News Column

Patent Application Titled "Polishing Method and Apparatus" Published Online

August 19, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- According to news reporting originating from Washington, D.C., by NewsRx journalists, a patent application by the inventor Torikoshi, Tsuneo (Tokyo, JP), filed on January 22, 2014, was made available online on August 7, 2014 (see also Patents).

No assignee for this patent application has been made.

Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to a polishing method and apparatus for polishing a surface of a substrate such as a semiconductor wafer by relative movement between the surface of the substrate and a polishing pad on a polishing table while the substrate is pressed against the polishing pad.

"In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.

"Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, while a polishing liquid (slurry) containing abrasive particles, such as silica (SiO.sub.2), ceria (CeO.sub.2) or the like, therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad and polished by using a polishing apparatus.

"The polishing apparatus which performs the above-mentioned CMP process includes a polishing table having a polishing pad, and a substrate holding apparatus, which is referred to as a top ring or a polishing head, for holding a semiconductor wafer (substrate). When the semiconductor wafer (substrate) is polished with such a polishing apparatus, the semiconductor wafer is held and pressed against a surface (polishing surface) of the polishing pad under a predetermined pressure by the substrate holding apparatus while a polishing liquid (slurry) is supplied from a polishing liquid supply nozzle onto the polishing pad. At this time, the polishing table and the substrate holding apparatus are respectively rotated to bring the semiconductor wafer into sliding contact with the polishing surface, so that the surface of the semiconductor wafer is polished to a flat mirror finish, as disclosed in Japanese laid-open patent publication No. 2007-75973.

"As described above, the polishing apparatus polishes the substrate by rotating the polishing table while the polishing liquid (slurry) is supplied from the polishing liquid supply nozzle onto the polishing pad. Therefore, there is a problem that mist of slurry supplied onto the polishing pad is scattered around. Further, after polishing of the substrate, water polishing of the substrate or cleaning of the substrate is performed by rotating the polishing table while pure water (deionized water) is supplied from the polishing liquid supply nozzle onto the polishing pad. Therefore, there is a problem that mist of pure water or the like supplied onto the polishing pad is scattered around. In this manner, the interior of the polishing apparatus is such an environment as to cause mist of slurry, pure water or the like, or water droplets to be scattered, and thus the scattered mist of slurry or the like is attached onto various portions in the polishing apparatus. If the attached mist is dried, the abrasive particles are agglomerated and fall onto the surface of the polishing pad during polishing, causing scratches on the surface of the substrate.

"Accordingly, in the CMP process, there is a risk that the scratches due to agglomerate of the particles such as slurry are increased, thus causing a lowering of the yield. The scratches are mainly caused by falling of the agglomerated abrasive particles onto the polishing pad. As a method for preventing the fallen abrasive particles from entering between the polishing pad and the substrate, it is common practice to take measures at the time of dressing of the polishing pad. For example, a dressing speed is lowered, or cleaning for washing the abrasive particles away with a mixed fluid of a liquid and a gas, or the like by an atomizer is performed after dressing.

"In order to remove the above-described agglomerated abrasive particles, existing on the polishing pad, as much as possible, the longer cleaning time of the polishing pad by the atomizer is more preferable. However, in the conventional polishing apparatus, the dressing step of the polishing pad or the cleaning step of the polishing pad by the atomizer has been set in a polishing recipe. Therefore, it is necessary to prolong the cleaning time by altering the polishing recipe so as to lengthen the cleaning time of the polishing pad by the atomizer, and thus there is a problem to lower a throughput extremely.

"The inventors of the present invention have reviewed various steps which have been conducted based on the polishing recipe in the polishing apparatus for the purpose of lengthening the cleaning time of the polishing pad (polishing surface) without lowering the throughput, and obtained the following knowledge. Specifically, after one substrate such as a semiconductor wafer is polished, there is a substrate transferring process for removing the polished substrate from the top ring and loading a new substrate on the top ring.

"The inventors of the present invention have focused on the fact that there is a so-called idle time, at the time of the substrate transferring process, during which no process is performed on the polishing table, and have considered the possibility to prolong the cleaning time by cleaning the polishing pad during the idle time. In this case, it is considered to add a recipe of 'execute cleaning of the polishing pad during the time until the polishing recipe is re-executed'. However, when an executive instruction of the polishing recipe is made from a controller, the polishing recipe becomes in execution, and thus the completion of the polishing recipe cannot be detected by the polishing recipe itself, resulting in continuing the check whether the polishing recipe has been completed or not while the polishing recipe itself is being executed. In other words, if it is set as 'during the time until the polishing recipe is re-executed', because neither the completion of the previous polishing recipe nor the start of a subsequent polishing recipe can be detected, the state where there is no other way than continuing the cleaning of the polishing pad, is continued. Accordingly, when 'cleaning of the polishing pad' is added to the polishing recipe, the cleaning time is forced to be set, thus lowering the throughput.

