Coating apparatus – Gas or vapor deposition – Work support
Reexamination Certificate
1999-06-22
2002-03-12
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Work support
C118S7230AN, C118S500000
Reexamination Certificate
active
06355108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for use in processing a substrate. More particularly, the invention relates to a shadow frame for aligning and stabilizing a substrate during processing.
2. Background of the Related Art
In the fabrication of flat panel displays, transistors, liquid crystal cells, metal interconnects and other features are formed by depositing and removing multiple layers of conducting, semiconducting and dielectric materials from a glass substrate. Glass substrate processing techniques include plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etching and the like. Plasma processing is particularly well-suited for the production of flat panel displays because of the relatively lower processing temperatures required to deposit a film and good film quality which should result from using plasma processes.
In general, plasma processing involves positioning a substrate on a support member (often referred to as a susceptor or heater) disposed in a vacuum chamber and striking a plasma adjacent to the upper exposed surface of the substrate. The plasma is formed by introducing one or more process gases into the chamber and exciting the gases with an electrical field to cause dissociation of the gases into charged and neutral particles. A plasma may be produced inductively, e.g., using an inductive RF coil, and/or capacitively, e.g., using parallel plate electrodes, or by using microwave energy.
During processing, the edge and backside of the glass substrate as well as the internal chamber components must be protected from deposition. Typically, a deposition-masking device, or shadow frame, is placed about the periphery of the substrate to prevent processing gases or plasma from reaching the edge and backside of the substrate and to hold the substrate on a support member during processing. The shadow frame may be positioned in the processing chamber above the support member so that when the support member is moved into a raised processing position the shadow frame is picked up and contacts an edge portion of the substrate. As a result, the shadow frame covers several millimeters of the periphery of the upper surface of the substrate, thereby preventing edge and backside deposition on the substrate.
However, while conventional shadow frames may reduce edge and backside deposition on a substrate, the usable area of the substrate is greatly reduced. Typically, shadow frames comprise a lip portion extending over the edge of the substrate. The lip prevents any portion of the masked area of the substrate from receiving deposition, an effect known as edge exclusion. Consequently, each processed substrate includes an unprocessed, unusable portion which reduces the usable surface area on a substrate and results in lower productivity of the processing system.
One attempt to reduce the edge exclusion is the use of finger-type shadow frames. Finger-type shadow frames comprise a plurality of “fingers” or tabs extending outwardly from the shadow frame to stabilize a substrate during processing. The fingers are disposed around the edge of a substrate, thereby increasing the amount of usable substrate surface area as compared to the lip-type shadow frame which comprehensively covers the edge of the substrate.
However, finger-type shadow frames exhibit poor control of the plasma during processing. Successful plasma processing requires a uniform plasma density across the entire upper surface of a substrate during processing. Anomalies in the plasma density result in non-uniform deposition of films on the substrate leading to defective devices and thus further reducing the throughput of the processing system. In the case of flat panel display manufacturing, maintaining a uniform plasma at the perimeter of the substrate is particularly difficult due to various components of the vacuum system which can act as energy sinks. In conventional systems using finger-type shadow frames, for example, the shadow frame and the outermost edge of the substrate define a gap provided to prevent arcing which can occur between the shadow frame and the substrate resulting in damage to the substrate. However, the gap exposes the perimeter of the support member to the plasma and provides a ground to drain the plasma constituents. Thus, the plasma density at a perimeter of the substrate is often substantially less than the plasma density over the central portion of the substrate. Because the deposition thickness is related to the plasma uniformity, non-uniform deposition results.
FIGS. 1 and 2
illustrate the non-uniform deposition resulting from anomalies in the plasma density using a finger-type shadow frame.
FIGS. 1 and 2
represent processes performed in a conventional processing chamber wherein the plasma experienced drainage at a perimeter portion of the substrate. Referring to
FIG. 1
, for example, the deposition rate between about 0 mm and 30 mm and between about 690 mm and 720 mm is shown tapering off rapidly indicating the loss of uniformity. Thus, the edge of the substrate constitutes unusable area, thereby decreasing the margin of the process and the productivity of the processing system.
Another problem with flat panel display processing is the detrimental effects of thermal dynamics. During processing, the support member is heated by means of a heating element, such as a resistive coil, or by other methods in order to heat the substrate disposed thereon. Uniform heat conduction between the support member and the substrate are necessary to ensure uniform deposition. Where the thermal profile across the substrate is not uniform, i.e., where the profile exhibits relative hot and cold spots, the deposition of material onto the substrate is non-uniform and results in defective devices. Flat panel displays are particularly susceptible to the detrimental effects of thermal non-uniformity because of the area of the substrates exposed to deposition material as compared to their thicknesses, and because of the differences in the thermal conductivity of the substrates, typically comprising glass, and the support member, typically comprising a metal. In a typical process, the substrate may be about 30-60° C. less than the temperature of the support member which may be heated to a temperature between about 250-470° C. The support member will typically be more conductive than the glass but also be locally heated to a greater temperature adjacent to the heating element. This leads to localized heating of the glass which, because of its low expansion coefficient and lower thermal coefficient, will expand at the localized hot spots resulting in warping or bowing. Warping is also induced where a cooling gas is supplied to the backside of the substrate. The cooling gas can provide a backside pressure causing the substrate to bow or warp. To ensure good heat conduction and minimize warping, the substrate and the support member must be maintained in close and uniform contact, thus warping and bowing should be avoided.
Current efforts to achieve good thermal conduction between the substrate and the support member include providing a clamping force at the perimeter of the substrate by use of a shadow frame as described above, which keeps the glass edges flat and helps trap the cooling gas in the space between the substrate and the support member. However, as noted previously, conventional shadow frames typically cover a substantial portion of the substrate edge resulting in reduced usable area on the substrate. Further, the clamping force is often excessive causing damage to the substrate. For example, U.S. Pat. No. 5,753,133 provides an apparatus using a spring-biased clamping mechanism to position a substrate in a vertical position during processing. The pressure supplied by such an arrangement can cause the substrate to fracture or warp during the elevated processing temperatures.
Yet another problem with flat panel display processing is the improper positioning of the substrate on the support member and r
Choi Soo Young
Greene Robert I.
Law Kam S.
Robertson Robert M.
Shang Quanyuan
Applied Komatsu Technology Inc.
Mills Gregory
Moser Patterson & Sheridan LLP
Zervigon Rudy
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