Bismuth Oxide Thin Films via Atomic Layer Deposition
Solution Overview
Problem
Existing methods for atomic layer deposition of bismuth-containing oxide thin films face challenges in finding suitable bismuth-oxygen source chemical combinations, particularly in achieving high-temperature stability and conformality on complex structures.
Innovation Solution
The use of organic bismuth compounds with monodentate alkoxide ligands as bismuth source materials, combined with alternative oxygen sources and additional metal precursors, in an atomic layer deposition process that involves sequential pulsing and annealing at elevated temperatures to produce high-quality bismuth-containing oxide thin films with excellent conformality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bismuth source materials are used in ALD processes, then deposition can proceed at lower temperatures, but the films lack stability at higher temperatures and exhibit poor conformality
Solution Approach 1:
The patent changes the chemical parameters of the bismuth source material from conventional options to specifically identified compounds (bismuth triisopropoxide, bismuth tris(2,3-dimethyl-2-butoxy), and bismuth pentachloride) that enable stable film formation at elevated temperatures up to 450°C. This parameter change resolves the contradiction by selecting materials with appropriate thermal stability and reactivity characteristics for high-temperature ALD processes.
2Adaptability or versatility
If complex 3-D structures are used for memory capacitors, then device functionality is improved, but achieving good conformality of the ferroelectric film becomes difficult
Solution Approach 1:
The ALD process utilizes self-limiting surface reactions where each deposition cycle automatically terminates when surface sites are saturated, ensuring uniform film thickness regardless of substrate geometry. This self-service mechanism enables excellent conformality on complex 3-D capacitor structures without requiring external control adjustments, resolving the contradiction between device functionality and manufacturing precision.
3Reliability
If higher deposition temperatures are used, then film stability and quality are improved, but conventional bismuth source materials decompose or fail to react properly
Solution Approach 1:
The patent identifies and employs bismuth source materials with specific molecular structures (alkoxide and halide compounds) that maintain volatility and reactivity at elevated temperatures up to 450°C. These parameter-changed materials resist decomposition and enable proper surface reactions at temperatures where conventional sources fail, simultaneously achieving high film quality and stable high-temperature processing.
4Productivity
If silicon-containing precursors are used for ALD, then deposition efficiency is improved, but unwanted silicon incorporation occurs in the bismuth oxide films
Solution Approach 1:
The patent extracts and eliminates silicon from the precursor chemistry system entirely, replacing silicon-containing ALD precursors with the identified bismuth alkoxide and halide compounds. This extraction of the harmful silicon element prevents unwanted silicon incorporation in the films while maintaining effective deposition rates through optimized bismuth source selection and reaction conditions.
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 allows for the deposition of bismuth-containing oxide thin films with improved stability at higher temperatures and excellent conformality, suitable for applications in ferroelectric memories, superconductors, and other complex structures, while avoiding silicon incorporation and enabling the formation of binary and multicomponent oxides.
Implementation Method 1
Atomic layer deposition (ALD) refers generally to vapour deposition-type methods in which a material, typically a thin film, is deposited on a substrate from vapour phase reactants. ALD is based on sequential self-saturating surface reactions.
Implementation Method 2
Undesired gaseous molecules can be effectively expelled from the reaction chamber, for example, by keeping the gas flow speeds high with the help of an inert purging gas.
Implementation Method 3
The purging gas can be used to push the extra molecules towards a vacuum pump, which is also used for maintaining a suitable pressure in the reaction chamber.
Implementation Method 4
the bismuth containing oxide thin films are annealed at a temperature of about 400° C. or greater, more preferably about at temperatures at about 600° C. or greater and yet more preferably at about 800° C. or greater.
Data Source
AI summary
Processes are provided for producing bismuth-containing oxide thin films by atomic layer deposition. In preferred embodiments an organic bismuth compound having at least one monodentate alkoxide ligand is used as a bismuth source material. Bismuth-containing oxide thin films can be used, for example, as ferroelectric or dielectric materials in integrated circuits and as superconductor materials.