Cleaning principles of SC1 and SC2

SC1 and SC2 are two commonly used wet cleaning processes in semiconductor manufacturing, primarily used to remove contaminants from the surface of silicon wafers. Their cleaning principles are as follows:

I. SC1 Cleaning Principle

1. Composition and Function

Cleaning solution components: SC1 is composed of ammonium hydroxide (NH₄OH), hydrogen peroxide (H₂O₂), and water (H₂O), with a typical ratio of 1:2:50 (volume ratio).

Main function: Removes particulate contaminants, organic matter, and some metallic impurities from the silicon wafer surface.

2. Cleaning Mechanism

Synergistic effect of oxidation and corrosion:

Strong oxidizing property of H₂O₂: Oxidizes the natural oxide film (SiO₂) on the silicon wafer surface into a more dense oxide layer, while simultaneously oxidizing organic matter and metallic contaminants.

Alkaline corrosion of NH₄OH: Corrodes the oxide layer (SiO₂) and silicon (Si) on the silicon wafer surface, causing the attached particles to lose their support and detach.

Dynamic equilibrium: The oxidation and corrosion processes alternate, with the oxide film continuously being generated and then corroded, thus continuously removing contaminants.

Electrostatic repulsion:

The alkaline environment (NH₄OH) causes the silicon wafer surface and particle surfaces to become negatively charged, creating electrostatic repulsion and preventing particle re-adsorption.

Megasonic assistance (optional):

High-frequency megasonic waves (e.g., 950 kHz) generate high-speed fluid impacts through liquid vibration, enhancing particle removal efficiency, especially for small particles (≥0.1 μm).

3. Characteristics

Applicable contaminants: Particles, organic matter, some metals (such as Al, Fe).

Limitations: Cannot effectively remove the natural oxide film and may introduce metallic contamination (due to the alkaline environment easily adsorbing metal ions).

II. SC2 Cleaning Principle

1. Composition and Function

Cleaning solution components: SC2 is composed of hydrochloric acid (HCl), hydrogen peroxide (H₂O₂), and water (H₂O), with a typical ratio of 1:1:50 (volume ratio).

Main function: Removes metal ions (such as Na⁺, Fe²⁺, Mg²⁺, etc.) from the silicon wafer surface.

2. Cleaning Mechanism

Acidic complexation:

Acidic dissolution of HCl: Hydrochloric acid provides H⁺ and Cl⁻, reacting with metal ions to form soluble chlorides (such as FeCl₂, MgCl₂), while simultaneously inhibiting the adhesion of metal oxides.

Oxidizing action of H₂O₂: Oxidizes metallic contaminants to higher valence states (such as Fe²⁺→Fe³⁺), enhancing the complexation ability with Cl⁻ to form stable soluble complexes.

Low pH environment inhibits particle adsorption:

Under acidic conditions (pH 3-5.6), the silicon wafer surface is positively charged, creating electrostatic repulsion with similarly positively charged metal ions, reducing metal re-adsorption.

Complexation effect of chloride ions:

Cl⁻ forms complexes with metal ions (such as Fe³⁺, Cu²⁺) (such as [FeCl₄]⁻, [CuCl₂]⁻), preventing metal precipitation on the silicon wafer surface.

3. Characteristics

Applicable contaminants: Metal ions (such as Na, Fe, Mg, Ca).

Limitations: Cannot remove particles or organic matter, and may corrode metal layers such as aluminum.

III. Synergistic Application of SC1 and SC2

Cleaning sequence: SC1 (remove particles/organic matter) → SC2 (remove metals)

Complementarity:

SC1's alkalinity easily adsorbs metals, while SC2's acidity can remove metals.

Combined use achieves comprehensive cleaning (core steps of RCA standard process)

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