Polysilicon Film Grain Growth via Germanium Cap Layer
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Solution Overview
Problem
Existing methods for forming polysilicon films with large grain sizes are limited in effectively promoting crystal growth in amorphous silicon films, particularly when used in high aspect ratio structures like 3D NAND channel layers, where cap layer removal is challenging.
Innovation Solution
A method involving the formation of an amorphous silicon film on a substrate, followed by a cap layer of amorphous germanium or silicon germanium, where crystal nuclei are formed at a first temperature and then grown at a higher second temperature after cap layer removal, enhancing grain size through controlled heat treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a cap layer is formed on an amorphous silicon film to promote crystal growth, then grain size of polysilicon film is improved, but removal of cap layer becomes difficult in high aspect ratio structures
Solution Approach 1:
The patent changes the material composition of the cap layer by forming a silicon germanium film with controlled germanium concentration (1-30 at%) rather than using pure germanium. This parameter modification allows the cap layer to maintain its crystal growth promotion function while improving etch selectivity and removal ease in high aspect ratio structures.
Solution Approach 2:
The patent applies different germanium concentrations at different locations within the cap layer. The germanium concentration is controlled to be higher near the amorphous silicon film interface (promoting crystal growth) and lower toward the top surface (facilitating removal). This local quality variation resolves the contradiction between grain size improvement and ease of removal.
2Reliability
If crystal growth is promoted in amorphous silicon film, then polysilicon film performance is improved, but the method is limited for high aspect ratio structures like 3D NAND channel layers
Solution Approach 1:
The patent modifies the cap layer composition by incorporating germanium at controlled concentrations (1-30 at%), which enhances crystal growth promotion effectiveness while improving processability in high aspect ratio structures. This parameter change enables the method to be applied to 3D NAND channel layers and other advanced structures.
Solution Approach 2:
The patent employs a two-stage heat treatment process with different temperatures and durations. The first stage (lower temperature, longer time) promotes initial crystal nucleus formation, while the second stage (higher temperature, shorter time) accelerates grain growth. This dynamic process adaptation enables effective crystal growth in high aspect ratio structures where static single-stage processing fails.
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 results in polysilicon films with increased grain size, improving transistor mobility and performance, especially in high aspect ratio structures by promoting crystallization and grain growth from formed nuclei.
Implementation Method 1
forming crystal nuclei of a silicon in the amorphous silicon film by heating the substrate at a first temperature
Implementation Method 2
growing the crystal nuclei by heating the substrate from which the cap layer is removed, at a second temperature equal to or higher than the first temperature
Data Source
AI summary
There is provided a method of forming a polysilicon film, which includes: forming an amorphous silicon film on a substrate; forming a cap layer, which is formed of an amorphous germanium film or an amorphous silicon germanium film, on the amorphous silicon film; forming crystal nuclei of a silicon in the amorphous silicon film by heating the substrate at a first temperature; removing the cap layer after the crystal nuclei are formed; and growing the crystal nuclei by heating the substrate from which the cap layer is removed, at a second temperature equal to or higher than the first temperature.