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Typical low-K
dielectric is a porous dielectric. Unfortunately, in a standard clean
room, enough moisture exists to react with the pore walls and slowly
produce a moisture layer that will reduce the K factor. However, if the
pores are sealed against the ingress of moisture, integrity of the
dielectric can be retained.
YES equipment uses a series of vacuum pulls and hot Nitrogen purges so
the sidewalls of the pores are completely dehydrated. This way, when the
atmosphere of the chamber is hot Nitrogen at 1 Torr, the atmosphere in
all pores is at 1 Torr.
Next, 4.7 mills of APTES are vaporized in the external vaporization
chamber, and the resulting pressure of hot APTES 6 Torr fills the
chamber. Every 1 Torr cavity of Nitrogen is filled with 6 Torr of hot
APTES vapor. |
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The vapor reacts with
the sidewalls of the pores, creating a 5 to 20 Angstroms-thick layer
that is totally hydrophobic. Not only is it hydrophobic, but the total
dehydration also ensures there are no water molecules below the APTES
SAM. This means the created layer cannot be destroyed with subsequent
exposure to atmospheric moisture.
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