Overview of ICFailure Analysis

What is Failure Analysis?

Failure Analysis (FA) is the process of identifying the causes of failure by analyzing and validating failure modes and phenomena. This involves simulating and reproducing the failure events to determine the root cause and understand the underlying mechanisms of the failure.

Why is Failure Analysis Important for Integrated Circuits?

1.Identifying and Preventing Reoccurrences: Failure analysis helps identify the causes of failure and implement effective measures to prevent similar incidents in the future, thus avoiding significant economic losses and potential safety hazards.

2.Advancing Scientific and Technological Development: Failure analysis contributes to the advancement of technology by providing insights into failure mechanisms and improving design practices.

3.Enhancing Product Quality and Reliability: It aids in improving the quality, safety, and reliability of products by identifying and addressing weaknesses and defects.

4.Supporting Technical Standards: Failure analysis provides the necessary information for developing or revising technical standards, ensuring that products meet required specifications and performance criteria.

5.Assisting in Arbitration and Claims: It serves as a crucial basis for resolving disputes, conducting technical insurance assessments, and making claims in international trade.

Common Failure Analysis Methods: Sample Preparation and Considerations

Integrated circuits commonly use failure analysis methods such as X-Ray, SAT, IV, Decap, EMMI, FIB, SEM, EDX, Probe, OM, and RIE. Since failure analysis equipment is expensive and many organizations may not have access to all the necessary equipment, using external resources and services to complete the analysis is a good option. What information needs to be prepared for various analysis methods?

(1) Ultrasonic Scanning Microscope (SAT):

Definition: An Ultrasonic Scanning Microscope (SAT) is a nondestructive testing device that uses ultrasonic waves as the transmission medium. By emitting high-frequency ultrasonic waves into the sample, the device detects defects such as delaminations, cracks, or voids within the sample. This is done by measuring the changes in the reflected or transmitted ultrasonic energy or phase information at interfaces between materials with different acoustic impedances. The varying degrees of absorption and reflection of the sound waves due to different acoustic impedances allow for the detection and evaluation of internal defects in the sample.

Detection Contents:

Impurities, Inclusions, and Deposits: Detection of internal particles, inclusions, and precipitates within the material. Internal Cracks: Identification of cracks present inside the material.

Delamination Defects: Detection of layer separation or delamination within the material.

Voids, Bubbles, and Cavities: Identification of voids, air bubbles, and other gaps within the material.

Figure 1:Identification of cracks present inside the material.

Sample Preparation and Considerations

SAT is a commonly used nondestructive testing method. The sample should be tested in deionized water and must meet specific requirements for sealing and surface flatness. It is suitable for plastic-encapsulated integrated circuits with smooth surfaces but not for ceramic or metal-encapsulated integrated circuits. For example, with SONIX equipment, the sample size should be within 20 cm.

SAT offers various probe frequencies, such as 15 MHz, 35 MHz, 75 MHz, 110 MHz, and 230 MHz. Higher probe frequencies provide greater scanning accuracy but result in longer scanning times and reduced penetration. Conversely, lower frequency probes offer less accuracy but greater penetration, allowing for deeper and faster scanning. This test is generally billed based on machine time, with factors like scanning accuracy and scanning area affecting the machine time. Users can make trade-offs between accuracy and depth based on the sample conditions and scanning requirements.

(2) X-Ray:

Definition: X-Ray uses a cathode ray tube to generate high-energy electrons that strike a metal target. During this process, the sudden deceleration of electrons results in the release of energy in the form of X-Rays. By penetrating through materials of varying densities, X-Rays create contrast effects that form images of the internal structure of the sample, allowing for observation of internal issues without damaging the sample.

Detection Contents

1.Observation of Different Package Types: Inspection of various semiconductor packages such as DIP, SOP, QFP, QFN, BGA, Flipchip, as well as electronic components like resistors, capacitors, and small PCB (Printed Circuit Board) assemblies.

2.Internal Structure Analysis: Examination of chip size, quantity, die stacking, and wire bonding within the device.

3.Detection of Packaging Defects: Identification of internal defects such as chip cracks, uneven adhesive application, broken or bridging wires, internal bubbles, as well as solder ball cold joints and soldering defects.

