Abstract:
An apparatus for monitoring the Z-axis position of a transfer blade on a wafer transfer robot which transfers wafers among multiple chambers in a semiconductor fabrication facility. The invention comprises a CCD laser displacement sensor which measures the height or Z-axis position of the transfer blade and generates an analog voltage the value of which depends on the height of the transfer blade. An analog controller connected to the CCD laser displacement sensor converts the analog voltage signal to physical distance, which may be displayed on an LCD display on the analog controller. The analog controller may further be connected to a robot controller through an interface PCB, in which case a voltage signal corresponding to an abnormal position of the transfer blade is transmitted to the robot controller and the wafer transfer operation is terminated.

Description:
FIELD OF THE INVENTION 
     The present invention relates to integrated cluster tools used in the processing of semiconductors. More particularly, the present invention relates to a z-axis monitoring apparatus for monitoring the Z-axis position of a wafer support blade on a transfer robot which transfers wafers among multiple chambers in an integrated cluster tool. 
     BACKGROUND OF THE INVENTION 
     In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include the deposition of layers of different materials including metallization layers, passivation layers and insulation layers on the wafer substrate, as well as photoresist stripping and sidewall passivation polymer layer removal. In modern memory devices, for example, multiple layers of metal conductors are required for providing a multi-layer metal interconnection structure in defining a circuit on the wafer. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. Other processing steps in the fabrication of the circuits include formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked pattern; removing the mask layer using reactive plasma and chlorine gas, thereby exposing the top surface of the metal interconnect layer; cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate; and removing or stripping polymer residues from the wafer substrate. 
     CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers. 
     The chemical vapor deposition, etching and other processes used in the formation of integrated circuits on the wafer substrate are carried out in multiple process chambers. The process chambers are typically arranged in the form of an integrated cluster tool, in which multiple process chambers are disposed around a central transfer chamber equipped with a wafer transport system for transporting the wafers among the multiple process chambers. By eliminating the need to transport the wafers large distances from one chamber to another, cluster tools facilitate integration of the multiple process steps and improve wafer manufacturing throughput. 
     A typical conventional integrated cluster tool is generally indicated by reference numeral  10  in FIG.  1 . An integrated cluster tool  10  such as a Centura HP 5200 tool sold by the Applied Materials Corp. of Santa Clara, Calif., includes one or a pair of adjacent loadlock chambers  12 , each of which receives a wafer cassette or holder  13  holding multiple semiconductor wafers  28 . The loadlock chambers  12  are flanked by an orientation chamber  14  and a cooldown chamber  16 . Multiple process chambers  18  for carrying out various processes in the fabrication of integrated circuits on the wafers  28  are positioned with the orientation chamber  14 , the cooldown chamber  16  and the loadlock chambers  12  around a central transfer chamber  20 . A transfer robot  22  in the transfer chamber  20  is fitted with a transfer blade  24  which receives and supports the individual wafers  28  from the wafer cassette or holder  13  in the loadlock chamber  12 . The transfer robot  22  is capable of rotating the transfer blade  24  in the clockwise or counterclockwise direction in the transfer chamber  20 , and the transfer blade  24  can extend or retract to facilitate placement and removal of the wafers  28  in and from the load lock chambers  12 , the orientation chamber  14 , the cooldown chamber  16  and the process chambers  18 . 
     In operation, the transfer blade  24  initially removes a wafer  28  from the wafer cassette  13  and then inserts the wafer  28  in the orientation chamber  14 . The transfer robot  22  then transfers the wafer  28  from the orientation chamber  14  to one or more of the process chambers  18 , where the wafer  28  is subjected to a chemical vapor deposition or other process. From the process chamber  18 , the transfer robot  22  transfers the wafer  28  to the cooldown chamber  16 , and ultimately, back to the wafer cassette or holder  13  in the loadlock chamber  12 . 
