Modern semiconductor devices are becoming smaller while delivering more performance than ever before. Technologies such as chiplets, 2.5D packaging, and 3D integration depend on tiny vertical connections called vias. These structures must be manufactured with exceptional precision.
That is why metrology of through-glass and through-silicon vias has become an essential part of semiconductor manufacturing.
What Are Through-Glass Vias (TGVs)?
A Through-Glass Via (TGV) is a small vertical hole created through a glass substrate to carry electrical signals from one side to the other. After the hole is formed, it is filled with conductive material to create an electrical connection.
If you are wondering why glass is used instead of silicon, the answer lies in its unique properties. Glass offers excellent dimensional stability, low electrical loss, high electrical resistivity, and good thermal stability. These advantages make it an ideal material for many advanced packaging applications.
Today, TGVs are widely used in:
- RF packaging
- MEMS devices
- Photonics
- High-performance computing
- Wafer-level packaging
- Glass interposers
- Heterogeneous integration
As semiconductor devices continue to shrink, TGV technology supports higher input and output (I/O) density while helping manufacturers reduce signal loss and improve package performance.
What Are Through-Silicon Vias (TSVs)?
A Through-Silicon Via (TSV) is a vertical electrical connection that passes directly through a silicon wafer or silicon die. Instead of sending signals around the edge of a chip, TSVs allow signals to travel straight through the silicon.
This shorter path improves electrical performance and enables multiple semiconductors dies to be stacked together in a compact package.
You will commonly find TSVs in:
- 3D integrated circuits
- 2.5D semiconductor packages
- Silicon interposers
- High Bandwidth Memory (HBM)
- AI processors
- Image sensors
- Chiplet-based architectures
TSVs have become one of the key building blocks of modern semiconductor packaging because they support faster communication, higher connection density, and more efficient use of space.
Through-Glass Vias vs Through-Silicon Vias
| Feature | Through-Glass Vias (TGVs) | Through-Silicon Vias (TSVs) |
| Base Material | Glass substrate | Silicon wafer or silicon die |
| Primary Purpose | Vertical electrical connection through glass | Vertical electrical connection through silicon |
| Common Applications | RF packaging, photonics, MEMS, glass interposers | 3D ICs, HBM, AI processors, chiplets |
| Electrical Performance | Very low electrical loss at high frequencies | Very high-speed electrical communication |
| Thermal Expansion | Can be tailored to closely match silicon | Fixed by silicon properties |
| Signal Integrity | Excellent for RF and high-frequency applications | Excellent for high-density digital communication |
| Manufacturing Method | Laser processing followed by selective etching | Deep silicon etching followed by metallisation |
| Typical Via Density | High | Very high |
| Inspection Difficulty | Challenging due to transparent glass | Challenging due to deep, narrow silicon structures |
| Key Metrology Focus | Diameter, taper angle, aspect ratio, transparency effects | Diameter, depth, sidewall quality, alignment, aspect ratio |
Although both technologies perform the same basic function, they serve different packaging requirements. As a result, each presents its own measurement challenges and requires carefully selected metrology techniques.
Why Metrology Is Critical for TGVs and TSVs
Ensures Dimensional Accuracy
Every via must match its design dimensions. Even a small variation in diameter, depth, or taper angle can affect electrical performance. Accurate metrology helps you verify these dimensions before manufacturing continues.
Supports Process Control
Manufacturing consists of many steps. Small process changes can gradually create larger problems. Regular measurements allow engineers to monitor production, identify variation early, and maintain stable manufacturing conditions.
Improves Product Reliability
Poorly formed vias may develop electrical or mechanical failures over time. Measuring important dimensions helps manufacturers detect potential issues before devices reach final assembly or customer applications.
Reduces Manufacturing Defects
Early inspection prevents defective wafers from moving through expensive production stages. Finding problems sooner reduces wasted materials, lowers manufacturing costs, and improves overall production efficiency.
Increases Semiconductor Yield
Higher yield means more good devices are produced from every wafer. Consistent metrology helps manufacturers optimise processes, reduce scrap, and achieve repeatable production results across large manufacturing volumes.
Manufacturing Challenges That Make Metrology Essential
High Aspect Ratio Structures
Modern vias are becoming deeper while their diameters continue to shrink. Measuring these narrow structures accurately is challenging and requires high-resolution metrology capable of inspecting complex three-dimensional features.
