3D NOR Memory Channel Replacement Using SiGe Sacrificial Layers
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Solution Overview
Problem
The challenge in fabricating 3-dimensional NOR memory strings is to prevent undesirable thermal diffusion of dopants from the doped semiconductor layers into the adjacent channel regions, while also simplifying the fabrication process and improving electrical characteristics.
Innovation Solution
The use of silicon germanium (SiGe) as a sacrificial material in the channel-last fabrication process for NOR memory strings, where SiGe is replaced with the channel material after the charge-storage layer is formed, thereby avoiding high-temperature processing steps that can cause dopant diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature processing steps are used to form channel regions, then dopant diffusion into channel regions occurs, but manufacturing precision deteriorates
Solution Approach 1:
The patent applies preliminary action by forming the charge-storage layer before forming the channel region. This sequence allows the channel region to be formed at lower temperatures after the charge-storage layer is already in place, preventing dopant diffusion into the channel region while still achieving the desired electrical characteristics. The channel region is formed in a preliminary manner before final device completion, avoiding high-temperature processing that would cause harmful dopant diffusion.
Solution Approach 2:
The patent inverts the conventional fabrication sequence by forming the charge-storage layer first and then forming the channel region, rather than the traditional approach of forming channel regions first. This inversion allows the channel to be created in a low-temperature step after the charge-storage layer is established, thereby preventing dopant diffusion into the channel region while maintaining reliable electrical characteristics.
2Reliability
If conventional fabrication processes are used, then manufacturing complexity increases, but ease of manufacture deteriorates
Solution Approach 1:
The patent simplifies manufacturing by performing preliminary formation of the charge-storage layer before channel region creation. This preliminary action enables subsequent low-temperature channel formation using standard low-cost processes, reducing overall fabrication complexity while maintaining dopant diffusion prevention and ensuring reliable electrical characteristics.
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 reduces dopant out-diffusion and simplifies the fabrication process, leading to improved electrical characteristics and enhanced manufacturability of NOR memory strings.
Implementation Method 1
replacing the remainder of the dielectric filler material in the trenches by a charge-storage layer and a conductor; removing the silicon germanium sacrificial material followed by removing the semiconductor liner layer
Data Source
AI summary
A process for fabricating a three-dimensional NOR memory string of storage transistors implements a channel-last fabrication process with channel replacement using silicon germanium (SiGe). In particular, the process uses silicon germanium as a sacrificial layer, to be replaced with the channel material after the charge-storage layer of the storage transistors is formed. In this manner, the channel region is prevented from experiencing excessive high-temperature processing steps, such as during the annealing of the charge-storage layer.