Elastic mid-infrared light scattering: A basis for microscopy of large-scale electrically active defects in semiconducting materials

Abstract

A method of the mid-IR-laser microscopy has been recently proposed for the investigation of the large-scale electrically and recombination active defects in semiconductors and non-destructive inspection of semiconductor materials and structures in the industries of microelectronics and photovoltaics. The basis for this development was laid with a wide cycle of the investigations on the low-angle mid-IR-light scattering in semiconductors. The essence of the technical idea was to apply the dark-field method for spatial filtering of the scattered light in the scanning mid-IR-laser microscope. This approach enabled the visualization of large-scale electrically active defects which are the regions enriched with ionized electrically active centers. The photoexcitation of excess carriers within a small volume located in the probe mid-IR-laser beam enabled the visualization of the large-scale recombination-active defects like those revealed in the optical or electron beam induced current methods. Both these methods of the scanning mid-IR-laser microscopy are now introduced in detail in the present paper as well as a summary of techniques used in the standard method of the lowangle mid-IR-light scattering itself. Besides the techniques for direct observations, methods for analyses of the defect composition associated with the mid-IR-laser microscopy are also discussed in the paper.Special attention is paid upon potential applications of the above methods as characterization and testing techniques in the semiconductor science and industry. It is concluded that elastic mid-infrared laser light scattering is a basis for the development of a variety of research techniques and instruments which could be useful in different branches of basic and applied research work in the field of defect engineered semiconductors as well as for the development of devices for quality inspections in the semiconductor industry. Being contactless, non-destructive and non-polluting, techniques based on mid-infrared light scattering could also find many applications for automation of the technological process control as well as the process remote monitoring.

Scanning mid-IR-laser microscopy: an efficient tool for materials studies in silicon-based photonics and photovoltaics

“…A number of papers appearing since 1995 [[1]- [11]] have introduced a new method of microscopy of semiconductors which has as its basis the same physical approaches that were used in the law-angle mid-IR-light scattering (LALS) technique reported in numerous other publications (see e.g. Refs.…”

“…Refs. [ [11], [12]] and papers cited therein). The essence of the technical idea was to apply the dark-field method to the scanning mid-IR-laser microscope to cut away the scattered light components with low spatial frequencies.…”

“…The essence of the technical idea was to apply the dark-field method to the scanning mid-IR-laser microscope to cut away the scattered light components with low spatial frequencies. The cut-off frequency of the spatial filter was optimized to eliminate influence of the probe laser radiation on a detector signal and simultaneously allow large defect images to be transferred through the optical system without drastic suppression of their contrast or intensity [ [9], [11]]. If a mid-IR light source of the probe radiation (e.g., CO 2 , λ = 10.6 μm, or CO-laser, λ = 5.4 μm) is used, the microscope enables the imaging of accumulations of free carriers which are usually associated with crystal micron-scale domains enriched with ionized defects and impurities (see Refs.…”

“…If a mid-IR light source of the probe radiation (e.g., CO 2 , λ = 10.6 μm, or CO-laser, λ = 5.4 μm) is used, the microscope enables the imaging of accumulations of free carriers which are usually associated with crystal micron-scale domains enriched with ionized defects and impurities (see Refs. [ [11], [12]] and references therein)-we call them large-scale electrically active defect accumulations (LSDAs). As the light scattered with LSDAs forms the images in this basic mode of the instrument, we have designated it scanning LALS or SLALS.…”

“…All the above together with possibilities of the local lifetime determination, LSDA composition analysis, simultaneous OLALS and photoluminescence measurements discussed in Ref. [ [11]] and magneto-optical measurements for determination of LSDA conductance type proposed in Ref. [[13]] makes the scanning mid-IR-laser microscope a unique, and relatively inexpensive non-destructive and non-polluting tool for both defect investigation in research labs and industrial material testing and quality inspections.…”