Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a divisional application of co-pending prior U.S. patent application Ser. No. 10/186,941 filed on Jun. 28, 2002 entitled “METHOD AND APPARATUS FOR FLUID DELIVERY TO A BACKSIDE OF A SUBSTRATE”, which is herein incorporated by reference in its entirety for all purposes. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to semiconductor fabrication and, more particularly, to a method and apparatus for reducing consumption of fluid delivered to a backside of a substrate during a cleaning operation.  
           [0003]    Cleaning chemistries for single wafer cleaning operations are formulated for specific applications and are designed so that a small amount of the chemistry applied to the surface of the wafer is sufficient for cleaning the surface of the wafer. That is, a thin film of the fluid supplied to the surface of the wafer produces the desired cleaning effects. Because of the high costs for the purchase and the disposal of the cleaning chemistries, it is desired to only use the amount of chemistry that is necessary for effective cleaning.  
           [0004]    Applying a thin film of the cleaning chemistry to a top surface of a semiconductor substrate is easily accomplished as gravity is working to assist the process. A small amount of fluid can be puddled on a top surface of the substrate and the substrate can be rotated around its axis to spread the fluid over the surface of the substrate without spinning the fluid off of the wafer surface. The speed of the rotation can be used to control the thickness of the fluid layer. However, the cleaning chemistry can not be applied to the backside of the wafer in this manner as the fluid will be lost. FIG. 1 is a schematic diagram of a wafer having cleaning chemistries applied to a top and a backside of the wafer. Wafer  100  has a thin film applied to a top surface of the wafer by top nozzle  104   a . However, bottom surface  106  can not retain the fluid from bottom nozzle  104   b , where as much as 95% of the fluid delivered to bottom surface  106  can be lost. Thus, conventional spray-on techniques are not effective for low-volume chemistry cleaning of the wafer backside.  
           [0005]    One attempt to minimize the fluid loss associated with cleaning the backside of the wafer is to clean the top side of the wafer and then flip the wafer over to clean the other side. However, the throughput for the cleaning process is cut in half since the cleaning is performed sequentially. Accordingly, this alternative is not a viable one. Another attempt to address the shortcomings of the prior art is to provide a reservoir containing the cleaning chemistry and place the backside of the wafer in contact with a meniscus formed by the cleaning chemistry. FIG. 2 is schematic diagram of a wafer coming into contact with a meniscus of a cleaning solution in a reservoir. Bottom surface  106  of wafer  100  is brought into contact with meniscus  108 . Meniscus  108  is formed when the cleaning chemistry is filled to the top of reservoir  110 . However, a shortcoming with the use of a reservoir is due to each of the cleaning solutions having different surface tensions. Thus, the meniscus height can be different for each of the cleaning chemistries. Consequently, the distance for the wafer to be brought into contact with the cleaning chemistry will change with the different cleaning chemistries. This configuration is also difficult to implement mechanically. Additionally, the contents of reservoir  110  will have to be changed over time as the cleaning chemistry becomes dirty, which negatively impacts throughput and control of contaminants.  
           [0006]    In view of the foregoing, there is a need for a method and apparatus for reducing the volume of cleaning chemistry applied to the backside of a wafer in a single-wafer cleaning tool in a manner that does not negatively impact the throughput or defect rate.  
         SUMMARY OF THE INVENTION  
         [0007]    Broadly speaking, the present invention fills this need by providing a nozzle and delivery system for applying a minimal amount of fluid to the backside of a semiconductor substrate. It should be appreciated that the present invention can be implemented in numerous ways, including as an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.  
           [0008]    In accordance with one aspect of the present invention, a nozzle is provided. The nozzle includes an inner cylindrical tube having a top opening and a bottom opening. An upper cap overlying a top portion of the inner cylindrical tube is included. The upper cap is moveably disposed over the inner cylindrical tube. The upper cap includes a top with at least one hole defined therein. The top includes a sidewall extending therefrom.  
           [0009]    In accordance with another aspect of the invention, a fluid delivery system for cleaning a backside of a semiconductor substrate is included. The fluid delivery system includes a shaft configured to rotate about an axis of the shaft. An arm having a first end and a second end is included. The first end is affixed to the shaft and is in communication with a fluid source. A cap moveably disposed over the second end of the arm is included. The cap has a top with at least one hole defined therein. The top includes a sidewall extending therefrom. The sidewall extends over a portion of the second end of the arm.  
