Polishing process

Abstract

The present invention provides a polishing method that includes polishing the surface of a wafer by sliding the wafer, held by a polishing head, onto the surface of a polishing pad while simultaneously supplying a polishing paste to the polishing pad mounted on a rotary table, wherein the method is characterized in that it includes a correlation derivation to determine a correlation between a surface temperature of the polishing pad and a noise level of a wafer polished using the polishing pad prior to performing the polishing, and is also characterized in that the wafer is polished during polishing while the surface temperature of the polishing pad is regulated based on the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad.As a result, a polishing process is provided that can regulate noise when polishing a wafer and thus extend the lifespan of the polishing pad.

Description

technical field

[0001] The present invention relates to a polishing method. Background of the Invention

[0002] In recent years, with the advancement of miniaturization of semiconductor elements using silicon wafers and the like, there have been indications that very fine particles in the range of about 10 to 20 nm, which have not been a problem conventionally, can affect the performance of the elements.

[0003] In order to detect particles on a surface of each wafer, a scattered light inspection method is generally used. Since the particle detection sensitivity of a measuring instrument using scattered light is determined by a ratio between an error signal and its background noise, if the background or noise is high, the signal-to-noise ratio is lowered and accurate measurement cannot be performed. Since stray light due to surface roughness of a wafer is detected by noise, the noise is known to have a close relationship with the surface roughness, and reducing the surface roughness reduces the noise.

[0004] A typical method for suppressing noise involves regulating cleaning conditions performed after final polishing of wafers. For example, lowering the cleaning temperature of SC1, a mixed solution of NH, inhibits 3 and H 2 O 2 , the alkaline etching function on a wafer surface and reduces surface roughness, resulting in noise reduction. List of citations patent literature

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. Hei 9-38849 Disclosure of the Invention Problems to be Solved by the Invention

[0006] However, with the above-described method of lowering the temperature of SC1, cleaning efficiency is also reduced, so that particles on a surface of each wafer cannot be sufficiently removed. Thus, there is a need for noise reduction by a method other than adjusting the SC1 temperature.

[0007] It is known that noise is affected by polishing conditions of finish polishing and the like in addition to cleaning conditions. Therefore, conventionally, efforts have been made to avoid generation of noise by, for example, reducing relative speeds of a polishing pad and a wafer in the final stage of finish polishing, as in Patent Literature 1, for example. However, this method still has a problem that noise cannot be fully controlled compared to the method of reducing noise by controlling cleaning conditions.

[0008] Furthermore, it is known that noise is also affected by the usage time of a polishing pad. Since the noise deteriorates as the usage time of a polishing pad increases, the polishing pad needs to be replaced periodically when the noise of a polished wafer exceeds a predetermined management value. If a noise level cannot be controlled sufficiently, the polishing pad needs to be replaced frequently, resulting in a decrease in productivity and an increase in manufacturing cost of wafers.

[0009] The present invention was developed in view of such problems as described above, and it is a purpose of the present invention to provide a polishing method which can regulate noise in polishing a wafer and thus can extend the life of a polishing pad. Furthermore, another purpose is to carry out regulation in particular to inhibit noise. means of solving the problems

[0010] To achieve the purposes, the present invention provides a polishing method including polishing for polishing a surface of a wafer by sliding the wafer held by a polishing head on a surface of a polishing pad while supplying a polishing paste to the polishing pad attached to a turntable, the method being characterized in that it includes a correlation derivation to determine in advance a correlation between a surface temperature of the polishing pad and a noise level of a wafer polished using the polishing pad before performing the polishing, and characterized in that the wafer polishes during the polishing while controlling the surface temperature of the polishing pad based on the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad.

[0011] As described above, if the surface temperature of the polishing pad is regulated during polishing based on the correlation of the surface temperature of the polishing pad to the noise level determined in advance, the noise level of the wafer can be regulated. In particular, when the surface temperature of the polishing pad is adequately regulated based on the correlation, the noise level can be regulated to decrease. Furthermore, if the noise level of each polished wafer can be controlled to decrease in this way, the polishing pad can be used for a long time, and thus the life of the polishing pad can be extended.

[0012] In this case, it is advantageous to perform the correlation derivation by performing trial polishing on a plurality of sample wafers using polishing pads having different surface temperatures and measuring a noise level of each of the wafers after the trial polishing, and thus the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad is determined.

[0013] In this way, the correlation between the surface temperature of the polishing pad and the noise level can be derived ahead of time.

