Directional SiO2 Etch via Plasma Pre-treatment and Sublimation
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Solution Overview
Problem
Current precleaning techniques for semiconductor devices, such as conformal etching and sputter etching, either enlarge vias and trenches or redeposit oxides, leading to potential device failure due to inadequate control over etching between features, especially as device dimensions decrease.
Innovation Solution
A method involving directional etching of native silicon oxides using a substrate pretreatment with a low energy inert plasma to roughen horizontal surfaces, followed by exposure to a plasma comprising ammonium fluoride (NH4F) and subsequent heating to sublimate volatile products, allowing for selective etching of horizontal surfaces while preserving vertical surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conformal etching is used to remove native oxides, then oxide removal is achieved, but cross-sectional enlargement of vias and trenches occurs leading to leakage and device failure
Solution Approach 1:
The patent applies local quality by making the etching process directional rather than uniform. The plasma etching process is configured to etch horizontal surfaces preferentially while minimizing etching of vertical sidewalls. This is achieved through specific plasma chemistry and process parameters that create anisotropic etching, allowing oxide removal from the bottom of vias/trenches without enlarging the cross-sectional dimensions, thus resolving the contradiction between oxide removal and dimension control
Solution Approach 2:
The patent employs a preliminary plasma treatment step before the main etching process. This preliminary action modifies the oxide surface properties to enhance subsequent selective etching. The plasma exposure prepares the oxide surfaces to be more susceptible to directional etching while protecting underlying structures, enabling precise oxide removal without compromising dimensional integrity
2Reliability
If sputter etching is used to remove native oxides, then oxide removal from upper surfaces is achieved, but oxide redeposition occurs at via or trench openings preventing subsequent deposition
Solution Approach 1:
The patent replaces the mechanical sputtering process with a chemical plasma-based etching process. Instead of using physical ion bombardment that causes redeposition, the invention uses plasma chemistry to selectively remove oxides through chemical reactions. This substitution eliminates the redeposition problem inherent in sputtering while achieving complete oxide removal, thereby improving contact fill quality without oxide contamination
Solution Approach 2:
The patent changes the fundamental parameters of the etching process by using plasma chemistry rather than physical sputtering. The plasma process parameters (gas composition, power, pressure, temperature) are optimized to achieve selective oxide removal without the mechanical ejection and redeposition that characterizes sputtering. This parameter change transforms the removal mechanism from mechanical to chemical, preventing oxide redeposition at openings
3Reliability
If standard precleaning techniques are used, then oxide removal is achieved, but control over etching between neighboring features is insufficient causing feature damage
Solution Approach 1:
The patent applies local quality by creating spatially selective etching conditions. The plasma process is configured to affect different regions of the substrate differently - horizontal surfaces experience preferential etching while vertical sidewalls are protected. This local differentiation allows precise control over where etching occurs, preventing damage to neighboring features while effectively removing oxides from target areas
Solution Approach 2:
The patent employs specific parameter changes in the plasma etching process to achieve superior control. By optimizing plasma power, pressure, gas flow rates, and temperature, the process achieves high anisotropy and selectivity. These parameter adjustments enable precise control of etching between features, removing oxides only where needed while protecting adjacent structures from damage
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 preferential etching of native oxides from horizontal surfaces within vias and trenches without altering the cross-sectional dimensions, reducing the risk of device failure and ensuring effective contact fill in semiconductor devices.
Implementation Method 1
treating the substrate to roughen a portion of the silicon oxide layer
Implementation Method 2
exposing the exposed surface of the substrate to a plasma comprising ammonium fluoride (NH4F) to form one or more volatile products
Implementation Method 3
heating the substrate to a second temperature, which is higher than the first temperature, to sublimate the volatile products
Data Source
AI summary
Methods for processing a substrate are described herein. Methods can include positioning a substrate with an exposed surface comprising a silicon oxide layer in a processing chamber, biasing the substrate, treating the substrate to roughen a portion of the silicon oxide layer, heating the substrate to a first temperature, exposing the exposed surface of the substrate to a plasma comprising ammonium fluoride to form one or more volatile products while maintaining the first temperature, and heating the substrate to a second temperature, which is higher than the first temperature, to sublimate the volatile products.