Abstract:
The polish particle surface of the dresser of a chemical mechanical polish apparatus used for a planarization process in manufacturing semiconductor devices is inclined. Moreover, the pressure to be applied onto the polish surface of the dresser is linearly varied with a nonzero slope.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a chemical mechanical polish apparatus that is used for manufacturing semiconductor devices. In particular, the present invention relates to a polish adjustment of a polish pad using a dresser.  
           [0003]    2. Description of Related Art  
           [0004]    [0004]FIG. 9 shows drawings for explaining the prior art. It shows a state in which a polish pad  102  is pad-dressed. As shown in FIG. 9A, a dresser  103  is placed on a polish pad  102  that is adhered onto a surface plate  101 . When a pressure is applied to the dresser  103 , the surface of the polish pad  102  is ground by a diamond particle surface  103 A formed on the peripheral surface zone of the dresser  103 . As a result, the surface of the polish pad  102  is polished as shown in FIG. 9A. In general, an abrasive material or pure water is supplied to the polish pad during a dressing process.  
           [0005]    A polish is carried out in a planarization process in manufacturing a semiconductor device or the like. During such a polish, however, the abrasive material and/or polish dust stick to the surface of the polish pad  102 , which eventually causes the polish process to become unstable. For this reason, in order to maintain a stable polish, the polish pad  102  needs to be dressed and polished by the dresser  103 .  
           [0006]    However, the above-described prior art has the following problem. As shown in FIGS. 9B and 9C, the grind amount of the portion of the polish pad  102  at distance Rt from the center of rotation of the surface plate  101  is proportional to the contact length L of the diamond particle surface  103 A with the polish pad  102  at distance Rt from the center of the surface plate  101 . By a simple calculation, the length L is given by  
             L= 2· Rt ·(Cos −1 (( Rt   2   +Rx   2 −R 1   2 )/(2 ·Rt·Rx ))−Cos −1 (( Rt   2   +Rx   2 −R 2   2 )/(2 ·Rt·Rx ))  (1)  
           [0007]    Here, as shown in FIGS. 9B and 9C,  
           [0008]    Rx: the distance between the center of the dresser  103  and the center of the surface plate  101   
           [0009]    R 1 : the outside radius of the diamond particle surface  103 A  
           [0010]    R 2 : the inside radius of the diamond particle surface  103 A.  
           [0011]    [0011]FIG. 11 shows the dependency of the contact length L of the diamond particle surface  103 A with the surface of the polish pad  102  at distance Rt from the center of the surface plate  101  when, for example, Rx=17 cm, R 1 =16 cm, and R 2 =15.5 cm. The graph shows that the length L varies over a wide range within the polish pad. Since the grind amount of the polish pad  102  is proportional to the length L, the grind amount of the polish pad  102  varies over a wide range. As a result, the surface of the polish pad  102  cannot be made flat as needed. The minimum grind amount required to achieve a satisfactory state of polish is pre-determined. Therefore, even at a location where the value of L is the smallest, the required minimum grind amount must be secured. On the other hand, at a location where the value of L is large, the polish pad is over-ground.  
           [0012]    As discussed above, the value of L grows very large in a region near the periphery of the surface plate (at points 29 cm from the center of the surface plate) and in a region near the center of the surface plate (at points 1.5 cm from the center of the surface plate). Therefore, in these regions, the polish pad is ground by a large amount. The problem that the polish pad is ground by a large amount in a region near the periphery of the surface plate can be solved by increasing the diameter of the dresser  103 . FIG. 12 shows the dependency of L on the distance Rt from the center of the surface plate  101  in the case the diameter of the dresser  103  has been increased to Rx=20 cm, R 1 =19 cm, and R 2 =18.5 cm. In this case, as seen from FIG. 12, the value of L is 1.47 cm at the point where Rt=29 cm, which is shorter by 2.1 cm than the value of L at the point where Rt=29 cm in the case shown in FIG. 11. However, in the interior of the admissible range, the value of L achieves a maximum of 2.44 cm at the point where Rt=1.5 cm, which is not significantly smaller than the maximum value of L achieved at Rt=1.5 cm in the case shown in FIG. 11, resulting in practically no improvement at all.  
