Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state
Reexamination Certificate
1996-05-31
2001-01-16
Bueker, Richard (Department: 1763)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
C427S255500, C427S255700, C438S706000, C438S716000, C438S719000, C156S345420, C118S719000, C118S729000
Reexamination Certificate
active
06174366
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The object of the present invention is an apparatus used for processing silicon wafers, the apparatus comprising two or more reactors of essentially different type with respect to each other, the reactors being suitable for processing the various processing stages of silicon wafers, such as the epitaxial growth of silicon, plasma etching or metal deposition under vacuum, that is, for processing silicon wafers in two or more essentially different processing stages. The invention also relates to a method for processing silicon wafers in an apparatus comprising two or more reactors of essentially different type with respect to each other, for two or more essentially different types of processing of silicon wafers taking place in succession, such as the epitaxial growth of silicon, plasma etching or metal deposition.
Semiconductor technology has advanced considerably during the past three decades. The production of single transistors has been replaced by the processing of silicon wafers. One of the most significant recent developments in silicon technology has been the reduction in element dimensions which has made it possible to pack several million transistors in one circuit. At the same time, the size of silicon wafers has increased from a few centimeters up to 20 cm, which means that a considerably greater number of more efficient circuits can now be fitted on a single wafer.
In currently known furnaces or reactors intended for processing silicon wafers with a view to mass production, several dozen, or even a few hundred wafers can be processed simultaneously. To meet the continually growing commercial demand for silicon wafers, so-called cluster-type processing systems have been developed, in which several completely independent reactors used for typically similar processing of silicon wafers are connected around one common silicon wafer loading chamber. In this way it has been possible to increase the production of silicon wafers considerably.
The American patent no. U.S. Pat No. 4,951,601, for example, discloses a silicon wafer processing system which enables several different silicon wafers to be handled simultaneously at different processing stages. The system comprises several reactors to be used in the different phases of processing silicon wafers, the reactors being arranged in a cluster-like fashion around a common silicon wafer loading chamber. In this system, the silicon wafers are conveyed through the loading chamber, from one reactor to another, that is, from one processing stage to another. All the reactors operate simultaneously, and thus each is equipped with its own vacuum system and gas feed and control system as required by each process, to establish the required different conditions in each reactor.
The price of semiconductor processing apparatus has always been high. As the requirements for the accuracy and stability of temperatures have become more stringent, the prices have risen even further and are now beyond the means of ordinary universities and many research institutes.
To be able to give students at least some idea of the processes, a general solution has been to acquire used equipment suitable for handling small-diameter wafers and to lower the standard of the experiments. In this case, the apparatus of each processing stage thus typically forms a complete unit of its own, including a reaction chamber, its own separate automation, its own separate vacuum and heating equipment and gas distribution pipelines and valves. The number of pieces of equipment is thus considerable and the cost of the total equipment high. Such large equipment entities also require considerable clean room space in teaching or research institutes. The aim of the present invention is, therefore, to provide an apparatus intended for processing semiconductors, especially silicon wafers, where the above drawbacks have been minimized.
The aim of the invention is more particularly to achieve a compact apparatus, versatile in use and reasonable in price, for processing silicon wafers, especially for teaching and research purposes.
In order to achieve the above aims, the apparatus and method relating to the invention for processing semiconductors, particularly silicon wafers, are characterized by what is specified in the claims below.
In the apparatus used for processing silicon wafers according to a preferred embodiment of the invention, two or more reactors of essentially different types are connected to a common central unit which controls the functions of the apparatus. The reactors operate in succession, so that while one reactor is in operation, the others are at a waiting stage. Each reactor is typically used when it is operating in different conditions, for example, in a different pressure range, at a different temperature or in a different gaseous atmosphere than another reactor operating at a different time.
In the apparatus relating to the invention, the central unit comprises, for example, vacuum equipment common to all reactors, such as a vacuum pump and/or a turbo pump, to which the reactors are connected by means of vacuum valves that can be closed separately. During the waiting stage, a high vacuum is created in the reactors and the reactors are cut off from the system by valves. In the operating reactor the pressure is increased to the suitable level.
The central unit also includes a gas distribution and control system common to all the reactors. The reactors are connected to the gas distribution system by gas valves which can be closed and controlled separately, by means of which valves the reactors at the waiting stage at a given time can be cut off from the system, and by means of which the feeding of gas to the reactor activated at any given time can be controlled. For example the following gases are used in processing silicon wafers: gas containing oxygen, nitrogen, hydrogen, silane, arsine and/or phosphine. Gas pipelines are provided separately for each gas, the pipelines being connected to that reactor or those reactors which use the gas in question. The flow of gases is controlled by a common gas control system.
The central unit preferably also includes an electricity distribution system common to the reactors, and a common high-frequency alternator. In addition, the reactors preferably have a common silicon wafer loading chamber, through which the silicon wafer is transferred to the reactor desired at a given time. The loading chamber is preferably connected to the vacuum equipment of the central unit to create a negative pressure or vacuum also in the loading chamber. The negative pressure reduces to a substantial degree the mixing of different gas spaces in the system.
In applying the method relating to the invention, one or possibly several, silicon wafers are processed in only one active reactor at a time, the reactor active at a given time being connected to a common vacuum pump system and the other reactors being cut off from it, that is, at the waiting stage. The gas required for each processing of the silicon wafer—such as gas containing oxygen, nitrogen, hydrogen, silane, arsine and/or phosphine—is conducted, by controlling the common control equipment, only to the reactor active at a given time. During the waiting stage the other reactors are kept under a high vacuum, preferably under a vacuum of about 10-100 Pa.
When the development of the processing of silicon wafers in recent years is reviewed, the dimensions of integrated circuit elements nearing the &mgr;m limit, it may be noted that long heat treatments lasting for hours at temperatures ranging between 1000-1200° C. are no longer required. The temperatures used are lower and processing times shorter and, therefore, from the point of view of use of time it is often not important to be able to process several silicon wafers simultaneously, but they can be produced in smaller reactors intended for only one silicon wafer, one wafer at a time.
Other substantial changes relating to the processing of silicon wafers have also taken place. Etching in acids has
Bueker Richard
Nixon & Vanderhye P.C.
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