Extremely Small Dimensions
Many semiconductor vias measure only a few micrometres across. At this scale, even tiny dimensional differences can affect manufacturing quality. Precision measurement becomes essential throughout production.
Transparent Glass Materials
Glass offers many advantages but also introduces optical challenges. Reflection and light transmission can make inspection more difficult, requiring specialised optical metrology techniques for accurate dimensional measurements.
Process Variation
Every manufacturing process introduces small variations. Differences in drilling, etching, plating, or polishing can change the geometry. Continuous measurement helps engineers identify these variations before they affect product quality.
High-Density Via Arrays
Advanced packages may contain thousands of closely spaced vias. Inspecting every feature manually is impractical. Automated metrology systems help manufacturers inspect large numbers of vias consistently while maintaining production throughput.
Critical Dimensions That Must Be Measured
Via Diameter
The diameter determines whether the via can be properly filled and connected. Measuring both the entrance and exit diameters ensures the feature matches design specifications throughout the manufacturing process.
Via Depth
Depth controls the electrical connection through the substrate. Incorrect depth may prevent reliable electrical performance or interfere with later manufacturing steps.
Aspect Ratio
Aspect ratio compares via depth with its diameter. Higher aspect ratios improve package density but increase manufacturing difficulty. Accurate measurement confirms whether the designed geometry has been achieved.
Taper Angle
Many vias are slightly wider at one end than the other. Measuring the taper angle helps engineers evaluate drilling or etching quality and maintain consistent manufacturing performance.
Position and Alignment
Every via must be located in the correct position. Even small alignment errors can affect redistribution layers, microbumps, or stacked dies. Precision metrology verifies that each feature is correctly placed before assembly.
Metrology Throughout the Manufacturing Process
Raw Substrate Inspection
Inspection begins before any vias are created. Measuring substrate thickness, flatness, and surface quality establishes a reliable starting point and helps prevent defects during later processing steps.
After Via Formation
Once drilling or etching is complete, engineers measure the basic geometry of every via. This confirms the required diameter, depth, and aspect ratio have been achieved before further processing.
During Metallisation
After conductive materials are deposited, metrology verifies that the via has been filled correctly and that dimensional changes remain within acceptable manufacturing limits.
Before Final Packaging
Before dies are assembled, engineers inspect alignment, feature locations, and critical dimensions. Early verification reduces the risk of assembly failures and improves manufacturing consistency.
Final Quality Verification
The final inspection confirms that completed wafers meet dimensional specifications. These measurements provide confidence that the finished semiconductor package will perform as designed under operating conditions.
Measurement Technologies Used for TGV and TSV Metrology
Optical Metrology
Optical metrology measures features using light instead of physical contact. You can accurately inspect via diameter, position, profile, and critical dimensions without touching delicate semiconductor structures. This method is widely used because it offers high precision while preventing damage to fragile wafers.
Non-Contact Metrology
Non-contact metrology performs dimensional inspection without placing a probe on the surface. This approach protects thin wafers, glass substrates, and microstructures from mechanical stress while providing repeatable measurements suitable for semiconductor manufacturing and process control.
Video Measurement Systems
Video measurement systems use high-resolution cameras and advanced image processing to inspect tiny semiconductor features. They allow you to measure diameters, spacing, alignment, edge quality, and other critical dimensions quickly across large numbers of vias.
Confocal Microscopy
Confocal microscopy captures sharp images from different depths to build accurate three-dimensional surface information. It is useful for measuring via depth, sidewall geometry, and surface height while maintaining excellent vertical measurement accuracy.
White Light Interferometry
White light interferometry measures surface height using the interference of reflected light. You can inspect flatness, step height, surface roughness, and fine topographical features without making contact with the semiconductor surface.
Laser-Based Measurement
Laser measurement systems use focused laser beams to evaluate dimensions and surface profiles with high accuracy. They are suitable for measuring deep structures, inspecting complex geometries, and supporting automated semiconductor manufacturing processes.
Focus Variation
Focus variation combines optical imaging with controlled focus changes to reconstruct three-dimensional surfaces. This technique is effective for measuring steep surfaces, complex profiles, and microscopic features that are difficult to evaluate using conventional imaging.
