Micromachining is the basic technology for fabrication of
micro-components of size in the range of 1 to 500 µm. Their
need arises from miniaturization of various devices in
science and engineering, calling for ultra-precision
manufacturing and micro-fabrication.
Figure: Micro Machining Definition
Definition: material removal at
micro/ Nano level with no constraint
on the size of the component being
Removal of material in the form of chips having the
size in the range of microns.
Creating micro features or surface characteristics
(especially surface finish) in the micro/ Nano level.
WHY MICRO MACHINING?
Final finishing operations in manufacturing of precise parts are
always of concern owing to their most critical, labour intensive
and least controllable nature.
In the era of nanotechnology, deterministic high precision finishing
methods are of utmost importance and are the need of present
The need for high precision in manufacturing was felt by
manufacturers worldwide to improve interchangeability of
components, improve quality control and longer wear/fatigue life.
WHY MICRO MACHINING?
Present day High-tech Industries, Design requirements are stringent.
• Extraordinary Properties of Materials (High Strength, High heat Resistant,
High hardness, Corrosion resistant etc.)
• Complex 3D Components (Turbine Blades)
• Miniature Features (filters for food processing and textile industries having
few tens of microns as hole diameter and thousands in number)
• Nano level surface finish on Complex geometries (thousands of turbulated
cooling holes in a turbine blade)
• Making and finishing of micro fluidic channels (in electrically conducting &
non conducting materials, say glass, quartz, &ceramics)
• Photolithography, also termed optical lithography or UV
lithography, is a process used in micro fabrication to pattern parts
of a thin film or the bulk of a substrate.
• It uses light to transfer a geometric pattern from a photo mask to
a light-sensitive chemical "photoresist", or simply "resist," on the
• Etching is used in micro fabrication to chemically remove
layers from the surface of a wafer during manufacturing.
• Etching is a critically important process module, and every
wafer undergoes many etching steps before it is complete.
• It is characterized by etch rate , etch selectivity and etch
1. Wet etching
Etching processes used liquid-phase ("wet") etchants. The wafer can be immersed in a bath of
etchant, which must be agitated to achieve good process control. For instance, buffered
hydrofluoric acid (BHF) is used commonly to etch silicon dioxide over a silicon substrate.
2. Dry etching
• Modern VLSI processes avoid wet etching, and use plasma etching instead.
• plasma etching operates between 0.1 and 5 Torr
• The plasma produces energetic free radicals, neutrally charged, that react at the surface of
the wafer. Since neutral particles attack the wafer from all angles, this process is isotropic
• Bulk and surface micromachining are processes used to create
microstructures on microelectromechanical MEMS devices.
• While both wet and dry etching techniques are available to both
bulk and surface micromachining, bulk micromachining typically
uses wet etching techniques while surface micromachining
primarily uses dry etching techniques.
• Bulk micromachining selectively etches the silicon substrate to
create microstructures on MEMS devices.
• Unlike Bulk micromachining, where a silicon substrate (wafer) is selectively
etched to produce structures, surface micromachining builds microstructures
by deposition and etching of different structural layers on top of the substrate
• Generally polysilicon is commonly used as one of the layers and silicon
dioxide is used as a sacrificial layer which is removed or etched out to create
the necessary void in the thickness direction
• The main advantage of this machining process is the possibility of realizing
monolithic microsystems in which the electronic and the mechanical
components(functions) are built in on the same substrate.
• An important technology of MST
• Developed in Germany in the early 1980s
• LIGA stands for the German words
• Lithography (in particular X-ray lithography)
• Galvanoforming (translated electro deposition or
• Abformtechnik (plastic molding)
• The letters also indicate the LIGA process sequence
PROCESSING STEPS IN LIGA
• Apply resist, X-ray exposure through mask,
• remove exposed portions of resist,
• electrode position to fill openings in resist,
• strip resist for (a) mold or (b) metal part
ADVANTAGES IN LIGA
• LIGA is a versatile process – it can produce parts by several
• High aspect ratios are possible (large height-to-width ratios in the
• Wide range of part sizes is feasible - heights ranging from
micrometers to centimeters
• Close tolerances are possible
DISADVANTAGES IN LIGA
• LIGA is a very expensive process
• Large quantities of parts are usually required to justify its
• LIGA uses X-ray exposure
• Human health hazard