Figure 2: Detection of Packaging Defects

Sample Preparation and Considerations

For X-Ray analysis:

1.Sample Dimensions and Material: Ensure the sample size is within 50 cm. Smaller samples generally allow for higher scanning precision. For example, with YXLON equipment, the best achievable precision is 1 µm. Clearly state the dimensions, quantity, and material of the sample.

2.Imaging Basis: X-Ray imaging is based on density differences. Materials with higher density will be visible, while those with lower density will appear as transparent. This makes X-Ray suitable for observing low-density materials wrapped around high-density ones. For instance, observing gold wires in plastic-encapsulated samples is feasible.

3.Limitations: Note that low-density materials might not be visible. For example, aluminum wire bonds in integrated circuits are nearly invisible under X-Ray, while coarse aluminum wires in TO packages may only show faint shadows.

(3) IV Automatic Curve Measurement Instrument (IV):

IV testing and measurement evaluate the electrical properties, parameters, and characteristics of semiconductor electronic components, such as voltage-current relationships. Detection Contents:

1.Open/Short Test: Identifies open circuits and short circuits within the component. 2.I/V Curve Analysis: Analyzes the current-voltage (I/V) characteristics of the component. 3.Idd Measuring: Measures the supply current (Idd) to assess the component's power consumption. 4.Powered Leakage Test: Detects leakage currents when the component is powered, indicating potential issues such as insulation breakdown or unintended current paths.

Figure 3: Powered Leakage Test

Sample Preparation and Considerations

1. Detailed Information: Clearly specify the number of pins, package type, power supply method, voltage, current requirements, and any limitations.

2. Preparation of the Analysis Environment: Ensure that the analysis environment is properly set up and suitable for the test. Confirm the availability of appropriate sockets for connecting the samples.

3. Electrostatic Protection:

Implement adequate electrostatic discharge (ESD) protection during testing to prevent damage to the components.

(4) Decapsulation:

Definition: Decapsulation, also known as opening, involves partially etching the complete package of an integrated circuit (IC) to expose the internal chip while preserving its functionality. This process allows for examination and further testing, such as FIB or EMMI, without damaging the die, bond pads, bond wires, or lead frame. After decapsulation, the IC should remain functional.

Detection Contents:

1. IC Decapsulation (Front/Back): For packages such as QFP, QFN, SOT, TO, DIP, BGA, COB, etc.
2. Sample Thinning: Applies to non-ceramic and non-metallic samples.
3. Laser Marking: Used for identifying or labeling the sample.
4. Chip Decapsulation (Front/Back): Exposing the chip from both the front and back sides.
5. IC Etching: Removal of encapsulating material to expose the internal components.

Figure 4: Detection Contents

Sample Preparation and Considerations

1. Detailed Information:

Specify the sample dimensions, quantity, package type, wire bonding material, and decapsulation requirements. Clearly outline what is expected post-decapsulation.

2. Pre-Decapsulation Steps:

If the integrated circuit is mounted on a PCB board, it is advisable to remove the PCB beforehand. The large surface area and protrusions of the PCB can affect the protection of the chip during the decapsulation process.

3. Post-Decapsulation Actions:

Determine the subsequent steps after decapsulation, such as further examination or testing (e.g., FIB, EMMI).

(5) Micro-Light Microscopy (EMMI):

Definition: EMMI (Electroluminescence Microscopy) primarily detects photons emitted from inside an integrated circuit (IC). In IC components, electron-hole pairs (EHP) recombination releases photons. When a bias is applied to a P-N junction, electrons from the N region can diffuse to the P region, and holes from the P region can diffuse to the N region, leading to EHP recombination.

Detection Contents:

1. P-N Junction Leakage: Identifies leakage currents or breakdowns at the P-N junction.
2. Saturated Transistor Hot Electrons: Detects hot electrons in saturated transistors.
3. Oxide Layer Leakage Currents: Measures photons excited by leakage currents in the oxide layer.
4. Latch-Up, Gate Oxide Defects, Junction Leakage, Hot Carrier Effects, ESD: Identifies issues such as latch-up, gate oxide defects, junction leakage, hot carrier effects, and electrostatic discharge (ESD).

