Patent Publication Number: US-2011073469-A1

Title: Electrochemical deposition system

Description:
FIELD OF INVENTION 
     The present invention relates to a system for deposition of a metallic layer onto semiconductor workpieces, more particularly a system for electrochemical or electroless deposition of metallic thin films on semiconductor wafers from electrolyte solutions, chemically etching parts of the deposited films, cleaning the surface of the deposited films and thermally treating the deposited films. 
     RELATED ART 
     On-chip interconnects comprises multilayer of metallic wirings embedded in one or more insulating materials on the top of transistor circuit of logic or memory chips. As the circuit density in ultra large scale integrated (ULSI) circuits increases, the size of the features in the pattern of metallic wirings, such as vias and trenches, decreases to submicron level, and the levels of metallization increase. Furthermore, RC delay has become the most dominant effect in degrading the circuit speed as the length of conductive wirings in integrated circuits continues to grow. Copper is a favorable material for interconnect metallization because of its low resistivity and high electromigration resistance. While copper is good for interconnect metallization, it poses many challenges to metallization during device fabrication. 
     The main challenge for copper implementation is the deposition system to uniformly fill trench and via features without voids and seams across the entire semiconductor substrate, known as wafer, in a damascene process, or frequently dual damascene process at acceptable manufacture flow cost. 
     Typical electroplating systems usually comprise a plurality of plating cells for metal electrochemical or chemical (“electroless”) deposition and cleaning cells for rinse, clean and bevel etch after deposition. 
     Examples of such electroplating systems are disclosed in U.S. Pat. No. 6,258,220 and U.S. Pat. No. 6,527,920. Such systems include a mainframe with a mainframe transfer robot, a loading station disposed in connection with the mainframe, a plurality of electrochemical processing cells disposed in connection with the mainframe, a plurality of spin-rinse-dry and bevel etch chambers disposed in the mainframe, and a rapid thermal treatment subsystem attached adjacent the loading station. The locations of the processing cells, spin-rinse-dry and bevel etch chambers and the probably added units are designed in one plane, and such a design takes large clean room space for providing satisfactory throughout to meet the demands of the processing system. Said electroplating systems are used in today&#39;s IC manufacturing. 
     Because such a system utilizes a 2-D architecture with all process units placed on one plane, while it is expanded to accommodate newly added process units, the footprint of the system increases, thereby limiting its expandability practically. Additionally, a plurality of permanent heavy-duty supporting posts, erected from the base plate where the processing chambers are built upon, are needed in said electroplating system to support a plurality of plating cell head assemblies that receive wafers from a robot and carry the wafers into the electrolyte. These posts are bulky as they must provide stabilization and consistence to the cell head assemblies they support in order to control precisely the movement of the cell head assemblies. These supporting posts not only take spaces inside the frame enclosure, but also limit the reachability to the mainframe transfer robot, the wafer holder assemblies and the plating cells and make the maintenance of the system inconvenient. 
     Furthermore, when the dimensions of the vias and trenches in the pattern on a semiconductor wafer become smaller, the features of the wafer become difficult to be completely wetted when the wafer carried by the chuck of the wafer holder assembly immerses into the electrolyte. This incomplete wetting will lead to defects and voids in the features in the deposited metal films. An typical method to wet a wafer is to pre-rinse the wafer in an added spin-rinse-dry cell before electroplating, as described in US 2004/0069644 and US 2007/7223323. And another example of method to wet a wafer is splashing water to the wafer surface by an added nozzle just before the wafer is carried into plating electrolyte, as described in US 2006/7146994. But pre-wetting by liquid rinse still cannot wet very small features completely, and the rinse liquid may dilute the plating electrolyte both globally in a high volume factory and locally, leading to new problems. So these disclosed methods still cannot completely solve the problem of incomplete wetting without significantly introducing process variation and adding manufacturing cost. 
     The present invention was disclosed against this background. 
     SUMMARY 
     In view of the aforementioned problems, it is an object of the present invention to provide a new architecture of an electrochemical deposition system that may treat larger scale semiconductor wafers with great efficiency to provide high throughput with a small footprint. 
