By Pete Singer
In order to increase device performance, the semiconductor industry has slowly been implementing many new materials. From the 1960s through the 1990s, only a handful of materials were used, most notably silicon, silicon oxide, silicon nitride and aluminum. Soon, by 2020, more than 40 different materials will be in high-volume production, including more “exotic” materials such as hafnium, ruthenium, zirconium, strontium, complex III-Vs (such as InGaAs), cobalt and SiC.
These new materials create a variety of challenges with regard to process integration (understanding material interface issues, adhesion, stress, cross-contamination, etc.). But they also create new challenges when it comes to material handling.
“As we go through technology node advancements, people are looking at the potential of different materials on the wafer,” notes Clint Haris, Senior Vice President and General Manager of the Microcontamination Control Division at Entegris (Billerica, MA). “They’re looking at different chemicals that are required to clean those materials to reduce defects and improve their operational yield, and what we’re increasingly seeing is that fabs are concerned with the fact that contamination can be introduced in the fluid stream anywhere in that long process flow.”
Haris said that part of their mission at Entegris is to make sure that the entire supply chain – from the development of a chemistry at the supplier to its use on a wafer in a fab – is working in harmony, particularly with regard to any materials that might “touch” the chemicals. “Not only do you want to filter and purify things throughout the whole fluid flow,” he said, “but you want to have that last filtration right before the fluid touches the surface of the wafer.”
The goal of filtration is, of course, to remove contaminants and particles before they reach the wafer, but the exact purity required can be a moving target. “Today we’re seeing a lot of these materials and liquids, which have a parts per trillion purity level, but there’s a desire to move to parts per quadrillion,” Haris said. That’s the equivalent of one drop in all the water that flows over Niagra Falls in one day.
In addition to the filtration challenge of achieving that level, there’s the question of do the analytical tools exist to actually measure contaminants at that level. The answer – not yet. “It’s actually a real issue where some of the metrology tools cannot meet our customers’ needs at those levels, and so one of the things that we’ve done is we’ve developed some techniques internally to enhance the capability of metrology,” Haris said. “We also work on how we prepare our samples so you can detect contamination at those levels.” Because that level of detection is so difficult — in some cases impossible – Haris said fabs are increasingly putting additional filters at the process tool and at the dispense nozzle to “protect against the unknown.”
Earlier this year, Entegris introduced Purasol™, a first-of-its-kind solvent purifier that removes a wide variety of metal microcontaminants found in organic solvents used in ultraclean chemical manufacturing processes. Using tailored membrane technology, the purifier can efficiently remove both dissolved and colloidal metal contaminants from a wide variety of ultra-pure, polar and non-polar solvents. “One of the main things that our customers are seeing is a concern with metal contamination in the photo process that can result in particular defects (see Figure), such as bridge defects,” Haris explained. Increasingly, fabs are moving from just filtration (removing particles) to purification (removing ions and metals), he added.
Illustration of metal contamination inducing defects on lithography process.
Entegris also recently acquired W. L. Gore & Associates’ water and chemical filtration product line for microelectronics applications. “This is a Teflon-based product line, which is used in ultrapure water filtration for semiconductor fabs, but it’s also a product that we’re selling into some of the fine chemical purification markets for some of the chemistries that are brought into the fabs,” Haris said. “We are focused on new product development and M&A to enhance our capability to support our customers as they overcome these contamination challenges..”