Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
2000-11-10
2001-11-06
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C318S568160, C414S936000
Reexamination Certificate
active
06313596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for detecting and adjusting the position of a substrate on a robot blade.
2. Background of the Related Art
A common configuration for processing equipment utilizes a number of different processing chambers accessible from a central chamber, known as a transfer chamber. Typically, transfer of a substrate between the various processing chambers is performed by a robot disposed in the transfer chamber. To accommodate the high throughput requirements of semiconductor processing, the robots are adapted for accurate, high-speed movement. The robot includes a substrate seating surface for supporting a substrate thereon and is capable of rotation and extension. Clamping mechanisms are typically used to secure the substrate to the substrate seating surface and prevent slippage which can result in damage.
An exemplary frog-leg type robot
10
is shown in FIG.
1
. The robot
10
comprises a four-bar linkage
12
mounted to a pair of central hubs
14
(only one shown) which may be actuated by stepper motors (not shown). A robot blade
16
connected to the linkage
12
is adapted to support a substrate
18
thereon. Clamp fingers
20
are provided to secure the substrate
18
during movement of the blade
16
. In operation, the hubs
14
are rotated by the stepper motors to cause linear and rotational actuation of the robot blade
16
. Rotation of the hubs
14
in the same direction causes rotation of the blade
16
while rotation of the hubs
14
in opposite directions causes extension and retraction of the blade
16
. When a substrate
18
is disposed on the blade
16
, the clamp fingers
20
are actuated toward the edge of the substrate
18
to urge the substrate
18
against a shoulder
22
, or “shoe.” Thus, the shoulder
22
and the clamp fingers
20
cooperate to hold the substrate
18
during movement of the robot
10
.
FIG. 2
shows a substrate
18
properly positioned between the shoulder
22
and the clamp fingers
20
.
Normally, stepper motor driven robots under computer control, such as the one shown in
FIG. 1
, are capable of repeatedly transporting substrates through a processing system with great speed and precision. However, the effectiveness of such substrate handling techniques can be greatly diminished if the initial position of the substrate is not known. For example,
FIG. 3
shows a substrate
18
improperly positioned on the blade
16
, wherein a portion of the substrate
18
is disposed on the shoulder
22
. Such positioning of the substrate may occur during operation for various reasons. For example, the lift mechanism (lift pins) which deposits the substrate onto the blade may be improperly adjusted and vibrate, thereby causing the substrate to “walk” on the lift mechanism. Other causes include the effects of processing on the substrate due to gases delivered to the backside of the substrate and the plasma used during deposition of a material onto the substrate. Regardless of the cause for improper substrate positioning, upon actuation of the blade
16
, an improperly positioned substrate
18
will likely slip from the blade
16
and be damaged. The likelihood of slippage is particularly great during rotation of the blade
16
. Because current technology does not provide an accurate method of determining whether a substrate is securely clamped, substrates fall from the blade causing damage to the substrate, thereby requiring the system to be halted for operator intervention. The problems associated with unclamped substrates are heightened by use of increasingly faster robots.
Another problem associated with substrate transfer robots is the potential for misalignment of a properly clamped substrate in a chamber. In semiconductor processing, it is desirable to know the exact location of a substrate relative to the robot blade so that the substrate can be precisely positioned at an optimum location at a final destination such as within a processing chamber. Knowledge of the substrate position allows repeatably positioning substrates in a chamber at substantially the same location, thereby maximizing the effectiveness of the processing onto the desired surface area of the substrate to be processed. Ideally, clamped substrates being transferred by the robot are situated at the substrate's nominal position within the pocket of the blade. In practice, however, substrates are not always disposed at or substantially near the nominal position causing the robot to deposit the substrate in the chamber at a position displaced from the intended destination. Therefore, current methods utilize centerfinding techniques to determine the centerpoint of each substrate and position the substrate accordingly, thereby ensuring that each substrate is positioned uniformly relative to the known centerpoints.
While methods for substrate centerfinding are known, current technology does not provide a method or apparatus for detecting the clamped or unclamped state of a substrate as well as allow for corrections in substrate positioning to ensure proper alignment in a process chamber. Further, known methods of centerfinding have several disadvantages resulting in reduced throughput and increased complexity and cost. For example, one known method comprises a bank of sensors and detectors disposed inside the vacuum environment of a processing system. A substrate is moved into the optical paths of the signals emitted by the sensors, thereby blocking the signals. Once the signals become blocked the output of the detectors switches states. The change in the output of the detectors is then used to calculate the center of the substrate. The requirement of multiple sensors is a disadvantage because of the cost and increased complexity of the system. Typically, such an arrangement is feasible only at one location in the processing system requiring substrates to be transported to the location of the bank of sensors each time centerfinding is to be performed, thereby limiting throughput. Further, by positioning the sensors inside the vacuum environment the sensors can outgas particles leading to contamination of the substrates. Thus, it would be preferable to perform the centerfinding on-the-fly, i.e., during the normal operating sequences of a robot in order to minimize the impact on throughput. It would also be preferable to limit the number of electronic sensing components and to position the components outside the vacuum environment of the processing chamber.
Other centerfinding techniques utilize a spindle type apparatus whereby the substrate is transferred to a spindle assembly and incrementally rotated to determine the centerpoint offset by geometric analysis. Such an arrangement is undesirable because the apparatus is separate and distinct from the processing system, thereby requiring additional steps and costs to the manufacturing process and inhibiting productivity.
Therefore, there is a need for an apparatus and method to determine the clamped or unclamped state of a substrate on a robot support member as well as allow for necessary corrections in the position of the substrate in a process chamber. Preferably the apparatus is positioned outside a vacuum environment of a processing chamber and is adapted to operate on-the-fly.
SUMMARY OF THE INVENTION
The present invention generally provides a method and apparatus for deriving positional information about a substrate disposed on a robot blade. Initially, a determination is made whether a substrate is in a clamped or unclamped state on a robot blade. If the substrate is properly clamped, the center of the substrate is determined so that any misalignment of the center relative to a nominal position on the blade may be corrected.
In one aspect of the invention, a sensor unit, preferably comprising a radiation source and a detector and capable of transmitting and receiving a signal, is positioned to direct a signal along an optical path intersecting a substrate path. A substrate support member having a reflecting member disposed th
Carrera Jaime
Hoskins Van
Wyka Gary
Applied Materials Inc.
Duda Rina I.
Moser Patterson & Sheridan LLP
Nappi Robert E.
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