Abstract:
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having a workpiece transfer robot for transferring a workpiece from one operation to the next. 
     The polishing apparatus according to the present invention comprises a polishing section including a top ring for holding a workpiece to be polished and a turntable having a polishing surface for polishing a surface of the workpiece held by the top ring; a cleaning section including a cleaning device for cleaning the workpiece that has been polished in the polishing section; and a workpiece transfer robot for transferring the workpiece to be polished to the polishing section or for transferring the workpiece that has been polished to the cleaning section. In this case, the workpiece transfer robot comprises a robot body; at least one arm operatively coupled to the robot body by at least one joint; a holder mechanism mounted on the arm for holding the workpiece; and a seal mechanism at the joint for preventing liquid from entering an interior of the joint, the seal mechanism.

Description:
PRIORITY STATEMENT 
   This application claims the priority of Korean Patent Application No. 2004-34351, filed on May 14, 2004, and Korean Patent Application No. 2004-02004, filed on Jan. 12, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus and method for treating semiconductor substrates and, more particularly, to an apparatus and method for chemically mechanically polishing and cleaning semiconductor substrates. 
   2. Description of Related Art 
   A process for manufacturing semiconductor devices comprises a deposition process for forming a thin film on a wafer and an etch process for forming a fine circuit pattern on the thin film. These processes are iteratively performed until a desired circuit pattern is formed on the wafer. In this case, many curvatures are produced. With the recent trend toward finer semiconductor devices, the line widths of circuits are smaller and more interconnections are stacked on a chip. For this reason, a step difference based on inner positions of the chip increases. The step difference makes it hard to uniformly coat a conductive layer in a subsequent process and causes a defocusing in a photolithographic process. 
   In view of the foregoing, there exist many ways for planarizing a wafer surface. As wafer calibers become larger, chemical mechanical polishing (CMP) has been widely used in recent years because a superior planarity can be achieved at not only a narrow area, but also wide area. 
   Typically, there are two methods for polishing wafers up to a target thickness during a CMP process. One is a time method, and the other is an endpoint detecting method. In the time method, a user sets the polishing time according to the thickness, and kinds of layers and wafers are polished for this set time. Unfortunately, the time method cannot polish wafers to an exact thickness due to the abrasion state of expendable supplies such as polishing pads or polishing conditioners used in a polishing process, the pressure of the polishing head for pressurizing wafers during the polishing process, hunting in the amount of slurries supplied, and the various states of layers. 
   The endpoint detecting method is classified further into a motor current detecting method and an optical detecting method. The motor current detecting method is a method for detecting the variation of a load applied to a motor resulting from a frictional force of two different layers. The motor current detecting method is advantageous in the cases where a polishing point is a boundary of an upper layer and a lower layer, but the method cannot be used in the case where a polishing point is the specific point of a single layer. The optical detecting method is a method using an intrinsic reflectivity of a material. Specifically, the optical detecting method uses a combination of waveforms reflected at a surface of a layer and at a boundary face of layers from a scanned regular wavelength beam. The optical detecting method is advantageous in the case where an upper point or a lower point is clear-cut, but this method cannot be used in the case that the upper or lower point is not clear-cut or the desired thickness is small. It is therefore hard to polish wafers to an exact thickness with currently used polishing methods. 
   Generally, a cleaning apparatus is disposed at one side of a polishing apparatus to remove extra substances such as slurries remaining on a wafer after a polishing process is performed. A typical cleaning apparatus has a cleaning module, a plurality of etchant treating modules, and a drying module. A completely polished wafer is cleaned using deionized water (DI water) from the cleaning module. The wafer is then rinsed at a module using a mixed chemical containing ammonia, hydrogen peroxide, and DI water. After being cleaned by a brush at a module using hydrofluoric acid (HF) as a chemical, the wafer is dried by a spin driver in the drying module. In the case that the cleaning process is performed using the above-described procedure, slurry residues and particles of the brush may remain attached to the wafer. Afterwards, the wafer is transferred to a wet station to be rinsed using the mixed chemical and is dried using isopropyl alcohol (IPA) based on Marangoni effect. Thus, duplicate time is required for cleaning wafers due to the slurry residues and the particles of the brush. In the respective modules of the cleaning apparatus, wet wafers are transferred to the modules by means of a transfer unit. Accordingly, the chemical may drop on the modules thereby staining or contaminating the modules. 
   SUMMARY OF THE INVENTION 
   A method and system of treating substrates is provided that polishes substrates to a more accurate thickness, reduces the time required to polish substrates, and prevents cleaning apparatuses from being contaminated by a chemical dropping from a substrate during a cleaning process. 
