Quality of Materials in Semiconductor Fabrication

Semiconductor fabrication can be well-described as an all-or-nothing industry. This explains the astronomical investments which manufacturers make in technologies and materials. Every stage in the production of a semiconductor requires precision and quality assurance.

Precision is required to guide the substrate throughout the production process, from the growth of the crystalline silicon to the finished product. Steps like etching and lithography require extremely accurate tools and, except insofar as they are becoming automated, highly-skilled human labor and oversight. As the slightest mistake is total failure for semiconductor applications, precision in the highest degree is of the utmost importance.

Likewise, the high quality or purity of materials is just as important. Quality materials are the starting-point of the entire production chain and the purity of those materials used for photomasks, photoresists, thermal management, packaging and the silicon substrate for the wafers themselves must be necessarily beyond reproach (doping aside) or else failure is guaranteed. Semiconductor fabrication begins with the highest quality materials.

Silicon semiconductor substrate is synthetically grown from seed in cylindrical, crystalline ingots. These are then sliced into thin wafers capable of supporting integrated circuits (ICs). The cylinders vary in the diameter of their perpendicular cross-sectional area, yielding wafers of that same diameter. In the semiconductor fabrication industry, the largest universally accepted diameter for silicon wafers is 300mm, although there has been a big push in the semiconductor fabrication industry to move the standard ceiling to 450mm. It remains to be seen exactly how cost-effective 450mm wafers will be.

For the purposes of producing a fully functioning die, flaws and unwanted impurities can ruin the section of silicon wafer in which they’re located. In fact, this is another business-facing factor which has driven Moore’s Law over the decades, since smaller dice sets a higher die per wafer (DPW) ratio. This means that each wafer is more sub-divided and that, as a consequence, each defect disqualifies a smaller area of the wafer than it otherwise would; and therefore less of the overall mass of the wafer has to be discarded for any single flaw. The development of the new 10nm standard for transistors in 2018 now allows an even greater subdivision of the silicon substrate wafer and so proportionately even less waste.

Regardless of the degree of subdivision, higher quality silicon allows fewer flaws in absolute terms. These two factors of die size and silicon quality synergize to optimize the worth of a given ingot. The quality of the ingot determines the viable dice yielded, regardless of the degree of subdivision, and conversely the number of viable dice determines the return on investment.

Together, smaller dice and higher quality silicon minimize waste and maximize return. This is a crucial factor in the semiconductor business, given that the dice first have to pay for the high cost of growing the silicon ingots which yield them in the first place before any profits can be counted. It also affects the cost of production per die, which for consumer electronics ultimately affects the prices paid by end-user as well. 

Moreover, packaging a successful die depends also on the quality of other applied materials. This continues to apply once the die is used in a device and requires careful consideration of materials used in applications like molding, solder and thermal interface. For example, the use of high-grade silicones and epoxies protect otherwise vulnerable circuitry and increase the reliability and longevity of both the die itself and the larger device containing it. So, successful performance by semiconductors at market is therefore governed by the same principal concern found at the very beginning of the manufacturing process: namely, materials of the highest quality.

New and groundbreaking semiconductor technology is now emerging, with exciting implications for applications, quality and cost. The life of the semiconductor begins and ends with the quality of its construction. A better grade of materials mean better semiconductors and a better electronics industry. The use of higher quality materials means less waste, higher profits for manufacturers, lower costs for customers and a longer reliable lifetime for electronics of all kinds.

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