Abstract:
The present invention relates to a method of supplying the polishing liquid by periodically interrupt the supply of the polishing liquid, thus avoid over-supply or wastage of the polishing liquid. Hence, the consumption of the polishing liquid can be decreased and the production cost can be lower.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chemical mechanical polishing process. More particularly, the present invention relates to a method of supplying the polishing liquid for the chemical mechanical polishing process. 
     2. Background of the Invention 
     Among the very-large-scale-integration (VLSI) or ultra-large-scale-integration (ULSI) manufacturing processes, global planarization can only be achieved by the chemical mechanical polishing (CMP) process. Basically, CMP employs similar concepts of the grinding wheels in conjunction with chemical substances to planarize and flatten the uneven surfaces of the deposited layers over the wafer. Planarization is one of the key factors for achieving high-quality alignment accuracy. If the planarization process goes wrong, it will cause difficulties in focusing for the subsequent photolithographic processes and the misalignment rates may considerably increase. 
     In addition to the global planarization of the wafer, CMP processes can be applied to fabricate the damascene structures for the vertical or horizontal metal interconnects, the shallow trench isolation structures and to planarize other advanced devices. Furthermore, the planarization process is indispensable for the manufacture of the multi-level metal interconnects. 
       FIG. 1  is a schematic view of the conventional polishing equipment. The core elements of the equipment  100  are an automated rotating platen  102  and a wafer holder  104 . In general, the platen  102  is designed to be a round platen for the convenience of rotation with a polishing pad  106  arranged on the platen  102 . A provided wafer  110  is hold by the wafer holder  104  and the position of the wafer holder  104  is adjustable. The wafer holder  104  can both exert force on the wafer  110  and rotate the wafer  110  independent of the rotation of the platen  102 . During polishing, the wafer holder  104  ensures the wafer  110  touching the polishing pad  106 . A polishing liquid supply  108  is disposed above the platen  102  and provides a polishing liquid  112  for polishing. Polishing of the wafer  110  is accomplished through the polishing pad  106  and the polishing liquid  112 . A dresser  114  is usually incorporated in the equipment  100  for conditioning the polishing pad  106 . 
     The choices for different types of the polishing pads or the alterations of the slurry recipes in the polishing processes usually have great impacts on the polishing performance. For the CMP processes, because the used polishing liquid often causes pollution to the environments and needs to be recycled, it is necessary to carefully evaluate the way of using the polishing liquid and the required amount of the polishing liquid. 
     SUMMARY OF THE INVENTION 
     The present invention provides a polishing liquid supply method by periodically interrupting the supply of the polishing liquid to the polishing pad, namely, supplying the polishing liquid in the intermittent way. Hence, the consumption of the polishing liquid becomes less and the wastage or overflow of the polishing liquid can be minimized, thus providing stable and uniform chemical mechanical polishing. 
     The present invention also provides a method of supplying a polishing liquid. The method comprises at least the steps to (a) provide a wafer having a material layer thereon; (b) perform a polishing process to the material layer of the wafer by providing at least a polishing liquid and polishing for a first period T 1 , wherein the material layer is in contact with a polishing pad on a platen for polishing; (c) stop supplying the polishing liquid and keep polishing for a second period T 2 ; (d) provide the polishing liquid and keep polishing for a third period T 3 ; and 
     (e) repeat the steps of (c) to (d) until reaching an polishing endpoint of the CMP process, wherein a duration of the whole polishing process is T 0 , T 0 =T 1 +n×(T 2 +T 3 ), and n represents a total number of repeating the steps of (c) to (d), n is an integer larger than 0. 
     According to the preferred embodiment of the present invention, T 1  is at least larger than 40% of T 0 . Preferably, T 1  is about 50% of T 0 , and T 0  is between about 1˜200 seconds. 
     According to the preferred embodiment of the present invention, T 2  is about 0.5% of T 0  to about 7.5% of T 0 . Preferably, T 2  is about 1%, 2% or 3% of T 0 . 
     According to the preferred embodiment of the present invention, the material layer comprises at least a metal layer, a dielectric layer or a combination thereof. 
     According to the preferred embodiment of the present invention, T 2  is positively correlated to the remained life time of the polishing pad. 
     According to another embodiment of this invention, the method further comprising using a dresser to condition the polishing pad during the steps of (b) to (d). T 2  is positively correlated to the remained life time of the dresser. 
     According to the preferred embodiment of the present invention, T 2  is adjustable by on-line monitoring in real time. 
     According to the preferred embodiment of the present invention, the platen has a centripetal acceleration larger or equal to about 20 ft/sec 2 . 
     The supply method of the present invention can periodically cease the supply of the polishing liquid, and the ceased period or cycle can be adjusted depending on the requirements of the fabrication processes or environments. Therefore, the wastage of the polishing liquid can be reduced and the production costs can be cheaper. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       In the drawings,  FIG. 1  is a schematic side view of the conventional polishing equipment. 
         FIG. 2A  displays a process flow chart of the supply method according to a preferred embodiment of the present invention, while  FIG. 2B  is a cross-sectional display view of the process according to a preferred embodiment of the present invention. 
