Abstract:
An object of the present invention is to provide a wafer cleaning apparatus for cleaning wafers that have received various processing such as copper plating and chemical mechanical polishing. An apparatus for cleaning front and back surfaces of a wafer with solution while rotating the wafer that has been subjected to a fabrication process is disclosed. The apparatus comprises cleaning nozzles for spraying a cleaning solution, respectively, onto a front surface of the wafer that has been processed and onto a back surface thereof and also comprises an etching nozzle for spraying an etching solution onto a vicinity of the outer periphery of the wafer.

Description:
This application is a Divisional application of Ser. No. 09/572,432, filed May 17, 2000, now allowed as now U.S. Pat. No. 6,615,854. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a wafer cleaning apparatus for cleaning wafers, which are processed by various processing steps such as plating and chemical mechanical polishing. 
   2. Description of the Related Art 
   When metallic materials such as copper attach themselves to the surfaces and edges of semiconductor wafers electro-chemically as metallic copper, they become stable and cannot be removed by washing with pure water. Copper adhering in such a manner will diffuse into silicon wafers during heat treatment, and causes problems in device performances. 
   On the other hand, a copper seed layer is currently formed as a pre-treatment for copper plating by sputtering copper (or by CVD) on the silicon wafer, and the trend is to apply the layer over the entire front surface of the wafer, because it is a more efficient use of the area. That is, as shown in  FIG. 1 , a barrier layer  80  is formed on the front surface of the wafer W extending to its edge section E, a Cu seed layer  83  is formed thereon, and a plating layer  85  is formed on the seed layer  83 . 
   However, when a Cu seed layer  83  of 100 nm, for example, is formed by sputtering on the entire front surface of the wafer W, a sputtered Cu layer is formed not only on the front surface of the wafer but a thin sputtered Cu layer is formed also on the edge section E of the wafer as shown in  FIG. 2 . On the other hand, the formation of the plating layer  85  on the wafer W is carried out by sealing the outer peripheral section of the wafer W so as to prevent the plating layer from extending to the back surface of the wafer W. Therefore, the plating layer  85  can be formed only on the front surface of the wafer W not extending to the edge thereof, as shown in  FIG. 2 . For this reason, a portion of the Cu seed layer  83  remains on the edge section E and in the vicinity thereof as a thin layer. The residual Cu layer in such places can detach and be removed from the wafer during transport or processing of plated wafers or chemically mechanically polished (CMP) wafers, thereby leading to a high probability of causing Cu cross-contamination. 
   Also, it is difficult to prevent Cu from adhering to the back surface and edge of the wafer even if the edge and the back surface are protected by sealing the outer periphery thereof. 
   SUMMARY OF THE INVENTION 
   The present invention has been derived in view of the background problems outlined above, and an object of the present invention is to resolve such current problems and provide a wafer cleaning apparatus for completely cleaning surfaces of wafers processed by copper plating, a CMP process or so on. 
   The present invention provides an apparatus for cleaning front and back surfaces of a wafer while rotating the wafer that has been subjected to a fabrication process. The apparatus comprises: cleaning nozzles for spraying a cleaning solution, respectively, onto a front surface of the wafer that has been processed and onto a back surface thereof, and an etching nozzle for spraying an etching solution onto a vicinity of an outer periphery of the wafer. 
   According to cleaning the processed front surface of the wafer, particulate matter and detached copper are eliminated therefrom. According to cleaning the back surface of the wafer, particulate matter and/or copper adsorbed as metallic copper, are eliminated. And according to etching the edge portion of the wafer, it is possible to forcefully eliminate a thin copper film by etching. 
   As explained above, the present invention enables both sides and edges of the wafer to be cleaned at the same time as well as preventing potential device problems caused by metals, such as copper, adhering to the edge section of the wafer. That is, device performance problems caused by contamination from adhered metal on the edge section and back surface of the wafer, and problems of cross contamination caused by detached metal film from the copper formed on the edge section, are prevented. Thus, the invention provides beneficial effects of facilitating ideal cleaning of processed wafers that received various processing such as copper plating and a CMP process that follows the plating process. 
   The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an enlarged schematic view of a wafer W showing an edge portion and portions therearound; 
       FIG. 2  is an enlarged schematic view of a wafer W showing problems with conventional techniques; 
       FIG. 3  is a schematic diagram of the fundamental structure of a wafer cleaning apparatus of the present invention; 
       FIG. 4  is a diagram showing positioning of an etching nozzle; 
       FIG. 5  is a diagram showing another positioning of the etching nozzle; 
       FIG. 6  is an enlarged schematic view of a wafer being etched; 
       FIG. 7  is an enlarged schematic view of a wafer W having a poorly-defined step section of the outer periphery of a plating layer; 
       FIG. 8  is an enlarged schematic view of a wafer W whose outer periphery of the plating layer is also etched; 
       FIG. 9A  is a diagram of an example of a process of integrating a plating section and the present wafer cleaning apparatus into one unit, and  FIG. 9B  is a diagram of an example of a process of integrating a CMP section and the present wafer cleaning apparatus into one unit; 
       FIG. 10  is a diagram of an example of an apparatus produced by integrating a plating section and the present wafer cleaning apparatus into one unit; and 
       FIG. 11  is a diagram of an example of an apparatus produced by integrating a CMP section and the present wafer cleaning apparatus into one unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be explained in detail in the following with reference to the drawings. 
