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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). Brief Overview. Scope of FIB (Focused Ion Beam)

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ME 398 SEMINAR PRESENTATION

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Me 398 seminar presentation

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)


Brief overview

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


Scope and versatility of fib

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


Principles and procedures

Principles and Procedures

  • Ion – electron or Ion – atom interaction

  • A Gaussian ion distribution

Dept. of Mechanical Engineering,

IIT Bombay


Principles and procedures1

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


An fib system

An FIB System

  • LMIS:

  • Mass separator

  • Beam blanker and deflector

  • Aperture

Dept. of Mechanical Engineering,

IIT Bombay


Fib milling parameters

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


Effect on r a and milling time

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


Effect on broadening diameter and milling depth

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


Effect on mrr

Effect on MRR

  • Ion dose:

    A threshold value exists.

3 x 1016 cm-3

Dept. of Mechanical Engineering,

IIT Bombay


Effect on sputter yield y

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


Effect on redeposition

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


Effect of parameters summarized

Effect of Parameters Summarized

Dept. of Mechanical Engineering,

IIT Bombay


Numerical model

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


Feature attributes considered by the model

Feature Attributes considered by the Model

Dept. of Mechanical Engineering,

IIT Bombay


Mathematical approach

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

neighbouring pixel (k,l)

Dept. of Mechanical Engineering,

IIT Bombay


Advances

Advances

Dept. of Mechanical Engineering,

IIT Bombay


Conclusions

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


References

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


Thank you

THANK YOU!


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