Cryogenic Wafer Optical Mapping with Segmented Infrared Windows
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing mapping structures for semiconductor wafers larger than 3 inches are inadequate for cryogenic environments due to mechanical stresses on infrared windows, leading to bowing distortion, signal attenuation, and increased cost, with limitations on temperature and scalability.
Innovation Solution
A scanning setup using radial and rotational motion of the probe and detector, with a three-chamber arrangement maintaining ultra-high vacuum, reduces mechanical stress on windows and minimizes heat exchange, enabling thinner windows and precise optical measurements at cryogenic temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the area of infrared windows is increased to accommodate larger wafer samples, then the scan size capability is improved, but mechanical stresses on the windows increase dramatically causing bowing distortion and signal attenuation
Solution Approach 1:
The patent divides the infrared window into multiple smaller windows arranged in an array, each window covering a portion of the total scan area. This segmentation reduces the mechanical stress on individual windows, preventing bowing distortion while maintaining the overall scan area capability. The smaller windows can be manufactured with higher precision and thinner profiles, reducing signal attenuation.
Solution Approach 2:
The patent transitions from a single large window approach to a multi-window array configuration, effectively using the spatial distribution across the window array to achieve the required scan area. This dimensional reorganization allows the system to accommodate larger wafer samples without requiring each individual window to be excessively large, thereby reducing mechanical stresses.
2Strength
If the thickness of infrared windows is increased to reduce bowing distortion, then window mechanical strength is improved, but signal attenuation and distortion modes increase
Solution Approach 1:
By segmenting the window system into multiple smaller windows, the patent reduces the required thickness for each individual window to maintain mechanical strength. Thinner windows reduce signal attenuation and distortion modes such as absorption, reflection, and refraction, while the array configuration provides the necessary overall structural support.
3Area of stationary object
If the area of infrared windows is increased to cover entire sample region, then scan coverage is improved, but radiative energy transfer from ambient temperature increases imposing a hard limit on minimum achievable temperature
Solution Approach 1:
The patent uses multiple smaller infrared windows arranged in an array, each window occupying only a small portion of the total scan area. This segmentation reduces the total radiative energy transfer surface area from ambient temperature surroundings, allowing the system to achieve lower minimum temperatures during scanning without excessive heat input.
4Adaptability or versatility
If cartesian mapping coordinates are used for mapping structures, then mapping capability is improved, but scalability to larger wafers is limited due to sealing requirements in cryogenic environments
Solution Approach 1:
The patent segments the mapping system into multiple independent window elements that can be individually sealed and positioned. This segmentation allows for better integration with cryogenic sealing requirements, enabling scalability to larger wafer sizes without the complex sealing challenges of single large window designs.
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 cost-effective, precise, and non-destructive 2-dimensional mapping of semiconductor wafers with reduced signal absorption and reflection, allowing for stable temperature control and larger scan sizes.
Implementation Method 1
The electron bandgap of materials can be directly measured through infrared transmission measurement
Implementation Method 2
The measurement of excess free carrier absorption (FCA) decay behavior in materials enables the obtaining of the excess carrier recombination lifetime
Implementation Method 3
cool wafer or thin film samples through gaseous thermal transfer media to cryogenic temperatures down to 1.9 K under pumping
Implementation Method 4
the external chamber and cold chamber are held at ultra-high vacuum
Data Source
AI summary
A method of performing scans on a semiconductor wafer is provided wherein the scanning motion is actuated through a system including a linear one-dimensional motion of the scan head; and rotational motion of a scanned wafer and an associated wafer holder. The wafer to be scanned is placed in a vacuum cryogenic enclosure, into the walls of which has been set an infrared window such that transmitted and reflected radiation from probing beams is perceptible by detectors outside the cryogenic enclosure. The scanning of the wafer is conducted through infrared transmittance and reflectance measurements of a probe beam focused on a point on the scanned wafer which is pumped by a pulsed laser.