[0014] Moreover, when polishing, the surface temperature of the polishing pad can be regulated by adjusting at least one of a temperature of the polishing paste supplied to the polishing pad, the number of revolutions of the polishing head, and the number of revolutions of the turntable.

[0015] By changing the polishing conditions in this way, the surface temperature of the polishing pad can be regulated.

[0016] Moreover, when polishing, the surface temperature of the polishing pad can be regulated by heating the surface of the polishing pad using a heater and / or cooling the surface of the polishing pad based on cold air blowing.

[0017] The surface temperature of the polishing pad can also be regulated in this way.

[0018] In this case, it is advantageous to obtain the correlation by further performing the correlation derivation regularly and to regulate the surface temperature of the polishing pad based on the correlation obtained regularly.

[0019] Since the correlation between the surface temperature of the polishing pad and the noise level changes in some cases depending on the usage time of the polishing pad, if the correlation is regularly determined according to the usage time of the polishing pad as above and the surface temperature of the polishing pad is regulated based on it, wafers with desired noise levels can be provided with certainty in the long term. In particular, when the surface temperature of the polishing pad is regulated in this way, noise levels can also be further inhibited.

[0020] Furthermore, the polishing in this case is preferably the final polishing after the preliminary polishing.

[0021] Since the noise tends to be particularly affected by the finish polishing, application of the polishing method of the present invention to the finish polish is certain to provide wafers with desired noise levels. effect of the invention

[0022] According to the polishing method of the present invention, the noise level of each wafer can be regulated to a desired level. In particular, if the surface temperature of the polishing pad is adequately regulated based on the correlation during polishing, the noise level can be regulated to decrease. Furthermore, when the noise level of each polished wafer is controlled to be reduced in this way, the polishing pad can be used for a long time, and thus the life of the polishing pad can be prolonged. character list figure 1 shows graphs for illustrating an example of a correlation between a surface temperature of a polishing pad and noise; figure 2 shows photographs for illustrating surface observation results of a polished wafer provided by an atomic force microscope; figure Figure 3 shows graphs for illustrating mean mean roughness (Sa) and square root mean square (Sq) calculated from atomic force microscope images; figure 4 is a flowchart showing an example of a polishing method according to the present invention; figure 5 is a schematic diagram showing an example of a polishing apparatus that can be used in the polishing method according to the present invention; and figure 6 is a graph for illustrating a relationship between a noise level and a usage time of a polishing pad in each of Example 2 and Comparative Example 2. Preferred modes for carrying out the invention

[0023] Although an embodiment of the present invention will be described below, the present invention is not limited to this.

[0024] As described above, a conventional method has a problem that a noise level cannot be regulated sufficiently by polishing. Furthermore, since a polishing pad needs to be exchanged when a predetermined management value is exceeded, the polishing pad must be exchanged frequently when the noise level cannot be controlled sufficiently, resulting in a decrease in productivity and an increase in the manufacturing cost of wafers.

[0025] Thus, in order to solve such problems, the inventors of the present invention repeatedly performed the following analysis. First, the inventors considered that since the temperature of a liquid chemical in cleaning exerts a large influence on noise, the temperature of a polished surface of a wafer can also be an important factor for noise. However, since it is difficult to directly measure the temperature of a polished surface, great attention has been paid to the surface temperature of a polishing pad, which can be considered to have a value closest to that of the polished surface temperature, and the Inventors checked whether a noise level can be regulated by regulating the surface temperature of the polishing pad.

[0026] As a result of performing polishing operations at different surface temperatures of the polishing pad, as in figure 1, the noise level decreases as the surface temperature decreases, but that the noise deteriorates sharply when the surface temperature drops below a certain temperature. Consequently, it is considered that there exists a surface temperature of the polishing pad that provides the least noise.

[0027] Thus, the surface structure of a wafer polished at each surface temperature was observed using an atomic force microscope (AFM). The AFM was used to monitor an intermediate position between the center and an outer periphery of the wafer, and the observation range was set to 1 ▪ 1 ▪ m 2 fixed. As in figure2, it turned out that at a surface temperature that provides a minimum value for the noise level, as well as at higher temperatures, no discernible surface structure of the wafer could be observed. On the other hand, at a surface temperature below the surface temperature at which the minimum value of the noise level occurred, a fine scratch pattern (hereinafter referred to as a nano-scratch) was observed on the surface of the wafer.

