Selective Tungsten Contact Plugs for Low-Resistance Gate And S/D Contacts
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Solution Overview
Problem
Conventional wafer fabrication techniques face challenges in creating effective contact plugs due to the inability of selective tungsten to directly grow on metal gate surfaces like TiN or TiAlC, leading to increased resistance and inefficiencies in device performance.
Innovation Solution
The implementation of a transistor structure with a metal gate, a dielectric layer, and a metal cap over the gate, allowing for direct contact of tungsten with the cap, eliminating the need for a barrier layer and enabling self-aligned tungsten contact plugs that reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a barrier layer is inserted between tungsten contact and metal gate, then diffusion prevention is achieved, but contact resistance increases
Solution Approach 1:
The invention extracts and removes the barrier layer from the gate contact structure, allowing tungsten to directly contact the metal gate. This eliminates the high-resistance barrier layer while diffusion prevention is maintained through alternative means in the fabrication process.
Solution Approach 2:
The invention introduces an intermediary approach by using selective tungsten deposition that targets specific regions. The tungsten is deposited selectively on the metal gate surface through controlled deposition processes, creating a direct contact interface without requiring a barrier layer mediator.
2Ease of manufacture
If conventional CVD and etching are used to create gate contact, then contact can be formed, but manufacturing complexity and resistance increase
Solution Approach 1:
The invention employs self-aligned selective tungsten deposition where the tungsten automatically deposits only on the metal gate regions through surface selectivity. This self-service mechanism eliminates the need for separate etching and alignment steps, simplifying the fabrication process while maintaining precision.
Solution Approach 2:
The invention replaces the mechanical etching process with a chemical deposition process. Instead of physically removing material to create contacts, selective tungsten deposition chemically forms the contact structures directly on the metal gate, reducing fabrication complexity.
3Productivity
If metal gate size is reduced to increase density, then device integration improves, but contact area with barrier layer decreases, increasing resistance
Solution Approach 1:
By removing the barrier layer entirely from the gate contact interface, the invention eliminates the contact resistance problem that worsens with smaller gate sizes. The direct tungsten-to-metal-gate contact ensures adequate contact area even when gates are miniaturized for higher integration density.
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 results in reduced gate and source/drain contact resistances, enhancing device performance by allowing tungsten to be deposited directly on the metal cap without a barrier layer, thus improving the overall efficiency of the contact plugs.
Implementation Method 1
Selective tungsten cannot directly grow on metal gate surfaces such as TiN or TiAlC, which means that the tungsten gate contact cannot be a selective tungsten structure but must instead be created using chemical vapor deposition (CVD) and etching.
Implementation Method 2
a dielectric layer at least partially surrounding the metal gate
Implementation Method 3
a metal cap disposed over a portion of the metal gate that is not surrounded by the dielectric layer
Data Source
AI summary
In an aspect, a transistor comprises a gate structure having a metal gate, a dielectric layer at least partially surrounding the metal gate, a metal cap over a portion of the metal gate that is not surrounded by the dielectric layer, and a gate contact comprising tungsten in direct contact with the metal cap. In another aspect, a transistor comprises source, drain, and channel regions, a gate structure comprising a metal gate between gate spacers above the channel region, and a source or drain (S/D) contact structure. The S/D contact structure comprises an S/D barrier layer above at least a portion of the source or drain region and in direct contact with a gate spacer, and an S/D contact, comprising a first portion above the S/D barrier layer; and a second portion comprising tungsten, above the first portion.