           [0013]    Thus, in the case the grind amount of the polish pad varies over a wide range depending on the distance Rt from the center of the surface plate  101 , the life span of the polish pad is seriously shortened. A polish pad is dressed and ground after it has been used to polish a prescribed number of semiconductor wafers. FIG. 10 is a schematic cross sectional view of the grind surface  102 A of the polish pad  102  attached onto the polish surface plate  101 . In FIG. 10, the region  102 A 1  where the grind amount is the largest (position 1.5 cm from the center of the surface plate), the region  102 A 2  where the grind amount is the smallest (position 6.9 cm from the center of the surface plate), and the region  102 A 3  which is the outer limit of the admissible polish range (position 29.0 cm from the center of the surface plate) are indicated with arrows.  
           [0014]    As mentioned before, in order to carry out a stable polish, the polish pad must be ground at least by a minimum necessary amount. The region  102 A 2 , where the grind amount is the smallest (position 1.5 cm from the center of the surface plate), must also be ground at least by the same minimum necessary amount, which is 0.67 μm per wafer in this case. However, in the region  102 A 1 , where the grind amount is the largest (position 1.5 cm from the center of the surface plate), 1.67 μm per wafer is ground. The life span of the polish pad  102  is determined by the amount ground by the dressing. Therefore, if the polish pad  102  is dressed by an excessive amount, even the surface of the polish surface plate  101  can be ground. When this happens, the surface of the polish surface plate  101  is damaged, and the polish surface plate  101  needs to be replaced.  
         SUMMARY OF THE INVENTION  
         [0015]    As explained above, the polish pad  102  is ground by a large amount in the interior of the admissible polish range even though the other part of the polish pad  102  remains sufficiently thick within the admissible polish range. Therefore, the polish pad  102 , which is relatively expensive among the required members for manufacturing semiconductors, needs to be replaced at an early stage. This means that the semiconductor manufacturing cost is significantly increased. Moreover, it normally takes 1 to 1.5 hours to replace a polish pad, during which the CMP apparatus cannot manufacture any semiconductor, resulting in a low operation rate. As the life span of the polish pad  102  becomes shorter, the polish pad  102  must be replaced more frequently, which leads to a low operation rate of the apparatus.  
           [0016]    The present invention aims to solve the above-described problems. Therefore, it is an object of the present invention to provide a polish apparatus having a dresser equipped with a polish pad and an inclined polish particle surface for adjusting the polish. It is also an object of the present invention to provide a polish apparatus having a dresser equipped with a polish pad and a polish particle surface for adjusting the polish such that a pressure for adjusting a polish can be applied onto the polish particle surface. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.  
           [0017]    This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above-described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows a top view and a cross sectional view of a dresser ring according to the first embodiment of the present invention.  
         [0019]    [0019]FIG. 2 shows the relation between the press-down pressure of the dresser ring and the grind rate of the polish pad according to the first embodiment of the present invention.  
         [0020]    [0020]FIG. 3 shows the relation between the pressure of the polish pad and the amount of displacement of the polish pad according to the first embodiment of the present invention.  
         [0021]    [0021]FIG. 4 shows a cross sectional view of a polish apparatus for measuring the displacement amount of the polish pad according to the first embodiment of the present invention.  
         [0022]    [0022]FIG. 5 shows a top view of the polish pad according to the first embodiment of the present invention.  
         [0023]    [0023]FIG. 6 shows a graph of the relation between the distance from the center of the surface plate  1  and the grind rate of the polish pad according to the first embodiment of the present invention.  
         [0024]    [0024]FIG. 7 shows a cross sectional view of a dresser ring according to the second embodiment of the present invention.  
         [0025]    [0025]FIG. 8 shows a graph of the relation between the distance from the center of the polish surface plate  1  and the grind rate of the polish pad according to the second embodiment of the present invention.  
         [0026]    [0026]FIG. 9 shows a top view and a cross sectional view of a dresser ring according to the prior art.  
