Method for polishing a semiconductor substrate

Abstract

Method for polishing a semiconductor substrate, comprising: an intermediate polishing step of polishing in such a way that the number of surface defects with heights of less than 3 nm becomes 45% or more of the total number of surface defects on the surface of a semiconductor substrate; and a final polishing step of the polishing of the semiconductor substrate after the intermediate polishing step, wherein in the intermediate polishing step the polishing is carried out using a polishing composition comprising: first hydroxyethyl cellulose, water and abrasive grains, wherein the first hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less and the mass ratio of first hydroxyethyl cellulose to abrasive grains is 0.0075 or more and 0.025 or less, wherein in the final polishing step the polishing is carried out using a polishing composition comprising: second hydroxyethyl cellulose, water and abrasive grains, wherein the second hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less; and wherein the molecular weight of the second hydroxyethyl cellulose of the polishing composition used in the final polishing step differs from the molecular weight of the first hydroxyethyl cellulose of the polishing composition used in the intermediate polishing step.

Description

Related registrations

[0001] This patent application claims priority over Japanese patent application no. 2014-73797. Background of the invention

[0002] The present invention relates to a method for polishing semiconductor substrates such as semiconductor wafers. State of the art

[0003] The miniaturization of semiconductor devices has recently progressed with the high integration or similar of integrated circuits, and thus, in addition to high flatness, a high degree of reduction of surface defects has been required for semiconductor substrates (here also simply called substrates) such as semiconductor wafers (here also simply called wafers).

[0004] To flatten such semiconductor substrates and reduce surface defects, polishing the substrate surface with a polishing composition containing a water-soluble polymer has been proposed. This polymer is a component that improves the wettability of semiconductor substrates. Such a polishing composition for use in the polishing process is described, for example, in JP 2010 - 34 509 A. JP 2010 - 34 509 A describes a polishing composition containing hydroxyethyl cellulose as a water-soluble polymer.

[0005] Polishing a semiconductor substrate typically employs multi-step polishing methods. In a multi-step polishing process, the surface of the semiconductor substrate is flattened in an early polishing step, such as step one, step two, and so on. A final polishing step, specifically designed to achieve a more precise flatness, is then performed.

[0006] Generally, various surface defects of different sizes are present on the surface of a substrate before polishing. However, to perform polishing designed to achieve high-precision flatness, as described above in the final polishing stage, a polishing compound is used that primarily reduces surface defects of minute size. Such a conventional polishing compound, as described in JP 2010-34509A, cannot selectively remove surface defects of a specific size. Consequently, if such a polishing compound is used in the early polishing steps prior to final polishing, surface defects of relatively large and relatively small sizes will be polished equally on the substrate. Thus, there is a possibility that relatively large surface defects will remain.The problem is that even if final polishing is carried out at such a stage, the surface defects cannot be sufficiently reduced after the final polishing.

[0007] JP 2004-128070A discloses a process for polishing a semiconductor wafer, comprising a polishing step, and a polishing composition consisting of silicon dioxide, a water-soluble polymer compound, and an alkali compound. WO 2012 / 002525A1 discloses a process for polishing a silicon wafer, comprising a coarse polishing step and a fine polishing step. JP 2007-103515A discloses a polishing composition containing hydroxyethylcellulose, water, and abrasive grains, wherein the average molecular weight of the hydroxyethylcellulose is between 300,000 and 1,600,000. Summary of the invention: Technical problem

[0008] Accordingly, in view of such conventional problems as described above, the technical problem to be solved by the present invention is to provide a method for polishing a semiconductor substrate that is capable of sufficiently reducing the surface defects of the semiconductor substrate after final polishing. Solution to the problem

[0009] The method for polishing a semiconductor substrate according to the present invention comprises an intermediate polishing step of polishing in such a way that the number of surface defects having a height of less than 3 nm is less than 45% or more of the total number of surface defects on the surface of a semiconductor substrate, and a final polishing step of finishing the semiconductor substrate after the intermediate polishing step.

