Abstract:
A wafer dryer system which is suitable for drying rinse water from substrates in the event of a system malfunction or failure during or after rinsing of the substrates. The wafer dryer system typically includes a pair of drying chambers, each of which is fitted with at least one nitrogen gas inlet, at least one IPA gas inlet and an exhaust opening. A wafer boat which holds multiple wet wafers from an interrupted rinsing process typically in a wet bench system is placed in one of the chambers, after which the chamber is filled with hot nitrogen gas and mixed IPA gas to dry the wafers in the wafer boat. Upon resumption of operation of the wet bench system from which the wafers were taken or upon availability of a second wet bench system, the dried wafers are removed from the chamber for continued rinsing, as necessary.

Description:
FIELD OF THE INVENTION 
     The present invention relates to wet benches for removing photoresist polymer particles from WIP (work-in-process) semiconductor wafers after a wet etching process in the semiconductor fabrication industry. More particularly, the present invention relates to a wafer dryer system for drying a WIP wafer in the event of wet bench malfunction or shutdown. 
     BACKGROUND OF THE INVENTION 
     Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps, particularly the photoresist stripping step, provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface. 
     In the semiconductor fabrication industry, minimization of particle contamination on semiconductor wafers increases in importance as the integrated circuit devices on the wafers decrease in size. With the reduced size of the devices, a contaminant having a particular size occupies a relatively larger percentage of the available space for circuit elements on the wafer as compared to wafers containing the larger devices of the past. Moreover, the presence of particles in the integrated circuits compromises the functional integrity of the devices in the finished electronic product. Currently, mini-environment based IC manufacturing facilities are equipped to control airborne particles much smaller than 1.0 μm, as surface contamination continues to be of high priority to semiconductor manufacturers. To achieve an ultra clean wafer surface, particles must be removed from the wafer, and particle-removing methods are therefore of utmost importance in the fabrication of semiconductors. 
     The most common system for cleaning semiconductor wafers during wafer processing includes a series of tanks which contain the necessary cleaning solutions and are positioned in a “wet bench” in a clean room. Batches of wafers are moved in sequence through the tanks, typically by operation of a computer-controlled automated apparatus. Currently, semiconductor manufacturers use wet cleaning processes which may use cleaning agents such as deionized water and/or surfactants. Other wafer-cleaning processes utilize solvents, dry cleaning using high-velocity gas jets, and a megasonic cleaning process, in which very high-frequency sound waves are used to dislodge particles from the wafer surface. Cleaning systems which use deionized (DI) water currently are widely used in the industry because the systems are effective in removing particles from the wafers and are relatively cost-efficient. Approximately 4.5 tons of water are used for the production of each 200-mm, 16-Mbit, DRAM wafer. 
     A schematic of a typical conventional wet bench system for removing photoresist polymers from semiconductor wafers is generally indicated by reference numeral  8  in FIG.  1 . As a first step in the processing sequence, a set or lot of wafers (not shown), having previously been subjected to a photoresist process, is initially placed in a first acid wet clean chamber  10 , in which the wafers are subjected to an acid solution, such as ACT690, to remove much of the polymer material from the wafer. Next, the wafers are transferred from the first acid wet clean chamber  10  to a second acid wet clean chamber  12 , in which the wafers are again subjected to an acid such as ACT 690 to remove the remaining polymer residues from the wafers. The wafers are then transferred to a base clean chamber  14 , in which a base such as NMP is applied to the wafers to neutralize the acid thereon. The wafers are then transferred to a QDR (quick dump rinse) chamber  16 , and then to an ISO (isolation) bath chamber  18 , in each of which the base previously applied to the wafers in the base clean chamber  14  is rinsed off the wafer using DI (deionized) water. Finally, the wafers are transferred to a spin dryer chamber  20 , in which the wafers are rotated at high speeds to dry the rinse water from the wafers. 
     A problem commonly encountered in routine operation of the wet bench system  8  is that the system  8 , including the wafer transfer mechanism thereof, may fail due to any of a number of reasons. When this occurs, the wafers in transit through the wet bench system  8 , unable to progress to the spin dryer chamber  20 , may be delayed at either the QDR chamber  16  or the ISO bath chamber  18 . Accordingly, the metal components in the devices on the wafers must remain in contact with rinse water standing on the wafers for prolonged periods of time. The standing water on the wafers forms pits in the metal interconnects and other components on the wafers. Consequently, the yield of devices on the wafers is significantly reduced, and the affected wafers must be scrapped. 
