Patent Application
20100326637
The present invention relates to a load-lock apparatus for use in a vacuum processing unit which performs a vacuum process on a target object such as a semiconductor wafer, and a substrate cooling method for use in the load-lock apparatus.
In a manufacturing process of semiconductor devices, a vacuum process such as a film forming process and an etching process performed in a vacuum atmosphere is widely carried out on a semiconductor wafer serving as a target substrate. Recently, a multi-chamber type vacuum processing system has been attracted attention from viewpoints of efficiency of the vacuum process and prevention of oxidation or contamination, wherein the system has a cluster tool type structure in which vacuum processing units are connected to a transfer chamber maintained in a vacuum and a wafer is transferred to each of the vacuum processing units by a transfer unit provided in the transfer chamber (see, e.g., Japanese Patent Application Publication No. 2000-208589).
In the multi-chamber type processing system, in order to transfer a semiconductor wafer from a wafer cassette disposed in the atmosphere to the transfer chamber maintained in a vacuum, a load-lock chamber is provided between the transfer chamber and the wafer cassette, and the semiconductor wafer is transferred via the load-lock chamber.
When the multi-chamber type processing system is applied to a high temperature process such as a film forming process, a semiconductor wafer serving as a target object having a high temperature of, e.g., about 500° C. may be unloaded from the vacuum processing unit and transferred to the load-lock chamber. However, when the wafer having such a high temperature is exposed to the atmosphere, the wafer is oxidized. Further, when the wafer having such a high temperature is accommodated in a receiving vessel, there is a problem that the receiving vessel generally made of resin may be melted.
In order to avoid such problems, the wafer may be made to stand by until its temperature reaches a temperature at which such problems do not occur and, then, the wafer may be exposed to the atmosphere. In this case, however, a throughput is reduced. Accordingly, a cooling plate having a cooling unit for cooling the wafer is provided in the load-lock chamber, so that the wafer is cooled by being placed on or in proximity to the cooling plate while the load-lock chamber in a vacuum state is purged to have the atmospheric pressure.
In this case, if the semiconductor wafer is cooled rapidly, the wafer may be deformed due to a difference in thermal expansion between the front and rear surface of the wafer W. Accordingly, a central or edge portion of the semiconductor wafer is separated from the cooling plate, or the central and edge portions of the semiconductor wafer have different distances to the cooling plate, thereby reducing cooling efficiency. Consequently, the cooling time becomes longer or the semiconductor wafer still having a high temperature may be exposed to the atmosphere.
In order to prevent the deformation of the semiconductor wafer, it is required to manage a pressure increasing rate when the load-lock chamber is adjusted to have the atmospheric pressure or a vertical position of the wafer when the semiconductor wafer is moved closer to the cooling plate. Accordingly, a proper purge recipe, which provides a good combination of the pressure increasing rate and the vertical position of the wafer, is created for each temperature of the wafer.
However, semiconductor wafers are differently deformed according to types of films formed thereon. Further, there may exist a vast number of types of films according to users. Hence, it is very difficult to create an optimal purge recipe for each type of films. Accordingly, although a purge recipe corresponding to the temperature of the wafer is used, the semiconductor wafer can be deformed depending on the type of film formed thereon.
Therefore, the present invention provides a load-lock apparatus capable of cooling a substrate at a practical cooling rate while preventing deformation of the substrate to the maximum extent possible.
The present invention also provides a substrate cooling method for use in the load-lock apparatus to enable such a cooling of the substrate.
In accordance with a first aspect of the invention, there is provided a load-lock apparatus for use in transferring a substrate from the atmospheric atmosphere to a vacuum chamber maintained in a vacuum and transferring a substrate having a high temperature from the vacuum chamber to the atmospheric atmosphere. The load-lock apparatus includes: a vessel arranged to change a pressure between a pressure corresponding to the vacuum chamber and the atmospheric pressure; a pressure adjusting mechanism which adjusts a pressure in the vessel to a pressure corresponding to the vacuum chamber when the vessel communicates with the vacuum chamber, and adjusts a pressure in the vessel to the atmospheric pressure when the vessel communicates with a space having the atmospheric atmosphere; a cooling member having a cooling mechanism and arranged in the vessel to cool a substrate by having the substrate placed on or in proximity to the cooling member; and a substrate deformation detection unit for detecting deformation of the substrate in the vessel. The load-lock apparatus further includes a controller which reduces a cooling rate of the substrate when the substrate deformation detection unit detects deformation of the substrate that is equal to or larger than a predetermined value during a substrate cooling period until the vessel is adjusted to have the atmospheric pressure after the vessel is adjusted to have a pressure corresponding to the vacuum chamber and the substrate having the high temperature is loaded into the vessel from the vacuum chamber.
