Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-10-18
2003-10-28
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S411000, C219S390000, C392S418000
Reexamination Certificate
active
06639189
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to heating members, heating elements, and to apparatuses useful for heating and cooling a workpiece that incorporate the heating members and heating elements, including bake/chill apparatuses and prime/chill apparatuses used in the manufacture of microelectronic devices. The heating members can be made to have a relatively high flatness, allowing improved efficiency and uniformity of heat transfer during processing.
BACKGROUND
The manufacture of many products requires precise control of temperature and temperature changes. For example, the manufacture of microelectronic devices such as integrated circuits, flat panel displays, thin film beads, and the like, involves applying a layer of some material, such as a photoresist, to the surface of a substrate such as a semiconductor wafer (in the case of integrated circuits). Photoresists, in particular, must be baked and then chilled to set or harden selected portions of the photoresist during processing. The baking and chilling steps must be precisely controlled within exacting temperature constraints to ensure that the selected portions of the photoresist properly set with good resolution. Nowadays, with the size of features becoming ever smaller and approaching sub-micron magnitudes, precise temperature and uniform heating of a workpiece become even more important.
Other products and processes involving precise temperature constraints include medical products and processes including drug preparation, instrument sterilization, and bioengineering; accelerated life testing methodologies; injection molding operations; piezoelectric devices; photographic film processing; material deposition processes such as sputtering and plating processes; micromachine manufacture; ink jet printing; fuel injection; and the like.
Baking and chilling operations for microelectronic devices typically involve cycling a workpiece through a desired temperature profile in which the workpiece is maintained at an elevated equilibrium temperature, chilled to a relatively cool equilibrium temperature, and/or subjected to temperature ramps of varying rates (in terms of ° C./s) between equilibrium temperatures. To accomplish baking and chilling, some previous bake/chill operations have included separate bake and chill plates that require the use of a workpiece transport mechanism to physically lift and transfer the workpiece itself from one plate to another. This approach presents a number of drawbacks. First, workpiece temperature is not controlled during transfer between bake and chill plates. Second, the overall time required to complete the bake/chill process cannot be precisely controlled, because of the variable time required to move the workpiece to and from the respective plates. Third, the required movement takes time and thus reduces the throughput of the manufacturing process. Fourth, the cost of equipment includes the cost of components for handling the workpiece during transport from plate to plate. Fifth, the mechanical move from plate to plate introduces the possibility of contaminating of the workpiece. Thus, it is desirable to be able to accomplish both baking and chilling without having to physically lift and transport a workpiece from a heating member to a separate chill plate and vice versa.
A more recent approach of temperature control is described in U.S. Pat. No. 6,072,163, entitled “Combination Bake/Chill Apparatus Incorporating Low Thermal Mass, Thermally Conductive Bakeplate.” The patent describes methods that use a single apparatus having a low thermal mass heating member that supports a workpiece during both baking and chilling operations. While supporting the workpiece on one surface, the other surface of the heating member can be brought into and out of thermal contact with a relatively massive chill plate to easily switch between baking and chilling. A simple mechanism is used to physically separate the heating member and chill plate to effect rapid heating, or to join the heating member and the chill plate to effect rapid cooling. This approach eliminates the need to rely on workpiece handling to lift and transfer a workpiece from the heating member to a separate chill plate, and advantageously allows both chilling and baking to occur from a direction below the workpiece.
SUMMARY OF THE INVENTION
In bake and chill operations involving an apparatus with the combined ability to heat and cool, e.g., a bake/chill apparatus or a prime/chill apparatus, precise flatness has been found to be an important feature of the heating member. A typical gap between a supporting surface of a heating member and a workpiece supported by the heating member can be on the scale of several thousandths of an inch, e.g., less than six thousandths of an inch. It is important that the span of that gap be uniform over the entire area between the heating member and the workpiece so that heat is uniformly transferred between the two.
As an example of the effect of non-uniform heat transfer, consider the deposition of a reactive chemical layer such as a photoresist onto a microelectronic device. As noted above, finer and finer features are being placed on microelectronic devices, down to 0.13 microns and smaller. With continued reduction in feature size comes an attendant reduced tolerance for process non-uniformities. With smaller features, influences that in the past have had negligible effects on final quality of a processed workpiece become important. In the case of a photoresist used to produce such extremely small features, the temperature sensitivities of the photoresist may influence final product quality. Specifically, non-uniform temperatures across a layer of photoresist, even to a minute degree, can result in non-uniform thickness of a deposited photoresist layer or non-uniformity in the size of developed features, due to non-uniform solvent evaporation, or non-uniform reaction kinetics, e.g., development, chemical amplification, or photochemical reactions of a photoresist. These non-uniform processes, even if minutely small, can cause non-uniformities and imperfections in the details, e.g., feature sizes, of articles produced using the chemistries. Any methods of improving uniformity of heating a workpiece can improve product quality and reduce rejected products.
Another variable that can affect reaction kinetics, feature size, and uniformity, and ultimately the quality of manufactured products is the timing of heating and chilling processes. Many chemical reactions are temperature sensitive, meaning that they are designed to occur at a specific temperature. Optimum temperature control will involve a very rapid heating of a workpiece and its chemistry (e.g., photoresist) to the desired temperature, which will minimize the amount of time spent at a less-optimum temperature, and maximize the time spent reacting at the desired temperature. Overall, this increases the precision of the reaction and the uniformity of the reacted chemistry. Properties of a heating member that allow rapid, precise heating and cooling are particularly desirable. Agility in heating and cooling performance is desirable and very useful to provide high throughput and quality of workpieces.
It has been found that a high degree of uniformity in heating a workpiece can be achieved by selecting a low thermal mass heating member to have one or more of: an extreme degree of flatness of the supporting surface; high thermal conductivity of the thermally conductive layer; independent zones of temperature control; and a thermally conductive layer that has rigidity, stiffness, and thermal properties to achieve the desired flatness and thermal conductivity. Improved uniformity in heating a workpiece can improve the uniformity of chemical processing (e.g., solvent evaporation or chemical reactions) over the surface area of the workpiece, which improves the uniformity of feature sizes and ultimately increases product quality and yield.
Typical processes that have been used in constructing heating members have involved subjecting heating mem
Ramanan Natarajan
Sims James B.
FSI International Inc.
Fuqua Shawntina
Kagan Binder PLLC
Walberg Teresa
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