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Microscopy study of correlation between residual elastic strain and defects in He+ ion irradiated 4H-SiC
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| Title: | Microscopy study of correlation between residual elastic strain and defects in He+ ion irradiated 4H-SiC |
| Authors: | Yang, Subing Browse this author |
| Issue Date: | 25-Sep-2020 |
| Publisher: | Hokkaido University |
| Abstract: | Silicon carbide (SiC) has drawn great attention for electronic and optical applications owing to its excellent mechanical, optical and electronic properties, which has also been proposed as structure and cladding materials in nuclear or aerospace environment. However, for its extensive applications, there are still lots of problems to overcome, especially for the irradiation-induced strain in SiC. An accurate non-destructive evaluation of the residual strain in SiC devices has become increasingly important, in particular with the development of the advanced micro/nano SiC-based devices. Besides, clarifying the contribution to the strain/swelling of each defect type is important to accurately evaluate the strain or swelling. In this study, selected-area He+ ion irradiation was performed on n-type 4H-SiC (0001) single-crystal substrates with an energy of 100 keV at room temperature. The irradiation-induced swelling/strain and defects were investigated in the He+ ion irradiated 4H-SiC using various characterization techniques, including confocal Raman microscopy (CRM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM).
A detailed normal strain distribution in the ion-irradiated 4H-SiC was first provided using the non-destructive techniques of EBSD and CRM, whose results showed good agreement. This result validated the application of EBSD and CRM to evaluate the detailed strain distribution in selected-area ion-implanted SiC. In addition to the strain introduced in the irradiated area, excessive strain also extended into the surrounding substrate owing to irradiation-induced swelling. Furthermore, a higher compressive strain is concentrated around the interface between the irradiated and unirradiated areas. An anisotropic strain distribution in the irradiated area is also detected using EBSD, which indicates a correlation of strain degree and crystallographic orientation.
Using TEM techniques, a great anisotropy of defect distribution was first deduced in the selected-area He+ ion irradiated 4H-SiC, that interstitial type defects preferentially redistribute into the surface normal direction ([0004] direction) with more negative volume defects locating in the lateral direction ([101̅0] and [112̅0] direction), which might account for the detected anisotropic strain using EBSD. This anisotropy decreased upon annealing at 600 °C, and it was quite lower in the non-selected-area He+ ion irradiated 4H-SiC. It was found that great compressive stress was introduced in the lateral direction in the selected-area He+ ion irradiated 4H-SiC due to the constraint against lateral expansion, and these compressive stresses were introduced at the beginning of ion irradiation. These findings provided a direct evidence that compressive stress was supposed to inhibit the interstitial type defect formation, enhancing the anisotropic defect distribution.
Using TEM and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS), the correlation of the swelling with various defects, including point defects or tiny clusters, defect clusters, amorphous transition and helium atoms, was separately analyzed. These results provided the volume swelling range for the different defect regions, which is helpful for the prediction of SiC swelling in actual application. Helium atoms in the form of helium bubbles increase the volume swelling at relatively high irradiation fluences. However, decreasing effect of He+ ion irradiation on volume swelling also seems to be possible as below a certain irradiation fluence. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第14233号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Examination Committee Members: | (主査) 教授 柴山 環樹, 教授 大沼 正人, 教授 渡辺 精一 |
| Degree Affiliation: | 工学院（量子理工学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/88806 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 工学院(Graduate School of Engineering)
学位論文 (Theses) > 博士 （工学）
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