Atomic Layer Metal Etching for Selective Copper Pad Recess
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Solution Overview
Problem
Existing methods for selective dry etching of metals like copper at the atomic scale face challenges in achieving precise control of metal pad recess depth and maintaining etch uniformity as feature sizes decrease, especially when both metal and dielectric surfaces are polished at the same rate, leading to difficulties in creating reliable electrical contacts.
Innovation Solution
A method involving cycles of surface modification, hydrogen treatment, and cleaning treatment using plasma-excited gases to form and remove reaction products on metal surfaces, ensuring selective etching of copper relative to dielectrics without sputtering, with each cycle etching a controlled thickness of 3-4 Å, and optionally including a surface modifying step to maintain etch linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical planarization (CMP) is used to recess metal pads, then metal pad recess can be achieved, but as feature sizes decrease, both metal and dielectric surfaces are polished at the same rate, making it difficult to achieve selective recess and proper electrical contacts
Solution Approach 1:
The etching process is divided into multiple atomic layer cycles, where each cycle removes a precise thickness (3-4 Å) of metal. This segmentation allows cumulative control of total recess depth while maintaining selectivity, as each atomic layer cycle is self-limiting and selective to metal over dielectric.
Solution Approach 2:
The process uses periodic cyclic treatment with alternating plasma treatments (e.g., fluorocarbon plasma followed by oxygen plasma or argon plasma). Each cycle consists of multiple steps that periodically modify and remove atomic layers, enabling precise depth control through number of cycles while maintaining metal selectivity.
2Measurement precision
If conventional dry etching is used for metal etching, then etching can be performed, but achieving atomic-scale precision and uniformity is difficult
Solution Approach 1:
The process changes parameters by using low-power plasma conditions and controlling plasma chemistry to achieve atomic layer precision. By adjusting plasma power, pressure, and gas composition, each cycle removes a controlled thickness (3-4 Å) with high uniformity across the wafer, enabling atomic-scale etch depth control.
Solution Approach 2:
The atomic layer etching process incorporates in-situ monitoring and feedback control to maintain precise etch rates and uniformity. Process parameters are adjusted based on real-time measurements of etch depth and rate, ensuring consistent atomic-scale precision across multiple cycles.
3Ease of manufacture
If high energy plasma is used for cleaning, then reaction products are removed effectively, but damage may occur to the metal surface and adjacent dielectrics
Solution Approach 1:
The cleaning process uses localized quality by applying different plasma chemistries at different stages: fluorocarbon plasma for volatile product formation, followed by oxygen or argon plasma for gentle removal. This localized approach ensures effective cleaning while minimizing damage to metal surfaces and adjacent dielectrics through selective plasma chemistry.
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 method provides precise control over etch rate and uniformity, reduces damage to adjacent dielectrics, and enhances surface smoothness, facilitating reliable electrical contacts and hybrid bonding processes.
Implementation Method 1
exposing the rough or oxidized surface to a plasma-excited H2 gas, where the plasma-excited H2 gas chemically reduces the oxidized surface of the metal layer and forms a layer of reaction products on the metal layer
Implementation Method 2
exposing the rough or oxidized surface to a plasma-excited Ar gas, where the plasma-excited Ar gas removes the layer of reaction products overlying the metal layer, where kinetic energy of the plasma-excited Ar gas is at or below a sputtering threshold for removing metal from the metal layer
Implementation Method 3
exposing the metal layer to a plasma-excited H2 gas; exposing the metal layer to a plasma-excited noble gas
Data Source
AI summary
A method of etching a metal includes performing at least two cycles of an etch process. A cycle of the etch process includes: performing a surface modification on an exposed surface of a metal layer over a substrate, performing a hydrogen treatment on the metal layer, and performing a cleaning treatment on the metal layer. The hydrogen treatment forms a layer of reaction products on the metal layer. The cleaning treatment removes the layer of reaction products.