Cleaning Flashcards
How does the surface become “dirty”? What type of contaminations could we expect on a wafer surface?
Particles - small pieces of solid residues and contaminants eg dust, pollen
Inorganic - salts, heavy metal atoms
Organic - smog, skin oil
Impurities - during the formation of substrates or overlay films
Which are the cleaning methods used in thin film manufacturing processes? Briefly outline their principle
Mechanical - adhesive materials fill the voids or pores of the surfaces and hold surfaces together by interlocking
Chemical - two materials may form a compound when joined, strongest joins are ionic and covalent bonding
Dispersive (adsorption) - two materials may be held together by van der waals focus
Electrostatic - attractive electrostatic force is created between materials charged with opposite polarity
Diffusive - some materials may merge at the joint by diffusion, when the molecules of both materials are mobile and soluble in each other
What is principle of precision cleaning? Which processes does it include?
Precision cleaning - complete removal of undesirable contaminants to a desired preset level, normally the minimum level at which no adverse effects take place in a subsequent operation
RCA clean - piranha strip, nitride clean - oxide strip, dry strip, solvent clean - dry clean
Please describe the factors directly influencing cleaning results?
Cleaning chemistry - adhesion
Scrubbing method
Process parameters
What is surface passivation. Please explain its purpose
Passivation - termination of bonds on the sample surface assuring chemical stability of surface
What is a cleanroom and why do we need it?
Cleanroom - super clean environment, remove particles smaller than 0.05 um
Why - production yield and product quality are affected by invisible airborne particles or dust
How are cleanrooms classified?
M1-7 - 1-100000
Which are the four main cleanroom principles?
Not to bring any dust, not to generate any dust, not to accumulate any dust, to remove any dust quickly
What are the main cleanrooms areas? Briefly outline their purpose
Gowning area
Airlock
Clean room bays
other
Which are the most important considerations about the design and use of cleanrooms?
Equipment should be arranges to minimise the amount of operator movement while maximising their comfort
The number of staff in should be kept to a minimum
Th flow of personnel should be limited to minimise exit and entry especially in the critical area
The number of transfers to the critical area of the cleanroom should be minimised
Excessive movement adjacent to the critical area should be restricted
