Abstract:
An apparatus for cleaning semiconductor wafers includes a chamber, a bubbler having a vapor generating part for generating alcohol vapor and a spray pipe for spraying the alcohol vapor into the chamber, a gas supply nozzle for spraying gas into the chamber to dry the wafers, a liquid supply nozzle for supplying cleaning liquid into the chamber and a discharge system. The spray pipe of the bubbler has a liquid retention portion that keeps condensate of the alcohol vapor from issuing into the chamber. The gas supply nozzle has a spray outlet configured to spray the same amount of the drying gas onto all of the wafers in the chamber. The liquid supply nozzle has liquid supply openings only in a side portion thereof so that liquid alcohol will not become trapped therein.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for manufacturing semiconductor devices. More particularly, the present invention relates to an apparatus for cleaning semiconductor wafers in accordance with the Marangoni principle. 
   2. Description of the Related Art 
   When a semiconductor wafer is manufactured into integrated circuit (IC) devices, the wafer is subjected to a series of semiconductor device manufacturing processes such as photolithography, chemical or physical vapor deposition and plasma etching processes. Foreign materials, such as residual chemicals, small particles, and other contaminants, may remain on the surface of the wafer after these processes are carried out. The foreign materials must be removed from the surface of the wafer to assure the quality of the IC devices. 
   A wafer cleaning process may include both rinsing and drying the wafer to remove foreign materials. A silicon wafer is generally rinsed using de-ionized water. However, the de-ionized water is an aggressive solvent against silicon and will thus eventually dissolve the silicon wafer. Accordingly, the wafer must be completely dried after being rinsed with the de-ionized water. 
   There are a number of semiconductor wafer cleaning systems commercially available. Recently, wafer cleaning systems based on the Marangoni principle have been widely used in the art. The Marangoni principle is based on the fact that when there is a liquid region wherein two different surface tensions exist, liquid flows from the region of the lower surface tension to the region of the higher surface tension. In Marangoni principle-based wafer cleaning systems, de-ionized water is typically used to rinse the wafer, and isopropyl alcohol (IPA) is typically used to dry the deionized water. The IPA has a lower surface tension than does the de-ionized water. Examples of conventional wafer cleaning systems using the Marangoni principle are disclosed in U.S. Pat. Nos. 5,569,330, 5,807,439, 6,027,574, and 6,354,313. These systems each include a chamber to accommodate wafers, and a bubbler for generating IPA vapor. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and which apparatus exhibits better wafer cleaning characteristics than do previous apparatus. 
   A specific object of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and which apparatus prevents condensed alcohol from issuing into the chamber of the apparatus from an exit end of a spray pipe of a bubbler that sprays alcohol vapor into the cleaning and drying chamber. 
   Yet another object of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and which apparatus prevents alcohol existing in the form of a mist within the bubbler from being introduced into the cleaning and drying chamber. 
   Still another aspect of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and by which the amount of alcohol vapor introduced into the cleaning and drying chamber and the velocity at which the alcohol vapor is introduced into the chamber can be established independently of one another. 
   Another specific object of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and which apparatus sprays drying gas uniformly onto a plurality of wafers in the chamber of the apparatus. 
   Another aspect of the present invention is to provide a wafer cleaning apparatus that uses the Marangoni principle, and which apparatus prevents the wafers from being contaminated when the level of cleaning liquid falls below the level of the liquid supply nozzle(s), such as when the cleaning liquid is discharged. 
   The apparatus for cleaning a semiconductor wafer of the present invention, comprises. a chamber in which a wafer cleaning process is performed, and a bubbler for producing alcohol (e.g., isopropyl alcohol) vapor. The chamber includes a bath that contains a wafer holder, and a lid that covers the bath. The height of the chamber is at least twice the diameter of the wafers to be cleaned therein. A first supply pipe is disposed at one side of the bath to supply liquid alcohol to the chamber. The liquid alcohol forms a layer on the de-ionized water in chamber. The bubbler includes a vapor generating part for generating the alcohol vapor, and a spray pipe for spraying the alcohol vapor and carrier gas for the alcohol vapor into the chamber. 
   According to an aspect of the present invention, the spray pipe has a liquid retention portion. This portion of the spray pipe retains liquid, namely the condensate of the alcohol vapor formed at an exit end of the spray pipe, within the spray pipe. 
