Discontinuous Mask Doping for Flash Memory Polysilicon
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Solution Overview
Problem
Conventional methods for doping metal impurities into polysilicon for flash memory devices face challenges such as low energy beam-line implantation limitations and plasma doping difficulties, particularly in achieving low-concentration doping levels required for thin charge storage structures, which affect data retention and device reliability.
Innovation Solution
The use of a discontinuous mask to selectively incorporate metal impurities into polysilicon, where the mask is formed as discrete islands on the material surface, allowing for controlled impurity distribution and subsequent removal without damaging the underlying structure, enabling low-concentration doping suitable for thin layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If beam-line implantation is used for metal impurity doping, then doping can be achieved, but low energy levels are required which are not viable for cost-effective implantation rates
Solution Approach 1:
The patent replaces the mechanical beam-line implantation process with a chemical vapor deposition process using metal-organic precursors. This substitution allows for low-concentration doping (achieving the desired metal impurity levels) while maintaining cost-effective processing rates, as the CVD process can be performed at higher throughput without the energy constraints of beam-line methods.
2Manufacturing precision
If plasma doping is used, then doping can be achieved, but it is difficult to form a plasma source from pure metal and additional impurities from metal source gases lead to undesirable impurity levels
Solution Approach 1:
The patent changes the chemical parameters of the doping process by using metal-organic precursor compounds instead of pure metal sources. This parameter change allows for precise control of metal impurity incorporation while the organic ligands decompose cleanly, avoiding the introduction of undesirable carbon and other impurities that plague plasma doping with metal source gases.
Solution Approach 2:
The patent employs an inert or reducing atmosphere during the chemical vapor deposition process to prevent oxidation and minimize unwanted impurity formation. This controlled atmosphere ensures that only the desired metal impurities are incorporated into the polysilicon at the target low concentrations, while excluding other harmful contaminants.
3Quantity of substance
If polysilicon charge storage structures become too thin (around 6 nm or less), then memory density increases, but data retention becomes impracticable
Solution Approach 1:
The patent changes the compositional parameters of the polysilicon by incorporating low concentrations of metal impurities (on the order of 1E20 atoms/cm³ or less). This parameter modification allows the polysilicon charge storage structures to maintain data retention capability even when reduced to thin dimensions (6 nm or less), thereby enabling continued memory density scaling without sacrificing reliability.
Data Source
AI summary
Methods of incorporating impurities into materials can be useful in non-volatile memory devices as well as other integrated circuit devices. Various embodiments provide for incorporating impurities into a material using a mask.