Figure 5: P-N Junction Leakage

Sample Preparation and Considerations

1. Detailed Information: Specify the power supply method, voltage and current requirements, and any limitations for the sample. Indicate whether the sample is a bare die, whether it has been decapsulated, and any special requirements.

2. Power Supply and Equipment: EMMI involves applying electrical power, so confirm the power supply requirements and connections. If the laboratory does not have a suitable source meter, you may need to bring your own to avoid unnecessary work.

3. Wavelength Range: EMMI can capture near-infrared light in the wavelength range of 900-1600 nm. It is commonly used to locate current anomalies in IC P-N junctions.

4. Sample Considerations: Note that metal layers in integrated circuits can block photons. It is generally recommended to perform EMMI on the back side of the sample after decapsulation to avoid interference from metal layers.

(6) Focused Ion Beam Microscopy (FIB):

Definition: FIB (Focused Ion Beam) uses an ion beam generated from a liquid metal ion source, accelerated by an ion gun, and focused onto the sample surface. This process generates secondary electron signals to produce electron images, similar to scanning electron microscopy (SEM). FIB can also use a high-current ion beam to remove surface atoms for micro- and nano-scale surface morphology processing.

Detection Contents:

1. Chip Circuit Modification and Layout Verification: Enables modifications to chip circuits and verification of layouts.
2. Cross-Section Analysis: Provides detailed cross-sectional analysis of the sample.
3. Probing Pad: Assists in creating or inspecting probing pads on the chip.
4. Localized Cutting: Allows precise cutting at specific locations on the sample.

Figure 5: Chip Circuit Modification and Layout Verification

Sample Preparation and Considerations for FIB

1. Detailed Information: Specify the sample dimensions, material, and whether it has good electrical conductivity. If the sample is large, it should be trimmed in advance. Generally, samples should be around 1-3 cm for effective handling and positioning.

2. Sample Conductivity: Samples with good conductivity will allow for faster analysis. For samples with poor conductivity, additional measures are required, such as coating with gold or applying conductive adhesive to improve analysis quality.

3. Preparation for Cutting: Clearly define the cutting points and requirements. Provide a detailed cutting plan and submit the GDS file for precise layout specifications.

4. Handling and Positioning: Ensure the sample is properly prepared to fit the FIB stage and is well-positioned for accurate analysis.

(7) Morphological Observation (SEM):

Definition:

SEM (Scanning Electron Microscopy) directly utilizes the material properties of the sample's surface to create microscopic images. It offers advantages such as a large depth of field and high magnification, with magnification capabilities reaching up to several hundred thousand times, allowing for observations with nanometer precision.

Detection Contents:

1. Surface Morphology Analysis: Observation of surface features and micro-area morphology.
2. Material Analysis: Examination of material shapes, sizes, surfaces, cross-sections, and particle size distributions.
3. Thin Film Analysis: Observation of the surface morphology of thin film samples, including roughness and film thickness analysis.
4. Nanometer Measurement and Marking: Measurement and labeling of nanometer-sized features.

Figure 6:Surface Morphology Analysis

Sample Preparation and Considerations for SEM

1. Detailed Information: Specify the sample dimensions, material, and whether it has good electrical conductivity. Samples should generally be around 1-3 cm to fit the sample stage effectively.

2. Sample Size and Trimming: If the sample is too large, it should be trimmed in advance to fit the SEM stage and ensure proper positioning.

3. Sample Conductivity: Samples with good conductivity will allow for faster analysis. For samples with poor conductivity, additional preparation is needed, such as coating with gold or applying conductive adhesive to improve analysis quality.

(8) Elemental Analysis (EDX):

Definition:

EDX (Energy-Dispersive X-ray Spectroscopy) analyzes the characteristic X-rays emitted by a sample to determine its elemental composition. By measuring the wavelength and intensity of these X-rays, EDX identifies the elements present in the sample. The intensity of different elemental X-ray lines allows for the quantification of elements. EDX is often used in conjunction with scanning electron microscopy (SEM) for micro-area compositional analysis.

