Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Reexamination Certificate
1999-05-14
2001-04-03
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
C034S103000, C034S106000, C034S107000
Reexamination Certificate
active
06209221
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wafer rack to be placed in a reactor, comprising a carrier frame provided with at least two accommodations for at least two wafers. A wafer rack of this type is generally known in the prior art and is used for batchwise treatment of two or more wafers. The number of wafers that is treated simultaneously can rise to far above 100.
BACKGROUND OF THE INVENTION
Wafers are subjected to various treatments, including chemical treatments in a wide variety of types of reactor. One treatment comprises etching wafers using HF vapour. Because of a wide variety of circumstances, it can be desirable to etch wafers between different deposition treatments. The problem then arises that such an etching substance also has to penetrate into relatively deep wells present in the wafer in order to be able to etch native silicon dioxide. In particular, problems have been detected if a layer of doped oxides deposited using CVD, such as borophosphosilicate glass (BPSG), has to be etched. The methods known in the prior art for etching batches of wafers do not give a uniform result.
This problem increases on increasing the diameter of the wafers. Recently there has been a discernible trend in the market to switch from 200 to 300 mm. If such wafers are etched using conventional techniques, this results in a difference between minimum and maximum etching depth in a range between, for example, 50 Å and 5000 Å. Moreover, it will hardly be possible to remove the native oxides in the mid section of such wafers.
In U.S. Pat. No. 4,798,165, drawn up in the name of ASM International N.V. in Bilthoven, it is proposed, for a reactor in which a single wafer is treated, to supply the gas via a distributor plate arranged above the wafer so that uniform distribution of gas over the wafer is produced. Such a process is satisfactory.
SUMMARY OF THE INVENTION
The aim of the present invention is to achieve the uniform distribution that is obtained with the equipment according to the above mentioned U.S. Pat. No. 4,798,165 for the batchwise treatment of various wafers as well.
This aim is achieved with a wafer rack as described above in that a gas distribution device effective for each accommodation is mounted on the carrier frame, said gas distribution device comprising a distributor plate, provided with at least one opening, for each accommodation as well as gas supply means.
According to the invention a gas distributor plate is arranged at least above each wafer, which gas distributor plate is provided with a large number of openings through which the gas is supplied to the wafer. That is to say feeding of gas no longer takes place from one side of the reactor in an uncontrolled manner towards the opposing side, producing a non-uniform distribution of gas, but a radial gas flow is now produced over each wafer. The invention has been described above with reference to a reactor in which the wafers are placed above one another in a wafer rack extending in the vertical direction. It must be understood that with the necessary modifications the construction according to the invention can also be used for the batchwise treatment of wafers placed vertically in a wafer rack oriented essentially in the horizontal direction.
The gas supply to the gas distribution device can be chosen depending on the design of the construction. If reactors which are still to be produced are taken as the starting point, according to a simple embodiment the wafer rack is provided with feed lines for the gas that is used for treatment or flushing, the inlet thereof being able to engage via a coupling with a corresponding coupling in the reactor. Preferably, coupling is automatically produced by the introduction of the wafer rack. If a wafer rack construction according to the present invention has to be arranged in existing reactors, with which the gas flow takes place from one side to the opposing side, it is preferable so to control the gas flow by fitting gas distributor plates that optimum metering to the distributor plate takes place, whilst provision must be made for directed discharge of the gas.
According to an advantageous embodiment of the invention, in a vertical reactor the gas is supplied at the top of the wafers. However, it is also possible to supply the gas at the bottom, on its own or in combination with the gas supply at the top.
The present invention also relates to a reactor for accommodating a wafer rack and provided with coupling means to produce a connection with a supply line for gas mounted on the wafer rack as described above.
The invention also relates to a method for simultaneous treatment of at least two wafers in a process installation with a gas, comprising placing said wafers in a wafer rack and introducing said filled wafer rack into said process installation, wherein the gas is supplied via a central feed from the reactor separately to, in each case, one chamber above/below the surface of each wafer and is moved over at least said surface of said wafer, uniformly distributed over said wafer.
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ASM International N.V.
Gravini Stephen
Knobbe Martens Olson & Bear LLP
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