     FIG. 3  shows a schematic diagram of the fundamental structure of a wafer cleaning apparatus of the present invention. As shown in this diagram, the wafer cleaning apparatus is comprised of a rotation mechanism  10  for holding and rotating a wafer W, two cleaning nozzles  31 ,  33 , and an etching nozzle  35 . Each of these components will be explained below. 
   The rotation mechanism  10  includes a motor M so that wafer holding device  11  can be rotated through a belt B and pulleys P 1 , P 2 . Only two supporting portions of a wafer holding device are shown in this diagram, but in practice, 4˜8 supporting portions of the wafer holding device are provided, and are arranged so as to hold an outer periphery of the wafer W to maintain the wafer W horizontal. The wafer may be oriented so that the front surface thereof faces either upwardly or downwardly. 
   On the other hand, the cleaning nozzle  31  is disposed facing close to the front surface of the wafer W, which is a surface that has been fabricated such as being plated or subjected to a CMP process. Cleaning solution from the nozzle is directed to the center of the wafer W. The cleaning nozzle  31  should be disposed below the wafer when the fabrication surface (front surface) of the wafer faces downwardly. 
   Cleaning solution “a” sprayed from the cleaning nozzle  31  should be a liquid substance that does not etch copper and is effective in removing metal and particulate contamination. For example, any one of pure water, diluted sulfuric acid, diluted hydrofluoric acid (DHF), ionized water, 2-stage processing with dilute hydrofluoric acid and ozonized water, and 2-stage processing with hydrogen peroxide (H 2 F 2 ) and diluted hydrofluoric acid may be used as necessary. 
   Next, the cleaning nozzle  33  is disposed facing the backside of the wafe; that is, the surface that has not been subjected to fabrication such as plating or a CMP process. The cleaning nozzle  33  should be disposed above the wafer when the back surface of the wafer faces upwardly. The cleaning nozzle  33  is constructed in such a way that when the back surface of the wafer W faces downwardly, cleaning solution is sprayed in a shape of a cone. 
   Cleaning solution “b” sprayed from the cleaning nozzle  33 , should be capable of removing Cu adhered on a silicon wafer when compared to the solution “a”, which is sprayed on the front or fabricated surface of the wafer. The cleaning solution “b” may use, for example, any one of pure water, diluted sulfuric acid, diluted hydrofluoric acid, 2-stage processing with ozonized water and diluted hydrofluoric acid, and 2-stage processing with hydrogen peroxide and diluted hydrofluoric acid, as necessary. 
   As shown in  FIG. 4 , the etching nozzle  35  is installed so that the spray opening of the nozzle is positioned at a specific distance so that k is less than 5 mm (k≦5 mm) from the edge section of the wafer W, and that the direction of the center line l of the spray opening at the tip of the etching nozzle  35  is at right angles (θ1=90°) relative to the surface of the wafer W. 
   The etching nozzle  35  may be installed, as shown in  FIG. 5  also, so that the spray opening of the nozzle is positioned at a specific distance so that k is less than 5 mm (k≦5 mm) from the edge section of the wafer W, and that the direction of the center line l of the spray opening at the tip of the etching nozzle  35  is inclined towards an outer edge at an angle other than right angles (θ2&lt;90°) relative to the surface of the wafer W. 
   Also, although only one etching nozzle  35  is provided in this embodiment, it is permissible to provide a plurality of etching nozzles. It is preferable that the fluid stream ejected from the etching nozzle  35  be shaped to a fine point as much as possible so as to produce well defined etching boundaries. 
   Etching solution “c” to be sprayed from the etching nozzle  35  should be selected so that its purpose is to etch away the copper. For example, such a solution may be any one of a mixture of sulfuric acid and hydrogen peroxide, and a 2-stage processing based on sodium persulfate, sulfuric acid, hydrochloric acid, nitric acid, ionized water or ozonized water and diluted hydrofluoric acid, as necessary. 
   Next, the operation of the wafer cleaning apparatus will be explained. That is, a wafer W that has been subjected to a fabrication process such as copper plating or a CMP process is held in the wafer holding device  11 , as shown in  FIG. 1 , with the surface to be fabricated (front surface) facing upwardly, and the motor M is operated to rotate the wafer W. Cleaning solutions “a” and “b” are sprayed from the cleaning nozzles  31 ,  33 , and concurrently, an etching solution “c” is sprayed from the etching nozzle  35 . Or, the etching solution “c” is sprayed from the etching nozzle  35  only initially for a given period of time, after which the cleaning solutions are sprayed from the nozzles  31 ,  33 . 
