Stack Capacitor Trench Etching and Static Drying Method
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Solution Overview
Problem
The existing methods for forming stack capacitors face challenges with reduced critical dimensions, including the 'bowing issue' caused by reactive ion etching, which leads to structural damage during spin-drying, especially as capacitors become closer and their effective area is reduced.
Innovation Solution
A method involving selective etching and static drying is employed, which includes forming a tapered trench, depositing a poly-Si layer, filling with a sacrificial layer, and using static drying to remove liquids without damaging the capacitors, along with a composite structure to increase effective area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If spin-drying is used to remove liquid after wet etching, then liquid removal is achieved, but the bowing issue causes capacitor columns to collapse and suffer damages
Solution Approach 1:
The patent inverts the conventional approach by using static drying instead of spin-drying. This reversal eliminates the centrifugal force that exacerbates the bowing issue, thereby preventing capacitor column collapse while still achieving liquid removal through capillary action and evaporation in the static state.
Solution Approach 2:
The patent converts the harmful bowing effect into a beneficial feature by using the tapered shape (with slight bowing) as a self-supporting structure during static drying. The tapered geometry provides structural stability that prevents collapse, transforming what was previously a defect into a design advantage that enables successful liquid removal without damage.
2Ease of manufacture
If reactive ion etching is used to form the capacitor rough shape, then the capacitor structure is formed, but the bowing issue appears at the collar of the capacitor column
Solution Approach 1:
The patent applies local quality by using selective etching that creates different profiles at different locations. The collar region is specifically designed with a tapered shape through controlled etching, while other regions maintain their intended geometry. This localized geometric modification eliminates the uniform bowing effect and provides structural support where needed.
Solution Approach 2:
The patent changes the geometric parameters of the capacitor column, specifically transitioning from a cylindrical shape to a tapered shape with a larger base diameter. This parameter change in the collar region's geometry fundamentally alters the stress distribution and eliminates the bowing issue that occurs with conventional cylindrical structures during etching.
3Productivity
If the critical dimension is reduced to increase capacitor density, then capacitors become closer, but the effective area on the capacitor structure is reduced
Solution Approach 1:
The patent extends the capacitor structure into the vertical dimension by creating a tapered shape with increased height-to-diameter ratio. This dimensional change allows the capacitor to achieve greater effective area by utilizing vertical space, thereby compensating for the horizontal space reduction caused by smaller critical dimensions and increased capacitor density.
Solution Approach 2:
The patent employs a stacked capacitor structure where multiple capacitor elements are nested vertically within the tapered column. This nesting arrangement allows multiple functional units to occupy a compact horizontal footprint, effectively increasing the total capacitance and usable area without increasing the planar critical dimension.
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 addresses the bowing issue and maintains structural integrity, while increasing the effective surface area by at least 30% in a limited space, making it suitable for smaller critical dimensions.
Implementation Method 1
In the process of forming the rough capacitor by dry etching
Implementation Method 2
the sacrificial material filled in the capacitor is removed by a wet etching
Implementation Method 3
the remaining fluid is removed by spin-drying
Data Source
AI summary
A method for forming a stack capacitor includes providing a substrate with a bottom layer, a BPSG layer, a USG layer and a top layer thereon; using the top layer as a hard mask and the substrate as a first etching stop layer to perform a dry etching process to form a tapered trench in the bottom layer, the BPSG layer and the USG layer; removing the top layer to perform a selective wet etching process to partially remove the BPSG layer; depositing conformally a poly-Si layer and filling the trench with a sacrificial layer; removing the poly-Si layer unmasked by the sacrificial layer; using the bottom layer as a second etching stop layer to perform a wet etching process to remove the USG layer and BPSG layer; performing a static drying process; and depositing a dielectric layer and a conductive material to form the stack capacitor.