"Further, separately from the polishing recipe, it can be considered to have such a setting as 'after completion of the polishing recipe, execute cleaning of the polishing pad for a predetermined time' in advance. However, the time between the polishing recipes is not constant because various substrates are supplied into the polishing apparatus, i.e. a variety of polishing recipes are executed. Accordingly, setting the cleaning time of the polishing pad each time for each substrate is troublesome and time-consuming. Further, if the cleaning time is not set each time, the cleaning time has to be set to the minimum time between respective polishing recipes, and therefore the idle time between the polishing recipes cannot be utilized to the utmost limit."

In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventor's summary information for this patent application: "Based on the above knowledge obtained from various experiments, the present invention has been made. It is therefore an object of the present invention to provide a polishing method and apparatus which can perform cleaning of a polishing pad on a polishing table, by using an idle time in a substrate transferring process which is performed between polishing processes, to the utmost limit.

"In order to achieve the above object, according to an aspect of the present invention, there is provided a polishing method for polishing a substrate, comprising: a polishing process for polishing a surface of the substrate by pressing the substrate against a polishing pad on a polishing table by a top ring, the polishing process being executed in accordance with a preset polishing recipe; a pad cleaning process for removing foreign matters on the polishing pad by ejecting a cleaning fluid onto the polishing pad; and a substrate transferring process in which the polished substrate is removed from the top ring at a substrate transferring position, a subsequent substrate to be polished is loaded onto the top ring, and then the top ring holding the subsequent substrate to be polished is returned to the polishing table; wherein the pad cleaning process is started after the completion of the polishing recipe is detected, and the pad cleaning process is terminated by detecting a position of the subsequent substrate to be polished which is undergoing the substrate transferring process.

"According to the present invention, the polishing process in which the substrate is polished by pressing the substrate against the polishing pad on the polishing table by the top ring is performed in accordance with the preset polishing recipe. Then, the substrate transferring process in which the polished substrate is transferred to the wafer transferring position and is removed from the top ring, and the subsequent substrate to be polished is loaded onto the top ring, and then the top ring holding the subsequent substrate to be polished is returned to the polishing table, is performed. After the completion of the polishing recipe is detected, spraying of the cleaning fluid onto the polishing pad is started, and the pad cleaning process is initiated. The pad cleaning process is performed in the substrate transferring process. Then, at any time during the substrate transferring process, the position of the subsequent substrate to be polished is detected and the pad cleaning process is terminated. For example, the pad cleaning process is terminated by detecting the arrival of the subsequent substrate to be polished to the substrate transferring position. The detection of the position of the subsequent substrate to be polished may be performed by direct detection of the substrate, or indirect detection of the substrate such as detection of the position of the top ring. According to the present invention, the cleaning of the polishing pad (polishing surface) on the polishing table can be performed by using the idle time, in the substrate transferring process which is performed between the polishing processes, to the utmost limit.

"In a preferred aspect of the present invention, the pad cleaning process is terminated by detecting the arrival of the subsequent substrate to be polished which is undergoing the substrate transferring process to the substrate transferring position.

"According to the present invention, the pad cleaning process is started after the completion of the polishing recipe, and the pad cleaning process is terminated when the arrival of the subsequent substrate to be polished which is undergoing the wafer transferring process to the wafer transferring position (pusher) is detected.

"In a preferred aspect of the present invention, a rotational speed of the polishing table is varied in the polishing process and the pad cleaning process.

"According to the present invention, the rotational speed of the polishing table is varied in the polishing process and the pad cleaning process. Further, during the pad cleaning process also, the polishing pad may be rotated at a low speed when spraying (blowing) of the cleaning fluid onto the polishing pad is started, and then the polishing pad may be rotated at a high speed while spraying of the cleaning fluid onto the polishing pad is continued.

"In a preferred aspect of the present invention, the rotational speed of the polishing table at the time of the pad cleaning process is higher than that at the time of the polishing process.

"In a preferred aspect of the present invention, the polishing process comprises a polishing step for polishing the surface of the substrate and a dressing step for dressing the polishing pad.

"In a preferred aspect of the present invention, the polishing process comprises a polishing step for polishing the surface of the substrate, a dressing step for dressing the polishing pad, and a polishing pad cleaning for removing foreign matters on the polishing pad by ejecting a cleaning fluid onto the polishing pad.

