Vertical Gate Separation via Remote Plasma Tungsten Etching
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Solution Overview
Problem
Current dry etch processes lack selectivity and uniformity in removing tungsten from patterned substrates, particularly in the context of vertical flash memory cell manufacturing, where tungsten slabs need to be electrically isolated while minimizing damage to surrounding materials.
Innovation Solution
The method involves exposing electrically-shorted tungsten slabs to remotely-excited fluorine in a remote plasma region, maintaining a low electron temperature in the substrate processing region to achieve high etch selectivity and uniformity, using a capacitively-coupled remote plasma with specific process parameters to selectively etch tungsten relative to other materials like silicon, polysilicon, and silicon nitride, and avoiding local plasma excitation to reduce physical disturbance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dry etch processes are used to remove tungsten, then material removal is achieved, but selectivity and uniformity are insufficient causing non-uniform etch rates and damage to surrounding materials
Solution Approach 1:
A remote plasma region is introduced as an intermediary between the plasma source and the substrate. The plasma is generated remotely and the activated species are transported to the substrate through a showerhead, separating the plasma generation zone from the processing zone to reduce physical disturbance and plasma damage while maintaining etch effectiveness
Solution Approach 2:
The electron temperature in the substrate processing region is controlled to be below 0.5 eV by adjusting plasma parameters (power between 100-500 watts, pressure between 5-12 Torr). This parameter change achieves high etch selectivity and uniformity while minimizing damage to surrounding materials
2Productivity
If local plasma excitation is used, then etching efficiency is improved, but physical disturbance and damage to miniature structures increase
Solution Approach 1:
The remote plasma region acts as an intermediary that generates activated species without direct plasma contact with the substrate. The showerhead transports these species to the substrate, enabling efficient etching while eliminating the physical disturbance associated with local plasma excitation
Solution Approach 2:
The mechanical/plasma-based local excitation is replaced with a remote plasma generation system that uses gas-phase chemical reactions and diffusion to deliver reactive species to the substrate, reducing physical disturbance to miniature structures
3Reliability
If tungsten slabs are etched to achieve electrical separation, then electrical isolation is achieved, but non-uniform recessing occurs without proper process control
Solution Approach 1:
By controlling plasma parameters (power 100-500 watts, pressure 5-12 Torr, electron temperature below 0.5 eV), the etch process achieves uniform tungsten recess while maintaining electrical isolation between slabs. The parameter optimization ensures consistent etch rates across the substrate surface
Solution Approach 2:
The process monitors and controls electron temperature and plasma parameters to maintain uniform etching conditions. This feedback control ensures that the tungsten slabs are recessed uniformly, achieving reliable electrical separation without non-uniform features
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 enables uniform recessing of tungsten slabs within trenches, improving electrical performance by maintaining a larger average tungsten film thickness and reducing process complexity, while avoiding non-uniform etch rates and plasma damage.
Implementation Method 1
The remote plasma region is fluidly coupled with the substrate processing region through a showerhead and the remote plasma is capacitively-coupled
Implementation Method 2
exciting the fluorine-containing precursor in a remote plasma in the remote plasma region to produce plasma effluents
Implementation Method 3
The tungsten etch may selectively remove tungsten relative to films such as silicon, polysilicon, silicon oxide, aluminum oxide, titanium nitride and silicon nitride
Implementation Method 4
remote plasma generation of nitrogen trifluoride in combination with ion suppression techniques enables silicon to be and selectively removed from a patterned substrate
Data Source
AI summary
Methods of selectively etching tungsten from the surface of a patterned substrate are described. The methods electrically separate vertically arranged tungsten slabs from one another as needed. The vertically arranged tungsten slabs may form the walls of a trench during manufacture of a vertical flash memory cell. The tungsten etch may selectively remove tungsten relative to films such as silicon, polysilicon, silicon oxide, aluminum oxide, titanium nitride and silicon nitride. The methods include exposing electrically-shorted tungsten slabs to remotely-excited fluorine formed in a remote plasma region. Process parameters are provided which result in uniform tungsten recess within the trench. A low electron temperature is maintained in the substrate processing region to achieve high etch selectivity and uniform removal throughout the trench.