Abstract:
Device for processing semiconductor wafers, comprising at least one processing chamber which is completely closed with the exception of a connection to a distribution. System. In said at least one processing chamber there are situated preferably two reactors and a common feed/removal system in order to be able to subject wafers, which may optionally be arranged in boats, to an identical processing operation.

Description:
The present invention relates to a device in accordance with the preamble of claim  1 . 
     The present invention relates to a device for processing semiconductor wafers, comprising at least one processing chamber with an gaslock system, a reactor, as well as feed and removal means for transferring said semiconductor wafers to and from the said reactor, being arranged in the said at least one processing chamber. 
     A device or this kind is known from U.S. Pat. No. 5,407,449 in the name of the applicant. In this device, a number of processing chambers is arranged around a centrally disposed distributing system or robot structure. From this centrally disposed robot, semiconductor wafers are transferred onto turntables which are situated in each of the processing chambers. In general, this takes place by the transfer of semiconductor wafers arranged in cassettes in the feed station or in a boat on a turntable in one of the processing chambers to a boat arranged a turntable in the other of the processing chambers. 
     SUMMARY OF THE INVENTION 
     A processing operation is carried out in each processing chamber, such as the doping of specific substances and the removal and/or application of (parts of) layers at elevated temperature. It is then necessary to allow the wafers to cool under controlled conditions before further processing operations can take place. Cooling of this nature may take place inside the processing chamber in question, but may equally be carried out in another processing chamber. 
     In the art, there is a constant desire to enlarge the semiconductor wafers further, i.e. for ever more extensive integration. As a result, the value of a series of semiconductor wafers in a boat is constantly increasing, especially for small batches, and the financial risk associated with the failure of a specific processing operation is constantly rising. Moreover, there is a demand for the capacity of devices for processing semiconductor wafers to be increased. 
     One proposal in the prior art comprises the provision of different processing chambers, which are each closed and each perform the same processing operation. This means that a specific series of semiconductor wafers is fed to a processing chamber, where it undergoes a processing operation, while another series is fed to another processing chamber, where it undergoes the same processing operation. This provides an initial saving, since it is possible to make use of the common robot or the common distributing system and the common feed and removal from the system. It has been found that, although a system of this kind functions in certain cases, primarily where the residence time of the semiconductor wafers in the processing chambers is relatively long, in many applications the capacity of the distributing system, and more particularly the robot arranged therein, forms the bottleneck in the capacity of a device of this kind. 
     By also placing a boat with semiconductor wafers to be processed in the “waiting position” in a system of this kind, three positions are provided in a processing chamber of this kind, with the result that optimum utilization can be achieved. This means that three boats are present on a turntable. It will be understood that this number can be greater. 
     U.S. Pat. No. 5,464,313 discloses a stand alone oven assembly comprising two adjacent ovens which are provided with boats of wafers by a single, linear operating system. This structure is not a space-saving one, and also cannot be used in the compact cluster structure as described in U.S. Pat. No. 5,407,449. 
     The object of the present invention is to increase further the processing capacity of a device described above without it being necessary to extend the distributing system and while utilizing the floor area in question as efficiently as possible. This is important because the device will generally be arranged in a clean room. 
     An object of the invention is a device for processing semiconductor wafers including a processing chamber. The processing chamber comprises a central distributing system for transferring wafers between a store or another processing chamber and a boat on a turntable in the processing chamber. The processing chamber is configured to be closed with respect to the central distributing system. The processing chamber comprises further a first reactor, first feed and removal means for transferring the boat with the semiconductor wafers from the turntable into the first reactor arranged in the processing chamber, at least a second reactor arranged within the processing chamber, and second feed and removal means for transferring the semiconductor wafers from the turntable into the second reactor. 
