Abstract:
An apparatus is disclosed wherein polishing slurry is supplied to a polishing pad affixed to a polishing platen to thereby polish semiconductor wafers. This apparatus is provided with at least one slurry-supply mechanism for supplying a controlled amount of polishing slurry to an intermediate region between outer end and central regions of a semiconductor wafer and to the central region per se. Control is made such that the amount of flow of polishing slurry supplied to the intermediate region of the semiconductor wafer is larger than that supplied to the central region thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a method of polishing a semiconductor wafer to flatten the surface thereof and to an apparatus for carrying out the polishing method.  
           [0003]    2. Description of the Related Art  
           [0004]    Processes for manufacturing an integrated circuit substrate of a semiconductor device typically include a process for flattening an inter layer insulating film, a wiring film and the like. In the flattening process, a particular technique generally referred to as a chemical mechanical polishing (CMP) is adopted.  
           [0005]    With a reduction in the design rule of semiconductor integrated circuits, respective circuit patterns must be minute, so that each kind of aligners is required to have a high resolution. However, an increase in the resolution of the aligner causes the depth of focus thereof to be made smaller. For this reason, in order to transfer the circuit patterns onto a semiconductor wafer at a high resolution, the surface of the semiconductor wafer needs to be finely flat to have no irregularity thereon.  
           [0006]    Polishing of the semiconductor wafer according to the CMP is performed in the following monmer. First, a polishing pad made of polyurethane foam is affixed to a rigid polishing platen, and a semiconductor wafer to be polished is held in position with a holding head. Then, the semiconductor wafer is pressed against the polishing pad and is rotated in one direction. At this stage, polishing slurry is supplied from a slurry-supply nozzle in a dropping manner to the surface of the polishing pad to polish the surface of the semiconductor wafer.  
           [0007]    However, with this method, although the polishing slurry is supplied from one single slurry-supply nozzle to be dropped onto a radially central region of the polishing pad, the slurry cannot be spread over the entire surface of the semiconductor, so that the surface of the semiconductor cannot be uniformly and evenly polished. Further, in order to uniformly spread the polishing slurry over the entire surface of the semiconductor, an excessive amount of polishing slurry may be supplied. This, however, results in the increased consumption of the polishing slurry which is undesirable in terms of cost.  
           [0008]    One typical polishing apparatus to solve the problem is disclosed in Japanese Patent Laid-open No. 70465/99. The polishing apparatus is provided with a spray means having a plurality of openings, which are arranged side by side in a radial direction of a polishing pad. The polishing slurry in the condition of spray or splash is blown against the radially entire portion of the polishing pad through the plurality of openings of the spray means, so that the polishing slurry comes into and is then squeezed out of finely small holes in the polishing pad. The semiconductor wafer is then polished at a reduced speed to obtain a uniformly polished surface of the semiconductor wafer.  
           [0009]    In the aforementioned polishing apparatus, although the polishing slurry may be uniformly and evenly supplied to the surface of the polishing pad, the time of contact of a radially central region of the semiconductor wafer with the polishing pad is obviously different from that of a radially outermost region of the semiconductor wafer with the polishing pad. Accordingly, a problem is encountered with the known polishing apparatus that even if the polishing slurry is evenly supplied to the semiconductor wafer, it is difficult to obtain a uinform amount of polishing over the entire surface of the semiconductor wafer.  
         SUMMARY OF THE INVENTION  
         [0010]    Therefore, it is an object of the present invention to provide a method of and an apparatus for uniformly polishing inside the surface of a semiconductor wafer with reduced consumption of polishing slurry.  
           [0011]    To achieve the above object, an apparatus for polishing a semiconductor wafer, according to the present invention comprises at least one slurry-supply mechanism for supplying a controlled amount of polishing slurry to both an intermediate position located between an outer end region and a central region of a semiconductor wafer, and the central region per se.  
           [0012]    Arranging one or more slurry-nozzles in a radial direction of a polishing pad, and control of an amount of polishing slurry supplied to the polishing pad that confronts the surface of the semiconductor wafer permit a uniform polishing of the inside of the surface of the wafer. Thus, a pattern or patterns can be transferred to the polished semiconductor wafer with a high resolution.  
