The cleaning process accounts for 20% to 30% of the workload...
The cleaning process accounts for 20% to 30% of the workload in the entire semiconductor manufacturing process. In the manufacturing of integrated circuit chips, the presence of small particles (dust) and trace is the main obstacle to high yield and high reliability. The dust-free room, literal meaning, is a very clean space designed to suppress generation of organic and inorganic impurities in dust.
It is impossible to completely avoid trace amounts of contamination during wafer storage, handling, processing, and manufacturing. Thus, the purpose of the cleaning process is to remove the dust that inevitably adheres to the wafer before the next wafer processing process, and send it to the next process in a clean state.
In this blog, detail introduction will be shown on the cleaning methods and techniques, to help you understand types of cleaning, and cleaning machines.
The cleaning craft in semiconductor industry can be divided into 2 types: wet cleaning and dry cleaning, in which wet cleaning is majorly used(≥90%).
Wet cleaning mainly uses chemicals or pure water to clean wafers. The chemicals include types of APM, FPM, HPM, SPM and DHF. The picture shows you more concretely what are in APM, FPM, HPM, SPM and DHF.
Firstly, wet cleaning processes use these chemicals to dissolve impurities on the wafer surface ,and secondly , rinse wafers with pure water. Pure water can only rinse those impurities whose adhesive ability is not that strong.
Different from wet cleaning who use fluid, dry cleaning use gas(CO2, Ozone gas,or plasma) to clean by blowing.
Wet cleaning machines can be also called wet benches. 90% cleaning machines in semiconductor industry adopt the wet cleaning craft.
Cleaning Methods: rotary spray, megasonic cleaning, two fluid cleaning, mechanical brushing, etc
Application Features: It has extremely high process environment control and particle removal capabilities, effectively solving the problem of cross contamination between wafers; Each cleaning chamber can only clean a single wafer at a time, resulting in lower equipment capacity.
Cleaning Methods: Soaking in solution, megasonic cleaning, etc
Application Features: High cleaning capacity, suitable for large-scale production; But the particles have poor control over the wet etching speed; hand over; The risk of cross contamination is high.
RCA Cleaning is also known as the 3-step clean method——
1st Step: Standard Clean 1 (sc-1), The SC-1 solution (NH4OH:H2O2:DI water, 1:1:5) cleans organic residues and deposits a thin silicon dioxide layer, adding extra protection to the wafer surface.
2nd Step: Rinse with deionized water to remove the SC-1 solution. Then, dip into the mixture of HCl and DI water.
3rd Step: Standard Clean 2 (SC-2), The SC-2 solution (HCl:H2O2:DI water, 1:1:5) This step eliminates metallic ions while forming another thin silicon dioxide layer. The process ends with a final rinse and a dip in 80°C deionized water to remove any remaining residues.
Cleaning method: Rotating spray
Application Features: Compared to traditional trough cleaning equipment, batch rotating equipment can achieve temperatures above 120 º C or even up to the
requirements for 200 º C high-temperature sulfuric acid process; The control of various process parameters is difficult, and there is a risk of scrapping all wafers in the entire cleaning chamber after wafer fragmentation.
Cleaning method: Mechanical brushing method
Application features: Equipped with a dedicated brush, utilizing the friction between the brush head and the wafer surface, combined with deionized water to
The cleaning method for removing particles.
Cleaning method: solution soaking+rotating spray combination cleaning
Application features: High production capacity, high cleaning accuracy, and can significantly reduce the use of concentrated sulfuric acid; The product cost is relatively high.
Silicon wafer cleaning: Removing particles and organic matter after initial cutting.
Cleaning before/after film formation: Ensure the uniformity of film deposition.
Cleaning after etching: Remove etching residues.
Pre packaging cleaning: Remove surface oxides and organic matter from the chip to improve Packaging Reliability
Cleaning after packaging: Removing contaminants introduced during the packaging process
Mainstream Technology:
Wet cleaning dominates (over 90% of steps), and single-chip equipment is gradually becoming the mainstream in the market due to improved precision requirements.
Technological Integration: Wet and dry methods complement each other, such as wet treatment of large particles and dry treatment of nanoscale residues.
Development Direction: Intelligence (automatic parameter optimization), environmental protection (reducing chemical usage), and efficiency (improving throughput)
The craft design of semiconductor cleaning machines needs to be based on specific process requirements, for example, advanced processes tend to favor single-chip wet equipment, while large-scale production may choose slot equipment. With the increasing complexity of chip structures, the combination of high precision and low pollution will become the core direction of technological iteration.
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