Patent Publication Number: US-6341995-B1

Title: Chemical mechanical polishing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus of chemical mechanical polishing (CMP), and more particularly to, an improved apparatus of chemical mechanical polishing, which reduces air sharp pressure on the polish head for preventing the breakage of unpolished wafers. 
     2. Description of the Prior Art 
     Chemical mechanical polishing (CMP) is the only technology, which can provide a total planarization for ULSI process. This technology comes from IBM company and has been developed through many decades, and been already applied on many products, such as central processing unit (CPU). The philosophy is the planarization technique that uses a “knife grinder” like mechanical polishing method and in accompanies with a proper chemical reagent to planarize the rough sketch on wafer surface. Once all parameters are controlled well, chemical mechanical polishing can offer a smooth degree of more than 94%. Therefore, semiconductor manufacturers and the suppliers of facilities and chemicals all over the world are continually investing the development of CMP technology. 
     Referring to FIG. 1, which indicates a partial structural drawing the conventional traditional chemical mechanical polishing apparatus  10  which is composed of a wafer head  110 , and a polish head  120 . Wafer head  110  includes a wafer air inlet  112 , a carrier firm  114  and a wear ring  116 . Polish head  120  includes a polish air inlet  122 , a polish air outlet  124 , a pad air inlet  126  and a slurry diaphragm  128 . When an unpolished wafer  118  is placed on the wafer head  110 , the carrier firm  114  is put smoothly on the unpolished wafer  118 , which is composed of high molecule polymerization, for example, plastic, rubber . . . etc, and then pouring in air from the wafer air inlet  112 . The air pressure on the wafer head  110  is P wafer , which is being pressed uniformly on the unpolished wafer  118  through the carrier firm  114 , and the function of the wear ring  116  is to prevent the unpolished wafer  118  from slipping out from the wafer head  110  to break. Then, to pour air into the wafer air inlet  122  and the air will press uniformly on the slurry diaphragm  128 , which is composed of high molecule polymerization, such as plastic, rubber . . . etc, and then leave from the polish air outlet  124 . The air pressure on polish head  120  is P polish . Especially to take notice on the difference between P wafer  and P polish , which should be negative (it means ΔP=P wafer −P polish &lt;0). By means of letting P polish  to be greater than P wafer  unpolished wafer  118  can stick on the carrier firm  114  to process polishing. When the difference is positive (It means ΔP=P wafer −P polish &gt;0), the unpolished wafer  118  can&#39;t stick on the carrier firm  114 , and the unpolished wafer  118  will slip out the wear ring  116  and break. Besides, when polishing pad directly polishes the surface of the unpolished wafer  118 , not only the slurry diaphragm  128  will release slurry to increase efficiently, but also the pad air inlet  126  will pour in air to maintain the system operation balance. 
     A partial air pressure regulation system is illustrated in FIG.  2 . When air goes into the polish head  120  (through an air supply line  132 ), it needs to pass a regulator E/P first. Because the air pressure controlling system (not shown in Figure) must change way to send signal from digital to analog through this regulator and to adjust air pressure from the polish head  120 . When the air leave the polish head  120  through another air line  134 , it needs to pass a second polish pressure transducer P/I  138 , which functions to change signal from analog to digital and to send back to air pressure control system. It owes to adjust air pressure through the wafer head  120 . 
     But when pouring air to process chemical mechanical polishing, no matter the wafer air inlet  112 , the polish air inlet  122  or the pad air inlet  126 , the air pressure curves will all be the one illustrated in FIG.  3 . The curve first show some time a sharp pressure, and gradually become air pressure steady state. In sharp pressure condition, due to the curve range of air pressure is huge: 
     (1) When P wafer  on the top point of the sharp pressure, and P polish  is on the low point, it will increase the probability of ΔP=P wafer −P polish &gt;0, and the unpolished wafer  118  will slip out the wear ring  116  and break. 
     (2) When the pressure difference between P wafer  and P polish  is too huge, it will cause slurry diaphragm  128  to break. In polishing process, slurry flows into the polish air inlet  122 /outlet  124  from break and flows through the air supply line  132 ,  134  to the first regulator E/P  136 , the second regulator E/P  138 . It will make the real air pressure not be detected, and will send out a wrong signal to the air pressure control system. It will cause error on adjustment of air pressure, ΔP=P wafer −P polish &gt;0, and make unpolished wafer  118  slip out the wear ring  116  and break. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved chemical mechanical polishing apparatus is provided for processing chemical mechanical polishing that substantially overcomes drawbacks of above mentioned problems aroused form the conventional methods. 
     Accordingly, it is an object of the present invention to provide an improved chemical mechanical polishing apparatus which can reduce the sharp pressure and the probability of ΔP=P wafer −P Polish. &gt;0. 
     Another object of the present invention is to provide an improved chemical mechanical polishing apparatus that can detect whether slurry flows from the broken point of diaphragm to air supply line or not. 
