Robot arm with specimen edge gripping end effector

Details Robot arm with specimen edge gripping end effector Robot arm with specimen edge gripping end effector

1998-12-02

2001-07-03

Cuchlinski, Jr., William A. (Department: 3661)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Robot control

C700S248000, C700S249000, C700S250000, C700S258000, C700S259000, C700S260000, C700S261000, C700S262000, C700S263000, C700S264000, C700S900000, C074S490030, C294S008000, C291S027000, C701S023000

Reexamination Certificate

active

06256555

ABSTRACT:

FIELD OF THE INVENTION
This invention is directed to a specimen handling apparatus and method and, more particularly, to an edge gripping semiconductor wafer robot arm end effector that substantially reduces wafer backside damage and particulate contamination.
BACKGROUND OF THE INVENTION
Integrated circuits are produced from wafers of semiconductor material. The wafers are typically housed in a cassette having a plurality of closely spaced apart slots, each of which can contain a wafer. The cassette is typically moved to a processing station where the wafers are removed from the cassette, placed in a predetermined orientation by a prealigner or otherwise processed, and returned to the cassette, or another cassette, for moving to another location for further processing.
Various types of wafer handling devices are known for transporting the wafers to and from the cassette and among processing stations. Many employ a robotic arm having a spatula-shaped end that is inserted into the cassette to remove or insert a wafer. The end of the robotic arm is referred to as an end effector that typically employs a vacuum to releasably hold the wafer to the end effector. The end effector typically enters the cassette through the narrow gap between a pair of adjacent wafers and engages the backside of a wafer to retrieve it from the cassette. The end effector must be thin, rigid, and positionable with high accuracy to fit between and not touch the closely spaced apart wafers in the cassette. After the wafer has been processed the robotic arm inserts the wafer back into the cassette.
Unfortunately, transferring the wafer among the cassette, robot arm, and processing stations, such as a prealigner, may cause backside damage to the wafer and contamination of the other wafers in the cassette because intentional engagement as well as inadvertent touching of the wafer may dislodge silicon particles that can fall and settle onto the other wafers. Wafer backside damage can include scratches as well as metallic and organic contamination of the wafer material. Robotic arms and prealigners that employ a vacuum to grip the wafer do minimize backside damage and particle creation. Nevertheless, when handling large wafers having small features, even the few particles created are sufficient to contaminate adjacent wafers housed in the cassette. Reducing such contamination is particularly important to maintaining wafer processing yields, which is particularly true for large wafers.
Furthermore, robotic arms and prealigners that grip a wafer with a vacuum have heretofore been limited to handling wafers having diameters smaller than 200 millimeters (“mm”). Semiconductor production systems may soon utilize 300 mm diameter wafers, with larger diameter wafers under consideration. Robot arms and prealigners employing vacuum gripping may be incapable of securely handling these larger wafers quickly and accurately. Because increasing semiconductor yield “is the name of the game, ” it is important to grip such larger wafers securely so they can be prealigned quickly and accurately while minimizing wafer backside damage and particulate contamination.
What is needed, therefore, is a specimen gripping end effector that can securely, quickly, and, accurately transfer 150 mm diameter and larger semiconductor wafers to and from a cassette while minimizing backside damage and silicon particle contamination.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide a specimen handling device that minimizes specimen damage and the production of silicon particles.
It is a further object of this invention to provide a semiconductor wafer handling device that can quickly and accurately transfer 150 mm diameter and larger wafers between a wafer cassette and a wafer processing station.
It is still another object of this invention to reduce contamination of semiconductor wafers housed within a cassette.
Yet another object of this invention is to provide a wafer handling device that can be retrofit to existing robot arm systems.
Robot arm end effectors of this invention rapidly and cleanly transfer 150 mm and larger diameter semiconductor wafers between a wafer cassette and a processing station. The end effectors include at least one proximal rest pad and at least two distal rest pads having pad and backstop portions that support and grip the wafer within an annular exclusion zone that extends inward from the peripheral edge of the wafer. The end effectors also include an active contact point that is movable between a retracted wafer-loading position and an extended wafer-gripping position. The active contact point is movable to urge the wafer against the distal rest pads so that the wafer is gripped only at its edge or within the exclusion zone.
The end effectors are spatula-shaped and have a proximal end that is operably connected to a robot arm. The active contact point is located at the proximal end, which allows the end effector to be lighter, stronger, and more slender than end effectors having moving mechanisms that may not fit between adjacent wafers in a cassette. The lack of moving mechanisms further causes the end effector to produce less contamination within the cassette. Additionally, locating the active contact point at the proximal end of the end effector ensures that it is remote from harsh conditions such as heated environments and liquids.
A vacuum pressure-actuated piston moves the active contact point between a retracted position, in which the wafer is loaded into the end effector, and an extended position in which the wafer is gripped. The vacuum pressure assists in the elimination of particles to maintain a clean environment. A first embodiment of the piston employs vacuum pressure to move the active contact point between both positions, and a second embodiment of the piston employs vacuum pressure to retract the active contact point and a spring to extend the active contact point.
Alternate embodiments of the end effector include flat or inclined, narrow or arcuate rest pads onto which the wafer is initially loaded. The narrow and arcuate inclined rest pad embodiments assist in centering and gripping the wafer between the active contact point and the distal rest pads. The arcuate rest pads more readily accommodate gripping and handling flatted wafers.
The end effectors further include fiber optic light transmission sensors for accurately locating the wafer edge and bottom surface. Alternate embodiments of the sensors place the bottom surface sensors and respective proximal and distal ends of the end effector. In both embodiments, the sensors provide robot arm extension and elevation positioning data that support methods of rapidly and accurately placing and retrieving a wafer from among a stack of closely spaced apart wafers stored in a wafer cassette. The methods effectively prevent accidental contact between the end effector and the wafers in the cassette while effecting clean, but secure, gripping of the wafer within its exclusion zone.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceed with reference to the accompanying drawings.


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