Chamber matching is closely related to chamber conditioning. Plasma parameters can vary significantly within a wet clean cycle, sometimes by a factor of two.
The range of plasma parameters within a wet clean cycle with device parameters still in spec provides also the range of harmless deviations between different chambers.
The diagram shows the collision rate of mainframe with four chambers over a period of 4 months (about 70.000 wafers). Short-term variations are due to chamber conditioning after wet clean (see arrows). The long-term driftsindicate chamber aging Chamber C exhibits a higher electron collision rate and differs from the other chambers.
The diagram shows the electron density of the mainframe as above and indicates good chamber matching. Whereas the electron density of the chambers A, B, and D show a small decreasing trend, chamber C exhibits a long-term increase. After a maintenance measure (wet clean) on Nov. 20th, Chamber C, including the exchange of many square parts, again matches the other chambers.
Note: Date are shown as dd.mm.