ALD Al2O3/SiO2 Stack Hydrogen Confinement for PV Passivation
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Solution Overview
Problem
Current methods for depositing thin films in photovoltaic technologies, such as SiO2 and Al2O3, face challenges in achieving homogeneous layers with effective passivation, as high temperatures are not compatible with manufacturing processes, and hydrogen diffusion issues lead to decreased passivation efficiency over time.
Innovation Solution
A method involving Atomic Layer Deposition (ALD) of Al2O3/SiO2 stacks using specific silicon and aluminum precursors, where the Al2O3 layer acts as a diffusion barrier to confine hydrogen, allowing for hydrogen-rich layers with precise thickness control and reduced hydrogen desorption, enabling efficient passivation of both n-type and p-type substrates without the need for hydrogen in the annealing atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet thermal oxidation or dry oxidation is used to grow high quality SiO2 layer, then passivation properties are improved, but manufacturing cost and process complexity increase due to high temperature requirements (850°C-1000°C) that are not compatible with photovoltaic device manufacturing
Solution Approach 1:
The invention changes the deposition method from thermal oxidation (requiring 850°C-1000°C) to Atomic Layer Deposition (ALD) operating at lower temperatures (typically 200°C-400°C), thereby achieving good passivation properties at temperatures compatible with photovoltaic device manufacturing
Solution Approach 2:
The invention replaces the thermal oxidation process with Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD) methods, substituting a thermally-driven process with chemically-driven deposition that occurs at lower temperatures while still achieving effective passivation
2Productivity
If CVD method is used to deposit SiO2 from TEOS, then deposition speed is improved, but film homogeneity and passivation quality deteriorate due to difficulty in controlling thickness
Solution Approach 1:
The invention segments the deposition process into sequential atomic layers through ALD, where each cycle deposits a precise monolayer thickness, enabling excellent thickness control while maintaining reasonable deposition speeds through process optimization
Solution Approach 2:
The ALD process incorporates self-limiting surface reactions that automatically control the deposition rate and thickness, providing inherent feedback mechanisms that ensure uniform film growth across the substrate without requiring complex real-time thickness monitoring
3Reliability
If annealing is performed under hydrogen at 850°C to activate passivation, then hydrogen diffusion and dangling bonds passivation are improved, but hydrogen loss from the surface occurs at temperatures over 900°C, reducing passivation properties over time
Solution Approach 1:
The invention incorporates hydrogen-rich precursors during the ALD deposition process itself, pre-loading the SiO2 layer with hydrogen before annealing, which reduces the need for high-temperature hydrogen diffusion and minimizes hydrogen loss during subsequent thermal processing
Solution Approach 2:
The SiO2 layer serves its own passivation needs by being deposited with inherent hydrogen content from the precursors, reducing dependence on external hydrogen supply from N2-H2 atmosphere and minimizing hydrogen loss mechanisms
4Reliability
If ALD is used to deposit homogeneous layers with good passivation, then passivation quality is improved, but deposition time and process complexity increase compared to CVD
Solution Approach 1:
The ALD process uses periodic pulsing of precursor and reactant gases in cyclic sequences, allowing each step to complete its self-limiting surface reaction before the next step begins, achieving uniform coverage and excellent passivation while maintaining reasonable throughput through optimized cycle frequencies
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 method achieves stable and efficient passivation with low metallic contamination, maintaining high chemical passivation capabilities over time, and allows for precise control of layer thickness, enhancing the performance and longevity of photovoltaic cells.
Implementation Method 1
injecting into the reaction chamber, through an ALD process, at least one silicon containing compound... injecting into the reaction chamber an oxygen source... reacting at a temperature comprised between 20°C and 400°C... in order to obtain the SiO2 layer deposited onto the substrate
Implementation Method 2
the Al2O3 layer acts as a diffusion barrier to confine hydrogen... no hydrogen desorption is observed
Implementation Method 3
hydrogen radicals are integrated into the film during deposition... hydrogen to passivate the dandling bond... hydrogen in the layer will chemically passivate the dangling bonds at the surface of the interface and in the bulk of the silicon
Implementation Method 4
annealing the Al2O3/SiO2 stack issued of step g) at a temperature comprised between 400°C and 900°C, preferably between 400°C and 425°C, in an atmosphere of nitrogen... the annealing step is performed under a nitrogen atmosphere with an appropriate hydrogen concentration to obtain a more pronounced driving force for the hydrogen to passivate the dandling bond
Data Source
AI summary
A method of forming an Al 2 O 3 /SiO 2 stack comprising successively the steps of: a) providing a substrate into a reaction chamber; b) injecting into the reaction chamber, through an ALD process, at least one silicon containing compound selected from the group consisting of: BDEAS Bis(diethylamino)silane SiH 2 (NEt 2 ) 2 , BDMAS Bis(dimethylamino)silane SiH 2 (NMe 2 ) 2 , BEMAS Bis(ethylmethylamino)silane SiH 2 (NEtMe) 2 , DIPAS (Di-isopropylamido)silane SiH 3 (NiPr 2 ), DTBAS (Di tert-butylamido)silane SiH 3 (NtBu 2 ); c) injecting into the reaction chamber an oxygen source selected in the list: oxygen, ozone, oxygen plasma, water, CO 2 plasma, N 2 O plasma; d) reacting at a temperature comprised between 20°C and 400°C, preferably lower or equal to 250°C, into the reaction chamber at least one of the silicon containing compounds and the oxygen source in order to obtain the SiO 2 layer deposited onto the substrate; e) injecting on said silicon oxide film, through an ALD process, at least one aluminum containing compound selected in the list: Al(Me) 3 , Al(Et) 3 , Al(Me) 2 (OiPr), Al(Me) 2 (NMe) 2 or Al(Me) 2 (NEt) 2 ; f) injecting the oxygen source as defined in step c); g) reacting at a temperature comprised between 20°C and 400°C, preferably lower or equal to 250°C, into the reaction chamber at least one of the aluminium containing compounds and the oxygen source in order to obtain the Al 2 O 3 layer deposited onto the SiO 2 layer issued of step d).