Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2000-10-12
2002-06-11
Paik, Sang (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S444100, C118S725000
Reexamination Certificate
active
06403933
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved thermal conditioning apparatus and methods of using the same. More particularly, the present invention relates to improved thermal conditioning plate and method for use in controlling the temperature in the placement and curing of photoresist on a semiconductor substrate wafer.
2. Description of the Invention Background
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or “wafer”. The individual layers of the integrated circuit are, in turn, produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonaphtaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light, resulting in an irradiated material having differing solvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Photoresist and developer materials are typically applied to the wafer using a spin coating technique in which the photoresist is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the photoresist over the surface of the material and exerts a shearing force that separates the excess photoresist from the wafer thereby providing for a thin layer of photoresist on the surface of the wafer. Following the spin coating of the wafer, the coating is heated, or soft baked, to remove the volatile solvent components, thereby hardening the photoresist.
The properties of the photoresist, and, therefore, the suitability of the photoresist for use in the subsequent processing steps, are largely dependent upon the ability to uniformly harden the photoresist. The heating of the photoresist can be performed either by convection, infrared heating or through the use of a hot plate. While convection and infrared heating can be performed in bulk, the use of a hot plate to individually bake the wafer on a heating surface has become the preferred method. This is because the hot plate method provides for rapid heating of the wafer and the heating occurs from the wafer-photoresist interface toward the surface of the photoresist, which tends to drive off gas pockets present in the photoresist and also prevents the formation of a surface crust on the photoresist. In order for the hot plate soft baking technique to be cost effective in comparison with the batch techniques, an automated wafer handling system must be used to maximize the throughput of the wafers. In addition, cooling assemblies are often employed to reduce the cooling time for the wafer so as to enhance the overall throughput of the system. As such, the heating and cooling system are directly tied into the automated wafer handling system.
A problem that arises with the prior art integrated spin coating systems is that when the heating or cooling assemblies must be repaired or replaced, extensive and costly amounts of downtime occur because of the integration of the system. The costs are especially significant in a clean room environment in which all operations in the clean room have to be shut down until cleanliness can again be achieved at a cost of thousands of dollars an hour. For instance, if the heating element must be replaced in the hot plate, not only must the system be shut down for the replacement, but following the replacement of the heating element the system will have to be recalibrated prior to restarting the system and the cleanliness procedure followed to reestablish cleanliness in the clean room.
In the operation of the heating or cooling assemblies, the wafers are placed either directly upon the heating/cooling surface of the plate, or, alternatively, upon a plurality of receiving pins, from which the wafers are placed on the surface using an assembly such as that described in U.S. Pat. No. 4,955,590 issued to Narushima et al. The use of receiving pins and/or a table that reciprocates is a preferred method of loading in the industry because it provides access to the exposed uncoated surface for the loading and unloading of the wafers with automated handling equipment when the wafer is seated upon the receiving pins. One problem with this method as discussed in the Narushima patent (col. 1, lines 38-41) is that, if the receiving pins are lowered, the air resistance causes the wafer to float, which can result in misalignment of the wafer on the pins. The Narushima patent (col. 4, lines 37-44) indicates that by moving the table and not the pins this problem is eliminated, because the wafer is not moved; however, the raising of the table will exert a force on the bottom of the wafer that is analogous to the force exerted when the wafer is lowered, thus floating of the wafer will occur even when the table is raised and the pins are stationery. A possible solution to this problem suggested in the Narushima patent (col. 5, lines 3-6) is to draw a vacuum through the distal end of the receiving pins to chuck the wafer against the distal end of the pins to prevent movement. While this solution appears to provide a more plausible method of preventing the wafer from floating, the method greatly complicates the overall design of the system. This is because the wafer must be removed from the receiving pins requiring that the vacuum be released when the wafer reaches the table either through the use of a sensing system or by moving the table at a speed so as to dislodge the wafer from the receiving pins; however, this type of mechanical release would most likely result in misalignment problems and could also potentially damage the wafer. As such, there is need for an improved apparatus and method for receiving wafers, and plate-like material in general, in a plate-like material treating apparatus.
A number of methods exists
Davis Shawn D.
Hayes Bruce L.
Molebash John S.
Smith Rex A.
Strodtbeck Timothy A.
Kirkpatrick & Lockhart LLP
Micro)n Technology, Inc.
Paik Sang
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