Objective Electron bombardment complementary metal-oxide semiconductors (EBCMOS) is an advanced imaging technology that combines electron beam bombardment and CMOS technology. In order to improve the image quality of EBCMOS and obtain high resolution low-light level imaging devices, the factors affecting the spatial resolution of EBCMOS doped with electron multiplier layer were studied.

Methods Based on carrier transport and recombination theory combined with Monte Carlo method, the theoretical calculation model of the spatial resolution in the electron multiplication layer in EBCMOS is established. The effects of substrate thickness, substrate doping concentration and incident electron energy on the resolution of EBCMOS were simulated and analyzed.

Results and Discussions The influence of different thickness of substrate on resolution under homogeneous substrate doping was studied. The base thickness was selected from 10-25 μm. Figure 3 shows the PSF image of multiplying electrons at different base thicknesses. Figure 4(a) shows the corresponding LSF curves under different base thicknesses. Figure 4(b) shows the corresponding MTF curves under different base thicknesses. When the MTF value is the same, the larger the thickness of the substrate, the smaller the corresponding spatial frequency, and the smaller the limit resolution, that is, increasing the thickness of the substrate will lead to the decrease of the device resolution. In the subsequent simulation, the thickness of P-type substrate is selected to be 10 μm, and the limiting resolution of the device can reach 31 lp/mm. The influence of different substrate doping concentrations on the resolution of uniform substrate doping was studied. The doping concentration of the substrate was selected as 10¹⁴-10¹⁷ cm⁻³. Figure 5 shows the PSF images of multiplying electrons at different substrate doping concentrations. Figure 6(a) shows the corresponding LSF curves under different substrate doping concentrations. Figure 6(b) shows the MTF curves corresponding to different substrate doping concentrations. With the same MTF value, the larger the substrate doping concentration, the smaller the corresponding spatial frequency and the smaller the limiting resolution, that is, increasing the substrate doping concentration will lead to lower device resolution. The doping concentration of P-type substrate is 10¹⁴ cm⁻³, and the limiting resolution of the device can reach 37 lp/mm. The effect of incident electron energy on resolution under uniform substrate doping is studied. The energy of incident electron was selected from 1 to 2. 5 keV. Figure 7 shows the PSF images of multiplying electrons at different substrate doping concentrations. Figure 8(a) shows the corresponding LSF curve under different incident electron energies. Figure 8(b) shows the MTF curves corresponding to different incident electron energies. When the incident electron energy changes, the MTF curves under different incident electron energies almost coincide, that is, the incident electron energy has little influence on the resolution, and the corresponding limit resolution is also little different. Due to the randomness of the doubling electrons, the influence of the incident electron energy on the resolution can be ignored.

Conclusions The results show that thinning the substrate and reducing the doping concentration of the substrate can reduce the diffusion radius of the multiplier electrons, and then obtain high resolution devices. Changing the energy of the incident electron has little effect on the focus and resolution of the doubling electron. When the substrate thickness is 10 μm, the substrate doping concentration is 10¹⁴ cm⁻³, and the incident electron energy is 1 keV, the limit resolution can reach 37 lp/mm. The work in this paper will provide theoretical basis for optimizing the electron multiplier layer structure and improving the resolution of EBCMOS.