In the load-lock apparatus, the controller may reduce the cooling rate by stopping increasing or reducing a pressure in the vessel when the substrate deformation detection unit detects the deformation of the substrate that is equal to or larger than the predetermined value while increasing the pressure in the vessel by the pressure adjusting mechanism.
The controller may resume an increase in pressure in the vessel when the substrate deformation detection unit detects that the deformation of the substrate becomes smaller than the predetermined value after the controller reduced the cooling rate.
The load-lock apparatus may further include wafer supporting pins which are provided to be protruded from and retracted into the cooling member, receive the substrate while being protruded from the cooling member, and descend with the substrate placed thereon such that the substrate is placed on or in proximity to the cooling member. When the substrate deformation detection unit detects the deformation of the substrate that is equal to or larger than the predetermined value, the controller may reduce the cooling rate by raising the wafer supporting pins or stopping descending of the wafer supporting pins if the wafer supporting pins descend with the substrate placed thereon.
In the load-lock apparatus, when the substrate deformation detection unit detects that the deformation of the substrate becomes smaller than the predetermined value after the controller reduced the cooling rate, the controller may restore the wafer supporting pins to their original positions or resumes descending of the wafer supporting pins if the descending of the wafer supporting pins was stopped.
The substrate deformation detection unit may include a first sensor for measuring a displacement of a central portion of the substrate and a second sensor for measuring a displacement of an edge portion of the substrate, and may detect deformation of the substrate based on a difference between the detection value of the first sensor and the detection value of the second sensor. The first sensor and the second sensor may be laser displacement sensors.
The vacuum chamber may be a transfer chamber including a transfer unit for transferring the substrate to a vacuum processing chamber that performs a high temperature process on the substrate in a vacuum, and a high temperature substrate is transferred to the vessel through the vacuum chamber after the high temperature process has been performed on the substrate in the vacuum processing chamber.
In accordance with a second aspect of the invention, there is provided a substrate cooling method for use in a load-lock apparatus for use in transferring a substrate from the atmospheric atmosphere to a vacuum chamber maintained in a vacuum and transferring a substrate having a high temperature from the vacuum chamber to the atmospheric atmosphere, the load-lock apparatus including a vessel arranged to change a pressure between a pressure corresponding to the vacuum chamber and the atmospheric pressure, a pressure adjusting mechanism which adjusts a pressure in the vessel to a pressure corresponding to the vacuum chamber when the vessel communicates with the vacuum chamber, and adjusts a pressure in the vessel to the atmospheric pressure when the vessel communicates with a space having the atmospheric atmosphere, and a cooling member having a cooling mechanism and arranged in the vessel to cool a substrate by having the substrate placed on or in proximity to the cooling member. The method may include: detecting deformation of the substrate in the vessel during a substrate cooling period until the vessel is adjusted to have the atmospheric pressure after the vessel is adjusted to have a pressure corresponding to the vacuum chamber and the substrate having the high temperature is loaded into the vessel from the vacuum chamber; and reducing a cooling rate of the substrate when the deformation of the substrate that is equal to or larger than a predetermined value is detected.
In the cooling method, the cooling rate may be reduced by stopping increasing or reducing a pressure in the vessel when the deformation of the substrate that is equal to or larger than the predetermined value is detected by the pressure adjusting mechanism while increasing the pressure in the vessel. An increase in pressure in the vessel may be resumed when it is detected that the deformation of the substrate becomes smaller than the predetermined value after the cooling rate was reduced.
