Patent Publication Number: US-6702658-B2

Title: Wafer polishing apparatus utilizing an Oldham&#39;s coupling mechanism for the wafer carrier

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wafer polishing apparatus, which polishes a wafer by a Chemical Mechanical Planarizer (CMP). 
     2. Description of the Related Art 
     In polishing by a CMP, a wafer which is rotating is pressed against a rotating polishing pad in a predetermined pressure and mechano-chemical polishing agent is supplied into a space between the polishing pad and the wafer. In this case, the wafer is pressed against the polishing pad while being held with a carrier, and the wafer receives a rotation force. 
     A conventional wafer polishing apparatus has three pins at the bottom of a rotating table which is connected to a drive source, and the three pins are fit into openings for the pins which are formed on the carrier, so that rotation of the driving force is transmitted to the carrier. 
     In fact, the wafer is generally polished at a position which is out of the center of the polishing pad; hence a friction force in side directions, acted on the wafer, affects the carrier. In the conventional wafer polishing apparatus, the force in side directions is received by the pins. 
     However, if the pins receive the force in side directions, polishing accuracy of the wafer deteriorates. This is because the pins receive the force while rotating and a position for receiving the force is varied, thus the carrier receives a wobbling force. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide a wafer polishing apparatus by which a wafer can be accurately manufactured. 
     In order to achieve the above-described object, the present invention provides a wafer polishing apparatus which polishes a surface of a wafer, comprising: a rotary shaft connected to a drive source; and a carrier that holds the wafer and presses the surface of the wafer against a polishing pad that is rotating, the carrier being connected to the rotary shaft through an Oldham&#39;s coupling mechanism. 
     According to the present invention, since rotation from the rotary shaft is transmitted to the carrier through the Oldham&#39;s coupling mechanism, the carrier can be rotated in a stable condition even though the carrier receives a force in side directions; thus the wafer can be accurately polished. 
     As described hereinabove, according to the present invention, the carrier can always rotate in a stable condition even though it receives a force in side directions, because the rotation from the rotary shaft is transmitted to the carrier through Oldham&#39;s coupling mechanism. Therefore, the wafer can be accurately polished. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein: 
     FIG. 1 is a perspective view showing an entire structure of a wafer polishing apparatus; 
     FIG. 2 is a vertical section view showing a structure of a wafer holding head; 
     FIG. 3 is a plan view showing a structure of a carrier driving device; 
     FIG. 4 is a section view along the line  4 — 4  of the carrier driving device in FIG. 3; and 
     FIG. 5 is another section view along the line  5 — 5  of the carrier driving device in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder a preferred embodiment for a wafer polishing apparatus of the present invention will be described in detail in accordance with the accompanying drawings. 
     FIG. 1 is a perspective view showing an entire wafer polishing apparatus  10 . As seen from FIG. 1, the wafer polishing apparatus  10  comprises a polishing stage  12  and a wafer holding head  14 . 
     The polishing stage  12  is formed like a disk, and a rotary shaft  16  is connected to the bottom center of the polishing stage  12 . The polishing stage  12  rotates by driving a motor  18 , which is connected to the rotary shaft  16 . A polishing pad  20  is adhered onto the top face of the polishing stage  12 , and mechano-chemical agent is supplied from a nozzle (not shown) on the polishing pad  20 . 
     As seen now from FIG. 2, the wafer holding head  14  comprises a head body  22 , a carrier  24 , a retainer ring  26 , a guide ring  28 , an air bag  30  for the carrier, and another air bag  32  for the retainer ring. 
     The head body  22  is formed like a disk, and a rotary shaft  34  is connected onto the top face of the head body  22 . The head body  22  is driven by a motor (not shown) which is connected to the rotary shaft  34 , whereby the head body  22  rotates in a direction of an arrow B in FIG.  1 . 
     The carrier  24  is also formed like a disk, and is arranged at the bottom center of the head body  22 . The carrier  24  is driven by a carrier driving device  36 , so that the carrier  24  rotates. 
     The retainer ring  26  is arranged at an outer periphery of the carrier  24 . 
