PCM Pad Structure with Embedded Contact Bars for Crack Resistance
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Solution Overview
Problem
Conventional multi-level interconnect structures in semiconductor ICs are susceptible to cracking during the singulation process due to the brittleness of low-k dielectric materials used in the ILD layer, which can lead to mechanical stress and failure when bond pads are cut by a die saw.
Innovation Solution
The PCM pad structure is reinforced with contact bars embedded into the substrate, which serve as pillars to reduce peeling and cracking, and an isolation structure is formed around the contact bars to prevent current leakage and further electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If low-k dielectric materials are used in the ILD layer to reduce RC delay and resistance, then interconnect performance is improved, but the dielectric becomes more brittle and susceptible to cracking during singulation
Solution Approach 1:
The patent applies beforehand cushioning by forming a stress relief structure (such as a trench or void) in the scribe line beneath the bond pad before the cracking occurs during singulation. This pre-formed structure absorbs and redistributes the mechanical stress generated during die saw cutting, preventing stress concentration that would cause cracks to initiate and propagate through the low-k dielectric material, thus protecting the brittle ILD layer while maintaining its low-RC-delay properties
Solution Approach 2:
The patent applies local quality by creating a localized stress relief structure only in the scribe line region beneath the bond pad, rather than modifying the entire dielectric layer. This targeted approach maintains the low-k dielectric material's excellent electrical properties in the interconnect regions while providing mechanical stress relief only where needed during singulation, thus resolving the contradiction between overall dielectric performance and local mechanical vulnerability
2Reliability
If conventional multi-level interconnect structures with bond pads in scribe lines are used, then testing functionality is achieved, but cracking occurs during the die saw process
Solution Approach 1:
The patent forms a stress relief structure in advance in the scribe line beneath the bond pad configuration, creating a protective feature before the harmful mechanical stress of die saw cutting is applied. This pre-formed structure acts as a cushion that absorbs and redistributes stress during singulation, preventing cracks from forming in the low-k dielectric material while preserving the bond pad's testing functionality
Solution Approach 2:
The stress relief structure acts as an intermediary element between the bond pad structure and the mechanical cutting process. It mediates the interaction by providing a stress-absorbing interface that protects the low-k dielectric material from the harmful effects of die saw cutting, thus allowing testing functionality to be maintained without suffering from mechanical stress-induced cracking
Data Source
AI summary
A wafer including a substrate having a plurality of integrated circuits formed above the substrate, and at least one scribe line between two of the integrated circuits. The wafer further includes a plurality of dielectric layers formed in the at least one scribe line having a process control monitor (PCM) pad structure formed therein, the PCM pad structure having: a plurality of metal pads interconnected by a plurality of conductive vias. The PCM pad further includes a plurality of contact bars in contact with a bottom-most metal pad, the contact bars extending substantially vertically from the bottom-most metal pad into the substrate. Additionally, the PCM pad includes an isolation structure substantially surrounding the plurality of contact bars to isolate the PCM pad structure.