Semiconductor Pre-Cleaning With Ammonium Fluoride Protection Layer
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Solution Overview
Problem
The self-aligned contact (SAC) process in semiconductor manufacturing faces challenges with excessive removal of protective interlayer dielectric material and silicon nitride from insulating caps, leading to increased risk of metal gate/metal drain shorting and reduced epitaxial loss window due to pre-clean and etch processes.
Innovation Solution
The use of an ammonium fluoride gas formed through an oversupply of nitrogen trifluoride during the pre-clean etch process creates a protective layer on interlayer dielectric layers, insulating caps, and source/drain regions, which reacts with oxide layers to prevent etching by fluorine ions and reduces material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-clean and etch processes are used to remove oxide layers, then cleaning effectiveness is improved, but excessive removal of protective interlayer dielectric material and silicon nitride occurs
Solution Approach 1:
An ammonium fluoride protection layer is introduced as an intermediary substance between the fluorine-based pre-clean/etch process and the interlayer dielectric material. This protection layer selectively allows oxide layer removal while preventing excessive etching of the interlayer dielectric and silicon nitride, acting as a mediator that enables the cleaning process to proceed effectively without causing harmful material loss.
Solution Approach 2:
The process parameters are changed by controlling the temperature (e.g., 25°C to 40°C) and the composition of the pre-clean solution to optimize the balance between oxide removal and material protection. By adjusting these parameters, the etch rate of oxides is enhanced while the etch rate of protective materials is suppressed, resolving the contradiction between cleaning effectiveness and material preservation.
2Manufacturing precision
If pre-clean process is performed to clean source/drain regions, then oxide layer removal is improved, but metal gate/metal drain shorting risk increases
Solution Approach 1:
The ammonium fluoride protection layer serves as an intermediary barrier that enables thorough cleaning of source/drain regions while protecting the metal gate and metal drain structures from direct exposure to fluorine ions. This intermediary layer prevents the formation of conductive pathways that would cause shorting, thus maintaining reliability while achieving effective cleaning.
Solution Approach 2:
The protection layer is applied in advance before the fluorine-based pre-clean process to preemptively counteract the potential harmful effects of fluorine ion exposure. By establishing this protective barrier beforehand, the process prevents metal gate/metal drain shorting before it can occur, allowing aggressive cleaning to proceed safely.
3Productivity
If fluorine ions are used for etching oxide layers, then etching effectiveness is improved, but material loss increases
Solution Approach 1:
The protection layer provides local quality differentiation by allowing high etching effectiveness in regions where oxide layers need removal (source/drain regions) while simultaneously providing protection in regions where material loss must be minimized (interlayer dielectric and metal structures). This spatially selective protection enables the fluorine-based etch process to be both effective and selective.
Solution Approach 2:
The ammonium fluoride protection layer acts as a mediator that modulates the interaction between fluorine ions and different materials. It allows fluorine ions to effectively etch oxides while blocking or reducing their interaction with protective materials, thus maintaining high etching effectiveness while minimizing unwanted material loss.
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 reduces the risk of metal gate/metal drain shorting, minimizes SAC loss loading, and increases the epitaxial loss window, allowing for more robust temperature control and reduced material loss during the pre-clean process.
Implementation Method 1
forming an ammonium fluoride gas in a processing chamber to cause a chemical reaction between the ammonium fluoride gas and an oxide layer on a source or drain region of a semiconductor device
Implementation Method 2
forming a protection layer on the interlayer dielectric layer, the insulating cap, and the source/drain region that protects the interlayer dielectric layer, the insulating cap, and the source/drain region from being etched
Data Source
AI summary
An ammonium fluoride gas may be used to form a protection layer for one or more interlayer dielectric layers, one or more insulating caps, and/or one or more source/drain regions of a semiconductor device during a pre-clean etch process. The protection layer can be formed through an oversupply of nitrogen trifluoride during the pre-clean etch process. The oversupply of nitrogen trifluoride causes an increased formation of ammonium fluoride, which coats the interlayer dielectric layer(s), the insulating cap(s), and/or the source/drain region(s) with a thick protection layer. The protection layer protects the interlayer dielectric layer(s), the insulating cap(s), and/or the source/drain region(s) during the pre-clean process from being etched by fluorine ions formed during the pre-clean process.