Abstract
The multi-annular backscattered electron detector (BSED) proposed in this thesis has been evolved so that collecting BSEs is already adequate for the display of Z-contrast as well as surface topography. Compared with the traditional multi-fan shaped BSED, the BSED proposed in this thesis can provide higher sensitivity of Z-contrast and better surface topography contrast. With the consideration that different angular distribution of BSEs can be resulted from different tilt angles between the BSEs and specimens, a multi-annular BSED has been proposed in this thesis. Benefited by this structure, BSEs from different angular distribution can also be collected, improving the quality of the surface topography contrast. The material used for this multi-annular BSED is silicon wafer with resistance of 2000 □. The depletion region is formed by ion implantation under the conditions that the ion implantation energy, angle and dose are 10 keV、7 o and 5×1015 atoms/cm-2 respectively and the temperature for rapid thermal annealing is kept at 950 ℃ for 30 sec. The width of the depletion region obtained is 15.2 μm. According to the test results, electron-hole pairs produced by 1-30 keV BSEs can be collected by the BSED and the charge collection efficiency can be up to 80%. The test results show that when the electron-beam energy is 20 keV, the traditional BSED has the sensitivity of Z-contrast of about 14.44 nA/Z and the surface topography contrast of 40.08 nA/μm. However, the sensitivity of Z-contrast of the proposed multi-annular BSED is about 16.71 nA/Z and its surface topography contrast is 82.11 nA/μm. Based on the test results, it clearly shows that compared with the traditional multi-fan shaped BSED, which measures the surface topography by detecting the strength of the current signals produced by the BSEs, the multi-annular BSED proposed in this thesis possesses a larger working area. Besides, it can collect BSEs from different tilt angles so as to analyze specimens, providing higher sensitivity of Z-contrast and better surface topography contrast.