3D Optical Profilometry
3D optical profilometry creates detailed three-dimensional models of semiconductor features. It allows engineers to evaluate via depth, taper angle, sidewall profile, surface texture, and other dimensional characteristics important for process verification.
Coordinate Measurement Systems
Coordinate measurement systems determine the precise location of critical features across the wafer. These systems verify via position, pitch, alignment, and geometric relationships, helping ensure every structure matches the intended semiconductor design.
Common Defects Identified During Via Metrology
Early defect detection improves product quality and prevents manufacturing problems from progressing through expensive production stages. Accurate metrology helps engineers identify both dimensional variation and structural defects before final assembly.
Diameter Variation
A via that is too large or too small may not perform as intended. Measuring diameter helps confirm manufacturing consistency and ensures the electrical connection meets design requirements.
Misalignment
Each via must be positioned accurately. Even slight positional errors can affect redistribution layers, stacked dies, or microbumps. Alignment measurement verifies that every feature is correctly located.
Excessive Taper
A large taper angle changes the internal shape of the via. This may affect metallisation quality and electrical performance. Measuring taper helps evaluate drilling and etching accuracy.
Surface Damage
Small cracks, chips, or rough edges can weaken the substrate or reduce manufacturing reliability. Metrology systems inspect surface quality so these defects can be identified before further processing.
Incomplete Via Formation
Some vias may not reach the required depth or may contain irregular geometry after fabrication. Measuring depth and profile confirms the via has been produced according to specification.
Challenges in Measuring Through-Glass Vias
Although glass offers many packaging advantages, it also creates unique inspection challenges that require specialised metrology approaches.
Transparent Material
Glass allows light to pass through it. This transparency can create reflections and optical effects that make accurate dimensional measurement more difficult if the inspection method is not properly designed.
High Aspect Ratio Vias
Many TGVs are narrow and deep. Measuring both diameter and depth accurately becomes increasingly challenging as aspect ratios increase and manufacturing tolerances become tighter.
Small Taper Angles
Modern glass interposers often require very small taper angles to maximize via density. Precision measurement is needed to verify these subtle geometric differences consistently across the wafer.
High-Density Via Arrays
Thousands of closely spaced TGVs may exist on a single substrate. Automated optical metrology helps inspect these dense patterns efficiently while maintaining measurement repeatability.
Large Glass Panels
Glass substrates are now manufactured in both wafer and panel formats. Measuring dimensional accuracy consistently across larger surfaces requires stable and highly repeatable metrology systems.
Challenges in Measuring Through-Silicon Vias
TSVs present different measurement challenges because they are formed directly inside silicon and are often used in extremely dense semiconductor devices.
Deep Silicon Structures
TSVs extend through the silicon wafer and often have significant depth compared with their diameter. Measuring these structures accurately requires high-resolution three-dimensional inspection techniques.
Small Feature Sizes
Modern TSVs continue to decrease in size as packaging density increases. Tiny dimensional variations become more significant, making precision metrology essential throughout manufacturing.
Sidewall Quality
The silicon etching process can produce sidewall irregularities. Measuring sidewall geometry helps engineers evaluate process quality and maintain consistent manufacturing performance.
Dense Via Patterns
Advanced chiplets and memory devices contain large numbers of closely spaced TSVs. Automated inspection is necessary to evaluate these complex patterns without slowing production.
Thin Silicon Wafers
Many semiconductor packages use very thin wafers after grinding. These delicate substrates require non-contact measurement techniques that provide accurate results without introducing mechanical stress.
How Metrology Improves Semiconductor Yield
Detects Process Variation Early
Small manufacturing changes can gradually affect via dimensions and alignment. Regular measurements help engineers identify these changes before they develop into larger quality problems or reduce production yield.
Reduces Scrap and Rework
Finding dimensional issues before final assembly prevents defective wafers from moving through expensive manufacturing stages. This reduces unnecessary material waste, lowers production costs, and improves manufacturing efficiency.
Improves Process Optimization
Metrology provides accurate measurement data throughout production. Engineers use this information to adjust manufacturing processes, improve repeatability, and maintain stable production across multiple wafer batches.