Detection Contents:

1. Micro-Area Qualitative Analysis: Determining the presence of elements in specific micro-regions of the sample.
2. Elemental Composition and Approximate Proportions: Measuring the types and relative amounts of elements in the sample.

Figure 7:Micro-Area Qualitative Analysis

Sample Preparation and Considerations for SEM

Sample Preparation and Considerations for EDX:

1. Detailed Information: Specify the sample dimensions and material.

2.Analysis Suitability: EDX is a qualitative analysis method that provides information about the material composition and approximate proportions of elements. It is particularly suitable for analyzing metallic elements.

3. Preparation Notes: Ensure that the sample is appropriately prepared for analysis, including any necessary surface cleaning or coating to enhance signal quality.

(9) Probe Station:

Definition: A probe station is primarily used in the semiconductor and optoelectronic industries. It is designed for testing integrated circuits and their packaging. The probe station is widely employed for precise electrical measurements of complex, high-speed devices, aiming to ensure quality and reliability while reducing development time and manufacturing costs.

Detection Contents:

1. Micro-Connection Point Signal Extraction: Testing and analyzing signals from very small connection points.
2. Failure Analysis Confirmation: Verifying failures during failure analysis.
3. Electrical Characteristics Verification Post-FIB Circuit Modification: Confirming the electrical properties of circuits after modification using FIB.
4. Wafer Reliability Testing: Evaluating the reliability of wafers.

Figure 8:Micro-Connection Point Signal Extraction

Sample Preparation and Considerations for Probe Station:

1. Testing Environment Requirements: Clearly specify the environmental conditions required for testing, such as temperature and humidity control.

2. Source Measurement Unit (SMU): Identify the type of source measurement unit needed for the probe station.

3. Probes: Detail the type of probes to be used. There are typically two types:  Soft Probes: These are finer and less likely to cause secondary damage to the sample.  Hard Probes: These are cost-effective but may cause more wear and tear.

4. Consumables: Note that probe testing involves consumable costs, which should be considered in the overall testing budget.

(10) Optical Microscopy (OM):

Definition: Optical microscopy is used to observe the surface shape, dimensions, structure, and defects of devices and their failure sites.

Detection Contents:

1. Sample Appearance and Morphology Inspection: Examining the external appearance and surface features of the sample.
2. Metallographic Analysis of Prepared Samples: Analyzing the structure and characteristics of samples through metallographic microscopy.
3. Defect Detection: Identifying various types of defects in the sample.
4. Transistor Bonding and Inspection: Checking point welds and other bonding aspects of transistors.

Figure 9:Sample Appearance and Morphology Inspection

Sample Preparation and Considerations for Optical Microscopy (OM):

1. Sample Details: Clearly describe the sample’s condition, including its surface characteristics and any specific areas of interest.

2. Magnification Requirements: Specify the required magnification level based on the details you need to observe.

3. Surface Observation: Note that OM is used for surface observation and cannot reveal internal structures or defects. Ensure that the sample's surface is adequately prepared for clear imaging.

(11) Reactive Ion Etching (RIE):

Definition: RIE is a type of dry etching process. It operates by applying high-frequency voltage (10-100 MHz RF) between planar electrodes, generating a plasma sheath with ions. These ions then bombard the sample surface, performing chemical etching.

Detection Contents:

1. Isotropic and Anisotropic Etching: RIE is used for etching materials that use fluorine-based chemicals. This includes carbon, epoxy resins, graphite, indium, molybdenum, nitrides, photoresists, polyimides, quartz, silicon, oxides, nitrides, tantalum, tantalum nitride, titanium nitride, tungsten-titanium, and tungsten.
2. Etching of Device Surface Patterns: It is utilized for patterning and etching on the surface of devices.

Figure 10:Isotropic and Anisotropic Etching

Sample Preparation and Considerations for Reactive Ion Etching (RIE):

1. Sample Material: Clearly specify the material of the sample to ensure compatibility with the etching process.

2. Area of Interest: Indicate the specific areas on the sample that require etching.

3. Additional Considerations: Ensure that the sample is appropriately prepared and cleaned before etching to avoid contamination and achieve accurate results.