Apparatus for optical inspection of wafers during polishing

Details Apparatus for optical inspection of wafers during polishing Apparatus for optical inspection of wafers during polishing

2001-06-11

2002-04-09

Morgan, Eileen P. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

By optical sensor

C451S287000, C356S503000, C356S630000, C356S908000

Reexamination Certificate

active

06368182

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to wafer polishing apparatus in general and to measuring systems incorporated into such apparatus in particular.
BACKGROUND OF THE INVENTION
Wafer polishing systems are known in the art. They polish the top layer of semiconductor wafers to a desired thickness. To do so, the wafer being polished is immersed in a slurry of water and chemicals during the polishing process. Once the wafer has been polished and washed down, it is placed into an exit station known by some companies as a “water track”, after which the wafer is placed into a cassette of wafers. The cassette is maintained within a water bath until full, after which the entire cassette is brought to a cleaning station to remove any chemicals and slurry particles still remaining on the wafers in the cassette and to dry the wafers. After cleaning, the wafers are brought to a measurement station to determine if the polisher produced the desired thickness of their top layers.
FIG. 1
, to which reference is now briefly made, illustrates a prior art water track, such as the water track of the #372 Polisher manufactured by IPEC Westech Inc. of Phoenix, Ariz., USA. The water track, labeled
10
, comprises a frame
12
and a base
14
. Frame
12
has jet holes
16
connected to jets (not shown) which emit streams
18
of water through holes
16
. Base
14
has holes
20
connected to bubblers (not shown) which bubble small amounts of water
22
through holes
20
. When a wafer
25
is dropped into water track
10
, pattern-side down, the jets and bubblers are activated. Streams
18
, from the water jets, serve to force the wafer
25
in the direction indicated by arrow
24
. Small streams
22
push the wafer
25
slightly away from the base
14
and ensure that, while the wafer
25
moves through the track, it never rubs against base
14
and thus, the pattern on the wafer is not scratched.
Other companies produce polishers whose exit stations are formed just of the cassettes. Such a polisher is produced found in the 6DS-SP polisher of R. Howard Strasbaugh Inc. San Luis Obispo, Calif., USA.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a measurement system installable within a polishing machine and, more specifically, within the exit station of a polishing machine.
In accordance with a preferred embodiment of the present invention, the present invention includes an optical system, which views the wafer through a window in the exit station, and a gripping system, which places the wafer in a predetermined viewing location within the exit station while maintaining the patterned surface completely under water. The present invention also includes a pull-down unit for pulling the measurement system slightly below the horizontal prior to the measurement and returns the measuring system to horizontal afterwards.
In accordance with a first preferred embodiment of the present invention, the gripping system includes a raisable gate which collects the wafer in a predetermined location, and a gripper which grips the wafer, carries it to the viewing location and immerses the wafer, along a small angle to the horizontal, in the water or water. The gripper also holds the wafer in place during the measurement operation, after which, it releases the wafer and the raisable gate is raised.
The present invention incorporates the method of immersing an object into water such that very few bubbles are produced on the wafer surface. The method of the present invention preferably includes the step of immersing the object while it is held such that its surface plane is at a small angle to the horizontal.
In a second embodiment, the measurement system includes a water bath and a gripping system thereabove. The gripping system includes wafer holding elements, which receive the wafer, and a gripper whose initial location is above the expected reception location of the wafer. The gripper is flexibly connected at an angle to a piston such that the wafer is immersed in the water at an angle to the horizontal.


REFERENCES:
patent: 5433651 (1995-07-01), Lustig et al.
patent: 5492594 (1996-02-01), Burke et al.
patent: 5730642 (1998-03-01), Sandhu et al.
patent: 6045433 (2000-04-01), Dvir et al.
patent: 6110011 (2000-08-01), Somekh et al.

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