Mega-trends like artificial intelligence and robotics, smart homes and cars, and the Internet of Things are driving a need for new levels of integrated circuit (IC) speed, scale, and reliability. At the same time, device manufacturers striving to meet new worldwide consumer and business data demands at lower costs face significant challenges in terms of process control, yield, and economics.
As logic devices migrate to smaller line widths, 3D NAND architectures increase layers, and DRAM memory density increases, sensitivity to contamination and defects have a greater impact on device performance. And given the critical human impact of applications like AI and self-driving cars, flawless device performance has taken on a heightened importance with which the industry traditionally hasn’t had to contend.
To achieve optimum wafer yield and reliability, the microelectronics industry needs to address the increased materials consumption requirements—and critically, the material purity challenges—for these high-performance technologies from chemical manufacture to their point of use.
Controlling contamination begins with the chemicals that come into direct contact with every wafer. Increasing chemical purity is the first step in enabling process cleanliness and improving device yield. This is why device manufacturers continue to pressure chemical suppliers to deliver a higher level of purity, soon approaching parts per quadrillion (ppq), and avoid introducing contaminants during chemical packaging, transport, and distribution.
Equally important are material purity and the materials of construction in fluid delivery systems. Without contamination-controlled chemical packaging, filtration, pumps, and fluid handling components, chemicals are vulnerable to recontamination by particles, metals, and impurities.
Conducting contamination mapping to understand the contamination source is critical to defect control, yet it can be especially challenging when manufacturers source products with varying levels of cleanliness and combine batches from many different vendors.
Chemical manufacturers, OEMs, and device manufacturers must work together with component suppliers to manage contamination and maintain higher purity levels in chemicals, storage tanks, and fluid delivery systems.
Let’s look at purity challenges and the benefits of investing in cleaner fluid systems to more comprehensively meet the purity specifications required by leading-edge technologies.
Maintaining Chemical Purity Throughout the Manufacturing Supply Chain
As the consumption of high-purity chemicals increases and purity requirements become more stringent, chemical manufacturers are investing considerably in preventing particle contamination, as well as in maintaining chemical purity during transportation to the fab.
A large portion of the time and expense of qualifying a new chemical line comes from flushing tubing, fluid components, and filters to eliminate surface contamination. Particles are often resistant to initial flushing and as a chemical sits in long tubing runs or in re-circulation loops, particles shed off the material, contaminate the fluid stream, and become defects on the wafer.
To mitigate the need for this expensive and time-consuming flushing, and to reduce long-term particle shedding, chemical manufacturers are very interested in components using ultra clean and stable polymers. Component suppliers are working to develop solutions that have lower surface particulates, and to determine what impact these new solutions have on their system.
Clean chemical delivery is more important than ever because as circuit line widths continue to shrink and process nodes approach sub-10 nm levels, surface particles become especially detrimental to logic devices. Similarly, as the number of transistors increase in a 3D NAND memory stack, one defect could block more than one cell, affecting the performance of the entire device. Consequently, all potential contamination areas must be identified and proper steps taken to avoid defects.
Maintaining Purity During Transportation
Once a system is qualified and a chemical meets the required purity specification, the focus turns to maintaining that purity as the material is transported to the fab. Chemicals can be susceptible to particle contamination that may be introduced during chemical transport or transfer from bulk chemical containers to smaller drums, transportation packs, and fluid delivery systems. To maintain chemical purity, all the fluid paths require a contamination-controlled, stable environment.
The choice of chemical storage container plays a large role in maintaining chemical purity. If an initially clean photoresist, for example, fails the particle specification when it arrives at the fab, the transport container is a likely source of contamination. Sourcing containers based solely on material of construction and volume leaves out the critical aspect of the long-term contamination prevention performance.
Manufacturers will benefit from working with materials experts who are constantly testing and developing materials of construction and product manufacturing methods that result in lower particle-generating containers. Investing in contamination-controlled chemical transport and delivery systems can help ensure chemical integrity, increase product yield, and reduce financial loss.
Overcoming Purity Challenges at the Fab: Fluid Handling
Once delivered to the fab, the equipment that dispenses the chemical out of the container, filters it, and distributes it through the fab must maintain the cleanliness of that chemical and not add contaminants to it. The latest SEMI® World Fab Forecast report shows that in 2018, global spending on fab equipment investments will reach an all-time high of $63 billion.
With so much invested in equipment, it’s imperative this equipment be capable of delivering very high purity chemicals to the fab tools—now and into the future. Device makers and OEMs shoulder the burden of evaluating different components to understand relative cleanliness levels and specify components that will maintain the incoming chemical delivery specification. OEMs and fab contractors receive those component specifications and are challenged to choose the right solutions for their equipment to ensure the incoming chemical remains clean throughout their entire system.
With every fab startup and new build, an enormous amount of fluid handling systems are installed that require pre-flushing, testing, and purging before any chemical is run through them. Pre-flushing is used to leak test the system and rid the system of surface contaminants. Once a chemical is going through the system, fab engineers continually monitor chemical purity and wafer defects, and flush the chemical and exercise their process until they get the desired yields.
All of this consumes time, wastes chemical, and is very costly. The goal is to reduce the time and expense of qualifying a process line by sourcing cleaner components and employing metrology early for better defect detection and prevention.
Like chemical manufacturers, device makers benefit from sourcing a contamination-controlled fluid system that has been evaluated to ensure it’s not contaminating the process, but rather improving it, if possible. As particle sensitivities increase for more complex memory and logic devices, the need to remove these particles becomes critical.
One proven method of controlling contaminants in process streams is through sophisticated liquid filtration. Filter membrane technology has advanced to enable sub-10 nm particle removal, which is vital to improving overall operating efficiency and enabling leading-edge technologies.
Through novel polymer design, diverse membrane manufacturing techniques, and advanced cleaning technologies, filter solutions enable device makers to tailor their contamination control based on the chemicals used, and the conditions required. Using process monitoring, statistical analysis, and customer collaboration, these fluid components provide a stable and repeatable solution to control contaminants.
However, not all components are the same in terms of particle cleanliness and contamination. For instance, not all HDPE drum suppliers are created equal and this is particularly evident in understanding the importance of resin selection and continued testing, and how to employ process controls to maintain drum purity consistency. Conducting daily particle testing is one way to achieve this goal.
Additionally, using an assortment of tubing suppliers can significantly increase the risk of contamination variability. It’s important to select suppliers that have a proven understanding of fluoropolymer processing and regularly engage in contamination mapping evaluations to understand potential sources of contamination and how to control them.
In Part Two of this article, we’ll explore the concept of contamination mapping, along with steps the industry is taking to avoid metallic leaching, and why adopting materials purity best practices is essential to driving technology innovation.
Brett Reichow is Director, Fluid Handling with the Advanced Materials Handling Division at Entegris, a leading advanced sciences and technology company.