Oxide Semiconductor Contact Stack for Heat-Stable Threshold Voltage
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Solution Overview
Problem
Oxide semiconductor transistors used in memory cells face challenges with heat treatment, leading to fluctuations in threshold voltage due to oxygen diffusion, which affects their performance and reliability.
Innovation Solution
Incorporating a barrier layer made of aluminum nitride with alternating titanium and aluminum high concentration portions, and a contact layer containing indium and tin, to prevent oxygen diffusion and reduce electrical resistance, thereby stabilizing the threshold voltage and enhancing heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxide semiconductor transistor undergoes heat treatment for memory cell fabrication, then wiring and memory cell structure are formed, but threshold voltage fluctuates due to oxygen diffusion
Solution Approach 1:
A barrier layer comprising aluminum nitride is introduced between the oxide semiconductor layer and the source/drain electrodes. This barrier layer acts as an intermediary that prevents oxygen diffusion from the electrodes into the semiconductor channel during heat treatment, thereby maintaining threshold voltage stability while allowing the heat treatment process to proceed for memory cell fabrication.
Solution Approach 2:
The barrier layer is formed as a composite structure with alternating high-concentration regions of titanium and aluminum within the aluminum nitride matrix. This composite material composition enhances the barrier properties against oxygen diffusion while maintaining structural integrity during high-temperature processing.
2Reliability
If barrier layer is added to prevent oxygen diffusion, then threshold voltage stability improves, but device structure becomes more complex
Solution Approach 1:
The barrier layer is selectively positioned only in the critical regions where oxygen diffusion would affect the channel, specifically between the oxide semiconductor layer and the source/drain electrodes. The layer has varying composition with localized high-concentration regions of titanium and aluminum, providing enhanced protection precisely where needed while minimizing overall structural complexity.
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 solution effectively reduces threshold voltage fluctuations and increases heat resistance, ensuring stable performance of oxide semiconductor transistors even after heat treatment, making them suitable for high-temperature applications like DRAM memory cells.
Implementation Method 1
A barrier layer is provided between the oxide semiconductor layer and the source electrode and between the oxide semiconductor layer and the drain electrode
Implementation Method 2
when a heat treatment is performed after the transistor is formed, oxygen in the oxide semiconductor layer on which the channel is formed diffuses to the source electrode and the drain electrode
Data Source
AI summary
A semiconductor device includes a semiconductor layer including first and second regions and a third region therebetween, a gate insulating layer between the third region and a gate electrode, first and second electrodes connected to the first and second regions in a first direction, a first conductive layer between the first region and the first electrode and/or between the second region and the second electrode. The first conductive layer includes a metal element, aluminum, and nitrogen, and has first and second portions. An atomic concentration of the metal element is higher than that of aluminum in the first portion. An atomic concentration of aluminum is higher than that of the metal element in the second portion. The device further includes a second conductive layer between the oxide semiconductor layer and the first conductive layer. The second conductive layer includes oxygen and at least one of indium, zinc, tin, and cadmium.