Multilayer Passivation for Metal Oxide TFT Hydrogen Barrier
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Solution Overview
Problem
Metal oxide semiconductors, such as zinc oxide and indium gallium zinc oxide, are susceptible to instability and variability due to interactions with hydrogen and water, leading to inconsistent performance in thin film transistors (TFTs).
Innovation Solution
A multi-layer approach is employed, where a dense etch stop or passivation layer is formed over a less dense back channel protection layer, using hydrogen-containing precursors to create a barrier that prevents hydrogen from reaching the semiconductor layer, and the layers are deposited using processes like PECVD with specific conditions to ensure stability and repeatability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer passivation or etch stop layer is used, then the device structure is simpler, but hydrogen can penetrate through to the semiconductor layer causing instability
Solution Approach 1:
The passivation or etch stop function is divided into multiple layers with different compositions and densities. The first layer provides initial protection while the second layer acts as a dense barrier against hydrogen penetration, collectively solving the reliability issue without requiring excessive complexity
Solution Approach 2:
The patent uses composite material structure where layers of different materials (e.g., silicon nitride, silicon oxide, silicon oxynitride) are combined to achieve both protection function and hydrogen barrier properties, resolving the contradiction between structural simplicity and device reliability
2Reliability
If a dense capping layer is formed to prevent hydrogen penetration, then semiconductor layer stability improves, but manufacturing complexity increases
Solution Approach 1:
The dense barrier function is segmented across multiple layers rather than requiring a single ultra-dense layer, which would be difficult to manufacture. Each layer contributes to the overall hydrogen barrier effectiveness while maintaining manufacturability
Solution Approach 2:
The patent varies composition parameters and deposition conditions between layers to achieve different density levels. The second layer uses specific processing conditions to achieve high density for hydrogen blocking, while the first layer has different properties for other functions
3Ease of manufacture
If hydrogen-containing precursors are used for deposition, then manufacturing cost is reduced, but hydrogen contamination of the semiconductor layer increases
Solution Approach 1:
The first passivation or etch stop layer acts as an intermediary between the deposition process and the semiconductor layer. It allows the use of hydrogen-containing precursors during deposition while preventing hydrogen from reaching the semiconductor layer, thus enabling cost-effective manufacturing without contamination
Solution Approach 2:
The first layer is deposited first to create a protective barrier before the semiconductor layer is exposed to hydrogen-containing environments. This preliminary protective action prevents hydrogen contamination while allowing the use of economical hydrogen-containing deposition 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 method enhances the stability and repeatability of metal oxide TFTs by reducing hydrogen penetration, resulting in consistent performance and improved manufacturing yield by forming a dense capping layer with few pinholes.
Implementation Method 1
The etch stop layer and the passivation layer can be deposited by plasma enhanced chemical vapor deposition (PECVD) from a silane, oxygen and nitrogen containing precursor mixture
Implementation Method 2
The capping layer can be sufficiently dense so that few pin holes are present and thus, hydrogen may not pass through to the semiconductor layer
Data Source
AI summary
The present invention generally relates to TFTs and methods for fabricating TFTs. For either back channel etch TFTs or for etch stop TFTs, multiple layers for the passivation layer or the etch stop layers permits a very dense capping layer to be formed over a less dense back channel protection layer. The capping layer can be sufficiently dense so that few pin holes are present and thus, hydrogen may not pass through to the semiconductor layer. As such, hydrogen containing precursors may be used for the capping layer deposition.