Functional Modeling of Dry Etch at Semiconductor Manufacturing
The dry etch system is used to transfer a lithographic pattern into a semiconductor layer, such as silicon oxide, by using plasma chemistry and ion-assisted material removal. The wafer is coated with a sacrificial light-absorbing layer and photoresist, which define the openings for vias or trenches.
During the process, the wafer is placed on an electrostatic chuck inside a vacuum chamber. Process gases are introduced into the chamber and converted into plasma by the plasma source generator. Fluorine-containing radicals chemically react with exposed SiO₂ and convert it into volatile silicon-fluoride products, mainly SiF₄, which are removed by the vacuum pump.
At the same time, the bias generator accelerates ions toward the wafer surface. Ion bombardment helps remove polymer or passivation from the bottom of the feature, activates the surface reaction, and provides directional etching needed to form vertical vias and trenches.
The main useful function of the system is to remove exposed SiO₂ according to the resist pattern while preserving protected areas and maintaining the required profile.
However, the same process can also generate harmful effects. Plasma can erode photoresist and sacrificial layers, producing carbon-, oxygen-, and hydrogen-containing by-products. SiF₄ can react with moisture and form silicon-oxide or silicon-oxyfluoride particles. Excessive ion bombardment can sputter material from the wafer, mask, chamber parts, or focus ring, causing redeposition, micromasking, blocked vias, residues, and underetch defects.
Therefore, the dry etch process should be modeled as a system with two coupled mechanisms:
Chemical etching: radicals convert SiO₂ into volatile reaction products.
Mechanical / ion-assisted etching: ions activate the surface and control etch directionality.
The functional model should help identify how equipment components, plasma species, wafer materials, reaction products, and process parameters interact to produce both useful etching and harmful defect formation.
Operational Effectiveness – OE
Effective
Ineffective
OE 0.45
Operational Perfectness - OP
Basic functions
Components
Supersystems
OP 0.02
Electrostatic Chuck - ESC | 16 |
Ions | 11 16 |
Plasma | 9 |
Dielectric material (SiO2) | 6 26 |
Helium | 6 |
Gases | 5 |
MHz generator | 5 |
Dry etch Chamber | 5 |
SLAM | 4 18 |
Electrons | 3 |
The Functional Model shows that defects are generated during the dry etch process itself by two main mechanisms.
First, the chemical etch mechanism converts SiO₂ into volatile SiF₄. If SiF₄ interacts with water or moisture-containing by-products, SiO₂ or silicon-oxyfluoride particles can form and redeposit on the wafer.
Second, the mechanical / ion-assisted etch mechanism provides directional etching, but excessive ion energy can sputter SiO₂, resist, SLAM, or chamber materials. These sputtered fragments can also redeposit as particles, residues, or micromasks.
Therefore, defect formation can be managed by properly adjusting the two plasma generators:
- Source generator — controls plasma density, radical concentration, and chemical etch intensity.
- Bias generator — controls ion energy, directionality, and sputtering intensity.
The key is to balance these two mechanisms: provide enough chemical etching to remove SiO₂ efficiently, while keeping ion bombardment below the level where sputtering creates defects.
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