We know about wafer cleaning, but how should it be done to meet the required standards? Let’s go into detail and explain the correct method for wafer cleaning. We hope everyone can learn and share together, because only by using the correct method can we achieve the final goal.
01
Overview of the Most Accurate Wafer Cleaning Methods
The correct wafer cleaning method must take multiple factors into account to ensure that the cleaned wafers have good quality and performance. Below are some key steps:
✅ Pre-cleaning
Brushing: For wafers with many particles or dust on the surface, use a soft brush to remove loose particles and dirt. Be careful with the force to avoid damaging the wafer surface.
Ultrasonic Rough Cleaning: Place the wafers into an ultrasonic cleaning tank filled with optical cleaning solution, set the ultrasonic temperature to 50–60°C, and clean for 10–15 minutes. Ultrasonic cleaning uses pressure changes in the liquid medium to desorb surface impurities on the wafers. However, this method is less effective for removing particles smaller than 1μm.
✅ Chemical Cleaning
Alkaline Cleaning Solution Soaking: Common alkaline solutions include sodium hydroxide and ammonium hydroxide. Place the wafers into the alkaline solution with the temperature controlled at 50–60°C and soak for about 5–10 minutes to remove organic substances, inorganic contaminants, and photoresist from the wafer surface.
Acid Cleaning Solution Soaking: After alkaline cleaning, use acidic solutions such as hydrochloric acid or sulfuric acid at the same temperature range of 50–60°C and soak for 5–10 minutes to neutralize any remaining alkaline solution and remove impurities not fully eliminated during alkaline cleaning.
Hydrogen Peroxide System Cleaning: First, clean the wafers with an acidic solution at a ratio of H₂SO₄:H₂O₂ = 5:1 or 4:1, then use an alkaline solution at a ratio of H₂O:H₂O₂:NH₄OH = 5:2:1, 5:1:1, or 7:2:1, and finally clean with an acidic solution at a ratio of H₂O:H₂O₂:HCl = 7:2:1 or 5:2:1. This method is highly effective and environmentally friendly.
✅ Fine Cleaning
Megasonic Cleaning: High-energy sound waves with a wavelength of 1.5μm and a frequency of 0.8 MHz are generated by a transducer. These waves accelerate the movement of solution molecules, creating high-speed fluid waves that continuously impact the wafer surface. This removes particles smaller than 0.2μm and combines mechanical scrubbing with chemical cleaning.
Ozone Microbubble Method: Ozone dissolved in water generates highly active hydroxyl radicals (OH•), which chemically react with organic matter to remove organic impurities from the wafer surface. This also forms an atomically smooth oxide film that prevents re-adsorption of contaminants.
✅ Rinsing
Overflow Rinsing: Use deionized water to rinse wafers that have undergone chemical and fine cleaning to remove any remaining chemical reagents.
Slow Pull Dehydration: Place the rinsed wafers into a slow pull dehydration machine and use pure deionized water to slowly dehydrate and remove surface moisture.
✅ Drying
Oven Drying: Place the dehydrated wafers into an oven at 80–100°C for drying. The duration depends on specific circumstances, usually 10–15 minutes, to ensure the wafer surface is completely dry and to prevent moisture from affecting subsequent processing or use.
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