Tungsten Pullback Etch for Silicon Nitride-Safe MOL Fill
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Solution Overview
Problem
Conventional tungsten pullback methods in semiconductor manufacturing, particularly in middle-of-line (MOL) integration, are limited by the use of high resistive nitridation layers and bottom anti-reflective coatings (BARC), which hinder scaling of small critical dimension structures and can damage underlying silicon nitride layers during dry etching.
Innovation Solution
A method involving a metal cap layer deposition, followed by a polymer fill process using a flowable polymer layer, and a two-step etch process with molybdenum hexafluoride and chlorine/nitrogen trifluoride plasma for selective tungsten cap layer removal, along with a polymer removal and pre-clean process to enable void-free metal fill in features with small critical dimensions without damaging dielectric layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a dry etch method is used for tungsten pullback, then etching speed and precision are improved, but underlying silicon nitride layers are damaged
Solution Approach 1:
A polymer layer is introduced as an intermediary protective barrier between the dry etch process and the silicon nitride layer. The polymer layer is selectively removed after tungsten removal, allowing the dry etch to proceed at high speed without damaging the underlying silicon nitride structure
Solution Approach 2:
The etch selectivity is optimized by adjusting process parameters (gas composition, power, pressure) to achieve differential etching rates between tungsten and silicon nitride, enabling selective tungsten removal while preserving the dielectric layer
2Ease of manufacture
If high resistive nitridation layers and BARC are used in conventional tungsten pullback, then tungsten cap layer removal is achieved, but scaling of MOL structures is limited
Solution Approach 1:
The harmful nitridation layer and BARC steps are extracted and removed from the process flow. The invention achieves tungsten pullback using only a polymer layer and selective dry etching, eliminating the scaling limitations imposed by thick nitridation layers and BARC processes
Solution Approach 2:
The process is simplified by changing the fundamental approach from chemical nitridation-based removal to polymer-based protective layer removal, enabling better control over critical dimensions and supporting continued scaling
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 allows for the selective removal of tungsten cap layers over dielectric layers without damaging them, enabling efficient metal fill in small critical dimension features with improved scalability and reduced risk of damage to underlying layers.
Implementation Method 1
a first etch process including a chemical etch process using molybdenum hexafluoride (MoF6) to remove the metal cap layer selectively to the dielectric layer
Implementation Method 2
a first etch process including a dry etch process using chlorine (Cl2) and nitrogen trifluoride (NF3) plasma
Implementation Method 3
a second etch process including a dry etch process using chlorine (Cl2) only
Data Source
AI summary
A method of filling a feature in a semiconductor structure with metal includes depositing a metal cap layer on a bottom surface of a feature formed within a dielectric layer and top surfaces of the dielectric layer, partially filling the feature from the bottom surface with a flowable polymer layer, performing a metal pullback process to remove the metal cap layer on the top surfaces of the dielectric layer selectively to the dielectric layer, wherein the metal pullback process includes a first etch process including a chemical etch process using molybdenum hexafluoride (MoF6) to remove the metal cap layer selectively to the dielectric layer, and a second etch process to remove residues on etched surfaces of the dielectric layer, removing the flowable polymer layer, pre-cleaning a surface of the metal cap layer, and filling the feature from the surface of the metal cap layer with metal fill material.