Atomic Layer Etching Tungsten Halide Plasma Control
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Solution Overview
Problem
Conventional etching methods for tungsten and cobalt in semiconductor fabrication face challenges such as lack of precise control, surface roughness, and poor etch selectivity, particularly in advanced logic and memory applications where feature sizes are small and uniformity is critical.
Innovation Solution
The implementation of atomic layer etching (ALE) using halide chemistry to form a modified surface layer, followed by exposure to a plasma with controlled bias voltage, allowing for precise removal of the modified layer with directional control and minimal surface damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used for tungsten and cobalt, then etching can be performed, but precise etch control and uniformity are poor
Solution Approach 1:
The etching process is divided into two distinct sequential steps: (1) surface modification by exposing to halide chemistry to form a modified surface layer, and (2) removal of the modified layer by plasma exposure with bias voltage. This segmentation allows each step to be independently optimized, achieving precise control over etch depth and rate while improving selectivity.
Solution Approach 2:
Before the actual etching step, the metal surface is pre-modified by exposure to halide chemistry (e.g., chlorine-containing plasma or gas) to form a halide-containing surface layer. This preliminary action creates a chemically distinct layer that is more susceptible to subsequent plasma removal, enabling precise etch control and improved selectivity.
2Manufacturing precision
If conventional etching is used, then metal can be removed, but surface roughness increases
Solution Approach 1:
The process uses controlled parameter changes including maintaining substrate temperature below 150°C during halide exposure to prevent spontaneous etching, applying specific bias voltage ranges (50-80 Vb) during plasma removal, and controlling plasma power and pressure. These parameter optimizations ensure smooth surface finish while achieving desired etch depth.
3Length of moving object
If feature sizes are reduced for advanced devices, then device scaling is achieved, but filling becomes harder and etch control becomes more difficult
Solution Approach 1:
The halide modification step is self-limiting, forming a surface layer of controlled thickness that naturally stops growing after monolayer coverage. This self-service characteristic provides inherent control over etch depth, ensuring uniformity even in sub-20nm features without requiring complex external control mechanisms.
4Productivity
If plasma exposure is increased to improve etch rate, then productivity increases, but surface damage and re-deposition increase
Solution Approach 1:
The halide-containing surface layer acts as an intermediary between the metal substrate and the plasma removal step. This intermediate layer allows plasma to remove material efficiently while protecting the underlying metal from direct plasma damage, reducing surface roughness and minimizing re-deposition of etch products.
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
ALE provides precise etch control down to atomic levels, achieving uniformity within 1 nm and reducing surface roughness, enabling effective etching of tungsten, cobalt, and their nitrides with improved selectivity and reduced re-deposition of etch products.
Implementation Method 1
exposing a surface of the metal to a halide chemistry to form a modified halide-containing surface layer
Implementation Method 2
applying a bias voltage to the substrate while exposing the modified halide-containing surface layer to a plasma to thereby remove the modified halide-containing surface layer
Implementation Method 3
applying a bias voltage to the substrate while exposing the modified halide-containing surface layer to a plasma
Data Source
AI summary
Provided herein are methods of atomic layer etching (ALE) of metals including tungsten (W) and cobalt (Co). The methods disclosed herein provide precise etch control down to the atomic level, with etching a low as 1 Å to 10 Å per cycle in some embodiments. In some embodiments, directional control is provided without damage to the surface of interest. The methods may include cycles of a modification operation to form a reactive layer, followed by a removal operation to etch only this modified layer. The modification is performed without spontaneously etching the surface of the metal.