[0010] According to the present invention, the polishing in the intermediate polishing step is carried out using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the mass ratio of the hydroxyethyl cellulose to the abrasive grains is 0.0075 or more and 0.025 or less.

[0011] According to the present invention, alternatively, the polishing in the intermediate polishing step is carried out using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the proportion of hydroxyethyl cellulose absorbed to the abrasive grains is 45% or more and 90% or less.

[0012] According to the present invention, a double-sided polishing step of polishing on both surfaces of the semiconductor substrate can be included prior to the intermediate polishing step.

[0013] According to the present invention, the polishing in the final polishing step is carried out using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less, and wherein the molecular weight of the hydroxyethyl cellulose of the polishing composition used in the final polishing step differs from the molecular weight of the hydroxyethyl cellulose of the polishing composition used in the intermediate polishing step. Brief description of the drawings Fig. Figure 1 shows a graph that shows the proportions of surface defects after polishing. Detailed description of a preferred embodiment

[0014] The following describes the method for polishing a semiconductor substrate according to the present invention.

[0015] The method for polishing a semiconductor substrate of the present embodiment comprises an intermediate polishing step of performing the polishing in such a way that the number of surface defects with heights of less than 3 nm becomes 45% or more of the total number of surface defects on the surface of a semiconductor substrate, and a final polishing step of finishing the polishing of the semiconductor substrate after the intermediate polishing step. (semiconductor substrate)

[0016] A semiconductor substrate polished by the polishing process of the present embodiment is a semiconductor substrate such as a silicone disk for electronic devices, on which tiny surface defects with a width or height of a few nanometers must be removed. (Two-sided polishing step)

[0017] The polishing method of the present embodiment can include a two-sided polishing step of polishing both surfaces of a semiconductor substrate prior to the intermediate polishing step.

[0018] In the two-sided polishing step, both surfaces of a semiconductor substrate are polished using a polishing composition that includes abrasive grains.

[0019] By performing such a double-sided polishing step, surface defects of relatively large sizes on the semiconductor substrate can be reduced. (Intermediate polishing step)

[0020] In the polishing process of the present invention, the intermediate polishing step polishes a semiconductor substrate in such a way that the number of surface defects with heights of less than 3 nm is 45% or more, preferably 70% or more, and more preferably 90% or more, of the total number of surface defects on the surface of a semiconductor substrate. In other words, the polishing is carried out in such a way as to achieve a state in which the remaining proportion of surface defects, apart from relatively small surface defects, is small.

[0021] Surface defects of various sizes are present on the surface of a semiconductor substrate; examples of such surface defects include relatively large surface defects with heights of 10 nm or more, tiny surface defects with heights of less than 10 nm, tiny surface defects with heights of less than 3 nm and widths of 50 to 200 nm, and tiny surface defects with heights of less than 3 nm and widths of 150 to 350 nm.

[0022] The height and width of the surface defects referred to in the present embodiment are those measured using an atomic force microscope (AFM).

[0023] Additionally, the number of surface defects referred to in the present embodiment refers to the number of counts of surface defects, each of which represents a quantity measured using a surface defect inspection device such as a confocal optical system laser microscope (MAGICS M5640, manufactured by Lasertec Corporation).

[0024] In the polishing method of the present invention, surface defects can be effectively and accurately reduced after the final polishing in the following way: Surface defects of a relatively large size are made smaller in the intermediate polishing step or in the double-sided polishing step before the final polishing step, and tiny surface defects are removed in the final polishing step.

[0025] The presence or absence of surface defects is determined by counting the number of surface defects. Accordingly, if countable defects are present, regardless of their size, the number of counts will be high, and it will be determined that the defects have not been reduced.

