Test Pad Structure with Lateral Extensions for Mask Reuse

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Solution Overview

Problem

Conventional test pad structures in semiconductor manufacturing lead to electrical shorting when reusing mask sets for different metal levels, limiting the ability to test optional metal levels effectively due to parallel structures being electrically connected.

Innovation Solution

A two-dimensional array of test pads with lateral extension portions that enable electrical connections between different metal levels, allowing for the reuse of the same mask set to form test pad structures at various levels, ensuring each test pad is electrically isolated from directly underlying pads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the same mask set is reused for multiple metal levels, then mask cost is reduced and productivity is improved, but electrical shorting occurs between parallel test structures at different levels

Engineering Contradiction:

Improvemask set reuse efficiencyVSAvoidelectrical isolation between test structures

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces a lateral dimension to the test pad structure by adding lateral extension portions that extend in the plane of the mask pattern. This allows test pads at different vertical levels to be electrically connected through lateral extensions without creating vertical short circuits, enabling mask reuse while maintaining electrical isolation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The lateral extension portions act as intermediary conductive elements that bridge test pads at different levels. These extensions serve as mediators that allow electrical connections to be established laterally rather than vertically, preventing direct vertical short circuits while enabling indirect electrical connectivity for testing purposes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If conventional test pad structures are used with mask reuse, then manufacturing cost is reduced, but testing capability at optional metal levels is compromised due to parallel electrical shorting

Engineering Contradiction:

Improvemask set cost efficiencyVSAvoidtesting capability at multiple levels

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The test pad structure is segmented into multiple functional components: the original test pad, lateral extension portions, and connection paths. This segmentation allows the test pad to serve multiple levels independently while maintaining electrical isolation through the segmented lateral connections, enabling versatile testing across different metal levels with a single mask set.

Inventive Principle:

Principle #1Segmentation

3Reliability

If additional mask sets are fabricated for each metal level, then testing capability at all levels is ensured, but development cost increases significantly

Engineering Contradiction:

Improvetesting coverage at all metal levelsVSAvoidnumber of mask sets required

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The modified test pad structure with lateral extension portions creates a universal design that can be used across multiple metal levels. The same mask set can generate test pads at different levels, and the lateral extensions provide the necessary electrical connectivity for testing at any level, making the mask set multi-functional and eliminating the need for separate masks for each level.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS9348216B2Test pad structure for reuse of interconnect level masks

Publication Date: 2016.05.24 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A test pad structure in a back-end-of-line metal interconnect structure is formed by repeated use of the same mask set, which includes a first line level mask, a first via level mask, a second line level mask, and a second via level mask. The test pad structure includes a two-dimensional array of test pads such that a first row is connected to a device macro structure in the same level, and test pads in another row are electrically connected to another device macro structure of the same design at an underlying level. The lateral shifting of electrical connection among pads located at different levels is enabled by lateral extension portions that protrude from pads and via structures that contact the lateral extension portions. This test pad structure includes more levels of testable metal interconnect structure than the number of used lithographic masks.