Self-Aligned Metal Gate Protective Cap for Transistor Short Prevention
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Solution Overview
Problem
As transistor pitch scaling increases, the formation of unwanted electrical connections (shorts) between source/drain terminals and the gate becomes unavoidable due to limitations in registration and critical dimension control in existing manufacturing techniques, especially at gate dimensions below 35 nanometers.
Innovation Solution
A method is developed to form a self-aligned protective cap on aluminum and other metal gate transistors using a sacrificial capping layer, which involves depositing a selective tungsten capping layer, forming an insulating layer, removing the capping layer to create a trench, and filling it with an insulating material to act as an etch stop layer, thereby preventing shorts and allowing for larger contact registration margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pitch scaling is increased to increase transistor density, then transistor density is improved, but registration control and critical dimension control deteriorate, leading to unwanted electrical connections between source/drain terminals and gate
Solution Approach 1:
A protective cap structure is formed over the gate electrode before source/drain contact formation. This preliminary protective structure prevents unwanted electrical connections between source/drain terminals and the gate, allowing pitch scaling to continue without sacrificing manufacturing precision.
Solution Approach 2:
The protective cap acts as an intermediary barrier between the gate electrode and source/drain contacts. This intermediate structure isolates the gate from potential short circuits while allowing the underlying transistor density improvements to be maintained.
2Productivity
If pitch scaling is increased to increase transistor density, then transistor density is improved, but critical dimension control deteriorates, leading to unwanted electrical connections between source/drain terminals and gate
Solution Approach 1:
The protective cap is formed in advance over the gate electrode, establishing a predefined boundary that protects against critical dimension variations. This allows continued scaling while maintaining control over electrical connection integrity.
Solution Approach 2:
The protective cap structure provides a buffer or cushion against potential manufacturing variations. By having this protective layer in place beforehand, the structure tolerates critical dimension control deterioration without resulting in unwanted electrical connections.
3Reliability
If protective structures are added to prevent shorts, then reliability is improved, but device complexity increases
Solution Approach 1:
The protective cap structure applies protection only where needed - specifically over the gate electrode region where short prevention is critical. This localized approach improves reliability without unnecessarily increasing overall device complexity across the entire transistor structure.
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 solution enables the formation of robust self-aligned protective caps on metal gate transistors even at dimensions below 35 nanometers, reducing contact resistance and preventing unwanted electrical connections, thus maintaining transistor density and performance.
Implementation Method 1
selectively removing the sacrificial capping layer to form a trench aligned to the gate metal in the electrically insulating layer
Implementation Method 2
filling the trench with an electrically insulating material to form an electrically insulating cap centered on the gate metal
Data Source
AI summary
A method of manufacturing a metal gate structure includes providing a substrate (110) having formed thereon a gate dielectric (120), a work function metal (130) adjacent to the gate dielectric, and a gate metal (140) adjacent to the work function metal; selectively forming a sacrificial capping layer (310) centered over the gate metal; forming an electrically insulating layer (161) over the sacrificial capping layer such that the electrically insulating layer at least partially surrounds the sacrificial capping layer; selectively removing the sacrificial capping layer in order to form a trench (410) aligned to the gate metal in the electrically insulating layer; and filling the trench with an electrically insulating material in order to form an electrically insulating cap (150) centered on the gate metal.