     In order to achieve the aforementioned object, an electrochemical deposition system according to the present invention which has a three dimensional (3-D) stacked architecture that comprises a factory interface for receiving semiconductor wafers, a mainframe comprising a mainframe transfer robot, a plurality of wafer holder assemblies which are disposed on the top thereof, a plurality of electroplating cells disposed within a first layer of the 3-D stacked architecture at the upper part of the mainframe, a plurality of cleaning and bevel etch cells disposed within a second layer of the 3-D stacked architecture at the lower part of the mainframe, a plurality of thermal treatment chambers disposed within either the first layer, or the second layer, or both layers in the part of the mainframe connected to the factory interface, a plurality of vapor phase pre-wetting modules disposed within the mainframe, a fluid distribution system to provide electrolyte to the plating cells and process fluids to the cleaning cells, a gas delivery system to provide gas mixture to the thermal treatment chambers. The mainframe transfer robot transfers the semiconductor wafers between the factory interface, the wafer holder assemblies, the cleaning cells and the thermal treatment chambers. 
     Comparing to the system disclosed in the prior art, an advantage of the system of the present invention which has a 3-D stacked architecture is that it has a smaller footprint and may treat larger scale semiconductor wafers with great efficiency to provide high throughput because additional footprint took by some processing cells such as plating cells is saved, and another advantage of the system of the present invention is that it could be expandable to accommodate newly-added processing units without overmuch increased footprint because the newly-added processing units could be disposed on the corresponding layer or layers other than on only one layer as in the prior art, and yet another advantage of the system of the present invention is that it can be serviced and maintained conveniently because the wafer holder assemblies are disposed on the top of the mainframe, eliminating the need of bulky supporting posts which greatly limit tool accessibility, and they can be moved to the corners of the mainframe during user intervention. 
     The further characteristic of said electrochemical deposition system according to the present invention is that the thermal treatment chamber comprises a heating plate and a heating fluid dispenser for double-side heating the semiconductor wafer, a cooling plate and a cooling fluid dispenser for double-side cooling the semiconductor wafer, at least two wafer holders for receiving the semiconductor wafer and transferring the semiconductor wafer from the heating plate to the cooling plate, and at least two actuators for controlling the movement of the wafer holders. As a result, the system in accordance with the present invention may provide a uniform post electroplating thermal treatment process to improve the electrical and physical properties of the deposited metal films on semiconductor wafers by double-side thermal treating of the wafer, and the thermal treatment chamber could thermally treat multiple wafers simultaneously so that the number of thermal treatment chambers in the mainframe is reduced and throughput of the system of the present invention is increased. And the processing wafer is transferred onto the heating plate in the thermal treatment chamber by the mainframe robot before the beginning of the process and transferred out from the cooling plate in the thermal treatment chamber by the front robot after the process ends. No mainframe/factory-interface hand-off station is needed post processing, so that the robot handoff points are reduced and the transfer efficiency of the system is improved. 
     The still further characteristic of said electrochemical deposition system according to the present invention is that it may also comprise a vapor phase pre-wet device connected to a vapor generating and delivery system to realize liquid molecules adsorption onto the front surface of a semiconductor wafer that will be processed in the electroplating cell from vapor phase. The adsorbed, or condensed liquid molecules form a thin pre-wetting layer on the front surface of the semiconductor wafer before the semiconductor wafer bearing such a film is put into contact to the electrolyte solution. As a result, the system in accordance with the present invention could provide the reliable process to deposit copper films in ultra-small features on the semiconductor wafer surface without voids caused by incomplete wetting. 
     While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematically perspective view of an electrochemical deposition system of the invention. 
         FIG. 2  is a side view of an electrochemical deposition system of the invention. 
         FIG. 3  is a schematically perspective view of an electroplating cell of an electrochemical deposition system of the invention. 
         FIG. 4  is a schematically perspective view of a wafer holder assembly of an electrochemical deposition system of the invention. 
         FIG. 5  is a schematically perspective view of thermal treatment module of an electrochemical deposition system of the invention. 
         FIG. 6  is a schematic diagram of the fluid supply system in the electrochemical deposition system of the invention. 
