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OM Optical Microscope

The optical microscope (OM) illuminates the surface of the sample with visible light, using visible light to expose the macro morphology of components, materials, and structures through reflection, scattering, and optical contrast differences, providing an important reference point for subsequent analysis. In the processes of failure analysis, process development, and materials research, the OM is the first-line observation tool, assisting engineers in quickly grasping the overall condition of the sample and determining whether it is necessary to proceed to higher resolution techniques such as SEM, FIB, or TEM.

OM technology principles

Optical microscope utilizationVisible light (wavelength 400–700 nm)When irradiating, different image contrasts are formed when light interacts with the sample surface to produce reflection or scattering. However, since the wavelength of visible light is longer, the theoretical resolution of OM (i.e., the minimum distance at which two points can be resolved) is only about0.2 μmThis also makes OM'sThe maximum effective magnification is about 1000X.The function of OM is not to "analyze nanometer details," but to "quickly obtain a complete macro structural status," which is the starting point for all in-depth analysis.

Although the resolution is not as good as that of electron microscopes (SEM/TEM), OM has significant advantages:
Large field of view: can quickly scan large areas, making it the best tool for assessing process consistency and identifying widespread defects.
High speed: suitable for mass production monitoring, process comparison, and failure localization.
High tolerance: suitable for various samples such as metal layers, silicon wafers, packaging bodies, PCBs, cross-sections, Delayer, etc.
Non-destructive: No vacuum or metal coating is required, allowing for rapid observation in the original state of the sample.

OM Analysis Applications

Optical microscopes (OM) cannot resolve details at the nanoscale, but theirHigh field of view, high speed, low destructiveness, and high toleranceThe characteristics make it the most commonly used and the most valuable observation method in real-time in the fields of electronics, semiconductors, and materials. The following are the most representative analytical uses and engineering scenarios of OM in the industry:

1. Cross-section Analysis

After cross-section preparation, the overall structural arrangement and interface behavior of the sample can be clearly observed through OM, making it the most commonly used preliminary structural inspection method in packaging, PCB, module, and materials engineering.

Observable content	Application scenarios
Metal layer thickness:Compare design specifications, confirm coating uniformity and process stability. VIA / TSV structure integrity:Check the completeness of the filling holes, sidewall morphology, and whether there are voids, offsets, or shrinkage in the copper pillars or vias. Solder morphology and wetting behavior:Evaluate whether the solder joints are uniform, whether there are any Voids, and whether the IMC layer (intermetallic compound) is abnormal. Packaging interface observation:Including: die attach surface, molding filling, underfill distribution, etc. Delamination, cracks, and failure behavior between materials:Used to locate failure positions and determine damage caused by mechanical/thermal stress.	Package development and structural verification PCB/PCBA solder joint quality inspection WLCSP, BGA, QFN packaging inspection RA reliability post-structural failure analysis (after Drop, TC, HTS)

Observable content

Application scenarios

Metal layer thickness:Compare design specifications, confirm coating uniformity and process stability.
VIA / TSV structure integrity:Check the completeness of the filling holes, sidewall morphology, and whether there are voids, offsets, or shrinkage in the copper pillars or vias.
Solder morphology and wetting behavior:Evaluate whether the solder joints are uniform, whether there are any Voids, and whether the IMC layer (intermetallic compound) is abnormal.
Packaging interface observation:Including: die attach surface, molding filling, underfill distribution, etc.
Delamination, cracks, and failure behavior between materials:Used to locate failure positions and determine damage caused by mechanical/thermal stress.

Package development and structural verification
PCB/PCBA solder joint quality inspection
WLCSP, BGA, QFN packaging inspection
RA reliability post-structural failure analysis (after Drop, TC, HTS)

2. IC Delayer structure confirmation

Delayer analysis (planar delayering) involves the stepwise removal of metal and dielectric layers to observe the internal circuit structure without damaging the operational logic of the chip. OM is the most important preliminary observation and process monitoring tool in IC delayering analysis.

