Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
2000-05-12
2002-05-21
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
C033S645000
Reexamination Certificate
active
06389702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to positioning systems and methods, and more specifically to positioning systems and methods which control the movement of a substrate such as a semiconductor wafer which includes numerous integrated circuits located on the substrate.
2. Background Information
Positioning systems are used in different areas of semiconductor fabrication. For example, wafer probers, photolithographic systems and other semiconductor integrated circuit fabrication devices often use a wafer positioning system. Most wafer positioning systems are based on combinations of linear motions of one or more stages along orthogonal directions. An example of a conventional linear motion wafer positioning system in a wafer prober will now be described with reference to
FIGS. 1 and 2
.
A semiconductor wafer usually includes numerous integrated circuits arranged in a grid pattern. Located on each integrated circuit (IC) is a plurality of bonding pads that are used to connect the IC to external circuitry to allow the IC to function. Because the packaging of each IC is rather expensive, it is desirable to test each IC before packaging to avoid packaging defective IC's. This process of testing devices before packaging is called the sort process, and it also involves connecting a probe card to a special tester.
FIG. 1
depicts a prior art wafer prober system
10
that includes a basic example of a probe card
16
mounted on a support
15
. Probe card
16
includes a number of pins
17
that act as substitutes for the normal pins and wire leads of a package device. Pins
17
are made to come into electrical contact with the bonding pads
13
of at least one integrated circuit on a semiconductor wafer
12
that rests on a wafer chuck
11
, which is also called a wafer holding platform. Wafer prober system
10
positions each IC on the wafer with respect to probe card
16
so that the appropriate pins
17
on probe card
16
contact the appropriate bonding pads
13
for a particular IC on semiconductor wafer
12
.
As the art of semiconductor processing advances, semiconductor wafers become larger, die geometries become smaller, the number of pads on each die increases, and the size of each pad decreases. Thus, the alignment accuracy and speed requirements for a wafer prober become more stringent, placing great demands on the positioning stages used in a wafer prober. The positioning stages are aided by modern vision systems that use cameras, such as cameras
14
and
19
that are designed to view probe card
16
and semiconductor wafer
12
, respectively, to attempt to accurately align an IC on a semiconductor wafer with respect to the pins on a probe card.
FIG. 2
depicts a conventional prior art wafer positioning system that can be used in a wafer prober or other semiconductor fabrication device. When used in wafer probers, positioning systems must provide four axes (X,Y,Z,&thgr;) of motion. A common implementation includes an X,Y stage for positioning in X,Y and an independent Z to stage and an independent &thgr; stage.
FIG. 2
shows a wafer positioning system
20
using a conventional rectilinear X,Y stage. A wafer chuck
25
is positioned on top of a Y-motion stage
21
which moves along guide rails
22
a
and
22
b
to provide translation in the Y axis. Wafer chuck
25
may include a rotary motor located on top of Y motion stage
21
and below wafer chuck
25
to provide &thgr; motion for wafer chuck
25
. An X-motion stage
23
moves along guide rails
24
a
and
24
b
to provide translation in the X axis. A semiconductor wafer
30
is positioned on top of wafer chuck
25
and is typically held in place by a vacuum generated under the surface of the semiconductor wafer by the wafer chuck. A separate Z stage (not shown) provides translation in the Z axis by either changing the distance between wafer chuck
25
and Y-motion stage
21
or by moving both X-motion stage
23
and Y-motion stage
21
along with their corresponding guide rails in the Z axis.
FIG. 3A
shows a side view of a simplified representation of a prior art wafer positioning system that uses linear motors, such as Sawyer motors. A wafer holding stage
40
comprises electromagnetic assemblies
37
bonded to each other by a permanent magnet
38
; the coupling of two electromagnetic assemblies and a permanent magnet forms a motor. The motor is bonded to a material layer
39
. Wafer holding stage
40
is located above and separated from a platform
35
by a thin air gap
36
.
A limitation of prior art wafer positioning systems that are based on
82
combinations of linear motions along orthogonal directions is that the wafer is moved on along only one direction by one set of motors or one stage. For example, with reference to
FIG. 2
, semiconductor wafer
30
is moved in the X direction by only X-motion stage
23
, and it is moved in the Y direction by only Y-motion stage
21
. Thus, at any time the wafer is being moved, one stage is left unused. As speed requirements for wafer positioning systems increase, it is desirable to provide a wafer positioning system that utilizes multiple avenues of movement concurrently and works within current physical constraints of wafer positioning systems.
SUMMARY OF THE INVENTION
The present invention provides a wafer positioning system which includes in one embodiment a motor system to move a wafer holding stage and a motion control system to control a path of the wafer holding stage. The motor system constrains the wafer holding stage to a first set of two movement axes, which are the physical axes, and the motion control system controls the path of the wafer holding stage along a second set of two movement axes, which are the non-physical axes. The first set of movement axes comprise axes at an angle to each other, and the second set of movement axes also comprise axes at an angle to each other. The first and second sets of axes are also located at an angle to each other. The distance a wafer on the wafer holding stage is to be moved is measured along one of the non-physical axes. To move the wafer along this distance, the motion control system moves the wafer holding stage along the physical axes of the motor system concurrently.
The present invention also provides a method for moving a wafer holding stage in a wafer positioning system. In one example of this method, the movement of the wafer holding stage is constrained to a first and a second axis, and the path of the wafer holding stage is controlled along a third and a fourth axis. In another example of this method, the step of controlling the path of the wafer holding stage includes the steps of measuring along the third or fourth axes the distance a wafer is to be moved and moving the wafer holding stage along the first and second axes concurrently.
Additional features and benefits of the present invention will become apparent upon review of the following description.
REFERENCES:
patent: 4575942 (1986-03-01), Moriyama
patent: 5757160 (1998-05-01), Kreuzer
patent: 5760500 (1998-06-01), Kondo et al.
patent: 6005309 (1999-12-01), Chitayat
patent: 6082010 (2000-07-01), Lee
Bennett G. Bradley
Blakely , Sokoloff, Taylor & Zafman LLP
Electroglas, Inc.
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