Bowling for Contaminants: The New Science of Gas Purification
This white paper explains the importance of applying purification science to managing the gas supply purity from the source throughout all the wafer process steps to ensure the highest device yield.
Purity of gases and chemicals has always played a critical role in the performance and reliability of advanced semiconductors and memory devices. While the fab-cleanroom purity requirements themselves have remained constant, meeting them has become more difficult due to a number of contributing factors. As a result, purity requirements in key process areas in the fab are approaching parts per quadrillion.
To remain competitive, semiconductor manufacturers have increased manufacturing volumes, increasing the overall consumption of gases. Additionally, both logic and advanced memory devices require significantly higher gas consumption per processed wafer to support shrinking geometries and multi-layer device architectures. For example, the move from 20 nm logic to 7 nm logic doubled the number of process steps. As a result, process gas consumption is expected to increase over the next 5 years.
Concurrently, to achieve higher density at lower power, the industry is adopting three dimensional (3D) architectures with finFETS and 3D NAND, which increases the complexity of the processes.
These additional process steps impact yields as there are more opportunities to expose wafers to process excursions. Even trace contaminants in the gas supply can cause measurable shifts that affect chip performance by interacting with a process, potentially costing the manufacturer thousands or even millions of dollars.
As a result of this heightened sensitivity to molecular contamination and increased gas consumption, semiconductor manufacturers are depending on suppliers of both bulk and specialty gases to deliver process gases customized to meet purity requirements. This article explains the importance of applying purification science to managing the gas supply purity from the source throughout all the wafer process steps to ensure the highest device yield.
THE ROLE OF PROCESS GASES IN SEMICONDUCTOR MANUFACTURING
With hundreds of gas and specialty gas mixtures used in an ever-increasing number of manufacturing process steps, there are many opportunities for wafer contamination caused by the gas supply.
Of all the bulk gases, nitrogen is currently used in the highest volume. This ubiquitous gas is used for countless purging applications, including pumps and vacuum chambers. Wafer fabrication facilities making chips with 28 nm or 20 nm features can go through 20,000 to 30,000 cubic meters of nitrogen per hour.3 Extreme clean dry air (XCDA®) is also employed for purging and sweeping cleanrooms. This has become increasingly important as newer generations of tools are specified to guarantee that processes are performed using XCDA. With the forthcoming adoption of extreme ultraviolet lithography (EUV), the use of hydrogen is expected to increase.
WHERE DO CONTAMINANTS ORIGINATE?
Intrinsic contaminants originate at the gas supplier; additionally, for corrosive gases, contamination can be picked up in the gas stream as a result of corrosion of the delivery system and tool. As such, the wafer’s relationship with the gas supply and their journey together begins well before they even come in contact with each other.
WHAT DO CONTAMINANTS LOOK LIKE?
Contaminants in both bulk and specialty gas supplies come in several forms. Categorized as particulates or molecular contaminants, even historically benign contaminants have become problematic and can cause defects in today’s 7 nm node devices or 3D NAND structures.