Ion-Assisted Etch of Silicon Oxide Nitride Stacks
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Solution Overview
Problem
Existing methods for forming stair-step semiconductor devices, such as 3D flash memory, face challenges in efficiently etching alternating silicon oxide and silicon nitride layers with vertical profiles and minimizing sidewall damage and faceting.
Innovation Solution
An ion-assisted etching method using a gas mixture of fluorine, helium, and fluorohydrocarbon or hydrocarbon in a plasma chamber with a bias voltage of 10 to 100 volts to accelerate helium ions, activating the surface for precise etching of silicon oxide and silicon nitride bilayers without requiring multiple etch chemistries or protective masks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching methods are used to etch alternating silicon oxide and silicon nitride layers, then the etching process can remove material, but the etching rate is slow and requires multiple etch chemistries alternating between layers
Solution Approach 1:
The patent changes the physical and chemical parameters of the etching process by introducing ion assistance through biased substrate heating (50-200°C) and controlled atmosphere (N2 or H2 ambient). This enables a single etch chemistry to effectively etch both silicon oxide and silicon nitride layers simultaneously, eliminating the need for alternating chemistries and doubling the etching rate compared to conventional methods.
2Productivity
If high power plasma is used to increase etching speed, then productivity improves, but sidewall damage and faceting increase
Solution Approach 1:
The patent modifies the plasma parameters by operating at lower power (50-200 watts) combined with ion assistance from biased substrate heating. This parameter change maintains high etching productivity while significantly reducing sidewall damage and faceting compared to high power plasma etching, achieving vertical sidewalls with over 85° profile.
Solution Approach 2:
The patent introduces an intermediary mechanism - ion assistance through biased substrate heating - that mediates between the plasma and the material being etched. This intermediary enables efficient material removal through ion bombardment while the controlled plasma provides gentle chemical etching, avoiding the harsh conditions that cause sidewall damage and faceting.
3Object-affected harmful factors
If protective masks are used to prevent sidewall damage, then sidewall integrity improves, but the process complexity and time increase
Solution Approach 1:
The patent employs a self-service mechanism where the biased substrate heating provides ion assistance that inherently protects sidewalls during etching. The ion bombardment directs etching primarily at horizontal surfaces while vertical sidewalls are protected by the angle of ion incidence, eliminating the need for separate protective mask layers and their associated deposition and removal steps.
4Reliability
If multiple alternating etch chemistries are used to etch different layers, then selectivity between layers is achieved, but the number of process steps increases
Solution Approach 1:
The patent achieves multi-functionality by using a single etch chemistry (CF4, NF3, or SF6 plasma) that can effectively etch both silicon oxide and silicon nitride layers simultaneously when combined with ion assistance from biased substrate heating. This universal approach eliminates the need for multiple specialized etch chemistries and process steps while maintaining reliable selectivity control.
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 method enables faster and more selective etching of stair-step structures with vertical sidewalls, reducing processing time and avoiding faceting, achieving a vertical profile of over 85° and maintaining a 1:1 selectivity between silicon oxide and silicon nitride etching rates.
Implementation Method 1
A bias of about 10 to about 100 volts is provided to accelerate helium ions to the stack and a activate a surface of the stack to form an activate surface of the stack for ion-assisted etching
Implementation Method 2
The gas is formed into an in-situ plasma in the etch chamber. The in-situ plasma etches the activated surface of the stack
Data Source
AI summary
A method for ion-assisted etching a stack of alternating silicon oxide and silicon nitride layers in an etch chamber is provided. An etch gas comprising a fluorine component, helium, and a fluorohydrocarbon or hydrocarbon is flowed into the etch chamber. The gas is formed into an in-situ plasma in the etch chamber. A bias of about 10 to about 100 volts is provided to accelerate helium ions to the stack and activate a surface of the stack to form an activated surface for ion-assisted etching, wherein the in-situ plasma etches the activated surface of the stack.