[0026] However, if even a small number of large defects remain in the final polishing step after the intermediate polishing step, these defects cannot be adequately removed during the final polishing, which is designed to eliminate minute defects. Therefore, it is important to remove defects of a size that are difficult to eliminate during the final polishing step, rather than simply reducing the number of surface defects.

[0027] In the intermediate polishing step of the present invention, polishing is carried out in such a way that surface defects with heights of 3 nm or more are selectively removed, and the number of surface defects with heights of less than 3 nm after polishing becomes 45% or more of the total number of surface defects. Accordingly, in the final polishing step, which is carried out after the intermediate polishing step, when the minute surface defects with heights of less than 3 nm remaining on the semiconductor substrate are removed, most of the surface defects present on the semiconductor substrate can be removed, and thus the surface defects can be sufficiently reduced after the final polishing step.

[0028] In the intermediate polishing step, in order to perform the polishing in such a way that the number of surface defects with heights of less than 3 nm is 45% or more of the total number of surface defects, the following polishing composition is used. (Polishing compound)

[0029] A polishing composition according to the invention, which is used in the intermediate polishing step of the present embodiment, comprises a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the mass ratio of the hydroxyethyl cellulose to the abrasive grains is 0.075 or more and 0.025 or less.

[0030] Hydroxyethyl cellulose refers to hydroxyethyl cellulose with a molecular weight of 500,000 or more and 1,500,000 or less.

[0031] The molecular weight, which falls within the range described above, allows the polishing composition to exert a removal capability that is particularly well suited for surface defects of a certain size on the object being polished.

[0032] Hydroxyethyl cellulose can improve wettability; in particular, hydroxyethyl cellulose with a molecular weight falling within the range described above improves the wettability of the polishing object and reduces particles and the like on the surface of the polishing object after polishing.

[0033] The molecular weight of the hydroxyethyl cellulose according to the present embodiment means the weight average of the molecular weight measured using the GFC (gel filtration chromatography) method, and in particular the value measured by the measurement methods shown in the examples described below.

[0034] The polishing compound includes water. Hydroxyethyl cellulose is a hydrophilic polymer and therefore readily forms an aqueous solution when mixed with water. As described above, this solution improves the removal of surface defects of a certain size on the object being polished and enhances its wettability.

[0035] The water content is not particularly restricted; water can be added in a suitable quantity.

[0036] If the polishing composition is used in such a way that it is diluted at the time of use, the polishing composition is produced as a highly concentrated liquid with a concentration that is higher than the concentration desired at the time of use, and water can be added as a diluent at the time of dilution.

[0037] The polishing compound includes abrasive grains.

[0038] Examples of abrasive grains include: grains made of metal oxides such as silicon dioxide, aluminum oxide, cerium oxide, and titanium oxide; silicon nitride grains; silicon carbide grains; and boron nitride grains. Of these, silicon dioxide is preferred; particularly preferred is colloidal silicon dioxide such as spherical or non-spherical colloidal silicon dioxide.

[0039] If the abrasive grains are colloidal silicon dioxide, an aqueous solution of hydroxyethyl cellulose is readily adsorbed onto the abrasive grains and the removal of surface defects of a certain size can be further improved, as described below, which is therefore preferred.

[0040] Non-spherical colloidal silicon dioxide is preferred for colloidal silicon dioxide.

[0041] Non-spherical colloidal silicon dioxide allows an aqueous solution of hydroxyethyl cellulose to be adsorbed onto it through the simultaneous presence of hydroxyethyl cellulose in the polishing composition, thereby making it easier to remove surface defects of a certain size, as described below, which is therefore preferred.

[0042] In the polishing composition, the mass ratio of hydroxyethyl cellulose to abrasive grains is 0.0075 or more and 0.025 or less.

[0043] If the ratio of hydroxyethyl cellulose content (wt.%) to abrasive grain content (wt.%) falls within the range mentioned above, this allows for further improvement in the removal of surface defects of a certain size. At the same time, such a ratio as described above improves the wettability of the polished object's surface after polishing.

