Abstract:
There is provided a method for unloading an object vacuum-chucked on a mounting table having one or more gas flow paths opened at one or more locations on the mounting table, including the steps of (a) turning off a vacuum-chucking of the object vacuum-chucked via the gas flow paths; (b) lifting the object from the mounting table by using an object lifting unit; and (C) supplying a gas between the mounting table and the object during the step (b) via at least one of the gas flow paths. Further, there is also provided a program storage medium storing therein a computer executable program for executing the unloading method.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method for unloading an object from a mounting table of a semiconductor manufacturing apparatus, and a program storage medium and a mounting mechanism; and, more particularly, to a method capable of unloading an object quickly and smoothly, which is vacuum-chucked on a mounting table, from the mounting table, a program storage medium storing a program for executing the method and a mounting mechanism. 
   BACKGROUND OF THE INVENTION 
   A mounting mechanism is used when performing a processing on an object such as a wafer. The mounting mechanism includes: a mounting table for mounting thereon the object; a plurality of elevating pins protrusible above and below a mounting surface of the mounting table; and a plurality of air flow paths opened at plural locations on the mounting surface to fixedly vacuum-chuck the object onto the mounting surface of the mounting table. By performing a vacuum pumping through the plurality of air flow paths with a vacuum pump, the object is fixedly vacuum-chucked on the mounting surface of the mounting table. 
   When performing a preset processing on the object, a transfer mechanism transfers the object to the mounting table and hands it over to the plurality of elevating pins protruded from the mounting surface. Then, the transfer mechanism retreats from the mounting table. Meantime, in the mounting mechanism, the plurality of elevating pins is moved down below the mounting surface of the mounting table so that the object is loaded on the mounting surface. Once the object is loaded and fixedly vacuum-chuck onto the mounting surface, the object is hermetically attracted and held by the mounting surface. After completing the processing on the object, the processed object is unloaded from the mounting table. The vacuum-chucking for the unloading process of the object onto the mounting table is released, and the plurality elevating pins are raised from the mounting table to lift the processed object therefrom. The transfer mechanism then receives the processed object lifted by the elevating pins to finally unload the object from the mounting table. 
   Further, disclosed in, for example, Japanese Patent Laid-open Application No. S63-142653 (Patent Reference 1) is a prober having a mounting mechanism (chuck) different from the type of the above-described mounting mechanism. The prober includes a chuck having a suction port in communication with a vacuum pump, wherein the air inlet of the chuck is slantingly installed toward the side of a loader and a blower is connected to the suction port via a changeover switch. In the prober having this configuration, air is blown through the suction port by the blower when unloading a wafer from the chuck. Accordingly, the wafer can be rapidly transferred from the chuck to the loader side by the air force generated in the air flow direction. 
   Moreover, disclosed in Japanese Utility Model Laid-open No. S50-127097 (Patent Reference 2) is a suctioning and vacuuming apparatus for a vacuum table. In this apparatus, an exhaust side and a suction side of a pump is connected with a chamber of the vacuum table via a direction changeover valve. By switching over the direction changeover valve, the chamber is made to communicate with either one of the exhaust side and the suction side of the pump selectively. When unloading a wafer W from the vacuum table, the vacuum table is configured to communicate with the exhaust side of the pump by means of controlling the direction changeover valve. 
   With regard to the conventional mounting mechanism having the elevating pins, however, the object is vacuum suctioned by the mounting surface and firmly adhered thereto. Thus, in order not to incur a depressurized state when unloading the processed object from the mounting surface of the mounting table, the object needs to be lifted up by the elevating pins at a very low speed while concurrently supplying exterior air between the object and the mounting surface gradually. Therefore, unloading the processed object takes a long time. For example, about 6 to 7 seconds are required to lift the processed object from the mounting surface to a transfer location. If the unloading of the object is quickly carried out rather quickly, a depressurized state may still persist between the object and the mounting table while the object is pushed up by elevating the plurality of the elevating pins; then, the central portion of the object would be lifted up earlier than the periphery thereof. As a result, the object would be bent greatly, which in turn may damage in the breakage of the wafer W. As the object increases in size and decreases in thickness, the likelihood of the object being damaged increases. In case of the apparatuses disclosed in Patent References 1 and 2, such problems of the mounting mechanism having the elevating pins do not exist since they do not have elevating pins. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide: a method, for use in a mounting mechanism having a plurality of elevating pins, capable of unloading an object such as a wafer, from a mounting table in a expeditious and smooth manner without damaging the object even in case the size of the object increases and the thickness thereof decreases; and a program storage medium and a mounting mechanism for use in executing the method. 
