Patent Publication Number: US-2003234929-A1

Title: Method and system to reduce/detect a presence of gas in a flow of a cleaning fluid

Description:
[0001] The present invention relates to semiconductor manufacturing processes. More particularly, the present invention relates to a method and a system to reduce/detect a presence of gas in fluids employed in semiconductor manufacturing processes.  
       [0002] Formation of an integrated circuit requires multiple manufacturing steps and a variety of chemicals. To facilitate control of the chemical reactions, it is desired to remove chemical residue after certain manufacturing steps. To that end, cleaning fluids are employed.  
       [0003] One such cleaning fluid is deionized water. Deionized water is typically employed to clean residue produced by etching processes. Specifically, the deionized water, or deionized water vapor, is employed to remove chemical residue from a substrate.  
       [0004] Referring to FIG. 1, a conventional deionized water cleaning system  10  is employed in a metal-etch system  20 . Cleaning system  10  includes a reservoir  12 , a pump  16 , and a filter  18 . System  10  delivers deionized water to metal-etch system  20  by operation of pump  16 . Pump  16  extracts deionized water from reservoir  12  and directs the same into metal-etch chamber  20  via flow passages  22  and  26 . The operation of pump  16  often generates air bubbles in the flow of deionized water traversing flow passage  22 .  
       [0005] The presence of air bubbles in the deionized water decreases the amount of water in a unit volume. This reduces the amount of water available to remove post-etch residue from a substrate. This leads to an insufficient passivation process that may cause severe metal corrosion of conductive traces on the substrate.  
       [0006] For example, aluminum is often employed to create conductive traces on substrates. Chlorine is a chemical often employed during etch processes and is left as a residue on the substrate. Failure to provide a sufficient amount of water to remove the chlorine residue may produce hydrochloric acid. Hydrochloric acid corrodes the aluminum conductive traces. This may lead to catastrophic failure of the integrated circuit being fabricated on the substrate.  
       [0007] To avoid the aforementioned problem, prior attempts have been made to remove air bubbles from the flow of deionized water. To that end, connected between pump  16  and metal-etch chamber  20  is filter  18 , which traps and separates air from the flow of deionized water. The air then egresses from system  10  through a valve (not shown). A supply of deionized water is then released from outlet  26  to metal-etch chamber  20 . Often, filter  18  is unable to trap and separate bubbles that generate as a result of filter replacement or during the reservoir  12 .  
       [0008] Another prior art attempt to trap and separate air from a flow of deionized water is disclosed in U.S. Pat. No. 5,792,237 to Hung et al. Hung et al. disclose a method and an apparatus for eliminating trapped air from a liquid flow by utilizing a buffer tank and an electrical control box to supply a substantially air bubble-free liquid flow to semiconductor processing equipment. The method for eliminating trapped air from a liquid flow is carried out by first providing a liquid holding tank that has a top surface, a bottom surface and a generally cylindrical sidewall connecting the two surfaces. A first liquid inlet and a first liquid outlet are provided on the top surface. The first liquid inlet and first liquid outlet are placed in fluid communication with a cavity contained in the holding tank. A second liquid outlet is provided on or near a bottom surface of the tank. The second liquid outlet is placed in fluid communication with the cavity in the tank. A liquid is flowed into the first liquid inlet, and the cavity is filled substantially to the top. The liquid is flowed out of the first liquid outlet and into a liquid circulating means and re-enters the liquid flow into the first liquid inlet such that substantially all trapped air is accumulated at the upper portion of the liquid holding tank. A liquid that is substantially without trapped air is withdrawn from the second liquid outlet.  
       [0009] A need exists, however, to reduce/detect the presence of a gas in cleaning fluids that is less complicated than the prior art gas reduction/detection techniques.  
       SUMMARY OF THE INVENTION  
       [0010] The present invention provides a method and a system to reduce/detect the presence of gas in fluids employed in semiconductor manufacturing processes. One embodiment of the invention includes creating the flow of the cleaning fluid and impinging electromagnetic radiation upon a region of the flow. The electromagnetic radiation is sensitive to phase state changes in the flow, i.e., changes between liquid and gas so that gas bubbles in the liquid flow may be detected. The electromagnetic radiation is sensed and a signal is produced in response to phase state changes in the flow. The flow of the cleaning fluid is terminated in response to the signal. In accordance with another embodiment a system is provided that operates in accordance with the method. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a simplified block diagram view showing a prior art deionized water cleaning system;  
     [0012]FIG. 2 is a simplified block diagram of an etch system employing one embodiment of the present invention;  
     [0013]FIG. 3 is a detailed plan view of a phase state change sensor shown in FIG. 2;  
     [0014]FIG. 4 is a graph of magnitude vs. time of a signal produced by a sensor shown in FIGS. 2 and 3;  
     [0015]FIG. 5 is a simplified block diagram of an etch system employing the present invention in accordance with an alternate embodiment; and  
     [0016]FIG. 6 is a detailed plan view of an alternate embodiment of the phase state change sensor shown in FIG. 3. 
    
