PCM Pad Interconnect Structure for Crack Resistance

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Solution Overview

Problem

Conventional multi-level interconnect structures in semiconductor ICs are susceptible to cracking during the die saw process due to high metal density in bond pads, leading to mechanical stress and failure, especially when using low-k dielectric materials.

Innovation Solution

The introduction of a conductive structure that connects the topmost PCM pad to a device under test with a smaller aluminum block or contact, reducing the cumulative metal density and minimizing the area of the aluminum pad, thereby reducing the likelihood of cracking during the die saw process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If large bond pads are used for WAT, then probe access and parallel testing capability are improved, but mechanical stress and cracking during die saw process increase

Engineering Contradiction:

Improveprobe accessVSAvoidcracking resistance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The bond pad structure is segmented into multiple metal layers (first through fourth metal layers) with dielectric material between them. This segmentation distributes the metal density across different levels, reducing the cumulative metal density in any single plane and thereby reducing mechanical stress during die sawing while maintaining adequate probe access area.

Inventive Principle:

Principle #1Segmentation

2Reliability

If high metal density is used in bond pads, then electrical connectivity and testing capability are improved, but mechanical stress and failure during die sawing increase

Engineering Contradiction:

Improveelectrical connectivityVSAvoidmechanical stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The metal conductive structures are distributed across multiple vertical layers (first through fourth metal layers) separated by dielectric material. This dimensional distribution moves the problem from a two-dimensional high-density plane to a three-dimensional distributed structure, maintaining total metal volume for electrical connectivity while reducing the metal density in any single horizontal plane, thereby reducing mechanical stress during die sawing.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Speed

If low-k dielectric material is used, then RC delay and interconnect performance are improved, but brittleness and susceptibility to cracking increase

Engineering Contradiction:

Improvesignal transmission speedVSAvoidmechanical strength

Core Design Contradiction:

SpeedVSStrength

Solution Approach 1:

Dielectric material is placed between adjacent metal layers to electrically isolate them and provide mechanical support. This dielectric cushioning layer prevents direct metal-to-metal contact and distributes mechanical stresses, protecting the brittle low-k dielectric material from cracking during die sawing while maintaining the low RC delay performance enabled by using low-k material.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS7679195B2PAD structure and method of testing

Publication Date: 2010.03.16 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An interconnect structure includes: a plurality of dielectric layers having aligned process control monitor (PCM) pads, and a conductive structure above a topmost one of the PCM pads. The conductive structure electrically connects the topmost PCM pad to a device under test above a level of the topmost PCM pad. The conductive structure is sized and shaped so as to leave a majority portion of the topmost PCM pad exposed for access by a test probe.