Atomic Layer Etching for Bottom-Up Cobalt Fill
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Solution Overview
Problem
Current semiconductor fabrication processes face challenges in filling small features with metals due to issues like void formation and electromigration, particularly in advanced logic and memory applications, where existing wet clean techniques are not selective and can remove metal or catalytic layers, leading to incomplete filling and pinch-off.
Innovation Solution
The use of directional atomic layer etching (ALE) to selectively etch the field and neck regions of semiconductor features, followed by electroless deposition (ELD) to achieve a bottom-up fill, ensuring the bottom of the feature is filled without altering the metal or catalytic layer, thereby preventing void formation and enhancing fill efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet clean is used to prepare the feature, then the feature surface is cleaned, but the metal or catalytic layer is removed from the bottom of the feature resulting in failure of bottom-up fill
Solution Approach 1:
The patent applies atomic layer etching with directional ion bombardment to create local selectivity: the neck region receives sufficient ion flux to etch the metal/catalytic layer, while the feature bottom receives reduced ion flux that preserves the seed layer. This spatial variation in etching intensity enables selective removal of material from specific regions without affecting others.
Solution Approach 2:
The patent modifies the etching process parameters by controlling ion energy, gas composition, and exposure time to achieve differential etching rates. By adjusting these parameters, the process selectively removes material from the neck region while maintaining the seed layer at the feature bottom, enabling successful bottom-up fill.
2Reliability
If wet clean is used to clean the feature, then contamination is removed, but early pinch-off and void formation occur due to incomplete or excessive metal removal
Solution Approach 1:
The directional ALE process creates spatially selective etching where the neck region is preferentially cleaned of metal/catalytic material while the feature bottom retains its seed layer. This local differentiation prevents both complete removal (which would cause voids) and insufficient removal (which would cause pinch-off).
Solution Approach 2:
The patent replaces the chemical wet clean process with a physical/chemical hybrid ALE process using directional ion bombardment. This substitution provides better control over material removal by using physical ion flux directionality rather than isotropic chemical etching, enabling precise control of pinch-off and void formation.
3Manufacturing precision
If conventional etching is used to open the feature top, then the neck region is cleared, but the field surrounding the feature is not selectively etched leading to residual metal on the field
Solution Approach 1:
The directional ALE process applies ion bombardment at specific angles that preferentially reach the neck region and surrounding field areas while being blocked from the feature bottom by the sidewalls. This creates local etching in the neck and field regions while preserving the seed layer at the feature bottom.
Solution Approach 2:
The patent uses asymmetric ion bombardment geometry where ions approach the substrate at oblique angles. This asymmetry causes ions to preferentially etch exposed surfaces like the neck region and field areas, while the vertical sidewalls shield the feature bottom from ion impact, creating selective material removal in different regions.
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 effective filling of small feature structures on semiconductor substrates, reducing void formation and electromigration concerns, and ensuring complete and reliable metal fill in advanced technology nodes.
Implementation Method 1
exposing the substrate to a halogen-containing gas to modify the surface of the substrate, exposing the substrate to an activation gas to etch the modified surface
Implementation Method 2
exposing the substrate to an activation gas and an activation source (e.g., a plasma) to etch one or more layers on the substrate
Implementation Method 3
depositing a metal in the feature by a bottom-up fill deposition technique
Data Source
AI summary
Atomic layer etching (ALE) enables effective filling of small feature structures on semiconductor and other substrates, such as contacts and vias, by bottom-up fill, for example electroless deposition (ELD) of cobalt.