Oxide Semiconductor Contact Stack for Threshold Voltage and Resistance Control
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Solution Overview
Problem
The scaling-down of oxide semiconductor devices leads to short-channel effects, making it difficult to control threshold voltage (Vth) and increasing contact resistance due to reduced channel layer dimensions and contact area between the channel and source/drain, particularly when forming an oxide semiconductor layer on metal source/drain, where precursor reactions enhance contact resistance.
Innovation Solution
A semiconductor device structure incorporating a metal nitride layer between the oxide semiconductor layer and the metal oxide layer, with the metal nitride layer acting as a barrier to reduce oxygen reactivity and control the thickness of the metal oxide layer, thereby minimizing contact resistance and improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxide semiconductor devices are scaled down to increase integration density, then device integration density is improved, but contact resistance increases and threshold voltage control deteriorates
Solution Approach 1:
A metal nitride layer is introduced as an intermediary barrier layer between the metal oxide layer and the oxide semiconductor layer. This nitride layer prevents excessive oxygen diffusion from the metal oxide layer into the oxide semiconductor layer, thereby controlling the carrier concentration and threshold voltage while maintaining low contact resistance. The intermediary layer resolves the contradiction by mediating the oxygen transport between the electrode structure and the semiconductor channel.
Solution Approach 2:
The electrode structure employs a composite multi-layer configuration consisting of a metal oxide layer and a metal nitride layer stacked together. This composite structure combines the high conductivity of metal oxide with the oxygen barrier properties of metal nitride, achieving both low contact resistance and effective threshold voltage control simultaneously, thus resolving the technical contradiction.
2Volume of moving object
If the channel layer dimensions are reduced to decrease transistor size, then device size is reduced, but threshold voltage control becomes difficult
Solution Approach 1:
The invention controls the thickness and composition parameters of the metal oxide layer and metal nitride layer to precisely regulate oxygen diffusion into the oxide semiconductor layer. By adjusting these layer parameters, the carrier concentration and threshold voltage can be controlled with high precision even in scaled-down transistors, overcoming the short-channel effects that typically degrade voltage control.
Solution Approach 2:
The metal nitride layer serves as an oxygen diffusion barrier that mediates the interaction between the metal oxide electrode layer and the oxide semiconductor channel layer. This intermediary structure prevents uncontrolled oxygen penetration into the channel, maintaining stable threshold voltage characteristics despite the reduced transistor dimensions.
3Area of stationary object
If the contact area between channel layer and source/drain is reduced to minimize device footprint, then device footprint is reduced, but contact resistance increases
Solution Approach 1:
The composite electrode structure of metal oxide and metal nitride layers achieves low contact resistance through optimized material combination. The metal oxide provides high electrical conductivity for efficient charge transport, while the metal nitride ensures good adhesion to the oxide semiconductor and controls oxygen diffusion, collectively reducing contact resistance even with minimized contact area.
Solution Approach 2:
By optimizing the thickness parameters of the metal oxide and metal nitride layers, the contact resistance is minimized while maintaining a compact device footprint. The parameter optimization ensures that the contact interface properties are tuned to achieve low resistance without requiring large contact areas.
4Reliability
If a metal oxide layer is formed directly on metal source/drain to reduce contact resistance, then contact resistance is reduced, but precursor reactions increase contact resistance
Solution Approach 1:
The metal nitride layer is positioned as an intermediary between the metal oxide layer and the oxide semiconductor layer to prevent harmful precursor reactions. This nitride barrier layer stops the precursor materials from reacting with the metal source/drain during the deposition process, eliminating the source of increased contact resistance while still allowing the metal oxide layer to provide low resistance contact.
Solution Approach 2:
The metal nitride layer is formed in advance to create a protective barrier that prevents precursor reactions before they can occur. This preliminary protective action blocks the harmful chemical interactions between precursor materials and the metal electrode, thereby preventing the generation of high contact resistance regions.
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
The introduction of a metal nitride layer between the oxide semiconductor and metal oxide layers reduces contact resistance and enhances the control over threshold voltage, improving the overall performance and integration density of oxide semiconductor devices.
Implementation Method 1
a metal nitride layer between the metal oxide layer and the oxide semiconductor layer
Data Source
Figure 1
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Figure 2B
AI summary
A semiconductor device includes an oxide semiconductor layer, a first electrode and a second electrode, which are arranged apart from each other on the oxide semiconductor layer, a metal oxide layer arranged between the oxide semiconductor layer and at least one of the first electrode and the second electrode, and a metal nitride layer arranged between the metal oxide layer and the oxide semiconductor layer.