1. Failure Analysis Flow – actual scenario…2. What is Semiconductor Failure Analysis (FA)…3. Your Exposure on FA…4. Advanced FA technique & methodology…5. Other advanced FA technique…6. FA Process Flow - die (wafer) vs. package (IC)…

Semiconductor Failure Analysis

Your Exposure on Failure Analysis

a) Non destructive test (ujian tanpa musnah) : radiographic X-ray or C-SAM / SAT.

b) Electrical characterization (pencirian elektrikal) : curve tracer, semiconductor parametric analyzer (SPA), logic analyzer, digital oscilloscope and microprobe station.

c) Destructive test (ujian musnah) : cross-sectioning and decapping system of IC packages.

d) Visual inspection : by using optical microscope or high power microscope for inspection purposes.

e) External inspection and measurement : IC packages.

FAILURE ANALYSIS FAILURE ANALYSIS TECHNIQUES AND TECHNIQUES AND

EQUIPMENTEQUIPMENT

Figure: Radiography X-Ray Inspection system Figure: Top view X-Ray photoof an IC.

Radiography X-RayRadiography X-ray is a non-destructive semiconductor failure analysis technique used to examine the interior details of the package. It is commonly used to inspectfor wire-sweeping and other wirebond problems, die attach voids, package voids and cracks. It is excellent for determining leadframe outlines as well.

Today, X-Ray systems use a micro spot source, real-time detection and automated manipulation of the sample to achieve higher resolution and throughput. These systems are capable of detecting much finer package details and defects.  

Scanning Acoustic Microscopy (SAM) is a failure analysis technique used

for detecting disbonds or delaminations between package interfaces, e.g.,

interfaces between the plastic resin package material, the die, the die paddle,

the leadframe, the die attach material, etc.

Scanning Acoustic Microscope (SAM)

Figure: Sonoscan Model D6000 C-Mode Scanning Acoustic Microscope (C-SAM)

Figure: Examples of C-SAM photos. The red areas, denote the full delamination, while the yellow areas denote slight delamination

The C-scan mode is the display of the image of reflected echoes at the focused plane of interest. It furnishes a two-dimensional (area) description at a particular depth (Z) for precise determination of the depth of flaws.  

Basic principle: sending a sound wave through the package, and interpreting

the interaction of the sound wave with the package.

2 methodology for sending sound wave, which are:-

a) Pulse echo inspection – interpreting echoes sent back by the pkg.

b) Through transmission inspection – interpreting the sound wave at the other end of the package, after it has passed through the latter.

Side note: the ultrasonic wave frequency used ranges from 5 to 150 MHz.  

A typical scanning acoustic microscope (SAM) may employ either pulse echo

or through transmission inspection to scan for disbonds or delaminations.

Side note: The sound wave may be generated by a piezoelectric crystal, or transducer,

that has been cut to provide a specific frequency. It is activated by a high voltage pulse

from a transmitter, which is also known as the pulser. The activation would cause the

transducer to vibrate at the specified frequency, which transmits an ultrasonic wave

through the package.

Scanning Acoustic Microscope (SAM)

When performing Scanning Acoustic Microscopy, the following must be observed :           1) The units must be placed in the sample holder such that their upper surfaces are parallel to the scanning plane of the acoustic transducer. Air bubbles must be swept away from the unit surfaces and from the bottom of the transducer head.    2) The transducer with the highest center frequency that still provides sufficient signal-to-noise ratio for good imaging must be selected. The transducer must be normal to the plane of the sample and the scan path must be parallel to the plane of the stage.   Failure Mechanisms/Attributes Tested For: Plastic-to-Leadframe Delamination, Plastic-to-Die Delamination, Plastic-to-Die Attach Delamination, Die Attach Voids, Internal Cracks, etc.

Internal delaminations generally need to be addressed (especially those that occur on the die surface and bonding fingers) because they can lead to serious reliability issues such as neck breaks, heel breaks, and corrosion.  

Scanning Acoustic Microscope (SAM)

Photoemission Microscopy (PEM)

Photoemission microscopy, or light emission microscopy (LEM), is a relatively new failure analysis technique for detecting recombination radiation. Some defect sites emit light during operation which would otherwise be absent in a normal device. Such photoemissions are not visible to the naked eye. 

Figure: Light Emission Images

Photoemission microscopy uses a powerful image intensification technology to amplify the light emitted by such defect sites, therefore useful in locating defects that exhibit light emissions.   

Microthermography or Hot Spot DetectionMicrothermography or Hot Spot Detection is a semiconductor failure analysis technique used to locate areas on the die surface that exhibit excessive heating. Excessive heating indicates a high current flow, which may be due to die defects or abnormalities like dielectric ruptures, metallization shorts, and leaky junctions.  

An inexpensive yet effective Hot Spot Detection technique consists of dropping liquid crystal on the die surface of a biased device. The bias is chosen such that the defect site is allowed to conduct enough current to generate the amount of heat needed to change the visual characteristics of the liquid crystal.   This technique is popularly known as the 'Liquid Crystal Technique.'