[0044] The content of abrasive grains in the polishing composition of the present embodiment is not particularly limited, but is, for example, 5 wt.% or more and 20 wt.% or less.

[0045] The abrasive grain content in the range described above is preferred because such a content allows the polishing speed to be adequately regulated.

[0046] The grain size of the abrasive particles is not particularly restricted, but examples include an average grain size of 85 nm or larger. An average grain size of the abrasive particles in the range described above is preferred because surface defects of a certain size present on the surface of the object being polished can be reduced more effectively.

[0047] The average particle size according to the present embodiment is measured using the DLS (dynamic light scattering) method. More precisely, average particle size according to the present invention refers to the average particle size in the polishing compound as measured using a device described in the examples below. In other words, if the abrasive particles in the polishing compound form clusters as described below, average particle size refers to the average particle size of the clusters.

[0048] The polishing composition includes hydroxyethyl cellulose, water and abrasive grains, and therefore the following interactions are expected to occur.

[0049] In particular, in the polishing compound, some of the hydroxyethyl cellulose is adsorbed onto the surface of the abrasive grains, such as colloidal silicon dioxide. Therefore, the polishing compound contains both hydroxyethyl cellulose in a state where it is adsorbed onto the abrasive grains and hydroxyethyl cellulose that is not adsorbed and is present in a mixed state. It is assumed that when the hydroxyethyl cellulose is adsorbed onto the abrasive grains, the activity of the hydroxyethyl cellulose causes the grains to form clusters. The greater the molecular weight of the hydroxyethyl cellulose, or the higher its concentration in the polishing compound, the greater the tendency to form clusters.

[0050] It is assumed that, depending on the size and quantity of clusters, the reduction performance of surface defects of a certain size present on the surface of the polished object will change.

[0051] The hydroxyethyl cellulose, which is present mixed in the polishing composition without being adsorbed onto the abrasive grains, can improve the wettability of a polishing object.

[0052] Accordingly, it is assumed that by establishing an equilibrium between the hydroxyethyl cellulose adsorbed onto the abrasive grains and the hydroxyethyl cellulose not adsorbed onto the abrasive grains, the polishing composition of the present embodiment can reduce surface defects of a certain size that are present on the surface of the object being polished.

[0053] An alternative polishing composition used in the intermediate polishing step of the present embodiment is a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the proportion of hydroxyethyl cellulose adsorbed onto the abrasive grains is preferably 45% or more and 90% or less.

[0054] The hydroxyethyl cellulose, which has a molecular weight of 500,000 or more and 1,500,000 or less, and the proportion of hydroxyethyl cellulose adsorbed onto the abrasive grains, which is 45% or more and 90% or less, allows, as described above, the size and quantity of clusters to be regulated so that they fall within appropriate ranges, and the surface defects of a certain size that are present on the surface of a polishing object to be adequately removed.

[0055] According to the present invention, the proportion of hydroxyethyl cellulose adsorbed onto the abrasive grains is the percentage calculated by the following method.

[0056] The TOC (total organic carbon) amount of supernatant obtained by centrifuging 1.5 mg of the polishing composition at 14,000 rpm for 10 min, and the TOC content of the polishing composition are measured, and the proportion of hydroxyethyl cellulose adsorbed onto the abrasive grains (the percentage of adsorbed hydroxyethyl cellulose (%)) is calculated using the following formula 1. Percentage of adsorbed hydroxyethyl cellulose (%) = (TOC of polishing composition - TOC of supernatant) / (TOC of polishing composition) × 100

[0057] According to the present invention, the grain size of the abrasive grains (clusters) and the ratio of hydroxyethyl cellulose adsorbed onto the abrasive grains refer to the grain size or ratio at the time of use of the polishing composition.

[0058] The polishing compound may still contain ammonia.