   In accordance with one aspect of the present invention, there is provided an unloading method of an object vacuum-chucked on a mounting table having one or more gas flow paths opened at one or more locations on the mounting table, including the steps of (a) turning off a vacuum-chucking of the object vacuum-chucked via the gas flow paths; (b) lifting the object from the mounting table by using an object lifting unit; and (c) supplying a gas between the mounting table and the object during the step (b) via at least one of the gas flow paths. 
   Further, the lifting step (b) may include a first and a second lifting step, and an object lifting speed in the second object lifting step is higher than that in the first object lifting step. 
   Further, the lifting step (c) may be performed during the first lifting step. 
   In accordance with another aspect of the present invention, there is provided a program storage medium storing therein a computer executable program for executing the unloading method in the above aspect of the present invention. 
   In accordance with still another aspect of the present invention, there is provided a mounting mechanism including a mounting table for mounting an object thereon; an object lifting unit moved up and down with respect to the mounting table to lift the object to and from the mounting table; one or more gas flow paths formed in the mounting table to be opened at one or more locations on a mounting surface of the mounting table, for vacuuming-chucking the object on the mounting table; and a gas supply unit for supplying a gas between the mounting table and the object via at least one of the air flow paths. 
   Further, the object lifting unit may have at least two lifting speeds. 
   Further, the mounting table may be configured to mount thereon one of at least two types of objects having different sizes, and one or more openings of said at least one of the gas flow paths is formed in a region of the mounting table on which an object of the smallest size is placed. 
   Further, an exhausting unit may be connected to each of the gas flow paths, and said at least one of the gas flow paths selectively communicates with either one of the exhausting unit and the gas supply unit via a valve. 
   Further, the valve may include a device for controlling a flow rate of the gas. 
   In accordance with the present invention, an object such as a wafer can be unloaded, from a mounting table in a expeditious and smooth manner without damaging the object even in case the size of the object increases and the thickness thereof decreases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a configuration view of a mounting mechanism in accordance with a preferred embodiment of the present invention; and 
       FIGS. 2A to 2D  provide cross sectional views describing an unloading process of a object performed by using the mounting mechanism shown in  FIG. 1  in accordance with the preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As illustrated in  FIG. 1 , a mounting mechanism  10  in accordance with the embodiment of the present invention includes, for example, a mounting table  11  for mounting an object (e.g., a wafer) W thereon; an object lifting unit  12  which moves up and down with respect to a mounting surface  11 A of the mounting table  11  to transfer the wafer W to and from the mounting table  11 ; and a plurality of air flow paths provided in the mounting table  11  in such a manner as to be opened at plural locations on the mounting surface  11 A. The mounting mechanism  10  is operated under the control of a controller  14  to vacuum-chuck the wafer W on the mounting surface  11 A. The mounting mechanism  10  can be advantageously employed in a semiconductor manufacturing apparatus such as an inspection apparatus for inspecting electrical characteristics of the wafer W, for example. 
   The mounting table  11  has a mounting surface having a size capable of mounting thereon for example two types of wafers W having different diameters (for example, wafers having diameters of 200 mm and 300 mm). As illustrated in  FIG. 1 , the object lifting unit  12  configured to be moved up and down with respect to the mounting surface  11 A includes, for example, three elevating pins  12 A (only two are shown in  FIG. 1 ) and a connection member  12 B for connecting lower ends of the elevating pins  12 A. The object lifting unit  12  is set up to be moved up and down by a conventional elevation driving mechanism  12 C. The three elevating pins  12 A move up and down through three through holes  11 B arranged, e.g., to form a regular triangle at a central portion of the mounting table  11 , and serve to transfer the wafer W at their uppermost raised position. Further, the elevation driving mechanism  12 C is operated according to a sequence program stored in, e.g., a program storage medium  14   b  of a computer  14   a  of the controller  14  and changes step-by-step the rising speed of the wafer W being raised by the three elevating pins  12   a,  so as to allow the wafer W to be lifted up to the uppermost raised position from the mounting surface  11 A in a short period of time. 
   Further, a number of circular grooves are formed in a concentric manner on the mounting surface  11   a  of the mounting table  11 , and the plurality of air flow paths  13  are opened in the circular grooves. The air flow paths  13  have a dual system with a first air flow path  13 A opened at a region for placing thereon a wafer W of 200 mm and a second air flow path  13 B opened at a region outside where the first air flow path  13 A is formed and for placing thereon a wafer W of 300 mm. In case of vacuum-chucking the wafer W of 300 mm on the mounting surface  11 , the first and the second flow path  13 A and  14 B are both used. Further, the circular grooves in which the first air flow path  13 A is opened are communicated with each other via, e.g., one or more grooves formed in diametrical directions, and the circular grooves in which the second air flow path  13 B is opened are also communicated with each other in a same manner. 
