Semiconductor industry, Clean Room

The company also supplies filters for industrial clean rooms, primarily to semiconductor and air-... 

One of SACHEM s products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. Suspended particles in TMAH solutions could cause severe mechanical damage to the electronic devices manufactured by their customers. The determination of the particle content in such solutions is therefore critical. It is performed with a laser-equipped particle counter, which provides 70% detection efficiency. The counting must take place in a clean room because tiny airborne particles can land in the solutions and give them a false high reading. A class 1000 environment is required in this case, which means that the count of particles in the air that are greater than or equal to 0.5 jrm in diameter must be less than 1000 per cubic foot. Typically, a customer s specification for TMAH solutions is less than 100 particles per milliliter for particles greater than or equal to 0.5 fim in diameter. 

SACHEM Inc., located in Cleburne, Texas, is a producer of high-purity bulk chemicals for companies that have high-purity requirements in their chemical processing. As stated in Workplace Scene 1.2, one of their products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. The analysis of TMAH for trace anions such as chloride, nitrate, nitrite, and carbonate is critical for SACHEM s quality control laboratory. If these ions are present on the integrated circuit boards manufactured by one of their semiconductor customers, they may cause corrosion severe enough to affect the functionality and performance of the electronic devices in which the circuit boards are used. In SACHEM s quality control laboratory, ion chromatography procedures have been developed to measure the anion concentrations in TMAH. Because the concentration levels are trace levels, a clean room environment, like that described in Workplace Scene 1.2, is used. A special procedure for carbonate analysis is required so that the absorption of carbon dioxide from the atmosphere can be minimized. 

The current analytical capabilities of ICP-MS provide a means to assess new low levels of contamination in the semiconductor industry [385]. Contamination in clean room air can be detected at very low levels. Dopant and trace metal contamination on semiconductor wafer surfaces can be monitored. Ultratrace metals in deionized water, high-purity acids, and other process chemicals can often be measured at concentrations less than 1 part per trillion. 

Thus chlorine trifluoride has high reactivity and is somewhat easier to handle, to store and to transport than elemental fluorine because it is liquid at room temperature. These properties have been recognized to be attractive as an effective cleaning gas for some CVD processes in the semiconductor industries. 

The semiconductor industry has become the largest user of automated vision systems. A silicon wafer that will become hundreds of microchips starts as a finely machined disc about 7.9 in (200 mm) in diameter. Before the disc is split into individual chips, the wafer undergoes dozens of steps—some of which are indiscernible by the human eye. To ensure the wafer maintains that sequence, sorting systems using optical character recognition (OCR) identify each wafer, sort it in a clean room environment and report the results to a central network. 

Ion chromatography is frequently used to determine anions and cations at very low concentration levels, often in the low xg/L (ppb) range. In the electric power industry the water used in steam generators must be almost free of Na", Cl" and other ions to avoid stress corrosion cracking. The ionic content of ultrapure water used in the electronics industry must be kept to extremely low levels. Semiconductor chip manufacturers require clean-rooms with utility impurities of no more than 1 ppb for 0.35 pm devices [1]. 

Contamination. Contamination of samples by external sources can be a serious source of error and may be extremely variable. An excellent example of how serious this can be has been documented in the analysis of samples for polychlorinated biphenyls (PCBs). PCBs are synthetic mixtures of organochlorine compounds that were first manufactured in 1929 and have become of concern as significant environmental pollutants. It has been demonstrated that samples archived since 1914, before PCBs were manufactured, picked up measurable amounts of PCBs in a few hours just sitting in a modem laboratory (Erickson). Aluminum levels in the dust in a normal laboratory are so high that dust prohibits the determination of low ppb levels of aluminum in samples. A special dust-free clean lab or clean bench with a filter to remove small dust particles may be required, similar to the clean rooms needed in the semiconductor industry, for determination of traces of aluminum, silicon, and other common elements such as iron. When trace (inorganic analysis is required, the laboratory environment can be a significant source of contamination. 

A silicon crystal ingot grown in a clean room facility in the semiconductor industry. 

Clean Room Flammability Standard for The Semiconductor Industry (NFPA 318 [77] FMR 4910 Test Standard [78] and UL 2360 Test Standard [79])... 

Based on the research on fire propagation and smoke development [20-22, 40, 41, 80-84, 86], the following criteria are used in the FMR 4910 test standard for the selection of polymers for clean rooms of the semiconductor industry [78] ... 

FM Global Approval Class 4910 [43] (NFPA 318 [56]) Standard Test Methods for Clean Room Materials for the Semiconductor Industry... 

The question is now whether there is a textile counterpart to the triad. In the semiconductor industry triads are made in highly controlled, clean room facilities in well-defined atmosphere and/or vacuum and with nanometer precision. The contact between the layers is good and the interface is well defined, both geometrically and chemically. Oxygen and moismre, most often devastating factors for electrical performance, are minimized. 

Fig. 1 7. The use of compressed gases in the manufacture of semiconductors for the electronics industry has become a major application. Here, a portable clean room and advanced pipe welding techniques are used to ensure highest possible gas purity.

Within the semiconductor industry a variety of continuous gas monitors are used (see Sec. 2.5 and Ch. 11, Toxic Gas Monitoring, for additional information). Historically, thesemonitors were primarily used to determine if a toxic gas leak had occurred, rather than actual measurements of breathing zone concentration of chemicals. Sample points for the monitors were located in exhausted enclosures as well as in potential release points in the clean room. 

The efficiency of particulate removal will depend on the analytical requirements, but for the semiconductor industry it is typical to work in environments that contain 1 or 10 particles (<0.2 p) per cubic foot of air (class 1 and 10 clean rooms, respectively). These kinds of precautions are absolutely necessary to maintain low instrn-ment background levels for the analysis of semiconductor-related samples, but might not be required for other types of applications. So, even though contamination-free analysis is important, it might be sufficient to work in a class 100, 1000, or 10,000 clean room and still meet your cleanliness objectives. ... 

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