           [0010]    In accordance with yet another aspect of the invention, a method for reducing an amount of a cleaning chemistry applied to a backside of a wafer during a cleaning operation is provided. The method initiates with positioning a nozzle having a moveable top under a backside of a wafer to be cleaned. Then, a fluid flow occurs through the moveable top to raise the moveable top into close proximity with the backside of the wafer. Next, a fluid barrier is created between a top surface of the moveable top and a backside of the wafer while the fluid flows through the moveable top. Then, the backside of the wafer is cleaned by the fluid barrier.  
           [0011]    It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0013]    [0013]FIG. 1 is a schematic diagram of a wafer having cleaning chemistries applied to a top and a backside of the wafer.  
         [0014]    [0014]FIG. 2 is schematic diagram of a wafer coming into contact with a meniscus of a cleaning solution in a reservoir.  
         [0015]    [0015]FIG. 3 is a simplified schematic diagram of a chemical delivery system in accordance with one embodiment of the invention.  
         [0016]    [0016]FIG. 4 is a cross-sectional schematic diagram of the nozzle of FIG. 3 in an activated state in accordance with one embodiment of the invention.  
         [0017]    [0017]FIG. 5A is a cross-sectional view of a schematic diagram of a sealed nozzle in a relaxed state in accordance with one embodiment of the invention.  
         [0018]    [0018]FIG. 5B is a cross-sectional view of a schematic diagram of the nozzle of the FIG. 5A in an active state.  
         [0019]    [0019]FIG. 6A is a cross-sectional view of a schematic diagram of a nozzle having a bellows seal in accordance with one embodiment of the invention.  
         [0020]    [0020]FIG. 6B is a cross-sectional view of a schematic diagram of a nozzle having a continuous wall with a thinned section in an extended position in accordance with another embodiment of the invention.  
         [0021]    [0021]FIG. 6C is a cross-sectional view of a schematic diagram of the nozzle of FIG. 6B having a continuous wall with a thinned section in a retracted position.  
         [0022]    [0022]FIG. 7A is a top view of a nozzle for delivering a fluid to the backside of a wafer in accordance with one embodiment of the invention.  
         [0023]    [0023]FIG. 7B is a top view of an alternative orifice arrangement to FIG. 7A.  
         [0024]    [0024]FIG. 7C is a top view of another alternative nozzle configuration in accordance with one embodiment of the invention.  
         [0025]    [0025]FIG. 8 is a flowchart of the method operations reducing an amount of a cleaning chemistry applied to a backside of a wafer during a cleaning operation in accordance with one embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Several exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings. FIGS. 1 and 2 are discussed above in the “Background of the Invention” section. As used herein, the term about refers to a reasonable approximation of the specific range provided.  
         [0027]    [0027]FIG. 3 is a simplified schematic diagram of a chemical delivery system in accordance with one embodiment of the invention. Nozzle  126  is positioned under the backside of wafer  120 . Nozzle  126  is disposed over an end of supply arm  124 . In one embodiment, supply arm  124  is a cylindrical tube compatible with the cleaning chemicals used to clean the backside of wafer  120 . It should be appreciated that supply arm  124  acts as an end effector. Another end of supply arm  124  is affixed to shaft  122 . In one embodiment, shaft  122  rotates about its axis so that nozzle  126  can move in a radial direction under the backside of wafer  120 . Fluid delivery source  128  is in communication with supply arm  124 . One skilled in the art will appreciate that fluid delivery source  128  can include a pump for delivering a cleaning chemistry to the backside of wafer  120  through nozzle  126 , in one embodiment.  
         [0028]    It should be appreciated that wafer  120  can be cleaned after a semiconductor fabrication process, such as chemical mechanical planarization (CMP), etch operations, etc. Examples of single wafer cleaning chemistries commonly used for post-etch cleaning include commercially available proprietary chemicals, such as EKC 640, EKC 6800 and Ashland NE89. Commercially available non-proprietary chemicals used for post chemical mechanical planarization cleaning are generally known and include SC-1 (NH 4 OH/H 2 O 2  mixture), SC-2 (HCl/H 2 O 2  mixture), dilute HF or ozonated DIW (H 2 O/O 3 ).  
