Common semiconductor wafer cleaning equipment and devices
The key to cleaning is that as the feature size continues to shrink, semiconductors become increasingly sensitive to impurity content, and semiconductor manufacturing inevitably introduces pollutants such as particles, organic matter, metals, and oxides. In order to reduce the impact of impurities on chip yield, in actual production, it is not only necessary to improve the efficiency of single cleaning, but also to frequently clean almost all processes before and after. The cleaning step accounts for about 33% of the overall step.
Four commonly used semiconductor silicon wafer cleaning equipment and devices:
The wet chemical cleaning system can be either immersion or rotary. The general equipment mainly includes a set of wet chemical cleaning tanks and corresponding water tanks, and may also be equipped with a drying device. The silicon wafers are placed in a dedicated cleaning basket and placed in a chemical tank for a specified period of time, and then taken out and placed in the corresponding sink for rinsing.
For the design of cleaning equipment, the selection of materials is crucial. When using, select the corresponding tank material based on the concentration, pH, and operating temperature of the chemical solution. Generally speaking, there are materials such as NPP, PVDF, PrFE, quartz glass, etc. For example, PVDF, IyIFE, quartz glass, etc. are generally used for strong acid and strong alkali cleaning that requires heating. Quartz glass cannot be used for HF cleaning, while NPP is generally used for weak acid and weak alkali cleaning at room temperature. And normal temperature chemical tanks are generally made of NPP materials.
The solution inside the tank can be heated to 180 ℃ or even higher, and it generally consists of a quartz inner tank, an insulation layer, and a plastic (PP) outer tank. Heating of quartz grooves can be achieved by pasting heating films or directly coating heating materials on quartz glass. Temperature and liquid level sensors need to be installed inside the quartz tank to achieve precise temperature control and detection of the liquid level inside the tank, preventing the heater from drying out due to low liquid level inside the tank.
In addition, PVDF (PTEE) heating tanks are also commonly used, which are often used for cleaning HF solutions. Due to the limitations of the tank material, this type of heating tank can only use embedded heating. Embedded heaters generally have two types: coil type and flat plate type, and the heater is covered with PFA tubes.
2. Megasonic cleaning tank
RcA or improved RcA cleaning combined with megaacoustic energy is currently a widely used cleaning method. After adding megaacoustic energy, the temperature and process time of the solution can be significantly reduced, and the cleaning effect is more effective. The commonly used frequency for megasound cleaning is 800kHz to 1 MHz, with megasound power ranging from 100 to 600W. Mega sound transducers come in various forms such as flat plate and circular arc plate. The megasound transducer can be directly installed at the bottom of the tank; The quartz cleaning tank can be used in a water bath, and the megaacoustic transducer is installed at the bottom of the outer tank, which can avoid the erosion of the megaacoustic transducer by the cleaning solution.
The megasonic transducer will generate a large number of bubbles at the bottom of the quartz groove during operation. These bubbles will absorb a large amount of megaacoustic energy, greatly reducing the effectiveness of megaacoustic cleaning. Therefore, the bottom of the inner groove quartz cylinder generally needs to have a tilt angle of 10-15 degrees. When bubbles are generated, due to the buoyancy effect, the bubbles move upwards along the inclined quartz groove bottom, detaching from the quartz groove wall and floating out of the water surface, reducing the loss of sound energy caused by bubbles.
In addition, the outer tank of the water bath can use stainless steel tanks, quartz tanks, etc. according to different needs. Due to its unique structure, the circular arc plate acoustic transducer has a more reasonable direction and energy distribution in the propagation of acoustic energy, resulting in a more significant cleaning effect. Generally, the circular arc plate acoustic transducer only requires a half power reduction of the flat plate acoustic transducer to achieve the same cleaning effect.
3. Rotating spray cleaning
Rotating spray cleaning is a variant of immersion cleaning. The system generally includes automatic liquid dispensing system, cleaning chamber, and waste liquid recovery system. Spray cleaning completes chemical cleaning, deionized water flushing, rotary drying, and other processes in a sealed working chamber at once, reducing the impact of human operation factors in each cleaning step. In spray cleaning, due to the effects of rotation and spraying, the solution on the surface of the silicon wafer is more uniform. At the same time, the solution in contact with the surface of the silicon wafer is always fresh. This allows for precise control of the cleaning and corrosion effect of the silicon wafer through process time settings, achieving good consistency. A sealed working chamber can isolate the volatilization of chemical liquids, reduce solution loss, and mitigate the harm of solution vapor to human health and the environment. Each system is stored in different chemical reagents and mixed before reaching the nozzle during use to maintain freshness and maximize potential, resulting in the fastest reaction during cleaning. When spraying with N2, the liquid passes through a very small nozzle, forming a fine mist and achieving better cleaning on the surface of the silicon wafer.
This method is suitable for removing oxide films or organic matter. Because chemicals stay on the surface of silicon wafers for a relatively short time, the cleaning effect that requires a certain amount of time for the reaction is not good. The use of few chemical reagents during the spraying process is beneficial for cost control and environmental protection.
4. Brusher
The scrubber is mainly used for cleaning silicon wafers after polishing, which can effectively remove both sides of the silicon wafer μ M and larger particles. The main configuration includes a dedicated scrubber, optimized chemical cleaning solution, and ultrapure water or IPA. Under hydrodynamic conditions, particles are driven out by a rotating sponge like brush.