The load-lock apparatus may further include wafer supporting pins which are provided to be protruded from and retracted into the cooling member, receive the substrate while being protruded from the cooling member, and descend with the substrate placed thereon such that the substrate is placed on or in proximity to the cooling member. When the deformation of the substrate that is equal to or larger than the predetermined value is detected, the cooling rate may be reduced by raising the wafer supporting pins or stopping descending of the wafer supporting pins if the wafer supporting pins descend with the substrate placed thereon. When it is detected that the deformation of the substrate becomes smaller than the predetermined value after the cooling rate was reduced, the wafer supporting pins may be restored to their original positions or descending of the wafer supporting pins is resumed if the descending of the wafer supporting pins was stopped.
In accordance with the present invention, after a high temperature substrate is loaded into a vessel from a vacuum chamber, during a substrate cooling period until the vessel is adjusted to have the atmospheric pressure, a substrate deformation detection unit detects deformation of a substrate. When deformation of a substrate that is equal to or larger than a predetermined value is detected, cooling of the substrate is modified to restore the deformed wafer to its original state. Thus, it is possible to cool a substrate at a practical cooling rate while preventing deformation of the substrate to the maximum extent possible.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
The vacuum processing system includes four vacuum processing units 1, 2, 3 and 4, each unit performing a high temperature process such as a film forming process in a vacuum. The vacuum processing units 1, 2, 3 and 4 are connected to four sides of a hexagonal transfer chamber 5, respectively. Further, load-lock apparatus 6 and 7 in accordance with the embodiment of the present invention are connected to the other two sides of the transfer chamber 5, respectively. A loading/unloading chamber 8 is connected to the load-lock apparatus 6 and 7 to be opposite to the transfer chamber 5. Ports 9, 10 and 11, to which three Front Opening Unified Pods (FOUPs) F capable of accommodating semiconductor wafers W serving as substrates to be processed are attached, are provided at the side of the loading/unloading chamber 8 to be opposite to the load-lock apparatus 6 and 7. Each of the vacuum processing units 1, 2, 3 and 4 is configured to perform a specific vacuum process at a high temperature, e.g., a film forming process, on a target object mounted on a processing plate placed therein.
As shown in
The transfer chamber 5 includes a transfer unit 12 for loading/unloading the semiconductor wafers W into/from the vacuum processing units 1, 2, 3 and 4 and load-lock apparatus 6 and 7. The transfer unit 12 is disposed at an approximately central portion of the transfer chamber 5. The transfer unit 12 includes two supporting arms 14a and 14b for supporting the semiconductor wafers W. The two supporting arms 14a and 14b are attached to a leading end of a rotatable and extensible/contractible portion 13 to be directed in opposite directions. The transfer chamber 5 is maintained at a predetermined vacuum level.
A shutter (not shown) is provided at each of the three ports 9, 10 and 11 of the loading/unloading chamber 8, to which the FOUPs F capable of accommodating the wafers are attached. The FOUPs F accommodating the wafers or empty FOUPs F may be attached directly to the ports 9, 10 and 11. When the FOUPs F are attached to the ports 9, 10 and 11, the shutters are opened such that the FOUPs F can communicate with the loading/unloading chamber 8 while preventing outside air from entering the loading/unloading chamber 8. Further, an alignment chamber 15 is provided at one side of the loading/unloading chamber 8 to perform an alignment of the semiconductor wafers W.
Further, the loading/unloading chamber 8 includes a transfer unit 16 for loading/unloading semiconductor wafers W into/from the FOUPs F and the load-lock apparatus 6 and 7. The transfer unit 16 has a multi-joint arm structure and is movable on a rail 18 in an arrangement direction of the FOUPs F. The semiconductor wafer W is transferred by the transfer unit 16 while being loaded on a hand 17 provided at a leading end of the transfer unit 16.
The vacuum processing system includes a process controller 20 having a micro processer (computer) for controlling each component of the processing system (e.g., the vacuum processing units 1 to 4, the transfer chamber 5, the load-lock apparatus 6 and 7, and the loading/unloading chamber 8). Each component of the processing system is connected to and controlled by the process controller 20. The process controller 20 is connected to a user interface 21 including a keyboard with which an operator inputs commands to manage the vacuum processing system, a display for showing an operational status of the vacuum processing system, and the like.
