Cyclic SiN Spacer Etching for Vertical Profile Control
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Solution Overview
Problem
Conventional etching processes for silicon nitride (SiN) spacers in semiconductor applications face challenges in achieving perfect anisotropy, profile control, and damage-free etching, especially with increased aspect ratios at advanced technology nodes.
Innovation Solution
A cyclic atomic layer etch (ALE) method using hydrofluorocarbon (HFC) gases with the formula CxHyFz (x=2-5, y>z) is employed. This method involves alternating steps of depositing a polymer layer on the SiN surface using HFC plasma and removing it using inert gas plasma, repeated until the SiN layer is fully etched, forming vertically straight SiN spacers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional plasma etching using fluorocarbon-based chemistry is used for SiN spacer etching, then etch selectivity is achieved, but profile control (footing and surface roughness) deteriorates and damage to underlying layers occurs
Solution Approach 1:
The continuous etching process is segmented into cyclic atomic layer etching (ALE) steps, where each cycle consists of a deposition step followed by an etching step. This segmentation allows precise control over the etching front progression, maintaining vertical spacer profiles and minimizing footing while preserving selectivity between SiN and underlying layers.
Solution Approach 2:
The etching process employs periodic cyclic ALE cycles rather than continuous etching. Each cycle deposits a thin polymer layer on the etching front, then removes it along with a controlled amount of SiN material. This periodic action enables precise profile control and prevents damage to underlying layers while maintaining high selectivity.
2Productivity
If conventional plasma etching is used to achieve high etch rates, then productivity is improved, but manufacturing precision (profile control and CD control) deteriorates
Solution Approach 1:
The etching process is divided into multiple cyclic ALE cycles, where each cycle removes a thin layer of SiN (1-5 nm). This segmentation transforms a single high-rate etch into multiple controlled low-rate etches, achieving both high overall productivity and precise profile control with vertical sidewalls and minimal footing.
Solution Approach 2:
Before each etching step, a thin polymer layer is deposited on the SiN surface and etching front. This preliminary action protects the underlying layers from damage while enabling controlled removal of SiN in the subsequent etching step, maintaining both productivity and precision.
3Adaptability or versatility
If aspect ratio is increased for advanced technology nodes, then device density is improved, but etching difficulty increases leading to loss of profile control and increased damage
Solution Approach 1:
The cyclic ALE process segments the etching of high aspect ratio structures into multiple thin-layer removal cycles. Each cycle deposits and removes a thin polymer layer, progressively etching the SiN spacer with precise profile control even for high aspect ratios, preventing footing and maintaining vertical sidewalls.
Solution Approach 2:
The polymer deposition step performed before each etching cycle serves as a preliminary protective action. This polymer layer prevents damage to the underlying high aspect ratio structures while enabling controlled SiN removal, solving the etching difficulty associated with increased aspect ratios.
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 cyclic ALE process achieves improved profile control, minimizing footing and surface roughness, while maintaining high selectivity of SiN over underlying layers and avoiding chemical damage or fluoride residuals.
Implementation Method 1
exposing a SiN layer covering structures on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer
Implementation Method 2
exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on etch front
Implementation Method 3
cyclic atomic layer etch (ALE) method using hydrofluorocarbon (HFC) gases with the formula CxHyFz (x=2-5, y>z) is employed... selectively etch SiN
Data Source
AI summary
Cyclic etch methods comprise the steps of: i) exposing a SiN layer covering a structure on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer, the HFC having a formula CxHyFz where x=2-5, y>z, the HFC being a saturated or unsaturated, linear or cyclic HFC; ii) exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on an etch front; and iii) repeating the steps of i) and ii) until the SiN layer on the etch front is selectively removed, thereby forming a substantially vertically straight SiN spacer comprising the SiN layer on the sidewall of the structure.