The semiconductor industry was born in the late 1950s when the first microchip, or integrated circuit, was created. Continuing advances have made possible the current generation of semiconductor chips, which can store 3,355 pages of text on a device approximately the size of a dime.
Chemical engineers, who contributed to the invention of semiconductor devices, are also routinely involved with the development of advanced semiconductor materials and the manufacturing processes required to produce them.
Chip materials
A semiconductor is essentially any material whose ability to conduct electricity lies between that of an insulator and that of a conductor. Germanium was the semiconductor material used in the first integrated circuit. Next, silicon was used as the base material, which led the way to the first commercial-scale production of integrated circuits.
The power behind the electronics
Turning silicon into a semiconductor chip is a meticulous undertaking. It requires the multidisciplinary expertise of chemical engineers, along with many other technical specialists.
Wafers
The process starts with the creation of a pure, monocrystalline ingot of silicon, typically 6 to 12 inches in diameter. The ingot is then sliced into ultrathin wafers, each less than 1/40th of an inch thick.
. . . into chips
The wafers are first polished using a specialized technique that blends nanosized abrasive particles into a polishing slurry. The highly polished wafers next undergo a successive series of process steps. Each step involves the deposit of a complex layer of either a conductor, a semiconductor, or an insulating material. These materials deposited in many layers produce the transistors, resistors, and capacitors that ultimately make up an integrated circuit.
Modern transistors are many times smaller than the transistors that were first invented only 60 years ago and many more times smaller than the vacuum tubes used in radios, TVs, and early computers only 30 years ago. The circuits in these tiny, almost nanoscale transistors are the basic tools for cell phones, iPods, computers, and so many other appliances that were not available even 20 years ago.
Ultra pure materials
As chip makers add more and more transistors to ever-smaller semiconductor chips, the presence of even the tiniest of impurities can literally ruin an individual chip and severely reduce manufacturing capacity. So the purity requirements for the chemicals used in chip manufacturing have been dramatically increased.
Making it clear
The purity requirements of today’s semiconductor facilities are even more stringent than those used in the food-processing industry. Unwanted impurities—dissolved and particulate contaminants and trace metals—can easily ruin individual wafers and severely cut back on a manufacturing facility’s output.
Keeping impurities at bay
Even the tiniest of impurities found in process chemicals and gases can create a huge problem. Unless various engineered solutions are used to remove them, such impurities may be found in the chemicals employed during the manufacturing process. Chemical engineers are constantly pursuing advanced technologies and procedures to ensure that critical process ingredients maintain low levels of contaminants—so low, in fact, that they are measured in parts per million to parts per trillion.
To meet these standards, chemical engineers must specify the appropriate combination of purification techniques. These scientists must also select construction materials for all vessels, piping, valves, pumps, tanks, and other components in order to minimize the introduction of dissolved impurities. To ensure that acceptable purity levels are maintained, various measurements are made throughout the process.
Mass production
After the integrated circuit was first created and the appropriate materials identified, the focus shifted to the challenge of manufacturing on a commercial scale. Here, many specialized chemical-engineering disciplines, from fluid mechanics to kinetics, have been instrumental in developing current semiconductor manufacturing processes.
Putting it all together
The manufacture of semiconductor devices generally involves four basic processing steps:
- Deposition of key active materials onto the underlying silicon wafer;
- Selective removal of unwanted materials;
- Lithography to create the desired connections and circuits; and
- Modification of electrical properties.
Many common chemical engineering concepts are used throughout the manufacturing process. The successful growth of silicon ingots requires an understanding of fluid mechanics, heat and mass transfer, and crystallization. During the deposition process a knowledge of kinetics is also necessary.
It is critical to the manufacturing process that the process be carried out in an ultra clean atmosphere.
Clean gets even cleaner
Today’s typical dime-sized semiconductor chip contains millions of microscopic transistors. On that ultrasmall scale the tiniest speck of dust in relation to the chip would appear as a dinosaur-sized footprint would to us. A speck of dust is enough to obstruct the chip’s many pathways, rendering it useless.
Semiconductor fabrication facilities, known as fabs, depend heavily on their specialized clean rooms to maintain a controlled, low level of environmental pollutants.
Clean rooms
Modern clean rooms rely on highly engineered systems developed by chemical engineers to capture, contain, and control dust, airborne microbes, and chemical vapors. The objective is to minimize drastically the level of contamination. These desired levels are typically specified in terms of the number of particles of a given size per cubic foot of air.
Complex, high-efficiency particle-arrestor filtration systems are typically used in fab clean rooms. The areas are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects. Protective clothing is worn by clean-room technicians more to protect the semiconductor devices from human contamination than the other way around.
Ultra clean processing
Semiconductor manufacturing facilities rely on clean rooms. The goal is to remove from these rooms even the smallest particle that could come in contact with the chips. Standards allow for no more than 1 dust particle per cubic foot of air compared with the approximately 10,000 dust particles per cubic foot found in our modern hospitals.
Clean gets even cleaner
Today’s typical dime-sized semiconductor chip contains millions of microscopic transistors. On that ultrasmall scale the tiniest speck of dust in relation to the chip would appear as a dinosaur-sized footprint would to us. A speck of dust is enough to obstruct the chip’s many pathways, rendering it useless.
Semiconductor fabrication facilities, known as fabs, depend heavily on their specialized clean rooms to maintain a controlled, low level of environmental pollutants.
Clean rooms
Modern clean rooms rely on highly engineered systems developed by chemical engineers to capture, contain, and control dust, airborne microbes, and chemical vapors. The objective is to minimize drastically the level of contamination. These desired levels are typically specified in terms of the number of particles of a given size per cubic foot of air.
Complex, high-efficiency particle-arrestor filtration systems are typically used in fab clean rooms. The areas are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects. Protective clothing is worn by clean-room technicians more to protect the semiconductor devices from human contamination than the other way around.