Supports Reliable Packaging
Correctly manufactured TGVs and TSVs improve electrical connections between semiconductor components. Accurate inspection reduces the risk of failures that may appear later during package assembly or product operation.
Enables Consistent High-Volume Manufacturing
Modern semiconductor factories produce thousands of wafers every day. Automated optical metrology ensures dimensional measurements remain accurate and repeatable, helping maintain consistent product quality across large production volumes.
How to Select the Right Metrology Solution for TGV and TSV Inspection
Measurement Accuracy
The system should measure microscopic dimensions with high precision. Accurate results improve confidence during process development, production monitoring, and final quality verification.
Non-Contact Inspection Capability
Thin silicon wafers and glass substrates are delicate. Non-contact metrology reduces the risk of surface damage while maintaining accurate dimensional measurement throughout the inspection process.
Three-Dimensional Measurement
Many critical via characteristics include depth, taper angle, and sidewall geometry. A metrology solution should accurately measure both two-dimensional and three-dimensional features.
Automation and Throughput
High-volume semiconductor manufacturing requires automated inspection. The measurement system should inspect large numbers of vias efficiently while maintaining repeatable results across multiple wafers.
Software and Data Analysis
Modern metrology includes advanced software for measurement, reporting, process monitoring, and statistical analysis. Clear measurement data helps engineers make faster manufacturing decisions and improve overall process control.
About VIEW Micro Metrology
Advanced packaging technologies demand highly accurate dimensional measurement throughout every manufacturing stage. This includes inspecting critical dimensions, verifying alignment, measuring via geometry, and supporting process control.
VIEW Micro Metrology develops high-performance optical metrology, non-contact metrology, and critical dimension measurement systems used for precision semiconductor inspection. These technologies support manufacturers working with advanced packaging, wafer-level applications, and other high-accuracy measurement requirements where repeatable dimensional data is essential.
Need guidance on selecting the right metrology approach for your application?
Get in touch with the VIEW Micro Metrology team to discuss your application and measurement requirements.
Conclusion
Through-Glass Vias and Through-Silicon Vias have become fundamental technologies for modern semiconductor packaging. As devices continue to become smaller and more complex, accurate metrology becomes increasingly important.
Precision measurement supports dimensional accuracy, manufacturing consistency, product reliability, and higher semiconductor yield, making it one of the most valuable processes throughout advanced packaging production.
Frequently Asked Questions
What is TGV metrology?
TGV metrology measures the dimensions and geometry of through-glass vias. It verifies diameter, depth, taper angle, alignment, and other critical dimensions throughout glass interposer manufacturing.
What is TSV metrology?
TSV metrology measures through-silicon vias used in advanced semiconductor packaging. It confirms dimensional accuracy, via profile, depth, sidewall quality, and positioning before package assembly.
Why is via metrology important?
Via metrology identifies dimensional variation before manufacturing defects become expensive. It improves process control, supports product reliability, reduces scrap, and increases semiconductor production yield.
Which measurements are most critical?
The most important measurements include via diameter, depth, aspect ratio, taper angle, sidewall profile, position accuracy, pitch, alignment, flatness, and surface quality.
What technologies are commonly used?
Common technologies include optical metrology, non-contact metrology, video measurement systems, confocal microscopy, white light interferometry, laser measurement, focus variation, and 3D optical profilometry.
What challenges exist with glass substrates?
Glass creates measurement challenges because of transparency, light reflection, refraction, high aspect ratio vias, and extremely small taper angles that require specialised optical inspection methods.
How does metrology improve semiconductor yield?
Accurate measurement detects manufacturing variation early. This reduces defects, improves process consistency, lowers production costs, and increases the number of acceptable semiconductor devices.
What is non-contact metrology?
Non-contact metrology measures dimensions using light or optical technologies instead of physical probes. This prevents damage while providing accurate measurements for delicate semiconductor structures.
How are high aspect ratio vias measured?
High aspect ratio vias are measured using advanced optical techniques capable of capturing accurate diameter, depth, taper angle, and three-dimensional geometry without damaging the substrate.
How does optical metrology differ from tactile measurement?
Optical metrology uses light to measure features without touching the surface. Tactile measurement uses physical probes. Optical methods are generally preferred for delicate semiconductor wafers and microscopic structures.