[0059] The absorption of ammonia allows for a more effective reduction of surface defects of a certain size that are present on the surface of the polishing object, and is therefore preferred.

[0060] The ammonia content is not particularly restricted, but examples of ammonia content include 0.1 wt.% or more and 1.0 wt.% or less, and preferably 0.25 wt.% or more and 0.75 wt.% or less.

[0061] The ammonia content, which falls within the range described above, allows for a more sufficient reduction of surface defects of a certain size that are present on the surface of the polished object, and is therefore preferred.

[0062] The ammonia content, which falls within the range described above, also allows the pH value of the polishing composition to be adjusted so that it falls within a suitable range, and is therefore preferred.

[0063] The polishing compound may also contain other components.

[0064] Examples of other components include a pH adjuster, a surfactant, and a chelator.

[0065] The polishing compound can be produced as a highly concentrated liquid, which has a higher concentration than the desired concentration at the time of use, and can be diluted at the time of use.

[0066] If the polishing compound is produced as a highly concentrated liquid, the highly concentrated liquid is suitable for storage and transport.

[0067] If the polishing composition is produced in a highly concentrated form, examples of the preparation include a preparation in which the highly concentrated liquid is produced such that it has a concentration which, at the time of use, can be diluted by a factor of about, for example, 5-100, preferably 20-60 and more preferably 21-41. (Final polishing step)

[0068] The polishing process of the present embodiment comprises a final polishing step of finishing the semiconductor substrate after the intermediate polishing step.

[0069] In the final polishing step, while relatively small, tiny defects with a height of less than 3 nm on the surface of the semiconductor substrate are removed after performing the intermediate polishing step, the semiconductor substrate is polished to a substrate with a high flatness that is free of haze or similar defects.

[0070] The final polishing step involves polishing using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less.

[0071] When such a polishing composition is used during the final polishing step, surface defects after polishing can be reduced more effectively.

[0072] The method for polishing a semiconductor substrate according to the present invention is as described above, but it should be understood that the disclosed embodiment is illustrated in all aspects by way of example to describe the present invention, and that the present invention is not limited to this embodiment. The scope of the present invention is not defined by the preceding description, but by the appended claims.

[0073] According to the present invention, the polishing method comprises an intermediate polishing step such that the number of surface defects with a height of less than 3 nm becomes 45% or more of the total number of surface defects on the surface of a semiconductor substrate, and a final polishing step of polishing the semiconductor substrate after the intermediate polishing step; accordingly, the surface defects on the surface of a semiconductor substrate can be sufficiently reduced after the final polishing step.

[0074] According to the present invention, the polishing in the intermediate polishing step is carried out using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the mass ratio of hydroxyethyl cellulose to abrasive grains is 0.0075 or more and 0.025 or less.

[0075] According to the present invention, the polishing in the intermediate polishing step is alternatively also carried out using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the proportion of hydroxyethyl cellulose adsorbed onto the abrasive grains is preferably 45% or more and 90% or less.

[0076] By polishing with such a polishing composition as described above during the intermediate polishing step, surface defects on the surface of a semiconductor substrate can be sufficiently reduced after the final polishing step.

[0077] If the polishing in the final polishing step is performed using a polishing composition comprising hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less, surface defects on the surface of a semiconductor substrate can be reduced more effectively after the final polishing step.

[0078] As described above, according to the present invention, surface defects on the semiconductor substrate can be sufficiently reduced after final polishing. Examples

[0079] Examples of the present invention are described below; however, the present invention is not limited to these examples.

[0080] In the present example, a polishing test was carried out using a polishing composition that is used in the intermediate polishing step. (Hydroxyethyl cellulose)

[0081] The hydroxyethyl celluloses shown in Table 1 with different molecular weights (500,000 and 1,000,000) were produced.

[0082] The molecular weights of the hydroxyethyl celluloses are the molecular weights as measured by the following method. (Measurement of molecular weight)

[0083] The molecular weight is the weight-averaged molecular weight obtained through the following measurement.