   A first and a second electromagnetic valve  16  and  17  are switchably connected to an inlet of the first air flow path  13 A via a first exhaust line  15 A. By means of switching the first and the second electromagnetic valve  16  and  17 , the first exhaust line  15 A is set up to communicate with an exhausting unit  20  and an air supply unit  30 , respectively. Further, the second electromagnetic valve  17  has a throttle valve  17 A which operates when the first exhaust line  15 A is connected to the air source side, and the flow rate of the air supplied between the mounting table  11  and the wafer W can be properly controlled by means of the throttle valve  17 A. In addition, the first exhaust line  15 A is also connected to an inlet of the second air flow path  13 B via a second exhaust line  15 B. Also, a third electromagnetic valve  18  is installed on the second exhaust line  15 B, and the first and the third electromagnetic valve  16  and  18  are operated together when necessary. Further, a vacuum sensor  19  having a switch is connected to the first exhaust line  15 A to detect a vacuum level between the mounting table  11  and the wafer W when its switch is on. 
   Thus, to vacuum-chuck a wafer of 300 mm on the mounting table  11  hermetically, the first and the third electromagnetic valve  16  and  18  are actuated, whereby the first and the second flow path  13 A and  13 B are allowed to communicate with the vacuum pump via the first and the second exhaust line  15 A and  15 B. Concurrently, the vacuum sensor  19  detects a vacuum level between the mounting table  11  and the wafer W. To lift up the wafer W from the mounting table  11 , the first and the third electromagnetic valve  16  and  18  are deactivated and the second electromagnetic valve  17  is activated, whereby the first air flow path  13 A is set up to communicate with the air source via the first exhaust line  15 A. 
   Now, an operation of the mounting mechanism  10  will be explained with reference to  FIGS. 2A to 2D . In  FIGS. 2A to 2D , only the first air flow path  13 A is shown. In case of performing a processing on a wafer W having a diameter of 300 mm, a transfer mechanism transfers the wafer W to the three elevating pins  12 A of the object lifting unit  12  which are in a stand-by state at the uppermost raised position. Then, the transfer mechanism retreats and the three elevating pins  12 A are moved down through the through holes  11 B by the elevation driving mechanism  12 C so that the wafer W is loaded on the mounting surface  11 A. In the meantime, the first and the third electromagnetic valve  16  and  18  are actuated, and the first and the second flow path  13 A and  13 B are set to communicate with the vacuum pump, so that the wafer W is vacuum-chucked on the mounting surface  11 A with a suction force of, e.g., about −40 kPa. At this moment, the elevating pins  12 A of the object lifting unit  12  are positioned at the lowermost position, and their top ends are positioned below the mounting surface  11 A. Then, upon completing the processing on the wafer W, the wafer W is unloaded from the mounting table  11 . 
   To unload the wafer W from the mounting table  11 , the first to the third electromagnetic valve  16 ,  17  and  18  are operated according to the sequence program of the controller  14 , and, at the same time, the elevation driving mechanism  12 C is driven to lift up the object lifting unit  12  (three elevations pins  12 A) such that the wafer W is raised from the mounting surface  11 a up to a position where its transfer is performed. 
   Specifically, the three elevating pins  12 A are moved up by the elevation driving mechanism  12 C at a high speed (e.g., 20 mm/s) until their top ends reach a height lower than the mounting surface  11 A by 1.0 mm, as shown in  FIG. 2A . Thereafter, the first and the second electromagnetic valve  16  and  18  are actuated, whereby the vacuum chucking of the wafer W to the mounting surface  11 A is released. Then, after confirming that the vacuum sensor  19  is turned off, the three elevating pins  12 A are elevated by the elevation driving mechanism  12 C up to a height shown in  FIG. 2B  from the position shown in  FIG. 2A  at a low speed (e.g., 1.5 mm/s) for one second, finally contacting the rear surface of the wafer W and then lifting up the wafer W from the mounting surface  11 A by 0.5 mm. Therefore, a misalignment of the wafer W can be prevented even with the air supplied between the wafer W and the mounting table  11 . 
   Subsequently, the second electromagnetic valve  17  is actuated, and the first air flow path  13 A is set to communicate with the air source, whereby air of 0.4 to 0.45 MPa is supplied into the first air flow path  13 A from the air source via the second electromagnetic valve  17  and the first exhaust line  15 A. After the lapse of 50 milliseconds, the three elevating pins  12 A are elevated by the elevation driving mechanism  12 C at a low speed (e.g., 1.5 mm/s) for one second, thereby lifting the wafer W from the mounting surface  11 A by 2.0 mm, as shown in  FIG. 2C . As a result, introduction of the air into the gap between the wafer W and the mounting surface  11 A can be facilitated. Further, the amount of the air introduced into the first air flow path  13 A can be set at an optimum value by using the throttle valve  17 A of the second electromagnetic valve  17 . 