Observable content	Application Scenarios
Metal Routing:Confirm whether each layer of metal is arranged as designed, and check for broken lines, short circuits, burnouts, and bias. Circuit Integrity (Integrity Check):Ensure that the delayering process has not caused any damage and confirm whether the location to be analyzed is correct. Process Residue or Dry Etching Anomalies:such as polymer residues, incomplete cleaning of residual films, local corrosion, etc. Large area defect localization:Burnout caused by overvoltage, hotspots caused by electromigration, metal open circuits, blackening, charring.	IC design verification, competitive comparison Failure Analysis (FA) locating open circuit / short circuit anomalies Process comparison or batch difference analysis Preliminary positioning after ESD, EOS, and latch-up failures

Observable content

Application Scenarios

Metal Routing:Confirm whether each layer of metal is arranged as designed, and check for broken lines, short circuits, burnouts, and bias.
Circuit Integrity (Integrity Check):Ensure that the delayering process has not caused any damage and confirm whether the location to be analyzed is correct.
Process Residue or Dry Etching Anomalies:such as polymer residues, incomplete cleaning of residual films, local corrosion, etc.
Large area defect localization:Burnout caused by overvoltage, hotspots caused by electromigration, metal open circuits, blackening, charring.

IC design verification, competitive comparison
Failure Analysis (FA) locating open circuit / short circuit anomalies
Process comparison or batch difference analysis
Preliminary positioning after ESD, EOS, and latch-up failures

3. Precipitate Free Zone (PFZ) analysis

PFZ is a zone of depletion of precipitates that appears near the grain boundaries in metallic materials (such as aluminum alloys) after heat treatment or strain. It is an important parameter in materials engineering used to assess the effects of heat treatment and material degradation.

Observable content	Application scenarios
Width and distribution of PFZ Microstructural changes of Al alloys The impact of precipitates on material strength, ductility, and reliability.	Al Wire Wire Bond evaluation Reliability analysis of packaging materials Aluminum metal deposition process quality control Evaluation of structural changes after heat treatment Long-term reliability testing (HTS, HTOL, Burn-in) after material degradation

4. Dislocation lines, etching anomalies, and crystal defects observation

OM can quickly identify surface defects caused by crystal growth, heat treatment, or etching processes, making it an important inspection item in the front-end-of-line (FEOL) processes and materials research.

Observable content	Application scenarios
Dislocation line: Misalignment caused by defects in crystal growth or stress. Dents and morphological changes caused by over-etching: Reflect whether the dry etching and wet etching processes are normal. Process residues, surface profile: used to confirm etching rate, undercut, etching uniformity, etc. Macroscopic defects such as crystal rupture, slip, and coating delamination.	Wafer FEOL process monitoring Analysis of Failure Mechanisms in Material Heat Treatment RA reliability post-die failure verification Observation of crystal slip caused by high temperature stress

5. Oxidation stacking faults（Oxidation Induce Stacking Fault, OISF） Study

Oxidation stacking faults are stacking faults generated during high-temperature oxidation processes due to the diffusion of twin defects or crystal defects. OM can clearly present the distribution and diffusion profile of oxidation stacking faults, which is an important quality indicator for silicon wafer materials, used in growth and oxidation process analysis.

Observable content	Application Scenarios
OISF location and radius Defect diffusion behavior Dislocation changes caused by the wafer oxidation process Defect distribution of SOI and special substrates	Silicon wafer incoming quality inspection Oxidation process improvement assessment Comparison of silicon material suppliers SOI (Silicon On Insulator) material analysis

MA-tek OM equipment capabilities

MA-tek offers a variety of OM optical microscopes, covering a complete imaging capability from low magnification wide-field observation to high magnification fine structure identification, allowing for in-depth presentation of material structures, surface morphology, and process characteristics, meeting the observation needs of different fields such as semiconductors, packaging, and materials engineering.

Figure | (a) 50-1000X (b) 100-500X / 40-200X / 5-75X (c) 50-1000X
Figure | (a) Metal (b) Poly (c) OD/AA

magnification	Magnification range	Application
50–1000X	High magnification, used for IC delayering, metal layer structure, interface observation, and detection of small defects (such as over-etch, IMD anomalies, etc.).	High-resolution structural comparison, micro defect and process anomaly localization, Delayer fine layer analysis
100–500X	Medium to high magnification is used for PCB/PCBA solder joints, packaging interfaces, film thickness, and metal distribution analysis.	solder joint IMC, packaging interface, metal layer and wire morphology
40–200X	Medium magnification is used for grain analysis, delayer layer position confirmation, and preliminary structural inspection.	Structural layer confirmation, grain analysis, etching profile scanning
5–75X	Low magnification with a wide field of view is used for appearance inspection, cross-section scanning, wafer breakage, packaging delamination, and other macro defect localization.	Appearance inspection, cross-section large field of view, packaging failure, wafer defect scanning