Reverse Masking Profile for High Aspect Ratio Etch Twisting
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Solution Overview
Problem
High aspect ratio etching in semiconductor manufacturing leads to twisting issues due to asymmetric mask geometry, causing differential electric charging and resulting in lateral electric fields that distort ion trajectories and lead to systematic twisting at the edge of the array, particularly in DRAM container oxide etches, where differences in mask heights between the array and periphery result in uneven etching and potential defects like open capacitors or shorts.
Innovation Solution
A method to achieve uniform mask heights between the array and periphery by adjusting the thickness of the amorphous carbon layer and using a combination of photodefinable material layers and hard mask layers to ensure consistent etching across the substrate, reducing faceting and lateral charging differences during high aspect ratio plasma etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If high aspect ratio etching is performed with standard mask geometry, then etching depth is achieved, but twisting occurs due to asymmetric charging and lateral electric fields
Solution Approach 1:
The patent applies local quality by creating different mask heights in different regions of the wafer. Specifically, the mask is intentionally made taller at the periphery compared to the array region, compensating for the lateral electric field effects that cause twisting. This localized modification of mask geometry addresses the asymmetric charging problem without changing the overall etching process parameters.
Solution Approach 2:
The patent deliberately introduces asymmetry in the mask structure to counteract the asymmetric charging that occurs during high aspect ratio etching. By making the periphery mask taller than the array mask, the patent creates a symmetric electrical field distribution that prevents lateral ion deflection and twisting of etched features.
2Manufacturing precision
If mask height is increased at periphery to compensate for twisting, then feature alignment improves, but mask geometry complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-compensating for the expected twisting effect through reverse masking profilering. The mask is prepared with different heights before etching begins, specifically making the periphery mask taller to counteract the lateral electric field that will develop during etching. This preliminary geometric adjustment prevents twisting without requiring complex real-time corrections during the etching process.
3Device complexity
If uniform mask height is maintained across array and periphery, then mask simplicity is preserved, but lateral electric fields cause systematic twisting at array edges
Solution Approach 1:
The patent resolves this contradiction by applying local quality - making the mask height a variable parameter that changes with position on the wafer. The periphery region receives a taller mask while the array region receives a standard height mask. This localized differentiation eliminates lateral electric fields and prevents systematic twisting at array edges, while maintaining overall mask simplicity through a straightforward geometric modification.
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 mitigates twisting by maintaining uniform mask heights across the substrate, reducing lateral electric fields and minimizing defects such as open capacitors or shorts, thereby enhancing the reliability of high aspect ratio etching processes.
Implementation Method 1
For ions, the directed velocity is normal to the wafer, due to their acceleration by the plasma sheath
Implementation Method 2
most of the electrons will deposit their charge near the top of an HAR feature while the ions deposit their charge more toward the bottom
Implementation Method 3
Asymmetric charging is caused by asymmetric mask geometry, which results in different view angles for electron and ion fluxes at different locations around the circumference of the contact or container
Implementation Method 4
If this vertical charging becomes azimuthally asymmetric than the lateral electric field results, causing twisting
Implementation Method 5
Oxide etch chemistries are typically done at high bias and the dominant ion is argon (Ar+). This means that the oxide etch ions are, in fact, quite physically driven, and prone to faceting
Implementation Method 6
facets naturally develop because the peak angular yield of incident ions occurs at off-normal incidence. Typically, this is about 60 degrees
Data Source
AI summary
A method of improving high aspect ratio etching by reverse masking to provide a more uniform mask height between the array and periphery is presented. A layer of amorphous carbon is deposited over a substrate. An inorganic hard mask is deposited on the amorphous carbon followed by a layer of photodefinable material which is deposited over the array portion of the substrate. The photodefinable material is removed along with the inorganic hard mask overlaying the periphery. A portion of the amorphous carbon layer is etched in the exposed periphery. The inorganic hard mask is removed and normal high aspect ratio etching continues. The amount of amorphous carbon layer remaining in the periphery results in a more uniform mask height between the array and periphery at the end of high aspect ratio etching. The more uniform mask height mitigates twisting at the edge of the array.