Nanoprobing SEM for Characterising 10 nm CMOS Transistors on Semiconductor Devices

How to used SEM-based nanoprobing to characterise CMOS transistors on semiconductor devices. An overview of the benefits of in-situ nanoprobing, with example experiment and results.

Blue Scientific is the official distributor for Imina Technologies in the UK and Nordic region. For more information or quotes, please get in touch.

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PDF application note

 Contact us on +44 (0)1223 422 269 or info@blue-scientific.com


  

Nanoprobing in Integrated Circuits

Nanoprobing in scanning electron microscopes (SEM) is a used by engineers in integrated circuit (IC) design and failure analysis. As electrical components and devices become smaller, nanoprobing is increasingly useful for investigating small-scale components in IC:

  • Evaluate the performance of microchips
  • Locate and analyse the causes of defects

SEM-Based Nanoprobing

SEM-based nanoprobing systems are compact and versatile, and can be added to existing microscopes in your lab. They are a convenient way of adding your microscope’s functionality and expanding to your lab’s in-house capabilities without having to purchase an entire new instrument.

There are several key benefits to SEM-based nanoprobing, when working with ≤45 nm technology nodes and high-κ materials:

  • Positioning resolution
  • Protect delicate probes and samples – when using lower acceleration voltages and working distances
  • Maneuverability
  • Tip stability when in contact with the sample
  • Perform measurements accurately
SEM Nanoprobing

Imina Nanoprobing System

Imina Nanoprobing Systems

Imina Technologies’ Nanoprobing Solutions are compatible with virtually all commercially-available SEMs. They incorporate Imina miBot nanoprobers, which are the world’s smallest micro-positioning robots.

  • 2-8 miBots on each system
  • “Stage-mounted” or “load-lock” versions
  • System-shielded cabling for transistor characterisations, EBIC and EBAC/RCI analysis
  • Excellent signal-to-noise ratio
  • Step-by-step assistance for nanoprober placement, landing the probe tips in contact, setting up test recipes, acquiring measurements and saving data.

Meet the miBots: the world’s smallest nanomanipulators

Imina miBot Micromanipulator for SEM, TEM & LM

miBot nanomanipulators are the basis of all Imina products

Example Experiment

In this example, Imina Technologies’ Nanoprobing Solution was used to characterise NMOS and PMOS transistors on processors with 22 nm, 14 nm, and 10 nm technology nodes. The experiments were carried out at different sites, using two different microscopes (no permanent modifications required) and a platform with 8 miBots.

To achieve the best image quality without damaging the sample, the acceleration voltage should be kept under 500 V for technology nodes ≤ 45 nm. At low acceleration voltage, a short working distance (here less than 2.5mm) is used to resolve single transistor contact. For the 22 nm sample, the acceleration voltage was set to 1 kV for the highest image quality.

Imina miBot Selector

Four nanoprobes above a delayered area of a 14 nm Intel processor, and the prober selector in Precisio.

Workflow

  • Positioning: 8 nanoprobers were positioned around the sample and adjusted for the best probe orientation and tip positioning. The miBots slide onto the platform by hand, then positioned using their piezoelectric actuators. The microscope chamber is only open for 10-20 minutes.
  • Vacuum and cleaning: Vacuum is established, followed by 10-40 minutes of in-situ plasma cleaning to remove contamination and reach thermal stabilisation.
  • Set up test recipes: While cleaning is taking place, test recipes can be set up using Imina’s Precisio nanoprobing software. This controls the parameter analyser remotely and configures the wiring from the measurement channels (SMUs) and probes. Pre-defined test recipes were used for NMOS and PMOS transistor characterisation. Parameters were adjusted to suit the device, including current compliance, current and voltage range and number of test points.
  • Transistor probing: The sample was positioned a few hundred nanometers away, then the probe tips were brought in contact with the sample surface. The SEM stage was moved up to reduce the working distance as the probes were lowered. Once contact was achieved, they were lifted and moved horizontally above the transistor for characterisation. The probe tips were then sequentially lowered down to each transistor node, and the beam was deflected away from the test area so as not to influence the measurements. Electrical contacts can be tested with fast measurements, and the positioning adjusted as necessary.
  • Measurement: Measurements were run using Imina’s Precisio software. Results are displayed as a graph and a table. Both are stored on your PC, with the test parameters for post-processing and reporting.
Nanoprobers

Three nanoprobes in contact

Results

The curves are consistent and smooth. The difference between Drain and Source currents was calculated over the measured range. The standard deviation was <0.2%, showing excellent contact resistance stability. Noise and resolution are also very good eg on NMOS transistor with VGS = 0V (transistor OFF), drain current ID was lower than 10 pA with VDS = 0V and lower than 5 nA with VDS = 0.6V.

NMOS Transistor Nanoprobing Curves

PMOST Transistor Nanoprobing

NMOS transistor (10 nm) 
Top: Drain current vs drain-source voltage sweep.
Bottom: Drain current vs gate-source voltage sweep. (Click to enlarge)

PMOS transistor (10 nm)
Top: Drain current vs drain-source voltage sweep.
Bottom: Drain current vs gate-source voltage sweep. (Click to enlarge)

Thermal drift is inevitable at such small dimensions, and can sometimes cause electrical contact to be lost. On the 22 nm sample, I-V sweeps were repeated every 10 minutes for more than an hour, with no loss in contact. On the 10 nm sample, the first probe tip lost contact after about 10-15 minutes. Drift was less than 1 nanometer per minute – because of the compact, robust design of the miBots, the short distance between the probe tip and the robot body, and the fact that the sample and the nanoprobers are mounted on the same support.

Application note with full details of the experiment and results

Conclusions

Nanoprobing experiments were performed to characterise NMOS and PMOS transistors of commercially available processors with 22 nm, 14 nm, and 10 nm semiconductor technology nodes. The results illustrate the proficiency of the system to provide reliable results from different scanning electron microscopes.

Probe tips can be positioned easily with the miBot nanoprobers, and electrical contact can be maintained for periods of up to 1 hour and more.

Further Information

To find out more about Imina products and the Nanoprobing Solution, please get in touch. Blue Scientific is the official UK and Nordic distributor for Imina. We’re available to answer all your questions and provide quotes and demonstrations:

 Contact us on +44 (0)1223 422 269 or info@blue-scientific.com

Imina product range

PDF application note with full experiment details