Semiconductor operations produce integrated circuits on small components called “chips” and probably require the cleanest chemicals, and the most pure gases of any industry. Consequently, the manufacturing operations are very filtration intensive.
An example of the stringency in this industry is that operators must follow an elaborate “gown up” procedure before entering a cleanroom, and cannot enter a cleanroom immediately after smoking. The cleanliness of the operations directly impacts yield (the % of product that is not rejected and can be sold), and so the benefits of good filtration are very tangible.
The sophisticated demands (testing, quality, packaging, etc.) and aggressive chemicals in semiconductor manufacturing translate into filters that can be the most expensive to make and are sometimes among the highest priced. As in the pharmaceutical industry, switching costs can be high because of the testing necessary to qualify a new filter, however, once an engineer has decided to switch based on performance or cost, the semiconductor engineer will not face the type of regulatory hurdles his/her counterpart in the pharmaceutical industry would face. As a result, progress in the semiconductor industry can be fast compared to the relatively sluggish pharmaceutical industry.
Delta Pure Filtration enjoys quite a bit of business from the semiconductor industry even though we manufacture economical industrial style filters (such as string wound filters) which are not manufactured in clean rooms (at the writing of this article).
One important driver for cleanliness in the semiconductor industry is the ever deceasing “line width.” The line width is the size of the miniscule microscopic wire through which electrical information flows. The smaller these electronic pathways are, the more sensitive they become to contamination. The tiniest particles can block the formation of these microscopic circuits and decimate the process yield – or worse.
We can see from the ever shrinking size and increasing functionality of cell phones, tablets and other devices that these semiconductor components are getting more powerful by the minute! The shrinking size and growing computing power of these devices is often thought of as inevitable due to “Moore’s Law” – which is simply an observation that the number of transistors (a type of electronic switch) per circuit has roughly doubled every two years.
High tech semiconductor manufacturing is a segment of the broader electronics industry which also includes magnetic memory devices, liquid crystal displays, printed circuit boards, and other related products. There are also an array of suppliers to the semiconductor industry – including manufacturers of high purity chemicals, fluoropolymer products (such as tubing), flexible chemical containers, “tools”, and many others.
The semiconductor chip might be thought of as a “brain” inside a smart phone, tablet, or game, and sits on a printed circuit board. The chip starts out life as a wafer that is formed in multiple steps, each step laying down a “layer” in a semiconductor wafer sandwich. Some steps will add material, other steps etch some of it away, and other steps will modify the materials via a process called “doping.” Photo resists, resist strippers, acids, polishing chemicals for CMP (chemical mechanical planarization), high purity gasses and clean-room air are among the fluids filtered. Specialized equipment, often called “tools”, are used in the controlled environment manufacturing areas, and these tools are often equipped by the tool OEMs with customized, non-standard-size filters that can be difficult to retrofit.
On the periphery of the ultra-clean manufacturing areas (e.g., in a “gray zone”) however, a semiconductor manufacturer may filter incoming bulk chemicals with a string wound filter. The string wound filter may be of “fibrillated polypropylene” because the fibrillated polypropylene filter medium does not use a liquid finishing agent. Another popular filter medium used is PTFE, often asked for by the brand name Teflon® (trademark of Dupont).
String wound filters using PTFE yarn may use a stainless steel core, or may use a core of fluoropolymer such as PFA or PTFE. PTFE yarn is compatible with the most difficult acids over a broad temperature range. Deltapure Filtration also offers specialized materials such as PPS (polyphenylene sulfide), which is sometimes referred to as Ryton® (a brand of the Chevron Phillips Company). Glass fiber is another material used in string wound filters for acids and challenging solvents. Operations such as printed circuit board manufacture can often be associated with the semiconductor manufacturer – a previous blog discussed filtration operations in the plating and printed circuit board areas.
De-ionized water is an important fluid to filter in many industries, and this is especially the case in the semiconductor industry. These water systems my sometime include ozonation, which can sometimes pose chemical compatibility issues for some filter materials – and so filters must be carefully selected. MB series meltblown filters are used to protect DI beds. Pleated polypropylene or PES membrane filters are often employed. Water is often filtered to the 0.1 micron level or finer.
Subsequent treatment of the ultrapure water may render it so completely depleted of ions that it has a resistivity of 18 megaohms! Highly specialized ion adsorbing filter cartridges are often used at the POU, at a tool.
A frequently-used format in the semiconductor and electronics industry is the “recirculating bath” whereby an operation such as plating, etching, coating or cleaning occurs in a tank, and a fluid is recirculated through the filter in order to keep the tank as clean as possible.
It is important to remember that the cleanliness of the fluid in the bath will not only depend on the efficiency of the filter (the ability of the filter to remove a high percentage of small particles), but will also depend on the flow rate or recirculation rate (sometimes measured in tank volumes per unit time). It is often more prudent to have a higher recirculation rate (achieving more filter passes per unit time) rather than to sacrifice some flow in order to achieve a slightly higher filter efficiency per filter pass. For this reason, filter performance in a recirculating process might not always be easy to predict and can be best determined by an actual test in the actual process.