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Semiconductor Nanoprobing Boosts TEM Analysis Success Rates on Advanced Logic Devices

By 07.01.2024

Growing need for semiconductor nanoprobing

As the semiconductor industry continues to push technological boundaries, utilization of advanced analysis techniques becomes imperative. The advent of sub-5 nm FinFET and gate all around technologies has delivered enhanced performance and power efficiency in advanced logic semiconductor devices; however, it has also introduced new semiconductor failure analysis challenges. In the past, physical failure analysis (PFA) success rates would typically exceed 90% without using nanoprobing, but these success rates have plummeted with each technology node shrink (Figure 1). Why? The most common targets for physical failure analysis, the transistors, are getting smaller with each technology node. This, in turn, means that physical failure analysis must hit ever smaller targets, requiring increasingly precise localization.

Nanoprobing addresses this challenge and increases the PFA success rate from less than 5% to greater than 90% at the most advanced logic nodes. For this reason, the PFIB (plasma focused ion beam) delayering and nanoprobing workflow is becoming established as an essential step before physical analysis.

Physical failure analysis with semiconductor nanoprobing: success rate vs technology node

Figure 1. Physical failure analysis success rate vs technology node.

This blog post delves into the significance of incorporating xenon ion milling with proprietary Dx chemistry in conjunction with nanoprobing for the analysis of advanced logic devices based on FinFET or gate all around (GAA) architectures.

Nanoprobing in semiconductor analysis

Like an electrical contractor using a multimeter to probe points in a household wiring circuit to find a defect, nanoprobing performs this same function but at the nanometer scale (hence the term “nanoprobing”). Nanoprobing enables the electrical characterization of the most critical components within a semiconductor device, from the individual transistors to the increasingly complex metal interconnect layers. Nanoprobers have been in semiconductor failure analysis labs for many years, but most of these legacy systems do not possess the probing precision or the scanning electron microscopy (SEM) performance to probe current logic devices.

Today’s most advanced semiconductor nanoprobing solutions, such as the Thermo Scientific nProber IV System precisely place electrical probes on the device, enabling critical parameters such as voltage, current, and resistance to be measured. Nanoprobing can also be used to probe entire logic cells or groups of gates to narrow down a defect. In short, nanoprobing provides valuable insights into the functionality and performance of specific regions of a device, enabling accurate physical analysis.

To accurately analyze and characterize advanced logic devices, the PFIB-nanoprobing workflow greatly increases the analysis success rate. Let’s explore the key steps involved (Figure 2).

Semiconductor nanoprobing from defect localization to root cause analysis

Figure 2. Key steps in semiconductor nanoprobing from defect localization to root cause analysis.

  1. Decapsulation (if required): To begin the analysis, a sample is initially prepared for the delayering–nanoprobing workflow by removing any encapsulation material, if present, using conventional mechanical or chemical deprocessing techniques.
  2. PFIB delayering: The introduction of xenon ion milling with the Thermo Scientific Helios PFIB DualBeam revolutionized the delayering process. Xenon ions, with their higher mass and lower reactivity, offer improved precision and control during layer removal. The xenon ion beam selectively etches away metal and dielectric layers, exposing targeted regions without causing damage to the underlying structures. To further enhance the delayering process, proprietary Dx chemistry is employed. This specialized chemical solution works together with the xenon ion milling to ensure that only the desired layers are removed. This preserves the integrity and planarity of the analyzed regions, which is an absolute necessity for accurate nanoprobing. Passive voltage contrast (PVC) can also be used during the delayering process to check for the presence of connectivity defects. It is also worth noting that there is a configuration of the Helios PFIB DualBeam, called the Helios Hydra DualBeam, which not only includes the PFIB delayering capability but also includes Ar+ ion species, ideal for making large-volume SEM cross sections and Ga-free TEM samples.
  3. Functional electrical analysis and debug: Optical and/or e-beam probing is often used to electrically probe the device, providing additional insights and further isolating the functional area of interest.
  4. Nanoprobing: Once the desired regions are exposed through the PFIB delayering process and electrical test, the sample is passed to the nProber System. Using the LEEN2, low-dose SEM (<200 eV), the nProber IV System facilitates highly automated and precise placement of up to eight electrical probes on the device circuit. After precise positioning, the probes establish electrical contact with specific components of interest, enabling accurate and comprehensive electrical measurements on single layers, or across multiple wiring layers on the front side or the back side of a device. A wide variety of electrical analysis techniques are typically employed, such as EBIRCH, EBAC, and pulsed probing (to localize resistive gate faults).
  5. PFIB delayering/nanoprobing: Nanoprobing may be carried out on multiple layers by successively probing and delayering in the PFIB until the exact defect location is determined.
  6. Localization and characterization data: The output from nanoprobing is used to identify and locate potential defects, performance variations, and optimization opportunities for future designs. This also provides valuable defect location data to physical failure analysis (PFA) engineers. The PFA team can then use TEM analysis with a high degree of confidence that the defect location is going to be accurately captured and successful root cause analysis achieved.

Focused ion beam milling advantages and applications

Using the Helios 5 PFIB DualBeam’s xenon ion milling with proprietary Dx chemistry and the nProber IV System’s nanoprobing workflow offers numerous benefits and applications:
1. Enhanced precision—Xenon ion milling and Dx chemistry provide improved control and precision during layer removal. Combined with low-dose, high-performance SEM technology and automated end-pointing, this approach ensures the integrity and planarity of the region of interest and the best possible electrical characterization outcomes.
2. High-success-rate process optimization and device performance—By leveraging the insights gained from the Helios 5 PFIB DualBeam–nProber IV System workflow, device designers and manufacturers can maximize their physical failure analysis (PFA) success rates. This achievement translates to optimized process yields, enhanced device performance, and increased product reliability.

 

By incorporating xenon ion milling, proprietary Dx chemistry, and precision nanoprobing, the Helios 5 PFIB DualBeam to nProber IV System workflow is becoming the process of record for analyzing advanced logic devices. Offering improved precision, reduced damage, and enhanced selectivity, the combination enables semiconductor engineers to gain critical insights into device performance and functionality. As the semiconductor industry continues to evolve and as devices become more complex, this workflow plays an increasingly vital role in the development of reliable, high-performance semiconductor devices.

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