The Challenge: Contamination Control in Polysilicon Wafer Cleaning

Polysilicon wafers, used in semiconductor device production, must undergo rigorous cleaning processes to ensure their performance and reliability. Even trace contamination can lead to device failure. The goal of cleaning is to remove surface contaminants, including both organic and inorganic impurities. These contaminants may exist as atoms, ions, thin films, or particles on the wafer surface. Organic contaminants include photoresist, organic solvent residues, synthetic waxes, and oils or fibers introduced by handling. Inorganic contamination, such as heavy metals (gold, copper, iron, chromium), alkali metals (e.g., sodium), and particles (silicon slag, dust, bacteria, microorganisms, and organic colloidal fibers), can significantly affect the wafer’s performance by reducing carrier lifetime, surface conductivity, and causing leakage or defects.

• Organic Contaminants: These include residues from photoresists, organic solvents, and oils or fibers introduced by human handling or tools.
• Inorganic Contaminants: Heavy metals like gold, copper, and iron, and alkali metals like sodium can cause severe electrical leakage and reduce wafer quality.
• Particle Contaminants: These include silicon slag, dust, bacteria, and fibers that can cause defects and reduce the overall yield of the semiconductor devices.

The Challenge: Ensuring Water Purity in Integrated Circuit Production

In integrated circuit (IC) production, ultrapure water (UPW) is crucial for several key processes, with 80% of the steps involving wafer cleaning. The quality of water directly impacts the quality and yield of the final IC products. Contaminants in water, such as alkali metals (e.g., K, Na), heavy metals (e.g., Au, Ag, Cu), group III elements (e.g., B, Al, Ga), and group V elements (e.g., P, As, Sb), can severely affect the performance of the semiconductors. Bacteria and particulates in the water can lead to short circuits or poor electrical characteristics, while specific elements can degrade the properties of both N-type and P-type semiconductors. Maintaining a high level of purity is essential to avoid these detrimental effects and ensure optimal performance.

• Alkali Metals: Elements like potassium (K) and sodium (Na) can weaken the insulating layer and cause poor dielectric breakdown.
• Heavy Metals: Metals such as gold (Au), silver (Ag), and copper (Cu) can degrade the integrity of PN junctions.
• Group III and V Elements: Elements like boron (B), aluminum (Al), and gallium (Ga) can negatively affect N-type semiconductors, while phosphorus (P), arsenic (As), and antimony (Sb) can impair P-type semiconductors.
• Bacteria and Particles: Particles, including bacteria, can adhere to wafer surfaces and cause short circuits or deteriorate the device’s characteristics.

The Challenge: Purity Requirements in Solar Cell Wafer Production

The production process of solar cell wafers involves multiple stages, including surface texturing, acid etching, diffusion, and the removal of phosphorus silicon glass. Each of these processes requires stringent cleanliness standards to ensure the performance and reliability of the final solar cells. One of the critical steps, the removal of phosphorus silicon glass, involves the use of hydrogen fluoride acid, which reacts with silicon dioxide to form a volatile gas, thereby dissolving the glass. This step, along with others such as diffusion and cleaning, requires ultrapure water (UPW) to remove residual chemicals, particles, and impurities that could impact the final product.

• Phosphorus Silicon Glass Removal: Involves the use of hydrogen fluoride to dissolve silicon dioxide, generating volatile silicon tetrafluoride gas and removing the phosphorus layer from the silicon wafer.
• Cleanliness of Wafers: During various stages, including diffusion and etching, any residual contaminants must be removed to prevent defects in the solar cell performance.
• Process Sensitivity: Even minor contaminants such as metal ions, organic substances, or particulates can affect the quality of the solar cells, making ultrapure water essential at each stage of production.

The Challenge: Ensuring Purity in Lithium Battery Production

In the lithium battery manufacturing industry, ultrapure water (UPW) is essential in multiple stages, including the preparation of electrolyte solutions and cleaning battery components such as the grids for lead-acid batteries. The purity of the water directly affects the performance and safety of the final battery product. Lithium battery production, in particular, requires extremely strict water purity standards to prevent contaminants from affecting the chemical balance and performance of the battery cells.

• Purity Requirements: The water used in battery production must have a conductivity of less than 0.1 µS/cm (resistivity of 10 MΩ), ensuring the absence of impurities like organic and inorganic substances.
• Traditional Methods: Ion exchange systems have been traditionally used, but the need for frequent resin regeneration and maintenance limits their efficiency.
• Advanced Technology: As membrane separation technology improves, reverse osmosis (RO) and mixed-bed deionization (EDI) systems have become common methods for producing ultrapure water in the lithium battery industry.

The Challenge: Contamination Control in Power Battery Production

Power batteries, used in electric vehicles, electric trains, e-bikes, and golf carts, are key components that provide the power source for these tools. Unlike the starting batteries used in traditional car engines, power batteries are designed to provide continuous energy. In the production process of power batteries, several steps require ultrapure water (UPW) to ensure quality and efficiency. These processes include the uniform mixing of the positive and negative electrodes, the preparation of the electrolyte, and the final cleaning of the battery after the electrolyte is injected and capped.

In the production process of power batteries, Ultrapure Water (UPW) is essential for:

Anode/Cathode Slurry Mixing: To ensure material purity and prevent conductive interference.

Electrolyte Preparation: To avoid ionic contamination in the chemical formulation.

Final Product Cleaning: Washing after injection and capping to prevent corrosion and ensure seal quality.

• Contamination Risks: Contaminants such as metal ions, organic compounds, and particulate matter can compromise the performance and safety of power batteries.
• Critical Manufacturing Steps: Key stages in battery production, such as electrode mixing, electrolyte preparation, and post-injection cleaning, require ultrapure water to remove any impurities that could affect the battery’s performance.
• Performance Impact: Even small traces of impurities can negatively affect battery efficiency, charge capacity, and overall lifespan, making contamination control crucial.