BEOL Interconnect Via Shrink via Subtractive Etch

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Solution Overview

Problem

In semiconductor interconnect technology, existing BEOL processes face challenges with large via lithographic critical dimension (CD) limitations and issues such as via chamfering and bowing, which affect the design and reliability of interconnect structures.

Innovation Solution

A method is developed to form BEOL interconnect structures by creating a via metal layer, shrinking it through a subtractive etch to relax critical dimensions, ensuring a straight profile and maximizing metal volume, and performing top trench metallization to eliminate reactive ion etch lag and metallization voids.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a large via lithographic critical dimension is used, then the via size is increased, but the design ground rule is broken when two vias are spaced closely together

Engineering Contradiction:

Improvevia sizeVSAvoiddesign ground rule compliance

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by forming a mandrel structure before the via metal, then using it to define the via opening dimensions. The mandrel is formed with a first dimension, and the via metal is deposited around it, allowing the final via dimensions to be controlled by the mandrel rather than direct lithography, thus achieving small effective via dimensions while maintaining design rules.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The via formation process is segmented into multiple steps: forming a mandrel, depositing via metal around the mandrel, and selectively removing the mandrel. This segmentation allows independent control of each dimension and step, enabling precise via dimensions that comply with design ground rules while maximizing metal volume.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If conventional via formation processes are used, then via openings are formed, but via chamfering and bowing occur

Engineering Contradiction:

Improvevia formationVSAvoidvia profile straightness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The mandrel is formed preliminarily with a straight profile, and the via metal is deposited around it in a controlled manner. This preliminary structure guides the via metal formation, ensuring straight via profiles without chamfering or bowing that typically occur in conventional direct via formation processes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The mandrel acts as an intermediary structure that mediates between the lithography step and the final via formation. It provides a template that ensures straight via profiles, and its selective removal leaves clean via openings without the profile defects (chamfering and bowing) that occur in conventional processes.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If via metal volume is maximized, then resistance-capacitance performance improves, but via opening size must be increased

Engineering Contradiction:

Improveresistance-capacitance performanceVSAvoiddesign ground rule compliance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent transitions from controlling via dimensions in the planar lithographic dimension to controlling them in the vertical dimension through the mandrel height and metal deposition thickness. This dimensional change allows maximizing metal volume for improved R/C performance while maintaining small planar footprints that comply with design ground rules.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The mandrel is formed preliminarily to define the via opening, allowing subsequent metal deposition to maximize volume within the constrained opening. This preliminary structuring enables optimal metal volume for R/C performance without increasing the via opening size beyond design rule limits.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach improves resistance-capacitance (R/C) performance by avoiding via chamfering and bowing, ensuring reliable and efficient interconnect structures with enhanced metal volume and reduced void issues.

Implementation Method 1

a via metal layer is created by a first metallization process and thereafter shrunk by a subtractive etch

Methodology Applied

Scientific EffectEtching:

Implementation Method 2

A first interconnect dielectric material layer is then formed, by deposition and planarization, laterally adjacent to the upper portion of each of the first metal-containing structures

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Data Source

PatentUS11398409B2Method of forming a BEOL interconnect structure using a subtractive metal via first process

Publication Date: 2022.07.26 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method of forming a BEOL interconnect structure having improved resistance-capacitance is provided in which a via metal layer is created by a first metallization process and thereafter shrunk by a subtractive etch; these steps relax the critical dimension, ensure a via straight profile, avoid via chamfering and bowing, and maximize metal volume. Top trench metallization is then performed above the via metal layer; this step eliminates reactive ion etch lag and ensures no metallization void issues.