         [0029]    Still referring to FIG. 3, top nozzle  121  can add a cleaning agent to the top surface of wafer  120  simultaneously while cleaning the backside of the wafer. Here, the same cleaning chemistry or a different cleaning chemistry can be added to each side of wafer  120 . For example, where a post-etch cleaning operation is being performed on the top surface of wafer  120 , there may be photoresist pieces deposited on the backside of the wafer which carried over from a lithography step. Accordingly, different chemistries can be applied to the top surface and the backside of wafer  120  simultaneously due to the efficiency enabled through the nozzle described herein. Thus, the system throughput can be increased by performing separate cleaning operation on the two sides of wafer  120  simultaneously.  
         [0030]    [0030]FIG. 4 is a cross-sectional schematic diagram of the nozzle of FIG. 3 in an activated state in accordance with one embodiment of the invention. Nozzle  126  is disposed over a top portion of supply arm  124 . A degree of travel of nozzle  126  in an up and down direction is limited in one embodiment. That is, shoulder  134  of nozzle  126  is configured so as to be unable to move past protrusion  136  of supply arm  124 . Here, supply arm  124  is fixed and protrusion  136  acts as a travel limiter for the moveable nozzle. Nozzle  126  moves to a raised position as fluid is delivered through supply arm  124 . Nozzle  126  includes orifice  132  which is defined through a top surface of the nozzle. Orifice  132  is configured to provide some back-pressure, thereby causing nozzle  126  to raise while fluid is escaping through the orifice.  
         [0031]    Still referring to FIG. 4, nozzle  126  continues to rise as fluid is provided from supply arm  124 . Eventually, a thin film, i.e., fluid barrier, is defined between wafer  120  and a top surface of nozzle  126 . The pressure exerted by nozzle  126  on the thin film, which has a thickness  130  defined between the backside of wafer  120  and a top surface of nozzle  126 , becomes insufficient to further compress the thin film. In one embodiment, the thin film is composed of the cleaning chemistries mentioned above. It should be appreciated that the thin film acts as a fluid barrier and a fluid bearing as wafer  120  rotates and nozzle  126  is radially swept across the backside of the rotating wafer. Top surface of nozzle  126  is substantially flat and self-aligns to the backside of the wafer. The self alignment is due to the sliding mechanism of nozzle  126  over supply arm  124  caused by the flow rate and pressure at which the cleaning chemistry is delivered. It should be appreciated that the top surface of nozzle  126  does not physically contact the backside of the wafer  120 . That is, the top surface of nozzle  126  is in contact with the backside of wafer  120  through the fluid barrier interface. Opposing surfaces of the fluid barrier physically contacts the backside of wafer  120  and a top surface of nozzle  126 . Thus, should wafer  120  have a wobble or run-out as it rotates, nozzle  126  will accommodate the wobble and run out and not come in contact with the backside of the wafer. In one embodiment, the thin film between the backside of wafer  120  and a top surface of nozzle  126  has a thickness of between about 0.1 millimeter (mm) and about 2 mm.  
         [0032]    It should be appreciated that a portion of the fluid delivered to nozzle  126  of FIG. 4 can escape through gap  138  between nozzle  126  and supply arm  124 . Alternatively, the nozzle  126  and supply arm  124  can be machined so that gap  138  is minimized, i.e., the tolerance between the nozzle inner diameter at shoulder  134  and the supply arm outer diameter does not allow for the fluid to escape. The configuration of nozzle  126  allows for a lower flow rate to be applied because the losses of the fluid applied to the backside of the wafer are reduced. In one embodiment, a flow rate of between about 25 milliliters (ml) and about 50 ml is sufficient to supply the necessary backpressure to lift nozzle  126  and to create a fluid barrier Of course, the flow rate can change depending on the application, cleaning chemistry, pump, etc. Thus, the above flow rate is meant to be exemplary and not restrictive.  
         [0033]    [0033]FIG. 5A is a cross-sectional view of a schematic diagram of a sealed nozzle in a relaxed state in accordance with one embodiment of the invention. Nozzle  126  is disposed over supply arm  124 . As there is no fluid being delivered from supply arm  124 , nozzle  126  is in a relaxed position. Thus, gap  142  between the backside of wafer  120  and a top surface of nozzle  126  is larger here. O-ring  140  acts as a seal between nozzle  126  and supply arm  124 . It should be appreciated that the composition of O-ring  140  can be any material suitable for allowing the up and down motion of nozzle  126  and the material is chemically compatible with the cleaning chemistries. Similarly, the composition of nozzle  126  and supply tube  124  can be any material suitable for the cleaning process that is compatible with the cleaning chemicals.  