Figure: Photo of a hot spot during liquid crystal analysis; note the rainbowcolor of the liquid crystal 

Failure Mechanisms / Attributes Tested For:

Dielectric Shorts/Breakdowns, Metallization Shorts, Junction Leakages, Mobile Ionic Contamination, etc.  

Die De-layering / De-processingDie delayering or deprocessing is the semiconductor failure analysis technique of stripping off the upper layers of the die to expose a defect site that is buried underneath these layers. Die delayering is usually done as a sequence of steps, removing a layer or two at a time. Since each layer is chemically and physically different from the others, the delayering steps are different from each other as well.  

Figure: Examples of Reactive Ion/Plasma Etchers

Layer to be Etched Example of Useable Etch

Nitride Passivation RIE using 90%/10% CF4/O2 gas mixture

Silicon Dioxide Silox Etch at 25 deg C

Aluminum Metal LinePhosphoric/Acetic/Nitric Acid (PAN) Etch at 60 deg C

Ti-W Barrier Metal Hydrogen Peroxide at 60 deg C

SiCr Thin Film Resistor RIE using 90%/10% CF4/O2 gas mixture

Polysilicon Layer Polysilicon Wet Etch at 25 deg C

Table: Examples of Die Deprocessing Steps

Many die delayering techniques exist, e.g., plasma etching, reactive ion etching, wet chemical etching, etc. A typical die delayering sequence starts with either plasma or reactive ion etching to remove the nitride passivation on top of the die surface, followed by a series of wet chemical etching steps to remove the rest of the die layers.  

Fig: Examples of Focused Ion Beam (FIB) Stations

Focused Ion Beam (FIB)

Focused Ion Beam (FIB) techniques are used in a variety of applications. In terms of failure analysis, FIB techniques are commonly used in high magnification microscopy, die surface milling or cross-sectioning, and even material deposition.

A FIB system works very similarly to a scanning electron microscope, except that it uses a finely focused beam of gallium (Ga+) ions instead of the latter's use of electrons. This focused primary beam of gallium ions is rastered on the surface of the material to be analyzed. As it hits the surface, a small amount of material is sputtered, or dislodged, from the surface.

Application:-3-D defect and structure review.Precision x-sectioning on sub-Micron scale.IC circuit diagnostics & modifi-cation.Metrology measurement & TEM sample preparation.

Scanning Electron Microscopy / Energy Dispersive Analysis X-Ray (SEM / EDX)

Failure Mechanisms/Attributes Used For:- Die/Package Cracks, Die Attach Failures/Defects, Bonding Failures/Defects, Wire Defects/Fractures, Lead Defects/Failures, Foreign Materials on Die/Package, Die Surface Defects, Seal Cracks/Defects, etc.

Scanning electron microscopy is used for inspecting topographies of specimens at very high magnifications using a piece of equipment called the scanning electron microscope. SEM magnifications can go to more than 300,000 X but most semiconductor manufacturing applications require magnifications of less than 3,000 X only. SEM inspection is often used in the analysis of die/package cracks and fracture surfaces, bond failures, and physical defects on the die or package surface.

Transmission Electron Microscope / Energy Dispersive Analysis X-Ray (TEM / EDX)

Application:-Microstructure, defect and composition examination for routine analysis and subnanometer research. Thin film and interfacial structure characterization Electron diffraction and phase identification High resolution imaging and low dose imaging. Devices from data storage, MEMS, semiconductor and other industries

Transmission Electron Microscopy (TEM) is a technique used for analyzing the morphology, crystallographic structure, and even composition of a specimen. TEM provides a much higher spatial resolution than SEM, and can facilitate the analysis of features at atomic scale (in the range of a few nanometers) using electron beam energies in the range of 60 to 350 keV. 

EDX and WDX AnalysisEDX stands for Energy Dispersive Analysis X-Ray. It is sometimes referred to also as EDS or EDAX analysis. It is a technique used for identifying the elemental composition of the specimen, or an area of interest thereof. The EDX analysis system works as an integrated feature of a scanning electron microscope, and cannot operate on its own without the latter. 

WDX Analysis stands for Wavelength Dispersive X-ray analysis. It is sometimes referred to also as WDS analysis.

Fig: Elements in an EDX spectrum are identified based on the energy content of the X-rays emitted by their electrons as these electrons transfer from a higher-energy shell to a lower-energy one

Fig: Example of an EDX Spectrum

Fourier Transform Infra-Red (FT-IR)

FTIR (Fourier Transform Infra-red) is a failure analysis technique that provides information about the chemical bonding or molecular structure of materials, whether organic or inorganic. It is used in failure analysis to identify unknown materials present in a specimen, and is usually conducted to complement EDX analysis. 

