Table 0296a lists the comparison between Electron-Beam-Probing (eBP) and Laser Voltage Imaging/Probing (LVI/LVP), which is also referred to collectively as LVx.
Table 0296a. Comparison between Electron-Beam-Probing (eBP) and Laser Voltage Imaging/Probing (LVI/LVP).
| |
eBP |
LVI/LVP |
| Mechanism |
eBP uses an electron beam to directly probe the metal interconnects or transistors within an integrated circuit (IC). The beam interacts with the surface of the device, creating secondary electrons. Voltage contrast is used to map electrical activity by detecting changes in surface potential as the device operates. |
LVx techniques use photons (light) to probe the electrical activity of circuits by observing voltage-dependent optical properties of the device. The laser either images or probes the switching activity of transistors through the bulk silicon. |
| Probing Method |
It involves scanning electron microscopes (SEMs) and focuses on generating secondary electrons for probing signals. When combined with FIB (Focused Ion Beam), it can target specific interconnects or transistors even if buried under dense metal layers. |
It uses laser-based techniques that can image or measure voltage changes in active devices by exploiting the interaction between laser light and the electrical fields generated by switching transistors. |
| Signal Measurement |
Direct measurement of electron emissions enables the capture of electrical activity even at lower layers of the IC, where optical access is blocked. |
LVx captures the electrical activity by detecting modulations in the reflected or emitted light from the transistor layer. |
| Probing Depth |
Strength |
eBP can probe deep layers, including metal interconnects and active transistors that are otherwise inaccessible to optical methods due to photon opacity. |
LVx techniques have direct access to the transistor layer in traditional flip-chip architectures because photons can penetrate through the silicon. |
| Weakness |
eBP often requires sample preparation, such as FIB, to expose certain layers for probing. |
When dense metal layers (such as in PowerVia) are introduced, LVx becomes ineffective because photons cannot penetrate the metal layers to reach the transistor layer. |
| Performance Factors |
Speed |
eBP can be slower than LVx due to the need for sample preparation and the time required for capturing signals from the electron beam. |
LVx tends to be faster, with real-time imaging of electrical activity through the bulk silicon without the need for complex preparation. |
| Signal Quality |
eBP can maintain signal quality even in cases where LVx fails, especially in the presence of dense metal layers that block optical signals. |
LVx provides good signal quality but becomes ineffective if the signal is blocked by materials that are not transparent to light, such as metal interconnects or power planes in advanced architectures like PowerVia. |
| Complexity |
eBP is more complex, requiring advanced tools (e.g., SEM, FIB) and often more complicated sample preparation. |
Less complex |
| Limitations |
Photon Opacity |
eBP is not affected by photon opacity, making it ideal for architectures, where metal layers obstruct optical access. |
LVx techniques are limited when photons cannot penetrate the material layers, as in advanced transistor designs like PowerVia, where metal layers block optical access to the transistor layer. |
| Sample Prep |
Requires sample preparation (like FIB) to expose the appropriate layers, adding time and complexity to the analysis process. |
|
| Scaling Limits |
|
As devices scale down and incorporate more metal layers, LVx becomes less effective due to increased complexity in probing through those layers. |
| Use Cases |
- Advanced Architectures (e.g., PowerVia): Preferred for probing in modern architectures where metal layers decouple the signal interconnects and power planes, as it can directly access and measure electrical signals even in deeper layers.
- Lower Frequency Signals: eBP excels at probing metal interconnects and transistors even when signals are low frequency or irregular.
|
- Traditional Flip-Chip Designs: Ideal for flip-chip designs where photons can directly access the transistor layer through bulk silicon.
- High-Frequency Signals: LVx is very effective at capturing high-frequency electrical activity due to its non-contact optical-based probing, making it faster in certain scenarios.
|
| Technological Applicability |
- Gaining prominence in modern failure analysis techniques.
- eBP has seen a resurgence in use as new transistor architectures block photon-based techniques.
|
- Still dominant in many failure analysis labs for traditional architectures where optical access is unobstructed.
- As technologies move towards more complex designs (e.g., PowerVia), the effectiveness of LVx diminishes.
|
As mentioned in Table 0296a, eBP can probe deep layers. That is, in cases where deeper layers need to be accessed, Focused Ion Beam (FIB) sample preparation is often used. FIB removes overlying material (e.g., metal layers) to expose deeper layers that the electron beam can then probe.
Therefore, it's not that the electrons themselves probe deep layers (see page4967), but the eBP technique combined with sample preparation allows access to these deeper structures by removing overlying obstacles. In LVI and LVP, the wavelength of the laser typically falls in the near-infrared (NIR) range, around 1,064 nm. This wavelength is commonly chosen because near-infrared light can penetrate through silicon, allowing access to the transistor layer in traditional flip-chip designs (see page881).
