backside alignment by utilizing the wafer's transparency to electromagnetic radiation. This eliminates the need for specialized alignment equipment, reducing manufacturing costs while maintaining high alignment precision through the same existing tooling.
Solution Approach 2:
The wafer's inherent transparency to electromagnetic radiation is utilized as a natural property to enable the alignment process. The existing stepper equipment is adapted to use this self-service property of the wafer material, eliminating the need for additional specialized equipment and reducing overall system 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
Enables efficient and cost-saving front-to-backside alignment with high precision, utilizing existing OEM steppers and achieving alignment accuracy without the need for expensive new equipment, while maintaining high contrast images from 3D alignment targets.
Implementation Method 1
the electromagnetic radiation propagates through the wafer and is scattered at three-dimensional structures of a three-dimensional alignment target located at the frontside or inside the wafer
Implementation Method 2
the wafer is transparent for electromagnetic radiation of a specific wavelength
Data Source
AI summary
Structures of a backside of a wafer can be aligned to structures of a frontside of the wafer for a lithographic treatment of the backside. The wafer is transparent for electromagnetic radiation of a specific wavelength. The wafer is placed on a wafer stage such that the frontside is facing the wafer stage and the backside is facing alignment optics. The backside is illuminated with electromagnetic radiation of the specific wavelength in a dark-field configuration, such that the electromagnetic radiation propagates through the wafer towards three-dimensional structures of a three-dimensional alignment target located at the frontside or inside the wafer and is scattered at the three-dimensional structures. The scattered electromagnetic radiation is captured with the alignment optics, and the backside is aligned to the frontside of the wafer based on the scattered electromagnetic radiation.