   The cleaning solution “a” sprayed from the cleaning nozzle  31  rushes to the center section of the front surface of the wafer W, and is then spread on the wafer surface throughout by the rotational action of the wafer W. Thereby, metal and particulate contaminants are washed away from the front surface of the wafer W, thus cleaning the front surface of the wafer W. 
   The cleaning solution “b” sprayed from the cleaning nozzle  33  rushes to the back surface of the wafer W in a shape of a cone, and is spread out along the entire back surface by the rotational action of the wafer W, thereby removing metal and particulate contaminants from the back surface of the wafer W and cleaning the back surface thereof. It is permissible to reverse the facing direction of the front/back surfaces of the wafer W. 
   In the meantime, the etching solution “c” sprayed from the etching nozzle  35  rushes to the peripheral portion of the surface of the wafer W at right angles, as shown by the arrow in  FIG. 4 . However, because the wafer W is rotating, it flows from the ejected position towards the outside by centrifugal force, and flows only to the outer periphery thereof This action causes only the outer periphery, where the etching liquid “c” has adhered, to be selectively etched as shown in  FIG. 6 . In other words, because of the action of this selective etching, it is possible to remove an unnecessary thin Cu layer, formed by sputtering and the like on the edge section E of the wafer W shown in  FIG. 2 , and create the condition shown in  FIG. 1 . Therefore, there is no danger of the adhered Cu causing performance problems in a device during subsequent heating processes, or causing cross contamination by Cu during transport or post processing of the wafer W. 
   Also, when the step produced by a seal on the outer periphery of the plating layer  85  is not well defined, as illustrated in  FIG. 7 , a thin portion U is also formed on the plating layer  85  and may cause detachment. Therefore, it is necessary to etch seed layer  83  and the plating layer  85  together at thin portion U. When this thin portion U is selectively etched as described above, the condition shown in  FIG. 8  can be obtained. 
   On the other hand, when the etching nozzle  35  is installed so that it is inclined away from the vertical toward the outer periphery as shown in  FIG. 5 , it is obvious that only the outer portion of the wafer W is selectively etched to produce the effects described above. 
   In the above embodiment, copper is used as an object metal for etching treatment, but this invention is not limited to copper, so that the invention can be applied to other metals such as gold, silver, or solder. Also, there are many types of rotational devices for the wafer, and any type of rotation device may be used so as long as rotational action can be produced. 
   Because the wafer cleaning apparatus is used for cleaning wafers that have been subjected to copper plating or CMP process, it is preferable that the wafer cleaning apparatus is constructed as an integrated unit by combining it with a plating section for performing copper plating or a CMP section for performing chemical mechanical polishing. 
     FIG. 9A  shows an example of the process performed by a combined unit of a plating section and the wafer cleaning apparatus, and  FIG. 9B  shows an example of the process performed by a combined unit of a CMP section and the wafer cleaning apparatus. 
     FIG. 10  shows a schematic diagram of an example of an apparatus that combines a copper plating section and the wafer cleaning apparatus. As shown in this diagram, a plating section  100  is comprised of a plurality of plating vessels  101 , a robot  103 , a loading stage  105  and a rough wash section  107 . And, a cleaning section  110  is comprised of the present wafer cleaning apparatuses  111 ,  113 , rinser dryers  115 ,  117 , a robot  119 , a loading wafer cassette  121 , and an unloading wafer cassette  123 . One wafer at a time is removed from the loading wafer cassette  121  by the robots  119 ,  103  and is transported to the plating vessel  101  by way of the loading stage  105  for plating. Then, the plated wafer is washed in the rough washing section  107 , and is etched in the present wafer cleaning apparatuses  111 ,  113  to etch the front and back surfaces and the outer periphery of the wafer. Then, the wafer is passed through the rinser dryers  115 ,  117  to clean and dry the wafer, and the dried wafer is returned to the unloading wafer cassette  123 . In other words, a plating operation and a cleaning operation are carried out in an interleaved manner on each wafer. 
   Also,  FIG. 11  shows a schematic diagram of an example of the apparatus that combines CMP and the present wafer cleaning apparatus. As shown in this diagram, a CMP section  130  is comprised of a turntable  134  provided with a polishing surface, a rotating top ring  137  having a top ring head  135  for holding a wafer; a dresser  141  for dressing the polishing surface; and a pusher  143  for exchanging a wafer with the top ring head  135 . A cleaning section  150  is comprised of a primary washer  155 ; a secondary washer  157 ; a spin dryer  159 ; robots  151 ,  153 ; wafer inverters  161 ,  163  and wafer loading/unloading cassette  165 . The wafers are taken one at a time from the wafer cassette  165 , and are mounted on the top ring head  13   5  by way of the wafer pusher  143 . Then, the wafer is subjected to chemical mechanical polishing using the polishing surface of the turntable  134 , and is again handled by the wafer pusher  143  for rinsing in the primary washer  155  and the secondary washer  157 . Then the wafer is spin dried in the spin dryer  159 , and is returned to the wafer cassette  165 . In other words, CMP operations and a cleaning operation are carried out in an interleaved manner on each wafer. The primary washer  155  may be represented by the present wafer cleaning apparatus. 
   Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.