Double-sided polishing method and double-sided polished silicon wafer

Abstract

A double-sided polishing method is provided, characterized by first polishing a wafer, and after the first polishing, second polishing the wafer for 15 seconds or less using a slurry containing a water-soluble polymer, the first polishing using a slurry of abrasive grains having an association degree of less than 1.0, which is obtained from (volume-based average particle diameter determined by a dynamic scattering method) / (number-based average actual particle diameter determined using a scanning electron microscope). Thus, a double-sided polishing method that can obtain a double-sided polished wafer with a roughened back surface, and a double-sided polished silicon wafer with a roughened back surface, can be provided.

Description

Technical Field

[0001] This invention relates to a method for double-sided polishing of wafers and to double-sided polished silicon wafers. Background Technology

[0002] Current polishing processes are exploring components and polishing conditions to create the most smooth and precise surfaces possible. Therefore, most fabricated wafers have an AFM (Atomic Force Microscope) roughness (roughness obtained through atomic force microscopy analysis) Ra of less than 0.1 nm, indicating low roughness and making it easy to achieve flat surfaces on both the front and back sides. Previous reports have also described methods such as: as described in Patent Document 1, increasing the polishing rate by adjusting the association degree of the associated colloidal silica in the slurry; and as described in Patent Documents 2 and 3, setting the abrasive grain association degree to, for example, 1.0 or higher and less than 5.0, thereby increasing the polishing rate while simultaneously achieving good surface roughness due to the abrasive grain shape.

[0003] Patent document 4 describes a method in which, in a single-sided polishing process, a water-soluble polymer is added to a fine polishing slurry in a subsequent second (fine) polishing step, and a fine polishing cloth is used to polish watermark defects that occurred in the first (coarse) polishing step, thereby forming a protective film and reducing watermark defects.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-155242

[0007] Patent Document 2: International Publication No. WO2017 / 163942

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-169687

[0009] Patent Document 4: Japanese Patent Application Publication No. 2016-51763 Summary of the Invention

[0010] The technical problem to be solved by the present invention

[0011] In recent years, customer demand has driven a need for double-sided polished wafers with a roughened back side, as a rougher back side compared to the vacuum pinch chuck in the photolithography process reduces friction between the pins and the wafer. Furthermore, with the increasing integration of semiconductor devices, wafer surface quality has become increasingly important, leading to a surge in demand for roughened double-sided polished wafers. As mentioned above, while the demand for double-sided polished wafers with a roughened back side is high, current polishing methods or components struggle to achieve the required surface roughness (e.g., increasing roughness per 2μm). 2 The AFM roughness Ra is above 0.2 nm.

[0012] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a double-sided polishing method for obtaining a double-sided polished wafer with a roughened back side and a double-sided polished silicon wafer with a roughened back side.

[0013] Technical means to solve technical problems

[0014] To solve the above-mentioned technical problems, the present invention provides a double-sided polishing method, characterized in that...

[0015] The wafer is first polished using a slurry with an association degree of less than 1.0, calculated as (average particle size based on volume as determined by dynamic scattering) / (average actual particle size based on number as determined by scanning electron microscopy).

[0016] After the first polishing, the wafer is polished for less than 15 seconds using a slurry containing a water-soluble polymer.

[0017] By performing a first polishing on the wafer, and using a slurry with an association degree of less than 1.0 calculated based on (average particle size in volume as determined by dynamic scattering) / (average actual particle size in number as determined by scanning electron microscopy), a double-sided polished wafer with a roughened back side can be obtained, for example, with a roughened back side per 2 μm. 2 The double-sided polished wafer has an AFM roughness Ra of 0.3 nm or higher. Furthermore, by performing a second polishing (hereinafter referred to as fine polishing) on ​​the wafer for less than 15 seconds using a slurry containing a water-soluble polymer after the first polishing, the roughness of the back side can be maintained, and protection of both the surface and the back side can be achieved.

