Monitoring of UPW Systems Using Ultra DI® 20

 

Abstract

Through continuous process and equipment advancements, semiconductor manufacturers are approaching 14 nm feature sizes and heading even smaller, while hard-disk drive fly heights are now less than 10 nm. This ever-reducing device feature size requires comparable cleanliness-level improvements in ultrapure water (UPW). UPW purity is especially important with its high use in direct contact with wafers as a final cleaning and rinsing agent in many production steps. Leveraging recent advances in laser optics and detector technology, the Ultra DI® 20 can effectively monitor UPW particle concentration ≥20 nm, or, in the case of metallic particles, ≥9 nm. Monitoring is continuous and occurs in real time to enable maximum process control. This industry-leading sizing sensitivity is provided in a system that correlates well with legacy 50 nm particle metrology for data continuity. The Particle Measuring Systems^® (PMS) Ultra DI 20 was specifically developed to meet the challenges of microelectronics UPW cleanliness monitoring. 

Overview of UPW system

UPW is treated through a multi-step process (Figure 1) to meet the high quality standards for leading semiconductor, hard-disk drive and MEMs manufacturing. Advancements in water treatment and filtration at critical UPW facilities provide water at cleanliness levels better than many existing metrology devices can accurately measure.  In fact, most modern UPW systems are so clean that there are fewer than 100 particles/Liter greater than 50 nm in size. At these low contamination levels, changes in particle concentration at 50 nm become nearly invisible as they approach detection limits of older instruments. This continuous UPW quality improvement requires a new monitoring solution that can detect significantly smaller particles at very low concentrations.

Within many ultrapure water systems, particle concentration is measured only after the final filtration step. Particle levels need to be as low as possible at the point of use where the water contacts the wafer. It is recommended that the final particle monitoring be located as close to the UPW’s point of use as possible to assure that it is capturing a true measurement of the wafer exposure.

Introduction to Ultra DI 20

The Ultra DI 20 is the industry’s first 20 nm (PSLs) and 9 nm (metals) sensitivity liquid particle counter. This new instrument is equipped with advanced laser and detector technologies in order to collect sufficient scattered light from these extremely small particles. The Ultra DI 20 is designed to operate continuously, providing stable real-time data, with reduced water consumption so that it may be applied inside process equipment areas with restricted flow capacity. This is an ideal solution to enable continuous particle monitoring of a UPW system for modern semiconductor, hard-disk drive and MEMs manufacturing.

Comparison to existing solutions

A comparison of the counting efficiency (CE) between Ultra DI 20 and Ultra DI 50 vs. competitive 25 nm and 30 nm products has been completed. The data, shown in Figure 2, demonstrates the capability of the Ultra DI 20 to detect PSL particles as small as 20 nm and metal particles at 9 nm. Competitive products struggle to see 29 nm PSL particles.

This paper provides you with a comparison of three models of UPW particle counters to help you identify the best solutions for your application.