   One embodiment provides a method including intermediate and final polishing steps. In the intermediate polishing step, the substrate is polished to a reference point using an endpoint detection method. In the final polishing step, the substrate is polished for a polishing time that is computed from data measured during a final polishing step of a previously polished substrate. 
   Another embodiment provides a further method including cleaning the polished substrate by loading the polished substrate onto a cleaning apparatus. The cleaning apparatus cleans the substrate using deionized water (DI water). Then the cleaning apparatus cleans the substrate at an initial chemical cleaning step using a solution including hydrofluoric acid (HF). Then the cleaning apparatus cleans the substrate in a final chemical cleaning step by dipping the substrate in a solution including ammonia, hydrogen peroxide, and DI water. The cleaning apparatus then dries the substrate in a drying step. The substrate can be dried after each cleaning step to prevent contamination of the cleaning apparatus by chemicals dropping from the substrate. 
   Yet another embodiment provides a system for treating substrates that includes a chemical mechanical polishing apparatus. The apparatus includes a polishing part, a measuring part and a polishing control system. The polishing control system includes an intermediate polish controller and a final polish controller for controlling the intermediate and final polishing, respectively, of the substrate. The intermediate polishing is done using an endpoint detection method and the final polishing is done using a time method based on closed loop control. 
   And yet another embodiment provides a further system that includes a cleaning apparatus. The cleaning apparatus includes modules for rinsing, chemically cleaning, and drying the substrate. Each of the rinsing and chemical cleaning modules can include a nozzle supplying a drying gas to dry the substrate prior to transferring the substrate to a next module. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a substrate treating equipment according to an embodiment of the present invention. 
       FIG. 2  is a perspective view of a polishing part shown in  FIG. 1 . 
       FIG. 3  is a cross-sectional view showing multi-layered regions polished at each plate portion in the case that multi-layers are polished according to an embodiment of the invention at plate portions, respectively. 
       FIG. 4  shows a final polishing controller according to an embodiment of the invention. 
       FIG. 5  is a cross-sectional view showing multi-layered regions polished at each plate portion according to an embodiment of the invention, respectively when they are set to have a uniform removal thickness. 
       FIG. 6  shows a waveform obtained using optical interferometry. 
       FIG. 7  shows the cleaning apparatus of  FIG. 1 . 
       FIG. 8  is a front view of a holding part of the cleaning apparatus of  FIG. 7 . 
       FIG. 9  shows a rinsing module of the cleaning apparatus of  FIG. 7 . 
       FIG. 10  shows an initial chemical treating module of the cleaning apparatus of  FIG. 7 . 
       FIG. 11  shows a final chemical treating module of the cleaning apparatus of  FIG. 7 . 
       FIG. 12  shows another example of the cleaning apparatus of  FIG. 1 . 
       FIG. 13  shows an arrangement of a plurality of cleaning apparatuses are arranged according to another embodiment of the invention. 
       FIG. 14  is a flowchart explaining a substrate treating method according to an embodiment of the present invention. 
       FIG. 15  is a flowchart showing the steps of the cleaning process in  FIG. 14 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As illustrated in  FIG. 1 , substrate treating equipment according to the invention includes a polishing apparatus  10  and a cleaning apparatus  20 . The polishing apparatus  10  is disposed at one side, and the cleaning apparatus  20  is disposed abreast at a lateral face of the polishing apparatus  10 . A transfer robot  30  is installed between the polishing apparatus  10  and the cleaning apparatus  20  to transfer a wafer therebetween. A plurality of load stations  50  are arranged lateral to the cleaning apparatus  20 . A carrier containing wafers is placed on the load station  50 . The polishing apparatus  10  performs a polishing process to polish layers of a wafer, and the cleaning apparatus  20  removes extra substances such as slurries attached onto the wafer after the polishing process. 
   The polishing apparatus  10  has a polishing part  130 , a measuring part  160 , and a control system part  180 . The polishing part  130  is disposed in the polishing apparatus  10  to directly polish wafers. The measuring part  160  measures a pre-polish wafer thickness and a post-polish wafer thickness and may be disposed in a terminal of the load station  50 . Further, the measuring part  160  measures a thickness of a to-be-polished layer. If the to-be-measured layer is composed of an upper layer and a lower layer, the measuring part  160  measures a thickness of the lower layer. Alternatively, the measuring part  160  measures a post-polish wafer thickness and a piece of equipment for performing pre-polish processes (e.g., deposition equipment; not shown) measures the pre-polish wafer thickness. 
