Epitaxial Growth Monitoring via Full-Wafer Light Scattering
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Solution Overview
Problem
Current techniques for in situ monitoring of epitaxial growth, such as RHEED and pyrometry, are limited in their ability to characterize flux and temperature uniformities across large substrate areas, failing to detect macroscopic defects like gallium balls, surface haze, and pinholes, which can lead to substrate roughening and growth disruptions.
Innovation Solution
A method and apparatus that illuminate the entire wafer surface with white light and use a video camera to observe scattered light, allowing continuous monitoring of the entire wafer for defects like gallium balls, haze, and pinholes, enabling adjustments to growth conditions to maintain surface smoothness and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RHEED technique is used for in situ monitoring, then surface stoichiometry and evaporant build-up can be monitored, but only a small area (several square millimeters) of the substrate surface can be sampled, failing to characterize flux and temperature uniformities across the entire wafer
Solution Approach 1:
The patent uses optical imaging to create a visual copy of the entire wafer surface, allowing macroscopic defect detection across the full substrate area. The camera captures light scattered from the wafer surface, producing an image that represents the entire growth area, thereby resolving the area limitation of RHEED while providing complementary macroscopic information.
2Loss of information
If RHEED beam is used for monitoring, then surface information can be obtained, but the high energy electron beam may alter the growth in the monitored region
Solution Approach 1:
The patent introduces light as an intermediary for monitoring the growth process. Instead of using a high energy electron beam that directly interacts with and potentially alters the growing film, the system uses optical illumination that reflects or scatters from the surface without significantly affecting the epitaxial growth, thus maintaining growth reliability while still providing monitoring capability.
3Temperature
If pyrometry is used for temperature measurement, then substrate temperature can be measured, but the measurement area is less than 10% of the surface area of a 3-inch wafer, failing to characterize temperature uniformity
Solution Approach 1:
The patent merges the monitoring functions by using the same optical system to detect both macroscopic defects (through scattered light patterns) and temperature information. The light scattering characteristics provide information about both surface morphology and thermal conditions across the entire wafer, combining multiple monitoring capabilities into a single full-area measurement system.
4Reliability
If monitoring is performed with RHEED less than 10% of the time, then growth disruption is minimized, but continuous monitoring capability is lost
Solution Approach 1:
The patent enables continuous monitoring throughout the entire growth process using optical illumination and imaging. The system maintains constant observation of the wafer surface without interrupting the epitaxial growth, providing uninterrupted feedback on defect formation while the growth process proceeds undisturbed, thereby achieving both continuous monitoring and growth continuity.
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 continuous monitoring of the entire wafer during epitaxial growth, allowing for real-time adjustments to prevent large gallium balls and surface defects, improving material quality and uniformity across the entire wafer, thus optimizing semiconductor film growth.
Implementation Method 1
illuminate an entire surface of the wafer with a source of light mounted to illuminate an entire surface of the wafer in the apparatus during growth of the epitaxial layer on the entire surface of the wafer; and apparatus for observing scattering of the light from the entire surface of the wafer
Data Source
AI summary
Apparatus and method for growing and observing the growth of epitaxial layers on a wafer. The apparatus includes: epitaxial growth apparatus; a source of light mounted to illuminate an entire surface of the wafer in the apparatus during growth of the epitaxial layer on the entire surface of the wafer; and apparatus for observing scattering of the light from the entire surface of the wafer during growth of the epitaxial layer on the entire surface of the wafer. The method includes growing the epitaxial layer on a surface of the wafer and observing scattering of the light from the entire surface of the wafer during growth of the epitaxial layer on the entire surface of the wafer. The growing process is varied in accordance with the observation. With an epitaxial layer of gallium nitride (GaN) the entire surface of the wafer is observed for balls of gallium.