User Manual

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Siemens Building Technologies
Cerberus Division
01.2002
5 Information on microchip production
5.1 Introduction into the semiconductor industry
The semiconductor industry has its roots in the 1947 discovery of the transistor. Integrating
electronics into every aspect of life has provided the impetus for the development of cheap-
er and yet more powerful devices. Progress has continued at an accelerated pace from
discrete transistors, operational amplifiers through to the modern microprocessor. In 1995
total sales of semiconductors reached US$140 billion. The trend towards a greater use of
semiconductors in replacing discrete components will increase the percentage of semi-
conductor usage. One prediction puts sales for the year 2030 at $12,000 billion.
Huge worldwide demand for microprocessors and microcontrollers has meant the major
manufacturers have had to make large investments in purpose-built semiconductor
manufacturing plants. They are found all over the developed world and while the detailed
design of the building housing the manufacturing plant may vary, the concept is the same.
Strictly speaking the manufacturing plant is concerned with the production of semiconduc-
tor wafers. These wafers , literally thin slices of semiconductor material such as silicon, are
the basis of integrated production. After processing, the individual units are „packaged”.
Packaging in this case refers to the final assembly of protective encapsulation and external
conductors or pins.
5.1.1 Manufacturing process
Specialist machinery is used in the manufacture of semiconductors. In addition a carefully
controlled environment must be created. The area where semiconductor wafers are
manufactured and processed is known as a „clean room”. Clean rooms are categorised by
the ratio of one particle of a defined size to a volume of air. Contamination is a major source
of product failure in this industry. Dust particles are regarded as wholly unacceptable and
operatives are required to wear complete protective coveralls when working in the clean
room.
The technology that produces high filtration levels for clean rooms is also found in other
industries, particularly pharmaceuticals. High Efficiency Particulate Air-filters (HEPA) and
Ultra Low Penetration Air filters (ULPA) are used to help achieve the required air cleanli-
ness. Typically air movement is high and travels vertically, from ceiling to floor.
Within this environment the process itself takes place. Simplistically, the process is analo-
gous to photographic development. It can take between ten and thirty steps to complete the
process depending upon the complexity of the devices being manufactured.
There can be as many as four hundred separate steps for a 16MB DRAM (dynamic RAM) in
the manufacture of integrated circuits. Starting point is the creation of high purity single
crystal silicon ingots. These are sliced into wafers of varying diameters. Improving technol-
ogy has meant the diameter of wafers has increased over the past few years. The greater
the diameter , the larger the number of finished products obtainable from each wafer. Re-
cently, 20cm to 30cm wafers have become commonplace.
The major steps in the process are outlined below:
Polishing
High levels of cleanliness are essential for the success of the manufacturing process. Disc-
shaped wafers are polished before moving on to the next stage.
Thin film deposition
It is essential to coat the wafer with layers of material that create the structure necessary for
the operation of the millions of transistors within the integrated circuit. This is achieved by
thermal deposition of high purity oxygen into the silicon. A uniform layer of silicon dioxide is
thus created.