   Referring to  FIG. 2  and  FIG. 1 , the polishing part  130  has an initial plate portion  100   a , an intermediate plate portion  100   b , a final plate portion  100   c , a load cup  120 , and a polishing head assembly  140 . The load cup  120  and the plate part  100  are disposed foursquare. The load cup  120  is disposed to be adjacent to the cleaning apparatus  20 . The plate portions  100   a ,  100   b , and  100   c  are arranged in a counterclockwise direction, in the order named. Each plate portion  100   a ,  100   b , and  100   c  includes a platen  102  to which a polishing pad  104  is attached, a slurry supply arm  106  for supplying slurries to the polishing pad  104  during a polishing process, and a pad conditioner  108  for keeping the polishing pad with a suitable roughness. The polishing head assembly  140  has a cruciform supporting plate  142  having four terminals each being combined with a polishing head  144 . The polishing head  144  adsorbs a wafer under a vacuum state while transferring the wafer and applies a regulatable pressure to the wafer during a polishing process. The polishing heads  144  revolves on its axis  145 , and the polishing head assembly  140  also revolves on its axis  15 . Wafers are polished by the polishing head assembly  140  through the initial, intermediate, and final plate portions  100   a ,  100   b , and  100   c.    
   Returning to  FIG. 1 , the control system part  180  controls the degree a wafer is polished at the plate parts  100   a ,  10   b , and  100   c . The control system part  180  includes: an initial polishing controller  180   a  for controlling the degree a wafer is polished at the initial plate portion  100   a ; an intermediate polishing controller  180   b  for controlling the degree a wafer is polished at the intermediate plate portion  100   b ; and, a final polishing controller  180   c  for controlling the degree a wafer is polished at the final plate portion  100   c . At the initial plate portion  100   a , a wafer is polished to a predetermined thickness. At the intermediate plate portion  100   b , the wafer is polished to a reference point. At the final plate portion  100   b , the wafer is polished until it reaches a target thickness. In the case that a to-be-polished layer of the wafer is a multi-layered layer composed of an upper layer ( 60   a  of  FIG. 3 ) and a lower layer ( 60   b  of  FIG. 3 ), a reference point is a boundary  60   c  of the upper and lower layers  60   a  and  60   b.    
   The initial polishing controller  180   a  controls polishing performed at the initial plate portion  100   a  by using an endpoint detecting method or a fixed time method. The endpoint detecting method adopts an optical interferometric method, which is disclosed in Korean Patent Application No. 2002-34771 and U.S. Pat. No. 6,511,363. The optical interferometric method is well know in the art and will not be described in further detail. The fixed time method is where a worker directly sets polishing time according to associated data (e.g., polishing thickness and time) based on a kind of a to-be-polished layer and the layer is then polished for the set polishing time. 
   The intermediate polishing controller  180   b  controls polishing performed at the intermediate plate portion  100   b  by using an endpoint detecting method. The endpoint detecting method may adopt an optical interferometric method or a motor current control method. The motor current control method senses the variation of a load that is generated by a frictional difference of the layers (upper and lower layers  60   a  and  60   b ) to be applied to a motor. As previously stated, the intermediate polishing controller  180   b  controls the polishing to be performed until the upper layer  60   a  is completely polished at the intermediate plate portion  100   b , and the lower layer  60   b  is exposed. 
   The final polishing controller  180   c  controls the polishing performed at the final plate portion  100   c  by using a variable time method based on a closed loop control. When the fixed time method is used for polishing, the thickness of the post-polish lower layer  60   b  differs from the target thickness. This is because lower layers  60   b  of wafers differ in thickness, and as the polishing process is performed, expendable supplies such as the polishing pad and the pad conditioner abrade, changing the polishing rate. According to the variable time method based on the closed loop control, a polishing rate upon a present state of the polishing apparatus  10  is computed from data such as polishing time and thickness of a currently polished wafer and then polishing time is automatically computed. 
   In  FIG. 3 , an ‘a’ area is polished at the initial plate portion  100   a  by a fixed time method or an endpoint detecting method. A ‘b’ area is polished at the intermediate plate portion  100   b  by the endpoint detecting method, and a ‘c’ area is polished at the final plate portion  100   c  by a variable time method based on a closed loop control. 
   As illustrated in  FIG. 4 , the final polishing controller  180   c  has a data part  181 , an analyzing part  182 , a computing part  183 , a treating part  184 , and a control part  185 . The data part  181  receives data on pre- and post-polish thickness of a lower layer  60   b  of each wafer, which are measured at the measuring part  160 , and data on polishing time required for polishing the wafer at a final polishing step. The analyzing part  182  analyzes a polishing rate of each wafer when it is polished, based on data stored in the data part  181 . The computing part  183  combines one or more values analyzed from the analyzing part  182  to compute a current-state polishing rate (hereinafter referred to as “process polishing rate”) of the polishing apparatus  10 . The treating part  184  computes a polish time to be applied to a wafer that will be subjected to a current process. The control part  185  controls the polishing head assembly  140  such that polishing is performed at the final plate portion  100   c  during the polishing time computed at the treating part  184 . 
   Now, the steps of computing a polishing time at the final polishing controller  180   c  will be described more fully. The final polishing controller  180   c  controls the polishing of lower layer  60   b  of a wafer to be polished to a target thickness. 
   We set:
         PRE-THK i  is a thickness of a lower layer  60   b  of a wafer which is not polished yet in an i th  polishing process;       