         FIG. 7  is a schematic diagram of the electrical control system in the electrochemical deposition system of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     With reference to  FIG. 1-FIG .  2 , the electrochemical deposition system in accordance with the present invention comprises a factory interface  10  and a mainframe  11 . The factory interface includes a plurality of wafer load ports  101 , a wafer transfer robot  102 , and a wafer aligner  191 , all enclosed in a class  1  mini-environment. The mainframe comprises a mainframe transfer robot  106 , a plurality of electroplating cells  107 , a plurality of cleaning cells  108 , a plurality of thermal treatment chambers  104  and at least one vapor pre-wet module  110 . The electroplating cells  107  and the cleaning cells  108  are positioned within the first layer and second layer of the mainframe  11  separately, with one electroplating cell  107  stacked over one cleaning cell  108 . The thermal treatment chambers  104  are positioned in the mainframe  11  and connected to the factory interface  10 . Furthermore, the system comprised a delivery cassette  103  and a temporary storage cassette  112  which are attached to the factory interface  10  and located over the thermal treatment chambers  104 . The delivery cassette  103  is used for transportation of a semiconductor wafer from the factory interface  10  into the mainframe  11 . And the temporary storage cassette  112  is used to store affected wafers in case of excursion taking place to any one of the process chambers. In this case the mainframe transfer robot  106  will place wafers that are partially processed in the whole electroplating process into the temporary storage cassettes  112  for further treatment. The system further comprises a fluid distribution system that is connected to the process cells and provides plating electrolyte to the plating cells and chemical solutions to the cleaning cells. The system further comprises a gas mixing and delivery system which is connect to the thermal treatment chambers and provides mixed process gas to the thermal treatment chambers. 
     The factory interface  10  includes a plurality of load ports  101  for receiving and positioning wafer pods  192 , a front interface robot  102  and at least one wafer aligner  191 . In the present embodiment, the factory interface  10  comprises three load ports  101  and one wafer aligner  191 . The pod  192 , which preferably is the industrial wafer FOUP (front opening unified pod) accommodating multiple wafers, is transferred and disposed onto one of the load ports  101  after previous treatment of process of the wafers is ended, such as physical vapor deposition, chemical vapor deposition, or atomic layer deposition of a thin conductive layer on the wafer surface before the electro-chemical plating process. The front interface robot  102  is a typical transfer robot commonly known to the persons skilled in the field which comprises one or two arms. 
     All process modules are located inside the mainframe. Referring to  FIG. 2  again, each of the electroplating cells  107  locates vertically over one of the cleaning cells  108 . In the present embodiment, the mainframe  11  comprises four electroplating cells  107  and four cleaning cells  108  corresponding to the number of loading ports  101 . It should be understood that the number of the electroplating cells  107  in the mainframe  11  of the chemical-electroplating system in accordance with the invention are not limited by the exemplary embodiment. The person skilled in the field could increase or decrease the number of the cells according to the desired throughput of the system. And it should be noticed that stacked plating cells  107  and cleaning cells  108  save places for the mainframe  11  and reduce the footprint of the electrochemical deposition system. And it will be noted in the following specification that the 3-D architecture of the system with the plating cells  107  stacked over the cleaning cells  108  are expandable to accommodate newly-added processing units without overmuch increased footprint. 
     The mainframe  11  also comprises pluralities of wafer holder assemblies  105 , each of which is disposed above one of the electroplating cells  107  and mounted on the top of the mainframe  11 . In this embodiment of the electrochemical deposition system in accordance with this present invention, the mainframe  11  comprises four wafer holder assemblies  105  corresponding to the number of the electroplating cell  107 . 