     As illustrated in FIG. 2, a standard optical wafer sensor  30  is typically provided on the transfer chamber lid  26  of the transfer chamber  20  and emits a light beam  32  which passes first through a view port (not shown) in the transfer chamber lid  26  and then through an opening  25  in the transfer blade  24  when no wafer is supported on the transfer blade  24 , as illustrated. The light is reflected back through the opening  25  to the sensor  30 , which transmits a DI signal to the system controller (not shown) to indicate that a wafer is not supported on the transfer blade  24 . When a wafer is supported on the transfer blade  24 , the light from the sensor  30  is absorbed by the wafer, which covers the opening  25 . Consequently, the sensor  30  transmits an appropriate signal to the system controller to indicate the presence of the wafer on the transfer blade  24 . The optical wafer sensor  30  typically operates on 24V DC current. 
     One of the problems associated with the conventional wafer sensor  30  is that the sensor  30  is incapable of detecting the Z-axis position of the transfer blade  24  for accurate insertion and retrieval of the wafers  28  into and out of the wafer cassette  13  in the loadlock chamber  12 . The tolerance space between the transfer blade  24  and the wafer cassette  13  in the wafer insertion and retrieval operations is typically about 3 mm. Consequently, distortions in the configuration of the transfer blade  24  due to, for example, heat from the process chambers  18  may cause the transfer blade  24  to exceed the permissible Z-axis tolerance of the transfer blade  24 . Consequently, the tilted transfer blade  24  may scratch the wafers upon removal or replacement thereof in the wafer cassette  13 , significantly reducing the wafer yield. 
     Accordingly, an apparatus is needed for monitoring the Z-axis position of a wafer transfer blade on a transfer robot. 
     An object of the present invention is to provide an apparatus for reducing loss in wafer yield in the processing of wafers in an integrated cluster tool. 
     Another object of the present invention is to provide an apparatus for preventing scraping of wafers in the removal and insertion of semiconductor wafers from and into a loadlock chamber of an integrated cluster tool due to a distorted transfer blade on a transfer robot. 
     Still another object of the present invention is to provide an apparatus for monitoring the Z-axis position of a transfer blade on a wafer transfer robot. 
     Another object of the present invention is to provide an apparatus for detecting and indicating the presence or absence of a wafer on a transfer blade of a wafer transfer robot. 
     Yet another object of the present invention is to provide an apparatus for facilitating corrective Z-axis positioning of a transfer blade on a wafer transfer robot in order to prevent inadvertent scraping of wafers in the insertion and removal of the wafers into and out of a loadlock chamber. 
     A still further object of the present invention is to provide a method of enhancing the yield of semiconductor wafers processed in a semiconductor fabrication facility by reducing or preventing inadvertent scraping of the wafers due to distortion of a wafer transfer blade on a transfer robot. 
     SUMMARY OF THE INVENTION 
     In accordance with these and other objects and advantages, the present invention comprises an apparatus for monitoring the Z-axis position of a transfer blade on a wafer transfer robot which transfers wafers among multiple chambers in a semiconductor fabrication facility. The invention comprises a CCD laser displacement sensor which measures the height or Z-axis position of the transfer blade and generates an analog voltage the value of which depends on the height of the transfer blade. An analog controller connected to the CCD laser displacement sensor converts the analog voltage signal to physical distance, which may be displayed on an LCD display on the analog controller. The analog controller may further be connected to a robot controller through an interface PCB, in which case a voltage signal corresponding to an abnormal position of the transfer blade is transmitted to the robot controller and the wafer transfer operation is terminated. 
    