"According to the present invention, the pad cleaning process can be performed continuously after the polishing pad cleaning performed in the polishing process. Therefore, a longer time for the polishing pad cleaning can be secured.

"In a preferred aspect of the present invention, when a substrate or substrates are polished by at least two polishing tables, the polishing recipes in the respective polishing tables differ from each other.

"According to the present invention, in the case where the substrate or substrates are respectively polished in two-steps by using the two polishing tables, the polishing recipes of the two polishing tables differ from each other. Because the polishing recipes differ, the time required for one of the polishing recipes differs from the time required for the other of the polishing recipes. Specifically, the time required for one of the polishing recipes in which the wafer is primarily polished by one of the polishing tables differs from the time required for the other of the polishing recipes in which the wafer is secondarily polished by the other of the polishing tables. Further, the time between the polishing recipes in one of the polishing tables and the time between the polishing recipes in the other of the polishing tables differ from each other. Therefore, the time for the polishing pad cleaning performed between the polishing recipes in one of the polishing tables differs from the time for the polishing pad cleaning performed between the polishing recipes in the other of the polishing tables.

"In a preferred aspect of the present invention, when a plurality of substrates are polished sequentially by the one polishing table, the pad cleaning process is performed between the polishing recipe for polishing a preceding substrate and the polishing recipe for polishing a subsequent substrate.

"According to another aspect of the present invention, there is provided a polishing apparatus capable of performing a polishing method; the polishing method comprising: a polishing process for polishing a surface of the substrate by pressing the substrate against a polishing pad on a polishing table by a top ring, the polishing process being executed in accordance with a preset polishing recipe; a pad cleaning process for removing foreign matters on the polishing pad by ejecting a cleaning fluid onto the polishing pad; and a substrate transferring process in which the polished substrate is removed from the top ring at a substrate transferring position, a subsequent substrate to be polished is loaded onto the top ring, and then the top ring holding the subsequent substrate to be polished is returned to the polishing table; wherein the pad cleaning process is started after the completion of the polishing recipe is detected, and the pad cleaning process is terminated by detecting a position of the subsequent substrate to be polished which is undergoing the substrate transferring process; wherein the polishing apparatus has a control unit configured to be able to set whether the pad cleaning process is executed.

"According to the present invention, the control unit of the polishing apparatus has a setting mode, separated from setting of the polishing recipe, for setting whether the pad cleaning process is performed. By operating the setting mode, the pad cleaning process can be added between the polishing recipes.

"The present invention offers the following advantages:

"According to the present invention, the cleaning of the polishing pad (polishing surface) on the polishing table can be performed by using the idle time, in the substrate transferring process which is performed between the polishing processes, to the utmost limit. Therefore, the following effect can be expected.

"(1) Without altering the polishing recipe, and without setting the polishing pad cleaning time, the polishing pad cleaning time can be secured. Therefore, desired polishing pad cleaning time can be secured without lowering a throughput.

"(2) Because desired polishing pad cleaning time can be secured, agglomerated abrasive particles, existing on the polishing pad, can be removed as much as possible. Therefore, the occurrence of scratches on the surface of the substrate due to agglomerate of the particles on the polishing pad, can be dramatically reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a plan view showing an entire structure of a polishing apparatus according to one embodiment of the present invention;

"FIG. 2 is a schematic perspective view showing an entire structure of a first polishing unit of four polishing units shown in FIG. 1;

"FIGS. 3A and 3B are timing diagrams for making a comparison of recipe processes, in the conventional example and the present invention, executed based on respective preset polishing recipes;

"FIG. 4 is a flowchart showing a procedure of the recipe process executed based on the polishing recipe in the conventional example;

"FIG. 5 is a flowchart showing a procedure of 'polishing recipe' and 'polishing pad cleaning' according to the present invention;

"FIG. 6A is a timing diagram showing a case where a two-step polishing is performed by using two polishing tables at which different polishing recipes are executed respectively; and

"FIG. 6B is a timing diagram showing a case where cleaning of a wafer and cleaning of a top ring are performed at a wafer transferring position, and a case where neither cleaning of the wafer nor cleaning of the top ring is performed at the wafer transferring position."

For more information, see this patent application: Torikoshi, Tsuneo. Polishing Method and Apparatus. Filed January 22, 2014 and posted August 7, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2516&p=51&f=G&l=50&d=PG01&S1=20140731.PD.&OS=PD/20140731&RS=PD/20140731

Keywords for this news article include: Patents, Electronics, Transferrin, Semiconductor, Beta-Globulins, Blood Proteins, Acute-Phase Proteins, Iron-Binding Proteins.

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Source: Life Science Weekly


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