     Referring to  FIG. 4 , the wafer holder assembly  105  comprises a semiconductor wafer chuck assembly, which further comprises a semiconductor wafer chuck  511  and a cathode contact (not shown), and an actuator. The actuator may comprise step motors  521 ,  523  and servo motor  525 . The cathode contact may comprise a plurality of soft stainless steel coil springs to maintain a uniform cross section profile which improves electrical contact to the wafer and reduces damage to the underlying film stack caused by compressive stress from mechanical contact. The wafer chuck may comprise a bottom section and a top section and the wafer is held between the bottom section and the top section, thereby the wafer chuck assembly suitably being configured to open, close and rotate the wafer chuck for inserting, removing and rotating the wafer, and the cathode contact being disposed between the bottom section and the top section of the wafer chuck and could electrically contact to the wafer front-side when the wafer chuck is closed by the actuator before the electro-chemical plating process starts. Electrical information from contact locations is monitored and fed back to the control system. Additionally, the wafer holder assembly  105  could be moved to the corner of the mainframe  11  for performance maintenance. The semiconductor wafer could be held by the chuck  511  and moved along Z axis and rotated along the X axis and Z axis respectively with the chuck  511  drove by the step motors  521 ,  523  and servo motor  525  of the actuator. For a more detailed description of wafer chuck component which comprises a wafer chuck and a cathode contact, see U.S. Pat. No. 6,495,007, entitled “Methods and apparatus for holding and positioning semiconductor wafer during electropolishing and/or electroplating of the workpieces”, the entire content of which is incorporated herein by reference. In present invention, the entire wafer holder assembly is supported by the mounting arm  527  which connects the wafer holder assembly  105  to the top of the mainframe. It should be noted that the configuration of wafer holder assembly  105  being disposed on the top of the mainframe strengthens reachability of the mainframe transfer robot  106  to the wafer holder assemblies and the plating cells and saves spaces due to needless of supporting post. 
     The mainframe  11  also comprises a vapor phase pre-wet device which may be integrated on the wafer holder assembly  105  or be an independent module (as shown in drawing). This pre-wet device is connected to a vapor generating system and provides liquid vapor to front surface of a semiconductor wafer for posing an ultra-thin pre-wetting layer on the front surface to improve the wetting performance during electroplating process. Pre-wetting by liquid vapor can wet very small features, such as vias and trenches, completely and does not cause appreciable dilution to the plating electrolyte. Therefore the system of the present invention will satisfy the needs to eliminate any incomplete wetting-related defects brought about by the increase of circuit density in ULSI. 
     Referring to  FIG. 3 , in the present embodiment, the electroplating cell  107  comprises an electrolyte chamber  700 . The electrolyte chamber  700  comprises a plurality of annular electrodes  711  and a plurality of annular insulating walls  713  which separate the whole electrolyte chamber  700  into a plurality of independent regions, each of which containing a single annular electrode  711 . The electrode  711  are charged by a plurality of power supplies (not shown) respectively by applying different waveforms and turning on or off in different sequence or at different time during the electroplating process. 
     For a more detailed description of the said electrolyte chamber, also see U.S. Pat. No. 6,495,007, entitled “Methods and apparatus for holding and positioning semiconductor wafer during electropolishing and/or electroplating of the workpieces”, the entire content of which is incorporated herein by reference. 
     However, the electrolyte chamber  700  in the deposition system according to the present invention have some difference with the said electrolyte chamber in the prior art. The electrolyte chamber  700  in the deposition system according to the present invention is separated into a lower cell body  701  which receives low cell feed electrolyte and an upper cell body  702  which receives upper cell feed electrolyte by a bubble coalescence assembly  720 . 
     An inlet and an outlet connected to each independent region of the lower cell body  701  of the electrolyte chamber  700 . Electrolyte is pumped into each independent region of the electrolyte chamber  700  by a pump from an electrolyte tank (which will be described in details in the following passage) through the inlet and then flows out through the outlet and finally returns to said electrolyte tank to realize an independent electrolyte circulation in each region of the lower cell  701  body of the electrolyte chamber  700 . 
     For each region of the upper cell body  702  there is an electrolyte inlet which is controlled by a LMFC (Liquid Mass Flow Controller) respectively to each separate region so that the electrolyte flow rate in each region of the upper cell body  702  to surface of a processing wafer can be controlled independently. The LMFCs are acid and corrosion resistant. Both the lower cell body  701  and the upper cell body  702  are made of or coated with electrical isolative and acid and corrosion resistant materials, such as PVC or PVDF. 
     The bubble coalescence assembly  720  comprises a cone-shape frame having pluralities of V-shape grooves and a porous membrane attached closely on the cone-shape frame. A tube is disposed at the top of the bubble coalescence assembly  720  which is connected to the outside of the electroplating cell  107 . Bubbles generated at the electrodes  713  during electroplating will first coalesce in V-shaped grooves and move upward to the top and then exit the chamber through the said tube. 
