Abstract
For silicon carbide (SiC) processed by ion-implantation, dedicated test structure fabrication or destructive sample processing on test wafers are usually required to obtain depth profiles of electrical characteristics such as carrier concentration. In this study, a rapid and non-destructive approach for depth profiling is presented that uses confocal Raman microscopy. As an example, a 4H–SiC substrate with an epitaxial layer of several micrometers thick and top layer in nanoscale that was modified by ion-implantation was characterized. From the Raman depth profiling, longitudinal optical (LO) mode from the epitaxial layer and longitudinal optical phonon-plasmon coupled (LOPC) mode from the substrate layer can be sensitively distinguished at the interface. The position profile of the LOPC peak intensity in the depth direction was found to be effective in estimating the thickness of the epitaxial layer. For three kinds of epitaxial layer with thicknesses of 5.3 μm, 6 μm, and 7.5 μm, the average deviations of the Raman depth analysis were −1.7 μm, −1.2 μm, and −1.4 μm, respectively. Moreover, when moving the focal plane from the heavily doped sample (~1018 cm−3) to the epitaxial layer (~1016 cm−3), the LOPC peak showed a blue shift. The twice travel of the photon (excitation and collection) through the ion-implanted layer with doping concentrations higher than 1 × 1018 cm−3 led to a difference in the LOPC peak position for samples with the same epitaxial layer and substrate layer. Furthermore, the influences of the setup in terms of pinhole size and numerical aperture of objective lens on the depth profiling results were studied. Different from other research on Raman depth profiling, the 50× long working distance objective lens (50L× lens) was found more suitable than the 100× lens for the depth analysis 4H–SiC with a multi-layer structure.
Highlights
As a third generation semiconductor material, silicon carbide has many outstanding characteristics such as a wide forbidden bandgap, high thermal conductivity, high mobility, and high electrical breakdown strength [1]
To evaluate the electrical properties of the material obtained after ion-implantation and annealing treatment, where the carrier concentration and carrier mobility are of particular interest, and many methods are being used to measure the electrical properties of silicon carbide such as the Hall effect [3], point contact current voltage technique (PCIV) [4], four-point probe [5], and mercury-probe capacitance voltage [6]
The results of the depth analysis corresponded well to the surface single-point spectra we reported earlier and provides plentiful information on the following
Summary
As a third generation semiconductor material, silicon carbide has many outstanding characteristics such as a wide forbidden bandgap, high thermal conductivity, high mobility, and high electrical breakdown strength [1]. To evaluate the electrical properties of the material obtained after ion-implantation and annealing treatment, where the carrier concentration and carrier mobility are of particular interest, and many methods are being used to measure the electrical properties of silicon carbide such as the Hall effect [3], point contact current voltage technique (PCIV) [4], four-point probe [5], and mercury-probe capacitance voltage [6]. The most relevant method for rather thin implanted 4H–SiC layers with high doping concentrations is secondary ion mass spectroscopy (SIMS) depth profiling. Only a small number of confocal depth analysis results have been published, but most of them have focused on the damage distribution after high energy (MeV range) implantation, which is not the typical case for silicon carbide doping in the SiC electrical device industry. Information on the heavily doped substrate and epitaxial layer were distinguished, the thickness of the epitaxial layer was evaluated, and the influence of the top ion modified layer on the Raman depth analysis was explained in detail
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