     This invention is related to an improved chemical mechanical polishing apparatus, which is composed of a wafer head, a polish head, a damper and a sensor. The flowing speed of gas is reduced by making the diameter of the gas line connected to the damper air inlet smaller than the diameter of the gas line connected to the damper air outlet. The initial air sharp pressure is reduced and make ΔP=P wafer −P polish &lt;0, by adding an air temporary storage machine in between the inlet and the outlet. It means that an unpolished wafer can stick on the carrier firm and won&#39;t slip out to break when polishing. Besides, putting a sensor on the air lines under the air temporary storage machine, when slurry flows in the air line owing to the breaking of slurry diaphragm, the sensor will send a signal to a control system of the improved apparatus of chemical mechanical polishing, and make the related parts stop operating automatically to avoid breaking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a portion of structure in the conventional chemical mechanical polishing apparatus; 
     FIG. 2 shows a portion of air pressure regulation system in the conventional chemical mechanical polishing apparatus; 
     FIG. 3 shows a pressure curve of entering air into the conventional chemical mechanical polishing apparatus; 
     FIG. 4 shows a portion of structure in the improved chemical mechanical polishing apparatus of present invention; 
     FIG. 5 shows a show a pressure curve of entering air into the conventional chemical mechanical polishing apparatus; 
     FIGS. 6A to  6 B shows the operation principle of the sensor in the improved chemical mechanical polishing apparatus of present invention; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As illustrated in FIG.4, and in accordance with the partial structure drawing of an improved chemical mechanical polishing  20  been disclosed by the specification. The apparatus is composed of a wafer head  210  for installing an unpolished wafer, a polish head  220  for providing slurry to the surface of the wafer, a damper  230  which is connected to an air inlet of the polish head for reducing the air sharp pressure curve, and a sensor  240  which is connected to an air inlet or outlet of the polish head or damper for detecting an unusual flowing liquid. Wafer head  210  includes a wafer air inlet  212 , a carrier firm  214 , and a wear ring  216 . Polish head  220  includes a polish air inlet  222 , a polish air outlet  224 , a pad air inlet  226 , and a slurry diaphragm  228 . Damper  230  includes a damper air inlet  232  a damper air outlet  234  and an air temporary storage machine  236 . Sensor  240  includes emitter  242  and a receiver  244 . 
     When the unpolished wafer  218  is placed on the wafer head  210 , the carrier firm  214  is put smoothly on the unpolished wafer  218 , which is composed of high molecule polymerization, for example, plastic, rubber . . . etc, and then pouring in air from the wafer air inlet  212 . The air pressure on the wafer head  210  is P wafer , which is pressed uniformly on the unpolished wafer  218  through the carrier firm  214 . The function of the wear ring  216  is to prevent the unpolished wafer  218  from slipping out from the wafer head  210  to break. Then, to pour air into the polish air inlet  222 , and the air will press uniformly on the slurry diaphragm  228 , and then leave from the polish air outlet  224 . The air pressure on the wafer head  220  is P polish.  The difference between P wafer  and P polish  is negative, it means that ΔP=P wafer −P polish &lt;0. By means of letting P wafer  to be greater then P polish  can make the unpolished wafer  218  stick on the carrier firm  214  for polishing. Besides, when polishing the unpolished wafer  218 , the slurry diaphragm  228  will release slurry for polishing the unpolished wafer  218  more efficiently. Simultaneously, the pad air inlet  226  will also pour in air for maintaining the system operation balance. 
     FIG.  4 . and FIG.  5 . will be used in conjunction for detail structure and the operation principle of the damper  230 . When air flows into the air temporary storage machine  236  from the damper air inlet  232  and leaves from the damper air outlet  234 , the air flowing speed will be reduced. That is because the radius of the line which is connected to the damper air inlet  232 , for example ¼ inches, is smaller than the radius of the line which is connected to the damper air outlet  234 , for example ⅜ inches. According to the principle of hydromechanics, when air flows from a smaller transverse area to a bigger transverse area, the speed will slow down, and it can reduce the initial air sharp pressure curve. Moreover, the improved chemical mechanical polishing apparatus  20  of the present invention further includes the air temporary storage machine  236  between the damper air inlet  232  and the damper air outlet  234 . Thus, the ΔP=P wafer −P polish &gt;0 can be reduced in a more effective way. It also means that the unpolished wafer  218  can stick on the carrier firm  214  to process polishing and it will not break due to slip out from the wear ring  216 . 
     Besides, according to real condition, the damper  230  can also be placed on any air line, for example, on the wafer air inlet  212 , the pad air inlet  226  . . . etc. Furthermore, in order to avoid a greater pressure difference between P wafer  and P polish  for causing breakage on the slurry diagram  228 , slurry flows from the breaking point to the polish air inlet  222 /outlet  224 , and flows along an air supply line to the first regulator E/P and the second polish pressure transducer P/I. The real air pressure will not be detected, and a wrong signal will be send out to the air pressure control system to cause a wrong air pressure adjustment. ΔP=P wafer −P polish &gt;0 will happen and unpolished wafer will slip out the wear ring  216  and break. 
     The present invention installs a sensor  240  on an air line  238  under the air temporary storage machine  236 . As illustrated in FIG. 6, when light emits from an emitter  242 , normally, it should go through air directly and forth to a receiver  244  to be received. But if there is slurry flowing in the air line, the light emitted by the sensor  240  from the emitter  242  will refract when goes through slurry, and makes the receiver  244  undeceived. (As illustrated in FIG.6) When the situation happens, sensor  240  will send a signal to the control system of the improved chemical mechanical polishing apparatus  20  to make related parts stop operating to prevent the unpolished wafer  218  from slipping out the wear ring  216  and break. 
     Of course, the mode of sensor is not limited to light passing function; it also can be light refraction sensor, radiation sensor or any other that can recognize the air and liquid. Besides, sensor also can be install on any air line of the improved chemical mechanical polishing apparatus. 
     Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.