[0028] figure 3 shows the mean mean roughness (Sa) and the mean square roughness (Sq) calculated from the atomic force microscope images. In figure 3, “Center” stands for the center of the wafer, “R / 2” for an intermediate position between the center and the outer periphery, and “Edge” for data obtained from observation of a position extending from the outer periphery toward the center by 10 mm has been moved. Analogous to the noise trend, it became apparent that there exists a surface temperature of the polishing pad that provides a minimum value of roughness, and this surface temperature is identical to the surface temperature that provides the minimum value of noise.

[0029] A reason for the minimum values ​​thus provided can be considered as follows. When a polishing temperature decreases, the etch rate of an alkali on silicon is inhibited, and thus excessive surface roughness is inhibited. However, it is expected that if the etch rate is inhibited excessively, the softening function of the alkali to the silicon surface will also be lost, resulting in a polishing mode in which surface damage such as nano-scratches occurs as in mechanical polishing by abrasives.

[0030] Thus, the inventors have confirmed that regulating the surface temperature of the polishing pad based on, for example, a correlation between the surface temperature of the polishing pad and the noise level as in FIG figure 1 as a method for adjusting the noise enabled adjusting the noise level by polishing, and thus have completed the present invention.

[0031] A polishing method according to the present invention will be described in detail below. As in a flow chart in figure 4, the polishing method according to the present invention includes: correlation derivation for obtaining a correlation between a surface temperature of a polishing pad and a noise level of a wafer polished using the polishing pad; and polishing for polishing a surface of a wafer.

[0032] In the polishing method of the present invention, correlation derivation is first performed before polishing is performed as described above. In the correlation derivation, for example, a correlation between a surface temperature of a polishing pad and a noise level of a wafer polished using the polishing pad is calculated as in FIG figure 1 shown.

[0033] In the present invention, this correlation can be obtained by performing trial polishing on a plurality of sample wafers using polishing pads having different surface temperatures and measuring noise levels of the respective wafers after the trial polishing. In trial polishing, each trial wafer can be polished with the same polishing pad whose surface temperature changes, for example, by adjusting the polishing conditions.

[0034] After obtaining the correlation in this way, polishing (main polishing) is performed. Here, a polishing apparatus that can be used for the polishing (main polishing) as well as the trial polishing will now be described with reference to FIG figure 5 described. A polishing device 1 can essentially consist of a polishing head 2 , holding a wafer W, a turntable 3 , on which a polishing pad 4 attached, a polishing paste supplying mechanism 5 etc. exist. Also, both the polishing head 2 as well as the turntable 3 rotate. Furthermore, since it is advantageous, a surface of the polishing head 4to stably cover with a polishing paste while polishing is being performed, the polishing paste is desirably stably by providing a pump or the like to the polishing paste supplying mechanism 5 fed. In addition, it is possible as a polishing paste supplying mechanism 5 one with a function to adjust the temperature of the polishing paste applied to the polishing pad 4 is supplied to use.

[0035] With such a polishing device 1 a surface of the wafer W is polished by that from the polishing head 2 held wafer W on the surface of the polishing pad 4 is shifted while on the turntable 3 attached polishing pad 4 the polishing paste is supplied.

[0036] Such a polishing apparatus as described above is used to polish the wafer while controlling the surface temperature of the polishing pad based on the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad.

[0037] According to such a polishing method of the present invention, when the surface temperature of the polishing pad is regulated based on the correlation obtained in advance, the noise level of the polished wafer can be regulated to a desired value. In particular, when the noise level is desirably further inhibited, polishing should be performed while controlling the surface temperature to a level so low that nano-scratches are not generated. For example, if such a correlation as in figure 1, the surface temperature of the polishing pad can be regulated to a temperature as low as 25°C, but not lower than 22.7°C, because at this value nano-scratches are generated on the polished wafer and the noise level increases degraded to regulate the noise level to decrease as much as possible.

[0038] In addition, when polishing is performed while regulating the surface temperature of the polishing pad to reduce the noise level, a duration of exceeding a management value set for the noise level can be prolonged compared to conventional examples, so that the life of the polishing pad can be increased . Consequently, it is possible to restrain a decrease in productivity and an increase in manufacturing cost of wafers.

[0039] Furthermore, in the present invention, the surface temperature of the polishing pad can be regulated by adjusting at least one of a temperature of the polishing paste supplied to the polishing pad, the number of revolutions of the polishing head, and the number of revolutions of the turntable.

