In IBM, a stream of charged atoms (ions) of an inert gas, such as argon, is accelerated and directed toward a solid workpiece in a vacuum. By transferring energy and momentum to atoms on the object’s surface, the beam removes atoms from the workpiece.
When an atom collides with an atom cluster on the workpiece, it dislodges between 0.1 and 10 atoms from the workpiece material. IBM allows for the precise machining of virtually any material and is used in the semiconductor industry as well as the production of aspheric lenses.
The technique is also used for texturing surfaces to improve bonding, producing atomically clean surfaces on devices such as laser mirrors, and modifying the thickness of thin films and membranes.
Working Principle of Ion Beam Machining
Ion beam machining (IBM) is an atomic-bit machining technique that produces a product with a high resolution of the order of 0.1 m. Ions of inert gases such as argon, which have a high kinematic energy of the order of 10 KeV, are used to bombard and eject atoms from the workpiece surface through elastic collision.
Unlike machine tool technologies such as cutting, grinding, and lapping, IBM does not have an inherent reference surface; instead, a patterning mask is used. With a micro-ion beam of 1–2 m diameter and a high-precision position control machine tool, IBM could be used for micromachining.
IBM can also be used to aphorize lenses, sharpen diamond microtone knives and cutting tools, and etch IC patterns, among other things. The cost of an IBM machine is extremely high, which drives up the cost of machining and makes the process unprofitable.
Working of Ion Beam Machining
Ion beam machining (IBM) takes place in a vacuum chamber using charged ions fired from an ion source toward the workpiece by means of an accelerating voltage. The mechanism of material removal in IBM differs from that of EBM.
It is closely related to the ejection of atoms, from the surface, by other ionized atoms (ions) that bombard the work material. The process is, therefore, called ion etching, ion milling, or ion polishing. The machining system, shown in Fig., has an ion source that produces a sufficiently intense beam, with an acceptable spread in its energy for the removal of atoms from the workpiece surface by impingement of ions.
A heated tungsten filament acts as the cathode, from which electrons are accelerated by means of high voltage (1 kV) toward the anode. During the passage of these electrons from the cathode toward the anode, they interact with argon atoms in the plasma source, to produce argon ions.
Ar + e − → Ar+ + 2e
A magnetic field is produced between the cathode and anode that makes the electrons spiral. The path length of the electrons is, there- fore, increased through the argon gas, which, in turn, increases the ionization process. The produced ions are then extracted from the plasma toward the workpiece, which is mounted on a water-cooled table having a tilting angle of 0° to 80°.
Machining variables such as acceleration voltage, flux, and angle of incidence are independently controlled.
What Are The Applications of Ion Beam Machining ?
It is primarily used for micro-machining (etching) of electronic components such as computer parts, figuring optical surfaces, and precision fabrication of fine wire dies in refractory materials. Glass, alumina, quartz, crystals, silica, agates, porcelain, cermets, and numerous metals and oxides are examples of etchable materials.
Some of the applications are :-
1. IBM is used in smoothing of laser mirrors as well as reducing the
thickness of thin films without affecting their surface finish. In this regard thinning of samples of silicon to a thickness of 10 to 15 µm has been reported using argon ions impinging at normal incidence by McGeough (1988).
2. Using two opposing beams, a thin circular region on a rotating sample
can produce samples for transmission electron microscopy.
3. Polishing and shaping of optical surfaces by direct sputtering of pre- forms in glass, silica, and diamond is performed using patterning masks.
4. The process can produce closely packed textured cones in different materials including copper, nickel, stainless steel, silver, and gold . Sputter etching can also create microscopic surface texture using the sputter deposition of a lower yield material on the surface.
5. Atomically clean surfaces can be produced by IBM that are used in
the adhesion of gold films to silicon and aluminum oxide substrate. Higher ion energies can be used to remove a layer of the surface oxide.
6. IBM can mill a line width of 0.2 µm, which is used in the fabrication
of bubble memory devices of depth-to-width ratios of 2:1 (McGeough,
1988). Problems associated with the alternative chemical etching method such as the lack of undercutting are avoided since masking is only needed to shadow the beam.
Advantages and Disadvantages of Ion Beam Machining
Some of the advantages of IBM are following :-
1. The procedure is nearly universal.
2. There is no need for any chemical reagents or etching compounds.
3. As with other chemical etching processes, there is no undercutting.
4. Etching rates are easily adjustable.
However, the process has a number of drawbacks, which are as follows:
1. It is not cheap.
2. Etching rates are slow.
3. Despite the fact that almost no heat is generated, there is little chance of thermal or radiation damage.
People Also Ask
Q. How does the ions strike the workpiece in ion beam machining ?
b) Normal incident striking
c) Oblique & Normal incident striking
d) None of the mentioned
Answer: c. Oblique & Normal incident striking
Explanation: The ions may strike obliquely or at normal incidence in Ion Beam machining.
Q. Which of the following are the components of ion beam machining
b) Voltage source
c) Tungsten filament cathode
d) All of the mentioned
Explanation: Main components of IBM are vacuum chamber, voltage source, tungsten cathode filament, plasma source of argon atoms and lens.
Q. What is the value of voltage required for machining in ion beam machining ?
a) 1 kV
b) 2 kV
c) 3 kV
d) 4 kV
Explanation: The value of voltage required for machining in Ion beam machining process is about 1 kV.
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