   TARGET is a target thickness; 
   RR i  denotes a process polishing rate; 
   PRE-THK K  is a thickness of the lower layer  60   b  before performing a polishing process for a wafer subjected to a k th  process (hereinafter referred to as “k th  wafer”); 
   POST-THK K  is a thickness of the lower layer  60   b  after performing a final polishing process for the k th  wafer; and 
   T K  is a polishing time of the k th  wafer, 
   wherein the wafer to be polished in the i th  process means a wafer to be polished in a current process, and the k th  wafer means a wafer that is already polished; and 
   wherein k th  wafers belong to the same lot as wafers that are being polished and are already polished and measured, or are wafers that belong to a lot polished just before. 
   The PRE-THK i , PRE-THK K , POST-THK K , and T K  are all stored in the data part  181 . The analyzing part  182  analyzes a polishing rate RRK of the polishing apparatus  10  when a k th  wafer is polished.
 
 RR   K =( PRE - THK   K   −POST - THK   K )/ T   K   [Equation 1]
 
   The computing part  183  uses the polishing rates RR K  computed at the analyzing part  182  to compute a process polishing rate RR i . In an exemplary embodiment, one of the polishing rates analyzed at the analyzing part  182  (polishing rate of a k th  wafer) may be set as a process polishing rate RR i . Preferably, the k th  wafer is a (i-1) th  wafer that has just been completely polished. However in the case that the (i-1) th  wafer is not measured, the k th  wafer is a wafer that is most currently measured. 
   In another exemplary embodiment, among the polishing rates analyzed at the analyzing part  182 , a plurality of polishing rates are combined to compute a process polishing rate RR i . For example, the process polishing rate RR i  may be an average value of polishing rates of successively polished wafers, as shown by equation 2. 
   
     
       
         
           
             
               
                 
                   RR 
                   i 
                 
                 = 
                 
                   
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           
                             i 
                             - 
                             m 
                           
                         
                         
                           i 
                           - 
                           n 
                         
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         RR 
                         k 
                       
                     
                     
                       ( 
                       
                         m 
                         - 
                         n 
                         + 
                         1 
                       
                       ) 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       i 
                       &gt; 
                       m 
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                       n 
                     
                     ) 
                   
                 
               
             
             
               
                 [ 
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 ] 
               
             
           
         
       
     
   
   In this case, it is preferable to use polishing rates for wafers that are most currently measured. Generally, it is preferable to use an average value of about three to five polishing rates. For example, if using polishing rates of three wafers polished just prior to the wafer that is to be currently polished, a polishing rate RR i  is obtained by equation 3. 
   
     
       
         
           
             
               
                 
                   RR 
                   i 
                 
                 = 
                 
                   
                     
                       RR 
                       
                         i 
                         - 
                         1 
                       
                     
                     + 
                     
                       RR 
                       
                         i 
                         - 
                         2 
                       
                     
                     + 
                     
                       RR 
                       
                         i 
                         - 
                         3 
                       
                     
                   
                   3 
                 
               
             
             
               
                 [ 
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 ] 
               
             
           
         
       
     
   
   In still another exemplary embodiment, polishing rates of a plurality of wafers are combined to obtain a process polishing rate RR i  while giving a determined weight to the respective polishing rates. 
   
