Introduction

High-purity sputtering targets are key materials used for depositing thin films by physical vapor deposition (PVD) in the metallization process of integrated circuits. The more advanced the chip manufacturing node, the higher the purity required for the target:

• Mature process nodes (≥ 28 nm): purity ≥ 99.995% (4N5)
• Advanced process nodes (< 7 nm): purity must reach 99.9999%–99.99999% (6N–7N)

During the smelting, purification and casting of high-purity sputtering targets, strict control must be exercised over transition metals, light elements (such as carbon, oxygen, nitrogen and hydrogen) and radioactive elements. Measuring these trace impurities accurately is essential for guiding process development and ensuring product quality.

Advanced analytical methods, such as inductively coupled plasma mass spectrometry (ICP-MS) and glow discharge mass spectrometry (GD-MS), enable simultaneous or continuous measurements of multiple trace and ultra-trace elements, with detection limits for some elements reaching the ppt level. These analyses require high detection accuracy, suppressing interference and the ability to analyze complex materials, and also pose a stringent requirements to background control during the experiment. Above all, the quality of the ultrapure water (UPW) used in the process is critical in minimizing background interference.

Element	Detection limit w/(μg·g–¹)	Element	Detection limit w/(μg·g–¹)	Element	Detection limit w/(μg·g–¹)
Li	0.001	Mn	0.001	Sn	0.005
Be	0.001	Ni	0.001	Sb	0.001
B	0.001	Co	0.005	Te	0.05
Na	0.001	Zn	0.01	Ba	0.001
Mg	0.005	Ge	0.005	W	0.001
Al	0.001	As	0.005	Au	0.05
K	0.005	Se	0.01	Hg	0.005
Ca	0.005	Zr	0.001	Pb	0.001
Ti	0.001	Nb	0.005	Bi	0.001
V	0.001	Mo	0.005	Th	0.0001
Cr	0.001	Cd	0.005	U	0.0001

*Data excerpted from the reference: Determination of Trace Impurity Elements in Ultra-High-Purity Copper Sputtering Targets by Glow Discharge Mass Spectrometry and Derivation of Their Relative Sensitivity Factors.

What Happens When Water Quality Falls Short?

Ultrapure water is used throughout the testing process, from rinsing samples, preparing standard solutions to cleaning labware. Fluctuations in trace impurities in the water will directly affect the analytical results:

• Distorted purity of test results: Residual trace metal ions in the water raise the analytical background and inflate measured values, causing conforming products to be wrongly rejected.
• “False defects” on the surface: Fine particles in the water adhere to the sample surface and are easily mistaken for native scratches or void defects in the target under microscopic observation or surface analysis.
• Risk of pitting corrosion: Halide and other ions such as chloride remaining on the target surface may induce pitting during long-term storage, ultimately affecting the uniformity and quality in the later coating processing steps.

A UPW Solution for Trace Analysis of High-Purity Sputtering Targets

Water used for trace analysis of high-purity sputtering targets must not only achieve a resistivity of 18.2 MΩ·cm at 25 °C, but also meet the strict limits on individual metal ion content, total organic carbon (TOC), particles, microorganisms and other key parameters.

The RephiLe Genie G ultrapure water system, paired with the Genie De-ion purification and dispensing kit for trace analysis, employs an advanced multi-stage purification process specialized in trace and ultra-trace elemental analysis, producing reliable and stable ultrapure water for trace analysis of high-purity sputtering targets.

Core Advantages of Genie G & Genie De-ion

• Sub-ppt ionic control: By combining advanced purification technologies including reverse osmosis (RO), continuous electrodeionization (EDI) and ICP ultra-purification cartridge, ions in the water are reduced to sub-ppt levels. All water-contact components are made of low-leaching non-metallic materials to minimize the risk of contamination from leached substances.
• Low TOC with precise monitoring: The RephiAC activated carbon effectively reduces organic compounds in the feed water, while a mercury-free 172 nm UV lamp efficiently degrades trace organic compounds. An online detection system based on the total oxidation principle accurately monitors the total organic carbon (TOC) of the product water, consistently maintaining excellent water quality with TOC < 2 ppb.
• Rigorous particle and microorganism removal: A 0.1 μm absolute filter effectively retains particles and microorganisms larger than 0.1 μm in the ultrapure water.
• Comprehensive monitoring for long-term stability and reliability: Water quality data and system operating status are monitored in real time, ensuring that every dispense meets the required water quality and fully satisfies the stringent analytical QC requirements of ICP-MS/GD-MS.

Successful production and accurate testing of high-purity sputtering targets depend on a stable supply of ultrapure water. For optimal performance, freshly purified water should be drawn on demand, with the initial flush discarded. Additionally, appropriate vessels must be used, and dispensing should take place in a contamination-free area. RephiLe ultrapure water delivers the highest water quality for the most demanding analytical applications.

For more information, please visit www.rephile.com/.

About RephiLe: Driven by innovation and quality, RephiLe is a dedicated provider of water purification systems and laboratory filtration products. At the same time, RephiLe produces comprehensive consumables that can be used in Millipore lab water system with reliable performance. It is RephiLe’s commitment to becoming a partner of choice for customers in the area of life science and biotechnology. The company is striving to bring superior quality, high-value and innovative purification tools to enable and accelerate the advancement of the life sciences and technologies. Products are being sold to over 100 countries worldwide.