Non-destructive characterization of extended crystalline defects in confined semiconductor device structures

Abstract

Semiconductor heterostructures are at the heart of most nanoelectronic and photonic devices such as advanced transistors, lasers, light emitting diodes, optical modulators and photo-detectors. However, the performance and reliability of the respective devices are often limited by the presence of crystalline defects which arise from plastic relaxation of misfit strain present in these heterogeneous systems. To date, characterizing the nature and distribution of such defects in 3D nanoscale devices precisely and non-destructively remains a critical metrology challenge. In this paper we demonstrate that electron channeling contrast imaging (ECCI) is capable of analyzing individual dislocations and stacking faults in confined 3D nanostructures, thereby fulfilling the aforementioned requirements. For this purpose we imaged the intensity of electrons backscattered from the sample under test under controlled diffraction conditions using a scanning electron microscope (SEM). In contrast to transmission electron microscopy (TEM) analysis, no electron transparent specimens need to be prepared. This enables a significant reduction of the detection limit (i.e. lowest defect density that can be assessed) as our approach facilitates the analysis of large sampling volumes, thereby providing excellent statistics. We applied the methodology to SiGe nanostructures grown by selective area epitaxy to study in detail how the nature and distribution of crystalline defects are affected by the dimensions of the structure. By comparing our observations with the results obtained using X-ray diffraction, TEM and chemical defect etching, we could verify the validity of the method. Our findings firmly establish that ECCI must be considered the method of choice for analyzing the crystalline quality of 3D semiconductor heterostructures with excellent precision even at low defect densities. As such, the technique aids in better understanding of strain relaxation and defect formation mechanisms at the nanoscale and, moreover, facilitates the development and fabrication of next generation nanoelectronic and photonic devices.

Improved thin film quality and photoluminescence of N-doped epitaxial germanium-on-silicon using MOCVD

“…The stress fields associated with threading dislocations cause a local deformation of the crystal lattice, which can be imaged using ECCI. TDD measured by ECCI for undoped Ge were in good agreement with EPD and transimisson electron microscopy (TEM) results [34]. Therefore, we believe that ECCI can overcome the weakness of EPD methods for doped Ge, and provide more accurate TDD measurements.…”

A demonstration of donor passivation through direct formation of V-Asi complexes in As-doped Ge1−xSnx

“…[26,27] The samples had threading dislocation densities (TDD) of ∼ 3 − 6 × 10 7 cm −2 as extracted from defect etching and confirmed by electron channeling contrast imaging (ECCI). [28,29] The growth conditions were kept identical except the partial pressure of AsH 3 , which was tuned to reach different As-doping levels in Ge 1−x Sn x layers. The associated material properties of the samples considered in this study are listed in Table I.…”

Microscopy of defects in semiconductors

“…Any deviation in crystallographic orientation or in lattice constant due to local strain, may then be revealed by variation in the contrast in the electron channelling image constructed by monitoring the intensity of backscattered or forescattered electrons as the electron beam is scanned over the sample. Extremely small changes in orientation and strain are detectable, revealing, for example, low angle tilt and rotation boundaries and atomic steps and enabling extended defects such as dislocations and stacking faults to be imaged [21,22,23,24,25,26,27,28,29]. ECCI can provide similar information on defects as the transmission electron microscope (see sections 10.2.3 and 10.3.1.4) where the defects either thread to the surface or lie within around 50 nm of the surface.…”