Silicon Etching Composition for Crystal Plane Isotropy
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Solution Overview
Problem
Current silicon etching solutions face challenges in achieving crystal plane isotropy and high etching selectivity ratio of silicon to silicon oxide films, particularly in producing semiconductor devices like 3D NAND and Fin-FET structures, where alkaline etching solutions cause surface irregularities and acid-based solutions lack sufficient selectivity.
Innovation Solution
A silicon etching solution containing quaternary ammonium hydroxide, an oxidizing agent, and an acid group-containing compound with a specific pKa range (3.5 or more and 13 or less) is developed, which selectively reduces the etching rate on the (110) plane, improving crystal plane isotropy and etching selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an alkaline etching solution is used to achieve high etching selectivity ratio of silicon to silicon oxide film, then the etching selectivity is improved, but crystal plane anisotropy occurs causing surface irregularities and pyramid-shaped hillocks
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching solution by adding specific organic compounds (carboxylic acid with pKa 3.5-13 or sulfuric acid at controlled concentrations) to the alkaline etching solution. This parameter change suppresses crystal plane anisotropy while preserving the high etching selectivity ratio of the alkaline solution, achieving both smooth surfaces and selective etching.
2Shape
If an acid-based etching solution (hydrofluoric acid-nitric acid) is used to achieve crystal plane isotropy, then the surface smoothness is improved, but the etching selectivity ratio of silicon to silicon oxide film becomes low
Solution Approach 1:
The patent merges the advantages of both alkaline and acid-based etching solutions by combining the alkaline etching solution (which provides high selectivity) with specific organic acid compounds (which suppress crystal plane anisotropy). This hybrid approach achieves both high etching selectivity ratio and crystal plane isotropy, resolving the contradiction between the two requirements.
3Manufacturing precision
If the concentration of oxidizing agent is increased to reduce etching rate on (100) plane, then the etching rate equivalence between (100) and (111) planes is achieved, but the etching rate on (110) plane cannot be sufficiently reduced
Solution Approach 1:
The patent introduces a new parameter (organic acid compound concentration) to the etching solution composition to specifically control the etching rate of the (110) plane. By adjusting the concentration of carboxylic acid or sulfuric acid, the etching rate ratio between (110) and (111) planes can be controlled within 0.5-2.0, achieving comprehensive crystal plane isotropy that cannot be achieved by oxidizing agent concentration 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
The solution achieves low crystal plane anisotropy and high etching selectivity ratio of silicon to silicon oxide films, enhancing the smoothness and accuracy of silicon etching processes for semiconductor manufacturing.
Implementation Method 1
an alkaline etching solution which is an alkaline aqueous solution usually exhibits crystal plane anisotropy in etching with respect to crystalline silicon
Implementation Method 2
an acid group-containing compound having at least one pKa of 3.5 or more and 13 or less
Implementation Method 3
an oxidizing agent
Data Source
AI summary
In etching of a single crystal silicon substrate having a Si crystal plane ((100) plane, (110) plane, and (111) plane) as a main plane, an etching rate on the (110) plane cannot be sufficiently reduced, and there is room for improvement in an etching rate ratio between the (110) plane and the (111) plane. An object of the present invention is to provide a silicon etching solution having excellent crystal plane isotropy in silicon etching and having a high etching selectivity ratio of silicon to a silicon oxide film.The problem is solved by a silicon etching solution containing: an acid group-containing compound having at least one acid group selected from the group consisting of a carboxy group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group, and having pKa of 3.5 or more and 13 or less; a quaternary ammonium hydroxide; an oxidizing agent; and water.