Safeguarding High-Value ASICs: Why KGD Verification is the Strategic Key to Unlocking CPO Commercialization

While the industry is well-versed in the failure modes of ASICs and EICs, the Photonic Integrated Circuit (PIC) remains the most unfamiliar territory in CPO verification. Each of the five core components within a PIC operates under unique physical mechanisms, leading to entirely distinct failure pathways. Precisely locating and isolating these microscopic anomalies relies heavily on cutting-edge Failure Analysis (FA) techniques to achieve final risk convergence before mass production.

1.Grating Couplers (GC)：

(1)Operational Principle
Grating Couplers utilize periodic trench structures to enable external optical fibers to couple into chip waveguides at specific angles. This process requires precise calculations of coupling angles and dimensions, as these factors directly dictate light-gathering efficiency and polarization selectivity.
(2)Representative Failure Modes
Surface morphology variations driven by alignment deviations, process residues, or environmental particle contamination can lead to performance degradation. Additionally, physical damage caused by mechanical stress often triggers optical leakage or significant wavelength shifts.
(3)Analytical Techniques
The iST Laboratory utilizes Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Dual beam FIB, and Transmission Electron Microscopy (TEM) to perform microscopic defect analysis. Furthermore, cross sectional inspections are employed to verify the physical integrity of the laser to grating coupling interface.

2.Waveguides (WG)：

(1)Operational Principle
Waveguides serve as the primary channels for optical transmission. They utilize the refractive index contrast between the core and cladding materials to achieve total internal reflection, effectively confining the light beam within the channel. Silicon, silicon nitride, and silicon carbide are commonly utilized materials for this purpose.
(2)Representative Failure Modes
Material absorption rates must be rigorously examined, as excessive absorption leads to significant transmission attenuation. Furthermore, sidewall roughness of the waveguide can trigger scattering loss, while thermal stability remains a critical factor due to its direct impact on the refractive index.
(3)Analytical Techniques
The iST Laboratory performs precision cross sectional analysis to observe whether the structural dimensions of the waveguide transmission channels align with the original design. This process also involves inspection for structural variations or defects that could result in optical signal loss.

3.Heaters：

(1)Operational Principle
Heaters generate thermal energy via electrical current to locally modify the waveguide temperature, inducing refractive index changes for precise phase tuning. Common materials utilized for these components include Titanium (Ti), Tungsten (W), and Titanium Nitride (TiN).
(2)Representative Failure Modes
Insufficient spacing between conductive lines or poor insulation can easily lead to electrical leakage or even catastrophic structural burnout caused by Electrostatic Discharge (ESD). Furthermore, inadequate thermal isolation may result in thermal crosstalk, interfering with adjacent components.
(3)Analytical Techniques
The iST Laboratory performs cross sectional inspections specifically targeting leakage points. This is complemented by precision IC Delayer to identify the exact location of burnout or leakage sites layer by layer.

4.PN Junction Modulator：

(1)Operational Principle
PN Junction Modulators apply a reverse bias to the PN junction to alter the depletion region’s width, thereby modulating the refractive index and the speed of light. Utilizing interference principles, this process converts electrical signals (0s and 1s) into high speed optical signals.
(2)Representative Failure Modes
Common issues include high temperature induced transient failures as thermal drift, permanent ESD breakdown, and modulation inefficiency caused by variations in ion implantation concentration.
(3)Analytical Techniques
The iST Laboratory utilizes Scanning Capacitance Microscopy (SCM) or Atomic Force Microscopy (AFM) to visualize carrier concentrations and doping profiles, ensuring they align with the original design specifications. Furthermore, cross sectional inspections of the PN junction remain an indispensable part of the verification process.

5.Ge Photodiodes, PD：

(1)Operational Principle
Photodiodes are responsible for converting optical signals back into electrical signals. In the industry, Germanium (Ge) is commonly integrated into the silicon process to significantly enhance sensing sensitivity for specific optical wavelengths.
(2)Representative Failure Modes
The most critical failure is dark current issue. This typically originates from lattice defects during epitaxial growth or metallic micro-contamination such as residual Gold (Au) or Aluminum (Al), which can create leakage paths. Other failures include component degradation or physical burnout caused by external thermal stress, prolonged improper hardware operation, or sudden high-current surges.
(3)Analytical Techniques
Analyzing Germanium photodiodes is extremely challenging. iST utilizes Electron Beam Induced Current (EBIC) technology for high resolution electrical failure localization. This is further supported by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX), and Secondary Ion Mass Spectrometry (SIMS) for in depth lattice defect and metallic contamination analysis, ensuring the root cause of Ge photodiode failure is identified.