[0040] Furthermore, the surface temperature of the polishing pad can be regulated by heating the surface of the polishing pad using a heater, cooling the surface of the polishing pad based on blowing cool air, or by performing both heating and cooling. In this case, for example, as the polishing device 1 in figure 5 one with a surface temperature regulating mechanism 6 such as a heater and a cooler can be used.

[0041] Furthermore, in the present invention, it is advantageous to obtain the correlation between the surface temperature and the noise level by regularly performing the correlation derivation made before polishing and to regulate the surface temperature of the polishing pad based on the regularly obtained correlation. Since the surface condition of the polishing pad may change depending on the usage time of the polishing pad, the correlation also changes depending on the usage time of the polishing pad in some cases. It is therefore advantageous to determine the correlation regularly. In addition, if polishing conditions are regularly readjusted based on the correlation between the surface temperature and the noise level in consideration of the usage time of the polishing pad, so that the surface temperature can be regulated to be the optimum surface temperature at the moment, it is possible to perform regulation to provide the surface temperature at which a desired noise level can be obtained with certainty. Consequently, the excellent noise level can be maintained longer, and the life of the polishing pad can be extended. The frequency of readjustment of the polishing conditions is not particularly limited, but can be set to about 1,000 lots of polishing.

[0042] In particular, if the correlation between the surface temperature and the noise level is determined ahead of time according to the usage time of the polishing pad, it is also possible to determine a surface temperature at which nano-scratches are generated after a certain usage time of the polishing pad. Thus, if the noise level is desirably suppressed as much as possible, the surface temperature can be regulated to a temperature so low that nano-scratches are not generated after a period of use of the polishing pad.

[0043] In addition, it is advantageous to apply such a polishing method according to the present invention to the finish polishing as described above. That is, the polishing of the present invention is preferably the final polishing after the rough polishing. Since the noise tends to be particularly affected by the finish polishing, application of the polishing method of the present invention to the finish polish is certain to provide wafers with desired noise levels. examples

[0044] The present invention is described below in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. (Example 1)

[0045] The final polishing was carried out in accordance with the polishing method of the present invention as in FIG figure 4 performed. A pre-polished silicon wafer having a diameter of 300 mm was used as the wafer as the polishing object.

[0046] Furthermore, the polishing conditions were as follows. Initially, the in figure 5 used polishing apparatus shown. A velor pad was used as a polishing pad, and a mixture obtained by adding ammonia and a water-soluble high-molecular polymer to colloidal silica was used as a polishing paste. The number of wafers to be polished in one batch was two, and the number of revolutions of a turntable and a polishing head were 30 rpm each.

[0047] Further, in the example before the main polishing (polishing), the correlation derivation was performed as follows. First, a plurality of sample wafers identical to the silicon wafer polished in the main polishing and a polishing pad identical to that used in the main polishing were used. The supply temperature of the polishing paste was regulated such that the surface temperature of the polishing pad changed at 2°C intervals, and the sample wafers were polished at each of the surface temperatures (trial polishing). Furthermore, a correlation between the surface temperatures of the polishing pad and the noise levels of the silicon wafers polished using the polishing pad was obtained from the result of trial polishing. The surface temperatures of the polishing pad were measured using a non-contact temperature probe. In addition, the noise levels were measured using a Surfscan SP3 manufactured by KLA-Tencor in a DWO mode. In the figure 1 correlation was determined in this way.

[0048] Then, the main polishing was performed while controlling the surface temperature of the polishing pad to 24.7°C by adjusting a temperature of the polishing paste based on the correlation to minimize the noise level. (Comparative Example 1)

[0049] The polishing was performed in the same manner as in Example 1, except that the surface temperature of the polishing pad was not regulated based on the correlation between the surface temperatures of the polishing pad and the noise levels of the silicon wafers polished using the polishing pad.

[0050] The noise levels and a sum of defects (SOD) of the silicon wafers polished in Example 1 and Comparative Example 1 were measured using Surfscan SP3 manufactured by KLA-Tencor, and the average values ​​were calculated.

