Mitigation of corner polysilicon residues through nitride liner etch relocation

NAND flash memory has grown enormously and becomes the most popular non-volatile SSD (Solid State Drives). After 2D NAND reaches its limit, the 3D structure has become the mainstream of NAND. 3D NAND increases capacity in a given footprint without an excessive shrinking of the flash memory chips to...

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Main Author: Zheng, Zhe
Other Authors: Wang Hong
Format: Thesis-Master by Coursework
Language:English
Published: Nanyang Technological University 2023
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Online Access:https://hdl.handle.net/10356/166578
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Institution: Nanyang Technological University
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spelling sg-ntu-dr.10356-1665782023-07-04T16:17:43Z Mitigation of corner polysilicon residues through nitride liner etch relocation Zheng, Zhe Wang Hong School of Electrical and Electronic Engineering Technical University of Munich EWANGHONG@ntu.edu.sg Engineering::Electrical and electronic engineering NAND flash memory has grown enormously and becomes the most popular non-volatile SSD (Solid State Drives). After 2D NAND reaches its limit, the 3D structure has become the mainstream of NAND. 3D NAND increases capacity in a given footprint without an excessive shrinking of the flash memory chips to fit more on the limited die size. In 3D NAND, a vertical polysilicon channel connects the source line and bit line. In the previous technologies, the contact between the pillar and the source polysilicon was performed by dry etching by punching a hole in the pillar bottom. However, as the number of 3D NAND layers increases, dry etching becomes increasingly difficult to perform precise vertical etching without damaging critical cell films deposited on the pillar sidewall. To overcome this limitation of the dry etch, a new Lateral Contact flow was developed in 3D NAND where pillar to source connection is made from source side through sideway etch rather than vertical etch, hence the name 'Lateral Contact'. In the lateral contact process, polysilicon is deposited and recessed through a slit to make contact between source and pillar. However, there are unique challenges observed in poly recess via slit region. The structure of the slit has corners, and the polysilicon recess etchant cannot etch the corner polysilicon before reaching the polysilicon seam. Those corner polysilicon residues lift off after the replacement gate process and are attached to the tiers to cause word line short issues. The proposed flow introduces a new integration flow which fundamentally removes the root cause of polysilicon lift-off problem. This thesis verifies the proposed flow through the blanket wafer test, topography wafer test, and production wafer test. The blanket wafer test finds the chemistry which has high nitride etch rate and low oxide, polysilicon etch rate. The result of topography wafer test shows that the proposal flow can successfully solve the polysilicon stringers issue without causing any other issue. The efficacy of proposed flow was also tested in the production wafer and the test result shows that the new flow significantly improves the yield loss by eliminating the poly stringers. Master of Science (Green Electronics) 2023-05-05T07:57:46Z 2023-05-05T07:57:46Z 2023 Thesis-Master by Coursework Zheng, Z. (2023). Mitigation of corner polysilicon residues through nitride liner etch relocation. Master's thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/166578 https://hdl.handle.net/10356/166578 en application/pdf Nanyang Technological University
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Engineering::Electrical and electronic engineering
spellingShingle Engineering::Electrical and electronic engineering
Zheng, Zhe
Mitigation of corner polysilicon residues through nitride liner etch relocation
description NAND flash memory has grown enormously and becomes the most popular non-volatile SSD (Solid State Drives). After 2D NAND reaches its limit, the 3D structure has become the mainstream of NAND. 3D NAND increases capacity in a given footprint without an excessive shrinking of the flash memory chips to fit more on the limited die size. In 3D NAND, a vertical polysilicon channel connects the source line and bit line. In the previous technologies, the contact between the pillar and the source polysilicon was performed by dry etching by punching a hole in the pillar bottom. However, as the number of 3D NAND layers increases, dry etching becomes increasingly difficult to perform precise vertical etching without damaging critical cell films deposited on the pillar sidewall. To overcome this limitation of the dry etch, a new Lateral Contact flow was developed in 3D NAND where pillar to source connection is made from source side through sideway etch rather than vertical etch, hence the name 'Lateral Contact'. In the lateral contact process, polysilicon is deposited and recessed through a slit to make contact between source and pillar. However, there are unique challenges observed in poly recess via slit region. The structure of the slit has corners, and the polysilicon recess etchant cannot etch the corner polysilicon before reaching the polysilicon seam. Those corner polysilicon residues lift off after the replacement gate process and are attached to the tiers to cause word line short issues. The proposed flow introduces a new integration flow which fundamentally removes the root cause of polysilicon lift-off problem. This thesis verifies the proposed flow through the blanket wafer test, topography wafer test, and production wafer test. The blanket wafer test finds the chemistry which has high nitride etch rate and low oxide, polysilicon etch rate. The result of topography wafer test shows that the proposal flow can successfully solve the polysilicon stringers issue without causing any other issue. The efficacy of proposed flow was also tested in the production wafer and the test result shows that the new flow significantly improves the yield loss by eliminating the poly stringers.
author2 Wang Hong
author_facet Wang Hong
Zheng, Zhe
format Thesis-Master by Coursework
author Zheng, Zhe
author_sort Zheng, Zhe
title Mitigation of corner polysilicon residues through nitride liner etch relocation
title_short Mitigation of corner polysilicon residues through nitride liner etch relocation
title_full Mitigation of corner polysilicon residues through nitride liner etch relocation
title_fullStr Mitigation of corner polysilicon residues through nitride liner etch relocation
title_full_unstemmed Mitigation of corner polysilicon residues through nitride liner etch relocation
title_sort mitigation of corner polysilicon residues through nitride liner etch relocation
publisher Nanyang Technological University
publishDate 2023
url https://hdl.handle.net/10356/166578
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