[0018] The first polishing can be performed using a foamed urethane polishing cloth or a non-woven polishing cloth with a Shore A hardness of 70 or higher.

[0019] For example, a polishing cloth of this hardness can be used for the first polishing.

[0020] Furthermore, the present invention provides a double-sided polished silicon wafer, characterized in that, every 2μm on the back side... 2 The AFM roughness Ra is above 0.3 nm.

[0021] Although such a double-sided polished silicon wafer is polished on both sides, the back side is still sufficiently roughened. This double-sided polished silicon wafer can meet the needs of customers seeking double-sided polished wafers with a roughened back side. By using the double-sided polished silicon wafer of this invention in processes such as photolithography, friction between the needles of the vacuum chuck and the wafer can be reduced.

[0022] Invention Effects

[0023] As described above, if the double-sided polishing method of the present invention is used, a double-sided polished wafer with roughened back side can be obtained.

[0024] Furthermore, the double-sided polished silicon wafer of the present invention can meet the needs of customers seeking double-sided polished wafers with roughened back side. Attached Figure Description

[0025] Figure 1 This is a cross-sectional schematic diagram illustrating an example of a double-sided polished silicon wafer according to the present invention.

[0026] Figure 2 A graph showing the AFM roughness Ra of the first polished wafer in the embodiments and comparative examples.

[0027] Figure 3 A graph showing the relationship between the second polishing time and the AFM roughness Ra. Detailed Implementation

[0028] As described above, the aim is to develop a double-sided polishing method for obtaining double-sided polished wafers with roughened back surfaces, and double-sided polished silicon wafers with roughened back surfaces.

[0029] The inventors of this application have carefully studied the above-mentioned technical problems and found that by polishing the wafer and using a slurry with an association degree of less than 1.0 obtained by (average particle size based on volume as determined by dynamic scattering method) / (average actual particle size based on number as determined by scanning electron microscopy), and then performing fine polishing of the wafer for less than 15 seconds using a slurry containing a water-soluble polymer, a double-sided polished wafer with roughened back side can be obtained, thus completing the present invention.

[0030] That is, the present invention is a double-sided polishing method, characterized in that,

[0031] The wafer is first polished using a slurry with an association degree of less than 1.0, calculated as (average particle size based on volume as determined by dynamic scattering) / (average actual particle size based on number as determined by scanning electron microscopy).

[0032] After the first polishing, the wafer is polished for less than 15 seconds using a slurry containing a water-soluble polymer.

[0033] Furthermore, the present invention relates to a double-sided polished silicon wafer, characterized in that, every 2μm on the back side... 2 The AFM roughness Ra is above 0.3 nm.

[0034] The present invention will now be described in detail, but it is not limited thereto.

[0035] (Double-sided polishing method)

[0036] The double-sided polishing method of the present invention performs a first polishing and a second polishing (fine polishing) on ​​the wafer sequentially. The first polishing and the second polishing will be described below.

[0037] Furthermore, the wafer to be polished in the double-sided polishing method of the present invention is not particularly limited, and can be, for example, a silicon wafer.

[0038] Furthermore, the double-sided polishing apparatus used in the double-sided polishing method of the present invention is not particularly limited.

[0039] [First Polishing]

[0040] In the first polishing, a slurry with a cohesion of less than 1.0 is used, calculated as (average particle size on volume basis determined by dynamic scattering method) / (average actual particle size on number basis determined by scanning electron microscopy).

[0041] The aforementioned degree of association can be roughly referred to as an index representing the aspect ratio of the abrasive grains. In addition, besides scanning electron microscopy, the degree of association at the concentration of abrasive grains in the actual solution state used during the polishing process can also be determined by using dynamic scattering methods.

