【Semiconductor etching process】The soul of semiconductors teaches the etching process and the practice of engineers on defective rate problems from 0 to 1 (CH3-CH4)

CH3. The purpose of the Etch process and the plasma concept

The purpose of the Etch process

After the pattern is formed on the photoresist (PR) through the photoresist process, the pattern on the photosensitive adhesive is transferred to the actual film.

This is the process of removing unwanted parts in semiconductor device manufacturing→ This process determines the degree of integration of the device/divided into selective etching and non-selective etching.

What is Plasma?

Plasma is an ionized gas, composed of neutral particles (radicals), ions and electrons, and is electrically neutral as a whole.

Radical (free radicals) are responsible for chemical etching (isotropy) and ions are responsible for physical etching (anisotropy), both occurring simultaneously and are adjustable.

Methods of Etch

Dry etching：Utilizes activated plasma gas

•Definition: A process in which a gas is injected into a vacuum chamber and then power is applied to form a plasma, which initiates a physical or chemical reaction to etch a thin film through ions and free radicals.

•Features: Easy time control / Etching profile (isotropy & anisotropy) / Easy key dimension (CD) control / Confirmation and detection of etching end.

•Advantages: Isotropic and anisotropic etching/gas selection and flow control (MFC) are simple, ensuring accurate patterning/high degree of automation→ improving yield and production efficiency.

•Disadvantages: Numerous process parameters / difficult to understand the process / plasma damage leads to substrate damage and contamination / difficult to etch materials.

Wet etching：Use solution-based chemicals

•Definition: The process of using chemicals to chemically react with the film to be etched to dissolve it, so as to achieve etching.

•Features: Very high selectivity between films / Batch processing of wafers at one time (batch method) / Isotropic etching / Less product deterioration.

•Advantages: Very high selectivity between membranes

•Disadvantages: Low uniformity / low accuracy.

CH4. Plasma generation and properties

Plasma generation and disappearance

•Paschen's Law：In a uniform electric field, the breakdown voltage is proportional to the gas pressure (p) and the electrode spacing (d) →V = Ks × p × d

•Accelerated by the action of an electric field→ collides with neutral particles to undergo ionization reactions → generate free electrons and secondary electrons → avalanche effect → form plasma.

Through the process of electrode disappearance - electrons disappear due to recombination on the wall / ions disappear in the cathode plate due to high energy.•Energy supply method - Thermal energy / Energetic beam / Electric field (mainly used, RF waves).

•=>Plasma can be used for CVD and etching processes.

[ Conditions for ionization of atoms or molecules in their natural state]

Heating, the relationship between temperature, electric field and pressure, the ionization process

1.Rebound: Unaccelerated electrons collide with ions (elastic collisions) → no reaction.

2.Excitation and luminescence: Insufficient energy of accelerated electrons or ions → the transition of outer electrons to a higher energy level (unstable) → Release of light upon return.

3.Ionization: Accelerated free electrons or ions collide with molecules, creating new ions and free electrons → to form plasma.

Properties of plasma

Electrical properties: Conductive.

Magnetic properties: Density can be increased by magnetic fields → energy can be concentrated in the desired location.

3.Chemical Properties: The excited molecule tends to react with other molecules or atoms → Applied to PECVD, Etching (RIE).

Sheath

= A "quasi-neutral" destroyed area formed at the junction of plasma and non-plasma regions (cavity walls or wafers).

→ As the plasma density increases, the voltage increases - the plasma voltage.

•Inside Sheath

1.Positive ions bombard the cathode: release secondary electrons.

2.Positive ion bombardment.

3.Momentum – Collision Energy Exchange: Electrons gain energy through collisions with neutral particles in an electric field.

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