Patent Number: 047059516
Section: summary

FIELD OF THE INVENTION This invention pertains to a system for processing semiconductor wafers sequentially using robot arms stored inside isolating valves between multiple sequential chambers. BACKGROUND OF THE INVENTION Removal techniques, e.g., etching and cleaning, are universally practiced on semiconductor materials, metal materials, and/or dielectric materials in the production of electronic devices and/or materials. Because of the importance of these procedures, extensive research has been expended in improving established techniques and developing novel approaches. Through this research, processing times have been significantly diminished, and the quality of these processes has been substantially improved. As semiconductor wafer processing machines move toward more automation, cassettes are used to move the wafers from one machine to another. The cassettes in many cases, are made of soft plastic to avoid damage to the wafers. Such cassettes, however, are subject to warping and deformation in use and are not dimensionally stable. Sometimes wafers are broken or otherwise removed from the group of wafers in the cassette, thereby creating a blank space in the cassette. Valuable processing time is thereby wasted. Semiconductor wafer processing requires many steps in many processing chambers. Isolation means must be provided between chambers and means for moving wafers must be provided compatible with the isolation. All this must be provided in a way which generates a minimum of particulates which might contaminate the wafer. Generally, isolation is provided by valves and wafer movement is handled by an independent mechanism. U.S. Pat. Nos. 4,433,951 and 4,483,654 to Koch et al disclose a transfer mechanism in an isolation chamber. Separate valves are required on either side of the isolation chamber. The transfer mechanism within the isolation chamber is complex and prone to particulate generation problems. U.S. Pat. No. 4,533,069 to Purser discloses a wafer handling arm having four trapezoidally-shaped sides. The side arms extend sideways as the arm is shortened, thereby requiring a large opening in which to operate the arm. U.S. Pat. No. 3,921,788 to Roberson, Jr. et al discloses a wafer handling mechanism on a slide mechanism. The slide mechanism is inherently present in the work area and subject to generation of particulates. In prior art wafer processing machines the holding of the semiconductor wafer was often a simple device since the wafers were loaded by hand. As semiconductor processing moved into more sophisticated sequential automated processing, wafer handling means had to be devised which would pass a wafer to a wafer holding device. Where it is necessary to temperature regulate the wafer during processing, various means can be employed. Heat transfer problems arise where a temperature controlled chuck is used in a vacuum to regulate the temperature of a wafer. One of the most reliable heat transfer means is to provide gas at the back of the wafer at a pressure between 3 and 20 Torr (depending on the process) and allow this gas to equilibrate the temperature of the chuck and wafer through conduction and/or convection as shown in U.S. Pat. Nos. 4,512,391; 4,514,636; and 4,565,601. In order to efficiently control the temperature of the wafer it is necessary that the wafer holding means clamp the wafer firmly to the temperature controlled chuck. The wafer clamping means and handling means must interact in a reliable manner. OBJECTS OF THE INVENTION It is an object of the invention to combine a chamber vacuum isolation valve with a simple compact wafer handling arm including a means of completely isolating the wafer handling arm from the chamber on either side of the valve when the valve is closed, and including a means for pumping continuously on the valve housing and the wafer handling arm in any valve position. It is a further object of the invention to provide a wafer positioning system which compensates for distorted individual wafer cassettes. It is another object of the invention to provide a wafer positioning system which takes into account wafers missing from the cassette and provide random access to wafers in the cassette. It is a still further object of the invention to provide a means of holding the door of a vacuum chamber until pumping on the chamber begins in a way which can be electrically controlled. It is still another object of the invention to provide reliable means for receiving a wafer from a wafer positioning system centering and clamping on a temperature controled chuck. It is a still further object of the invention to provide means for controlling efficient and rapid processing of the wafers without fixed sequential control. It is another object of the invention to provide a wafer handling and processing system wherein a combined isolation valve and wafer handling arm are removeable as a unit from the system to enable rapid removal of a worn unit and replacement with a new or rebuilt unit, so that the entire system will not be incapacitated for a long period when the valve sealing rings and moving parts of such unit become worn. SUMMARY OF THE INVENTION These objects of the invention and other objects, features and advantages to become apparent as the specification progresses are accomplished by the invention, according to which, briefly stated, a wafer handling arm is formed of a proximal extensor piece, a distal extensor piece, a proximal support arm, and a distal support arm. The distal extensor piece and the proximal support arm are pivotally attached to the distal support arm at two different points. The proximal extensor piece is pivotally attached to the distal extensor piece. The proximal extensor piece and the proximal support arm are each connected fixedly to a one of a pair of concentric shafts. Rotating one shaft rotates the entire arm. Rotating the other shaft extends or retracts the arm. The distal support arm is formed as a flat blade with cushions to support the wafer. The wafer handling arm is mounted through the center of the moveable wedge of a valve. A space at the center of the wedge valve is used to provide storage for the arm folded closed when the valve is closed. A pumping port is provided in the valve housing for pumping on the arm when the valve is closed (or open depending on process requirements). There are provided input and output loadlocks equipped with elevators and optical sensors connected to a computer operated in a manner so that the position and presence of each wafer in a cassette slot is measured and recorded in the computer. The computer is programmed to skip blank slots and to move a manipulator apparatus to find the wafer at the measured position or to move the wafer into a measured position of an empty slot. The manipulator is also designed in such a manner that wafers may be removed or inserted in a cassette in a nonsequential order. Small vacuum chambers are formed in the walls of the larger vacuum chamber (or the door). Each small vacuum chamber is surrounded by a sealing means at the front opening of the small chamber. The surface of the door (or chamber) where it contacts the sealing means is smooth and conforms to the seal as the door is closed. Pumping on the small vacuum chamber holds the door closed while the larger vacuum chamber is evacuated. After the larger chamber is returned to atmospheric pressure, a switch in the door handle operates electrically actuated valves which stop the pumping on the small chambers and vents them to the atmosphere. In one embodiment of a wafer holding means, a group of lifting pins receives the wafer from the transport device and lowers the wafer to the surface of a temperature controlled chuck. A group of holding pins then lowers to center and clamp the wafer to the chuck. The lifting pins and the holding pins are driven from a common shaft drive mechanism to provide foolproof mechanical interlock of the lifting and holding functions. In another embodiment of a wafer holding means, a group of lifting pins receives the wafer from the transport device and lowers the wafer to the surface of a temperature controlled chuck. A group of thin holding clamps then pivot and lower to center and hold the wafer to the chuck. The clamps are made thin so that from 3 to more than 70 may be closely placed around the rim of a 6-inch wafer. The clamps are driven from two rings around the chuck. One ring lifts and lowers all clamps. The second ring pivots all clamps over the wafer. To provide good thermal transfer between the chuck and the wafer, helium is led in the chuck through channels into grooves on the face of the chuck. The temperature of the chuck is controlled by means of heaters, water cooling, temperature sensors and a control computer. By this means, a helium pressure of greater than 3 Torr can be maintained at the backside of the wafer while maintaining a vacuum (less than 1 Torr) at the wafer surface. These and further constructional and operational characteristics of the invention will be more evident from the detailed description given hereinafter with reference to the figures of the accompanying drawings which illustrate preferred embodiments and alternatives by way of non-limiting examples.