     One technique which has been used to prevent prolonged exposure of the wafers at the rinsing step in the wet bench system  8  in the event of system malfunction or shutdown involves transferring the affected wafers to a separate wet bench system  8  for continuation of the drying process in the spin dryer chamber  20  thereof. However, in the event that the second wet bench system is loaded with wafers, there is a significant delay before the second system is available to receive and dry the affected rinsed wafers from the first system. Accordingly, a wafer dryer system is needed for drying wafers at the wafer rinsing stage in the event of a wet bench system failure or malfunction. 
     An object of the present invention is to provide a wafer dryer system for drying wet wafers in the event of system malfunction or shutdown. 
     Another object of the present invention is to provide a wafer dryer system which significantly enhances the yield of devices on a wafer. 
     Still another object of the present invention is to provide a wafer dryer system which prevents scrapping of wafers due to system malfunction in a wet bench system for removing photoresist polymers from substrates. 
     Yet another object of the present invention is to provide a wafer drying system which may be adapted to dry wafers in a variety of semiconductor fabrication processes. 
     A still further object of the present invention is to provide a wafer drying system for reducing or preventing formation of metal line pits in metal interconnects and other components in devices on a substrate. 
     Yet another object of the present invention is to provide a wafer drying system which reduces the costs associated with processing substrates in the fabrication of semiconductor integrated circuits. 
     SUMMARY OF THE INVENTION 
     In accordance with these and other objects and advantages, the present invention is generally directed to a wafer dryer system which is suitable for drying rinse water from substrates in the event of a system malfunction or failure during or after rinsing of the substrates. The wafer dryer system typically includes a pair of drying chambers, each of which is fitted with at least one nitrogen gas inlet, at least one IPA gas inlet and an exhaust opening. A wafer boat which holds multiple wet wafers from an interrupted rinsing process typically in a wet bench system is placed in one of the chambers, after which the chamber is filled with hot nitrogen gas and mixed IPA gas to dry the wafers in the wafer boat. Upon resumption of operation of the wet bench system from which the wafers were taken or upon availability of a second wet bench system, the dried wafers are removed from the chamber for continued rinsing, as necessary. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic view illustrating typical components of a conventional wet bench system for removing photoresist polymers from substrates; 
     FIG. 2 is a schematic view illustrating two wet bench systems in typical implementation of a wafer dryer system of the present invention; 
     FIG. 3 is a perspective, partially schematic, view of a wafer dryer system of the present invention; and 
     FIG. 4 is a typical piping schematic for a wafer dryer system of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention has particularly beneficial utility in drying WIP semiconductor wafers in the event of malfunction or shutdown of a wet bench system to prevent pit formation in the metal components of the wafers. However, the invention is not so limited in application, and while references may be made to such semiconductor wafers and wet bench systems, the present invention is more generally applicable to drying substrates or objects in a variety of mechanical and industrial applications. 
     Referring initially to FIGS. 3 and 4 of the drawings, an illustrative embodiment of the wafer dryer system of the present invention is generally indicated by reference numeral  65  and typically includes an upper drying chamber  67  which may be separated from a lower drying chamber  77  by a partition  70 . The upper drying chamber  67  includes a chamber wall  69  which defines a chamber interior  68  and includes a chamber opening  75  through which a wafer boat  76  loaded with multiple, typically twenty-five, WIP wafers  97  may be placed for drying in the chamber interior  68 , as hereinafter further described. A chamber door (not shown) may be provided for closing the chamber opening  75 . A suitable wafer support  74  typically rests on the partition  70  for supporting the wafer boat  76  in the chamber interior  68 . A pair of nitrogen gas inlet conduits  72 , each of which is connected to an exterior nitrogen gas source  88  through nitrogen gas piping  89 , as shown in FIG. 4, extends into the chamber interior  68 , typically on opposite sides of an exhaust opening  71  provided in the chamber wall  69 . A nitrogen gas inlet opening  72   a  may be provided in the extending end of each nitrogen gas inlet conduit  72  for discharging nitrogen gas from the conduit  72  into the chamber interior  68 . Alternatively, one or more of the inlet openings  72   a  may be provided along the length of each conduit  72 . An IPA gas inlet conduit  73 , connected to an exterior IPA gas source  92  through IPA gas piping  93 , in like manner extends into the chamber interior  68 , and may terminate in a IPA gas inlet opening  73   a , or multiple inlet openings  73   a  may be provided along the length of the conduit  73  for discharging IPA gas into the chamber interior  68 . The IPA gas inlet conduit  73  may extend into the chamber interior  68  between the nitrogen gas inlet conduits  72  and above the exhaust opening  71 , as shown. The exhaust opening  71  is provided in the chamber wall  69  typically opposite the chamber opening  75 , and is connected to exhaust piping  95 , as shown in FIG. 4, for the removal of nitrogen gas and IPA gas from the chamber interior  68  during or after the drying process. 
