Novolak Resin Floating Gate Protection in Flash Memory
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Solution Overview
Problem
The challenge in flash memory device fabrication is the inadvertent etching of floating gates during the removal of polysilicon material, which deteriorates the device characteristics.
Innovation Solution
A flash memory device is fabricated with an ONO layer, polysilicon gates, a gate oxide layer, and a low temperature oxide layer, along with a novolak resin formed between polysilicon gates to prevent inadvertent etching, using a method that includes forming and patterning layers, and anisotropic etching to create sidewall spacers and control gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polysilicon material is removed by dry etching at an etch selectivity ratio of oxide to polysilicon, then the polysilicon layer can be removed uniformly, but the floating gate may be inadvertently etched
Solution Approach 1:
A sacrificial oxide layer is introduced as an intermediary between the floating gate and the polysilicon layer. This sacrificial oxide layer is selectively removed to expose the floating gate for formation, then a new oxide layer is grown to protect the floating gate during subsequent polysilicon removal processes. The sacrificial oxide acts as a temporary mediator that enables precise control of the etching process.
Solution Approach 2:
The floating gate is formed in advance before the polysilicon layer is deposited. By preliminarily forming the floating gate and protecting it with an oxide layer before polysilicon deposition, the structure is prepared in a state that prevents inadvertent etching during later removal processes.
2Ease of manufacture
If the polysilicon layer is completely removed to form control gates, then the control gate lines can be formed, but the floating gate structure may be damaged
Solution Approach 1:
An oxide layer serves as a protective intermediary between the polysilicon control gate and the underlying floating gate structure. This oxide layer is selectively grown and removed to enable precise patterning of control gates while shielding the floating gate from damage during the etching process.
Solution Approach 2:
The fabrication process is segmented into distinct stages: first forming the floating gate, then protecting it with an oxide layer, depositing polysilicon, and finally selectively removing polysilicon to form control gates. This segmentation allows each structure to be formed and protected independently, preventing cross-contamination and damage.
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 approach effectively prevents the inadvertent etching of floating gates, thereby improving the characteristics and reliability of the flash memory device.
Implementation Method 1
a novolak resin is formed between polysilicon gates. As a result, inadvertent etching of the floating gates during a conventional process of removing the polysilicon material when forming the patterned polysilicon gates may be prevented
Implementation Method 2
forming sidewall spacers on the plurality of floating gates (or patterned first polysilicon layer) by removing the second polysilicon layer on the resin between the nearest adjacent floating gates in an anisotropic etching process
Data Source
AI summary
A flash memory device and a method for fabricating the same are disclosed. The flash memory device includes an ONO layer on a substrate, polysilicon gates on the ONO layer, a gate oxide layer on the substrate, the ONO layer and the polysilicon gates, and a low temperature oxide layer and polysilicon sidewall spacers on outer side surfaces of the polysilicon gates, except in a region between nearest adjacent polysilicon gates.