Abstract:
A method for detecting the endpoint of a chemical mechanical polishing (CMP) process uses the slope variation of temperature difference of polishing pad. The method combines temperature measurement at polishing pad and atmosphere, and numerical analysis to figure out the curve of temperature difference variation versus polishing time. The endpoint of CMP is determined by the change of the slope of the curve. The method allows endpoint to be detected in-situ at the polishing apparatus, without stopping polishing process.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a semiconductor manufacturing process, and more particularly to a method to detect the endpoint of a chemical mechanical polishing (CMP) process based on the temperature slope of the polishing pad. 
   BACKGROUND OF THE INVENTION 
   Advances in semiconductor manufacturing technology have enabled progress to be seen in the scale finely. In the semiconductor manufacturing of a deep submicron process, the depth of focus shrinks constantly to reach the need for increasing speed and the resolution for lithography raises constantly as well. In order to accomplish the above purposes, global planarization of the wafer surface is highly required, and therefore a CMP process to achieve the goal is also needed. 
     FIG. 1  shows a conventional CMP apparatus. With reference to  FIG. 1 , the CMP apparatus constitutes of at least one carrier  110 , for holding a semiconductor wafer  120 . The carrier  110  holds the wafer  120  against the surface of the polishing pad  130  attached to the rotary polishing platen  131 . And the wafer  120  and the polishing pad rotate mutually. During planarization, the wafer  120  oscillates with the polishing pad, and polishing slurry  140  comprised of abrasive fluid, such as silica or alumina abrasive particles suspended in either a basic or an acidic solution, is dispended on the polishing pad and goes into the space between the wafer  120  and the polishing pad  130 , through a conduit  141 . Then mechanical and chemical polishing effects take place on the wafer  120  between the carrier  110  and the polishing pad  130 . The combination of mechanical and chemical polishing effects removes the excessive layers of metal material from the surface of the wafer  120 , and accomplishes global planarization. 
   In the CMP process, the wafer  120  is pressed on the polishing pad  130  because of the downward pressure. Therefore, it is difficult to consistently stop the CMP process at a desired endpoint and to produce a uniform, planar surface on the wafer by measuring the wafer surface. The general statistics shows that two more hours is demanded to measure the wafer surface produced by the conventional CMP process to determine if the wafer surface is planarized well or not. For this reason, the productivity of the CMP process decreases 50%, and the cost of the wafer produced consumes more. The following then says the prior art about the endpoint detection method for the conventional CMP process. 
   U.S. Pat. No. 5,196,353 entitled “Method for controlling a semiconductor (CMP) process by measuring a surface temperature and developing a thermal image of the wafer” issued on Mar. 23, 1993 to Gurtej S. Sandhu et al. describes the use of an infrared radiation detection in the polishing pad to take the thermal image of the surface of a wafer to adjust the parameters of the process. In application, the surface of a wafer posts to the polishing pad tightly, and therefore it is difficult to take the thermal image of the wafer surface. 
   U.S. Pat. No. 5,597,442 entitled “Chemical/mechanical planarization (CMP) endpoint method using measurement of polishing pad temperature” issued on Jan. 28, 1997 to Hsi-Chich Chen et al. describes the endpoint for planarization process is determined by monitoring the temperature of the polishing pad with an infrared temperature measuring device. The method determines the endpoint when the temperature decreases by 2° C. In application, it needs to control the temperature of the slurry, and the detected temperature jounces with the slurry. Therefore, it is difficult to determine the endpoint by measuring the polishing pad temperature decreases by 2° C. 
   U.S. Pat. No. 5,643,050 entitled “Chemical/mechanical polish (CMP) thickness monitor” issued on Jul. 1, 1997 to Lai-Juh Chen et al. describes the method comprises monitoring the temperature of the polishing pad or the polished substrate versus polishing time, integrating the polishing temperature change versus polish time curve with polish time, and applying computer stored integration coefficients to the integrated area to derive the removed thickness. In application, it needs complicated operation processes, and the thickness of the thin film of the wafer surface is not uniform. Therefore, it is difficult to determine the endpoint accurately. 
   U.S. Pat. No. 5,647,952 entitled “Chemical/mechanical polish (CMP) endpoint method” issued on Jul. 15, 1997 to Lai-Juh Chen et al. describes the method for measuring the temperature of the specific area of the polishing pad, and determining the endpoint by detecting a change in said temperature. In application, it needs to control the temperature of the slurry, and the detected temperature jounces with the slurry. Therefore, it is difficult to determine the endpoint by measuring the polishing pad temperature. 
   U.S. Pat. No. 5,722,875 entitled “Method and apparatus for polishing” issued on Mar. 3, 1997 to Mitsuaki Iwashita et al. describes the use of an infrared temperature sensor to determine the end point of CMP. In application, the detected temperature jounces with the slurry. Therefore, it is difficult to determine the endpoint. Accurately by measuring a single point temperature of the polishing pad. 