           [0013]    Furthermore, since there is no necessity of supplying an excess amount of polishing slurry with a fixedly arranged single slurry nozzle, and since polishing of the surface of the semiconductor is conducted according to the position and the number of the slurry nozzles as well as control of an amount of flow of polishing slurry, waste of the polishing slurry can be prevented, thereby reducing the manufacturing cost of the semiconductor wafer.  
           [0014]    According to one embodiment of the present invention, the slurry-supply mechanism comprises a pair of first slurry-supply nozzles arranged side by side in a radial direction of the polishing pad and confronting the intermediate position between the outer end region and the central region of the semiconductor wafer, a second slurry-supply nozzle arranged between the pair of first slurry-supply nozzles and confronting the central region of the semiconductor wafer, and a flow amount varying means for independently supplying the controlled amount of polishing slurry to the pair of first slurry-supply nozzles and the second slurry-supply nozzle.  
           [0015]    The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1A is a top plan view of a polishing apparatus for a semiconductor wafer according to an embodiment of the present invention;  
         [0017]    [0017]FIG. 1B is a side view of the apparatus of FIG. 1A;  
         [0018]    [0018]FIG. 2 is a graph illustrating a relationship between a position in a semiconductor wafer surface and an amount of polish obtained when the semiconductor is polished with the dropping amount of the polishing slurry from slurry-supply nozzles being varied;  
         [0019]    [0019]FIG. 3 is a schematic view of a first variant of the slurry-supply mechanism shown in FIG. 1;  
         [0020]    [0020]FIG. 4 is a schematic view illustrating another variant of the slurry-supply mechanism of FIG. 3;  
         [0021]    [0021]FIG. 5 is a schematic view illustrating another variant of the slurry-supply mechanism of FIG. 1; and  
         [0022]    [0022]FIG. 6 is a schematic view illustrating another variant of the slurry-supply mechanism of FIG. 5. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring now to FIGS. 1A and 1B, there is shown a polishing apparatus which comprises polishing pad  2  attached to turnable platen  5 , wafer holding head  3  which holds semiconductor wafer  21  and rotates in a direction shown by an arrow while pressing the wafer  21  against the surface of polishing pad  2  under a given pressure, slurry-supply mechanism  1  which controls an amount of flow of polishing slurry to be supplied to an intermediate region between a central region and an outer end region of the wafer  21  and to the central region per se, respectively.  
         [0024]    Slurry-supply mechanism  1  comprises a pair of slurry-supply nozzles  4   a  disposed side by side on sleeve pipe  6  at positions confronting the intermediate region between the central region and the outer end region of wafer  21 , sleeve  6  being held above polishing pad  2  and extending in a radial direction of polishing pad  2 . Slurry-supply mechanism  1  further comprises another nozzle slurry-supply for  4   b  between a pair of slurry nozzles  4   a  on sleeve pipe  6  at a position confronting the central region of wafer  21 , pumps  7  for individually supplying pair of slurry-supply nozzles  4   a  and slurry-supply nozzle  4   b  with the polishing slurry, and slurry-supply sources  8  for supplying respective pumps  7  with the polishing slurry under pressure.  
         [0025]    The amounts of the polishing slurry, i.e., the amount of flow of the polishing slurry dropped from these three nozzles  4   a  and  4   b  are determined by the numbers of rotations of respective pumps  7 . Instead of controlling the number of rotations of pumps  7 , flow control valves may be provided in respectives three fluid supply tubes introduced in the sleeve pipe  6 . However, since the openings of the three flow control valves may be choked or plugged with the polishing slurry it is desirable to control the flow of polishing slurry the number of rotation of the pumps  7 .  
         [0026]    [0026]FIG. 2 is a graphical representation of distribution of the polished amount of wafer surface when wafer  21  is polished while changing the amount of polishing slurry dropped from slurry nozzles  4   a  and  4   b.    
         [0027]    More specifically, polishing of a tungsten film of the wafer was conducted under the two different conditions. That is to say, in the first condition, the amount of polishing slurry supplied to the central region of the wafer was selected to be at the maximum as in the prior art, namely, in FIGS. 1A and 1B, the amount of polishing slurry dropped from the slurry nozzle  4   b  was larger than that from the slurry nozzles  4   a  and in the second condition, the amount of polishing slurry dropped from the slurry nozzles  4   a  confronting the intermediate region of the wafer was selected to be larger than that from the slurry nozzle  4   b  confronting the central region of the wafer. As a result, as seen from FIG. 2, when a larger amount of polishing slurry is dropped onto the center of wafer (at 200 mm position in wafer surface), as indicated by a curve of white circles, a difference between the polished amount at the central region of the wafer and that at the outer end region of the wafer is appreciably larger. On the other hand, when a larger amount of polishing slurry is dropped onto the intermediate region of the wafer between the central and outer end regions of the wafer, as indicated by a curve of black circles, a difference between the polished amounts at the two regions of wafer is rather small.  