[0084] The measurement was performed using a GFC instrument (Model PU-2085 plus system, manufactured by JASCO Corporation) as the measuring instrument, two Asahipak GF-710HQ and Asahipak GF-310HQ columns connected in series, manufactured by Shodex Co., Ltd., and a 0.7% aqueous solution of sodium chloride as the eluent.

[0085] The hydroxyethyl cellulose (HEC), the abrasive grains (silicon dioxide produced by the sol-gel process, grain size in water: 66 nm, determined by dynamic light scattering), ammonia and the remaining water were mixed according to the compositions shown in Table 1 to obtain the polishing compositions 1 to 6.

[0086] The polishing compositions were each diluted by a factor of 41 with water. Silicone wafers (12 inches) were used as the object to be polished and were polished with the diluted polishing compositions under the polishing conditions below. The surface defects after polishing were measured using the procedure below, and the results obtained are shown in Table 1. (Polishing conditions) Polishing machine: SPP800S (manufactured by Okamoto Machine Tool Works, Ltd.) Polishing pad: POLYPAS 24T (manufactured by Fujibo Ehime Co., Ltd.) Record speed: 40 rpm Polishing charge: 120 gf / cm² 2 Flow rate: 0.6 l / min Object to be polished: 12-inch silicone wafer Polishing time: 300 sec (Measurement method for surface defects)

[0087] After polishing under the polishing conditions described above, the wafers were washed with a liquid mixture of ammonia / hydrogen peroxide and then the measurement (edge ​​exclusion EE: 5 mm, slice level: D37 mV) of the surface defects was carried out using a measuring instrument (MAGICS M5640, manufactured by Lasertec Corporation).

[0088] Based on the coordinates of the errors measured by MAGICS, a measurement of the errors was carried out using the AFM SAP465 measuring device (manufactured by Seiko Instruments Inc.).

[0089] Based on these two types of measurements, the surface defects were assigned to types A to F using the procedure below, and the ratios of the corresponding surface defects are shown in the graph of Figure 1. Table 1 gives the ratios of the corresponding types in percent. (Assignment of MAGICS verification images)

[0090] In the MAGICS verification image assignment procedure, the MAGICS verification images were assigned to the following types A to F according to the arrangement of the white and black areas, which varied from left to right in the image at the defective areas of each verification image. A bandpass filter was used for the analysis of the MAGICS verification images.

[0091] On the MAGICS verification images, due to the effect of the bandpass filter, the color changes three times when the errors are very small (low), either as a sequence of white→black→white or as a sequence of black→white→black. Which of the white→black→white and black→white→black sequences corresponds to a low-level error is analyzed using AFM. Type A: White-black-white and scratch-like images Type B: White-black-white Type C: Black-white-black Type D. White-black Type E: Black and white Type F: Black (Dimension of surface defects)

[0092] The corresponding types of defects were measured using the AFM and it was found that the dimensions of the corresponding types of defects fell into the following ranges.

[0093] In particular, the errors were assigned to the following types A to F. Type A: Height: less than 3 nm, Width: 50 to 200 nm, Length: 200 µm or more Type B: Height: less than 3 nm, Width: 150 to 350 nm Type C: Height: 3 nm or more and less than 10 nm, Width: 50 to 70 nm Type D: Height: 10 nm or more and 30 nm or less, Width: 70 to 250 nm Type E: Height: 10 nm or more and 50 nm or less, Width: 100 to 300 nm Type F: Height: more than 50 nm, Width: more than 150 nm

[0094] Type A defects are scratch-like defects with a length component, and types B to F are spot-like or irregular defects. (pH)

[0095] The pH of each of the polishing compositions and the pH of each of the 41-fold diluted liquids of this polishing composition at a liquid temperature of 25 °C was measured using a pH meter (manufactured by HORIBA, Ltd.). (Measurement of adsorbed hydroxyethyl cellulose)

