Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Summary

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Abstract

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities – high spatial resolution and richness of microstructural data – with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

Introduction

Detailed characterization of crystalline defects and microstructure is a vitally important aspect of semiconductor materials and device research since such defects can have a significant, detrimental impact on device performance. Currently, transmission electron microscopy (TEM) is the most widely accepted and used technique for detailed characterization of extended defects – dislocations, stacking faults, twins, antiphase domains, etc. – because it enables the direct imaging of a wide variety of defects with ample spatial resolution. Unfortunately, TEM is a fundamentally low-throughput approach due to lengthy sample preparation times, which can lead to si....

Protocol

This protocol was written with an assumption that the reader will have a working understanding of standard SEM operation. Depending upon the manufacturer, model, and even software version, every SEM can have significantly different hardware and/or software interfaces. The same can be said with respect to the internal configuration of the instrument; the operator must be cautious and observant when following this protocol, as even relatively small changes in sample size/geometry, sample orientation (tilt, rotation), and working distance, can present a risk for making contact with the pole–piece, especially if not at eucentric height. The instructions provided her....

Results

The GaP/Si samples for this study were grown by metal-organic chemical vapor deposition (MOCVD) in an Aixtron 3×2 close-coupled showerhead reactor following the authors’ previously reported heteroepitaxial process.¹⁷ All growths were performed on 4 inch Si(001) substrates with intentional misorientation (offcut) of 6° toward [110]. All ECCI imaging was performed on as-grown samples with no further sample preparation whatsoever (aside from cleaving to yield approximately 1 cm x 1cm pieces for loading into the S.......

Discussion

An accelerating voltage of 25 kV was used for this study. The accelerating voltage will determine the electron beam penetration depth; with higher accelerating voltage, there will be BSE signal coming from greater depths in the sample. The high accelerating voltage was chosen for this system because it allows for visibility of dislocations that are far from the surface of the sample, buried at the interface. Other types of defects/features may be more or less visible at different accelerating voltages depending on the ty.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sirion Field Emission SEM	FEI/Phillips	516113	Field emission SEM with beam voltage range of 200 V - 30 kV, equipped with a backscattered electron detector
Sample of Interest	Internally produced		Synthesized/grown in-house via MOCVD
PELCO SEMClip	Ted Pella, Inc.	16119-10	Reusable, non-adhesive SEM sample stub (adhesive attachment will also work)