ME 398 SEMINAR PRESENTATION

1. ME 398 SEMINAR PRESENTATION By Viraj Vajratkar 05D10021 Under the guidance of Prof. Joshi Dept. of Mechanical Engineering, IIT Bombay, April 2008 TOPIC: FIB (Focused Ion Beam) for Nanomachining (Milling)

2. Brief Overview • Scope of FIB (Focused Ion Beam) • Main Principles and Techniques • Process and Response Parameters for Ion Milling • A Numerical Model Dept. of Mechanical Engineering, IIT Bombay

3. Scope and Versatility of FIB • Main features of the FIB: • Site – specific analysis and machining. • Precise till the nanometer scale. • Constructive (addition) as well as destructive (deposition) • The main uses of the FIB: • Implanting/doping • Milling • Redeposition • Photomask repair • FIB Lithography • Ion induced etching… and many more… Dept. of Mechanical Engineering, IIT Bombay

4. Principles and Procedures • Ion – electron or Ion – atom interaction • A Gaussian ion distribution Dept. of Mechanical Engineering, IIT Bombay

5. Principles and Procedures • Heating effects … (1) … (2) … (3) ρ = 0.3μm, V = 150kV, J = 10A/cm2, K = that of SiO2{1.5 x 102 W/cm°C } … (4) Dept. of Mechanical Engineering, IIT Bombay

6. An FIB System • LMIS: • Mass separator • Beam blanker and deflector • Aperture Dept. of Mechanical Engineering, IIT Bombay

7. FIB Milling Parameters • Process parameters: Automatic/manual control, Aperture size, θ, n, dwell time, ion dose, aspect ratio, beam voltage (V). • Response parameters: Ra, milling depth, broadening diameter, MRR, sputter yield, redeposition. controls Dept. of Mechanical Engineering, IIT Bombay

8. Effect on Ra and Milling Time • Beam current: • Milling time decreases exponentially with beam current • Aperture size and manual/program mode • Incident angle: Smooth for low θ, but rough ripples at θ>45° sidewall edge tip Dept. of Mechanical Engineering, IIT Bombay

9. Effect on Broadening Diameter and Milling Depth • Dwell time: • Broadening diameter: A measure of smoothness of the edge periphery and follows the shown relationship. • Milling depth decreases with dwell time mainly due to redeposition effect. Dept. of Mechanical Engineering, IIT Bombay

10. Effect on MRR • Ion dose: A threshold value exists. 3 x 1016 cm-3 Dept. of Mechanical Engineering, IIT Bombay

11. Effect on Sputter Yield (Y) • Ion dose • Incident angle: • Beam voltage: Polynomial fits are made for the shown relation around 2.5 max. at 75°– 80° Dept. of Mechanical Engineering, IIT Bombay

12. Effect on Redeposition • Aspect ratio: Inversely proportional • Ion beam energy: Directly proportional • Aperture size: Directly proportional y x Aspect Ratio = x/y Dept. of Mechanical Engineering, IIT Bombay

13. Effect of Parameters Summarized Dept. of Mechanical Engineering, IIT Bombay

14. Numerical Model • Objective: To find out the varying dose level for each pixel of address grid over the surface by calculating dwell times. • Assumptions • Central: Gaussian • Beam tails (beyond 3σ): Exponential • Net effect of the beam tails on the overall dose is negligible. Dept. of Mechanical Engineering, IIT Bombay

15. Feature Attributes considered by the Model Dept. of Mechanical Engineering, IIT Bombay

16. Mathematical Approach • Divide cavity into layers • Divide layers using address grid • The LHS is related to ion beam distribution and RHS to position and sputter yield • Specifically, pixel (i,j) D l axis k axis 6σ neighbouring pixel (k,l) Dept. of Mechanical Engineering, IIT Bombay

17. Advances Dept. of Mechanical Engineering, IIT Bombay

18. Conclusions • FIB is used in various applications like doping,photomasks repair, material addition, (re)deposition, etc. • Sputtering or chemical effects like etching may be achieved. Sputtering yields are around 1 – 10 specimen atoms per incident ion. • Relatively high temperatures are attained during typical FIB milling operations (nearly 1500°C). • A typical FIB machine has an LMIS, a mass separator and a beam blanking and deflection system. • The FIB milling process is dependent on many process parameters which affect the final response parameters. The effect of the process parameters on the response parameters can be summarized neatly in the Table. • Solve numerical models offline and feed data into drive of the machine. Dept. of Mechanical Engineering, IIT Bombay

19. References • Journal papers: • Eric J. Klien and Fred W. Ramirez, 1999, Consideration of local shadowing and ion beam voltage effects in the prediction of a surface evolving under ion milling; • Lehrer C., Frey L., Petersen S., Rysell H., 2001, Limitations of focused fon beam nanomachining; • Meingailis John, 1986, Critical Review, Focused ion beam technology and applications; • Vasile M.J., Niu Z., Zhang W., Liu S., 1997, Focused ion beam milling: Depth control for three – dimensional microfabrication; • Vasile M.J., Jushan Xie, Raja Nassar, 1999, Depth control of focused ion beam from a numerical model of the sputter process; • Xin Xu, Anthony D. Della Ratta, Jane Sosonkina, John Meingailis, 1992, Focused ion beam induced deposition and ion milling as a function of angle of ion incidence; • Yongqi Fu, Ngoi Kok Ann Bryan, 1999, Investigation of 3D microfabrication characteristics by focused ion beam technology in silicon; • Yongqi Fu, Ngoi Kok Ann Bryan, 2004, Fabrication of three-dimensional microstructures by two-dimensional slice by slice approaching via focused ion beam milling. • Website references: • Fibics Incorporated (Introduction: Focused Ion Beam Systems), http://www.fibics.com/index.html Dept. of Mechanical Engineering, IIT Bombay

20. THANK YOU!