Abstract:
In one aspect, an apparatus is provided. The apparatus comprises a chamber; a plurality of rollers adapted to support a wafer in a vertical orientation within a chamber; a pair of brushes adapted to scrub a first and a second side of the wafer respectively; a first spray bar adapted to spray a liquid on the wafer to form a meniscus on the wafer as the wafer is lifted out of the chamber; and a second spray bar adapted to direct a vapor to the meniscus, the vapor being adapted to lower a surface tension of the liquid at the meniscus to perform Marangoni drying of the wafer as the wafer is lifted out of the chamber. Numerous other aspects are provided.

Description:
[0001]    This application is a division of, and claims priority to, United States Non-Provisional patent application Ser. No. 10/461,889, filed Jun. 13, 2003, and titled, “SINGLE WAFER METHOD AND APPARATUS FOR DRYING SEMICONDUCTOR SUBSTRATES USING AN INERT GAS AIR-KNIFE,” (Attorney Docket No. 7348) which claims priority to U.S. Provisional Patent Application Ser. No. 60/388,277, filed Jun. 13, 2002, and titled, “SINGLE WAFER METHOD AND APPARATUS FOR DRYING SEMICONDUCTOR SUBSTRATES USING AN INERT GAS AIR-KNIFE.” (Attorney Docket No. 7348/L) Both of these patent applications are incorporated by reference herein in their entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is concerned with semiconductor manufacturing and is more particularly concerned with techniques for drying a substrate. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known to process a semiconductor substrate to achieve a dry and low-contamination condition after processing steps such as chemical mechanical polishing (CMP) and scrubbing. It has also been proposed to employ immersion drying to semiconductor substrates using the so-called Marangoni effect. An example of a Marangoni dryer is disclosed in co-pending, commonly-owned U.S. provisional patent application Ser. No. 60/335,335, filed Nov. 2, 2001 (Attorney Docket No. 5877/L), entitled “Single Wafer Immersion Dryer and Drying Methods”, and which is hereby incorporated herein by reference in its entirety. 
         [0004]    In Marangoni drying, a substrate is raised in a vertical orientation from a fluid bath, and an alcohol vapor is delivered to a meniscus that is formed at the substrate/fluid interface. The alcohol vapor reduces the surface tension at the meniscus, thereby creating a “Marangoni” force resulting in a downward liquid flow opposite to the substrate lift direction. As a result, the substrate surface above the meniscus is dried. 
         [0005]    Marangoni drying is promising in terms of substrate throughput, absence of water marks, and low contamination levels achieved. However, it would be desirable to achieve comparable results without the inconveniences of delivering and exhausting hazardous alcohol vapor. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an aspect of the invention, a method of drying a substrate is provided. The inventive method includes raising the substrate out of a fluid bath. During the raising step, an air-knife is applied to a meniscus formed at an interface between the substrate and the surface of the bath. 
         [0007]    As referred to herein, an air-knife is not limited to using atmospheric air, but rather may use any suitable gas, including, for example, an inert gas such as nitrogen or argon. 
         [0008]    In another aspect of the invention, a method of drying a substrate includes (1) setting a gas delivery angle for an air knife used during an immersion-drying process; (2) using the air knife during immersion drying of a hydrophilic substrate; and (3) using the air knife during immersion drying of a hydrophobic substrate. The gas delivery angle is unchanged during immersion drying of both the hydrophilic substrate and hydrophobic substrate. 
         [0009]    It has been found that application of an air-knife to a fluid meniscus in conjunction with substrate immersion drying produces low contamination outcomes (e.g., with no water marks formed on hydrophobic substrates), matching the performance of Marangoni drying, with respect to absence of water marks and acceptable throughput, while avoiding the use of alcohol vapor. 