[0096] Each of the polishing compositions was diluted by a factor of 41 with water. A 1.5 mg sample of the diluted polishing composition was taken and centrifuged at 14,000 rpm for 10 minutes using an MCD-2000 (manufactured by AS ONE Corporation). Subsequently, each centrifuged sample was separated into precipitate and supernatant. The supernatant was removed, and the TOC (Total Organic Carbon) content of each supernatant and the TOC content of each polishing composition was measured using a Siervers 900 meter (manufactured by GE). From these measurements, the proportion of adsorbed hydroxyethyl cellulose in each of the polishing compositions was calculated using Formula 1 below, and the results obtained are shown in Table 1. Percentage of adsorbed hydroxyethyl cellulose (%) = (TOC of polishing composition - TOC of supernatant) / (TOC of polishing composition) × 100 (Measurement of the grain size of the clusters)

[0097] The grain size of the abrasive grains (clusters) in the 41-fold diluted liquid of each polishing composition was measured.

[0098] The grain size was determined using an ELSZ-2 zeta potential / grain size measurement system (manufactured by OTSUKA ELECTRONICS Co., LTD.). The results obtained are shown in Table 1.

[0099] As can be seen from Table 1, the proportion of Type B surface defects remaining on the wafer surface after polishing can be reduced to 45% or more, depending on the ratio of hydroxyethyl cellulose content to creep grain content and the proportion of adsorbed hydroxyethyl cellulose in the polishing compound. In other words, as is evident, if the intermediate polishing step is performed using a polishing compound capable of adequately removing surface defects other than Type B defects, a large number of easily removable surface defects can be left on the substrate during the subsequent final polishing step, thus sufficiently reducing the surface defects after the final polishing step.

Claims

Method for polishing a semiconductor substrate, comprising: an intermediate polishing step of polishing in such a way that the number of surface defects with heights of less than 3 nm becomes 45% or more of the total number of surface defects on the surface of a semiconductor substrate;and a final polishing step of polishing the semiconductor substrate after the intermediate polishing step, wherein in the intermediate polishing step the polishing is carried out using a polishing composition comprising: first hydroxyethyl cellulose, water and abrasive grains, wherein the first hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less and the mass ratio of first hydroxyethyl cellulose to abrasive grains is 0.0075 or more and 0.025 or less, wherein in the final polishing step the polishing is carried out using a polishing composition comprising: second hydroxyethyl cellulose, water and abrasive grains, wherein the second hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less;and wherein the molecular weight of the second hydroxyethyl cellulose of the polishing composition used in the final polishing step differs from the molecular weight of the first hydroxyethyl cellulose of the polishing composition used in the intermediate polishing step. Method for polishing a semiconductor substrate, comprising: an intermediate polishing step of polishing in such a way that the number of surface defects with heights of less than 3 nm becomes 45% or more of the total number of surface defects on the surface of a semiconductor substrate;and a final polishing step of polishing the semiconductor substrate after the intermediate polishing step, wherein in the intermediate polishing step the polishing is carried out using a polishing composition comprising: first hydroxyethyl cellulose, water and abrasive grains, wherein the first hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the proportion of first hydroxyethyl cellulose adsorbed onto the abrasive grains is preferably 45% or more and 90% or less, wherein in the final polishing step the polishing is carried out using a polishing composition comprising: second hydroxyethyl cellulose, water and abrasive grains, wherein the second hydroxyethyl cellulose has a molecular weight of 300,000 or more and 1,200,000 or less;and wherein the molecular weight of the second hydroxyethyl cellulose of the polishing composition used in the final polishing step differs from the molecular weight of the first hydroxyethyl cellulose of the polishing composition used in the intermediate polishing step. Method for polishing a semiconductor substrate according to claim 1 or 2, comprising, prior to the intermediate polishing step, a double-sided polishing step of polishing both sides of the semiconductor substrate.

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