     The cleaning cell  108  comprises a cell body having a window for transferring semiconductor wafer into or out of the cleaning cell  108  and a wafer holding part disposed at the center of the cell body which could be rotated by an actuator disposed at the bottom of the cleaning cell  108  with a speed of 10 to 4000 rpm. The wafer holding part comprises 3 pins with a small angled step at the top of each pin which positions the wafer within the cleaning cell  108  and a mechanical chuck disposed on each pin which could be activated by spinning. And when the wafer holding part spins, the mechanical chuck closes and holds the wafer tightly to prevent relative motion between the semiconductor wafer and the pins; when the wafer holding part stops spinning, the mechanical chuck opens and the wafer could be pick up by the mainframe transfer robot. 
     The cleaning cell  108  is configured with one front side nozzle, one backside nozzles, and one movable nozzle. The front side nozzle which is disposed on and extends from the upper portion of the cell body of the cleaning cell  108  provides DI water to the front surface of a semiconductor wafer. The backside nozzle which is disposed on and extends from the lower portion of cell body of the cleaning cell  108  provides DI water to the backside of the semiconductor wafer. The movable nozzle which is disposed on the central section of the cell body of the cleaning cell  108  and can radially move to the edge of a processing wafer provides mixed acid and dioxide to the edge bevel of the semiconductor wafer while working and moves away from the center of body of the cleaning cell during the semiconductor wafer transfer. The movement of the movable nozzle is controlled by an actuator. The cleaning cell  108  also comprises a lid disposed at the top of the body which prevents fluid splashing out of the cleaning cell and contaminating the parts of the present system. For more detailed description of the said cleaning cell  108 , see WO 03/087436, entitled “Electropolishing and/or electroplating apparatus and methods”, the entire content of which is incorporated herein by reference. 
     The mainframe  11  also comprises a fluid distribution system which comprises a electrolyte tank  109  located at the bottom part of the mainframe  11 , which supplies plating electrolyte to each electroplating cell  107 . With reference now to  FIG. 6 , the electrolyte tank  109  is separated into a lower cell electrolyte tank  191  and a upper cell electrolyte tank  192 . The lower cell electrolyte tank  191  is fluidly connected to the lower cell bodies of the electroplating cells  107  to provide lower cell feed electrolyte to the electroplating cells  107 , and the upper cell electrolyte tank  192  is fluidly connected to the upper cell body of the electroplating cells  107  to provide upper cell feed electrolyte to the upper cell bodies of the electroplating cells  107  for electroplating. The lower cell electrolyte tank  191  and the upper cell electrolyte tank  192  is connected to electroplating cell  107  with an electrolyte supply line  311  and  321  through pump  313  and valves respectively which comprise a two-way valve  315 , a check valve  316  and control valve  312 . Preferably, the electrolyte line connecting the maintank  109  to the electroplating cell  107  is coupled with a filter  317  to filter the impurities and a flow-meter  314  with analog output to monitor the flow rate. The maintank  109  is configured with a temperature sensor and a chiller to maintain the temperature of the electrolyte both in the lower cell electrolyte tank and the upper cell electrolyte tank at a fixed temperature. The lower cell electrolyte tank and upper cell electrolyte tank also respectively connects to a metrology tool  351  by two additional pipes  321  to provide a sample of the electrolyte to the metrology tool  351  which may monitor the concentration of components of the electrolyte in the lower cell electrolyte tank and upper cell electrolyte tank. 
     The fluid distribution system also comprises a chemical tank  330  where acid and dioxide are mixed homogeneously and then are provided to the movable nozzle in cleaning cells  108 . The chemical tank  330  connects to the chemical metrology tool  351  through a pipe  352  to provide a sample of the mixed chemicals made from the acid and dioxide to the metrology tool  351  to monitor the concentration of the components of the mixed chemicals. The mixed chemicals in the chemical tank  330  is transferred to the movable nozzle of the cleaning cell  108  through pump  353  and serial valves which preferably include a two-way manual valve  355 , control valve  352  and two-way pneumatic valve  359  for removing the deposited metal at the edge bevel of the wafer after electroplating. Preferably, the pipe connected the chemical tank  330  and the cleaning cell  108  interconnects a filter  357  to filter the impurities and a flow-meter  354  with analog output to monitor the flow rate. 