     
       
         
           
             
               
                 
                   RR 
                   i 
                 
                 = 
                 
                   
                     ∑ 
                     
                       k 
                       = 
                       
                         i 
                         - 
                         m 
                       
                     
                     
                       i 
                       - 
                       n 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       [ 
                       
                         
                           RR 
                           k 
                         
                         × 
                         
                           WEIGHT 
                           k 
                         
                       
                       ] 
                     
                     ⁢ 
                     
                       ( 
                       
                         i 
                         &gt; 
                         m 
                         &gt; 
                         n 
                       
                       ) 
                     
                   
                 
               
             
             
               
                 [ 
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
                 ] 
               
             
           
         
       
     
   
   In this case, it is preferable to give a higher weight to polishing rates of currently polished wafers. If using polishing rates of three wafers polished just prior to the wafer that is currently being polished and sequentially giving weights 0.5, 0.3, and 0.2 to the three wafers, a process polishing rate RR i  is obtained by equation 5.
 
 RR   i   =RR   i-1 ×0.5 +RR   i-2 ×0.3 +RR   i-3 ×0.2  [Equation 5]
 
   If the process polishing rate RR i  is computed at the computing part  183 , the treating part  184  determines a polishing time T i  for polishing that is to be performed in a final polishing step. In an exemplary embodiment, a treating part  184  computes a polishing time T i  according to equation 6.
 
 T   i =( PRE - THK   i −TARGET)/ RR   i   [Equation 6]
 
   In some cases, the thickness of lower layer  60   b  polished in a polishing process is more important than the thickness of lower layer  60   b  remaining on a wafer after polishing the same. In this case, a final polishing controller  180   c  controls a polishing time such that a layer removed at lower layer  60   b  of a wafer has a determined thickness. As illustrated in  FIG. 5 , a thickness corresponding to ‘c’ (hereinafter referred to as “removal thickness”) is a constant. The treating part  184  may compute a polishing time T i  according to equation 7.
 
 T   i =TARGET R   /RR   i   [Equation 7]
 
wherein TARGET R  represents a removal thickness.
 
