Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2000-05-03
2001-11-27
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S568150, C318S568160, C318S568210, C318S570000, C318S574000
Reexamination Certificate
active
06323616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wafer handling systems and more particularly to an apparatus for transferring wafers into and out of processing, wherein the apparatus automatically calibrates the necessary positions of its related parts.
2. Description of the Prior Art
In fabricating semiconductors, silicon wafers are often held in a cassette and then moved to various pre-programmed processing locations by a robotic handling system. The latter typically includes a mechanism with degrees of freedom in radial (R), angular (&thgr;) and vertical (Z) directions and has a robot arm with a vacuum or edge-gripping wand. The robot must be able to pick up wafers from a storage cassette and then transfer them to a designated station or a plurality of stations where the wafer will undergo a process such as heating or alignment. In order to perform these actions, the robot must have precise knowledge of the R, &thgr; and Z positions of where the wafer is to be placed at all cassette and station locations. A robot control system must include the knowledge required for positioning the robot arm with gripped wafer precisely within a cassette or process station for each robot function.
In a typical wafer handling layout the general geometry of both the robot and the various process stations such as the cassette stand are known, and the dimensional relationships between the robot and each station are known within nominal tolerances (e.g.=0.10 inches), available from CAD drawings or manual measurements. When in use, however, the robot must be controlled to move wafers more precisely in order to assure that the robot system operates properly without damaging any system component or the wafer being handled.
In order to assure the close tolerances required for the necessary precision, the controller of the robotic element must be reprogrammed or “re-taught” new location data whenever a component is changed, or upon initial setup or when restarted. The term “teach” or “teaching” will be used to describe the process of gathering and entering component/structural location data into the system controller. Due to the need to minimize contaminants in the semiconductor processing environment, most robotic systems are installed in enclosures for control of the atmosphere. In prior art systems, it is generally necessary for a technician to enter the enclosure to position the robot while performing the teaching/calibration operations. These entries can contaminate the clean enclosure. In addition, the cramped, confined enclosure with moving robot parts presents a significant safety problem for the technician. This manual and awkward process is also time consuming and costly, and an inherently subjective process that relies upon the judgment and skill of the technician.
For example, using conventional controls, a robot is installed and taught by jogging the robot around and, at each process station, the wafer placement locations are recorded with a teach pendant. Besides consuming many hours, this manual procedure introduces subjectivity and thus a significant possibility for errors. This creates a problem of reproducibility. Whenever a wafer cassette is not perfectly positioned within specification or a machine component wears, settles or malfunctions and requires replacement, the robot must be re-taught because it cannot automatically adapt to such variations. If the robot is not re-taught properly within close tolerances, serious damage or loss of expensive wafers can result.
It is clear from the above description of the prior art that an improved system for handling wafers is needed to eliminate the requirement of an operator entering the wafer handling enclosure environment for calibration/teaching operations.
SUMMARY
It is therefore an object of the present invention to provide a wafer handling system that avoids the need for an operator to enter the robotic enclosure for teaching/calibration of the system.
It is a further object of the present invention to provide a wafer handling system that is capable of self calibration.
It is a still further object of the present invention to provide a wafer handling system that eliminates enclosure contamination from operator intervention during system teaching operations.
It is another object of the present invention to provide a wafer handling system that minimizes the time required for system teaching.
Briefly, a preferred embodiment of the present invention includes a wafer handling apparatus having input and output robotic systems directed by a programmed controller. Each system has components including a robot, a twist and rotate, and a carrier and automated carrier rail. The input system is for removing wafers from their wafer pod, placing them in the carrier and transporting them via the rail to a wafer processing area. The output system performs the reverse operation, taking wafers from a carrier following processing and placing them in a pod. Each robot includes a plurality of interconnected, articulated cantilevered arms. The last one of the arms has a wand on one end and a laser emitter detector on the other end, and operates in cooperation with the controller to provide location detection of system components. The controller also includes circuitry for sensing contact of the wand with an object by measuring the increased robot motor torque occurring upon contact. The controller is pre-programmed with approximate physical dimensions of the system components and their relative positions. The controller is additionally programmed to automatically perform a precision calibration/teaching routine to gather more precise location data. The process of precision teaching/calibration begins by placing a pod calibration fixture on a pedestal. The controller then directs the input robot to sense the fixture position, which gives the controller precise data relating to the position of a pod on the pedestal. The robot then senses the position of the twist and rotate components. The process begins by sensing the height of two arms of the twist and rotate, and the controller adjusts the arm heights until they are level. The controller then directs the robot to sense the R and &thgr; dimensions of the twist and rotate, and these precise dimensions are saved in the controller.
REFERENCES:
patent: 5740062 (1998-04-01), Berken et al.
patent: 5789890 (1998-08-01), Genov et al.
Aggarwal Sanjay K.
D'Souza Kevin D.
Harding Nathan H.
Sagues Paul
Wiggers Robert T.
Berkeley Process Control, Inc.
Jaffer David H.
Masih Karen
Pillsbury & Winthrop LLP
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