[0042] The particle size distribution of abrasive grains obtained by the dynamic scattering method is a volume-based particle size distribution determined based on the scattering intensity. The volume-based average particle size measured by the dynamic scattering method is the volume-based average particle size (mode particle size, also known as abrasive grain size) obtained from the particle size distribution obtained in this way.

[0043] The particle size distribution of abrasive grains obtained using scanning electron microscopy is a number-based particle size distribution, which is the particle size distribution counted only by primary particles of the abrasive grains. The average actual particle size based on the number of particles, determined using scanning electron microscopy, is the number-based average particle size (mode particle size) obtained from the particle size distribution obtained in this manner.

[0044] The first polishing is performed using a slurry with an association degree of less than 1.0, calculated as (average particle size on a volume basis as determined by dynamic scattering) / (average actual particle size on a number basis as determined by scanning electron microscopy). Although the detailed rationale is unclear, it is possible to achieve roughening of the wafer back side, for example, achieving roughening per 2 μm. 2 The AFM roughness Ra on the back side of the wafer is above 0.3 nm.

[0045] On the other hand, if the degree of association is 1.0 or higher, then every 2 μm 2 The AFM roughness Ra on the back side of the wafer can only be below 0.2 nm.

[0046] The aforementioned degree of association is preferably 0.97 or less. Furthermore, there is no particular limitation on the lower limit of the aforementioned degree of association, and the aforementioned degree of association can be set to, for example, 0.9 or more.

[0047] For example, the degree of association of abrasive particles can be adjusted by adding a surfactant to an aqueous solution obtained by adding an alkaline compound (e.g., KOH) to the abrasive particles during slurry preparation, and adjusting the amount of surfactant added.

[0048] There are no particular limitations on the material of the abrasive grains; for example, silica (water glass, colloidal silica), SiC, etc. can be used as abrasive grains.

[0049] The slurry used in the first polishing process can contain a dispersion medium of abrasive grains. The dispersion medium is not particularly limited; for example, water can be used as a dispersion medium.

[0050] There are no particular limitations on the pH value of the slurry used in the first polishing; for example, it can be set to above 10 and below 12.

[0051] The slurry used in the first polishing step may further contain an alkaline compound. The alkaline compound is not particularly limited; for example, potassium hydroxide or tetramethylammonium hydroxide (TMAH) can be used.

[0052] The slurry used in the first polishing may further contain surfactants.

[0053] There are no particular limitations on the polishing cloth used in the first polishing process. For example, a foamed urethane polishing cloth or a non-woven polishing cloth with a Shore A hardness of 70 or higher can be used. There are also no particular limitations on the upper limit of the Shore A hardness of the polishing cloth. For example, a polishing cloth with a Shore A hardness of 90 or lower can be used.

[0054] The double-sided polished wafer can be cleaned with SC-1 after the first polishing and before the second polishing as described below.

[0055] [Second polishing (finish polishing)]

[0056] To protect the surface and back side, a slurry containing a water-soluble polymer is used to perform a second polishing (fine polishing) on ​​the wafer supplied after the first polishing for no more than 15 seconds.

[0057] By performing a second polishing for less than 15 seconds, the AFM roughness Ra of the back surface can be maintained at 2 μm. 2 It has a wavelength of 0.3nm or more and can provide protection for both the surface and the back side.

[0058] Furthermore, by setting the second polishing time to more than 5 seconds and less than 15 seconds, it is possible to maintain a high roughness on the back side and to more reliably protect both the surface and the back side.

[0059] On the other hand, in the second polishing process, which lasts for more than 15 seconds, the roughened surface obtained by the first polishing is corrected, resulting in a reduction of 2μm per 2 The AFM roughness Ra is less than 0.3 nm.

[0060] The water-soluble polymer contained in the slurry used in the second polishing is not particularly limited; for example, HEC (hydroxyethyl cellulose) and PVA (polyvinyl alcohol) can be listed.

[0061] The slurry used in the second polishing process may or may not contain abrasive particles.

