Selective Re-oxidation of Charge Trap Flash Gate Patterns
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Solution Overview
Problem
In charge trap flash (CTF) semiconductor devices, the oxidation of metal nitride layers such as TiN and TaN during the re-oxidation process leads to deteriorated gate characteristics, including bridge formation and irregular surface morphology, which degrades the reliability of the device.
Innovation Solution
A selective re-oxidation process is performed in a gas ambient containing hydrogen, oxygen, and nitrogen, with a partial-pressure ratio of H2O to H2 between 0.01 and 1.0 and NH3 to H2 between 0.1 and 10, which heals etching damage without oxidizing the metal nitride and tungsten nitride layers, using ammonia to reduce and nitride these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional re-oxidation process is performed to heal etching damage in the gate pattern, then etching damage is healed, but the metal nitride layer (TiN or TaN) is oxidized causing bridge formation and irregular surface morphology
Solution Approach 1:
The patent changes the chemical parameters of the re-oxidation process by introducing ammonia (NH3) into the gas ambient along with H2O and H2. This parameter modification allows the process to selectively oxidize polysilicon while preventing oxidation of metal nitride layers through ammonia-based reduction and nitridation reactions
Solution Approach 2:
Ammonia acts as an intermediary substance that mediates between the oxidizing environment (H2O) and the metal nitride layer. The ammonia provides a reducing and nitriding atmosphere that protects the metal nitride layer from oxidation while allowing the oxidizing environment to heal etching damage in polysilicon regions
2Stability of the object's composition
If the gate pattern is re-oxidized in H2O and H2 ambient, then polysilicon etching damage is healed, but metal nitride layer oxidation occurs deteriorating gate characteristics
Solution Approach 1:
The patent converts the potentially harmful oxidizing environment into a beneficial process by adding ammonia. The ammonia transforms the harmful oxidation effect on metal nitride layers into a protective effect through reduction and nitridation reactions, while maintaining the beneficial healing effect on polysilicon
3Reliability
If TiN or TaN is used in the gate pattern for CTF structure, then charge storage capability is improved, but the metal nitride layer is oxidized during re-oxidation causing threshold voltage scattering
Solution Approach 1:
The patent modifies the gas ambient parameters by incorporating ammonia (NH3) with specific partial pressure ratios (H2O/H2: 0.01-1.0, NH3/H2: 0.1-10.0). This parameter change enables selective oxidation that preserves metal nitride layers while healing polysilicon, thereby maintaining threshold voltage control
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 improves the surface state and threshold voltage scattering characteristics of the metal nitride layer, enhancing the reliability of the CTF device by preventing oxidation of the metal nitride layers and effectively healing etching damage.
Implementation Method 1
a selective re-oxidation process is performed on the gate pattern in gas ambient including hydrogen, oxygen, and nitrogen
Implementation Method 2
using ammonia to reduce and nitride these layers
Implementation Method 3
using ammonia to reduce and nitride these layers
Data Source
AI summary
One embodiment of a method for forming a semiconductor device can include forming a gate pattern on a semiconductor substrate and performing a selective re-oxidation process on the gate pattern in gas ambient including hydrogen, oxygen, and nitrogen. When the gate pattern includes a tunnel insulation layer, a metal nitride layer and a metal layer, the selective re-oxidation process heals the etching damage of a gate pattern and simultaneously prevents oxidation of the metal nitride layer and a tungsten electrode.