    
     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 top view of a typical conventional integrated cluster tool for the processing of semiconductor wafers; 
     FIG. 2 is a schematic view illustrating a conventional sensor for detecting the presence of a wafer on a transfer blade; 
     FIG. 3 is a perspective view of an integrated cluster tool in implementation of the present invention; 
     FIG. 4 illustrates a CCD displacement sensor in application of the present invention; 
     FIG. 5 is a schematic view illustrating the various components of the present invention; and 
     FIG. 6 is an electrical schematic illustrating a typical wiring configuration for an interface PCB of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention has particularly beneficial utility in monitoring the Z-axis position of a transfer blade on a wafer transfer robot in an integrated cluster tool used in the processing of semiconductors. However, the invention is not so limited in application, and while references may be made to such integrated cluster tools, the invention is more generally applicable to monitoring the vertical or Z-axis position of objects in a variety of industrial and product applications. 
     Referring to FIGS. 3-5, an integrated cluster tool in implementation of the present invention is generally indicated by reference numeral  36  in FIG.  3  and typically includes a pair of loadlock chambers  38  each having a chamber interior  39  that houses a cassette stage  40  for receiving a wafer-supporting cassette (not illustrated). The chamber interior  39  is closed by a loadlock door  42 . The loadlock chambers  38  are located adjacent to a transfer chamber  44  closed by a removable transfer chamber lid  46  having multiple viewing ports  47  for viewing the interior of the transfer chamber  44 . A transfer robot  48  is contained in the transfer chamber  44  and is fitted with a transfer blade  50  (FIG.  4 ). The transfer robot  48  is operated to remove wafers (not shown) from the loadlock chambers  38  and among an orientation chamber (not shown), multiple process chambers (not shown) and a cooldown chamber (not shown) positioned around the transfer chamber  44 , and the transfer robot  48  places the wafers back in the loadlock chamber  38  after processing. 
     The Z-axis monitoring apparatus of the present invention is generally indicated by reference numeral  34  in the schematic of FIG.  5  and includes a CCD sensor housing  52  (FIG. 4) which, as illustrated in FIG. 3, is mounted directly above a viewing port  47   a  in the transfer chamber lid  46  adjacent to the loadlock chamber  38 . As illustrated in FIG. 4, the CCD sensor housing  52  contains a CCD (charge-coupled device) displacement sensor  58 , which may be a CCD sensor manufactured and sold by the Keyence Co., Ltd. A laser diode  54  is included in the CCD sensor housing  52 , and a pair of spaced-apart optical lenses  56  is positioned directly beneath the laser diode  54 . The laser diode  54  and optical lenses  56  are located along a common vertical axis  55 . A set of condenser lenses  57 , which may be three in number, is provided in adjacent relationship to the CCD displacement sensor  58 . The condenser lenses  57  and CCD displacement sensor  58  are located along a common reflection axis  59  that is disposed at an angle with respect to the vertical axis  55 . The vertical axis  55  indicates the path of laser light emitted from the laser diode  54  and through the optical lenses  56  and the viewing port  47   a  (FIG. 3) in the transfer chamber lid  46 , to the transfer blade  50 , in application of the present invention as hereinafter further described. Some of the laser light is reflected from the transfer blade  50 , back through the viewing port  47   a  and through the condenser lenses  57  to the CCD displacement sensor  58 , respectively, along the path indicated by the reflection axis  59 . 
     As illustrated in FIG. 5, the CCD sensor  58  is connected to a CCD laser sensor controller  66 , which receives an operational current of typically 24 volts from a DC power supply  64 . The DC power supply  64  may receive 110 volts of AC current. A “signal out” port of the CCD laser sensor controller  66  is connected to a “signal in” port of an RD analog controller  60 , which receives an operational current of 24 volts from the DC power supply  64 . The analog controller  60  may include an LCD display  63  for displaying the height of the transfer blade  50 , as hereinafter further described. 
     In one embodiment of the present invention, the analog controller  60  includes five signal ports  61  for purposes hereinafter described. The signal ports  61  are connected to a “signal high” port and a “signal low” port on an interface PCB  62  which receives an operational current of 24 volts from the DC power supply  64 . A “signal out” port on the interface PCB  62  is connected to a wafer sensor signal (W/S) port on an AMAT system controller  68  which controls the various components of the integrated cluster tool  36 , including the robot  48 . An electrical schematic for the interface PCB is shown in FIG.  6 . As illustrated in FIG. 3, the RD analog controller  60  and the interface PCB may be mounted on the top of the loadlock chamber  38 . 