[0062] There are no particular restrictions on the polishing cloth used in the second polishing process; the polishing cloth commonly used in fine polishing can be used.

[0063] After the second polishing, a double-sided polished wafer is obtained. This double-sided polished wafer is polished on both sides, and the back side is sufficiently roughened, specifically, it can show a roughness of 2 μm. 2 The AFM roughness Ra is above 0.3 nm. Furthermore, a protective film is formed on the surface and back side of the double-sided polished wafer.

[0064] Furthermore, according to the double-sided polishing method of the present invention, the surfaces of the double-sided polished wafer that are opposite to the back side are also roughened. To achieve the desired surface roughness, this surface can be polished on one side or the like.

[0065] (Double-sided polished silicon wafer)

[0066] Figure 1 This is a cross-sectional schematic diagram illustrating an example of a double-sided polished silicon wafer according to the present invention.

[0067] The double-sided polished silicon wafer 1 has a surface 2 and a back surface 3 on its opposite side. Each 2 μm of the back surface 3 of the double-sided polished silicon wafer 1... 2 The AFM roughness Ra is above 0.3 nm. The back side 3 of the double-sided polished silicon wafer 1 has a roughness of 2 μm per inch. 2 There is no particular upper limit to the AFM roughness Ra, for example, it can be set to below 0.8 nm.

[0068] The double-sided polished silicon wafer 1 of the present invention can be obtained by, for example, the double-sided polishing method of the present invention.

[0069] The surface 2 of the double-sided polished silicon wafer 1 obtained by the double-sided polishing method of the present invention has a 2μm diameter. 2 The AFM roughness Ra of surface 2 can be 0.3 nm or higher, similar to that of surface 3. As described above, in order to achieve the desired surface roughness, surface 2 can be subsequently polished on one side, etc.

[0070] Although such a double-sided polished silicon wafer 1 is polished on both sides, it still has a sufficiently roughened back side 3, thus meeting the needs of customers seeking double-sided polished wafers with a roughened back side. By using the double-sided polished silicon wafer 1 of the present invention in, for example, a photolithography process, friction between the needles of the vacuum chuck and the wafer can be reduced.

[0071] The AFM roughness Ra of the back side of the double-sided polished silicon wafer 1 can be obtained by atomic force microscopy analysis.

[0072] Example

[0073] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited thereto.

[0074] (Comparative Examples 1-3 and Example 1)

[0075] In Comparative Examples 1-3 and Example 1, slurries A-D were prepared according to the following steps.

[0076] In Comparative Example 1, a polyoxyethylene glycol (EO / PO) surfactant was added to an aqueous solution obtained by adding KOH to colloidal silica in an amount of 5 ppm relative to 100 parts by mass of colloidal silica to prepare slurry A with a pH of 10.5.

[0077] In Comparative Example 2, except that the same surfactant as in Comparative Example 1 was added in an amount of 10 ppm relative to 100 parts by mass of colloidal silica, slurry B with a pH of 10.5 was prepared following the same steps as in Comparative Example 1.

[0078] In Comparative Example 3, except that the same surfactant as in Comparative Example 1 was added in an amount of 30 ppm relative to 100 parts by mass of colloidal silica, slurry C with a pH of 10.5 was prepared following the same steps as in Comparative Example 1.

[0079] In Example 1, except that the same surfactant as in Comparative Example 1 was added in an amount of 50 ppm relative to 100 parts by mass of colloidal silica, slurry D with a pH of 10.5 was prepared following the same steps as in Comparative Example 1.

[0080] Table 1 below shows the volume-based average particle size, the number-based average actual particle size, and the degree of association calculated using (volume-based average particle size) / (number-based average actual particle size) for abrasive particles in slurries A through D. The volume-based average particle size was determined using a Delsa-nano microscope manufactured by Beckman Coulter, Ltd., via dynamic scattering. The number-based average actual particle size was determined by observation using a SEM (Scanning Electron Microscope) manufactured by JEOL Ltd.

