A Micromachined Electron Source D.A. Crewe, D.0 Perng, S.E. Shoaf, and A.D. Feinerman University Of Illinois at Chicago Microfabrication Applications Laboratory Chicago, Illinois, 60680 Abstract A new microfabrication technique that allows the precise construction of large three dimensional structures with dimensional tolerances approaching 1 micron is being applied to the design of a Miniature Scanning Electron Microscope (MSEM). In this paper we will present the electron optic calculations of the MSEM source (gun). The MSEM measures less than one cubic centimeter and the source measures approximately lx I xO.20 cm3. The details of the MSEM fabrication are in an accompanying article.1 There are many advantages of a MSEM. The performance of an SEM is improved as its length is reduced.2 The need for mechanical adjustments and motion feedthroughs is eliminated since the microscope components are pre-aligned to the optic axis. All components are ultra high vacuum compatible and can be heated to 500 °C. A small, portable electron microscope can be brought to the sample to be inspected instead of the sample being brought to the microscope. Vacuum hardware requirements are minimized. The fabrication technology is inexpensive with respect to the conventional methods of electron microscope construction. Arrays of MSEMs can be built to allow applications in high throughput e-beam lithography. In addition two MSEMs can be mounted a few degrees apart to provide stereo imaging. 1. Electron Optic Calculations 1.1 Electrostatic Field Calculation A three electrode design is preferred since it offers more control over magnification and beam crossover as other parameters in the MSEM lens system are developed. Three possible electrode arrangements that can be made using our construction method are shown in figure 1. The three element electrostatic lens is laid out on a rectangular mesh of 30,000 points. The density of mesh points along each direction can be varied, and more points are placed in regions where large spatial deviations in the electric field are expected. A finite difference solution to LaPlace's equation is then obtained using initial boundary conditions described by the grid. The electrodes are fixed potential surfaces and planes of parallel or normal field components can be assigned where appropriate. One can take advantage of symmetry in the lens by calculating one half the lens and mirroring the result about the optic axis. 66 / SPIE Vol. 1778 Imaging Technologies and Applications (1992) 0-B 1 94-0950-2/92/$4.0O A Micromachined Electron Source D.A. Crewe, D.C Perng, S.E. Shoaf, and A.D. Feinerman University Of Illinois at Chicago Microfabrication Applications Laboratory Chicago, Illinois, 60680 Abstract A new microfabrication technique that allows the precise construction of large three dimensional structures with dimensional tolerances approaching 1 micron is being applied to the design of a Miniature Scanning Electron Microscope (MSEM). In this paper we will present the electron optic calculations of the MSEM source (gun). The MSEM measures less than one cubic centimeter and the source measures approximately lx 1 xO.20 cm3 . The details of the MSEM fabrication are in an accompanying article.' There are many advantages of a MSEM. The performance of an SEM is improved as its length is reduced.2 The need for mechanical adjustments and motion feedthroughs is eliminated since the microscope components are pre-aligned to the optic axis. All components are ultra high vacuum compatible and can be heated to 500 °C. A small, portable electron microscope can be brought to the sample to be inspected instead of the sample being brought to the microscope. Vacuum hardware requirements are minimized. The fabrication technology is inexpensive with respect to the conventional methods of electron microscope construction. Arrays of MSEMs can be built to allow applications in high throughput e-beam lithography. In addition two MSEMs can be mounted a few degrees apart to provide stereo imaging. 1. Electron Optic Calculations 1.1 Electrostatic Field Calculation A three electrode design is preferred since it offers more control over magnification and beam crossover as other parameters in the MSEM lens system are developed. Three possible electrode arrangements that can be made using our construction method are shown in figure 1 . The three element electrostatic lens is laid out on a rectangular mesh of 30,000 points. The density of mesh points along each direction can be varied, and more points are placed in regions where large spatial deviations in the electric field are expected. A finite difference solution to LaPlace's equation is then obtained using initial boundary conditions described by the grid. The electrodes are fixed potential surfaces and planes of parallel or normal field components can be assigned where appropriate. One can take advantage of symmetry in the lens by calculating one half the lens and mirroring the result about the optic axis. 66 / SPIE Vol. 1778 Imaging Technologies and Applications (1992) 0-81 94-0950-2/92/$4.O0 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/19/2015 Terms of Use: http://spiedl.org/terms