     Referring next to FIGS. 4 and 5, in typical application the Z-axis monitoring apparatus  34  of the present invention is capable of monitoring the Z-axis position of the transfer blade  50  inside the transfer chamber  44  of the integrated cluster tool  36  in order to prevent inaccurate insertion of the transfer blade  50  in a wafer cassette (not shown) contained in the loadlock chamber  38  and scratching wafers (not shown) upon removal of the wafers from the cassette. To this end, the CCD displacement sensor  58  is capable of detecting a Z-axis distortion of the transfer blade  50  to within about 1 μm. In operation, the transfer robot  48  initially extends the transfer blade  50  toward the loadlock chamber  38  preparatory to removing a wafer from the cassette in the loadlock chamber  38 . As it moves toward the loadlock chamber  38 , the transfer blade  50  passes beneath the viewing port  47   a  in the transfer chamber lid  46 . Simultaneously, the laser diode  54  in the CCD sensor housing  52  emits a laser beam having a path indicated by the vertical axis  55  in FIGS. 4 and 4A, which laser beam passes through the vertical optical lenses  56  and through the viewing port  47   a , respectively, and strikes the transfer blade  50 . Some of the laser light is reflected from the transfer blade  50  along the path indicated by the reflection axis  59 , and passes through the condenser lenses  57  which condense the reflected laser light onto the CCD displacement sensor  58 . The reflected laser light forms an image on the CCD displacement sensor  58 , and the image of the reflected light varies depending on the Z-axis position of the transfer blade  50 . The CCD displacement sensor  58  may be calibrated to detect variations in the reflected image corresponding to Z-axis positions of the transfer blade  50  throughout a range of typically about 10.0 mm. 
     Depending on the Z-axis position of the transfer blade  50 , the CCD displacement sensor  58  generates an analog voltage signal typically in the range of from +5 volts to −5 volts. For example, an ideal Z-axis position of the transfer blade  50  for wafer transfer may correspond to 0 volts, whereas a “LO” position of the transfer blade  50 , as illustrated in FIG. 5, may correspond to −3 volts and an “LL” (low—low) position of the transfer blade  50  may correspond to −5 volts. Conversely, a “HI” position of the transfer blade  50  may correspond to +3 volts, and an “HH” (high high) position of the transfer blade  50  may correspond to +5 volts. This analog voltage signal is transmitted from the CCD sensor  58  to the laser sensor controller  66  and from the “signal out” port of the laser sensor controller  66  to the “signal in” port of the analog controller  60 . The analog controller  60  converts the analog voltage signal to a Z-axis position of the transfer blade  50 , typically in millimeters, and may display this Z-axis position of the transfer blade  50  in millimeters on the LCD display  63  of the analog controller  60 . 
     In the embodiment of the apparatus  34  in which the analog controller  60  is connected to the system controller  68  through the interface PCB  62 , the analog controller  60  sends the analog voltage signal to the appropriate signal port  61 . The signal ports  61  may range from “high high” (HH), “high” (HI), “low” (LO), or “low low” (LL). In the event that the transfer blade  50  is at the ideal height for the wafer transferring operation and no wafer is supported on the transfer blade  50 , the analog voltage signal sent from the laser sensor controller  66  to the analog controller  60  is 0 volts. In that case, no analog voltage signal is transmitted from the signal ports  61  on the analog controller  60  to the “signal high” port or the “signal low” port on the PCB interface  62 . The wafer sensor signal transmitted from the “signal out” port of the interface PCB  62  to the W/S port on the system controller  68  is 24 volts. Accordingly, the transfer robot  48  continues the wafer-transfer operation as the transfer blade  50  is inserted in the chamber interior  39  of the loadlock chamber  38  prior to receiving a wafer (not shown) from a wafer cassette (not shown) in the chamber interior  39 . 
     After the transfer blade  50  is positioned in the chamber interior  39  of the loadlock chamber  38  and as the wafer is moved from the loadlock chamber  38  onto the transfer blade  50 , the CCD sensor  58  transmits the analog voltage signal corresponding to the “HI” Z-axis position to the “signal in” port of the analog controller  60  through the “signal out” port of the laser sensor controller  66 . The analog controller  60 , in turn, sends the analog voltage signal to the HI signal port  61  thereof. The HI signal port  61  then sends the analog voltage signal to the interface PCB  62  at the “signal high” port thereof, in which case the wafer sensor signal sent from the “signal out” port of the interface PCB  62  to the WIS port of the system controller  68  is 0 volts. This prompts the system controller  68  to continue operation of the transfer robot  48  and movement of the transfer blade  50  and wafer supported thereon to the appropriate chambers (not illustrated) of the integrated cluster tool  36 . 
