Near-field microprobes enable in-line THz metrology in a semiconductor fab

Researchers at Samsung Electronics, using key technology from Protemics GmbH, have demonstrated the first use of near-field terahertz (THz) time-domain spectroscopy (TDS) for in-line inspection within a semiconductor fab. The work, published in Communications Engineering, shows how electrical defects can be identified quickly and accurately during the critical integration steps of memory-chip production.

Measuring inside the cell, not beside it

The core of the method is the integration of THz-TDS with Protemics’ photoconductive near-field microprobes. These probes reach a spatial resolution below 10 µm, so on-chip micro-patterns can be measured directly within individual DRAM cell units. Conventional approaches often rely on destructive tests of separate, less representative test sites. The near-field technique is contact-free and non-destructive.

With shrinking node sizes, the challenge is to find electrical defects fast and without damaging wafers that are still in process. Existing methods are frequently too slow, destructive, or unable to resolve individual cell structures.

Two parameters from one measurement

THz waves penetrate several layers of the semiconductor structure. The near-field THz-TDS system therefore delivers information on both the sheet resistance of thin films, such as tungsten, and the properties of buried interfaces, such as gate oxide on silicon. The study demonstrates that the system detects

• variations in tungsten film deposition, and
• nitrogen infiltration at the gate-oxide/Si interface during rapid thermal nitridation (RTN) — a direct indicator of threshold-voltage changes.

Built for the production line

The robust probe design allows precise positioning and rapid scanning of the wafer surface, even on the warped or bowed wafers typical of advanced manufacturing. Long-term stability and operational lifetime of the Protemics components were critical for integration into a high-volume memory production line, where the system delivered results consistent with conventional — but destructive — reference methods.

In-line electrical assessment gives process control rapid feedback: higher yield, better reliability, better memory chips.

The successful deployment of this microprobe-based system in a working fab paves the way for a broader adoption of near-field THz metrology in semiconductor manufacturing. If you want to test the method on your own wafers, talk to our engineers.