Laboratory High-Contrast X-ray Microscopy of Copper Nanostructures Enabled by a Liquid-Metal-Jet X-ray Source

Area of Science:

• Materials Science
• Physics
• Electrical Engineering

Background:

• Advanced microelectronic products rely on on-chip interconnects, such as copper (Cu) embedded in low-k dielectric materials.
• High-resolution imaging is crucial for physical failure analysis and reliability engineering in the semiconductor industry.
• Current imaging techniques face challenges in achieving sufficient contrast for sub-micrometer copper nanostructures.

Purpose of the Study:

• To demonstrate high-resolution imaging of Cu/low-k on-chip interconnect stacks using full-field transmission X-ray microscopy (TXM).
• To compare the effectiveness of two different photon energies (8.0 keV and 9.2 keV) for imaging copper nanostructures.
• To highlight the advantages of specific X-ray energies for enhancing contrast in microchip analysis.

Main Methods:

• Utilized lens-based laboratory X-ray microscopes operating at 8.0 keV (Cu-Kα radiation) and 9.2 keV (Ga-Kα radiation).
• Employed liquid-metal-jet technology for generating Ga-Kα radiation from a Ga-containing target.
• Performed comparative imaging of copper nanostructures within organosilicate glass and Cu/SiO2 or Cu/low-k backend-of-line stacks.

Main Results:

• Achieved a 5-fold contrast enhancement for imaging copper nanostructures when using 9.2 keV (Ga-Kα) photons compared to 8.0 keV (Cu-Kα) photons.
• The enhanced contrast is attributed to the Ga-Kα emission line energy being slightly higher than the Cu-K absorption edge.
• Demonstrated effective imaging of copper interconnects with dimensions ranging from several 100 nm down to several 10 nm.

Conclusions:

• 9.2 keV Ga-Kα radiation offers significant advantages for high-contrast imaging of sub-micrometer copper interconnects in advanced microchips.
• Full-field transmission X-ray microscopy (TXM) with optimized photon energies is a valuable tool for semiconductor physical failure analysis and reliability engineering.
• This technique will benefit the semiconductor industry by enabling detailed examination of critical sub-μm copper structures.