Meeting new inspection demands in compound semiconductors
Compound semiconductors are the backbone of high-power electronics, high-frequency electronics, and opto-electronics. As global demand for compound semiconductors grows, the notoriously low yield rates of materials such as gallium nitride (GaN) and silicon carbide (SiC) become impossible to ignore. By developing better optical inspection tools, we seek to help manufacturers identify yield-killing defects in epitaxy layers long before the material is used in device production.
MONSTR Sense Technologies’ current line of products are designed for researchers and scientists developing the next generation of semiconductors and manufacturing processes. Our customers use our ultrafast spectrometers to improve the development of GaN devices, monolayer materials similar to graphene, colloidal quantum dots, gallium arsenide (GaAs)-based devices, and quantum materials such as vacancy centers. Though our primary market is focused on research right now, we are actively seeking input from individuals working in semiconductor manufacturing to build better tools for these applications.
When nonlinear optical measurements are better
A typical first step in bare wafer semiconductor inspection is dark-field imaging by scanning a tiny bright spot over the surface of a spinning wafer. This method is great for detecting every tiny surface defect that scatters light. For inspecting pristine silicon wafers, this inspection technique is great! However, the method does not work so well for epitaxy layers of compound semiconductors such as GaN for two reasons:
- Scattering sites do not necessarily correlate with killer defect sites. Nuisance events, where an anomaly is detected that is not a defect, are common in these epi layers. Better identifiable information about the anomaly is needed to characterize it.
- Subsurface defects that impact device performance can go unnoticed. The insensitivity of conventional inspection methods to killer defects that are under the surface leads to reduced yield that is not realized until electrical test measurements of devices are performed.
Nonlinear optical measurements solve these problems. Nonlinear measurements, particularly four-wave mixing, are sensitive to fundamental defects in the crystalline structure of the semiconductor that impact the carriers. This means that defects, even subsurface defects, will strongly impact the four-wave-mixing image if the defect has a strong impact on the electrical properties of the semiconductor.
In the figures below we show how a four-wave-mixing image detects an application-killing subsurface defect in gallium arsenide that is not visible with white-light imaging.
Check out our resources page for more details about advanced imaging microscopy techniques.
Measuring electrical properties without probes
Ultrafast spectroscopy techniques measure charge transfer and energy transfer in materials. Ultrafast imaging microscopy measurements therefore identify regions where electrical energy is lost. For finding defects in semiconductors that impede device performance, this is everything. Regions of a semiconductor with uncharacteristically long optical decay constants will have correspondingly high nonradiative decay. For LEDs these regions will have reduced efficiency, and for detectors and solar cells these regions will have weak absorption.
Emission and absorption efficiency is typically determined with electrical measurements, requiring construction of an entire device around the semiconductor for testing. Our measurements can perform these tests 100% non-contact saving manufacturers time and process steps.
Testers, advisors, feature recommendations, and more needed
If you have an interest or are an expert in semiconductor manufacturing, please reach out to us. We are actively working to improve defect inspection in compound semiconductors, and we can use your help. Let’s start with a call!
*Coming soon* A first-of-its-kind laser-scanning microscope that may integrate just about any laser-based measurement with high resolution imaging. It features a large sample area for cryostats and is designed to integrate well with our BIGFOOT spectrometer.