         [0028]    It is to be noted that the amount of polishing shown in FIG. 2 is an indication on a display, which was obtained, through conversion by a personal computer, from a thickness of the polished tungsten film of wafer measured by the four-terminal resistance measuring method that measures series resistances at respective portions of the wafer. This method is very simple and can be used to conduct evaluations as set forth below by monitoring the display indication.  
         [0029]    [0029]FIG. 3 illustrates a first variant of the slurry-supply mechanism. The slurry-supply mechanism of this variant is constructed by taking into consideration the fact that when, for example, the quality of film of a wafer is easy to be polished or a pattern density transferred onto a wafer is low, a single slurry nozzle is sufficient for achieving the desired polishing of the wafer. As shown in FIG. 3, single slurry nozzle  4   c  is attached to block  9 , which is guided by guide bar  11 , such that the slurry nozzle can be fixedly positioned at any position in a radial direction of polishing pad  2 . Flexible tube  13  connected to nozzle  4   c  via block  9  is spirally loosely wound around guide bar  11  held by bracket  10  so that block  9  is allowed to move in the radial direction along guide bar  11 . Upon conducting polishing operation, slurry nozzle  4   c  is adequately positioned to obtain a uniform finish of polishing, and subsequently block  9  is fixed to guide bar  11  with screw  12 . When the polishing operation is started, polishing slurry  22  is dropped onto the surface of polishing pad  2 .  
         [0030]    [0030]FIG. 4 is another variant of the slurry-supply mechanism shown in FIG. 3. As shown in FIG. 4, the slurry-supply mechanism of this variant includes a shifting and positioning mechanism having a block  9  mounting thereon nozzle  4   c  and accommodating therein a nut, for permitting slurry nozzle  4   c  to change its position in the radial direction of polishing pad  2  even during polishing operation, a feed screw  14  being in engagement with the nut of block  9 , and pulse motor  15  for rotating the feed screw  14 .  
         [0031]    [0031]FIG. 5 illustrates a second variant of the slurry-supply mechanism. As shown in FIG. 5, the slurry-supply mechanism of this variant has two slurry nozzles  4   c  and  4   d,  which are able to appropriately and arbitrarily change their respective positions on guide bar  11 . Block  9   a  on which slurry nozzle  4   c  is mounted and block  9   b  on which slurry nozzle  4   d  is mounted are able to slide on common guide bar  11 , and are fixed thereto with lock screws  12 .  
         [0032]    [0032]FIG. 6 illustrates a variant of the slurry-supply mechanism of FIG. 5. As shown in FIG. 6, the slurry-supply mechanism of this variant has two slurry nozzles  4   c  and  4   d,  which are positioned at any position on guide bar  11  during the polishing operation. The slurry-supply mechanism of this variant includes a shifting and positioning mechanism having block  9   c  mounting thereon slurry nozzle  4   c  and accommodating therein a nut, block  9   d  mounting thereon slurry nozzle  4   d  and accommodating therein a nut, two feed screws  14  being in engagement with the two nuts, respectively, and pulse motors  15   a  and  15   b  which are able to independently drive the rotational motion of respective feed screws  14 .  
         [0033]    Further, the slurry-supply mechanism of this variant can always polish inside a wafer surface uniformly by adequately combining a positioning program of two slurry nozzles  4   c  and  4   d  with a pumping out program of a slurry pump, with respect to a variety of polishing modes.  
         [0034]    In this variant, the guide bar may be provided for each block.  
         [0035]    Although the foregoing description has been made with reference to preferred embodiments having a single wafer holding head and a single slurry-supply mechanism, it should be appreciated that the present invention is applicable to an embodiment in which two wafer holding mechanisms and two slurry-supply mechanisms are provided.  
         [0036]    While preferred embodiment of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.