VISVESWARAIAH TECHNOLOGICAL UNIVERSITY
BELGAUM
Seminar on
“MICROMACHINING”
A Seminar Report Submitted in partial fulfillment of the requirement
For the degree of
Bachelor of Engineering
In
MECHANICAL ENGINEERING
By
RANGASWMY.P
USN: 4PA08ME401
INDEX
1. ABSTRACT
2. INTRODUCTION
3. BULK MICROMACHINING
3.1. LIMITATIONS
4. SURFACE MICROMACHINING
4.1. LIMITATIONS
5. LIGA (Lithographie, Galvanoformung, und Abformung)
6. LASER MICROMACHINING
6.1. SYNCHRONISED IMAGE SCANNING
6.2. BOW TIE SCANNING
6.3. MASK PROJECTION TECHNIQUE
7. THE FUTURE TRANSITION – FROM MICRO TO NANO
8. CONCLUSION
9. REFERENCES
1. ABSTRACT
 The miniaturization of products and their manufacturing processes is
considered one of the key trends in technology development.
 Micromechanical parts tend to be rugged, respond rapidly, use little power,
occupy a small volume, and are often much less expensive than conventional
macro parts, added to that they have high thermal, chemical, and mechanical
stability.
 Micro machining technologies make devices ranging in size from a dozen
millimeters to a dozen microns.
 These techniques combined with wafer bonding and boron diffusion allows
complex mechanical devices to be fabricated.
The Lithographie,
Galvanoformung, und Abformung (LIGA) technology makes miniature parts
with spectacular accuracy.
 The report also deals with conventional methods such as laser machining.
2. INTRODUCTION
 A micro- system is an intelligent miniaturized system comprising sensing,
processing and/or actuating functions.
 Micro engineering refers to the technologies and practice of making three
dimensional structures and devices with dimensions in the order of
micrometers.
 Micromachining is the basic technology used for the production of
miniaturized parts and components. Micromachining resulted in the
fabrication of a broad class of devices whose defining characteristics were
micrometer-scale feature size and electromechanical functionality, and these
systems are collectively called as MEMS (MICRO-ELECTRO –
MECHANICAL-SYSTEMS).
2.1 MICROMANUFACTURING
Micro manufacturing is the set of design and fabrication tools that precisely
machine and form structures and elements at a scale below the limits of our human
perceptive faculties.
The methods commonly used for the fabrication of micro elements are almost as
varied as their applications, but generally fall within two distinct categories:
Bulk micromachining.
Surface micromachining.
3. BULK MICROMACHINING
 Bulk micromachining is a subtractive process, the term is applied to a
variety of etching procedures, where the required structures are developed
using the etching agents that selectively remove material.
 Etching produces concave, pyramidal or other faceted holes, depending on
which face of the crystal is exposed to the chemicals.
 This technique has come to be known as bulk micromachining because the
chemical that pits deeply into the silicon produces structures that use the
entire mass of the chip.
Isotropic wet Etching
Most commonly used isotropic etching agents for Silicon are:
Etches dope extrinsic regions i.e. n+ and p+, more than intrinsic regions. In etching
prior to the expose of substrate to the etching agent, a mask is used which is placed
over the substrate material to obtain proper etched regions.
Most commonly used masks against this isotropic etch are:
Nitrides (Si3N4)
Noble metals
SiO2 (if HF ratio is low and for short etches)
Anisotropic Wet Etching
In this type of etching, the etching rate is orientation dependent in the crystal.
A. Inorganic alkaline solutions (KOH, LiOH, NaOH)
B. Organic alkaline solutions: (Ethylene diamine, pyrocatechol and water: EDP)
A completely anisotropic etchant will etch in one direction only. An isotropic
etchant will etch in all directions at the same rate.
3.1 LIMITATIONS OF BULK MICROMACHINING
 Bulk Micromachining has the disadvantage that it uses alkaline chemicals,
foreign to conventional chip process.

Consequently,
fabricating
multiple,
interconnected
micromechanical
structures of free-form geometry is often difficult or impossible.
4. SURFACE MICROMACHINING
It is called surface micromachining because it deposits a film of silicon a few
microns thick, from which beams and other edifices can be built
 Surface micromachining relies on encasing the structural parts of the device
in layers of a sacrificial material during the fabrication process.
 The sacrificial material (also called spacer material) is then dissolved away
in a chemical etchant that does not attack the structural parts.