         [0027]    [0027]FIG. 10 shows a cross sectional view of the polish pad during a polish according to the prior art.  
         [0028]    [0028]FIG. 11 shows a graph of the relation between the distance from the center of the polish surface plate  101  and the contact length of the diamond particle surface with the polish pad according to the prior art.  
         [0029]    [0029]FIG. 12 shows a graph of the relation between the distance from the center of the polish surface plate  101  and the contact length of the diamond particle surface with the polish pad in the case the diameter of the dresser is large according to the prior art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    The present invention will now be described based on preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. Not all of the features and the combinations thereof described in the embodiment are necessarily essential to the invention.  
         [0031]    [0031]FIG. 1 shows the first embodiment of the present invention. FIG. 1A shows a cross sectional view of a dresser ring  3 . The dresser ring  3  shown in FIG. 1A is installed on a polish surface plate  101  as in the prior art, and a dressing process is carried out. FIG. 1B shows the cross section across the line A-A′ of-the dresser ring  3  shown in FIG. 1A. FIG. 1C shows a magnified view of what is shown in FIG. 1B. In the first embodiment of the invention, as shown in FIG. 1B and FIG. 1C, the surface of the diamond particle surface  3 A of the dresser ring  3 A is inclined with respect to the surface of the polish pad  102 . Because of this inclination, when the dresser ring  3  is pressed onto the polish pad  102  at a constant pressure, the displacement amount of the polish pad  102  varies across the points between  3 A 1  and  3 A 2 . As a result, the press-down pressure varies across the points between  3 A 1  and  3 A 2 .  
         [0032]    As a consequence, each point on the polish pad  102  is ground by the dressing action at a different rate. In other words, the controlled grind rate is distributed in the radial direction of the diameter of the dresser ring  103 . In the present embodiment, the above-described inclination was prescribed by determining the value of D shown in FIG. 1C so that the grind rate of the polish pad  102  at outside diameter point  3 A 2  in the radial direction will be  5  times as large as the grind rate of the polish pad  102  at inside diameter point  3 A 1 . More specifically, using a dresser ring  103  identical to the one used in the prior art shown in FIG. 9, the relation between the press-down pressure of the dresser ring  103  applied onto the polish pad  102  and the grind rate with respect to the press-down pressure is obtained. If the relation between the pressure and the grind rate obtained in this way has turned out to be, for example, the one shown in FIG. 2, the desired grind rate ratio of 5 to 1 is obtained. As a result, the pressures P 1  and P 2  can be obtained.  
         [0033]    Next, the relation between the press-down pressure applied onto the polish pad  102  and the displacement amount of the polish pad  102  is obtained. If the relation between the press-down pressure applied onto the polish pad  102  and the displacement amount of the polish pad  102  is, for example, as the one shown in FIG. 3, the displacement amounts D 1  and D 2  of the polish pad  102  caused by the pressures P 1  and P 2 , respectively, are obtained. In this case, the value of the afore-mentioned quantity D is determined by the equation D=D 1 −D 2 . Here, the relation between the press-down pressure applied onto the polish pad  102  and the displacement amount of the polish pad  102  is obtained as follows. In FIG. 4, which shows a cross sectional view of a polish apparatus for measuring the displacement amount of a polish pad, a first load  4  and a second load  5  are placed on a polish pad  2 . The displacement amount d of the polish pad  2  in this case is obtained by measuring the displacement of the position f of the surface of the first load  4 . The position f is easily measured by a laser displacement gauge  6 . Similarly, by changing the weight of the second load  5 , the relation between the pressure and the polish pad displacement amount d is obtained a shown in FIG. 3.  
         [0034]    The dresser ring  3 , which has been formed using the value of D obtained in the above-described manner, is pressed onto the polish pad  2  with the press-down pressure P 0 =(P 1 +P 2 )/ 2 , and a dressing process is carried out. As a result, the dresser ring  3  is pressed onto the polish pad  2  with the pressures of P 1  and P 2  at positions  3 A 1  and  3 A 2  of FIG. 1C, respectively. In this case, the polish pad grind rate at  3 A 2  becomes 5 times as large as that at  3 A 1 . The grind rate obtained in the prior art depends solely on the contact length L of the polish pad with the dresser. In contrast, according to the present embodiment, the press-down pressures at distinct contact points differ from each other. Therefore, the grind rate of the polish pad  2  in the dressing process according to the present embodiment depends not only on the contact length L of the polish pad with the dresser but also on the press-down pressure at each contact point.  