         [0010]    In a further aspect, a meniscus of rinsing fluid may be formed on a substrate via a plurality of spray nozzles, rather than via immersion in a bath. For example, a rinsing fluid may be sprayed across the horizontal diameter of a vertically oriented substrate as it leaves a vertically oriented scrubber. An air knife may be applied at the meniscus or upper boundary of the rinsing fluid on the substrate, to thereby dry the substrate. 
         [0011]    Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]      FIG. 1  is a schematic side view illustrating the inventive apparatus and method; 
           [0013]      FIG. 2  is a flow chart that illustrates a method of operating the apparatus of  FIG. 1 ; and 
           [0014]      FIG. 3  is a schematic front elevational view of a scrubber that may employ an air knife. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  is a schematic side view of a vertical single wafer immersion drying apparatus  11  configured in accordance with the present invention. For example, the principles of the present invention may be applied to an immersion drying apparatus of the type disclosed in the above-referenced co-pending U.S. provisional patent application Ser. No. 60/335,335, filed Nov. 2, 2001. The inventive immersion drying apparatus  11  includes a tank schematically represented at reference numeral  13 . The tank  13  contains a fluid bath  15  constituted by a rinsing fluid  17  such as deionized water, a solution of a corrosion inhibitor such as BTA (benzotriazole) or the like. 
         [0016]    A substrate  19  that is being dried in the inventive apparatus  11  is shown being raised in a substantially vertical orientation from the fluid bath  15 . The substrate  19  may be, for example, a silicon wafer. A substrate raising mechanism schematically represented by an arrow  21  is provided to raise the substrate  19  from the fluid bath  15 . 
         [0017]    The substrate  19  has a front side  23  on which one or more material layers have been and/or will be formed. The substrate  19  also has a back side  25  that is opposed to the front side  23 . During raising of the substrate  19 , a first meniscus  27  of the fluid  17  is formed at an interface  29  between the front side  23  of the substrate  19  and a surface  31  of the fluid  17 . A second meniscus  33  is also formed at an interface  35  between the back side  25  of the substrate  19  and the fluid surface  31 . 
         [0018]    In accordance with the invention, a first air-knife, schematically indicated by an arrow  37   a , is applied to the meniscus  27  at the front side  23  of the substrate  19 . The first air-knife  37   a  prevents the fluid  17  at the meniscus  27  from advancing upwardly with the front side  23  of the substrate  19  as the substrate  19  is raised, thereby drying the substrate  19 . The first air-knife  37   a  is applied at an angle  39  which is inclined downwardly from a horizontal plane  41 . The angle  39  will be referred to as a “gas delivery angle”. The gas delivery angle may, for example, be in the range of 13°-30°, depending on the type of film formed on the substrate  19 . Other gas delivery angles may be employed. 
         [0019]    As shown, a second air-knife  37   b  may be applied to the meniscus  33  at the back side  25  of the substrate  19 , to aid in drying the back side  25  of the substrate  19 . The back side gas delivery angle may, but need not, be different from the front side gas delivery angle. A different gas delivery angle may be preferred for the back side if the surfaces on the two sides have different characteristics. However, it is also contemplated to embody the immersion drying apparatus  11  with an air-knife only at the front side or back side of the substrate. 
         [0020]    One advantage of the inventive immersion drying apparatus  11  including an air-knife applied to the fluid meniscus is that the same gas delivery angle  39  may be used in connection with drying both substrates having a hydrophilic film (e.g., TEOS) thereon and also with substrates having a hydrophobic film (e.g., a low k dielectric) thereon. In the absence of the air-knife  37   a , the meniscus  27  in the case of the substrate  19  having the hydrophilic film thereon would extend higher above the surface  31  of the fluid  17  than the meniscus formed with a substrate having a hydrophobic film thereon. However, the action of the air-knife  37   a  shortens or deforms the meniscus formed on the hydrophilic film so that drying may occur at substantially the same point above the fluid surface  31  as in the case of a substrate having a hydrophobic film thereon. 
