ALD Copper Seed Layer for Seamless BEOL Gapfill
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Solution Overview
Problem
Conventional deposition methods struggle to fill high aspect ratio features without forming seams or voids, especially in smaller features, due to substrate material dependence and limitations in reflow characteristics, particularly in copper interconnects for BEOL processes.
Innovation Solution
The method involves forming a copper gapfill seed layer by atomic layer deposition (ALD) at a first temperature and subsequent filling with copper using physical vapor deposition (PVD) at a higher temperature, with optional diffusion barriers and liners, to achieve a seam-free gapfill film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PVD copper deposition is used at high temperature, then copper reflow characteristics improve, but substrate material dependence increases and seam formation occurs
Solution Approach 1:
A copper seed layer is deposited beforehand using ALD or electroplating methods before the main PVD copper deposition. This preliminary copper layer serves as a foundation that enables subsequent copper to flow and refill seams during high-temperature reflow, reducing substrate material dependence and preventing defect formation.
Solution Approach 2:
The copper seed layer acts as an intermediary between the substrate and the main copper fill. It mediates the interaction by providing a controlled interface that reduces direct substrate-copper interaction, thereby reducing substrate material dependence while enabling seamless filling during reflow.
2Productivity
If conventional PVD deposition is used to fill high aspect ratio features, then deposition speed is maintained, but seams and voids form in the feature lower portions
Solution Approach 1:
The copper filling process is segmented into multiple stages: first depositing a thin conformal copper seed layer, then adding the bulk copper material. This segmentation allows the seed layer to establish continuous coverage at the feature bottom, preventing seam formation while maintaining efficient bulk deposition speed.
Solution Approach 2:
The copper seed layer is deposited as a preliminary step before main copper fill. This preliminary layer ensures continuous copper coverage at the feature bottom and sides, creating a foundation that prevents seam formation during subsequent high-speed deposition.
3Manufacturing precision
If ALD copper seed layer is deposited at low temperature, then conformal coverage is achieved, but subsequent PVD deposition requires higher temperature for reflow
Solution Approach 1:
The process utilizes different temperature parameters for different deposition stages: low temperature (e.g., 25-150°C) for ALD seed layer deposition to achieve conformal coverage, then high temperature (e.g., 200-400°C) for PVD copper deposition to enable reflow and seam elimination. This parameter change optimizes each stage's performance.
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 conformal and seamless filling of features with high aspect ratios, reducing voids and improving reflow characteristics, thereby enhancing the reliability of copper films in BEOL processes.
Implementation Method 1
A copper gapfill seed layer is formed by atomic layer deposition (ALD) at a first temperature on the substrate surface
Implementation Method 2
The feature is filled with copper by physical vapor deposition (PVD) at a second temperature greater than the first temperature to form a seam-free gapfill film
Data Source
AI summary
Methods and apparatus to fill a feature with a seamless gapfill of copper are described. A copper gapfill seed layer is deposited on a substrate surface by atomic layer deposition followed by a copper deposition by physical vapor deposition to fill the gap with copper.