   According to another aspect of the present invention, the vapor generating part comprises a housing, a second supply pipe for supplying liquid alcohol to the housing such that the housing becomes partially filled with the liquid alcohol, a third supply pipe submerged in the liquid alcohol inside the housing for supplying the carrier gas into the housing at a level below the surface of the liquid alcohol, and a fourth supply pipe for supplying the carrier gas to the housing at a level above the surface of the liquid alcohol in the housing. 
   The bubbler may further include a baffle in the form of a connector having a bend that is disposed between the spray pipe and the vapor generating part, and/or porous filter disposed in the vapor generating part. The bend of the connector and the filter serve to prevent the alcohol in the form of a mist from being carried to the spray pipe. 
   According to yet another aspect of the present invention, the cleaning apparatus comprises at least one gas supply nozzle for spraying drying gas uniformly over a number wafers disposed in the chamber. The gas supply nozzle includes an inlet end adjacent a side of the cleaning and drying chamber, a nozzle body extending from the inlet end, and a spray outlet spanning at least the length over which the number of wafers can be arranged in the chamber. The spray outlet may take the form of a plurality of circular openings having different sizes or spaced from one another by different intervals. Alternatively, the spray outlet of the gas supply nozzle may have the form of a slit extending longitudinally in the nozzle body. The slit is preferably flared outwardly at both ends and/or both sides thereof such that the outer opening of the slit is larger than the inner opening thereof. In addition, the width of the slit may increase along the length of the nozzle body in a direction from the side of the chamber where the inlet end of the nozzle is located. 
   The cleaning apparatus further includes at least one liquid supply nozzle disposed below a wafer holder for supplying liquid for cleaning the wafer into the chamber. The nozzle body of the liquid supply nozzle has a top portion that faces upwardly towards the wafer holder, and a side portion that faces laterally in a direction perpendicular to the top portion. According to still yet another aspect of the present invention, liquid supply openings of the supply nozzle are provided only in the side portion of the nozzle body. Thus, any liquid IPA on the surface of the cleaning liquid will not be trapped in the liquid supply nozzle during the discharging of the cleaning liquid from the chamber. 
   The discharge system includes a first discharge pipe for draining the liquid using gravity after the wafers are brought above the surface of the cleaning liquid, and a second discharge pipe for draining the liquid while a portion of the wafers are submerged in the liquid. A pump is connected to the second discharge pipe to control the velocity at which the liquid is drained. Preferably, the alcohol vapor and carrier gas in the chamber are exhausted through the second discharge pipe. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: 
       FIG. 1  is a front cross-sectional view of a cleaning apparatus according to the present invention; 
       FIG. 2  is a side cross-sectional view of the cleaning apparatus according to the present invention; 
       FIG. 3  is a perspective view of a bubbler of the cleaning apparatus shown in  FIGS. 1 and 2 ; 
       FIG. 4   a  is a cross-sectional view taken along line A-A of  FIG. 3 ; 
       FIG. 4   b  is a similar cross-sectional view but showing another form of the alcohol vapor generating part of the bubbler; 
       FIG. 4   c  is a similar cross-sectional view but showing yet another form of the alcoho vapor generating part of the bubbler; 
       FIG. 5  is a cross-sectional view taken along line B-B of  FIG. 3 , illustrating a spray pipe; 
       FIG. 6  is a cross-sectional view of a bubbler showing another example of a spray pipe; 
       FIG. 7  is a cross-sectional view of another example of the bubbler; 
       FIG. 8   a  is a bottom view of a gas supply nozzle of the cleaning apparatus shown in  FIG. 2 ; 
       FIG. 8   b  and  FIG. 8   c  are bottom views of modified examples of the gas supply nozzle 
       FIG. 9   a  is a side view showing another example of a gas supply nozzle of the cleaning apparatus shown in  FIG. 2 ; 
       FIG. 9   b  and  FIG. 9   c  are side views of modified examples of the gas supply nozzle; 
       FIG. 10   a  is a cross-sectional view of the gas supply nozzle taken along line C-C of  FIG. 9   a;  and 
       FIG. 10   b  is a cross-sectional view of a modified example of the gas supply nozzle. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the attached figures, in which preferred embodiments of the invention are shown. 