 The final stage of dissolving the sacrificial layer is called "release".
In other words, there are two primary components in a surface micromachining
process:
>> Structural layers -- of which the final microstructures are made;
>> Sacrificial layers -- which separate the structural layers and are dissolved in the
final stage of device fabrication.
Surface micromachining involves depositing, removing, and patterning thin films
on a substrate.
4.1 LIMITATIONS OF SURFACE MICROMACHINING
 Indeed, surface micromachining has an important limitation. It is inherently
a planar fabrication process, and is, therefore, limiting for mechanical
design.
 Hence, surface micromachining produces planar structures (i.e., low aspect
ratio devices) with little in the way of Z topology
5. LIGA (LITHOGRAPHIE, GALVANOFORMUNG, ABFORMUNG)
A technique that allows overcoming the two-dimensionality of surface
micromachining is the LIGA process. The technology was developed in Germany
It is the acronym for Lithographie (lithography), Galvanoformung (electroplating),
Abformung (molding). It displaces the achievable height of the microstructure
from few to hundreds microns and like bulk and surface micromachining relies on
lithographic patterning.
Lithography is the technique by which the pattern on a mask is transferred to a film
or substrate surface via a radiation-sensitive material. The radiation may be optical,
x-ray, electron beam, or ion beam
Pattern generation begins with mask design and layout using computer-aided
design (CAD) software, from which a mask set is manufactured. A typical mask
consists of a glass plate coated with a patterned chromium (Cr) film.
Metal is then plated into the structure; This metal piece can become the final part
or can be used as an injection mold.
Injection molding of microscopic parts can be carried out with a process. The
process can be used for the manufacture of high-aspect-ratio
6. LASER MICROMACHINING
Over many years such processes have become well established as production
techniques with improvements limited mostly to enhancements in laser drive
technology rather than changes to the basic mask projection, beam handling and
motion control techniques.
Pulsed laser micromachining techniques using mask projection methods are now
widely used for the creation of miniature structures in both massive and thin
substrates.
6.1 SYNCHRONISED IMAGE SCANNING (SIS)
In SIS the substrate moves continuously during pulsed laser triggering such that,
simultaneously with each laser pulse,
The image projected onto the substrate has moved by exactly one pitch
.
.
6.2 BOW TIE SCANNING
The laser scans in a straight line at high speeds across a section of the substrate by
a galvanometer-driven mirror deflection,
While the substrate is moved on a linear stage at constant speed in the orthogonal
direction.
After each transverse scan the galvanometer mirror decelerates, reverses and
performs a scan in the opposite direction
6.3 MASK PROJECTION TECHNIQUES (MPT)
.
7.
THE
FUTURE-
TRANSITION
FROM
MICROMACHINING
TO
NANOMACHINING
 Nano is the buzzword of the moment, which demands refinement in
micromachining resulting in evolution of nanomachining.
 Thus the transition from Micro-Electro-Mechanical-Systems (MEMS) to
Nano-Electro-Mechanical-Systems (NEMS) will take place.
 The smallest features that have been fabricated using lithography are only a
few tenths of a nanometer in dimension.
 Nanomachining has been used by a number of groups to fabricate quantum
devices such as single-electron transistors (SETs) and metal-oxide junctions.
8. CONCLUSION
Micro engineering not only provides a new manufacturing route for existing
products, but also, importantly, allows the creation of completely new products and
new markets providing large volumes of low cost sensors to the automotive
industry, and low volume high performance, small and light weight sensors to
aerospace and defense.
The predominant technology at present state is surface micromachining, and
current developments show that this trend will continue in the future. However the
LIGA process will grow in importance, as it is the only method for producing true
three-dimensional objects..
9. REFERENCES:
Micron Machinations”, G.Stix, Scientific American, Vol.267, November 1992.
“Engineering Microscopic Machines”, K.J Gabriel, Scientific American, Vol.273, September
1995
“International Workshop on Micro Electro Mechanical Systems”, Feb 1996.
“Laser Processing in Manufacturing”, Crafer, R.C. and Oakley, (Chapman and Hall).
“Production of novel 3D microstructures using excimer laser mask projection techniques”,
N.H.Rizvi.
“Excimer lasers: Principles of operation and equipment”, M.C.Gower.
“An introduction to Micro-Electro-Mechanical-System Engineering”, K.Hjort, G.Thornell,
R.Spohr, J.A.Schweitz.