In the chip design process, after completing circuit and layout design, the GDS data must be submitted to the foundry for manufacturing. Once the fabricated chips are returned, they undergo rigorous functional and performance testing. However, issues may arise during testing, requiring circuit modifications. To balance the complexity, time, and cost of modifications, engineers typically evaluate whether the changes can be implemented using FIB (Focused Ion Beam) or ECO (Engineering Change Order) instead of proceeding with a costly and time-consuming re-tapeout.Many distributors offer a wide range of electronic components to cater to diverse application needs, like excess inventory service
This article explores when to choose FIB for circuit modifications, when to adopt the ECO approach, and provides an analysis of their respective applications and suitability.
FIB-Based Circuit Modifications
What is FIB?
FIB (Focused Ion Beam) is a technique that uses a focused gallium (Ga) ion beam to perform nanoscale cutting, deposition, or material analysis on a chip surface. It enables physical modifications and microscopic structure observations, allowing engineers to quickly verify whether design adjustments meet expectations.
Application Scenarios of FIB
Circuit Modification on Fabricated Chips
FIB allows direct metal cutting or connection on a fabricated chip, making it suitable for small-scale local modifications, such as:
Adjusting metal interconnections
Fixing open circuits or short circuits
Advantages: No need to modify masks or perform a new tape-out Enables quick verification of circuit adjustments Supports multi-layer metal modifications and even cross-layer connections
Failure Analysis and Structural Observation
FIB enables cross-section cutting to analyze the internal structure of a chip and investigate electrical and physical defects, such as:
Grain boundary defects
Metal layer fractures
Insulation layer damage
By combining FIB with transmission electron microscopy (TEM), engineers can conduct in-depth material composition and microstructural analyses, improving the accuracy of failure analysis.
Probing Pad Creation for Signal Debugging
In complex circuits, FIB can be used to create probing pads, enabling direct signal observation using probe stations or electron beam (E-beam) tools, thereby improving debugging efficiency.
Rapid Engineering Sample Validation
Before mass production, FIB can modify engineering samples (ES), allowing customers to validate designs and perform functional debugging without requiring a new tapeout, thereby reducing time and cost.
Limitations of FIB
While FIB enables rapid modifications, it comes with high costs and is only suitable for localized adjustments. If a modification involves extensive changes or multiple circuit layers, FIB may not be feasible, and an ECO approach should be considered.
ECO-Based Circuit Modifications
What is ECO?
ECO (Engineering Change Order) is a method for making circuit adjustments at different stages of chip manufacturing. Compared to FIB, ECO is better suited for larger-scale and more systematic modifications, particularly before and after tapeout.
Application Scenarios of ECO
ECO During Tapeout
The foundry has already fabricated some masks or partially completed production (e.g., only device layers).
Since manufacturing is not yet complete, it is possible to pause production, modify specific layout layers, and re-fabricate only the necessary masks.
Cost impact: Relatively low—only new mask costs and minor production delays (a few days).
ECO After Tapeout
The foundry has completed all layers or the chip has already been fabricated.
Requires new masks and a new wafer fabrication run, leading to higher costs.
To minimize risks, foundries may stop wafer production at lower metal layers, allowing flexibility for future ECO modifications.
Advantages and Limitations of ECO
Suitable for large-scale, global modifications Ensures that the final mass-production chips meet design specifications High cost and longer turnaround time, especially for post-tapeout ECO, which impacts delivery schedules
Combining FIB and ECO in Chip Design
In practice, FIB and ECO are not mutually exclusive and can be used together:
Use FIB for rapid analysis and modification to diagnose issues and verify functional corrections.
Once validated, implement the necessary changes through ECO to ensure stability in mass production.
Conclusion
Both FIB and ECO play critical roles in chip design modifications, each with distinct advantages:
FIB is ideal for localized modifications, offering speed and mask-free adjustments, but it is costly and has limited applicability.
ECO is preferred for global modifications, supporting pre- and post-tapeout adjustments, but it involves higher costs and longer turnaround times.
By strategically combining FIB for rapid debugging and ECO for production optimization, engineers can effectively reduce design costs and risks, ensuring efficient and high-quality chip delivery.