Capacitor Structure with Uneven Electrode Walls
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Solution Overview
Problem
Conventional DRAM capacitor structures with straight-sidewall lower electrodes have reduced mechanical strength due to increased aspect ratio, making them prone to damage during fabrication processes.
Innovation Solution
A capacitor fabrication process involving a template layer with alternating layers of different etching selectivities, where the first layer is recessed relative to the second layer during wet etching, creating a bottom electrode with a substantially vertical tube shape and uneven walls, enhancing mechanical strength and capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the height of the lower electrode is increased to maintain capacitance as lateral area decreases, then the capacitance is maintained, but the mechanical strength is reduced and the electrode becomes more easily damaged
Solution Approach 1:
The template layer is divided into multiple alternating layers (first layer and second layer) with different etching selectivities. This segmentation allows the lower electrode to form with an uneven wall structure featuring wider and narrower portions, which segments the electrode structure to improve mechanical strength while maintaining capacitance.
Solution Approach 2:
Different portions of the lower electrode wall are created with different local qualities - wider portions provide enhanced mechanical strength and narrower portions maintain capacitance. The wet etching process creates local variations in wall thickness by selectively recessing the first layer relative to the second layer at the sidewalls.
2Ease of manufacture
If straight-sidewall openings are used in the template layer, then the fabrication process is simple, but the lower electrode has reduced mechanical strength due to high aspect ratio
Solution Approach 1:
The template layer is prepared in advance with a specific multi-layer structure featuring alternating layers of different etching selectivities. This preliminary structural preparation enables the subsequent wet etching process to automatically create the desired uneven wall structure in the lower electrode, improving mechanical strength before the electrode formation is complete.
Solution Approach 2:
The mechanical shaping of the lower electrode wall is replaced by a chemical etching process. Instead of using complex mechanical or lithographic methods to create the uneven wall structure, the patent uses wet etching that exploits the different etching selectivities of the alternating layers in the template layer to automatically form the wider and narrower portions.
3Productivity
If the lateral area of the lower electrode is decreased to increase integration degree, then the integration density is improved, but the capacitance decreases and the aspect ratio increases
Solution Approach 1:
The patent transitions from relying solely on lateral area for capacitance to utilizing the vertical dimension and surface area of the electrode walls. The uneven wall structure with wider and narrower portions increases the effective surface area of the lower electrode vertically, compensating for the reduced lateral area and maintaining capacitance while achieving higher integration density.
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
The process increases the surface area and mechanical strength of the lower electrode, reducing the likelihood of damage during subsequent fabrication steps while maintaining or increasing capacitance.
Implementation Method 1
A wet etching process is performed to recess the at least one first layer relative to the at least one second layer, at the sidewall of the opening
Data Source
AI summary
A process for fabricating a capacitor is described. A template layer including a stack of at least one first layer and at least one second layer is formed over a substrate, wherein the at least one first layer and the at least one second layer have different etching selectivities and are arranged alternately. An opening is formed through the template layer. A wet etching process is performed to recess the at least one first layer relative to the at least one second layer, at the sidewall of the opening. A bottom electrode of the capacitor is formed at the bottom of the opening and on the sidewall of the opening, and then the template layer is removed.