     The system in accordance with the present invention also comprises a dosing system  361 . The dosing system  361  electrically connected to an electrical control module (which will be described in details in the following context) will dose the required amount of metal ions or organic additives to lower cell electrolyte tank and upper cell electrolyte tank of the electrolyte tank  109  depending on algorithm provided by operator and the analyzing results from the chemical analyzing tool  351  to keep the stable electro-deposition performance of the electrolyte and the edge bevel removal performance of the mixed chemicals. 
     Referring to  FIG. 5 , in the present embodiment, there are two thermal treatment chambers  104  which are positioned in parallel in the mainframe  11  and connected to the factory interface  10 . The thermal treatment chamber  104  preferably comprises a rectangle shape body with two windows, one window facing against the mainframe  11  which is the heating cell window  421  and the other window facing against the factory interface  10  which is the cooling cell window  523 . The thermal treatment chamber  104  also comprises a heating plate  411  disposed within the body of thermal treatment chamber  104  which is near the heating cell window  421 , a cooling plate  413  disposed within the body which is near the cooling cell window  423 , and two wafer holders  431 , 433  respectively disposed at opposite sides of the heating plate  411  or cooling plate  413 . The wafer holders  431 , 433  are used for receiving a semiconductor wafer from the mainframe transfer robot  106 , loading the wafer onto the heating plate  411  or cooling plate  413 , transferring the wafer from heating plate  411  to cooling plate  413  and transferring the wafer to the front interface robot  102 . The wafer holder  411  or  413  comprises an arm  439  which is connected to an actuator  438  comprising two step or servo motors, and is configured with a supporting ring  437  with a plurality of support fingers thereon. The wafer holder  431  of the thermal treatment chamber  104  may rotates and moves vertically with the control of the actuator  438 . The thermal treatment chamber  104  also comprises a lid  441  with two fluid distribution parts  448 , 449  on the lid  441  and a fluid line  443  fluidly connected with the fluid distribution parts  448 , 449 . Each fluid distribution part  449  is positioned over one of heating plate  411  and the cooling plate  413  to provide required fluid into the thermal treatment chamber, such as mixture of N 2  and H 2 . The distribution part  449  over the heating plate  411  provides hot fluid to the front surface of the wafer to realize a double side heating of the wafer, with the heating plate heating the backside of the wafer. The distribution part  448  over the cooling plate  413  provides cool fluid to the front side of the wafer to realize a double side cooling, with the cooling plate cooling the backside of the wafer. This double-side thermal treatment mechanism provides a uniform thermal treatment process and reduces the thermal stress induced bowing of the wafer, and, together with the ability of thermal treating multiple wafers in the thermal treatment chamber, greatly increases the efficiency and throughput of the thermal treatment chamber. 
     The mainframe  11  further comprises an electrical control module at the back of the mainframe. The block diagram of the electrical control module is shown in the  FIG. 4 . The electrical control module typically comprises a host computer with a user interface in connection with the module, robot control system, motor driver, I/O interface chassis and plating power control board. The host computer is the key control equipment of the electrical control module, which provides all the I/O ports, RS232 ports and the motion control board. Host computer transmits the signals via I/O interface chassis to every process cell which needs the control signal for flow control, such as the electrolyte flow control of the electroplating cell and DI water or acid flow control of nozzles of the cleaning cell. Plating power control board, which electrically connected to the I/O interface chassis and the electroplating cell  107 , provides adjustable high voltage/current for the high power consumptions for the electroplating cell  107 . The host computer transmits all signals of the control parameters via robot control system to control the mainframe transfer robot and front interface robot. However, robot control system may be a stand-alone computer which communicates with host computer via RS232 port, so the robot control system still could control the mainframe transfer robot and the front interface robot without the host computer. The motor driver, which electrically connects to the host computer and servo/step motors of the electroplating cell, cleaning cell and the thermal treatment chamber respectively, transfers the control signal from the motion control board of host computer to servo/step motors of the thermal treatment chamber, the clean cell or the electroplating cell, and the encoding signal that servo/step motors feedback to host computer. 
     It should be noted that the whole electrochemical deposition process should be performed in a clean environment, so the system according to the present invention is preferably enclosed by panels. There are transparent windows configured on part of the panels so that the electrochemical plating process could be under monitoring by the operator. The panels are removable or configured to provide openings for convenience of performance maintenance. 
