Endpoint Detection in Non-Volatile Memory Fabrication
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Solution Overview
Problem
Current non-volatile memory fabrication processes face challenges in achieving high density and precise etching of charge storage layers, particularly in forming inverted-T charge storage structures, due to the difficulty in distinguishing between similar materials and varying feature sizes, which can lead to over-etching or under-etching, affecting device performance.
Innovation Solution
A method is introduced that involves forming a first charge storage layer over a tunnel dielectric layer on a semiconductor substrate, removing it from an endpoint region, and then forming a second charge storage layer, where the etching of the second layer is monitored using a detectable endpoint signal provided by the tunnel dielectric layer, ensuring precise etching without damaging the first layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional etching methods are used to remove charge storage layers, then material removal is achieved, but precise endpoint detection is difficult due to similar materials and varying feature sizes
Solution Approach 1:
An etch stop layer is introduced as an intermediary between the charge storage layers and the tunnel dielectric layer. This etch stop layer has distinct etching characteristics that enable precise endpoint detection during the removal of the second charge storage layer, solving the problem of difficult endpoint detection when materials are similar.
Solution Approach 2:
The patent changes the material composition or thickness parameters of the etch stop layer to create a detectable endpoint signal. By controlling the etch stop layer's properties, the system transitions from undetectable material removal to a process with a clear, measurable endpoint, resolving the precision contradiction.
2Reliability
If etching is continued to ensure complete removal of the second charge storage layer, then thorough cleaning is achieved, but over-etching damages the first charge storage layer
Solution Approach 1:
The etch stop layer is prepared in advance as a protective barrier between the etching process and the first charge storage layer. This preliminary protective measure allows the etching process to proceed aggressively to ensure complete removal of the second charge storage layer while automatically stopping before damaging the first layer, as the etch stop layer provides a detectable endpoint.
Solution Approach 2:
The etch stop layer acts as a cushioning layer that absorbs the risk of over-etching. By placing this sacrificial layer beforehand, the system gains a safety margin that prevents direct contact between the etching process and the sensitive first charge storage layer, eliminating the harmful effect of potential over-etching.
3Measurement precision
If the first charge storage layer is removed from the endpoint region, then endpoint detection becomes possible, but additional process steps are required
Solution Approach 1:
The patent merges the endpoint detection function with the existing charge storage layer structure by integrating the etch stop layer into the same fabrication sequence. Rather than adding a completely separate detection mechanism, the etch stop layer is deposited alongside other charge storage layers and serves dual purposes: as a structural component and as an endpoint detection reference, reducing overall process complexity.
Data Source
AI summary
A method of fabricating non-volatile memory is provided for memory cells employing a charge storage element with multiple charge storage regions. A first charge storage layer is formed over a tunnel dielectric layer at both a memory array region and an endpoint region of a semiconductor substrate. The first charge storage layer is removed from the endpoint region to expose the tunnel dielectric region. A second charge storage layer is formed over the first charge storage layer at the memory array region and over the tunnel dielectric layer at the endpoint region. When etching the second charge storage layer to form the stem regions of the memory cells, the tunnel dielectric layer provides a detectable endpoint signal to indicate that etching for the second charge storage layer is complete.