Applications of Raman Spectroscopy in Semiconductor industry

What can raman Spectroscopy do?

For analyzing semiconductor materials used for transistors, photovoltaic cells, light-emitting diodes, and other semiconductor devices, Raman spectroscopy is the best option. It provides information about the vibrational and electronic properties of semiconductors that are sensitive to crystalline quality, microstructure, strain, alloy composition and free carrier density. It is a powerful analytical method that works well in demanding semiconductor applications and is suitable to characterizing the homogeneity of raw materials such as Si, SiGe, InGaAs, GaAs, GaN, and graphene exhibit precise, distinct Raman bands.

In essence, Raman scattering examines the inelastic dispersion of inbound particles of monochromatic light by the atomic vibrations of a material (solid, liquid, or gas). Atomic movements in crystalline materials are quantized (called phonons), and they are extremely sensitive to both internal and external disturbances like doping and stress. The frequency of the scattered light (outgoing photons) serves as a nearby indicator of whether or not the medium has been perturbed.

Micro-Raman spectroscopy has developed into (like many other optical methods) a very alluring characterization instrument at the industrial level in contemporary clean room facilities. This is as a result of its frictionless and undamaging properties. The ability to explore the intricate profile of a particular semiconductor or gadget is made possible by the use of various laser wavelengths.

The Raman Imaging

Recently, Raman mapping systems have been transformed into Raman imaging systems that use CCD detectors to quickly gather data.

The spatial patterns of physical characteristics in narrow-gap III-V semiconductors, IV-IV semiconductors like Ge, Si, and diamond, wide-band-gap semiconductors including SiC and AlGaN, and other semiconductors have been examined using Raman imaging (mapping).

Characterization of crystal growth process

The dynamical mechanisms, like crystal growth, are revealed by raman imaging. The result of thermally annealed thin Si films (TSFs) on insulators provides a good illustration for this application (SOI). The Si layers were thermally annealed for five hours at 600 °C after being formed by low-pressure chemical vapour deposition using the gas sources silane (SiH4) and disilane (Si2H6). Using line illumination and translating the sample stage, intensity pictures of polarized Raman bands were measured on these films. The undulation may happen as a result of the film's grains being entwined at their grain borders and having various crystallographic orientations. The intensity patterns of Si films, on the other hand, that were produced in the liquid phase exhibit a sudden shift at grain boundaries.

Distribution of stress and carrier density around micropipes

The structural and electrical characteristics of semiconductors are strongly impacted by defects. Raman spectra can be used to detect flaws because they are susceptible to these characteristics. Micro-Raman imaging is anticipated to offer new insights into the types and locations of the flaws. Raman imaging has so far been used to assess the quantity of growth-related flaws and damage in ion-implanted semiconductors.

SiC crystals frequently have micropipes, which are anomalies that enlarge in the 0001 direction. The efficacy of SiC devices is known to suffer from flaws of this kind. A polarizing optical microscope and a Raman microscope were used to detect the stresses in the vicinity of micropipes. By incrementally advancing the sample under the line by 0.5 m, the two-dimensional Raman picture is constructed. The peak locations of each spectrum are exactly determined after meticulous fitting to an unique Lorentzian line shape.

Diodes and modulation-doped specimens

In p-n junction devices, epitaxially formed materials, and rarely in highly impurity-doped semiconductors, the free carriers density has an irregular distribution. The line form study of the LOPC mode can be used to calculate the free carrier concentration. By using micro-Raman imaging, the carrier concentration and motion in the p-n junctions of GaP diodes have been identified.

Samples with the (0001) face were taken from a 4H-SiC ingot that had been grown in the (11 00) orientation using a modified Lely technique. The N2 gas source was repeatedly turned on and off to create the modulation doping, which caused the impurity content to have a boxcar-like distribution. Line lighting was used to create one-dimensional Raman pictures of the LOPC mode at ambient temperature.