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Metal heaterRelated Patent Categories: Heating, Heat Generating Means Heats Heat Storage Mass Of Solid MaterialMetal heater description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060199135, Metal heater. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a metal heater that is mainly used in the semiconductor industry and optical industry. BACKGROUND ART [0002] With respect to an etching device, and a semiconductor producing/examining device including a chemical vapor deposition device or the like, metal heaters having substrates of a metal material such as stainless steel have been used. [0003] FIG. 4 is a cross-sectional view that schematically shows a metal heater having a structure that has been conventionally used. [0004] In this metal heater 450, a heater 453 in which a nichrome wire 452 is sandwiched between silicon rubbers 461 is provided to an aluminum plate 451 having a thickness of 15 mm. SUMMARY OF THE INVENTION [0005] However, metal heaters with such structures have the following problems. [0006] Metal plates to be used for the metal heaters are needed to have a thickness to a certain extent. It is because if the metal plates are thin, the rigidity are low and the metal plates are warped and sagged since the metal plates are pushed from the surrounding because of thermal expansion attributed to heating or there is a difference of thermal expansion coefficients between supporting cases and metal plates. [0007] If such warping, sagging and the like occurs in the metal plates, a semiconductor wafer placed on the metal plates cannot be heated evenly, so that a dispersion of temperature or a damage in the semiconductor wafer is generated in some cases. [0008] However, if the metal plates are made thick, the heat capacity of the metal plates is increased, and in the case of heating or cooling an object to be heated, the temperature of the heating faces of the metal plates cannot promptly follow the change of the voltage or the electric current applied to the heating elements, and there has been a problem that temperature control becomes difficult. [0009] Further, there has been a problem that it takes a long time (a long recovery time) to recover the previous temperature of the heating face and productivity reduces in the case a semiconductor wafer is placed on the metal plate and the temperature of the heating face of the metal plate abruptly drops. [0010] Further, such metal heaters may have, in the case temperature is increased, an overshoot phenomenon that the temperature temporarily goes over the set temperature. If the overshoot phenomenon occurs, it takes further longer time to bring the temperature of the heating faces of the metal plates to the set temperature. [0011] Additionally, along with the recent tendency of enlargement of the diameter of semiconductor wafers and the like, and other reasons, metal heaters with a larger diameter are desired. With the enlargement of the diameter of the metal plates, the uneven temperature distribution in the metal plates themselves tends to occur, and accordingly, the above temperature evenness of the semiconductor wafer is further deteriorated. [0012] In view of the above-mentioned problems, the present inventor has made extensive research efforts for the purpose of obtaining a metal heater which has a comparatively fast temperature-rising speed and a comparatively short recovery time, hardly causes temperature change in a semiconductor wafer and the like upon heating, and is free from warping and sagging in metal plates, and found that, by: sandwiching a heating element between a plurality of metal plates; and making the thickness of a metal plate on a heating face side larger than the thickness of a metal plate on the opposite side, it becomes possible to ensure the flatness of the heating face and consequently to maintain the temperature of the heating face in an even level; thus, a first aspect of the present invention has been completed. [0013] In other words, a metal heater according to a first aspect of the present invention comprises a metal plate and a heating element. Herein, the number of the metal plates is a plural number, the heating element is sandwiched between the metal plates, and the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to said heating face side. [0014] The metal heater according to the first aspect of the present invention comprises the plurality of metal plates, and the heater is sandwiched between the metal plates. The metal heater having this structure makes it possible to more quickly heat an object to be heated, such as a semiconductor wafer or the like, in comparison with a metal heater that is formed by a single metal plate with a heater placed on a side opposite to the heating face side of the metal plate, and also to shorten the recovery time. [0015] Since the metal heater according to the first aspect of the present invention is designed so that the thickness of the metal plate on the heating face side is the same as or larger than the thickness of a metal plate on the side opposite to said heating face side, it becomes possible to improve the flatness of the heating face upon heating and, also, to evenly heat the entire semiconductor wafer. [0016] The reason therefor will be briefly described below. [0017] In the metal heater according to the first aspect of the present invention, since the thickness of the metal plate on the heating face side is made larger, the mechanical strength becomes higher, making the metal plate less likely to have warping and the like upon heating. Therefore, upon heating, the flatness of the heating face is improved. [0018] Moreover, in the case where the thickness of the metal plate on the heating face side is made larger, the thermal capacity of the metal plate on the side opposite to said heating face side is made relatively smaller than the thermal capacity of the metal plate on the heating face side. For this reason, the metal plate on the side opposite to said heating face side is made less likely to have accumulation of heat in comparison with the metal plate on the heating face side. Therefore, even in the case where ordinary-temperature silicon wafers are successively placed on the heating face so as to carry out a continuous process, heat conduction hardly occurs from the metal plate on the side opposite to said heating face side to the metal plate on the heating face side. Of course, temperature change hardly occurs in the metal plate on the heating face side due to an overshoot phenomenon caused by the heat conduction from the metal plate on the side opposite to said heating face side to the metal plate on the heating face side. Therefore, it becomes possible to easily control the temperature of the metal plate on the heating face side, and consequently to maintain the heating treatment temperature at a constant level. [0019] The metal heater according to the first aspect of the present invention may have a structure in which another metal plate is further attached to the heating element placed on the metal plate, that is, a structure in which a heating element is sandwiched between two metal plates or a structure in which heating elements are sandwiched among three or more metal plates. [0020] In the case where the metal heater according to the first aspect of the present invention comprises three or more metal plates, the thickness of the metal plate on the heating face side refers to the thickness of metal plates located above the heater of the uppermost layer, and the thickness of the metal plate on the side opposite to said heating face side refers to the total thickness of the metal plates located below the heater on the uppermost layer. [0021] FIG. 3 shows a structure of a metal heater comprising three metal plates. Herein, FIG. 3 shows only the metal plate and the heater. Continue reading about Metal heater... Full patent description for Metal heater Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Metal heater patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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