   Referring to  FIG. 1  and  FIG. 2 , the cleaning apparatus includes a chamber  100  in which a cleaning process is performed, a bubbler  200  for producing an alcohol vapor and for supplying the alcohol vapor to the chamber  100 , gas supply nozzles  400  for spraying drying gas in the chamber  100 , at least one liquid supply nozzle  500  for supplying liquid into the chamber  100 , a discharge section  600  for discharging the liquid, a gas source  740  for storing the gas supplied to the bubbler  200  and the gas supply nozzles  400 , and an alcohol source  720  for storing the alcohol liquid supplied to the chamber  100  and the bubbler  200 . 
   The alcohol is isopropyl alcohol (hereinafter referred to as IPA), the drying gas is nitrogen, and the liquid is de-ionized water. 
   The chamber  100  comprises a bath  140  that contains the wafers  10 , and a lid  120  for opening and closing over an open top portion of the bath  140 . A wafer holder  160  for supporting the wafers  10  is disposed in the bath  140 . The wafer holder  160  can be re-positioned in a vertical direction while the de-ionized water is being discharged. A first supply pipe  310  extends into the bath  140  from the side thereof. Liquid IPA is supplied from the alcohol source  720  to the chamber  100  through the first supply pipe  310  to form an IPA liquid layer  142  on the surface of the de-ionized water in the bath  140 . 
   The lid  120  is semi-cylindrical such that the interior thereof defines a concavity. Accordingly, the wafers  10  can be moved upwardly into the hollow of the lid  120 . At this time, the wafer holder  160  may move upwardly without the de-ionized water being discharged from the bath  140 . The height of the chamber  100  is thus at least twice the diameter of the wafers  10  to provide enough space for accommodating the wafers  10  entirely above the surface of the de-ionized water. 
   Referring to  FIG. 3  and  FIG. 4A , the bubbler  200  includes a vapor generation part  220  for generating the IPA vapor and a spray pipe  240  for spraying the IPA vapor into the chamber  100 . The housing  230  of vapor generation part  220  has the shape of a rectangular parallelepiped, and a part of the housing  230  is filled with liquid IPA  222 . A second supply pipe  320  is connected to the bottom of the housing  230 . A third supply pipe  340  is connected to a side of the housing  230  and is immersed in the liquid IPA  222 . A plurality of holes are formed in an upper portion of the third supply pipe  340 . Carrier gas, such as nitrogen, is supplied to the housing  230  through the holes formed in the third supply pipe  340 . The carrier gas supplied through the third supply pipe  340  helps the IPA liquid to evaporate and carries the IPA vapor into the chamber  100 . The amount of the IPA vapor and the velocity of the IPA vapor are proportional to the amount of the carrier gas that is supplied through the third supply pipe  340 . 
   The vapor generation part  220  includes a fourth supply pipe  360  that is branched from the third supply pipe  340 . The fourth supply pipe  360  is located over the surface of the liquid IPA  222 . A plurality of holes are formed in the fourth supply pipe  360 . The carrier gas that flows through the fourth supply pipe  360  only serves to carry the IPA vapor to the chamber  100 , unlike the carrier gas that is supplied through the third supply pipe  340 . Accordingly, the amount of the IPA vapor that is produced and the velocity at which the IPA vapor flows into the chamber  400  are independent, i.e., can be established irrespectively of one another, as opposed to the vapor generation parts of conventional wafer cleaning apparatus. 
   For example, the diameter of the third supply pipe  340  may be different from that of the fourth supply pipe  360 . The third supply pipe  340  may be provided with a relatively large diameter to produce a large amount of IPA vapor to be moved to the chamber  100 , as shown in  FIG. 4B . The fourth supply pipe  360  may be provided with a diameter such that the IPA vapor is supplied rapidly to the chamber  100 . Alternatively, the third supply pipe  340  may have the same diameter as the fourth supply pipe  360 . In this case, as shown in  FIG. 4C , a flow control valve V is connected to the third or fourth supply pipe  340 ,  360  to control the amount of IPA vapor generated or the velocity of the vapor IPA. 
   The liquid IPA in the vapor generation part  220  is consumed due to vaporization of the liquid IPA. Therefore, the liquid IPA is continuously supplied to the housing  230  through the second supply pipe  320  to replenish the liquid IPA. 
