L-Shaped Source/Drain Isolation Structure for TDDB-Resistant Contacts
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Solution Overview
Problem
Conventional semiconductor manufacturing processes face challenges in forming adequate isolation between metal contacts and source/drain features due to aggressive scaling, leading to electrical shorting and time-dependent dielectric breakdown, especially with conventional dielectric layers and hardmasks that are prone to peeling during processing.
Innovation Solution
The implementation of a more robust L-shaped dielectric isolation structure using alternative materials with higher breakdown field strength, formed using a thicker hardmask that does not peel off during etching, and an L-shaped configuration to increase spacing between metal layers and source/drain regions, ensuring electrical isolation and improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dielectric layers are used for isolation, then manufacturing simplicity is maintained, but electrical isolation reliability deteriorates due to time-dependent dielectric breakdown
Solution Approach 1:
The isolation structure is divided into multiple dielectric layers (first dielectric layer and second dielectric layer) with different material compositions. The first dielectric layer has higher breakdown field strength while the second dielectric layer provides additional isolation, segmenting the isolation function to achieve superior reliability without excessive complexity.
Solution Approach 2:
The patent employs composite dielectric materials with different properties in different layers. The first dielectric layer uses materials with higher breakdown field strength (such as silicon nitride or silicon oxynitride) while the second layer may use different dielectric materials, creating a composite structure that leverages the strengths of each material for optimal isolation performance.
2Manufacturing precision
If aggressively-scaled cut metal region is used, then manufacturing precision is improved, but electrical isolation deteriorates leading to bridging between metal contact layer and source/drain feature
Solution Approach 1:
The isolation structure extends in the vertical dimension with multiple dielectric layers stacked above the substrate. This vertical stacking provides additional isolation distance and pathways, compensating for the reduced lateral spacing in aggressively-scaled cut metal regions and preventing electrical bridging.
Solution Approach 2:
The first dielectric layer with higher breakdown field strength is formed preliminarily before the second dielectric layer and metal contact layers. This preliminary high-strength isolation layer is positioned to prevent bridging between the metal contact layer and source/drain feature, establishing robust electrical isolation before subsequent processing steps.
3Ease of manufacture
If conventional hardmask is used, then ease of manufacture is maintained, but process reliability deteriorates due to hardmask peeling during etching
Solution Approach 1:
The hardmask structure is formed as a composite of multiple layers including a first hardmask layer and a second hardmask layer with different material compositions. This composite hardmask structure improves adhesion to the underlying dielectric layers and prevents peeling during etching processes while remaining compatible with standard manufacturing techniques.
Solution Approach 2:
Different regions of the hardmask structure have different material properties optimized for their specific functions. The first hardmask layer may have properties optimized for adhesion and pattern definition, while the second hardmask layer has properties optimized for etch resistance, creating local quality variations that prevent peeling throughout the structure.
4Productivity
If dielectric layer thickness is reduced for scaling, then device density is improved, but time-dependent dielectric breakdown susceptibility increases
Solution Approach 1:
The multi-layer dielectric structure uses materials with different breakdown field strengths in series configuration. The first dielectric layer with higher breakdown field strength compensates for the reduced overall thickness, maintaining adequate TDDB resistance while allowing the isolation structure to occupy less vertical space for improved device density.
Data Source
AI summary
A method and structure directed to providing a source/drain isolation structure includes providing a device having a first source/drain region adjacent to a second source/drain region. A masking layer is deposited between the first and second source/drain regions and over an exposed first part of the second source/drain region. After depositing the masking layer, a first portion of an ILD layer disposed on either side of the masking layer is etched, without substantial etching of the masking layer, to expose a second part of the second source/drain region and to expose the first source/drain region. After etching the first portion of the ILD layer, the masking layer is etched to form an L-shaped masking layer. After forming the L-shaped masking layer, a first metal layer is formed over the exposed first source/drain region and a second metal layer is formed over the exposed second part of the second source/drain region.