Cryogenic Noble Gas Etching for Vertical Sidewall Control
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Solution Overview
Problem
Conventional cryogenic fluorine-based etching processes tend to etch isotropically, leading to overetching of sidewalls in high aspect ratio features, making it difficult to maintain critical dimensions and achieve uniform etching across different structures on a chip, due to challenges in balancing etching and passivation rates.
Innovation Solution
A method involving cooling a substrate to a temperature below the triple point of a noble gas, forming an inert layer with a noble gas, followed by a fluorine-containing layer, and exposing these layers to an energy source to create a passivation layer that prevents lateral etching, allowing for anisotropic etching of silicon features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cryogenic fluorine-based etching processes are used, then etching can be performed at low temperatures with improved selectivity, but the process etches isotropically causing overetching of sidewalls and loss of critical dimensions
Solution Approach 1:
The etching process is segmented into distinct steps: a first etch step that etches the mandrel and spacer materials, followed by a second etch step that etches the target material. This segmentation allows each step to be optimized independently, with the first step creating the initial structure and the second step achieving precise final dimensions without overetching sidewalls.
Solution Approach 2:
A spacer layer is formed around the mandrel structure before the main etching process. This preliminary action creates a protective framework that prevents overetching of the sidewalls during subsequent etching steps, ensuring that critical dimensions are maintained while still allowing aggressive fluorine-based chemistry to be used for high selectivity.
2Reliability
If aggressive fluorine-based chemistry is used for high selectivity, then etching selectivity between materials improves, but spontaneous etching occurs on sidewalls leading to non-vertical profiles
Solution Approach 1:
The spacer layer is deposited and patterned before the main etching process begins. This preliminary structure acts as a physical barrier that prevents spontaneous sidewall etching, allowing the use of aggressive fluorine-based chemistry to achieve high material selectivity while maintaining vertical sidewall profiles through the protective spacer framework.
Solution Approach 2:
The process utilizes controlled atmosphere conditions during etching, where the spacer layer creates an inert protective environment around the sidewalls. This prevents direct exposure of the sidewalls to aggressive fluorine chemistry, eliminating spontaneous etching while allowing the chemistry to selectively etch exposed horizontal surfaces with high selectivity.
3Manufacturing precision
If passivation layer is formed on sidewalls to prevent overetching, then sidewall protection is achieved, but balancing etching and passivation rates becomes difficult and process complexity increases
Solution Approach 1:
Instead of dynamically balancing passivation and etching rates during a single complex process, the spacer layer is formed as a preliminary protective structure before etching begins. This eliminates the need for real-time rate balancing, simplifying process control while providing robust sidewall protection throughout the etching sequence.
Solution Approach 2:
The spacer layer serves as an intermediary protective element between the sidewalls and the etching chemistry. Rather than relying on complex passivation layer formation and balancing, the spacer acts as a physical mediator that automatically protects sidewalls without requiring precise control of passivation/etching rate ratios, thereby reducing process complexity.
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 the formation of features with smooth, vertical sidewalls and improved selectivity between materials, maintaining accurate critical dimensions and achieving consistent etching across various structures by suppressing spontaneous etching and allowing aggressive chemistries like fluorine to be used effectively.
Implementation Method 1
cooling a substrate positioned in a chamber to a temperature below a triple point temperature of a first noble gas. The method further includes flowing the first noble gas into the chamber to form an inert layer on exposed portions of the substrate
Implementation Method 2
exposing the fluorine-containing layer and the inert layer to an energy source to form a passivation layer on the exposed portions of the substrate
Implementation Method 3
exposing the substrate to ions to etch the substrate
Data Source
AI summary
The present disclosure generally relates to substrate processing methods, such as etching methods with noble gases at low temperatures. In an aspect, the method includes exposing a substrate, a first layer comprising a gas, and a fluorine-containing layer to energy to form a passivation layer while maintaining the substrate at conditions encompassing a triple point temperature of the gas, the substrate positioned in a processing region of a processing chamber. The method further includes etching the substrate with ions.