The process controller 20 is also connected to a storage unit 22 which stores control programs for implementing various processes in the vacuum processing system under the control of the process controller 20, programs for performing predetermined process in each component of the vacuum processing system under process conditions, e.g., a film formation recipe for a film forming process, a transfer recipe for the transfer of the wafer and a purge recipe for the pressure control of the load-lock apparatus, and the like. The recipes are stored in a storage medium (not shown) of the storage unit 22. The storage medium may be a fixed storage medium such as a hard disk, or a portable storage medium such as a CD-ROM, a DVD and a flash memory. Further, the recipes may be properly transmitted from another apparatus via, e.g., a dedicated line.
If necessary, a certain recipe may be retrieved from the storage unit 22 in accordance with the commands inputted through the user interface 21 and executed in the process controller 20 such that a desired process is performed in the vacuum processing system under the control of the process controller 20. Further, the process controller 20 can control the pressure and/or the height of the wafer W in order to prevent deformation of the wafer W while a process is performed on the wafer W based on a standard purge recipe in the load-lock apparatus 6 or 7.
Next, the load-lock apparatus 6 and 7 in accordance with the embodiment of the present invention will be described in detail.
At one sidewall of the vessel 31, there is provided an opening 34 to allow the vessel 31 to communicate with the transfer chamber 5 maintained in a vacuum. At a sidewall of the vessel 31 opposite thereto, there is provided an opening to allow the vessel 31 to communicate with the loading/unloading chamber 8 maintained at the atmospheric pressure. Further, the opening 34 can be opened and closed by the first gate valve G1, and the opening 35 can be opened and closed by the second gate valve G2.
A gas exhaust opening 36 for vacuum evacuating the vessel 31 and a purge gas inlet opening 37 for introducing a purge gas into the vessel 31 are provided at a bottom portion of the vessel 31. The gas exhaust opening 36 is connected to a gas exhaust line 41, and the gas exhaust line 41 is provided with an opening/closing valve 42, an exhaust rate control valve 43 and a vacuum pump 44. Further, the purge gas inlet opening 37 is connected to a purge gas introduction line 45 for introducing a purge gas into the vessel 31. The purge gas introduction line 45 extends from a purge gas source 48 and is provided with an opening/closing valve 46 and a flow control valve 47.
Further, when the wafer W is transferred to/from the transfer chamber 5 maintained in a vacuum, the opening/closing valve 46 is closed and the opening/closing valve 42 is opened. Then, the vessel 31 is evacuated to a vacuum level corresponding to that of the transfer chamber 5 by the vacuum pump 44 via the gas exhaust opening 36 at a predetermined exhaust rate by adjusting the exhaust rate control valve 43. In this state, the first gate valve G1 is opened such that the vessel 31 communicates with the transfer chamber 5.
Further, when the wafer W is transferred to/from the loading/unloading chamber 8 maintained at the atmospheric pressure, the opening/closing valve 42 is closed and the opening/closing valve 46 is opened. Then, a purge gas is introduced into the vessel 31 from the purge gas source 48 via the purge gas introduction line 45 at, e.g., a predetermined flow rate by adjusting the flow control valve such that the vessel 31 has a pressure close to the atmospheric pressure. In this state, the second gate valve G2 is opened such that the vessel 31 communicates with the loading/unloading chamber 8.
Further, a method of introducing a purge gas may include supplying the purge gas by using a brake filter (registered trademark) (not shown) formed of a porous ceramic at initial introduction stage and supplying the purge gas at a higher flow rate after the inner pressure of the vessel 31 reaches a predetermined level, in order to prevent particles from swirling around, but it is not limited thereto.
The opening/closing valve 42, the exhaust rate control valve 43, the flow control valve 47 and the opening/closing valve 46 are controlled by a pressure adjusting mechanism 49 based on an inner pressure of the vessel 31 measured by a pressure gauge 63, so that the inner pressure of the vessel 31 can be changed between the atmospheric pressure and a vacuum. The pressure adjusting mechanism 49 controls those valves according to the instructions from the process controller 20.
Three wafer supporting pins 50 (only two pins are shown) for transferring the wafer W are provided in the cooling plate 32 to be protruded from the surface of the cooling plate 32 and retracted under the surface of the cooling plate 32. The wafer supporting pins 50 are fixed on a supporting plate 51. Further, the wafer supporting pins 50 are elevated via the supporting plate 51 as a rod 52 is elevated by a driving unit 53 such as a motor capable of controlling its vertical position. Further, reference numeral 54 denotes a bellows.
