Ceramic heater

Abstract

An objective of the present invention is to provide a ceramic heater making it possible to prevent a short circuit in its resistance heating element and heat a semiconductor wafer evenly. The ceramic heater of the present invention is a ceramic heater comprising: a ceramic substrate; an insulating layer having volume resistivity higher than that of said ceramic substrate, being formed on at least a part of said ceramic substrate; and a resistance heating element formed on said insulating layer.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a ceramic heater which is used mainly in the semiconductor industry, particularly to a ceramic heater superior in insulation between circuits of resistance heating elements. BACKGROUND ART [0002] Semiconductors are very important goods necessary in various industries. A semiconductor chip, which is a typical product thereof, is produced, for example, by slicing a silicon monocrystal into a given thickness to produce a silicon wafer, and then forming various integrated circuits and the like on this silicon wafer. [0003] In order to form integrated circuits and so on of this type, it is necessary to conduct a process of applying a photosensitive resin onto the silicon wafer, exposing the resin to light, developing the exposed resin and then subjecting the resultant to post-curing and sputtering, to form a conductor layer. For this purpose, it is necessary to heat the silicon wafer. [0004] As this heater for heating the sil...

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Benefits of technology

[0009] The inventors made eager investigations to solve the above-mentioned problems. As a result, it has been found out that by arranging, on one surface of a ceramic substrate, an insulating layer having a volume resistivity higher than that of the ceramic substrate and then forming a resistance heating element thereon, a short circuit in the resistance heating element can be prevented and further unevenness of the temperature of a semiconductor wafer can be overcome by the presence of this insulating layer. Thus, the inventors have accomplished the present invention.

[0012] Even if the volume resistivity of the ceramic substrate drops at high temperature, the circuit of the resistance heating element can be prevented from being short-circuited since the volume resistivity of the insulating layer is higher than that of the ceramic substrate within the range of temperature at use.

[0015] About a nitride ceramic, its volume resistivity drops easily at high temperature by formation of solid solution of oxygen therein. A carbide ceramic has an electric conductivity so far as the purity thereof is not made particularly high. A resistance heating element cannot be formed on the surface of a substrate comprising such a ceramic or inside the substrate to which no treatment is applied. Thus, by forming an insulating layer comprising an oxide ceramic on the surface of a ceramic substrate comprising such a material in the present invention, a short circuit between circuits can be prevented and the ceramic substrate can be caused to function as a heater.

[0027] In the ceramic heater of the second aspect of the present invention, the ceramic substrate can be warped in one direction by forming the insulating layer on one face thereof and the like. According to this, in case that a semiconductor wafer is heated in the state that the wafer is separated from the ceramic substrate by a given distance, the distance between the semiconductor wafer and the ceramic substrate can easily be grasped. By performing temperature-control dependently upon the distance, the surface temperature of the semiconductor wafer can be made even.

[0029] In the present invention, however, irregular undulation can be removed by warping the ceramic substrate in one direction. Therefore, temperature-control becomes easy so that the surface temperature of the semiconductor wafer can be made even.

Problems solved by technology

Therefore, even if resistance heating elements are disposed on the surface of such a conductive carbide ceramic, a short circuit is caused between circuits so that the temperature thereof cannot be controlled.

However, even if circuits are formed on such a ceramic, a short circuit is caused.

Therefore, the ceramic cannot be used, as it is, as a ceramic substrate.

Furthermore, a ceramic comprising a nitride and the like which has insulation at ambient temperature has defects such as oxygen forming solid-solution.

This causes a drop in volume resistivity at high temperature to result in a problem that a short circuit is caused between circuits, thus making temperature-control impossible.

On the other hand, particularly when a semiconductor wafer is heated in the state that the semiconductor wafer and a ceramic substrate are separated from each other, a phenomenon that the temperature of the semiconductor wafer becomes uneven is observed even though the temperature of the surface of the ceramic substrate is made even.

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