Ferroelectric Layer Formation via Pulsed MOCVD
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Solution Overview
Problem
Ferroelectric random access memory (FRAM) devices face challenges in achieving high electrical characteristics due to the formation of PZT layers through metal-organic chemical vapor deposition (MOCVD), which results in a rough surface, poor electrical characteristics, and thermal defects, while alternative methods like atomic layer deposition (ALD) are time-consuming and require suitable source gas development.
Innovation Solution
A chemical vapor deposition (CVD) process involving the repeated provision of metal-organic source gases with intervals, along with an oxidation gas, at temperatures under 650°C, to form a ferroelectric layer with a cubic or cubic-like structure, such as perovskite, reducing defects and enhancing electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a PZT layer is formed by continuous source gas provision in MOCVD, then the layer can be formed efficiently, but the surface becomes rough and electrical characteristics deteriorate
Solution Approach 1:
The patent applies periodic action by dividing the continuous source gas provision into repeated cycles of source gas provision followed by oxidation gas provision. This periodic cycling allows controlled deposition and oxidation phases, preventing surface roughness while maintaining deposition efficiency. The repeated cycles enable better surface morphology control compared to continuous provision.
2Stability of the object's composition
If PZT layer is thermally treated at high temperature for crystallization, then the layer achieves proper crystal structure, but reactive defects are generated in the lower electrode
Solution Approach 1:
The patent changes the temperature parameter from high temperature (over 650°C) to low temperature (under 650°C) thermal treatment. This parameter change allows crystallization to occur at lower temperatures, preventing reactive defects in the lower electrode while still achieving the necessary crystal structure for proper ferroelectric functionality.
3Reliability
If ALD process is used to form ferroelectric layer at low temperature, then thermal defects are reduced, but the process time increases significantly
Solution Approach 1:
The patent segments the deposition process into distinct cycles of source gas provision and oxidation gas provision, repeated multiple times. This segmentation allows low-temperature processing that reduces thermal defects while maintaining reasonable process time. The segmented approach with repeated cycles achieves better surface morphology and fewer defects compared to continuous deposition, without requiring the extended time of ALD processes.
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 improves the electrical characteristics of ferroelectric capacitors by forming a ferroelectric layer with improved data preservation and polarization maintenance, while reducing the formation time compared to ALD processes, making it suitable for mass production.
Implementation Method 1
A chemical vapor deposition (CVD) process involving the repeated provision of metal-organic source gases with intervals, along with an oxidation gas, at temperatures under 650°C, to form a ferroelectric layer
Implementation Method 2
At least two different types of metal-organic sources may be vaporized. The metal-organic source gas may be provided into a chamber
Implementation Method 3
crystallization occurs at a temperature under 650° C. to form a ferroelectric layer
Data Source
AI summary
A method of forming a ferroelectric layer is provided. A metal-organic source gas is provided into a chamber into which an oxidation gas is provided for a first time period to form ferroelectric grains on a substrate. A ferroelectric layer is formed by performing at least twice a step of providing a metal-organic source gas into the chamber during the first time period using a pulse method to grow the ferroelectric grains.