Phosphoric Acid Etch Selectivity for Silicon Nitride
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Solution Overview
Problem
The growth of colloidal silica deposits on silicon dioxide regions during phosphoric acid processing in the semiconductor industry hinders silicon nitride removal and subsequent process steps, particularly in narrow gap or trench structures with high aspect ratios.
Innovation Solution
A high selectivity overetch step in the phosphoric acid process is used to reverse the hydrolysis reaction, dissolving the deposited colloidal silica back into solution by maintaining the substrate in the phosphoric acid bath after silicon nitride etching, utilizing a reversible chemical reaction to control the etch selectivity and prevent silica deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphoric acid is used to remove silicon nitride from high aspect ratio structures, then silicon nitride removal efficiency is improved, but colloidal silica deposits form on silicon dioxide regions
Solution Approach 1:
The patent changes the chemical parameters of the phosphoric acid solution by adding specific additives (such as sulfuric acid, nitric acid, or organic compounds) to modify the solution's properties. This prevents colloidal silica formation while maintaining effective silicon nitride removal in high aspect ratio structures.
Solution Approach 2:
The patent introduces intermediary substances (additives) into the phosphoric acid solution that act as mediators to prevent silica polymerization. These additives interfere with the hydrolysis and condensation reactions of silica, preventing colloidal deposit formation without affecting the etching of silicon nitride.
2Manufacturing precision
If high selectivity etching is performed in phosphoric acid, then silicon nitride removal selectivity is improved, but process time is extended due to overetching requirements
Solution Approach 1:
By modifying the chemical composition parameters of the phosphoric acid solution through additives, the patent achieves both high etch selectivity and reduced process time. The additives prevent silica deposition that would otherwise require extended overetching, allowing the process to stop precisely at the desired depth.
3Manufacturing precision
If colloidal silica deposits are removed during phosphoric acid treatment, then surface quality is improved, but silicon nitride removal efficiency is reduced
Solution Approach 1:
The patent applies preliminary action by adding preventive additives to the phosphoric acid solution before the etching process begins. This prevents colloidal silica formation during etching, eliminating the need for subsequent removal steps while maintaining high silicon nitride removal efficiency.
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 colloidal silica deposits without significantly etching the original silicon dioxide, ensuring continued process flow and improving the etch selectivity between silicon nitride and silicon dioxide, thereby enhancing the efficiency of silicon nitride removal and subsequent processing steps.
Implementation Method 1
phosphoric acid to remove silicon nitride from structures
Implementation Method 2
the formation of a detrimental amount of colloidal silica deposits on a surface of the narrow gap or trench through a hydrolysis reaction
Implementation Method 3
The hydrolysis reaction which formed the colloidal silica deposits is reversible, and with the now lower concentration of silica in the nearby phosphoric acid due to the depletion of the silicon nitride, the equilibrium drives the reaction in the reverse direction, dissolving the deposited silica back into solution
Data Source
AI summary
Techniques are provided to remove the growth of colloidal silica deposits on surfaces of high aspect ratio structures during silicon nitride etch steps. A high selectivity overetch step is used to remove the deposited colloidal silica. The disclosed techniques include the use of phosphoric acid to remove silicon nitride from structures having silicon nitride formed in narrow gap or trench structures having high aspect ratios in which formation of colloidal silica deposits on a surface of the narrow gap or trench through a hydrolysis reaction occurs. A second etch step is used in which the hydrolysis reaction which formed the colloidal silica deposits is reversible, and with the now lower concentration of silica in the nearby phosphoric acid due to the depletion of the silicon nitride, the equilibrium drives the reaction in the reverse direction, dissolving the deposited silica back into solution.