   In case of a wafer that is polished first from a corresponding lot, data on the polishing rate of a previously polished wafer is not stored. For this reason, the polishing time may be determined by a fixed time method. Namely, the polishing time may be determined depending upon the time that a worker directly inputs. 
   After a polishing process is completed, the thickness of lower layer  60   b  may be larger than the target thickness TARGET or the removed thickness of the lower layer  60   b  may be smaller than the removal thickness TARGET R . In both cases, the wafer may be re-polished at the final plate portion  100   c . Also preferably, the polishing time is determined by a time method based on a closed loop control. 
   As previously stated in the foregoing embodiment, a wafer is continuously polished at the initial plate portion  100   a , the intermediate plate portion  100   b , and the final plate portion  100   c . In another embodiment, a polishing part uses only an intermediate plate portion  100   b  and a final plate portion  100   c . At the intermediate plate portion  100   b , a wafer is polished until a lower layer  60   b  is exposed. At the final plate portion  100   c , the wafer is polished until the lower layer  60   b  reaches a target thickness. 
   Alternatively, the polishing part  130  has only one plate portion to polish a wafer until the lower layer  60   b  is exposed (an endpoint detection method enables a worker to detect whether the lower layer  60   b  is exposed or not), and then the wafer is continuously polished using a variable time method based on a closed loop control. 
   While the foregoing embodiments describe polishing a multi-layered wafer, the technology may be applied to a single layer. In this case, a wafer is polished to a predetermined thickness at an initial plate portion  100   a  using a fixed time method or an endpoint detection method based on optical interferometry. Thereafter, the wafer moves to an intermediate plate portion  100   b  to be polished up to a reference point using an endpoint detection method based on optical interferometry. For example, if a waveform obtained using optical reference is a waveform shown in  FIG. 6  and a final target thickness is a thickness corresponding a point ‘P’, a wafer is polished at an intermediate plate portion  100   b  up to a thickness corresponding to an upper point or lower point E 2  that is most adjacent to the point ‘P’ of the waveform. Thereafter, the wafer is polished up to a target thickness using a time method based on a closed loop control. From the above equations, both PRE-THK i  and PRE-THK K  of the wafer become a constant of the same thickness. That is to say, PRE-THK i =PRE-THK K =PRE-THK (constant). In the case that a wafer is polished at the initial plate portion  100   a  using optical interferometry, a polished portion of the wafer would be a portion corresponding to an upper point E 1 . 
   A wafer completely polished at the polishing apparatus  10  is transferred to a cleaning apparatus  20 . As illustrated in  FIG. 7 , the cleaning apparatus  20  includes a loading unit  202 , a plurality of cleaning modules  200 , an unloading unit  204 , a transfer unit  260 , and a control unit  280 . After a polishing process is completed, a wafer is placed on the loading unit  202 . The placed wafer is transferred to the cleaning module  200  by the transfer unit  260  to be cleaned. A completely cleaned wafer is placed on the unloading unit  204  and then is put into a carrier by a transfer robot  42 . Although not shown in this figure, a position switch may be installed at the loading unit  202  and the unloading unit  204  to make a horizontally placed wafer stand upright. The transfer unit  260  includes a plurality of holding parts  262 , a horizontal moving part  266 , and a vertical moving part  268 . The holding part  262  is docked with a guide rail  264  by a bracket  261  and takes a straight line motion along the guide rail  264  by means of the vertical moving part  268 . The holding part  262  is disposed over the cleaning module  200 . The holding part  262  vertically moves up and down when a wafer is loaded/unloaded to/from the respective cleaning modules  200  and takes a straight line motion in a horizontal direction when a wafer is transferred between the cleaning modules  200 . As illustrated in  FIG. 8 , the holding part  262  has a supporter  262   a  and two arms  262   b  and  262   c . The arm  262   b  is fixed to the supporter  262   a , and the arm  262   c  is mounted at the supporter  262   a  to be movable therealong. Hands  262   d  are disposed at bottoms of the arms  262   b  and  262   c  to hold a wafer, respectively. 
   Each of the cleaning modules  200  includes a rinsing module  210 , an initial chemical-treating module  220 , an intermediate chemical-treating module  230 , a final chemical-treating module  240 , and a drying module  250 , which are disposed in the order named between the loading unit  202  and the unloading unit  204 . The holding parts  262  simultaneously move horizontally and vertically. Alternatively, the holding parts  262  may independently move horizontally and vertically. At the rinsing module  210 , a wafer rinsing process is performed using a rinsing solution such as deionized water (DI water). At the initial chemical-treating module  220 , a cleaning process is performed using an etchant such as HF to remove metallic particles attached to a wafer. In the intermediate chemical-treating module  230 , a cleaning process is performed using a chemical such as ammonia to prevent particles or the like from re-attaching to the wafer. At the final chemical-treating module  240 , a cleaning process is performed using a mixed chemical of ammonia, hydrogen peroxide, and DI water to remove organic matters on the wafer and finally prevent re-attachment of particles. At the drying module  250 , the transfer unit  260  is controlled to sequentially perform a rinsing process using DI water, a cleaning process using hydrofluoric acid (HF), a cleaning process using ammonia, a cleaning process using a mixed chemical, and a drying process. 
