Within the semiconductor industry, the need for air purification equipment arises, not only from the concern for keeping electronic equipment from corroding, but also from the need for manufacturers to insure the safety of working personnel and the community surrounding the facility.
Gases & other hazardous chemical compounds are used in almost every stage of silicon integrated circuit production, from growing crystals of pure silicon to assembling completed circuits into electronic packages. Contaminants such as silane, arsine, phosphine, diborane, hydrogen chloride, nitric acid, sulphuric acid, lead sulphonic acid, ammonia, propanol, and in some cases, cyanide compounds, are chemically active and very toxic, and must, therefore, be carefully controlled so that there are no dangerous emissions.
Because of the delicate nature of the materials being manufactured, the semiconductor chips are produced inside a 'clean room' environment. In the past, cleanroom technology focused primarily on minimizing the particle count in the ambient cleanroom environment. However, shrinking devices and more complex processing semiconductor manufacturing, and the use of larger glass in flat panel manufacturing will increase the necessity to control gaseous molecular contamination.
Problems Faced in Manufacturing due to Presence of Contaminants
From Outside untreated air and emission of acid vapors during manufacturing
- Corrosion of silver contacts by strong oxidizing properties of S compounds, especially H2S
- Corrosion of Cu/Al by SO42-
- Crystals formed by neutralization with SO42- and NO3- with NH4+
- Defects in the chemical amplified resist process
- Defects in exposure/pattern generation processes (T-topping)
- Lower illuminance resulting from lens contamination
- Crystal formation by neutralization with dissolved acid on wafer surface, after de-ionized water cleaning
Presence of volatile organic compounds
- Current leakages and abnormal circuit voltage resistance
- Defects due to formation of oil film on wafer surface due to presence of high molecular weight organics
Presence of ozone
- Low molecular weight siloxane chemically reacts with ozone to form silica particles
Presence of Boron
- Defects in electric properties in the LSI and diffusion properties
- Defects in LCD --- low temperature poly-silicone
Methods for Seminconductor Manufacturing Facility
For controlling gaseous contaminants generated inside the facility
Three types of solutions are available for control and elimination of contaminants, depending on the size of the room and location of the gas emission areas inside the room. They are as follows:
- Provide in-room, stand-alone, powered re-circulation scrubbers at vantage points inside the room.
- In case, air-conditioning inside room is carried out by chilled water AHU, then the return air circuit can be provided with an un-powered dry air scrubber (after accounting for extra pressure drops).
- Air suction hoods to be placed at contaminant emission areas, which in turn connect via air ducts to a powered air scrubber, placed either inside or outside the protected room (in re-circulation mode).
Since, in all the three cases, treated air is supplied back to the room, there is virtually no loss of chilled energy in air. Other than the near total elimination of the toxic contaminants, both inside and outside the rooms, HVAC related costs are also reduced drastically due to reduction in fresh air intakes.
For controlling gaseous contaminants introduced in Fresh Air intakes, from outside
Install un-powered dry air scrubber provided with the required chemical media at the entry point of fresh air that is drawn from the atmospheric air. This scrubber would cleanse the air of low levels of contaminants present in atmospheric air, such as automobile exhaust fumes, traces of sulphur dioxide, nitric oxides etc.
The presence of airborne contamination in an EDP environment can have a devastating effect on the operation of the facility with resulting downtime.
Disk drives, magnetic tape, electronic circuits and computer room air conditioning systems are all affected by airborne contamination.
High-speed printers, together with collating and bursting equipment, generate large volumes of paper dust, toner and some chemical contamination.
In addition, electrostatic charges are produced by virtually all electronic and electrical equipment present in the computer facility. These electrostatic charges will drive airborne contamination to machine surfaces (like magnets causing them to precipitate from the air. The size of the particulate contamination is distributed from 0.1 to 10 microns. The presence and generation of some chemicals such as formaldehyde, ammonia, chlorides, sulphates, ozone, oxides of nitrogen, tin (tributyltinoxide) and VOCs present a significant corrosion potential in computer room hardware and air conditioning electronic circuits.
Since the majority of computer room facilities use minimal outside air, there is a tendency for computer rooms to have a negative pressure with respect to other portions of the building or the outside. Therefore, infiltration of external airborne contamination will further aggravate the EDP environment.
Current data processing room air conditioning systems are not designed to control the types of contamination present and for the tolerances of today’s computer equipment. More than 95% of all damaging contamination cannot be controlled by medium efficiency (20% ASHRAE rated) filters used by these systems.