The environmental impact of the manufacturing of seminconductors  (Page 2/8)

With the advent of nanotechnology, these transistors are becoming even faster and more powerful, and inaccordance with the law of accelerating returns, the industry has been producing smaller transistors at lower costs with each andevery passing year. As these semiconductors become smaller and smaller, they are quickly and surely pushing towards the limits ofthe nano-realm.

These innovations, however, do not come without their fair share of challenges. Physical issues that arenot problematic at the micron scale arise at the nano-scale due to the emergence of quantum effects, and in much the same way thatoptical microscopy cannot be utilized at the nano-scale, the semiconductor industry is fast approaching a similar diffractionlimit. Optical lithography, for instance, a process that uses theproperties of light to etch transistors onto wafers of silicon, will soon reach its limit.

At its most basic level, nanotechnology involves pushing individual atoms together one by one. Sinceapproximately 1.7 billion transistors are required for a single chip, this is obviously not a realistic method for mass production.Unless an alternative method for production or a solution to this problem is found, the development and manufacturing of transistorsare expected to hit a proverbial brick wall by the year 2015. This is the reason that research in nanotechnology is so important forthe world and future of semiconductors.

How are semiconductors manufactured?

Today’s semiconductors are usually composed of silicon, and they are manufactured in a procedure that combinesthe familiar with the bizarre; some steps that are involved in the process are as everyday as developing a roll of photographic filmwhile others seem as if they would be better suited to take place on a spaceship.

These semiconductors appear to the naked eye as being small and flat, but they are actually three-dimensional“sandwiches” that are ten to twenty layers thick. It can take more than two dozen steps and up to two full months to produce a singleone of these silicon sandwiches. Some of the basic and more essential steps involved in the manufacturing process of siliconchips are briefly detailed below.

First, silicon crystals are melted in a vat and purified to 99.9999% purity. The molten silicon is drawn intolong, heavy, cylindrical ingots, which are then cut into thin slices called wafersabout the thickness of a business card.

One side of each wafer must be polished absolutely smooth. This process is called chemical-mechanicalpolishing, and it involves bathing the wafers in special abrasive chemicals. After chemical-mechanical polishing, imperfectionscannot be detected on the wafers even with the aid of a laboratory microscope.

After a wafer is polished, layers of material must be stacked on top of the silicon wafer base. Insulating layersare laid down in alternation with conducting layers in a process called deposition. This is often achieved by spraying the chemicalsdirectly onto the surface of the wafer through chemical vapor deposition. Following deposition, the wafer is coated with anotherlayer of chemicals called a photoresist that is sensitive to light.