NH4OH/H2O2/H2O (called APM or
SC–1) cleaning combined with megasonic irradiation is found to feature
outstanding removal efficiency for various types of particulate contaminant.
The conventional APM cleaning, however, allows metallic impurity in solution
to adhere onto substrate surface, and it must be followed by acid cleaning
such as HCI/IH2O2/H2O (called HPM or SC–2)
cleaning to remove metallic impurity from substrate. The advanced APM
cleaning using MC–1 which is alkali cleaning agent containing chelating
agent has been developed, and this new cleaning is found capable for
preventing various metallic impurities including Al in solution from
contaminating substrate surface. Besides, with cleaning conditions
optimized, the advanced APM cleaning using MC–1 can also remove metallic
impurity from substrate surface. In short, this modified APM cleaning is
capable for removing particle and metallic impurity at the same time, which
is not possible with the conventional cleaning technology. The cleaning
process of semiconductor manufacturing process can be simplified if HPM
cleaning is eliminated by introducing the advanced APM cleaning using MC–1.
This leads to drastic reduction of cleaning cost and improvement of
throughput of the cleaning process.
Effects of electrolytes on bubble coalescence are investigated experimentally from fluid dynamic point of view. Collisions of a bubble with free surface in two kinds of liquids, namely, ultrapure water and sodium chloride solution, are observed using a high speed camera. It is found that the repetitive number of bubble bounces on a free surface in electrolyte solution is larger than that in ultrapure water when the equivalent bubble radii are the same. This result qualitatively shows that electrolyte works to prevent bubbles from coalescing. It is also revealed that the bubbles can coalesce if their Weber numbers, which are based on the radius of curvature of the front side of the bubble and the approach velocity just before the collision with the free surface, are less than a critical Weber number. Furthermore, the critical Weber number decreases with the increase in the concentration of the electrolyte solutions despite the fluid dynamic characteristics, such as bubble rise velocity and bubble shape, are not affected by the addition of the electrolytes. It is concluded that Weber number is the most important parameter to specify the effects of electrolytes on bubble coalescence.
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