   Referring again to  FIG. 1 , the spray pipe  240  is inserted through the side of the chamber  100  and the IPA vapor and the carrier gas from the bubbler  200  are supplied into the chamber  100  through the spray pipe  240 . While the IPA vapor and the carrier gas are sprayed to the chamber  100 , condensed liquid of the IPA vapor is formed on the upper portion of the exit end of the spray pipe  240 . If the condensed liquid were to fall into the chamber  100 , the liquid IPA layer  142  formed on the surface of the de-ionized water in the bath  140  would be destroyed. In this case, the drying process using Marangoni principle could not be performed properly until the liquid IPA layer  142  was restored. The spray pipe  240  has a liquid retention portion to prevent this problem from occurring. 
   According to one example shown in  FIG. 5 , the spray pipe  240  has a quadrilateral cross section. More specifically, the spray pipe  240  has an inclined upper wall as the liquid retention portion. The upper wall of the spray pipe  240  is gently inclined downwardly from the exit end of the pipe  240  at which the IPA vapor condenses. Accordingly, the spray pipe  240  is tapered so that condensed liquid flows from the exit end back into the spray pipe  240 . 
   Another example of the liquid retention portion is shown in  FIG. 6 . In this example, the liquid retention portion is a projection  244  in the form of a hook extending from the upper wall at the exit end of the spray pipe  240  back into the spray pipe  240 . The condensed liquid thus flows back into the spray pipe  240  along the projection  244  without falling into the chamber  100 . 
   If desired, the spray pipe may comprise both the inclined upper wall shown in  FIG. 5  and the projection  244  shown in  FIG. 6  as the liquid retention portion. 
   In addition, part of the IPA exists in the form of a mist. A porous filter  380  is installed on or over the surface of the IPA liquid in the bubbler  200  so as to prevent the IPA mist from being carried into the chamber  100 . The porous filter  380  can be heated by a heater (not shown). 
   Referring next to  FIG. 7 , the bubbler  200  may include a connector  260  between the housing  230  and the spray pipe  240 . The connector  260  is in the form of a baffle, i.e., has a bend, so as to prevent the IPA mist from being carried to the chamber  100 . Drops of any of the IPA mist will accumulate on the wall of the connector  260  and then fall back into the housing  230  of the vapor generation part  220  without ever having moved into the spray pipe  240 . 
   A plurality of liquid supply nozzles  500  extend into the bath  140  to supply liquid used in the cleaning process, such as a process for treating the wafers  10  with a chemical solution or a process for rinsing them. The chemical solution may be electrolysis-ionized or hydrofluoric acid that is of a strength sufficient to remove contaminants such as particles, metal, e.g., copper, and natural oxidation layers from the wafers. When the cleaning process is a rinsing process, the liquid may be de-ionized water. 
   A plurality of holes  510  are formed in each liquid supply nozzle  500 . If the holes  510  were formed in the top of the liquid supply nozzles  500 , the de-ionized water could flow easily into the liquid supply nozzles  500 , giving rise to this potential problem. Any liquid IPA contained in the deionized water inside of a liquid supply nozzle  500  would evaporate after the surface of the de-ionized water became disposed below the liquid supply nozzle  500  when the de-ionized water is discharged from the bath  140 . The evaporated IPA contains little, if any, de-ionized water, and thereby would surely contaminate the wafers  10 . However, in the present invention, the holes  510  are formed in a side of each liquid supply nozzle  500 . This prevents the de-ionized water containing liquid IPA in the bath  140  from flowing into the liquid supply nozzles  500 . 
   The de-ionized water containing the liquid IPA is discharged through the discharge section  600 . The discharge section  600  is connected to the bottom of the bath  140 . The discharge section  600  includes a first discharge pipe  620  and a second discharge pipe  640 . The first discharge pipe  620  is connected perpendicularly with the bottom of the bath  140  and the second discharge pipe  640  extends from the first discharge pipe  620  horizontally alongside the bottom of the chamber  100 . A directional flow control valve  660  is connected to the pipes  620 ,  640  at the location where the second discharge pipe  640  branches from the first discharge pipe  620  to select the pipe through which the de-ionized water is discharged. 