     As further shown in FIG. 3, the lower drying chamber  77  may have the same design and components as the upper drying chamber  67 , including a chamber wall  79  which defines a chamber interior  78  and has a chamber opening  85  through which a wafer boat  86  loaded with multiple, typically twenty-five, WIP wafers  98  may be placed for drying in the chamber interior  78 , as hereinafter further described. A suitable wafer support  84  typically rests on a base  80  for supporting the wafer boat  86  horizontally in the chamber interior  78 . A pair of nitrogen gas inlet conduits  82 , each of which is connected to the nitrogen gas source  88  through the nitrogen gas piping  89 , as shown in FIG. 4, extends into the chamber interior  78  for discharging nitrogen gas into the chamber interior  78 . The nitrogen gas inlet conduits  82  may extend into the chamber interior  78  on opposite sides of an exhaust opening  81  provided in the chamber wall  79 . A nitrogen gas inlet opening  82   a  may be provided in the extending end of each nitrogen gas inlet conduit  82  for discharging nitrogen gas from the conduit  82  into the chamber interior  78 . Alternatively, one or more of the discharge openings  82   a  may be provided along the length of each conduit  82 . An IPA gas inlet conduit  83 , connected to the IPA gas source  92  through the IPA gas piping  93 , in like manner extends into the chamber interior  78  for discharging IPA gas into the chamber interior  78 , and may terminate in a IPA gas inlet opening  83   a , or the openings  83   a  may be provided along the length of the conduit  83  for discharging IPA gas into the chamber interior  78 . The exhaust opening  81  is provided in the chamber wall  79  typically opposite the chamber opening  85 , and is connected to the exhaust piping  95 , as shown in FIG. 4, for the removal of nitrogen gas and IPA gas from the chamber interior  78  after the drying process. 
     The wafer dryer system  65  shown in FIGS. 3 and 4 has been described as having an upper drying chamber  67  disposed on top of a lower drying chamber  77 . However, it is understood that the drying chambers  67 ,  77  may alternatively be disposed in horizontally, rather than vertically, adjacent relationship to each other in the wafer dryer system  65 . Furthermore, it is understood that the nitrogen gas inlet conduits  72  and the IPA gas inlet conduit  73  of the upper drying chamber  67 , as well as the nitrogen gas inlet conduits  82  and the IPA gas inlet conduit  83  of the lower drying chamber  77 , may have any suitable alternative arrangement than that described above and shown in FIG.  3 . 
     In typical operation of the wafer dryer system  65  of the present invention, multiple lots of semiconductor wafers are simultaneously processed in each of two wet bench systems  28 ,  48  after the wafers are subjected to photoresist processing, in conventional fashion. The first wet bench system  28  includes a first acid wet clean chamber  30 ; a second acid wet clean chamber  32 ; a base clean chamber  34 ; a QDR (quick dump rinse) chamber  36 ; an ISO (isolation) bath chamber  38 ; and a spin dryer chamber  40 . Likewise, the second wet bench system  48  includes a first acid wet clean chamber  50 ; a second acid wet clean chamber  52 ; a base clean chamber  54 ; a QDR chamber  56 ; an ISO bath chamber  58 ; and a spin dryer chamber  60 . Accordingly, with regard to operation of the first wet bench system  28 , wafers are initially placed typically by lot in the first acid wet clean chamber  30 , in which the wafers are subjected to an acid solution, such as ACT690, to remove much of the polymer material from each of the wafers. Next, the wafers are transferred from the first acid wet clean chamber  30  to the second acid wet clean chamber  32 , in which the wafers are again subjected to an acid such as ACT 690 to remove the remaining polymer residues from the wafers. The wafers are then transferred to a base clean chamber  34 , in which a base such as NMP is applied to the wafers to neutralize the acid thereon. The wafers are then transferred to the QDR chamber  36 , and then to the ISO bath chamber  38 , in each of which the base previously applied to the wafers in the base clean chamber  34  is rinsed off the wafer using DI (deionized) water. Under normal circumstances, the wafers timely progress through the QDR chamber  36  and the ISO bath chamber  38  to a spin dryer chamber  40 , in which the wafers are rotated at high speeds to dry the rinse water from the wafers. Finally, the wafers are removed from the spin dryer chamber  40  and transferred to a separate processing tool (not shown) for further processing. Separate lots of wafers are similarly processed simultaneously during transit through the second wet bench system  48 . 
