Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
2002-03-19
2004-06-22
Clark, Sheila V. (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S701000, C361S748000, C361S234000
Reexamination Certificate
active
06753601
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ceramic substrates used mainly in the semiconductor industry, and particularly to ceramic substrates suitable for hot plates, electrostatic chucks, wafer probers and so on.
BACKGROUND ART
Semiconductors are very important products necessary in various industries. Semiconductor chips are produced, for example, by slicing a silicon monocrystal into a predetermined thickness to produce a silicon wafer, and then forming a plurality of integrated circuits and the like on the silicon wafer.
In a process for manufacturing such semiconductor chips, a silicon wafer put on an electrostatic chuck is subjected to various treatments such as etching and CVD to form conductor circuits, elements and so on. At this time, a corrosive gas as a gas for deposition or a gas for etching is used. Therefore, since it is necessary to protect an electrostatic electrode layer and it is also necessary to induce adsorption power, an electrostatic electrode layer is usually covered with a ceramic dielectric film and the like.
Nitride ceramics have hitherto been used as such a ceramic dielectric film. For example, electrostatic chucks using nitrides such as aluminum nitride are disclosed in JP Kokai Hei 5-8140. Carbon-containing aluminum nitride having an Al—O—N structure is disclosed in JP Kokai Hei 9-48668.
A process for manufacturing such electrostatic chucks is disclosed in JP Kokoku Hei 6-97677 and so on.
As disclosed, for example, in JP Kokai Sho 62-264638 and JP Kokai Sho 60-261377, such electrostatic chucks made of ceramic are manufactured by the so-called green sheet method wherein a lamination is prepared by laminating green sheets and then a ceramic substrate is produced by firing the lamination.
SUMMARY OF THE INVENTION
However, it was found: that an electrostatic chuck using a ceramic produced by the above-mentioned green sheet method has the problem in dispersion of chuck power, that a ceramic heater also has the problem in dispersion of temperature on a wafer treating face; and that a wafer prober has a problem in dispersion of applied voltage of a guard electrode or a ground electrode.
The present invention has been made for solving the above-mentioned problems. The objective of the invention is to provide: a ceramic substrate generating no dispersion of chuck power in case of a ceramic substrate with an electrostatic electrode embedded inside the ceramic substrate (an electrostatic chuck); a ceramic substrate having no temperature difference among positions on its wafer treating face and also being able to evenly heat an object to be heated such as a semiconductor wafer in case of a ceramic substrate with a resistance heating element provided on the surface of the ceramic substrate or inside the ceramic substrate (a hot plate); a ceramic substrate generating no dispersion of a voltage applied to the guard electrode or the ground electrode and being able to remove stray capacitor or noise with certainty in case of a wafer prober with a guard electrode or a ground electrode provided inside the wafer prober(a ceramic substrate).
Under the above-mentioned objective, the inventors of the present invention analyzed the causes for the generation of the above-mentioned problems and have found that a formed conductor layer has dispersion of thickness and thus the dispersion of thickness causes dispersion of chuck power, dispersion of temperature on a wafer treating face and dispersion of voltage applied to electrodes.
Thus, they have finally identified the following. By the adjustment of the dispersion of thickness of the green sheets, or roughness of surface of green sheets used for the preparation of a lamination, within predetermined ranges or, in case of the formation of a conductor layer using a metal foil and the like, by making the thickness of the metal foil and the like even and the like, local dispersion of thickness dependent on portions of a conductor layer of a ceramic substrate to be produced will be reduced with a consequent result of: the elimination of local dispersion of chuck power in case of the manufacture of an electrostatic chuck; the elimination of local dispersion of temperature on a wafer treating face in the manufacture of a hot plate; and the elimination of dispersion of voltage applied to a guard electrode or a ground electrode in the manufacture of a wafer prober.
Furthermore, besides above-mentioned problem, rapid temperature rising and rapid temperature falling are required for hot plates, electrostatic chucks and wafer probers in order to quicken through put, hence, ceramic substrates have another problem, in addition to the above-mentioned problems, that they tend to crack or warp due to such rapid changes in temperature.
However, the inventors have accomplished the present invention through their finding that such a problem can be solved by adjusting the dispersion of thickness of a conductor layer or by adjusting the ratio of the thickness of a conductor layer to that of a ceramic substrate.
That is, the ceramic substrate of the present invention is a ceramic substrate provided with a conductor layer on the surface of the ceramic substrate or inside the ceramic substrate,
wherein: the ratio (t
2
/t
1
) of the average thickness of the conductor layer (t
2
) to the average thickness of the ceramic substrate (t
1
) is less than 0.1 and; a dispersion of the thickness of the conductor layer to the average thickness of the conductor layer is in a range of −70 to +150%.
In the above-mentioned ceramic substrate, it is desirable that the ceramic substrate is in a disc-shape with a diameter exceeding 150 mm and is also desirable that the thickness of the ceramic substrate is 25 mm or less.
Moreover, in the above-mentioned ceramic substrate, it is desirable that the conductor layer is an electrostatic electrode and that the ceramic substrate functions as an electrostatic chuck.
Furthermore, in the above-mentioned ceramic substrate, it is desirable: that the above-mentioned conductor layer is a resistance heating element; and that the ceramic substrate functions as a hot plate.
Furthermore, in the above-mentioned ceramic substrate, it is desirable that the above-mentioned conductor layer is any of a chuck top electrode a guard electrode and a ground electrode and that the ceramic substrate functions as a wafer prober.
The conventional electrostatic chucks and ceramic heaters have a problem that the use of a green sheet
91
having large dispersion of thickness or having large roughness on its surface as shown in
FIG. 15
results in a formation of a conductor layer whose ratio of thickness thereof to a thickness of a ceramic substrate is extremely large, therefore, warp or cracks are generated when rapid temperature increase is conducted.
Furthermore, there also are problems such that when it is used as a hot plate, big local temperature difference is generated in a wafer treating face; that, when it is used as an electrostatic chuck, dispersion of adsorbing power is generated; and that, when it is used as a wafer prober, dispersion of voltage applied is generated.
Such tendencies become particularly noticeable for those in a disc-shape with a diameter exceeding 150 mm. At the times of the filing of JP Kokai Sho 62-264638 and JP Kokai Sho 60-261377, since only those with diameters as small as about 150 mm were required in the market, dispersion of chuck power or temperature difference in a wafer treating face caused little problem.
In addition, since the green sheets used had a thicknesses of about 50 to 150 &mgr;m, no serious problem was caused even if green sheets was uneven in thickness.
In the present invention, adjustment is made so that the ratio (t
2
/t
1
) of the average thickness (t
2
) of a conductor layer to the average thickness (t
1
) of a ceramic substrate becomes less than 0.1; and that a dispersion of the thickness of the conductor layer to the average thickness of the conductor layer is within a range of −70 to +150%.
The dispersion itself is desirably small, but it is not possible to make
Hiramatsu Yasuji
Ito Yasutaka
Clark Sheila V.
Ibiden Co. Ltd.
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