     In operation, the front interface robot  102  transfers a wafer from the pods  192  to the wafer aligner  191 . Then the wafer received by the wafer aligner  191  is rotated to a prearranged orientation by the wafer aligner  191  to facilitate the wafer to be precisely controlled in the next processes. After wafer alignment, the front interface robot  102  will transfer the wafer into wafer delivery cassettes  103  for further transportation into the mainframe  11 . 
     The mainframe transfer robot  106  transfers a semiconductor wafer from the wafer delivery cassette  103  into wafer holder assembly  105  or from an electroplating cell  107  to a cleaning cell  108  of the mainframe or from the cleaning cell  108  into the thermal treatment chamber  104 . The robot  106  is a transfer robot commonly known to persons skilled in the relevant field of technology, which preferably comprises a plurality of transfer arms. In this present embodiment, the mainframe transfer robot  106  comprises two transfer arms, which can be operable independently. The mainframe transfer robot  106  may rotate around a Z-axis shown in  FIG. 2  and move up and down vertically. The two robot arms of the mainframe transfer robot  106  may be controlled to extend and retract for transferring semiconductor wafers into or out of the electroplating cells  107  or the cleaning cells  108 , also to flip the semiconductor wafers to meet the requirements of different processes, for example, semiconductor wafers should be disposed downwardly in the electroplating process, but upwardly in the cleaning process. 
     For the process, firstly, the wafer holder assembly  105  stays at a receiving position and the chuck  511  of the wafer holder assembly  105  is at an open status. The mainframe transfer robot  106  picks up a semiconductor wafer from the delivery cassette  103  which disposed in between the mainframe  106  and the factory interface  10 , flips it face downward and transfers it to the vapor phase pre-wet device, where the pre-wet device is an independent module as shown in the figure. The pre-wet device splashes vapor to the front surface of the wafer and forms a thin layer of pre-wet liquid on it. Then the mainframe robot transfers the wafer into the chuck of wafer holder assembly  105 , and positions it on the cathode contact in the wafer holder assembly. After the arms of the mainframe transfer robot  106  retracts out of the wafer holder assembly  105 , the chuck of the wafer holder assembly  105  closes and holds the semiconductor wafer in tight contact with the cathode spring. And the backside of the semiconductor wafer is well sealed to prevent the backside of the wafer in contact with electrolyte during plating. The servo motor  525  begins rotating and thereby wafer holder assembly  105  starts spinning the wafer. The step motor  523  rotates to carry the wafer holder assembly  105  to a certain angle relative to the z direction and then step motor  521  moves the wafer holder assembly  105  along the z direction to a pre-process position to make the edge of the chuck  511  just over the liquid level of electroplating cell  107 . Thereafter motor  523  starts rotating the wafer holder assembly  105  back to vertical position, and brings the wafer holder assembly  105  into the electroplating cell  107  and thereby makes the front surface of the semiconductor wafer in contact with the electrolyte in the upper cell body  702  of the electroplating cell  700 . After that, the electroplating process starts. By controlling the waveform, working sequence and time of multiple anodes and electrolyte flow rate, a uniform metal film could be deposited on the semiconductor wafer. For more detailed electroplating process, see U.S. Pat. No. 6,391,166, entitled “plating apparatus and methods”, and the entire content of which is incorporated herein by reference. 
     In another embodiment, the vapor phase pre-wet device is integrated on the wafer holder assembly. In process the mainframe robot picks up the wafer from the delivery cassette and transfers it into the wafer holder assembly. Before the wafer holder assembly carries the wafer into the electrolyte, the pre-wet device moves in and slashes vapor onto the wafer surface. When the pre-wet process is done, the wafer holder assembly then carries the wafer into the electrolyte and the same electroplating process is carried out as above. 
     After the electroplating process is completed, the wafer holder assembly  105  moves up and brings the semiconductor wafer out of the electrolyte of the electroplating cell  107 . When the wafer holder assembly  105  moves to a spin position, it rotates with the processed wafer with a large rpm to remove the residual electrolyte on the wafer surface. Then the wafer holder assembly  105  moves to the receiving position and the chuck  511  opens. The arm of the mainframe transfer robot  106  extends into the wafer holder assembly  105 , transfers the semiconductor wafer out and flips it to face upward. 