   U.S. Pat. No. 6,007,408 entitled “Method and apparatus for endpointing mechanical and chemical-mechanical polishing of substrates” issued on Dec. 28, 1999 to Gurtej S. Sandhu et al. describes the method for measuring the temperature of the backside of the substrate, the polishing pad, planarizing liquid, and the CMP byproducts simultaneously. In application, the change temperature of the byproduct is not evident, and the temperature of the byproduct decreases before being detected. Therefore, it is difficult to determine the endpoint accurately. 
   U.S. Pat. No. 6,077,783 entitled “Method and apparatus for detecting a polishing endpoint based upon heat conducted through a semiconductor wafer” issued on Jan. 20, 2000 to Derryl D. J. Allman et al. describes the method for determining the endpoint by heating a semiconductor wafer so as to cause the surface of the semiconductor wafer to have a specific temperature, and the temperature of said semiconductor wafer changes as the surface of said semiconductor wafer is being removed. In application, the range of the change temperature of said semiconductor wafer would decrease after heat pass the carrier. Therefore, it is difficult to determine the endpoint accurately. 
   U.S. Pat. No. 6,150,271 entitled “Differential temperature control in chemical mechanical polishing processes” issued on Nov. 21, 2000 to William Graham Easter et al. describes the method for determining the endpoint of the CMP process by installing heating and cooling coils to control the rate of the material removed from the surface of the wafer. In application, the temperature of the carrier easily changes with the influence of environment. Therefore, it is difficult to control the temperature and determine the endpoint accurately. 
   Thus, there is a strong demand in a method for determining an endpoint of the CMP process accurately and efficiently. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a method for determining an endpoint of a CMP process by detecting the variation of temperature slope of a polishing pad is provided. 
   A feature of the invention is to measure the temperature distribution by a non-contact temperature measuring device, and to calculate the data detected by the temperature measuring device with simple numerical methods to make a curve which shows the trend of the temperature slope of the polishing pad versus polishing time. According to the curve, the method of the invention can easily find out the when the temperature changes obviously, and can thus determine the endpoint of CMP in situ without affecting the process to avoid that the prior art cannot determine the endpoint of the CMP process in situ accurately and efficiency. Furthermore, the method of the invention measures an environmental temperature as a reference to avoid the variation of the measured temperature due to the slurry or environment. 
   In an illustrative embodiment, an apparatus for carrying out the method of the invention includes: at least a carrier, which fixes the wafer to the surface of the polishing pad on the rotary polishing platen. The wafer and the polishing pad rotate mutually. During planarization, the polishing slurry comprising abrasive particles is dispended on the polishing pad through a conduit. It causes mechanical and chemical polishing effects to the wafer between the carrier and the polishing pad. The combination of mechanical and chemical polishing effects makes the excessive metal material removed from the surface of the wafer, and planarizes the wafer. Moreover, apparatus for carrying out the method of the invention further include at least a non-contact temperature measuring device, which measures at least one environmental temperature. 
   As described above, said non-contact temperature measuring device may be a single point temperature measuring device or a thermal image camera, and the single point temperature measuring device may be an infrared detection device. 
   As described above, the non-contact temperature measuring device measures the environmental temperature on the central portion of the polishing pad, the edge portion of the polishing pad, any portion of the CMP apparatus in addition to the rotary polishing platen, or any portion of the stable temperature in the environment. 
   Then, the non-contact temperature measuring device measures the temperature of at least one point in the friction surface, describes just after the wafer and the polishing pad rotate mutually. Thereafter, do a data processing for said measured temperature by at least one operation device. 
   The difference between the measured polishing pad and the environmental temperature is calculated to obtain a raised temperature difference of the polishing pad for polishing, in order to get the variation of the polishing pad temperature accurately and to eliminate the interference from the polishing slurry to said non-contact measuring device. 
   Furthermore, make the curve, describes the temperature difference versus time with simple numerical methods. Then, make a curve, describes the variety of temperature slope of the polishing pad versus polishing time, to determine the endpoint of CMP. 
   As described above, the operation device is built-in the measuring device or is linked to a computer. 
   As described above, the numerical methods may be the least square method or other linear regression methods. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a conventional CMP apparatus. 
       FIG. 2  shows the apparatus according to the method of the invention. 
       FIG. 3  shows spatial relationship between the wafer, the carrier, and the polishing pad of the invention. 
       FIG. 4  shows a wafer-to-polished for use in the method according to the invention. 
       FIG. 5  shows the measured data of surface temperature of the polishing pad during polishing time. 