   The de-ionized water is discharged through the second discharge pipe  640  while at least a portion of the wafers  10  is immersed in the de-ionized water. A pump is connected to the second discharge pipe  640  for controlling the rate of discharge. The de-ionized water is discharged through the first discharge pipe  620  by gravity once the wafers  10  are entirely located above to the surface of the de-ionized water. Unlike conventional wafer cleaning apparatuses, the cleaning apparatus of the present invention does not have an exhaust hole for exhausting the nitrogen gas or the IPA vapor. Rather, in the present invention, the nitrogen gas and the IPA vapor are exhausted through the second discharge pipe  640 . This prevents outside air from invading the chamber  100  through a dedicated exhaust hole. 
   After all of the de-ionized water is drained, the water and the liquid IPA that are adhered to the wafer  10  should be removed. Drying gas, such as heated nitrogen, is used for this purpose. The drying gas is supplied to the chamber  100  through a plurality of gas supply nozzles  400  installed on an upper surface of the lid  120 . A heater  760  is installed in the gas supply line extending between the gas source  760  (gas supply tank) and the gas supply nozzles  400  to heat the drying gas. It is very important that the drying gas is supplied uniformly to all the wafers  10 . 
   Referring to  FIG. 8   a , each gas supply nozzle  400  has a plurality of circular spray openings spaced therealong from one end thereof to the other. For instance, when a set of N wafers  10  is put in the wafer holder  160 , the openings are located over a top portion of and span the first wafer  10  to N-th wafer  10 . 
   Referring to  FIG. 8   b , which shows a modified example of the gas supply nozzle  400 , the spray openings  420  in the gas supply nozzle  400  have different sizes to ensure that the amount of nitrogen supplied to the N-th wafer  10  is the same as the amount of nitrogen supplied to the first wafer  10 . In particular, the size of openings  420  increases as the distance from the side of the chamber  100  from which the gas supply nozzle  400  extends increases. 
   Referring to  FIG. 8   c , which shows still another modified example of the gas supply nozzle  400 , the spray openings  420  are formed at different intervals to ensure that the amount of the nitrogen gas supplied to the N-th wafer  10  is the same as the amount of nitrogen gas supplied to the first wafer  10 . Specifically, the intervals between adjacent openings  420  increase as the distance from the side of the chamber  100  from which the gas supply nozzle  400  extends increases. 
   Referring to  FIG. 9   a  and  FIG. 10   a , the gas supply nozzle  400  may have a slit-type of opening  440  instead of a plurality of discrete spray openings. In this embodiment, the length of the opening  440  spans the set of wafers  10 , i.e., extends from the top of the first wafer  10  to the top of N-th wafer  10 . 
   Referring to  FIG. 9   b  and  FIG. 10   b , the slit-type of opening  440  may flare outwardly at both the sides and the ends thereof so that the nitrogen is sprayed over all of the wafers  10 . 
   Referring to  FIG. 9   c , the width of the slit-type of opening  440  may increase gradually as the distance from the side of the chamber  100  from which the gas supply nozzle  400  extends increases. 
   The wafers  10  are cleaned as follows. First, the rinse (or chemical treatment) process is performed with de-ionized water (or a chemical solution) in the bath  140 . For purposes of explanation, only the rinse process will be referred to. The de-ionized water with liquid IPA in the bath  140  is slowly discharged through the second discharge pipe  640 . IPA vapor is sprayed into the chamber  100  through the spray pipe  240  while the de-ionized water is being slowly discharged. The wafers  10  may be moved upwardly during the discharging of the de-ionized water to speed up the overall cleaning process. The de-ionized water is quickly discharged through the first discharge pipe  620  once the wafers  10  have passed completely through the surface of the de-ionized water. Then the heated nitrogen gas is sprayed onto the wafers  10  in the bath  140  through the gas supply nozzles  400  in order to remove the de-ionized water and the liquid IPA adhering to the wafers  10 . 
   According to the present invention, a condensed liquid of IPA formed at the exit of a spray pipe of a bubbler is retained within the spray pipe. Therefore, the IPA liquid layer in the bath  140  is not destroyed by the condensed liquid. 
   Furthermore, in the present invention, the holes of the gas supply nozzle  400  have different diameters or are spaced at different intervals. Therefore, the same amount of the nitrogen is supplied to all of the wafers  10  disposed in the bath  140 . 
   Finally, although the present invention has been described in connection with the preferred embodiments thereof, various changes and modifications can be made thereto without departing from the true spirit and scope of the invention as defined by the appended claims.