Failure Analysis and Characterization Techniques for Power Semiconductor Devices

Techniques for failure analysis and characterization of power semiconductor devices

Tools and techniques delivering advanced insights are essential for manufacturers aiming to improve power device reliability and performance. Achieve high-quality sample preparation and fault localization accuracy with Thermo Fisher Scientific’s comprehensive capabilities.

Sample preparation for power semiconductor devices

SEM sample preparation

To address the complexity of performing large-area cross-sections in compound semiconductor devices, the Thermo Scientific Helios Hydra DualBeam FIB-SEM provides selectable ion species with specific material compatibility. For example, argon allows for the fastest material removal and reduced curtaining in SiC.

Cross-sections of SiC MOSFET comparing cut-face quality and sample preparation time by Xe+ (55 min) and Ar+ (25 min).

TEM sample preparation

TEM image results are highly dependent on the quality of the lamella. For compound power devices that may be susceptible to gallium implantation, polishing with a combination of xenon and argon has been proven to reduce damage caused by the ion beam while maintaining throughput. Using Thermo Scientific AutoTEM 5 Software makes TEM preparation simple and efficient.

GaN HEMT TEM lamella prepared without Ga+ contamination and minimal damage.

Power semiconductor delayering

Power devices contain thick aluminum layers as well as thin titanium and titanium nitride layers that require a PFIB with gas precursors, such as iodine or other proprietary chemistries, for planar removal. This fundamental technique exposes the region of interest for more accurate localization and can be performed efficiently with the Thermo Scientific Helios Hydra DualBeam FIB-SEM. Using stage current or secondary ion or electron detection, this delayering process can be set to automatically stop at the target layer. 

Power device gate location prepared using no gas precursor (left) and Dx precursor (right).

Fault isolation in power semiconductor devices

Precise identification of the defect location is essential for successful failure analysis. Thermo Fisher Scientific offers a range of solutions for robust and reliable fault isolation, from multi-millimeter coverage down to sub-micron accuracy. 

Thermal fault isolation

Lock-in thermography provides non-destructive 3D information without material restrictions. Typically used as the coarse isolation step in an EFA to PFA workflow, the Thermo Scientific ELITE VX System uses LIT to identify hot spots caused by device defects and locate the region of interest. Burn-in testing for reliability characterization is also supported by LIT analysis when performed before and after to assess changes in device performance.

Hot spot signal identified using the Elite VX System on gate pad with a thick layer of aluminum.

Optical fault isolation

Optical beam-induced resistance change (OBIRCH) is a highly sensitive technique used once the thick metal layer covering the region of interest is removed via delayering. The Thermo Scientific Meridian S System is a fine-fault localization method capable of high-voltage OBIRCH, which is especially useful for compound semiconductor devices operating in this range.

OBIRCH results from a test chip showing showing negative (green) and positive (red) changes in current

Electrical fault isolation with nanoprobing

Electrical failures in power devices can often be hard to identify without first evaluating the voltage, current, waveform, timing, and frequency response. Further isolation of shorts, opens, and small leakage currents requires high precision and sensitivity, offered by the Thermo Scientific Hyperion II System, equipped with automated driving and adjustment to drastically improve accuracy of the tests.

 

Conductive atomic force microscopy (AFM) for electrically active crystalline faults may also be enabled by this system and complements other crystal defect analyses for comprehensive characterization. 

Simulation of AFM probe scanning action on 10nm SRAM

SEM and TEM imaging and analysis of power semiconductor devices

Power devices are fabricated from materials with sensitive electrical properties and varying physical properties. It is therefore crucial to use advanced, high-resolution imaging techniques to understand the behaviors and structures of interest. 

SEM imaging and analysis

Visual analysis is a powerful technique to understand device structures and even failure mechanisms. When paired with high-quality (curtain-free) cross-sectioning, a high-performance SEM column allows for resolution of critical information such as p/n junction dopant profiling and nanometer-scale structures.

SiC MOSFET device SEM image showing the p/n junction dopant profile.

3D reconstruction of FIB-SEM tomography data

Monitoring critical device structures is essential during design and process control. Combining Thermo Scientific Avizo Software with FIB-SEM or even TEM tomography data enables complete 3D reconstruction, feature segmentation, and automatic measurement of variations in key features, such as gate thickness. Such data also can reveal defect characteristics, like fault propagation in all directions.

GaN HEMT 3D reconstructed and segmented to show individual structures and interface voids using Avizo Software.

TEM imaging and analysis

With the transition to compound semiconductors in advanced power devices also comes a need for atomic-level analysis. Transmission electron microscopy has become the benchmark technique for measuring epilayer and oxide thickness, as well as analyzing defect propagation, diffusion, and strain across the epilayer stack. With such a wide application space, having a low-distortion, high-resolution, fast, and flexible instrument, like the Thermo Fisher Talos F200E TEM is essential.

STEM EDS (left) and darkfield imaging (right) show material and structural analysis of a power device

Electron channeling contrast imaging

Electron channeling contrast imaging (ECCI) is a non-destructive technique used to visualize crystalline defects in the SEM. ECCI isn't limited to specific materials and is used to measure defect density in single crystalline samples, as well as to reveal dislocations in patterned structures. As a localization technique, it can identify defects for extraction and further characterization.

ECCI example of a crystalline defect on a single crystal blanket layer (left) compared to a patterned structure (right).

Electrostatic discharge testing for power electronics quality standards

All semiconductor integrated circuits (ICs) are subject to environmental electrostatic discharge (ESD) throughout their lifecycles. However, the higher quality standards set for power devices require advanced testing capabilities for high current, temperature, and voltage with flexible configuration to meet evolving regulations. Both the Thermo Scientific MK.4TE and Thermo Scientific ORION 3 ESD test systems surpass industry requirements and offer intuitive software, data handling, and advanced test algorithms to maximize yield and enable down-stream PFA for failed devices to inform subsequent design improvements. 

Prior to physical failure analysis, for example SEM inspection, ESD compliance testing must be performed.

For Research Use Only. Not for use in diagnostic procedures.