    
     DETAILED DESCRIPTION  
     [0017] Referring to FIG. 2, a processing system  30  in accordance with one embodiment of the present invention includes a processing chamber  32  for example, an etch chamber, and a gas panel  34  having supplies of process gases (not shown) and a vapor generator  36  and a processor  35  connected to control operation of processing system  30 . Processing system  30  may be employed to perform any etch process known in the art. For purposes of the present discussion, processing system  30  is employed to etch metallization on substrate  37  disposed in processing chamber  32 . As a result of the etch processes, residue remains on substrate  37 .  
     [0018] Vapor generator  36  is employed to remove residue from substrate  37  by injecting a cleaning fluid into processing chamber  32 . In one example, the cleaning fluid consists of deionized water vapor. To that end, vapor generator  36  is in fluid communication with processing chamber  32  and a supply of deionized water  40 . A pump  42  is in fluid communication with supply  40  to create a flow of the deionized water that propagates from supply  40  to vapor generator  36  over conduit  44 . Vapor generator  36  is in fluid communication with processing chamber  32  via conduit  38 .  
     [0019] To remove residue from substrate  37  it is important to precisely control the amount of deionized water vapor injected into processing chamber  32 . One problem, well known in the art, is the presence of gases, such as air, in a flow of deionized water vapor that presents as air bubbles. The presence of gases reduces an amount of deionized water vapor injected into processing chamber  32  at any moment in time. This can prevent removal of residue on substrate  37  and cause well known deleterious effects, e.g., corrosion of metallization on substrate  37 .  
     [0020] To precisely regulate the amount of deionized water vapor injected into processing chamber  32 , one embodiment of the present invention includes a phase state change sensor  46  coupled between vapor generator  36  and supply  40 . Phase state change sensor  46  senses phase state changes in a flow of the cleaning fluid propagating through conduit  44 . This enables detection of the presence of gas in the liquid cleaning fluid.  
     [0021] Referring to FIG. 3, phase state change sensor  46  includes a transmitter  50  to direct electromagnetic radiation  52  into a region  54  of conduit  44  through which a flow  56  of the cleaning fluid traverses. A receiver  58  is positioned to sense electromagnetic radiation  52  after impinging upon region  54 . Electromagnetic radiation  52  is selected to propagate through conduit  44  and be responsive to a phase state change in region  54 . In the present example, electromagnetic radiation  52  has a wavelength that is substantially shorter than the diameter of the conduit  44 . In an alternate embodiment, the transmission is of an acoustic wave. Receiver  58  produces a signal  60  in response to the phase state change information contained in electromagnetic radiation  52 , discussed more fully below with respect to FIG. 4.  
     [0022] Referring to FIGS. 1, 2,  3  and  4 , signal  60  contains information concerning the presence of a gas, such as air bubble  61 , in flow  56  of liquid cleaning fluid. Signal  60  is transmitted to a warning apparatus  62 , shown in FIG. 2, that is in electrical communication with phase state change sensor  46 . Warning apparatus  62  may be any type known in the art that can provide a visual stimuli, audible stimuli or that is readily perceivable by an individual (not shown) processing system  30 .  
     [0023] Referring to both FIGS. 2 and 3, the present invention facilitates terminating or modifying an etch process before water vapor, produced by vapor generator  36  from flow  56  containing air bubble  61 , reaches processing chamber  32 . Specifically, the flow of deionized water to vapor generator  36  would be terminated by, for example, deactivating pump  42 . Air would be removed, bled, from conduit  44  and/or vapor generator  36  using known techniques. There after flow  56  could once again commence, free of air. This would prevent accumulation of air bubble  61  in vapor generator  36  facilitating regulation of the amount of moisture present in water vapor propagating along conduit  38  and into processing chamber  32 . As a result, the aforementioned deleterious effects would be avoided.  
     [0024] Referring to FIGS. 3, 4 and  5 , in an alternative embodiment, receiver  58  would be in electrical communication with processor  35 . In this manner, processor  35  would operate on signal  60  and cease operation of pump  42  were phase state change information contained in signal  60 . In addition, visual stimuli and/or audible stimuli could be generated on a monitor  70  and speaker  72 , respectively, that are in electrical communication with processor  35 .  
     [0025] In yet an alternative embodiment, processor  35  may be employed to analyze an amount of gas that propagates to vapor generator  36  over a period of time. As a result, termination of flow  56  could be dependent upon an amount of gas that is present in flow  56 , measured during a period of time, as opposed to the occurrence of any amount of gas in flow  56 . To that end, flow  56  may be terminated based upon signal  60  having predetermined characteristics indicative of the phase state change information contained therein. Alternatively the process may be modified to, for example, increase its duration so as to provide additional vapor.  
     [0026] With respect to FIGS. 3, 4 and  5 , for example, processor  35  could operate on signal  60  and terminate flow  56  were signal  60  to have a predetermined magnitude. This predetermined magnitude would be selected to be indicative of an amount of gas that is in excess of a threshold quantity, above which deleterious effects to substrate  37  would occur. The exact quantity would vary depending upon several factors, such as the volume and rate of flow  56 . As a result the exact quantity is dependent upon, inter alia, the size of conduit  44 , the type of cleaning liquid, pumping rate of pump  42 , as well as the chemistry employed during an etch process. Alternatively, processor  35  could terminate flow  56  were signal  60  to include, during a segment of time, a predetermined number of peaks  60   a , or a plurality of peaks having a predetermined magnitude. In one example, processor  35  would terminate flow  56  by deactivating pump  42 .  
     [0027] The embodiments of the present invention described above are exemplary, and it should be understood that several modifications may be made thereto while remaining within the scope of the invention. For example, as shown in FIG. 6, receiver  158  may be positioned to detect electromagnetic radiation, produced by transmitter  150 , that is reflected from region  154 , as opposed to sensing electromagnetic radiation  152  that propagates through conduit  144 . The scope of the invention should not be determined with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.