         [0034]    [0034]FIG. 5B is a cross-sectional view of a schematic diagram of the nozzle of the FIG. 5A in an active state. Here, a fluid flow through supply arm  124  provides the pressure to raise nozzle  126  while fluid escapes through orifice  132 . A fluid barrier is formed between the backside of wafer  120  and a top surface of nozzle  126 . The fluid barrier also acts as a fluid bearing, which in essence allows for the top surface of nozzle  126  to be in contact with the backside of wafer  120  through the fluid barrier interface. In one embodiment, the fluid is a cleaning chemistry. For example a post-etch or post CMP cleaning chemistry can be delivered to nozzle  126  through supply arm  124  for cleaning the backside of wafer  120 . O-ring  140  seals a gap between nozzle  126  and supply arm  124 , thereby forcing the fluid through orifice  132  without restricting the movement of nozzle  126 . In one embodiment, the flow rate of the cleaning chemistry from supply arm  124  is about less that 100 milliliters (ml)/minute. In a preferred embodiment, the flow rate is about less that 50 ml/minute.  
         [0035]    [0035]FIG. 6A is a cross-sectional view of a schematic diagram of a nozzle having a bellows seal in accordance with one embodiment of the invention. Nozzle  126 , which is disposed over an end of supply arm  124 , includes bellows seal  142 . As is known, bellows seal  142  contracts and expands as nozzle  126  moves from a relaxed state to an active state. It should be appreciated that there is no need for the protrusion and shoulders with reference to FIGS. 4, 5A and  5 B, since bellows seal  142  acts as a travel limiter. In one embodiment, top surface  144  of nozzle  126  provides a substantially flat surface where the fluid, i.e., cleaning chemistry, can reside as the nozzle moves radially across the wafer and as the wafer rotates. While some fluid will be lost, the losses are significantly reduced as compared with spray-on techniques of the prior art. In addition, the flow of fluid through orifice  132  is constantly replenishing any losses and maintains the fluid barrier which cleans the backside of the wafer.  
         [0036]    [0036]FIG. 6B is a cross-sectional view of a schematic diagram of a nozzle having a continuous wall with a thinned section in an extended position in accordance with another embodiment of the invention. Supply arm  147  is a continuous wall with thinned section  145 . As fluid flows through opening  132  of nozzle  126 , a back pressure forces the top portion of nozzle  126  to an extended state. Thinned section  145  acts as an extension point as it is flexible and the back pressure provides the necessary force to lift the top portion of nozzle  126  under a pressure or flow of fluid. In one embodiment, thinned section  145  has a thickness between about 0.01 mm and about 0.5 mm. Supply arm  147  can be fabricated from any suitable material such as plastic or metal that is compatible with the cleaning chemistries and is capable of being thinned while maintaining sufficient strength and pliability.  
         [0037]    [0037]FIG. 6C is a cross-sectional view of a schematic diagram of the nozzle of FIG. 6B having a continuous wall with a thinned section in a retracted position. Here, the flow of fluid causing the back pressure has been stopped and the top portion of nozzle  126  retracts. The retraction is due to the folding of thinned section  145  of supply arm  147 . In one embodiment, the range of travel between full extension and full retraction is less than 2 millimeters.  
         [0038]    [0038]FIG. 7A is a top view of a nozzle for delivering a fluid to the backside of a wafer in accordance with one embodiment of the invention. Orifice  132  is substantially centered on top surface  144  of cylindrically shaped nozzle  126 . Nozzle  126  can be referred to as a cap. It should be appreciated that orifice  132  has a suitable diameter for allowing enough back pressure to lift nozzle  126  while allowing a fluid flow out of the orifice to obtain a suitable fluid barrier. In one embodiment, the diameter of nozzle  126  is between about 5% and 30% of the diameter of the wafer being cleaned. In a preferred embodiment, the diameter of nozzle  126  is between about 25% of the diameter of the wafer being cleaned. In another embodiment, the diameter of the nozzle is configured to enable completion of the cleaning of the backside of the wafer within about 5 seconds, when the nozzle is moving radially across the wafer as the wafer is rotating.  