         [0021]    In one embodiment of the invention, the air-knife  37   a  (or  37   b ) may be implemented by means of a nozzle (e.g., a spray tube; not separately shown) of the same type as the gas delivery spray tubes disclosed in the above-referenced co-pending provisional patent application Ser. No. 60/335,335, filed Nov. 2, 2001. In addition, a suitable gas supply (not shown) is coupled to the nozzle. In one embodiment of the invention, the gas employed is nitrogen (N 2 ) although other gases may be used. 
         [0022]    In a particular embodiment, a nozzle tube having a perforated length of about 8.5 inches (which may be used, for example, in drying a 200 millimeter wafer) and having 114 holes of 0.005-0.007 inches in diameter, uniformly distributed along the perforated length of the nozzle tube may be used. The holes preferably should all be colinear and have the same orientation. The nozzle tube may be formed of stainless steel, quartz, or another suitable material. Other configurations may be employed. 
         [0023]    With such a nozzle tube, a gas flow rate of 15 liters per minute may be employed. Higher or lower gas flow rates could also be employed. For example, gas flow rates in the range of 10-30 liters/minute are specifically contemplated. In one embodiment, a gas delivery angle of 15° was found to be suitable for both hydrophilic and hydrophobic wafer surfaces. It is believed that this angle would also be appropriate for a patterned wafer surface having both hydrophilic and hydrophobic features. Further, it has been found that gas delivery angles in the range of 10°-20° may be preferred for drying a wafer having a hydrophilic film (TEOS). 
         [0024]    In the same embodiment, the substrate  19  was raised while being inclined away from the front side air-knife nozzle tube at an angle of 9° from the vertical. The direction of motion of the substrate was in the inclined plane defined by the substrate, as in the immersion tank disclosed in the above-referenced co-pending provisional patent application Ser. No. 60/335,335, filed Nov. 2, 2001. 
         [0025]    The cross-sectional center of the nozzle tube was a distance of 0.36 inches above the fluid surface, and at a perpendicular distance from the wafer surface of 0.63 inches for the front-side nozzle. For the back-side nozzle, the perpendicular distance to the wafer was 0.51 inches. In this same embodiment, the speed of raising the substrate was 2.5 millimeters per second. However, satisfactory results have also been obtained with a speed of raising the substrate of 10 millimeters per second. There may be, in general, a trade off between substrate-raising speed and number of contaminants after the drying process, with higher substrate-raising speeds possibly resulting in a greater number of contaminants. 
         [0026]      FIG. 2  is a flow chart that illustrates a method of operating the apparatus of  FIG. 1 . Initially, in step  51 , the gas delivery angle is set (e.g., at 15°). The setting of the gas delivery angle may be performed, for example, by fixedly mounting an air knife  37   a  and/or  37   b  (e.g., one or more nozzle tubes) relative to the tank  13 . Alternatively, each nozzle tube may be adjustably mounted relative to the tank  13  and may be manually or otherwise adjusted to set the gas delivery angle. 
         [0027]    Next, at step  53 , one or more hydrophobic substrates (i.e., substrates having a hydrophobic film on the front side thereof) are immersion-dried using an air-knife in accordance with the invention, with the gas delivery angle set at step  51 . 
         [0028]    Following step  53  is step  55 , at which one or more hydrophilic substrates (i.e., substrates having a hydrophilic film on the front side thereof) are immersion-dried using an air-knife in accordance with the invention, with the gas delivery angle set at step  51 . 
         [0029]    It will be noted that the gas delivery angle is not changed between steps  53  and  55 . 
         [0030]    The order of steps  53  and  55  may be reversed, and again it is not necessary to change the gas delivery angle between the two steps. 
         [0031]    The air-knife may be implemented using structure that is different from the nozzle tube described above. Gas flow rate may be varied and/or a gas other than nitrogen (N 2 ) may be employed. 
