Deep Trench Polysilicon Oxidation for Nitride Stringer Prevention
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Solution Overview
Problem
In semiconductor integrated circuit fabrication, the incomplete removal of silicon nitride layers during the hot phosphoric acid etch process leads to defects such as liner oxide grooves and silicon nitride stringers, causing yield loss and increased resistance due to residual nitride layers trapping under STI processing, which results in bridging between moats and high leakage currents.
Innovation Solution
A thermal oxidation step is introduced after the CMP process to form a polysilicon oxide layer on the exposed polysilicon fill before the hot phosphoric acid etch, ensuring complete removal of the silicon nitride layer and reducing the depth of liner oxide grooves, thereby preventing silicon nitride stringer defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If hot phosphoric acid etch process is used to remove silicon nitride layer, then silicon nitride layer removal is achieved, but incomplete removal occurs leading to residual nitride layers and defects
Solution Approach 1:
A thermal oxidation step is performed before the hot phosphoric acid etch process to form a polysilicon oxide layer on the exposed polysilicon fill. This preliminary oxidation modifies the surface properties and enables complete silicon nitride layer removal by the subsequent etch process, preventing residual nitride layers and associated defects.
Solution Approach 2:
The thermal oxidation process changes the physical and chemical parameters of the polysilicon fill surface by converting it to polysilicon oxide. This parameter change (from metallic polysilicon to oxidized polysilicon) fundamentally alters how the material interacts with the hot phosphoric acid etch, enabling complete nitride layer removal without leaving residues.
2Manufacturing precision
If hot phosphoric acid etch process is used, then silicon nitride layer is targeted for removal, but liner oxide grooves are formed
Solution Approach 1:
The thermal oxidation step performed before etching creates a protective polysilicon oxide layer that prevents the formation of deep liner oxide grooves during the hot phosphoric acid etch process. This preliminary protective action eliminates the harmful groove formation while maintaining effective nitride layer removal.
Solution Approach 2:
The polysilicon oxide layer acts as an intermediary between the hot phosphoric acid etch and the underlying structures. It mediates the etch process by being selectively removed in a controlled manner, preventing the formation of harmful liner oxide grooves while allowing complete nitride layer removal.
3Productivity
If silicon nitride layer is not completely removed, then etch process can be stopped earlier, but residual nitride causes bridging and leakage currents
Solution Approach 1:
The thermal oxidation step before etching enables the hot phosphoric acid etch process to completely remove the silicon nitride layer in a single controlled step. This preliminary oxidation ensures that the etch process can run to completion without needing extended time, achieving both complete removal and reasonable process efficiency.
Solution Approach 2:
By changing the polysilicon fill to polysilicon oxide through thermal oxidation, the etch selectivity parameters are optimized. This allows the etch process to completely remove nitride layers without requiring excessive time, maintaining productivity while ensuring complete removal for electrical isolation.
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
The thermal oxidation of the polysilicon fill effectively enables the hot phosphoric acid etch to remove all silicon nitride layers, reducing liner oxide groove depth and eliminating silicon nitride stringer defects, thus improving IC yield and reducing electrical resistance.
Implementation Method 1
a thermal oxidation oxidizes exposed regions of the polysilicon layer to form a polysilicon oxide layer
Implementation Method 2
the silicon nitride layer is removed
Data Source
AI summary
A method of fabricating an IC includes forming a layer stack thereon including silicon nitride layer on a first silicon oxide layer, with a second silicon oxide layer thereon on a substrate including a semiconductor material. The layer stack is etched to form ≥1 trench that is at least 2 microns deep into the semiconductor material. A dielectric liner is formed on sidewalls and a bottom of the trench. A polysilicon layer is formed on the dielectric liner that fills the trench and extends lateral to the trench. Chemical mechanical planarization (CMP) processing stops on the silicon nitride layer to remove the polysilicon layer and the second silicon oxide layer to form a trench structure having a polysilicon fill. After the CMP processing, thermal oxidation oxidizes exposed regions of the polysilicon layer to form a polysilicon oxide layer. After the thermal oxidizing, the silicon nitride layer is removed.