Polysilicon Surface Treatment for Thin-Film Transistors
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Solution Overview
Problem
Conventional chemical etching techniques fail to adequately remove contaminants and achieve a smooth surface at the nanometer level on polysilicon and amorphous silicon substrates with non-uniform crystal surfaces, leading to rough surfaces and incomplete removal of metal catalysts.
Innovation Solution
A method involving the formation of an oxide coating on the semiconductor surface using an oxidizing solution, such as nitric acid, followed by chemical etching to remove the coating, which efficiently reduces metal catalysts and contaminants, and smooths the surface to the nanometer level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional chemical etching techniques are used to remove natural oxide films, then etching progresses from terraces causing surface roughness, but the ability to remove contaminants and achieve atomic-level smoothness is insufficient
Solution Approach 1:
The invention changes the chemical parameters of the etching solution by using a specific composition containing ammonium fluoride, hydrofluoric acid, and sulfuric acid in controlled ratios, along with controlling temperature and processing time parameters to achieve uniform etching without terrace-dependent roughness
Solution Approach 2:
The invention replaces conventional mechanical polishing methods with a chemically-controlled etching process that uses solution composition and temperature control to achieve atomic-level smooth surfaces without physical contact or mechanical forces that cause roughness
2Reliability
If ammonium fluoride aqueous solution is used for etching, then natural oxide films are removed effectively, but contaminants and metal catalysts are not sufficiently removed
Solution Approach 1:
The invention uses a composite chemical solution system combining ammonium fluoride, hydrofluoric acid, and sulfuric acid, where each component contributes to different aspects of surface treatment: ammonium fluoride for oxide removal, hydrofluoric acid for contaminant dissolution, and sulfuric acid for enhanced cleaning action, achieving comprehensive surface purification
Solution Approach 2:
The invention introduces sulfuric acid as an intermediary substance that enhances the overall cleaning effectiveness by working synergistically with ammonium fluoride and hydrofluoric acid, facilitating the removal of metal catalysts and organic contaminants that neither reagent could remove alone
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 effectively removes metal catalysts and contaminants, improving the surface smoothness and performance of semiconductor apparatus by reducing surface roughness and enhancing mobility and reducing leakage current density.
Implementation Method 1
bringing the semiconductor substrate into contact with an oxidizing solution or gas to form an oxide film including at least a metal catalyst or a contaminant on the surface thereof
Implementation Method 2
removal of the oxide film (removal by chemical etching)
Data Source
AI summary
Disclosed is a thin-film transistor (10) manufacturing method that includes a process for forming a nitrate film (12x) that includes residual nickel (22) on a surface thereof, by bringing a nitric acid solution into contact with a polysilicon layer (11x); and a process for removing the nitrate film (12x) that includes residual nickel (22) from the polysilicon layer (11x) surface. With this surface treatment process, a polysilicon layer (11) with reduced concentration of a surface residual nickel (22) is provided, and a thin-film transistor (10) having excellent surface smoothness is attained.