         FIGS. 3A-3E  are cross-sectional display views of the fabrication process of a metal interconnect structure according to a preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2A  displays a process flow chart of the polishing liquid supply method according to a preferred embodiment of the present invention, while  FIG. 2B  is a cross-sectional display view of the polishing process according to a preferred embodiment of the present invention. Referring to  FIGS. 2A and 2B , a wafer or substrate  200  having a material layer  202  is provided in the step  20 . The material layer  202  can include at least a metal layer, a dielectric layer or a combination thereof, for example. The wafer or substrate  200  can be a semiconductor wafer, such as, a silicon wafer, a silicon germanium wafer or a silicon-on-insulator (SOI) wafer, or a non-semiconductor substrate, such as a glass substrate or a composite material substrate, for example. In the step  22 , at least a polishing liquid  208  is provided, for a polishing process, to polish the material layer  202 , and polishing lasts for a first period T 1 . For example, the polishing liquid  208  can be a polishing slurry comprising abrasive particles for a metal layer or a dielectric layer, or de-ionized water. The polishing process may be a chemical mechanical polishing process, a mechanical polishing process or an electro-chemical mechanical polishing process, for example. During polishing, the wafer holder  204  ensures the material layer  202  of the wafer  200  in contact with the polishing pad  206 , and the polishing pad  206  and the liquid  208  act together to perform polishing to the material layer  202 . In the following step  24 , the supply of the liquid  208  is ceased but keeps polishing the material layer  202 , and polishing lasts for a second period T 2 . Subsequently, in the step  26 , the supply of the liquid  208  is restored or resumed, and keeps polishing for a third period T 3 . Afterwards, in the step  28 , repeat the steps of  24 - 26  for a few times until the polishing endpoint is reached or the desired effect (e.g. desired thickness of the material layer) is achieved. 
     Moreover, the polishing process can be in time mode or endpoint mode, for example. For the polishing process in time mode, the required polishing time for the whole process or a certain part of the polishing process is specified or set in advance. For the polishing process in endpoint mode, the endpoint is obtained by measuring the thickness of the material layer with the detector of the polishing pad and over-polishing is performed for a while after reaching the endpoint. 
     If considering the time required for the whole CMP process toward the material layer  202  as T 0 , the relation between T 0  and the first, second, third periods T 1 , T 2 , T 3  should be: 
     T 0 =T 1 +n×(T 2 +T 3 ), wherein n represents the number of the repeated times of steps  24 - 26 , and n is an integer larger than 0. 
     T 1  is at least larger than 10% of T 0 . Preferably, T 1  is about 50% of T 0 , for wetting the polishing pad and avoiding dry polishing. T 2  is about 0.5%˜7.5% of T 0 . The process steps and the cited ratios or ranges are merely examples according to the preferred embodiments, and the scope of the present invention should not be limited by these examples mentioned herein. 
     If T 2  is 1% T 0 , n=4, T 3  is 11% T 0 , and T 1  is 52% T 0 , for example. 
     If T 2  is 2% T 0 , n=3, T 3  is 15% T 0 , and T 1  is 49% T 0 , for example. 
     If T 2  is 3% T 0 , n=3, T 3  is 14% T 0 , and T 1  is 49% T 0 , for example. 
     If T 2  is 4% T 0 , n=3, T 3  is 12% T 0 , and T 1  is 52% T 0 , for example. 
     If T 2  is 5% T 0 , n=3, T 3  is 12% T 0 , and T 1  is 49% T 0 , for example. 
     Based on the experimental results, considering T 2  being zero as the control (namely, the supply of the polishing liquid is constant and non-stopped), the comparison between the CMP processes using T 2  being 2%, 3% or 5% T 0  and the control indicates comparable or even better results regarding the removal rate of the material layer, non-uniformity and defect counts. Even when evaluating the center to edge index, the CMP results using T 2  being 2%, 3% or 5% of T 0  are acceptable. 
     In addition, if evaluated the existing compatible processes under the conditions of T 2  being 2%, 3% or 5% T 0 , the average polishing cost for each wafer can be 12%, 18% or 30% less by using less polishing liquid. Overall, it can save up to several millions every year if applied in the current polishing processes. 
     In general, for the specific material layer, one can calculate how much time is required for the whole polishing process (i.e. T 0 ) by measuring the pre-polish and post-polish thickness ex-situ, calculating the polishing rate from the difference between the pre-polish and post-polish thickness along with the polishing pad and the polishing liquid utilized in the process, and further determining the range of T 0  based on the pre-polish thickness and the polishing rate. The polishing pad used in the present invention can be fixed abrasive (FA) pad or polishing pads with various patterns or grooves, for example. Of course, other factors that may affect the polishing process, including the exerted pressure (or force) by the wafer holder, the rotation speed of the wafer or the polishing pad (or platen), have to be considered, in order to adjust the range of T 0 . For example, T 0  is about between 1˜200 seconds. 