[0081] [Table 1]

[0082]

[0083] Experimental conditions

[0084] As a double-sided polishing device, the DSP-20B manufactured by FUJIKOSHI MACHINERYCORP., a 4-axis double-sided polishing device, is used. The polishing cloth is a foamed urethane pad with a Shore A hardness of 90.

[0085] Prepare a single-crystal silicon wafer with a diameter of 300mm as the object to be polished.

[0086] In Comparative Examples 1 to 3 and Example 1, a first polishing was performed on a single-crystal silicon wafer using the aforementioned pastes A to D.

[0087] Each wafer after the first polishing was subjected to SC-1 cleaning under the condition of NH4OH:H2O2:H2O=1:1:15.

[0088] Using an AFM Park manufactured by Park Systems, at 2μm2 The AFM roughness Ra of the back side of each double-sided polished silicon wafer after SC-1 cleaning was measured internally. The results are shown in... Figure 2 .

[0089] • Measurement results

[0090] Figure 2 The area above the dashed line is the region where the AFM roughness Ra is above 0.3 nm.

[0091] like Figure 2 As shown, in Comparative Examples 1-3, which used slurries A-C with an abrasive grain association degree of 1.0 or higher, the back surface of the wafer had a surface area of ​​2 μm per inch. 2 The AFM roughness Ra is only below 0.2 nm, failing to achieve a roughening of the back side above 0.3 nm.

[0092] On the other hand, in Example 1, which used slurry D with an abrasive grain association degree of less than 1, every 2 μm on the back side of the wafer... 2 The AFM roughness Ra is above 0.3 nm, achieving roughening of the back side.

[0093] Then, multiple double-sided polished silicon wafers are prepared. These double-sided polished silicon wafers are obtained by using paste D, performing a first polishing and SC-1 cleaning under the same conditions as described above.

[0094] These double-sided polished silicon wafers were subjected to a second polishing (fine polishing) for different durations of 10 seconds, 15 seconds, and 20 seconds.

[0095] In the second polishing, a slurry containing silica as abrasive particles, HEC (hydroxyethyl cellulose) as a water-soluble polymer, and a pH of 10 is used.

[0096] Using an AFM Park manufactured by Park Systems, at 2μm 2 The AFM roughness Ra of the back side of each double-sided polished silicon wafer after the second polishing was measured internally. The results are shown in... Figure 3 .

[0097] like Figure 3 As shown, if it is a fine polishing (second polishing) of less than 15 seconds, then every 2μm on the back side... 2 The AFM roughness Ra is above 0.3 nm, achieving sufficient roughening and forming a protective film. Furthermore, it is known that during a second polishing process exceeding 15 seconds, the roughened surface is corrected, with improvements occurring every 2 μm. 2 The AFM roughness Ra is less than 0.3 nm.

[0098] Furthermore, it can be seen that if fine polishing is performed for more than 5 seconds, a protective film can be formed more fully. Therefore, the more appropriate time for fine polishing (second polishing) is more than 5 seconds and less than 15 seconds.

[0099] Furthermore, this invention is not limited to the above-described embodiments. The above embodiments are illustrative examples, and any technical solutions that have substantially the same composition and achieve the same technical effect as the technical concept described in the claims of this invention are included within the scope of protection of this invention.

Claims

1. A double-sided polishing method, characterized in that, The wafer is first polished, and the first polishing uses a slurry with a degree of association of less than 1.0, which is calculated based on (average particle size on volume as determined by dynamic scattering method) / (average actual particle size on number as determined by scanning electron microscopy). After the first polishing, the wafer is polished for less than 15 seconds using a slurry containing a water-soluble polymer.

2. The double-sided polishing method according to claim 1, characterized in that, The first polishing is performed using a foamed urethane polishing cloth or a non-woven polishing cloth with a Shore A hardness of 70 or higher.

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