     Surprisingly, it has been found that arranging two reactors in one processing chamber, i.e. no longer separated by the distributing system, allows the capacity to be increased considerably without substantially enlarging the floor area. Moreover, it is not necessary to provide separate retention for the reactors, so that the cost price is reduced. This inventive idea may optionally be combined with further processing stations, as known for example from U.S. Pat. No. 5,407,449. According to the invention, when feeding semiconductor wafers to the boat on the turntable of the processing chamber in question, preferably a first series of semiconductor wafers is processed by the first reactor and a second series of semiconductor wafers is processed by the second reactor, in which case the processing operation in these two reactors may be identical. The processing chambers can be loaded using the turntable structure which is known from U.S. Pat. No. 5,407,449, i.e. it is possible to use a turntable which has three positions for the boats. In this case, if the cooling is important, a substantial part of the waiting time of the semiconductor wafers is taken away before they can be removed from the reactor. This can be resolved, on the one hand, by providing a turntable with four positions for the cassettes, but in other cases this will not be important, because the ratio between the cooling time and the processing time is such that the processing time is longer than half the cooling time, so that sufficient time remains to take the cooled semiconductor wafers out of the processing chamber and to replace them with wafers to be processed. 
     The reactors may comprise any type of reactor, but preferably comprise two processing ovens. It will be understood that the idea according to the invention can be extended to a processing chamber in which there are three or more reactors. In that case, the turntable will have to have more than three positions, or else the structure with the turntable will need to be designed differently. 
     Obviously, in the structures described above, as in U.S. Pat. No. 5,407,449, in addition to a turntable there is also a lifting means for each reactor in order to remove the relevant boat from the turntable and introduce it into the reactor and then to remove it again from the reactor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail below with reference to exemplary embodiments which are illustrated in the drawing, in which: 
     FIG. 1 shows a diagrammatic plan view of a device according to the prior art; 
     FIG. 2 shows a diagrammatic plan view of part of the device in accordance with FIG. 1 in an amended version also incorporating the structure according to the invention; 
     FIG. 3 shows a perspective view of part of the device in accordance with FIG. 2; 
     FIGS. 4 a-c  show a method of loading and unloading the processing chamber according to the invention; 
     FIGS. 5 a-c  show the functioning of a first variant of the device according to the invention; and 
     FIGS. 6 a-d  show another possible functioning of the same variant in accordance with FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The device illustrated in FIG. 1 is intended for processing wafers comprising microcircuits, which are generally referred to by the expression semiconductor wafers. These semiconductor wafers are subjected to a number of treatments in order to form integrated circuits on their surface, which are later cut out of the wafer and processed further. 
     The use of the device  1  shown in FIG. 1 allows three, possibly successive, processing operations to be carried out on wafers of this kind. 
     It is usual to transport the wafers in cassettes, a number of which  9  are shown in plan view in FIG. 1 in the feed station  2 . Feed station  2  comprises a turntable  4 , in which  6  cassettes of this kind can be placed at three different levels, so that this table  4  can comprise a total of eighteen cassettes. 
     The feed unit  2  is connected, via wall  3  to a clean room in which an atmosphere with a very low dust level is maintained. The cassettes  9  can be placed on the turntable  4  via an inlet point  5 . The inlet point  5  may be connected to a special feed unit (not shown) which comprises an gaslock, thus ensuring that no undesirable gases, in particular oxygen, enter into the device  1  when the cassettes are introduced. 
     As is clear from FIG. 1, the unit  2  has in cross-section an at least partially regular polygonal periphery, i.e. three walls of unit  2  in FIG. 1 form part of a regular octagon in cross-section. The processing stations  10 ,  11  and  12  likewise have an at least partially regular polygonal periphery in cross-section. The units  2 ,  10 ,  11  and  12  are designed as separate units which are connected to other units in the region of the sides, such as side  7  of the regular polygonal periphery. 
     In the device  1 , the central unit is formed by the distributing unit  8 , which comprises a robot unit. This robot unit  8  can take wafers  13  out of cassettes  9  and place them in carriers for wafers, such as boats, in the processing stations  10 ,  11  and  12 . After the processing operation, the robot  8  again removes the processed wafers from the boats of the processing station and places them in a subsequent processing station or in an empty cassette  9  which has been placed in a specific position by means of the turntable  4 . The cassettes  9  with processed wafers  13  can be removed from the feed station  2  via exit  6 , which may comprise a separate exit station having, for example, a gaslock in the same way as inlet point  5 . 