     The range of T 2  should be adjusted according to the conditions of the polishing pad or the dresser. Furthermore, T 2  can be fine-tuned either in real time or based on the conditions or the process requirements of wafers in the previous batch. 
     When determining the range of T 2 , many factors needs to be considered or carefully evaluated. Taking the polishing pad as an example, T 2  is positively correlated to the remaining life of the polishing pad. During the beginning of using the polishing pad, the conditions of the pad surface are pretty good and the removal rate is high; in this case, the period of ceasing the polishing liquid supply can be longer (i.e. using larger T 2 ) so as to economize the usage of polishing liquid. 
     The rough surface of the polishing pad is favorable for increasing the material removal rate, and proper conditioning by using the dresser can boost the pad surface roughness and improve removal uniformity. Similarly, taking the dresser as an example, T 2  is positively correlated to the remaining life of the dresser. During the beginning of using the dresser, the conditions of the pad surface are pretty good and the removal rate is high; in this case, the period of ceasing the polishing liquid supply can be longer (i.e. using larger T 2 ) so as to economize the usage of polishing liquid. Additionally, T 2  is also inversely related to the conditioning ratio (the ratio of the conditioning time relative to the whole process). For example, the usage of the dresser can be synchronized with the supply of the polishing liquid. 
     The polishing efficiencies are critically determined by the surface conditions of the polishing pad. The supply method of this invention also comprises monitoring the surface conditions of the polishing pad in real time and adjusting T 2  based on the feedbacks or monitored results immediately. For example, a detector is disposed in the polishing liquid supply system (or on the supply arm) or by the platen to monitor the surface conditions in real time during the polishing process. For the wafers going through polishing processes in batches, T 2  can be modified according to the surface conditions estimated from the tested results of the polished wafers in the previous batch. 
     Moreover, other factors that may affect the polishing process, including the exerted pressure (or force) by the wafer holder, the centripetal acceleration of the wafer or the platen (or polishing pad), have to be considered for the best polishing performance. For example, the centripetal acceleration of the round platen can be at least equal to or larger than 20 ft/sec 2 . 
     The supply method of this invention may further includes the steps of advanced process control (APC) by inputting the related process parameters to the control platform, calculating these parameters based on different priority or formula, determining the ranges of T 0 , T 1 , T 2  or T 3  according to the calculation results and specifying the polishing recipes for the specific polishing platform. The process parameters may include, for example, T 0  related parameters (such as, pre-polish thickness of the material layer, the type or conditions of the polishing pad), T 1  related parameters (such as, idling time of the polishing platform or the idling time between various batches) and T 2  related parameters (such as, the remained life time of the polishing pad or dresser). 
       FIGS. 3A-3E  are cross-sectional display views of the fabrication process of a metal interconnect structure according to a preferred embodiment of the present invention. Referring to  FIG. 3A , a substrate  300  is provided to a polishing platen  310 . As the enlarged proportional view, a dielectric layer  302  having at least an opening  34  is disposed on the substrate  300 , and a conductive layer  306  is formed to cover the dielectric layer and fill up the opening  304 . The conductive layer can be a metal layer, of a material such as copper or tungsten, for example. Before forming the conductive layer  306 , a barrier layer  305  can be formed, conformally covering the surface of the opening  304 , for example. The polishing platen  310  comprises a polishing liquid supply system  316  that provides at least a polishing liquid  312  to the polishing pad  314 . For the convenience of descriptions, the following processes only display the partially enlarged view of the substrate portion and the display views have been rotated 180 degrees. 
     Referring to  FIGS. 3A and 3B , the polishing liquid  312  is provided to the polishing pad  314 . Polishing toward the conductive layer  306  lasts a first period T 1  with the assistance of the polishing liquid  312  and the polishing pad  314 , and a conductive layer  306   a  is obtained. 
     Referring to  FIG. 3C , the supply of the polishing liquid  312  is ceased but the polishing of the conductive layer  306   a  is remained for a second period T 2  along with the polishing pad  314 , to form a conductive layer  306   b.    
     Referring to  FIG. 3D , the supply of the polishing liquid  312  is restored (i.e. begin the polishing liquid supply) and the conductive layer  306   b  is polished for a third period T 3  with the polishing liquid  312  and the polishing pad  314 , to form a conductive layer  306   c.    
     Subsequently, the steps as shown in  FIGS. 3C to 3D  are repeated for a few times, until the conductive layer  306   c  over the dielectric layer  302  is completely removed and an interconnect  308  is formed ( FIG. 3E ). 
     Although the preferred embodiment describes the polishing process for forming the metal interconnect structures, the supply method of this invention should not be limited to fabricate the described structures, but can be applied to fabricate the shallow trench isolation structures, inter-layer dielectric layers, damascene structures and to planarize other advanced devices such as microelectronics or planar displays. 
     The polishing liquid supply method of the present invention can periodically cease the supply of the polishing liquid, and the ceased period or cycle can be adjusted depending on the requirements of the fabrication processes or conditions of the polishing pad and the dresser. Therefore, not only the wastage of the polishing liquid can be reduced and the production costs can be lower, but also satisfactory polishing performances can be achieved. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.