A coolant flow path 55 is formed in the cooling plate 32. The coolant flow path 55 is connected to a coolant introduction line 56 and a coolant exhaust line 57. A coolant such as cooling water supplied from a coolant supply unit (not shown) is circulated in the cooling plate 32 to cool the mounted wafer W.
A ceiling wall 31a of the vessel 31 is formed of a transparent material, e.g., glass. Displacement sensors 61 and 62 are respectively provided on the ceiling wall 31a at positions corresponding to a central and an edge portion of the wafer W. The two displacement sensors 61 and 62 serve as a wafer deformation detection unit. The displacement sensors 61 and 62 have a function of measuring, e.g., a distance to the wafer W. The displacement sensors 61 and 62 are, e.g., laser displacement sensors.
The process controller 20 controls the load-lock apparatus 6 and 7, and also controls the pressure adjusting mechanism 49 and the driving unit 53 based on distance data transmitted from the displacement sensors 61 and 62 so as to control an inner pressure of the vessel 31 and/or a vertical position of the wafer W.
Next, an operation of the multi-chamber type vacuum processing system will be described focusing on the load-lock apparatus 6 and 7 in accordance with the embodiment of the present invention.
First, a wafer W is unloaded from the FOUP F connected to a loading/unloading chamber 8 and loaded into the vessel 31 of a load-lock apparatus 6 (or 7). At this time, after the vessel 31 of the load-lock apparatus 6 is adjusted to have the atmospheric pressure, the second gate valve G2 is opened and the wafer W is loaded into the vessel 31.
Thereafter, the vessel 31 is vacuum evacuated until the vessel 31 has a pressure corresponding to that of the transfer chamber 5. The first gate valve G1 is then opened, and the wafer W is unloaded from the vessel 31 by the transfer unit 12. Then, the gate valve G of any one of the vacuum processing units 1, 2, 3 and 4 is opened and the wafer W is loaded into the corresponding vacuum processing unit. A vacuum process, e.g., a film forming process, is performed on the wafer W at a high temperature.
When the vacuum process is completed, the gate valve G is opened and the wafer W is unloaded from the corresponding vacuum processing unit by the transfer unit 12. The first gate valve G1 of the load-lock apparatus 6 or 7 is then opened and the wafer W is loaded into the corresponding vessel 31. While the wafer W is cooled by the coolant circulated in the coolant flow path 55 of the cooling plate 32, the purge gas is introduced into the vessel 31 such that the vessel 31 reaches the atmospheric pressure (wafer cooling period). Then, the second gate valve G2 is opened, and the process wafer W is accommodated in the FOUP F by the transfer unit 16.
Further, the load-lock apparatus 6 may be used only for loading the wafers W into the processing system and the load-lock apparatus 7 may be used only for unloading the wafers W from the processing system.
An operation for the wafer cooling period after the wafer W that has undergone the vacuum process is unloaded from the vacuum processing unit by the transfer unit 12 as described above will be described in detail.
The vessel 31 of one of the load-lock apparatus 6 and 7 is vacuum evacuated. The first gate valve G1 is then opened and the wafer W is loaded into the vessel 31. Subsequently, in a state where the wafer supporting pins 50 are protruded from the surface of the cooling plate 32 as shown in
At the time when the wafer W is loaded into the vessel 31, the wafer W has a high temperature of, e.g., 500° C. or more because the wafer w has undergone a high temperature process such as a film forming process in one of the vacuum processing units 1 to 4. Accordingly, when the wafer W is cooled down too rapidly, the wafer W is deformed as shown in
Thus, first, while a purge gas is introduced into the vessel 31 at a predetermined flow rate based on a standard purge recipe, the wafer W is cooled by moving down the wafer supporting pins 50. At this time, the displacement of the wafer W is measured by the two displacement sensors 61 and 62. If a minute deformation of the wafer W that is equal to or larger than a predetermined value is detected, the cooling of the wafer W is controlled to be slowed down. Specifically, a distance to the wafer W measured by the displacement sensor 61 is compared with a distance to the wafer W measured by the displacement sensor 62, and the cooling of the wafer W is controlled to be slowed down from a time point when the difference between the distances to the wafer W is equal to or larger than a predetermined value.