   Subsequently, while supplying air between the mounting table  11 A and the wafer W from the air source, the three elevating pins  12 A are raised upward at a high speed (e.g., 20 mm/s), to thereby lift the wafer W from the mounting surface  11 A up to the transfer position (i.e., the uppermost raised position), e.g., up to a height of 12.0 mm above the mounting surface  11 A very quickly for about 0.5 second. At this time, even if the speed for raising the wafer W is set high, the gap between the wafer W and the mounting surface  11 A does not turn into a depressurized state, because of an inflow of ambient air around the wafer W into the gap. 
   Accordingly, in accordance with the preferred embodiment of the present invention, the elevating pins  12 A can be raised from the position 1.0 mm below the mounting surface  11 A up to the transfer position in about 2.5 seconds. Thus, in comparison with 6 to 7 seconds conventionally required for the unloading of the wafer W, the unloading time of the wafer W can be reduced considerably in accordance with the embodiment of the present invention. 
   If the elevating pins  12 A are elevated as described above and finally stopped at the transfer position of the wafer W, the second electromagnetic valve  17  is actuated, and the communication of the first air flow path  13 A with the air source is cut. In this state, the wafer W raised from the mounting surface  11 A is unloaded by the transfer mechanism so as to be replaced with a new wafer W. 
   Though the above embodiment of the present invention has been described for the case of processing the wafer W having a diameter of 300 mm, the unloading process of a wafer having a diameter of 200 mm can also be performed through the same manner as that of the wafer of 300 mm excepting that the third electromagnetic valve  18  is always in an de-actuated state so as not to be used in vacuum-chucking the wafer W. Accordingly, as for the wafer of 200 mm, the same effect can be obtained as in the embodiment of the present invention. 
   In accordance with the preferred embodiment of the present invention as described above, the mounting mechanism includes: the mounting table  11  for mounting the wafer W thereon; the object lifting unit  12  moved up and down with respect to the mounting table  11  to transfer the wafer W on the mounting table  11 ; the first and the second air flow path  13 A and  13 B opened at plural locations on the mounting surface  11 A of the mounting table  11  to vacuum-chuck the wafer W onto the mounting surface  11 A; and the air source provided as an air supply unit for supplying air between the mounting table  11  and the wafer W via the first air flow path  13 A. Thus, when lifting up the wafer W from the mounting table  11  via the object lifting unit  12 , the wafer W being vacuum-chucked onto the mounting surface  11 A via the first and the second air flow path  13 A and  13 B opened at plural locations on the mounting table  11 , and then unloading the wafer W from the mounting table  11 , the depressurized state between the mounting surface  11 A and the wafer W can be released by supplying air between the mounting table  11  and the wafer W from the first air flow path  13 A after lifting up the wafer W by using the object lifting unit  12 . Thus, even if the wafer W is increased in size and decreased in thickness, the time required for the unloading of the wafer W by the object lifting unit  12  can be shortened, and the wafer W can be unloaded without being subject to any damages. 
   Further, in accordance with the preferred embodiment as described above, the mounting table  11  is designed to mount thereon either one of two types of the wafers W having diameters of 200 mm and 300 mm. Also, the first air flow path  13 A is disposed at a region of the mounting surface  11 A for placing thereon the wafer W of 200 mm. Thus, the unloading time of the wafer W from the mounting table  11  can be certainly reduced. Moreover, since the vacuum pump is connected with each of the first and the second air flow path  13 A and  13 B, and the first and the second electromagnetic valve  16  and  17  are connected to the air source to have the air flow paths  13 A and  13 B to selectively communicate with either one of the vacuum pump and the air source, it is possible to lift the wafer W smoothly while reducing the unloading time of the wafer W by way of terminating the communication of the air flow path  13 A with the vacuum pump and setting the air flow path  13 A to communicate with the air source. Furthermore, since the second electromagnetic valve  17  has the throttle valve  17 A, the amount of air supplied between the mounting table  11  and the wafer W can be properly controlled. 
   Moreover, in accordance with the preferred embodiment of the present invention, the wafer W is slightly raised from the mounting surface  11 A of the mounting table  11  by the object lifting unit  12  prior to starting the supply of air. Therefore, when it is lifted up by the object lifting unit  12  after starting the supply of air the mounting table  11  and the wafer W, the wafer W can be raised straightly upward without being misaligned at the object lifting unit  12 . Also, since the wafer W is lifted up in two stages with two different rising speeds such that the wafer W is first raised slowly and then raised at a higher speed, the bending of the wafer W can be suppressed as much as possible, and the wafer W can be unloaded smoothly and quickly without being subject to damages. 
   The air supply unit  30  can be used with gas other than air, instead of air. 
   While the invention has been shown and described with respect to the preferred embodiment, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.