     In the event that the first wet bench system  28  inadvertently shuts down or malfunctions, a first lot of wafers  97  (FIG.  3 ), loaded in a wafer boat  76 , may initially be delayed in the QDR chamber  36 , while a second lot of wafers  98 , loaded in a wafer boat  86 , may initially be delayed in the ISO chamber  38 , of the wet bench system  28 . The first lot of wafers  97  and the second lot of wafers  98  are typically wet and must be dried before standing DI water on the wafers  97 ,  98  forms pits in the metal interconnects and other components formed in the devices on the wafers  97 ,  98 . Normally under such circumstances, the wafers  97 ,  98  are unloaded from the QDR chamber  36  and the ISO chamber  38 , respectively, of the first wet bench system  28  and placed in the respective QDR chamber  56  and ISO chamber  58  of the second wet bench system  48  for continued DI water rinsing of the wafers  97 ,  98 . However, under circumstances in which operation of the QDR chamber  56  and ISO chamber  58  of the second wet bench system  48  is in progress, transfer of the wet wafers  97 ,  98  to the QDR chamber  56  and ISO chamber  58  is delayed. Accordingly, the first lot of wafers  97  is transferred instead to the upper drying chamber  67 , and the second lot of wafers  98  is transferred to the lower drying chamber  77 , of the wafer dryer system  65 . This is typically accomplished by sliding the first lot of wafers  97  and corresponding wafer boat  76  horizontally into the chamber interior  68  through the chamber opening  75 , and sliding the second lot of wafers  98  and corresponding wafer boat  86  horizontally into the chamber interior  78  of the lower drying chamber  77  through the chamber opening  85 . After the chamber openings  75 ,  85  are closed, the chamber interior  68  of the upper drying chamber  67  is filled with IPA gas by distributing the IPA gas from the IPA gas source  92  and through the exterior IPA gas piping  93  and the IPA gas inlet conduit  73  in the chamber interior  68 , respectively. Simultaneously, the chamber interior  78  of the lower drying chamber  77  is filled with IPA gas by distributing the IPA gas from the IPA gas source  92 , through the IPA gas piping  93  and into the chamber interior  78  through the IPA gas inlet conduit  83 . The IPA gas in the chamber interior  68  of the upper drying chamber  67  and in the chamber interior  78  of the lower drying chamber  77  both dries DI water and removes many of the photoresist polymer and other particles remaining on the surfaces of the wafers  97 ,  98 , respectively. Next, hot nitrogen gas, at a temperature of typically about 50° C. to about 70° C., is distributed from the nitrogen gas source  88  and into the chamber interior  68  of the upper cleaning chamber  67 , through the nitrogen gas piping  89  and the respective nitrogen gas conduits  72  in the chamber interior  68  of the upper drying chamber  67 . Simultaneously, some of the hot nitrogen gas is distributed from the nitrogen gas source  88  and into the chamber interior  78  of the lower cleaning chamber  77 , through the nitrogen gas piping  89  and the respective nitrogen gas conduits  82  in the chamber interior  78  of the lower drying chamber  77 . The hot nitrogen gas quickly dries the wafers  97  in the upper drying chamber  67  and the wafers  98  in the lower drying chamber  77 . The hot nitrogen remains in the chamber interior  68  of the upper drying chamber  67  and in the chamber interior  78  of the lower drying chamber  77  to maintain the wafers  97 ,  98  in a dry condition until the QDR chamber  56  and the ISO chamber  58  of the second wet bench system  48  are available for continued rinsing of the wafers  97 ,  98 , respectively. At that time, the IPA gas and nitrogen gas vapors in the chamber interior  68  of the upper drying chamber  67  and in the chamber interior  78  of the lower drying chamber  77  are evacuated from the respective chamber interiors  68 ,  78 , through the exhaust opening  71  of the upper drying chamber  67  and the exhaust opening  81  of the lower drying chamber  77 , respectively. The evacuated IPA gas and nitrogen gas vapors are directed to a suitable venting system through the exhaust piping  95 . Finally, the wafer boat  76  holding the wafers  97  is removed from the upper drying chamber  67  and placed in the QDR chamber  56  of the second wet bench system  48  for continued rising of the wafers  97 . In like manner, the wafer boat  86  holding the wafers  98  is removed from the lower drying chamber  77  and is placed in the ISO bath chamber  58  for continued rinsing of the wafers  98 . 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made to the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.