     In the event that a wafer supported on the transfer blade  50  inadvertently slides in and out of a wafer pocket (not illustrated) on the transfer blade  50  during the wafer-transfer operation, the analog voltage signal corresponding to the highest limit (HH) of the transfer blade  50  is sent from the CCD sensor  58  to the HH port  61  of the analog controller  60 , and from the HH port  61  to the “signal high” port on the interface PCB  62 . This causes the wafer sensor signal transmitted from the “signal out” port of the interface PCB  62  to the W/S port on the system controller  68  to increase from 0 volts to 24 volts. Consequently, the system controller  68  displays a “no wafer on blade” alarm message and terminates further operation of the transfer robot  48  and wafer-transferring movement of the transfer blade  50 . 
     In the event that the transfer blade  50  is distorted and the reflective portion of the transfer blade  50  is located at a Z-axis position which is higher than the ideal position, the CCD sensor transmits the analog voltage signal corresponding to the “HI” or “HH” Z-axis position to the “signal in” port of the analog controller  60  through the “signal out” port of the laser sensor controller  66 . The analog controller  60 , in turn, sends the analog voltage signal to the HI signal port  61  or HH signal port  61  thereof, as appropriate. The HI or HH signal port  61  then sends the analog voltage signal to the interface PCB  62  at the “signal high” port thereof, in which case the wafer sensor signal sent from the “signal out” port of the interface PCB to the W/S port of the system controller  68  decreases from 24 volts to 0 volts. This prompts the system controller  68  to display a “wafer on blade” alarm message and terminate operation of the transfer robot  48  and movement of the transfer blade  50  until the transfer blade  50  can be adjusted, fixed or replaced. 
     In the event that the transfer blade  50  is distorted and the reflective portion of the transfer blade  50  is located at a Z-axis position which is lower than the ideal position, the analog controller  60  sends the analog voltage signal from the CCD sensor  58  and laser sensor controller  66  to the LL signal port  61  or LO signal port  61  thereof, as appropriate. The LL or LO signal port  61  then sends the analog voltage signal to the interface PCB  62  at the “signal low” port thereof, in which case the wafer sensor signal sent from the “signal out” port of the interface PCB to the WIS port of the system controller  68  decreases from 24 volts to 0 volts. This prompts the system controller  68  to display a “wafer on blade” alarm message and terminate operation of the transfer robot  48  and movement of the transfer blade  50  until the transfer blade  50  can be adjusted, fixed or replaced. 
     Table I below summarizes the wafer sensor signal (W/S) and alarm message displayed by the system controller  68  for each status of the transfer blade  50 . 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                   
                 Wafer Sensor Signal 
                 Alarm 
               
               
                   
                 Status 
                 (W/S) 
                 Message 
               
               
                   
                   
               
             
             
               
                   
                 Wafer sliding 
                    0 V − − − − − − &gt; +24 V 
                 No wafer on 
               
               
                   
                   
                   
                 blade 
               
               
                   
                 Wafer on blade 
                    0 V 
                 N/A 
               
               
                   
                 No wafer on 
                 +24 V 
                 N/A 
               
               
                   
                 blade 
               
               
                   
                 No wafer on 
                 +24 V − − − − − − &gt; 0 V    
                 Wafer on 
               
               
                   
                 blade and blade 
                   
                 blade 
               
               
                   
                 distorted 
                   
               
               
                   
                   
               
             
          
         
       
     
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.