       FIG. 6 , according to the temperature curve of  FIG. 5 , shows the variety of temperature slope of the polishing pad versus polishing time. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  shows the apparatus according to the present invention. With reference to  FIG. 2 , the CMP apparatus of the invention includes a carrier  210 , for holding a semiconductor wafer  220 . The carrier  210  fixes the wafer  220  to the surface of the polishing pad  230  attached on the rotary polishing platen  231 . During planarization, the wafer  220  moves with the polishing, and polishing slurry  240  comprising an abrasive fluid, such as silica or alumina abrasive particles suspended in either a basic or an acidic solution, is dispended on the pad and flows into the gap between the wafer  220  and the polishing pad  230 , through a conduit  241  above the polishing pad  230 . Mechanical and chemical polishing effects take place on the wafer  220 . The combination of mechanical and chemical polishing effects makes the removal of the excessive metal material from the surface of the wafer  220 , and thus planarizes the wafer  220 . Furthermore, a non-contact thermal image camera  250  linked to a PC  260  is setup next to the CMP apparatus. 
     FIG. 3  shows spatial relationship between the wafer, the carrier, and the polishing pad of the invention. With reference to  FIG. 3 , in the CMP process, the temperature of the polishing pad  230  rises as polishing. And the rise in temperature is dependent on the relative velocity and the coefficient of friction between the polishing pad  230  and the wafer  220 . 
   At the beginning of the CMP process, the polishing pad  230  polishes the first film of the wafer  221  only, thus the rise in temperature is dependent on the relative velocity between the polishing pad  230  and the wafer  220  and the coefficient of friction between the polishing pad  230  and the first film of the wafer  221 , so that the rise in temperature of the polishing pad  230  varies linearly with time. 
   As described above, the first film of the wafer  221  may be made of metal material. 
   When one part of the first film of the wafer  221  is removed, the polishing pad  230  starts to polish the second film of the wafer  222 . Thereat, the polishing pad  230  polishes the first film of the wafer  221  and the second film of the wafer  222  at the same time. The rise in temperature is dependent on the relative velocity between the polishing pad  230  and the wafer  220  and the coefficients of friction of the first film of the wafer  221  and the second film of the wafer  222  with respect to the polishing pad. The rise in the measured temperature of the polishing pad  230  is a function of the relative amount of the first film of the wafer  221  and the second film of the wafer  222 , and so that the temperature varies non-linearly obviously. 
   As described above, the second film of the wafer  222  is made of dielectric material. 
   Furthermore, when the first film of the wafer  221  is fully removed, the rise in temperature of the polishing pad  230  is dependent on the relative velocity between the polishing pad  230  and the wafer  220  and the coefficient of friction of the second film of the wafer  222  with respect to the pad only. So that the rise in temperature of the polishing pad  230  varies linearly with time again. And the position correspondent with the turning point varying from non-linearly to linearly again is the endpoint of the CMP process. 
     FIG. 4  shows a wafer-to-polished for use in the method according to the invention. With reference to  FIG. 4 , the method of the invention measures an environmental temperature by the thermal image camera  250  initially, and the position of the environmental temperature may be on the central portion of the polishing pad  410 , the edge portion of the polishing pad  411 , any portion of the non-frictional area of the polishing pad. 
   The wafer and the polishing pad rotate with respect to each other, and it causes the wafer to move from a first portion  421  of the polishing pad to a second portion. So the method of the invention measures one temperature of the first portion of the polishing pad by the thermal image camera  250 . Moreover, a data processing for the measured temperature is done by PC, and the difference between the measured polishing pad and the environmental temperature is calculated to obtain the rise in temperature difference of the polishing pad for polishing, in order to get the variation of the polishing pad temperature. 
   The method of the invention repeats the above temperature measuring step. Then a curve is made according to the measured temperature, shows as  FIG. 5 , which includes a first constant value slope, a non-constant value slope, a second constant value slope, and the endpoint of the CMP process is determined by the turning point between the first constant value slope and the second constant value slope, shows as FIG.  6 . 
     FIG. 5  shows the measured data of the surface temperature of the polishing pad during polishing. With reference to  FIG. 5 , a dot represents a rise in the temperature of the first portion  421  of the polishing pad  421  for polishing verse time, and a line represents a curve, showing the rise in temperature of the area of the polishing pad  421  for friction verse time, calculated with the least square method by PC  260 . 
     FIG. 6 , according to the temperature curve of  FIG. 5 , shows the variation of the temperature slope of the polishing pad versus polishing time. With reference to  FIG. 6 , the first constant-value segment of line  601  represents that the polishing pad polishes the first film of the wafer only. The segment of non-constant-value line  602  represents that the polishing pad polishes the first film of the wafer and the second film of the wafer at the same time. The second constant-value segment of line  603  represents that the polishing pad polishes the second film of the wafer only, and means the first film of the wafer is removed fully. Therefore, the turning point  604  represents the endpoint of the CMP process. 
   As described above, the slope of the first constant-value segment of line  601  and the second constant-value segment of line  603  may be in a predetermined variation. 
   As described above, the predetermined variation may be within five percent, shows as the dash line in FIG.  6 . 
   Although the invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.