         [0035]    More specifically, in FIG. 5 which shows a top view of the polish pad  2 , the polish pad grind rate at points that are at distance Rt from the center of the polish surface plate  1  is obtained by integrating the function  
         K(r)·Rt  (2)  
         [0036]    from θ2 (the value of angle θ at which the circle of radius Rt centered the center of the polish surface plate  1  intersects the inner boundary circle of radius R 2  of the dresser ring  3 ) to θ1 (the value of angle θ at which the circle of radius Rt centered the center of the polish surface plate  1  intersects the outer boundary circle of radius R 1  of the dresser ring  3 ). Here, by a geometric analysis of the drawing on FIG. 5, K(r) is given by  
           K ( r ) k ·(( r −R 2 )·4/(R 1 −R 2 )+1),  k  constant.  (3)  
         [0037]    Since r is a function of angle θ, K(r) is expressed as a function of θ as follows.  
           K ( r )= K (θ)= k ·((( Rt ·cos θ− Rx ) 2   +Rt   2 ·sin 2 θ) 0.5   −R 2 )· 4/(R 1 −R 2 )+1)  (4)  
         [0038]    The grind rate V(Rt) of the polish pad at points that are at distance Rt from the center of the surface plate is given by  
         ∫ θ2   θ1   k ·((( Rt −cos θ− Rx)   2   +Rt   2 ·sin 2 θ) 0.5 −R 2 )·4/(R 1 −R 2 )+1)· Rt·dθ.   (5)  
         [0039]    Here,  
         [0040]    Rx: the distance between the center of the dresser  3  and the center of the polish surface plate  1 ;  
         [0041]    R 1 : the radius of the outer boundary circle of the dresser ring  3 ; and  
         [0042]    R 2 : the radius of the inner boundary circle of the dresser ring  3 .  
         [0043]    [0043]FIG. 6 shows a graph which expresses the relation between the grind rate V(Rt) and the distance Rt from the center of the polish surface plate  1  in the case Rx=20 cm, R 1 =19 cm, and R 2 =18.5 cm. In FIG. 6, for ease of comparison with the prior art, the constant k is prescribed so the minimum of the grind rate according to this embodiment is achieved at the same point at which the minimum of the grind rate is achieved in the prior art. As shown in FIG. 6, the grind rate according to the prior art is 2.44 (relative value) at the point where the grind rate of the polish pad  2  is the maximum in the interior of the admissible polish range. On the other hand, the grind rate according to the present embodiment is 2.03 (relative value). Thus, according to the present embodiment, the grind rate can be controlled. As a result, the polish pad cost is reduced and the operation rate of the CMP apparatus is improved.  
         [0044]    Next, a cross sectional view of a dresser ring according to the second embodiment of the-present invention is shown in FIG. 7. As in the case of the first embodiment, FIG. 7 shows a cross sectional view of the dresser ring  3  across the line A-A′. As shown in FIG. 7, according to the second embodiment of the present invention, the diamond particle surface of the dresser ring and its support part are divided into five parts  3 B 1 ,  3 B 2 ,  3 B 3 ,  3 B 4 , and  3 B 5 . Further, distinct pressures P 1 , P 2 , P 3 , P 4 , and P 5  are applied to  3 B 1 ,  3 B 2 ,  3 B 3 ,  3 B 4 , and  3 B 5 , respectively. The values of these pressures are determined as follows. Using the graph shown in FIG. 2, the value of P 2  is determined so that the grind rate at  3 B 2  will be 74% of the grind rate at  3 B 1 . Similarly, the values of P 3 , P 4 , and P 5  are determined so that the grind rates at  3 B 3 ,  3 B 4 , and  3 B 5  will be 48%, 39%, and 30% of the grind rate at  3 B 1 , respectively. In this way, the dresser ring is divided into five parts and pressures of distinct values are applied to the five parts so that the grind rates at these parts are sequentially inclined. Therefore, the grind rate of the polish pad V(Rt) (relative value) at points that are distance Rt from the center of the polish surface plate is given by the following equation (6).  
