In the field of integrated circuit manufacturing, the seal ring, though not directly involved in circuit signal processing, is a core component of the chip’s physical protection system. This seemingly simple annular structure carries multiple critical roles from layout design to process implementation and serves as a key barrier to ensure chip reliability. This article comprehensively analyzes the technical essence of this chip “guardian” from four dimensions: definition, structure, function, and potential risks of omission.
01
Definition from Multiple Perspectives
From the layout design perspective, the seal ring is a closed pattern formed by overlapping process layers such as diffusion (diff), contact, via, and metal according to strict design rules. These layers are not simply stacked but must match in terms of “dark/clear” attributes — only when the design and process layer attributes align will that layer be retained in the seal ring, creating a three-dimensional protective structure.
From the process implementation perspective, the seal ring appears as a composite of metal, oxide, and passivation layers. Essentially, it constructs an “electronic dam” around the chip edge: the underlying metal layer provides a conductive path, the oxide layer isolates moisture, and the passivation layer resists mechanical shock, working together to form a multidimensional protection system.
Physically, the seal ring is located between the chip and the scribe line, acting like a circular buffer zone. Its width typically follows a design rule of over 10 micrometers, reserving a safety margin for chip dicing and preventing cutting stress from directly impacting the core circuit area.
02
Structural Analysis of Precision Engineering
The core structure of the seal ring consists of four main process layers:
Diffusion (Active Area): Acts as the foundational layer, typically using P+ doping to form a conductive path connected to the substrate grounding network, providing a low-impedance path for electrostatic discharge. The diffusion region near the seal ring is specially designed with shallow salicide structures, enhanced by the addition of RPO (resist protect oxide) or SAB (salicide block) to boost ESD protection.
Contact and Via: Unlike discrete square hole designs in regular circuits, the seal ring uses continuous strip-like hole structures to form a “moat”-like conductive path. The via structures between adjacent layers are arranged in a staggered pattern to avoid straight vertical paths, a design that effectively absorbs moisture generated during dicing and prevents internal circuit contamination.
Metal Layers: Preferentially utilizes upper metal layers (e.g., Metal2 and above) to connect the core circuit with the seal ring, avoiding the mechanical fragility of thinner lower metal layers (e.g., Metal1). Wide metal connections must avoid slotting near the ring to ensure structural integrity.
Oxide and Passivation Layers: A dense oxide layer is formed through thermal oxidation to isolate moisture, and the surface is covered with passivation materials such as silicon nitride or polyimide to create a mechanical buffer layer that resists dicing stress.
03
Core Protective Functions
- Mechanical Protection: Absorbing Cutting Impact
As a physical buffer zone during chip dicing, the seal ring absorbs over 90% of mechanical stress. Vibrations and friction from the dicing blade in the scribe line are progressively attenuated through the seal ring’s composite metal-oxide structure, preventing cracks in the core circuit from stress concentration. Reinforced corner structures are especially effective in preventing edge damage caused by misaligned cuts. - Environmental Isolation: Blocking Moisture Intrusion
Microcracks formed during dicing may allow moisture penetration. The seal ring’s continuous via structure and multilayer passivation form a “labyrinthine” barrier: metal networks absorb free water, oxide layers block liquid water, and passivation layers isolate water vapor. Empirical data shows that chips with seal rings have more than triple the failure time under 85°C/85% RH conditions compared to those without. - ESD Protection: Establishing Discharge Paths
Static electricity generated during dicing is quickly routed to ground through the seal ring’s P+ active area. Surrounding ring structures form parallel discharge paths, dispersing transient current impact along the chip edge. This design improves ESD protection by 40%, particularly benefiting high-speed interface circuits. - Electromagnetic Shielding: Isolating External Interference
By grounding the entire seal ring, a surrounding electromagnetic shield is formed, effectively attenuating external electromagnetic field coupling to internal circuits. In RF chips, this structure reduces parasitic coupling noise by over 20dB, ensuring high-frequency signal integrity.
04
Potential Risks of Omission for Seal Ring
- Increased Risk of Mechanical Damage
Without a seal ring, mechanical stress during dicing acts directly on the IO ring region, increasing the probability of edge circuit fracture by 60%. In one MCU chip case, omitting the seal ring caused the dicing yield to drop from 98% to 82%, with edge transistor gate oxide rupture as the main failure mode. - Decreased Environmental Reliability
Moisture intrusion from the dicing edge accelerates metal electromigration, especially in mixed-signal chips, where moisture-induced leakage increases standby power consumption by over 30%. In memory chips, bitline leakage is more severe, reducing data retention time to one-fifth of the standard in humid conditions without a seal ring. - ESD Protection Failure
Without a seal ring, static electricity from dicing cannot be promptly discharged, concentrating ESD energy in the core circuit. In one ADC chip test, the absence of a seal ring caused 15% of channels to fail under ±2kV ESD, while the standard structure withstood ±4kV without damage. - Worsened Electromagnetic Compatibility
External electromagnetic interference couples directly into edge circuits, reducing analog signal SNR by 15dB and increasing digital clock jitter by 25%. In automotive-grade chips, such interference can cause logic errors and jeopardize system safety. - Process Compatibility Issues
Without a seal ring, the distance between the scribe line and core circuit is insufficient, and debris from the dicing wheel may splash onto the chip surface, causing metal layer short circuits. In a power chip case, 22% of short-circuit failures were attributed to the absence of a seal ring.
05
Conclusion: A Critical Balance in Design
The seal ring design is essentially a trade-off between reliability and cost: although it increases chip area by about 5–8%, it significantly improves yield and long-term reliability. With the advancement of advanced packaging technologies such as SiP and 2.5D integration, the seal ring is evolving from a simple mechanical shield to a multifunctional protection structure, potentially integrating stress sensors and environmental monitors. For designers, following foundry design rules and optimizing ring parameters are prerequisites for creating highly reliable chips. In the pursuit of extreme integration, never overlook this “invisible Great Wall” that protects the chip.
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