In this case, the deformation of the wafer W may occur during the descending of the wafer W. Accordingly, the driving unit 53 needs to be synchronized with the displacement sensors 61 and 62 to obtain absolute values of the distances to the wafer W from the displacement sensors 61 and 62.
The cooling rate (decreasing rate of the temperature) of the wafer W increases as an inner pressure of the vessel increases or/and the wafer W becomes closer to the cooling plate 32. Accordingly, the cooling rate of the wafer W can be reduced by stopping an increase in the inner pressure of the vessel 31 by closing the opening/closing valve 46, moving up the wafer supporting pins 50, stopping the descending of the wafer W during the descending of the wafer W, or the like. Consequently, the minute deformation of the wafer W can be prevented by reducing the cooling rate as described above.
Further, the cooling rate of the wafer W can also be controlled to be slowed down by decreasing the inner pressure of the vessel 31 by vacuum evacuation, which makes the operation complicated.
If the displacement sensors 61 and 62 detect that the minute deformation becomes smaller than the predetermined value by reducing the cooling rate as described above, the process controller 20 increases the cooling rate of the wafer W by opening the opening/closing valve 46 if the opening/closing valve 46 was closed, returning the wafer W to its original position by using the driving unit 53 if the wafer supporting pins 50 were moved up, or resuming the descending of the wafer W if the descending of the wafer W was stopped during the descending of the wafer W. Further, when the purge gas is introduced again by opening the opening/closing valve 46, the new flow rate of the purge gas may be set to be identical to or different from the previous flow rate.
Further, by performing those operations whenever a minute deformation of the wafer W that is equal to or larger than the predetermined value is detected, it is possible to control the inner pressure of the vessel 31 to become the atmospheric pressure while cooling the wafer W at a practical cooling rate without suffering from deformation which influences cooling efficiency of the wafer W.
As described above, it is possible to achieve optimization of the cooling operation in the load-lock apparatus and to create, based on the sequence of operations, an optimal purge recipe which does not cause deformation exceeding an allowable value in a target wafer. Afterwards, a wafer, which has undergone the same process as the process performed on the target wafer in the vacuum processing unit, can be cooled based on the created purge recipe. Further, such operation can be performed on each of wafers having different types of films formed thereon. Accordingly, it is possible to create optimal purge recipes for wafers having various films.
Further, errors in the cooling operation can be detected by the displacement sensors 61 and 62.
Further, as a conventional technique for preventing deformation of a wafer during cooling of the wafer, there is proposed a method for measuring an actual temperature of the wafer. In the temperature measurement method, generally, a radiation thermometer is provided above a ceiling wall of a processing vessel. In this case, the ceiling wall needs to be formed of expensive special glass applicable to the radiation thermometer. However, in the present invention, there is no need to directly measure the temperature of the wafer. Therefore, the ceiling wall may be made of any material that allows a displacement sensor (e.g., a laser displacement sensor) to perform detection. For example, pyrex glass (registered trademark) that is inexpensive can be used as a material of the ceiling wall.
While the invention has been shown and described with respect to the embodiment, various changes and modification may be made without being limited thereto. For example, although the multi-chamber type vacuum processing system including four vacuum processing units and two load-lock apparatus is employed in the above-described embodiment, the numbers are not limited thereto. Further, the load-lock apparatus of the present invention can also be applied to a system including a single vacuum processing unit without being limited to the multi-chamber type vacuum processing system. Further, although deformation of the wafer is detected by using two displacement sensors in the above embodiment, another means such as a CCD camera may be used without being limited thereto. Further, although deformation of the wafer that is equal to or larger than a predetermined value is detected based on the difference between outputs of the displacement sensors in the above embodiment, it may be detected based on a ratio of outputs of the displacement sensors. Further, a reducing means for the cooling rate is not limited to the means described in the above embodiment. Further, a glass substrate for FPD or the like may be used as a target object without being limited to the semiconductor wafer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-021321 | Jan 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP09/50627 | 1/19/2009 | WO | 00 | 7/29/2010 |