           V (Rt) = k·RL ·(Cos −1 (Rt+Rx 2 − R 11 2 ) /(2·Rt·Rx))−Cos 31 1 (Rt 2  −Rx 2 −   R 21 2 )/(   2·Rt·Rx)))− 0.74· k Rt·(Cos 31 1 (Rt 2 −Rx 2 − R 12 2 )/( 2·Rt·Rx)) −Cos −1 Rt 2 +Rx 2 − R 22 2 )/(2·Rt·Rx))) +0.48· k· Rt·(Cos −1 (Rt 2 +Rx 2 −R13 2 )/(2·Rt·Rx))−Cos −1 (Rt 2 +Rx 2 − R 23 2 )/(2· RL ·Rx)))+0.39· k· Rt·(Cos −1(Rt   2 +Rx 2 − R 14 2 )/(2·Rt·Rx))−Cos 31 1 (Rt 2 +Rx 2−   R 24 2 )/( 2·Rt·Rx)))+ 0.30· k· Rt·(Cos −1(Rt   2 +Rx 2−   R 15 2 )/(2·Rt·Rx))−Cos− 1 (Rt 2 +Rx 2 − R 25 2 )/(2·Rt·Rx)))   (6)  
         [0045]    Here the inner and outer diameters of the dresser ring are the same as in the prior art, and  
         [0046]    R 11 : the outer radius of  3 B 1 =19.0 cm, R 21 : the inner radius of  3 B 1 =18.91 cm;  
         [0047]    R 12 : the outer radius of  3 B 2 =18.89 cm, R 22 : the inner radius of  3 B 2 =18.81 cm;  
         [0048]    R 13 : the outer radius of  3 B 3 =18.79 cm, R 23 : the inner radius of  3 B 3 =18.71 cm;  
         [0049]    R 14 : the outer radius of  3 B 4 =18.69 cm, R 24 : the inner radius of  3 B 4 =18.61 cm; and  
         [0050]    R 15 : the outer radius of  3 B 5 =18.59 cm, R 25 : the inner radius of  3 B 4 =18.50 cm.  
         [0051]    Using these values, Equation (6) is evaluated. FIG. 8 shows the result of this calculation. For ease of comparison with the prior art, the minimum grind rate according to this embodiment is set equal to the minimum grind rate obtained in the prior art.  
         [0052]    As seen from the graph shown in FIG. 8, which shows the relation between the distance from the center of the polish surface plate  1  and the grind rate of the polish pad, in the interior of the admissible polish range, the maximum polish rate is 2.03 according to the present embodiment. This value is substantially equal to the maximum polish rate obtained in the first embodiment. This value is significantly better than the maximum polish rate obtained in the prior art, which is 2.44 (relative value). Therefore, according to the second embodiment also, the same polish pad cost reduction effect and the same degree of operation rate improvement of the CMP apparatus are achieved.  
         [0053]    According to the present invention, the pressure applied onto the polish pad  102  by the dresser  103  used in the prior art is varied linearly with a nonzero slope in the radial direction of the diameter of the dresser  103 . Therefore, the maximum grind amount of the polish pad within the admissible polish range is reduced. As a result, the life span of the polish pad  102  with respect to the number of semiconductor wafers to be polished is increased, the cost required for the polish pad to polish one semiconductor wafer is reduced, and the operation rate of the CMP apparatus is improved.  
         [0054]    Further, according to the present invention, the diamond particle surface of the dresser is inclined, and the pressure applied to the polish surface of the dresser is varied linearly with a nonzero slope. Therefore, the polish amount of the polish pad can be controlled to a uniform value. As a result, the length of the replacement period of a polish pad is increased, and the operation rate of the CMP apparatus is significantly improved.  
         [0055]    Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the spirit and the scope of the present invention which is defined only by the appended claims.