TMAH Etchant Composition for DRAM Capacitor Fabrication
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Solution Overview
Problem
Conventional DRAM capacitor fabrication processes face limitations due to low etching selectivity of poly-Si to TiN, leading to restricted capacitor height, potential destruction of TiN electrodes, and silicon residuals causing electrical shorts.
Innovation Solution
A liquid etchant composition comprising tetramethylammonium hydroxide (TMAH), hydroxylamine, or a metal corrosion inhibitor, and water is used to enhance the etching selectivity of silicon to TiN, preventing electrode damage and residual silicon formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an aqueous solution of TMAH is used as an etchant to wet-etch and remove the poly-Si layer, then the poly-Si layer can be removed, but the etching selectivity of poly-Si to TiN is limited, which restricts capacitor height and may destroy TiN electrode structures
Solution Approach 1:
The patent modifies the chemical composition parameters of the etchant by adding hydroxylamine and metal corrosion inhibitors to the TMAH solution. This changes the etching chemistry to achieve higher selectivity (poly-Si etching rate much faster than TiN), enabling deeper capacitors while preserving TiN electrode integrity. The additive concentrations are optimized to maximize selectivity while minimizing TiN corrosion.
Solution Approach 2:
Hydroxylamine acts as an intermediary substance that enhances the etching action on poly-Si while being relatively benign to TiN. The metal corrosion inhibitors serve as intermediaries that specifically protect TiN surfaces from excessive etching. These intermediary chemicals mediate between the need for aggressive poly-Si removal and the need to preserve TiN structures.
2Productivity
If conventional TMAH etching is used, then the poly-Si layer can be removed, but silicon residuals are left behind causing electrical shorts between memory cells
Solution Approach 1:
The etchant composition is modified by adding hydroxylamine, which changes the etching mechanism to produce fewer silicon residuals. The chemical reaction parameters are altered so that silicon is removed more completely as soluble species rather than leaving residual deposits that could cause electrical shorts between adjacent memory cells.
Solution Approach 2:
The patent converts the potential harm of aggressive etching (which could leave residuals) into a benefit by using hydroxylamine-enhanced chemistry that maintains high etching rates while producing cleaner surfaces. The modified chemistry transforms the etching process from one that leaves harmful residuals to one that produces a cleaner interface.
3Length of stationary object
If higher etching selectivity is achieved to increase capacitor height, then capacitor height can be increased, but the metal electrode structures may be destroyed
Solution Approach 1:
The etchant composition parameters are optimized to achieve high selectivity ratios that enable deeper etching for taller capacitors. The additive concentrations and temperature parameters are controlled to maintain TiN electrode structural integrity even at increased capacitor heights, allowing the process to scale to higher capacitance requirements.
Solution Approach 2:
Metal corrosion inhibitors act as intermediary protective agents that specifically adsorb to TiN surfaces during etching, preventing excessive corrosion even when high etching rates are needed for increased capacitor height. These intermediaries allow the process to achieve greater depths while maintaining electrode strength.
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 improved etching selectivity allows for increased capacitor height without damaging metal electrodes and reduces silicon residuals, preventing electrical shorts.
Implementation Method 1
hydroxylamine can selectivity increase the etching rate of Si
Implementation Method 2
the metal corrosion inhibitor can inhibit the corrosion of the metal material (e.g., TiN) of the metal electrodes
Data Source
AI summary
An etching process in a capacitor process for DRAM is described. A substrate is provided, which has thereon a silicon layer and metal electrodes in the silicon layer. The silicon layer is removed using a liquid etchant composition. The liquid etchant composition contains tetramethylammonium hydroxide (TMAH), an additive including hydroxylamine or a metal corrosion inhibitor, and water as a solvent.