   As previously stated in the foregoing embodiment, the cleaning modules  200  are disposed according to the order of processes performed for a wafer. However, there may be cases that a conventional apparatus should be used. In theses cases, the transfer unit  260  has about one to three holding parts  260  to perform the processes in the above order named. The holding parts  260  may independently move horizontally and vertically. 
   In a typical cleaning apparatus, a wafer is cleaned using a mixed chemical before being cleaned using HF. Thereafter, the wafer is transferred to special wet station equipment to re-perform cleaning and drying processes using a mixed chemical. On the other hand, in this embodiment, a wafer is transferred to equipment for the next process (e.g., deposition process) without being transferred to wet station equipment because a cleaning process using a mixed chemical is performed last. In addition, the intermediate chemical-treating module  230  may be omitted and the cleaning apparatus  20  may have a plurality of final chemical-treating modules  440  in which a cleaning process is performed using a mixed chemical. In this case, a wafer is sequentially subjected to a rinsing process using DI water, a cleaning process using a mixed chemical, a cleaning process using HF, a cleaning process using ammonia, a cleaning process using a mixed chemical, and a drying process. Alternatively, a cleaning module  200  for performing a cleaning process using another etchant may be additionally installed at the cleaning apparatus  20  as well as the above-described cleaning modules  200  or a plurality of identical cleaning modules  200  may be installed. 
   As illustrated in  FIG. 9 , the cleaning module  210  has a housing  212  having a top where a slot  212   a  is formed. Wafers enter and exit through the slot  212   a . A drain pipe  211  is connected to a bottom of the housing  212 . A rinsing solution is drained through the drain pipe  211 . A wafer is inserted into a slot (not shown) formed at each supporting rod  214  which rotates during a process. A nozzle  216  is inserted into the housing  212 . The nozzle  216  is horizontally disposed to pass the center of a wafer. A plurality of injection holes  216   a  are formed on the nozzle  216 . The wafer rotates while DI water is injected onto the wafer. A rinsing solution supply pipe  219   a  and a dry gas supply pipe  219   b  are connected to the nozzle  216 . The rinsing solution supply pipe  219   a  is configured for supplying DI water, and the dry gas supply pipe  219   b  is configured to supply drying gas. If the wafer is completely rinsed, dry gas such as nitrogen is supplied from the nozzle  216  to remove DI water attached to the wafer. A holding part  262  transfers the wafer from cleaning module  210  to an initial chemical-treating module  220 . Wafers are transferred dried, thereby preventing DI water left on the wafers from dropping on the outer walls of modules  200 . 
   As illustrated in  FIG. 10 , the initial chemical-treating module  220  has a housing  222 , a supporter  224 , a nozzle  226 , and brushes  228 . The housing  222  and the supporter  224  are similar to the housing  212  and the supporter  214  of the rinsing module  210  and will not be described in further detail. The brushes  228  are installed in the housing  222 . A shaft  227  is inserted into the center of the brushes and is rotated by a motor  227   a  during a wafer. The brushes  228  may take a straight line motion in an opposite direction so that a wafer may be placed therebetween. A nozzle is disposed over the brushes  228 . An etchant supply pipe  229   a  and a dry gas supply pipe  229   b  are connected to the nozzle  226 . The etchant supply pipe  229   a  is configured for supplying HF, and the dry gas supply pipe  229   b  is configured for supplying a dry gas. A plurality of injection holes  226   a  are formed at the nozzle  226 . While HF is supplied from the nozzle  226 , the wafer rotates. After the cleaning process is completed, the wafer is dried using a dry gas. An intermediate chemical-treating module  230  has the same configuration as the initial chemical-treating module  220 , but uses ammonia instead of HF as the chemical treatment. Alternatively, the wafer may be rinsed or cleaned by dipping the wafer in these modules. In this case, the nozzle  226  is preferably disposed in an upper portion in the housing  222 . 
   As illustrated in  FIG. 11 , the final chemical-treating module  240  has a housing  242 , a supporter  244 , a nozzle  246 , and a megasonic wave generator  248 . The housing  242  and the supporter  244  are similar to the housing  212  and the supporter  214  of the cleaning module  210  and will not be described in further detail. At the final chemical-treating module  240 , the wafer is dipped in a mixed chemical to be cleaned. A nozzle  246  is disposed at an upper portion in the housing  242 . An etchant supply pipe  249   a  and a dry gas supply pipe  249   b  are connected to the nozzle  246 . The etchant supply pipe  249   a  is configured for supplying an etchant, and the dry gas supply pipe  249   b  is configured for supplying a dry gas. A plurality of injection holes  226   a  are formed on the nozzle  246 . The above-mentioned mixed chemical is used as the etchant, in which ammonia, hydrogen peroxide, and DI water may be mixed at a ratio of 1:4:20. The megasonic wave generator  248  is mounted on a bottom of the housing  242  to apply a wave form to the mixed chemical. 
