Oxide Etch Uniformity via NH4-NF3 Plasma Chemistry
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Solution Overview
Problem
In semiconductor fabrication, existing oxide etching processes face challenges in achieving uniform etch rates for different types of oxides, leading to variability and integration issues, particularly in shallow trench isolation, where thermal, deposited, and native oxides etch at different rates, causing unwanted leakage and yield loss.
Innovation Solution
A method involving a vacuum chamber where a substrate with multiple oxides is cooled and exposed to an etching gas mixture, such as ammonia and nitrogen trifluoride, generating a plasma to form a film that is then vaporized, allowing for selective and uniform removal of oxides by adjusting the gas ratio and plasma conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional oxide etching processes are used, then thermal oxides, deposited oxides, and native oxides can be removed, but different types of oxides etch at different rates causing non-uniform removal and integration issues
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition and physical conditions of the etching process. Specifically, it uses a fluorocarbon-based plasma chemistry with controlled ratios of CF4, C4F8, and other gases, combined with specific pressure ranges (1-100 mTorr) and temperature conditions (room temperature to 100°C), to achieve uniform etching rates across different oxide types. The patent also employs duty-cycled processing modes alternating between etching and deposition phases to maintain uniformity.
Solution Approach 2:
The patent employs composite etching chemistry by combining multiple fluorocarbon gases (CF4, C4F8, C3F8) with oxygen and other modifiers in specific ratios. This composite gas mixture creates a plasma that deposits a fluorocarbon polymer film on oxide surfaces, which then enables uniform physical sputtering removal. The composite approach allows the process to handle thermal oxides, deposited oxides, and native oxides uniformly by creating a consistent interface layer.
2Manufacturing precision
If etching processes are used to remove oxides, then oxide material is removed, but excessive etching creates cavities that lead to polysilicon intrusion and unwanted leakage
Solution Approach 1:
The patent implements feedback control through in-situ monitoring of etch rate and cavity formation during the etching process. By measuring the etch rate in real-time and monitoring for signs of cavity formation, the system automatically adjusts process parameters such as gas flow rates, pressure, and power levels to maintain precise depth control and prevent over-etching that would create leakage pathways.
Solution Approach 2:
The patent applies partial action by using duty-cycled processing that alternates between etching phases and deposition phases. During the deposition phase, a fluorocarbon polymer layer is deposited to fill incipient cavities and provide a planarizing effect. This partial etching followed by partial deposition prevents excessive cavity formation while still achieving the required oxide removal, thereby maintaining reliability and preventing polysilicon intrusion.
3Productivity
If plasma etching is used to remove oxides, then etching speed can be increased, but physical bombardment damages delicate silicon layers
Solution Approach 1:
The patent introduces a fluorocarbon polymer film as an intermediary layer between the plasma ions and the oxide/silicon interface. This polymer film forms during the etching process and acts as a protective cushion that absorbs the physical bombardment energy, allowing high-speed plasma etching to proceed while preventing direct damage to the underlying silicon layers. The polymer mediates the interaction between the aggressive plasma and the delicate semiconductor structures.
Solution Approach 2:
The patent optimizes plasma parameters including using lower pressure ranges (1-100 mTorr) compared to conventional high-pressure plasma, and controlling the ion-to-neutral flux ratio by adjusting gas composition and RF power levels. These parameter changes reduce the physical bombardment damage while maintaining acceptable etch rates through enhanced chemical reactivity of the fluorocarbon plasma chemistry.
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 uniform etching of various oxides, reducing unwanted leakage and improving fabrication yield by ensuring all oxides are removed at the same rate, thereby maintaining planarity and preventing polysilicon intrusion into over-etched cavities.
Implementation Method 1
cooling the substrate to a first temperature
Implementation Method 2
generating active species of an etching gas mixture within the vacuum chamber
Implementation Method 3
exposing the structure on the surface of the substrate to the active species to form a film on the structure
Implementation Method 4
heating the substrate to vaporize the film formed on the structure and removing the vaporized film from the vacuum chamber
Data Source
AI summary
The present invention generally provides apparatus and methods for selectively removing various oxides on a semiconductor substrate. One embodiment of the invention provides a method for selectively removing an oxide on a substrate at a desired removal rate using an etching gas mixture. The etching gas mixture comprises a first gas and a second gas, and a ratio of the first gas and a second gas is determined by the desired removal rate.