Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-11-02
2001-08-21
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S408000
Reexamination Certificate
active
06278089
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatuses for providing uniform heating during the thermal cycling of material substrates. More particularly, the present invention relates to a heater capable of providing high temperature thermal cycling without failure.
BACKGROUND OF THE INVENTION
Certain stages of semiconductor manufacturing require thermal cycling of a semiconductor substrate, wherein the substrate is repeatedly heated and then cooled. For example, each photoresist processing stage of semiconductor manufacturing requires a heating, or baking, step to flow the photoresist material along the substrate surface, followed by a cooling step to set the photoresist. In order to produce high quality substrates suitable for state of the art integrated circuit applications, the temperature of a substrate during thermal cycling must be precisely controlled with respect to both temporal temperature profile and temperature uniformity across the substrate.
Conventional heaters typically employ resistive heating elements that are bonded/brazed to heat conduction plates, and/or employ integrated bake and chill plates having a plurality of cooling fluid channels and microchannels to affect cooling as described in commonly assigned U.S. patent application Ser. No. 08/939,926 filed Sep. 29, 1997. As a result of stresses introduced by repeatedly heating and cooling a heat conduction plate, delamination of bonded/brazed resistive heating elements can occur, requiring process downtime during heater replacement and generating safety concerns due to broken wires and/or open circuits. Further, the use of microchannels to affect cooling increases heater manufacturing costs and thus the cost per wafer processed.
Accordingly, it is an object of the present invention to provide an improved heater apparatus which can withstand repeated thermal cycling and that is easily manufacturable.
SUMMARY OF THE INVENTION
To address the shortcomings of the prior art, an inventive heater is provided for use in substrate processing.
In a first aspect of the invention, the heater is formed from a heater plate including an upper surface having at least one recess formed therein, a heater element wire disposed within the at least one recess and an electrically insulating and thermally conductive material disposed within the at least one recess so as to electrically insulate the heater element wire from the heater plate. The heater plate preferably comprises a ceramic such as aluminum nitride or a metal such as aluminum and/or copper.
Preferably a plurality of recesses are formed within the upper surface of the heater plate, and a heater element wire is disposed within each recess. An electrically insulating and thermally conductive material is disposed within each recess so as to electrically insulate the heater element wire disposed therein from the heater plate. For example, the plurality of recesses may comprise an inner recess that forms an inner heating zone for the heating plate and an outer recess that forms an outer heating zone for the heating plate. Alternatively, the plurality of recesses may comprise a plurality of stacked recesses such as at least one x-axis recess having a first depth within the heater plate and at least one y-axis recess having a second depth within the heater plate, so as to form a plurality of heating zones.
The electrically insulating and thermally conductive material preferably comprises a material (e.g., TEFLON™) deposited within the recess so as to embed the heater element wire within the electrically insulating and thermally conductive material, and further may form an electrically insulating and thermally conductive layer over the entire upper surface of the heater plate if desired. The electrically insulating and thermally conductive material also may comprise a plurality of insulating beads that surround the heater element wire. Most preferably the heater element wire is threaded through each insulating bead in the manner beads are threaded on a necklace. When insulating beads are employed, an electrically insulating and thermally conductive layer may be deposited prior to, and/or after the plurality of insulating beads are inserted within the recess to further reduce the probability of shorts.
In a second aspect of the invention, the heater comprises a heater plate including an upper and a lower surface, wherein the lower surface of the heater plate has a plurality of cooling fins or other surface features formed therein so as to increase surface area. The increased surface area increases the heater's cooling rate, therefore increasing throughput by decreasing the heaters cycle time from hot to cold.
In a third aspect, the invention comprises a method for cooling a heater by spraying the lower surface of the heater plate with a cooling liquid (e.g., water) so as to cool the heater. The temperature of the cooling liquid preferably is decreased from a first temperature (e.g., 100° C.) to a second temperature (e.g., 20° C.) so as to cool the heater gradually.
By providing the upper surface of the heater with a plurality of recesses, each having a heater element wire disposed therein, multiple heater zones may be defined within the heater to improve heater temperature uniformity. Cooling fins or other surface features increase the heater's cooling efficiency and varying the temperature of cooling fluid employed to cool the heater reduces the thermal stress experienced by the heater during thermal cycling, thereby extending heater life. Further, a heater having upper surface recesses and/or cooling fins is easier to manufacture than conventional heaters making the inventive heater more reliable, and less expensive than conventional heaters.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims, and the accompanying drawings.
REFERENCES:
patent: 535321 (1895-03-01), Delany
patent: 2387460 (1945-10-01), Myers
patent: 3110795 (1963-11-01), Bremer
patent: 3904850 (1975-09-01), Johnson
patent: 4481407 (1984-11-01), Stokes et al.
patent: 5225662 (1993-07-01), Schmidt
patent: 5835334 (1998-11-01), McMillin et al.
patent: 5927077 (1999-07-01), Hisai et al.
patent: 04150022 (1992-05-01), None
Bolandi Hooman
Schaper Charles D.
Young Douglas W.
Applied Materials Inc.
Dugan and Dugan
Paik Sang
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