     The guide ring  28 , on the other hand, is arranged at an outer periphery of the retainer ring  26 . The guide ring  28  is fixed to the bottom of the head body  22 , and a groove  28 A is formed on an inner peripheral face of the guide ring  28 . A flange  26 A formed on the outer peripheral face of the retainer ring  26  sits into the groove  28 A, whereby the retainer ring  26  is prevented from falling off when the wafer holding head  14  is lifted. 
     The air bag  30  for the carrier is arranged in a space between the carrier  24  and the head body  22 , and inner pressure of the air bag  30  is raised by supplying air from an air supply apparatus (not shown). The top face of the carrier  24  is pressed by the air bag  30  for the carrier, whereby a wafer W is pressed against the polishing pad  20 . 
     The air bag  32  for the retainer ring is arranged in a space between the retainer ring  26  and the head body  22 , and inner pressure of the air bag  32  is raised by supplying air from the air supply apparatus (not shown). The top face of the retainer ring  26  is pressed by the air bag  32  for the retainer ring, whereby the retainer ring  26  is pressed against the polishing pad  20 . 
     FIG. 3 is a plan view showing a structure of the carrier driving device  36 . FIGS. 4 and 5 are both sectional views along the line  4 — 4  and the line  5 — 5 , respectively, of the carrier driving device  36  in FIG.  3 . 
     The carrier  24  has a hollow form, and is constructed of a carrier body  24 A and a ring-shaped cover  24 B which covers an opening of the top face of the carrier body  24 A. The over  24 B is fixed with bolts (not shown) at the top part of the carrier body  24 A. 
     A disk-shaped drive plate (a rotation driving member)  40  is contained in an inner peripheral part of the carrier body  24 A. The drive plate  40  is secured to the bottom end of a drive shaft (rotary shaft)  42 , which is connected to the bottom center of the head body  22  (refer to FIG.  2 ). The drive plate  40  is formed to have a diameter whose size is a little smaller than that of the carrier body  24 A, and its outer peripheral edge is rounded. 
     A ring-shaped intermediate plate (rotation transmitting member)  44  is only placed on the drive plate  40 , and a drive shaft  42  is inserted with a little space through the inner peripheral part of the intermediate plate  44 . First U-shaped recesses (openings for the first pins to enter)  46  and  46 , and second U-shaped recesses (openings for the second pins to enter)  48  and  48  are alternatively formed at every  90  degrees interval on the outer peripheral part of the intermediate plate  44 . The first U-shaped recesses  46  and the second U-shaped recesses  48  are formed in a predetermined depth from the outer periphery toward the center of the intermediate plate  44 , and the recesses  46  and  48  are formed to have a wider width than a diameter of first pins  50  and  50 , and second pins  54  and  54 . 
     The first pins  50  and  50  are loosely fit into the first U-shaped recesses  46  and  46 . The first pins  50  and  50  stand straight on the drive plate  40 , and their top end parts are fixed to an assisting plate  52 , which is elongated and is fixed to the drive shaft  42 . Rotation of the drive plate  40  is transmitted to the intermediate plate  44  through the first pins  50  and  50 . 
     On the other hand, the second pins  54  and  54  are loosely fit into the second U-shaped recesses  48  and  48 . The second pins  54  and  54  stand straight on the bottom face of the inner periphery of the carrier body  24 A, and their top ends are fixed to the back face of the cover  24 B. Rotation of the intermediate plate  44  is transmitted to the carrier body  24 A through the second pins  54  and  54 . 
     Moreover, notches  40 A and  40 A having larger diameters than that of the second pins  54  are formed at two sections on the outer periphery of the drive plate  40  in order to prevent the second pins  54  and  54  from contacting with the drive plate  40 . The second pins  54  and  54  are inserted through the notches  40 A and  40 A. 
     As far as the second pins  54  are prevented from contacting with the drive plate  40 , openings having larger diameters than that of the second pins  54  may be formed on the drive plate  40  so that the second pins  54  are inserted through the openings. 
