Circuit extraction

Circuit extraction of an integrated circuit (IC) in the context of reverse engineering involves the process of extracting the design and functionality of an IC by analyzing its physical structure, electrical behavior, and sometimes the underlying silicon layout. This is often done for the purposes of understanding the IC’s design, identifying potential vulnerabilities, or replicating the functionality of a proprietary circuit. Here’s an overview of the general steps involved in IC circuit extraction:

1. Physical Decapsulation
   • Decapsulation is the process of removing the protective plastic or ceramic package that houses the IC. This is typically done using chemical etching or mechanical methods (such as grinding or laser ablation) to expose the silicon die.
   • Once the package is removed, the chip is usually examined under a microscope to understand its layout.
2. Imaging and Microscopy
   • Optical Microscopy: High-resolution optical microscopes are used to get an initial look at the surface of the chip. This can help identify visible components like bond pads, metal traces, and the general layout of the die.
   • Scanning Electron Microscopy (SEM): For more detailed imaging at the nanometer scale, SEM is often used. SEM can reveal intricate details about the metal layers, vias, and other features on the die.
   • X-ray Imaging: In some cases, X-ray imaging can be used to study internal layers of the IC without damaging it. This helps identify the layers and structures that are not visible from the surface.
3. Delayering (Physical De-layering)
   • Chemical Mechanical Polishing (CMP): These methods are used to selectively remove the metal layers, one layer at a time, to reveal the underlying structure of the chip. Each layer is carefully stripped away to expose the circuit patterns below.
   • This process can be repeated for multiple layers, revealing the metal traces, transistors, and other components in the chip’s multi-layered structure.
4. Imaging of Each Layer
   • As each layer is exposed, it is imaged (using SEM or other methods) and documented for analysis. The images of these layers will reveal the interconnections and the design of the IC at the metal and transistor levels.
5. Reverse Engineering of the Circuit Design
   • Once the physical layers are exposed and imaged, the next step is to reverse-engineer the schematic of the IC. This involves:
     • Identifying Components: Recognizing the functional blocks, such as transistors, capacitors, resistors, and logic gates.
     • Mapping Connections: Analyzing the metal traces and vias to understand how components are interconnected and how the signals flow.
   • Tools such as layout extraction software or circuit simulation tools can help reconstruct the logic and function of the chip.
6. Simulation and Validation
   • The extracted design is typically validated by running simulations to ensure it behaves as expected.
   • The simulation may involve running the IC’s function through a variety of input-output conditions to check if the reverse-engineered schematic matches the original IC behavior.
7. Reconstruction and Documentation
   • The final step involves documenting the circuit in a readable format, such as a netlist, schematic diagram, or design files, which can be used for analysis or replication.
   • This step is often a key part of reverse engineering for analysis, security research, or compatibility design.

Challenges in IC Reverse Engineering:

• Complexity: Modern ICs can have billions of transistors and multiple metal layers, making extraction and analysis extremely time-consuming and difficult.
• Protective Measures: Some ICs come with anti-reverse engineering measures, like protected layers or tamper detection, which can make the extraction process more challenging.
• Legal and Ethical Issues: Reverse engineering ICs for malicious purposes, like counterfeiting or stealing intellectual property, is illegal and unethical in many jurisdictions.

This process requires specialized equipment, a deep understanding of semiconductor design, and significant expertise in circuit analysis.