Radiation imagery chemistry: process – composition – or product th – Effecting frontal radiation modification during exposure,...
Reexamination Certificate
2001-02-06
2003-01-21
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Effecting frontal radiation modification during exposure,...
C430S311000, C430S313000
Reexamination Certificate
active
06509142
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to equipment and methods for the photolithography of photoresist-coated substrates such as those used for plasma display television screens.
BACKGROUND OF THE INVENTION
The exposure of small substrates such as those used for plasma display screens is generally performed with both the substrate and the photo tool or mask in a horizontal position by a single exposure from a vertically directed collimated light beam. However, for a number of reasons, such methods do not work well for large panels such as those used for large plasma display television screens. One problem is that for a large substrate, it is difficult to provide a collimated light beam of a sufficient size to permit the single exposure of the substrate at a uniform intensity over its entire surface. Another problem is that when a large mask is held in a horizontal mask frame for exposure of a substrate, the center of the mask tends to sag due to its weight. Similarly, unless it is properly supported, a horizontal substrate will tend to sag. Any such sagging in the mask or substrate makes the accurate photolithography of the substrate virtually impossible.
While a number of manufacturing techniques have been developed in attempts to avoid these problems, such techniques have proven to be difficult and costly to implement. Moreover, current methods do not generally permit the quick and accurate exposure of a large number of large substrates in an automated fashion.
Generally, the methods for exposing large substrates have required either scanning the entire surface of the panel with a moving beam and/or using a fixed beam and moving the mask and substrate so as to expose the substrate's entire surface by a scanning procedure. These scanning methods include the “step and repeat” method in which specific portions of the panel are sequentially exposed in incremental steps, each step by a timed exposure. Other methods include a continuous scan in which the substrate and light beam are moved with respect to one another in a moving exposure. One such continuous scan method moves the mask and substrate over a serpentine path to expose the substrate to a fixed collimated light beam in a single exposure until the entire substrate has been exposed.
Both step and repeat and continuous scan methods of exposure often lead to stitching errors, that is, errors where discrete lines of overexposure or underexposure are left in the substrate where adjacent paths of the collimated light beam do not perfectly mesh with one another. To the extent stitching errors can be reduced, these basic methods are nonetheless time consuming and often difficult to consistently repeat for a large batch of substrates. Problems with repeatability lead to the frequent rejection of substrates for failing to meet minimum quality control standards.
With regard to the problem of mask sagging when a large mask is held in a horizontal position for exposure of a substrate using a vertical light beam, this problem has largely been overcome through the use of a generally horizontal beam of exposure light that is directed through a mask and substrate held in a generally vertical orientation. However, when the mask and substrate are held perfectly vertical, they tend to be unstable and difficult to hold motionless during the exposure. The stability of the mask and substrate can be improved while reducing sag by holding the mask and substrate in planes that are slightly out of vertical. Nevertheless, while sag problems can generally be avoided by these methods, the handling of large, vertically oriented masks and substrates has proven to be difficult. These problems in handling make conventional exposure methods for large substrates costly, time consuming and unreliable.
Yet another difficulty with existing methods for exposing large substrates has been that such exposures must generally be done in a clean room so as to avoid contaminating either the mask or the photoresist coating on the substrate with dust or dirt. Because the equipment associated with the exposure of large substrates is very large, it is often difficult and costly to fit such equipment within a clean room. Moreover, once the equipment is installed in a clean room, any routine maintenance can be difficult and costly due to the steps that must be taken in maintaining the clean room atmosphere.
An improved apparatus and method for exposing large photoresist-coated substrates quickly, reliably and at low cost is desired.
SUMMARY OF THE INVENTION
According to the present invention, an improved apparatus and an improved method for exposing large photoresist-coated substrates are provided. The apparatus includes two key components: a light scanning assembly, and a mask and substrate handling assembly. One important advantage to the apparatus is that the two key components need not be physically located in the same room. Therefore, only the mask and substrate handling equipment need to be located in a clean room. The light source can be located in an adjacent room. By locating the light source outside the clean room the ability to perform routine maintenance on the light scanning assembly is greatly simplified.
According to the invention, the mask and substrate handling assembly includes a frame for holding the mask in a substantially vertical position. The mask is held in place on as vacuum chuck. It is generally desired to hold the mask at an angle slightly out of vertical, preferably at an angle up to about 5 degrees from vertical, and more about 2 degrees from vertical, in order to effectively eliminate sag while improving the stability of the mask. A 2 degree angle is achieved by mounting the frame perpendicularly to a ramp with a 2 degree slope from horizontal. The ramp is mounted on a base that is preferably anchored to a block of a heavy material such as granite so as to damp out any vibrations from the building in which the equipment is located. The frame is mounted to the ramp with slide bearings and a positioning table driven by a stepper motor is provided to enable the frame to be moved up and down the ramp.
A tiltable substrate platen, also mounted on the base, is provided for receiving the photoresist-coated substrate in a generally horizontal position. The platen includes pneumatically-driven snubbing pins which cooperate with banking pins to center the substrate on the platen. A vacuum chuck is provided on the platen to hold the centered substrate firmly in place. The side of the platen proximate the frame is hinged to permit the substrate to be tilted into a position parallel to the mask. The platen is tilted by a servo-driven jack screw assisted by a pair of pneumatic lift assists. Preferably, the mask and substrate are oriented with respect to one another so that the preferred 2 degree tilt of the mask is in the direction of the substrate.
The mask and substrate handling assembly further includes equipment for automatically moving a substrate into position on the platen. A horizontal in-feed conveyor is provided adjacent the platen with a plurality of drive rollers to feed a substrate to the platen. In order to assist the platen in receiving the substrate from the in-feed conveyor, the platen includes a plurality of retractable wheels which can be extended up from the surface of the platen and driven by a motor to assist in maneuvering the substrate to the proper position on the platen. The wheels retract to lower the substrate so that it can be held in place by the vacuum chuck. Similar to the in-feed conveyor, an out-feed conveyor is provided adjacent the platen to withdraw the exposed substrate from the platen for further processing. Like the in-feed conveyor, the out-feed conveyor includes a plurality of drive rollers for manipulating the exposed substrate.
The light scanning assembly includes collimated light beam projection equipment mounted on a shuttle. The collimated light beam projection equipment includes a lamphouse which directs a beam of ultra violet light to a reflecting mirror which, in turn, directs the light
Baxter Gregory R.
Beauchene James H.
Jacobo Victor M.
Melbon Eugene J.
Barreca Nicole
Christie Parker & Hale LLP
Huff Mark F.
ORC Technologies, Inc.
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