[0051] Table 1 shows the summary of the reaction results in Example 1 and Comparative Example 1. [Table 1] example 1 Comparative example 1 Total of errors (number) 85 87 DWO noise (ppm) 0,0491 0,0545

[0052] As can be seen from Table 1, the noise level in Example 1 was better than that in Comparative Example 1. In addition, Example 1 and Comparative Example 1 have an identical sum of defects of the polished silicon wafers in this case. This result shows that the adjustment to improve the noise level was possible without degrading the sum of errors in Example 1. (Example 2)

[0053] A silicon wafer was polished as in Example 1 using the polishing method of the present invention. Further, in Example 2, a correlation was determined for each point in time when a value relative to the life of the polishing pad of the usage time of a polishing pad of Comparative Example 2 described below was 9, 25, 100, or 200 (note that the value for the lifetime in Comparative Example 2 was set to 100). Readjusted the paste temperature of a polish to provide a surface temperature that minimized noise. As the matching conditions, the surface temperature of the polishing pad was set to 24.7°C at the beginning, 23.3°C at a relative value of 9 or more, 22.1°C at a relative value of 25 or more, 21.1°C at at a relative value of 100 or more and 20.5°C at a relative value of 200 or more.

[0054] Furthermore, the noise levels of the wafers at the respective times when the paste temperature of the polishing agent was readjusted were measured. Furthermore, in Example 2 and Comparative Example 2 described below, the upper limit of a management value of noise levels was set at 0.0653 (ppm), and when a measured noise level substantially reached this value, polishing was terminated and the polishing pad was replaced. (Comparative Example 2)

[0055] The polishing was performed under the same conditions as in Example 2, except that the surface temperature was not regulated based on the correlation between the surface temperatures of the polishing pad and the noise levels of the silicon wafers polished using the polishing pad. It is noted that the polishing conditions at the beginning of polishing were the same as in Example 2.

[0056] In addition, the noise level of the wafer was measured by the same method as in Example 2 at each point in time when the value relative to the life of the polishing pad in Comparative Example 2 was 9, 25 or 100 (life).

[0057] figure 6 shows a relationship between the noise level and the usage time of the polishing pad in each of Example 2 and Comparative Example 2. It should be noted that referring to Example 2 figure 6 shows the noise level up to when the polishing time shows the relative value 200 had achieved. How out figure 6 can be seen, in Example 2, in which the temperature of the polishing paste was readjusted based on the correlation between the surface temperature and the noise level, taking into account the usage time of the polishing pad, the noise deterioration is moderate compared to Comparative Example 2, and the noise level did not reach the upper limit of the management value even though the polishing pad was used for a period twice the life of the polishing pad in Comparative Example 2.

[0058] On the other hand, in Comparative Example 2, the noise deteriorated significantly towards the end compared to the initial polishing phase of the polishing pad, and the noise reached a value close to the upper limit of the management value in a significantly shorter time than in Example 2. As described above, the noise deterioration and the reduction in polishing pad life when the surface temperature was not regulated based on the correlation between the polishing pad surface temperature and the noise level of the wafer polished using the polishing pad.

[0059] It is noted that the present invention is not limited to the embodiment. The embodiment is an illustrative example, and any example that has substantially the same structure and exerts the same functions and effects as the technical concept described in claims of the present invention is included in the technical scope of the present invention. QUOTES INCLUDED IN DESCRIPTION

[0000] This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Patent Literature Cited

[0000] JP 9038849

[0005]

Claims

[1] Polishing process which includes polishing to polish a surface of a wafer by sliding the wafer held by a polishing head on a surface of a polishing pad while a polishing paste is supplied to the polishing pad attached to a rotary plate, wherein the method includes a preliminary correlation derivation prior to performing the polishing to determine a correlation between a surface temperature of the polishing pad and a noise level of a wafer polished using the polishing pad, and the wafer is polished during polishing, while the surface temperature of the polishing pad is regulated based on the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad. [2] Polishing method according to claim 1, wherein the correlation derivation is carried out by performing a trial polishing on a plurality of sample wafers using polishing pads with different surface temperatures, measuring a noise level of each of the wafers after the trial polishing and thus determining the correlation between the surface temperature of the polishing pad and the noise level of the wafer polished using the polishing pad. [3] Polishing method according to claim 1 or 2, wherein during polishing the surface temperature of the polishing pad is regulated by adjusting at least one of the temperature of the polishing paste supplied to the polishing pad, the number of revolutions of the polishing head and the number of revolutions of the rotary table. [4] Polishing method according to any one of claims 1 to 3, wherein during polishing the surface temperature of the polishing pad is regulated by heating the surface of the polishing pad using a heating device and / or cooling the surface of the polishing pad based on blowing in cold air. [5] Polishing method according to any one of claims 1 to 4, wherein the correlation is determined by further regular execution of the correlation derivation and the surface temperature of the polishing pad is regulated based on the regularly determined correlation. [6] Polishing method according to any one of claims 1 to 5, wherein the polishing is the final polishing after the pre-polishing.