The technique works on the fact that bonds and groups of bonds vibrate at characteristic frequencies. A molecule that is exposed to infrared rays absorbs infrared energy at frequencies which are characteristic to that molecule. The specimen's transmittance and reflectance of the infrared rays at different frequencies is translated into a plot consisting of peaks. The resulting FTIR spectral pattern is then analyzed to check if it is a known signature of an identified material.

Fig: Example of FT-IR spectra

Auger Analysis

Auger Analysis is a failure analysis technique used for analyzing the surface of a specimen. Auger Electron Spectroscopy and Scanning Auger Microanalysis are two Auger Analysis techniques. These techniques are used to identify the elemental composition of a spot on the sample surface or, with ion sputtering, measure the concentration of elements as a function of depth. Auger depth profiling can be used to identify a contaminant and to determine at what depth it is located in the sample. It can also be used to check the composition of oxide layers, check for Au-Al bond weaknesses, and the like.

Fig: Scanning Auger Microprobe

Secondary Ion Mass Spectrometer (SIMS)

Secondary Ion Mass Spectroscopy (SIMS) is a failure analysis technique for analyzing the surface of a specimen in terms of composition and energy state. It operates by measuring the mass of the material at the specimen's surface. A focused beam of ions with high energy, such as Argon accelerated to 0.5 to 20 keV, is used to bombard the surface of the specimen. This sputters off some sample material. A portion of the dislodged material becomes ionized, resulting in negative and positive ions referred to as 'secondary ions.' These secondary ions are then analyzed in a mass spectrometer, producing a spectrum of the quantity of ions as a function of their mass-to-charge ratios.   The penetration depth used in SIMS is typically 10 angstroms. The technique is very fast and sensitive, detecting all the elements in the periodic table, some of which to as low as parts per billion.

1. Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS)

2. X-Ray Photoelectron Spectrometer (XPS)

3. Atomic Force Microscope (AFM)

4. X-Ray Fluorescent (XRF)

Others Advanced Analytical Method

Time-of-Flight Simultaneously Ion Mass Spectroscopy (TOF-SIMS)

Typical applications include identification of hazes on semiconductor surfaces, failure analysis of laser components, identification of surface contaminants such as mold releases and lubricants on polymers and polymer films, microanalysis of biological specimens and biomedical implants, and image analysis of the uniformity of coatings on paper.

Unique AdvantagesChemical bonding information in the form of molecular ions or structurally-significant fragments Specific compound identification through high mass resolution and mass accuracy Ion imaging of elements and of compounds (for those producing structurally-significant mass peaks) Surface sensitive:1 monolayer for molecular ions; 2-3 monolayer for atomic ions Detection limits: <1 ppma (10E-4) for most elements Quantitative with standards Non-destructive analysis of the top monolayer Elemental and molecular fragment analysis during depth profiling

X-Ray Photoelectron Spectroscopy (XPS / ESCA)

X-Ray Photoelectron Spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA) is routinely used to obtain detailed chemical analysis of polymer surfaces. In XPS x-rays hit the sample producing photoelectrons whose energy is measured. The energy is specific to each element and is used to identify all elements (except hydrogen and helium) present in the outer 100 Å of the surface (detection limits ca. 0.1 atomic percent).

In summary, XPS provides information on a) Surface concentrations of elements present ( ± 10% or better). b) The bonding state (molecular environment) and/or oxidation state for most atoms. c) Aromatic or unsaturated structures from shake-up ( *) transitions. d) Surface electrical properties from charging studies. e) Surface heterogeneity using non-destructive depth profiling and assessment using angular dependent

ESCA. f) Underlying surface layers by destructive depth profiling using argon etching (for inorganic). g) Functional groups on surfaces by positive identification through the use of derivatization reactions.

Atomic Force Microscope (AFM)

Application• Surface roughness • Film thickness • Critical dimension measurement • Geometry measurement • Domain pattern analysis • Grain size measurement • Corrosion evaluation • 3D analysis

X-Ray Fluorescent (XRF)

Applications• Quantitative and qualitative elemental analysis • Multi-element surveys • Metallic contamination • Trace Analysis • Composition and thickness

Semiconductor FA TechniqueRadiographic x-ray Cross-sectioning

Scanning Electron Microscope (SEM)EDX spectra

1. Reliability terms & definitions – FR, MTBF, bathtub curve;

• Reliability distributions – exponential, binomial, Poisson, Weibull;

• System reliability models – serial, parallel, standby, k of n, combination.

Revision

2. Reliability Prediction Techniques-FMEA, FMECA, FTA; andReliability Testing-e.g Thermal Cycling, Vibration Cycling, HALT, ALT etc (refer to Industrial Talk Notes)

Revision

3. Failure Analysis

• What is FA, terminology, relevance to semiconductor industry, types of failure and FA process flow

Revision

4. Electrical Characterisation: curve tracer, semiconductor parametric analyzer (SPA), logic analyzer, digital oscilloscope and microprobe station.

Revision

5. Sample preparation: Wet etching, dry etching, cross-sectioning

Revision

6. FA techniques: destructive & non-destructive analysis, advanced FA equipment

Revision