         [0039]    [0039]FIG. 7B is a top view of an alternative orifice arrangement to FIG. 7A. Here, a plurality of orifices  146  are distributed over top surface  144  of nozzle  126 . In one embodiment, orifices  146  have a diameter between about 0.5 millimeters (mm) and about 5 mm. The holes defined by orifices  146 , have a suitable diameter for allowing enough back pressure to lift nozzle  126  while allowing a fluid flow out of the orifice to obtain a suitable fluid barrier. It will be apparent to one skilled in the art that any suitably-shaped hole or orifice can be used here.  
         [0040]    [0040]FIG. 7C is a top view of another alternative nozzle configuration in accordance with one embodiment of the invention. Nozzle  152  is configured as an elongated cylinder having a plurality of orifices  132 . In one embodiment, length  150  of nozzle  152  is slightly large than the radius of the wafer being cleaned. One skilled in the art will appreciate that by defining the length of the nozzle longer than a radius of the wafer, the backside of the wafer can be cleaned in one rotation of the wafer.  
         [0041]    [0041]FIG. 8 is a flowchart of the method operations reducing an amount of a cleaning chemistry applied to a backside of a wafer during a cleaning operation in accordance with one embodiment of the invention. The method initiates with operation  154  where a nozzle having a moveable top is positioned under a backside of a wafer. A suitable nozzle is described with reference to FIGS.  3 - 7 C. The method then advances to operation  156  where a fluid flow through the moveable top moves the moveable top into close proximity with the backside of the wafer. The fluid flow causes a back pressure which in turn, lifts the moveable top towards the backside of the wafer. In one embodiment, the moveable top is limited in the amount of travel towards the backside of the wafer. In another embodiment, the moveable top slides along a fixed supply arm in a manner that allows the moveable top to self align to the backside of the wafer being cleaned.  
         [0042]    The method of FIG. 8 then proceeds to operation  158  where a fluid barrier is created between the top surface of the moveable top and the backside of the wafer. Here, the fluid flow through an orifice in a top surface of the moveable top causes the moveable top to trap a fluid barrier between the backside of the wafer and the top surface. The fluid barrier acts as a fluid bearing as the wafer and the nozzle move. In one embodiment, the fluid is a post etch or post CMP cleaning chemistry. The method then advances to operation  160  where the backside of the wafer is cleaned with the fluid barrier. Here, the fluid barrier cleans the backside of the wafer since the nozzle is in close proximity to the backside of the wafer and the fluid flow maintains the fluid barrier. For example, the nozzle can be attached to a supply arm as described with reference to FIG. 3. Due to the configuration of the nozzle, with reference to FIGS.  4 - 6 , the loss of the fluid is significantly reduced and the residence time of the fluid barrier can be controlled by the speed of the movement of the wafer and the nozzle. In one embodiment, where the surface area of the top surface of the nozzle is about 25% of the surface area of the backside of the wafer, the backside of the wafer is cleaned in about 5 seconds.  
         [0043]    In summary, the present invention provides a nozzle configured to apply a thin coating of fluid, i.e., fluid barrier, to the backside of a wafer. In one embodiment, the thin coating of fluid is a cleaning chemistry for a post-etch cleaning or a post CMP cleaning. The nozzle makes use of an outer cylinder having an orifice on a top surface slidably disposed over a fixed inner cylinder in one embodiment. The sliding mechanism allows the nozzle to self align to the backside of the wafer. The top surface allows a fluid barrier to be formed so that the cleaning chemistry has a long enough residence time on the wafer backside to clean the wafer backside. In one embodiment, a system configured to perform different cleaning operations simultaneously on a top surface of a wafer and a bottom surface of a wafer in an efficient manner is enabled by the nozzle configuration. Thus, the throughput of the system is enhanced by performing different cleaning operations on the top and bottom surfaces of the wafer at the same time.  
         [0044]    The invention has been described herein in terms of several exemplary embodiments. For example, representative shapes and sizes of the nozzle, i.e., cap, have been described herein, however any suitable shape and size nozzle can be used to apply the cleaning chemistry to the backside of the wafer. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. The embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims.

Technology Category: 4