By Pete Singer, Editor-in-Chief
The semiconductor industry has slowly been implementing a growing array of new materials in an effort to boost speed and performance, reduce power consumption and reduce leakage. 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 (Figure 1).
At the same time, semiconductor manufacturing processes are executed at the atomic level. Atomic layer deposition, atomic layer etching and atomic layer epitaxy are now common.
One of the challenges with new materials and atomic-level processing is that new and unexpected reactions can occur due to the trace impurities in the gases used during production. These impurities may be organic materials or trace levels of oxygen, nitrogen or other elements.
Jean-Charles Cigal, market development manager at Linde in Pullach, Germany, said a growing concern is that gases that have the same specification as before suddenly are not working the same way. “There are a lot of impurities that weren’t a problem before. They are now reacting because you have new materials on the wafer,” he said. “Process engineers don’t know what to look at in terms of impurities. That’s the paradox of the unknown.”
To help customers avoid such problems, gas supplier Linde has implemented tools commonly used in the semiconductor industry, including statistical process control (SPC), statistical quality control (SQC) and a lab information management system (LIMS). “The advantage of having this statistical process strategy is the ability to more rapidly correct any quality issue,” Cigal said.
A “fingerprinting” strategy also comes into play. “We’re using broad spectrum analyzers to get a lot of data and check everything possible. We want to do detection and correction of any quality issue before it reaches the fab,” Cigal said. If an unexpected quality issue is later identified at the fab, Linde can step in with forensic analysis using a database of information.
It is not cost-effective to simply specify higher and higher levels of purity. Instead, Cigal says targeted specifications are now the norm. “In the past, people were asking for the highest purity. Give me a 7.0 silane. Now they are saying OK, give me a silane with 5.0 but I don’t want this organic material,” he said. Linde’s HiQ portfolio offers more than 100 different pure gases such as HiQ Nitrogen 5.0 and HiQ Argon 6.0. Purity is commonly expressed as a two digit number. For example, Helium with a purity of 99.9996% would be described as HiQ Helium 5.6 with the 5 representing the number of nines, while the 6 represents the first digit following the nines.
“What we want ultimately is to get a full picture of what is inside (the gas) and to make the customer aware,” Cigal said. “We don’t know everything about the customers’ processes, but Linde is building large database that will help electronics manufacturers identify what impurities might react in certain processes.”
Customers are now asking for specifications just under the detection limits. We are continuously acquiring analytical tools that will help them to better understand the composition of their materials, which ultimately helps to improve their manufacturing yield.
The semiconductor industry demands very high-purity materials and yet electronics materials suppliers often receive raw materials of very low quality. To ensure that customers get the high-quality materials they require, Linde takes on the responsibility of being the quality gate keeper and controls the whole supply chain – from the source, through purification, and transportation.
Editor’s Note: Jean-Charles Cigal is currently Market Development Manager at Linde Electronics. In his role, Jean-Charles supports electronics customers and equipment manufacturers to achieve their roadmap with the introduction of new processes and materials. He joined Linde as principal technologist in 2009, where he was technology consultant for the semiconductor and the photovoltaic industry. Prior to joining the Linde Group, Jean-Charles worked several years as senior process engineer in the semiconductor industry. He owns a M.Sc. in Applied Physics from Pierre et Marie Curie University, Paris, France, and a PhD in Applied Physics from Eindhoven University of Technology, the Netherlands.