     In the carrier driving device  36  which is constructed as presented above, when the head body  22  rotates, its rotation force is transmitted to the drive shaft  42  and to the drive plate  40 . When the drive plate  40  rotates, its rotation force is transmitted to the intermediate plate  44  through the first pins  50  and  50 , and rotation force of the intermediate plate  44  is transmitted to the carrier body  24 A through the second pins  54  and  54 . 
     In other words, the rotation force of the drive shaft  42  in the carrier driving device  36  is transmitted to the carrier  24  by using Oldham&#39;s coupling mechanism. The carrier  24  can rotate in a stable condition even though the carrier  24  receives a force in side directions since the rotation of the drive shaft  42  is transmitted to the carrier  24  through the Oldham&#39;s coupling mechanism. More specifically, when the carrier  24  receives a force in side directions, the drive plate  40  receives the force with its outer periphery, and the first pins  50  and the second pins  54  receives the rotation force; only thus, the carrier  24  can always rotate in a stable condition by eliminating a twisting force to the drive shaft  42 . 
     Now, an operation of the wafer polishing apparatus  10  which is constructed as described above is presented below. 
     First, the wafer W is held by the wafer holding head  14  and is placed on the polishing pad  20 . Compressed air is supplied from an air supply apparatus (not shown) into the air bag  30  for the carrier and the air bag  32  for the retainer ring in order to raise the inner pressure of the air bags  30  and  32 . The wafer W is pressed against the polishing pad  20  with the carrier  24  in a predetermined pressure whereas the retainer ring  26  is pressed against the polishing pad  20  in a predetermined pressure, both by the raised inner pressure of the air bags  30  and  32 . The polishing stage  12  rotates in a direction indicated by an arrow A in FIG. 1 in that state while wafer holding head  14  rotates in a direction indicated by an arrow B in FIG.  1 . Then mechano-chemical polishing agent is supplied onto the rotating polishing pad  20  from a nozzle (not shown). The bottom face of the wafer W is polished by the above-described process. 
     The wafer W which has been polished through the above-described process is held by the carrier  24  and is pressed against the polishing pad  20  so that rotation is given to the wafer W. The carrier  24  is driven and rotates by the carrier driving device  36 , of which operation is presented below. 
     When the rotary shaft  34  which is connected to the head body  22  is driven by a motor (not shown) so as to rotate the head  22 , the rotation is transmitted the drive shaft  42  for that to rotate. The rotation of the drive shaft  42  is transmitted now to the drive plate  40  and further to the intermediate plate  44  through the first pins  50  and  50 . The rotation of the intermediate plate  44  is then transmitted to the carrier body  24 A through the second pins  54  and  54 , whereby the carrier  24  rotates. 
     In the carrier driving device  36  in the present embodiment, the carrier  24  can rotate in a stable condition since the rotation force is transmitted from the drive shaft  42  through Oldham&#39;s coupling mechanism. More specifically, when the carrier  24  receives a force in side directions, the drive plate  40  receives the force with its outer periphery, and the first pins  50  and the second pins  54  receive the rotation force only; thus, the carrier  24  can always rotate in a stable condition by eliminating a twisting force to the drive shaft  42 . 
     Moreover, in the carrier driving device  36  in the present embodiment, the carrier  24  has a hollow form, in which the drive plate  40  is contained; hence the force from the polishing pad  20  can be received at the proximity (at the height H) of the polishing pad  20 . Thus the carrier  24  can be rotated in even a more stable condition. 
     Further, since the outer peripheral edge of the drive plate  40  is rounded, it can absorb vibrations (inclination) of the carrier  24  throughout polishing; thus, the vibrations are prevented from being transmitted to the drive shaft  42 . 
     According to the carrier driving device  36  in the present embodiment, the carrier  24  can rotate in a stable condition. Therefore, the wafer W can be accurately polished by eliminating overload to the wafer W and preventing the wafer W from slipping out of the machine. 
     In the present embodiment, the pins formed at both the drive plate and the carrier are loosely fit into U-shaped recesses that are formed at the intermediate plate in order to transmit the rotation. However, the pins formed at the intermediate plate may be loosely fit into the U-shaped recesses that are formed at the drive plate and the carrier in order to transmit the rotation. 
     It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.