         [0032]    The present invention may be applied to drying a substrate having a different size and/or a different shape than a 200 mm wafer (e.g., a square or rectangular glass substrate such as employed for flat panel displays). The length of the nozzle tube may be varied as appropriate. 
         [0033]    The substrate may be raised at an angle other than 9° from the vertical, or may be raised without inclination (i.e., at 90° from the horizontal). 
         [0034]    The air-knife/nozzle tube may be arranged so that the gas delivery angle is adjustable by, e.g., manual adjustment. 
         [0035]    An alcohol vapor (e.g., isopropyl alcohol vapor) or another gas or vapor that serves to lower the surface tension of the rinsing fluid (i.e., a Marangoni drying gas) may be included in the gas dispensed by the air-knife nozzle tube (e.g., by the type of arrangement disclosed in the above-referenced co-pending provisional patent application Ser. No. 60/335,335, filed Nov. 2, 2001) so that Marangoni effect drying is also employed in the inventive immersion drying apparatus. Alternatively, a separate Marangoni drying nozzle  43   a ,  43   b  (shown in phantom in  FIG. 1 ) may be employed to supply Marangoni drying gas to a meniscus. The Marangoni drying nozzle  43   a ,  43   b  may be employed in addition to the air-knife  37   a ,  37   b  that manipulates the meniscus. By employing both an air-knife and a Marangoni drying gas, consecutive drying of hydrophilic and hydrophobic surfaces (or vice versa) may be employed without needing to adjust the position of the Marangoni drying nozzle  43   a ,  43   b . Specifically, because the air-knife  37   a ,  37   b  manipulates the meniscus  27 ,  33  to the same position for both hydrophilic and hydrophobic surfaces, the Marangoni drying nozzle  43   a ,  43   b  may maintain the same position for drying of hydrophilic surfaces and hydrophobic surfaces. Accordingly, throughput may be increased and labor costs decreased. 
         [0036]    Moreover, with use of the present invention (with or without application of a Marangoni drying gas) surfaces having both hydrophilic and hydrophobic portions (such as patterned semiconductor wafers) may be dried with better results (e.g., fewer contaminants). 
         [0037]    In a further aspect, the invention may be employed within a vertically oriented scrubber.  FIG. 3  is a schematic front elevational view of a vertically oriented scrubber  101 , having a plurality of rollers  303  for supporting a substrate S. A front side and a back side scrubber brush  305  (only one shown) are positioned above the rollers  303  so as to contact the front and back sides of the substrate S positioned on the rollers  303 . A fluid spray nozzle  307  is positioned above the scrubber brushes  305 , and an air knife nozzle  309  is positioned above the fluid spray nozzle  307 . An optional Marangoni drying nozzle  311  (shown in phantom) may be included. After the substrate S is scrubbed it may be dried via the air knife nozzle  309  (with or without the aid of a Marangoni drying vapor supplied either via the air knife nozzle  309  or via the Marangoni drying nozzle  311 ) in the manner described above with reference to  FIGS. 1 and 2 , as the substrate S is lifted from the rollers  303  (e.g., via a wafer handler or substrate pusher, not shown). Note that the rinsing fluid nozzle  307 , the Marangoni drying nozzle  311  and the air knife nozzle  309  preferably are positioned above the upper perimeter of the substrate S when the substrate S is positioned on the rollers  303 . In this manner the entire substrate surface is lifted past the nozzles  307 - 311 . A second set of nozzles  307 - 311  may be similarly positioned along the back side of the substrate S. 
         [0038]    The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, a substrate may be held at any orientation while being dried by an air knife. As stated, the present invention may be employed, for example, within a system similar to that described in previously incorporated U.S. Provisional Patent Application Ser. No. 60/335,335, filed Nov. 2, 2001 (Attorney Docket No. 5877/L), entitled “Single Wafer Immersion Dryer and Drying Methods” or within any other suitable system. 
         [0039]    Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.