Etch Selectivity Control via Adsorption and Condensation Regimes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor processing techniques face challenges in selectively etching silicon nitride and oxide layers on substrates, particularly in high-aspect-ratio features, where achieving precise control over etch selectivity and rate is crucial to avoid undesired etching of underlying layers.
Innovation Solution
The method involves a two-step process where the etchant's partial pressure is controlled to switch between adsorption and condensation regimes, allowing for high or low silicon nitride etch selectivity, using etchants like ammonium fluoride and ammonium bifluoride, to selectively etch oxide layers without significantly etching nitride layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to remove oxide layers, then oxide removal is achieved, but silicon nitride layers are also etched undesirably
Solution Approach 1:
The patent changes the physical-chemical parameters of the etching process by controlling the partial pressure of the etchant to switch between adsorption regime (low nitride etch rate) and condensation regime (high oxide etch rate). This enables dynamic adjustment of etch selectivity to achieve precise oxide removal while protecting the nitride layer
Solution Approach 2:
The patent implements a dynamic two-step etching process where the etching conditions are changed mid-process. The first step uses condensation regime for rapid oxide removal, then transitions to adsorption regime for selective nitride protection. This dynamic switching resolves the contradiction between removal efficiency and selectivity
2Manufacturing precision
If etching process is optimized for high selectivity, then nitride layer is protected, but etching rate decreases
Solution Approach 1:
The patent segments the etching process into two distinct steps with different regimes: first step (condensation) for rapid oxide removal, second step (adsorption) for selective protection. This segmentation allows each step to optimize for its specific function, resolving the rate-selectivity tradeoff
Solution Approach 2:
The patent uses periodic switching between two etching regimes within a single continuous process. By periodically transitioning between condensation and adsorption modes, the system achieves both high overall etch rate and high final selectivity, eliminating the need for separate processes
3Manufacturing precision
If conformal etching is used to remove oxide completely from sidewalls, then oxide is removed uniformly, but underlying nitride layer becomes exposed and is etched
Solution Approach 1:
The patent performs preliminary oxide removal in the condensation regime before the nitride layer is exposed. By completing the majority of oxide removal while oxide still provides protection, the system prevents premature nitride exposure and subsequent undesired etching
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 precise control over etch selectivity, achieving selectivities greater than 70:1 or up to 200:1, allowing for efficient gap fill and pre-clean applications without damaging underlying silicon nitride layers, thereby improving the accuracy and throughput of semiconductor processing.
Implementation Method 1
exposing the workpiece to the etchant under conditions that thermodynamically favor adsorption but not condensation of the etchant onto the feature
Implementation Method 2
exposing the workpiece to the etchant under conditions that thermodynamically favor condensation of the etchant onto the feature
Data Source
AI summary
Etching of nitride and oxide layers with reactant gases is modulated by etching in different process regimes. High etch selectivity to silicon nitride is achieved in an adsorption regime where the partial pressure of the etchant is lower than its vapor pressure. Low etch selectivity to silicon nitride is achieved in a condensation regime where the partial pressure of the etchant is higher than its vapor pressure. By controlling partial pressure of the etchant, very high etch selectivity to silicon nitride may be achieved.