Implementation of Plasma Chemical Etching in Submicron Technology of Integrated Circuit Structures
How plasma helps create the nanochips of the future
Introduction: The Unsung Hero of the Semiconductor Revolution
At the heart of every modern electronic device—from smartphones to automobiles—lies an integrated circuit, an amazing creation of engineering thought where millions of transistors are placed on a tiny silicon chip. But how is it possible to create extremely complex circuits with elements hundreds of times smaller than the width of a human hair? The answer lies in one of the most important but almost invisible processes—plasma chemical etching 1 .
Submicron Technology
Elements smaller than 1 micrometer require precision etching techniques.
Plasma Applications
Used in semiconductor manufacturing for precise material removal.
What is Plasma Chemical Etching?
Plasma chemical etching is a high-tech process that uses ionized gas (plasma) for precise removal of material from a semiconductor surface. Unlike traditional "wet" chemical etching, where a wafer is immersed in an acid solution, plasma chemical etching is a "dry" process that takes place in a vacuum chamber 7 .
Comparison: Plasma vs. Chemical Etching
| Criterion | Plasma Etching | Chemical Etching |
|---|---|---|
| Precision | High precision, ideal for complex patterns | Lower precision, not suitable for fine details |
| Waste | Minimal waste, environmentally safer | Potential hazardous waste requiring disposal |
| Residues | No chemical residues, minimal further cleaning | Possible residues, additional cleaning needed |
| Cost | Higher cost, expensive equipment and maintenance | More economical, especially for mass production |
| Complexity | Complex setup, requires specialized training | Simple process, easier to implement |
| Materials | Suitable for various materials (metals, plastics, semiconductors) | Effective for thick materials and deep etching |
Three Key Stages of Plasma Etching
Stage 1
Silicon wafer with photoresist pattern is placed in a vacuum chamber
Stage 2
Plasma is initiated, generating high-energy reactive particles
Stage 3
Particles interact with surface material, creating volatile compounds removed by vacuum system 8
Fundamental Principles & Advantages
The secret to the effectiveness of plasma chemical etching lies in the combination of physical and chemical mechanisms. The chemical component provides high etching rate through the reaction of active radicals with the target material, while the physical component (ion bombardment) provides anisotropy—the ability to create nearly vertical walls in the material 8 .
Reactive species in plasma chemically react with surface atoms, forming volatile products
Ion bombardment provides directional etching for anisotropic profiles
Key Advantage
This anisotropy is a crucial advantage for submicron technologies as it allows creation of extremely dense structures without "undercutting" beneath the mask, which is characteristic of isotropic wet etching 7 . Additionally, the dry plasma etching process eliminates moisture problems that can occur when using liquid chemicals in semiconductor manufacturing 5 .Experiment: ICP Etching of Monocrystalline Diamond
Inductively Coupled Plasma (ICP) etching represents one of the most advanced forms of this technology. A recent study published in Scientific Reports detailed analyzed the ICP etching process for creating patterns on monocrystalline diamond—a material known for its extreme hardness and chemical inertness 2 .
Experimental Methodology
The study used a sequential one-dimensional optimization method to examine the influence of four key process parameters:
Sample Preparation
Diamond samples were pre-cleaned using piranha solution (mixture of sulfuric acid and hydrogen peroxide), after which an aluminum mask was applied by magnetron sputtering.
Photolithography
Used to transfer the pattern to the aluminum layer before direct etching in the ICP system 2 .
Etching Process
Optimization of parameters for maximum efficiency and surface quality.
Results & Analysis
Experiments showed clear dependencies between process parameters and etching characteristics. Etching rate significantly increased with increasing RF power and ICP power. The influence of O₂/Ar gas ratio and chamber pressure was more complex, showing optimal values for achieving maximum efficiency.
| Process Parameter | Impact on Etching Rate | Impact on Surface Roughness |
|---|---|---|
| O₂/Ar Ratio | Gradual increase with higher oxygen content | Minimal impact |
| ICP Power | Significant increase | Sharp increase, especially at high power |
| RF Power | Significant increase | Noticeable increase |
| Chamber Pressure | Increase followed by decrease | Minimal impact |
- O₂/Ar gas flow ratio: 50/50 sccm
- ICP power: 600 W
- RF power: 120 W
- Chamber pressure: 20 mTorr
- Etching selectivity: 1:46 (diamond to mask) 2
Chemical Etching:
C (diamond) + O₂ → CO↑ or CO₂↑
Physical Etching:
Ar⁺ + diamond → bombardment and sputtering of carbon atoms 2
The combination of these reactions ensures effective material removal and creation of clear patterns on one of the hardest materials in the world.
Researcher's Toolkit: Key Components for Plasma Etching Experiment
Successful execution of a plasma etching experiment requires careful selection of materials and equipment. Here are the key elements used in the described research:
ICP Etching System
Main equipment with radio frequency (13.56 MHz) generator for creating high-density plasma.
CVD Monocrystalline Diamond
Substrate size 3×3×0.5 mm³ with initial roughness of 5-10 nm.
Etching Gases (O₂ & Ar)
O₂ serves as the main reactive gas, while Ar assists in physical sputtering.
Aluminum Mask
Creates protected areas on the diamond surface during etching.
Piranha Solution
Aggressive mixture of H₂SO₄ and H₂O₂ for thorough surface cleaning before etching.
Laser Confocal Microscope
For precise measurements of etching depth and surface roughness.
Conclusion: The Future of Microchips in the Hands of Plasma
Plasma chemical etching has transformed from an exotic technology into a fundamental process behind the modern semiconductor industry. Research similar to the described diamond etching experiment demonstrates the incredible potential of this method for processing even the most resistant materials with incredible precision 2 .
As we advance into the nanoelectronics era, requirements for precision and miniaturization will only increase. The development of technologies such as atmospheric plasma etching, which eliminates the need for expensive vacuum equipment, opens new horizons for processing complex materials such as Ti-6Al-4V alloy used in aerospace and biomedical industries 9 .
Optimal Etching Parameters for Different Materials
| Material | Gases | Power | Pressure | Features |
|---|---|---|---|---|
| Diamond | O₂/Ar | ICP: 600 W, RF: 120 W | 20 mTorr | High selectivity (1:46) |
| Gold (Au) | CF₄/Ar | - | - | Complex due to chemical inertness |
| Silicon & Silicon Dioxide | CCl₄, CHF₃, O₂ | - | - | Widely studied, different gases for different layers |
| Titanium (Ti-6Al-4V) | SF₆ | - | - | For atmospheric etching |