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The semiconductor manufacturing
industry is a rapidly growing industry. In 2005, the industry value was
estimated around $285 billion [finance.yahoo.com]. As the use of
electronics pervades more into everyday life in the form of computers,
cell-phones etc., there is immense pressure on the semiconductor
manufacturers to increase product variety and reduce delivery times.
Due to rapid development, the industry is moving towards fully
automated manufacturing systems. High volumes and increasing product
variety make building to demand a complex proposition. The
manufacturing plant must be flexible. Equally important is an effective
planning and scheduling system to manage the complexity.
In addition to the actual complexity of the
manufacturing process in semiconductor manufacturing, there is a
substantial amount of investment involved. It typically costs around
$2-$3 billion to set up a 300mm wafer fabrication unit and around $1-$2
billion investment to set up a 200mm unit. The wafer fabrication
facilities are the state-of-the-art; highly automated facilities
replete with their own power plants, water and air purification
systems. The facilities typically consist of around 75 to100 different
tool types with 300+ pieces of equipment. These tools themselves are
highly sophisticated and expensive with a particular tool costing
around a million dollars.
Depending on the targeted market, these facilities
are loaded with differing variety of products. A high-volume, low-mix
facility would have around 10 different products at a particular time
but a high-volume, high-mix facility like a foundry can have hundreds
of products getting built in a facility at a time.
Typically,
300mm wafer fabrication units have about 500-600 wafer starts per day.
There has been a steady historical progress in the basic units which
undergo the semiconductor manufacturing process. The diameter of the
largest silicon wafer in semiconductor manufacturing has increased
linearly at about 7.5 mm/year since the 1960s in the following sequence
of diameters: 10, 12.5, 22, 25, 31.25, 50, 56.25, 75, 81.25, 100, 125,
150, 200 and 300 mm. The line or feature widths on each semiconductor
chips have decreased from 10micron in the 1970’s to 90nm and
65nm today.
Semiconductor cluster tools are
typical tools used in semiconductor manufacturing. A semiconductor
cluster tool is comprised of several different wafer processing modules
that are managed by a centralized control system. A wafer handling
robot interacts with the processing modules/chambers for transport. The
semiconductor cluster tool control system then manages the robot for
the wafer’s travel between each chamber. The type of chambers
used can include process, transport, buffer and cassette modules.
Cassette modules are used to store both processed and unprocessed
wafers. Process modules perform manufacturing techniques such as
deposition and etching Transfer modules move the wafers between the
process and cassette modules.
Semiconductor cluster tools allow wafers to be
processed in a closed environment with little operator interaction. A
semiconductor cluster tool may be one of two basic types: a cluster
tool with a single wafer handling chamber between the loadlock and the
process chambers, or a cluster tool with two or more chambers.
Demands
for smaller diameter wafers, improved device performance, and greater
reliability and yield are drivers for the development of cluster tools
for semiconductor processing operations. The semiconductor
manufacturing industry is moving towards a cluster approach for
semiconductor equipment in order to create a higher throughput for
wafer processing. The purpose of semiconductor cluster tools is to
reduce cycle times, reduce wafer handling by operators, and reduce
particulate and molecular contamination.
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