     Each of the processing chambers  10 ,  11 ,  12  contains a reactor (not shown in more detail) which is situated above the plane of the drawing. It is arranged above a lifting device  17  which transfers a boat containing semiconductor wafers from the turntable  33  into the reactor, such as an oven, which is not shown in more detail. 
     This means that starting from the position in which a boat is situated opposite robot  8  this boat is filled with wafers arriving from the relevant cassette  9  of unit  2  or one of the preceding processing chambers. After the boat in question has been filled, table  33  is rotated one position, it being possible for the boat in question to be brought into engagement with the lifting means  17  and to be placed in the oven. After being processed in the oven, the boat in question is placed back on table  33  and conveyed one position further for the purpose of cooling the semiconductor wafers situated therein. At the same time, a subsequent boat of semiconductor wafers is loaded into the reactor. After a subsequent rotation, the boat containing at least partially cooled semiconductor wafers is situated in front of robot  8  and can be unloaded into the cassettes in unit  2  or into a boat of a subsequent processing chamber. 
     According to the invention it is proposed to optimize the processing time using a device of this kind, i.e. to be able to subject a large number of wafers to the same processing given the amount of floor area available. It is also advantageous here that it is possible to use the same distributing system, i.e. the structure containing robot  8 , and the same entry system. The proposal according to the invention is illustrated in FIG.  2 . In that figure, the device according to the invention is denoted overall by  21  and the entry and exit by  25 . A cassette  9  containing wafers  13  is introduced into the device and the partition from the clean room is indicated by  23 . The table, which is comparable to table  4  in accordance with FIG. 1, is now denoted by  24 , and via this table the cassettes are placed opposite gaslock system  18 , in which there is a robot  8 , as in FIG.  1 . In FIG. 2, only two processing stations  29  and  30  are shown, processing station  29  being illustrated only diagrammatically. It should be understood that more processing stations may be present, as shown, for example, in FIG.  1 . By adapting the form, it is possible to use a considerably greater number of processing stations. 
     The design of processing chamber  30  will now be discussed. For this purpose, reference is also made to FIG.  3 . It can be seen from this figure that in contrast to the prior art two reactors  31  and  32  are provided. Moreover lifting devices  34  and  35 , which are illustrated only diagrammatically, for boats  19  are present. The chamber is fed by a common turntable  33  which, as in the prior art, has only three positions for receiving boats. 
     The progress of receiving wafers in the boats A, B and C is illustrated by way of example in FIGS. 4 a-c , the direction of rotation of the table  33  being indicated by an arrow. 
     If the cooling time plays a relatively major role in the processing, it is possible to provide the turntable with four positions for receiving boats. In such a case, the series of processing operations as in FIGS. 4 a-c  will be amended. 
     It will be clear to the person skilled in the art that numerous variants are possible for operating the various reactors, in particular the feed and removal of semiconductor wafers arranged in the boats. 
     Although it is preferred to carry out the same processing operation in the ovens  31  and  32 , it is quite conceivable to carry out different operations in these ovens. 
     It is clear from the above that simply by adding a reactor, such as an oven  32 , and associated lifting device  35  it is possible to increase the capacity of a processing chamber considerably without substantially enlarging the area of the device and without requiring further technically complicated measures which increase the cost price. 
     FIGS. 5 and 6 diagrammatically depict a variant of the device according to the invention, in which two reactors  31  and  32  are again provided. In contrast to the designs shown previously, the turntable  33  has four positions, and the arrows indicate diagrammatically how the movement of the various boats is realized. Reference is made here to the above discussion of FIGS. 4 a-c.    
     It should be understood that the invention described above is not limited to the variants mentioned, but also comprises designs which will strike the person skilled in the art after he/she has read the above description and which lie within the scope of the appended claims.