     Then the mainframe transfer robot  106  moves down until it reaches the level of the window of the cleaning cell  108 , the arms of mainframe transfer robot  106  extends and transfers the semiconductor wafer into the cleaning cell  108 . When the semiconductor wafer is transferred into the cleaning cell  108 , the arm of mainframe transfer robot  106  moves down a little bit, places the semiconductor wafer on the three pins of the cleaning cell  108  and then moves out. The wafer holding part of the cleaning cell  108  which holds the wafer with three pins starts rotating controlled by the actuator. The mechanical chuck on the pins turns on and holds the semiconductor wafer tightly to prevent relative motion. Then the front surface nozzle of the cleaning cell turns on and splashes DI water from DI water facility onto the front side of the semiconductor wafer to pre-rinse and remove residual plating electrolyte. After the pre-rinse, the movable nozzle of the cleaning cell moves to the edge of the semiconductor wafer and splashes mixed chemicals from the chemical tank onto the edge bevel of the semiconductor wafer to etch off the deposited metal film on the edge bevel. The wafer holding part of the cleaning cell  108  spins with a large rpm to confine the chemicals at a narrow range along the edge of the wafer to prevent etching of the deposited metal film in the inner area. When the metal film at the bevel is completely removed, the movable nozzle moves away from the center of the cleaning cell and both front and back face nozzles turn on and splash DI water on both sides of the semiconductor wafer to rinse off the residual chemicals from etching. When the cleaning process is completed, the wafer holding part stops spinning and the mechanical chuck opens. The mainframe transfer robot  106  extends into the cleaning cell  108 , picks up the semiconductor wafer and transfers it out of the cleaning cell  108 . 
     When the electroplating and cleaning process of a wafer (first wafer) is ended, the mainframe transfer robot  106  will transfer the first wafer into the thermal treatment chamber  104  through the heating cell window  421  and place it on the first wafer holder  433 . While the arms of the mainframe transfer robot  106  move out of the thermal treatment chamber  104 , the first wafer holder  433  moves down to a pre-heating position to pre-heat the first wafer for a scheduled time. After the pre-heating process is ended, the first wafer holder  433  moves down and positions the wafer onto the heating plate  411  such that the wafer is in contact with the heating plate  411  and heated for a scheduled time. Once heating process of the first wafer is ended, the first wafer holder  433  moves up and transfers the wafer onto the cooling plate  413  for cooling process. And it should be noted that the heating plate  411  is free now. While the first wafer is in cooling process, another wafer (second wafer) which has been treated with the electroplating and cleaning process is transferred into the thermal treatment chamber  104  by the mainframe transfer robot  106  and received by the second wafer holder  431  and starts pre-heating and heating process. Thus the thermal treatment chamber  104  does thermal treatment for two wafers simultaneously. When cooling process of the first wafer is ended, the first wafer holder  433  moves up and brings it to a transfer position and the front interface robot  102  extends into and transfers semiconductor it out of the thermal treatment chamber  104 . And the cooling plate  413  is free now. After heating process of the second wafer is ended, the second wafer holder  431  transfers it onto the cooling plate  413  for cooling process. While the second wafer is in cooling process, another wafer (third wafer) is transferred into the thermal treatment chamber  104 , received by the first wafer holder  433  and is treated with the same processes (pre-heating, heating, and cooling process). The process performed in the thermal treatment chamber  104  described above depends on the assumption that the time for heating is longer than that for cooling. If the time for cooling is longer than that for heating, the difference in the process is that, when the first wafer has been heated on the heating plate  411  and is transferred to the cooling plate  413 , the second wafer will not be transferred into the thermal treatment chamber  104  immediately until the remaining cooling time for the first wafer is smaller than the heating time. When the thermal treatment process of a wafer is ended, the wafer is transferred out of the thermal treatment chamber  104  through the cooling cell window  423  and placed into the pod  192  by the front interface robot  102  for the next manufacture step, such as chemical mechanical polishing. 
     While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised with out departing from the basic scope thereof. The scope of the invention is determined by the claims that follow.