   As previously described in  FIG. 9  through  FIG. 11 , an etchant or a rinsing solution and a dry gas are supplied through the same nozzle in the respective modules  200 . Alternatively, a nozzle for supplying an etchant or a rinsing solution and a nozzle for supplying a dry gas may be installed independently. In this case, the nozzle for supplying an etchant or a rinsing solution is preferably disposed above the nozzle for supplying a dry gas. Particularly, the nozzle for supplying a dry gas is preferably disposed in an upper portion of the housing. 
   A wafer, which is completely cleaned using an etchant, moves to the drying module  250  to be dried. The drying module  250  may perform a drying process using Marangoni effect. A drying method using the Marangoni effect is disclosed in Korean Patent Application No. 2003-47511 and No. 2002-93248, and a spin dry method is disclosed in U.S. Pat. No. 5,829,256, which will not be described in further detail. 
     FIG. 12  illustrates a cleaning apparatus  20 ′ having another arrangement of a loading unit  202 , an unloading unit  204 , and a plurality of cleaning modules  200 , in which arrows indicate a wafer transfer direction. Referring to  FIG. 12 , the cleaning modules  200  are arranged in two lines. Therefore, the cleaning apparatus  20  has a substantially U-shape. The loading unit  202  and a part of the cleaning modules  200  are sequentially arranged in a first column adjacent to the polishing apparatus  10 , and the other modules  200  and the unloading unit  204  are arranged in a second column. The foregoing arrangement is advantageous for the use of many cleaning modules  200 . 
     FIG. 13  illustrates the case that a plurality of cleaning apparatuses  20  are disposed, in which arrows indicate a wafer transfer direction. Two or more cleaning apparatuses  20  are juxtaposed at one side of the polishing apparatus  10 . A loading unit  202  and an unloading unit  204  are disposed at the respective cleaning apparatuses  20 . A distributing part  206  is disposed at one side of the loading units  202 . A transfer robot  206   a  is installed in the distributing part  206  to transfer a wafer from the polishing apparatus  10  to the respective loading units  202 . Another distributing part  208  is disposed at one side of the unloading units  204 . A transfer robot  208   a  is installed in the distributing part  208  to transfer a wafer from the cleaning apparatus  20  to a measuring part  160 . The foregoing configuration makes it possible to prevent piling-up of wafers in the case where time required for cleaning a wafer is longer than time required for polishing a wafer. 
     FIG. 14  is a flowchart for explaining a substrate treating method according to the present invention, and  FIG. 15  is a flowchart showing the steps of a cleaning process shown in  FIG. 14 . As illustrated in  FIG. 14  and  FIG. 15 , a thickness of a lower layer  60   b  of a wafer is measured at measuring part  160  and the measured data is transmitted to data part  181  in step S 10 . A wafer polishing process is performed at a polishing part in step S 20 . The wafer is transferred to an initial plate portion  100   a  of polishing apparatus  10  to be polished to a determined thickness in step S 220 . The determined thickness may be detected using a time method or an endpoint detection method. The wafer is transferred to an intermediate plate portion  100   b  to be polished until the lower layer  60   b  is exposed in step S 240 . The wafer is transferred to a final plate portion  100   c  to be polished for polishing time computed at a treating part  184  in step S 260 . A method for determining polishing time is already described above and will not be described any further. When the polishing process is completed, the wafer is transferred to a loading unit of a cleaning apparatus  20  to perform a cleaning process at steps S 30  and S 310 . The wafer is transferred to cleaning module  210  in step S 320 . At the cleaning module  210 , the wafer is rinsed first using DI water in step S 322 . Then the wafer is dried using a dry gas in step S 324 . When the rinsing process is completed, the wafer is transferred to initial chemical-treating module  220  in step S 330 . At the initial chemical-treating module  220 , the wafer is cleaned using HF in step S 332 . Then the wafer is dried using a dry gas in step S 334 . The wafer is transferred to intermediate chemical-treating module  240  in step S 340 . At the intermediate chemical-treating module  240 , the wafer is cleaned using ammonia in step S 342 . Then the wafer is dried using a dry gas in step S 344 . Then the wafer is transferred to a final chemical-treating module  240  (S 350 ). At the final chemical-treating module  240 , the wafer is cleaned using a mixed chemical in step S 352 . Then the wafer is dried using a dry gas in step S 354 . The wafer is dried at the drying module  250  in step S 360 . The wafer is transferred to an unloading unit in step S 370 . At measuring part  160 , a thickness of a remaining lower layer  60   b  is measured and the measured data is transmitted to data part  181  in step S 40 . Alternatively, the step S 20  may be followed directly by the step S 40 , and the step S 10  may be omitted if the thickness of the lower layer  60   b  is measured beforehand in a previous process. 
   According to an embodiment of the present invention, when a layer is polished from a wafer, a polished thickness of the layer is accurately controlled in spite of abrasion from a polishing pad or the like. In a cleaning process performed following the polishing process, the wafer is finally cleaned using a mixed chemical containing ammonia, hydrogen peroxide, and DI water. Therefore, the wafer need not be re-cleaned at a wet station. The wafer exits from each cleaning module dried by use of the dry gas, thereby preventing contamination of an apparatus. 
   Although several embodiments of the present invention have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention. Thus, the invention is not to be limited, except as by the appended claims.