Functional Modeling of Dry Etch at Semiconductor Manufacturing
Dry etch is one of the key pattern-transfer processes in semiconductor manufacturing. It is used to create vias, trenches, contact holes, and other micro- and nanoscale structures in dielectric, metal, or semiconductor layers. Unlike wet etching, dry etching uses plasma chemistry and ion bombardment, which allows better control of feature shape, directionality, and critical dimensions.
In a typical silicon oxide dry etch process, the wafer is coated with a sacrificial light-absorbing material and photoresist, which define the pattern. The wafer is placed in a plasma etch chamber. Fluorine-containing plasma species interact with exposed SiO₂ and convert it into volatile products, mainly SiF₄, which are removed by the vacuum system. At the same time, ion bombardment assists the reaction, removes passivation or polymer from the feature bottom, and helps form vertical vias or trenches.
Two coupled mechanisms control the process:
Chemical etching — reactive radicals convert SiO₂ into volatile reaction products.
Mechanical / ion-assisted etching — accelerated ions activate the surface, improve directionality, and remove material or polymer from the feature bottom.
The main challenge is that the same mechanisms that enable etching can also create defects. Plasma exposure can heat and erode the resist and sacrificial layers, generating water-containing and carbon-containing by-products. SiF₄ may react with moisture and form silicon-oxide or silicon-oxyfluoride particles. Excessive ion bombardment can sputter fragments from the wafer, mask, chamber parts, or focus ring, leading to redeposition, micromasking, residues, blocked vias, or underetched features.
Therefore, the goal of this project is to build a functional model of the dry etch system, identify useful and harmful interactions, and understand how process parameters such as plasma source power, bias power, gas chemistry, pressure, temperature, pumping efficiency, and overetch time affect defect formation. The model will help reveal process contradictions and generate practical guidance to reduce particles and residues while maintaining etch rate, profile control, and process stability.
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