Polishing liquid

Abstract

The invention discloses a polishing liquid, comprising the following components by mass: 5 to 25 parts of nano-scale abrasive particles, 0.1 to 0.5 parts of an oxidant, and 74 to 94.899 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles; the polishing liquid further comprises a pH regulator, and the pH regulator regulates the pH value of the polishing liquid to 3.5-6.0; the polishing liquid of the invention provides a weak acid environment, accelerates the passivation speed of the bismuth telluride wafer, forms a passivation layer on the surface of the bismuth telluride wafer, and reduces the concave area of ​​the uneven surface. Isotropic etching; and the hardness of bismuth telluride particles is low, and it is not easy to cause scratches on the surface of the bismuth telluride wafer, and it can also reduce the surface roughness of the wafer; in a weak acid environment, the zeta potential of nano-scale bismuth telluride particles can be as high as 40mV or more, with good dispersibility, no need to add dispersants, and it is not easy to remain on the bismuth telluride wafer. After ultrasonic cleaning with deionized water, very few bismuth telluride particles remain on the surface; an oxidant is added to the polishing liquid, and the oxidant has high chemical activity, which can increase the passivation speed of the bismuth telluride wafer surface.

Description

Technical Field

[0001] The invention relates to the field of chemical mechanical polishing, in particular to a polishing liquid. Background Art

[0002] Ultrafine thermoelectric devices are currently commonly used in optical communications, automotive laser radar, national defense and aerospace, and other fields involving precise temperature control of components. In order to improve the working conversion of ultrafine thermoelectric devices, it is necessary to reduce the resistance and thermal resistance of the overall device as much as possible during packaging, so the cutting and polishing requirements of thermoelectric blocks are getting higher and higher.

[0003] The existing technical solutions for ordinary thermoelectric devices are mainly mechanical polishing and sandpaper polishing. Mechanical polishing is a stress-existing grinding method. Since the thickness of ultra-fine thermoelectric wafers is 200 microns or less, mechanical polishing can easily cause the surface of the material to break, which can easily lead to block edge breakage and uneven edges during subsequent dicing. It will also directly affect the effect after subsequent device packaging. The surface roughness after polishing is low, and the contact resistance and thermal resistance are high. This technology is only applicable to the processing of thermoelectric materials in non-ultra-fine thermoelectric devices.

[0004] In the prior art, p-type bismuth telluride-based materials are treated by using roughening liquid and ash removal liquid. However, the formula contains a large amount of strong acid, which is dangerous in actual operation. After being treated by this method, the surface roughness of the bismuth telluride wafer is large, the overall resistance and thermal resistance of the device after packaging are large, and the efficiency performance is reduced. In the prior art, electrolytic polishing is also used to treat the surface of bismuth telluride wafers. However, the polishing liquid contains alkaline substances, organic acids, weak electrolytes and other substances. After being treated by this method, the surface roughness of the bismuth telluride wafer is large, the overall resistance and thermal resistance of the device after packaging are large, and the efficiency performance is reduced.

[0005] Chemical mechanical polishing (CMP) is the use of chemical oxidation reaction and mechanical wear to remove materials and achieve high flatness on the wafer surface. Currently, commercial CMP polishing fluids are only used for polishing integrated circuit silicon wafers, silicon carbide wafers, dielectric oxide layers, copper layers, tungsten layers, and some precision optical components. There is currently no polishing fluid for bismuth telluride-based materials. Bismuth telluride materials can only be polished by purchasing polishing fluids for integrated circuits or precision optical components. Usually, polishing fluids with silicon dioxide as abrasive particles are used. Since silicon dioxide has a high hardness (Mohs hardness of about 7) and bismuth telluride materials have a low hardness (Mohs hardness of about 1.8) and low chemical activity, the polishing process mainly uses mechanical removal of silicon dioxide. However, the surface flatness after polishing is not as expected, and scratches have been caused on the surface. At the same time, silicon dioxide polishing fluids are usually alkaline environments, while bismuth telluride is more easily passivated in a weakly acidic environment. In addition, after polishing with silicon dioxide polishing fluid, silicon dioxide is likely to remain on the surface of the bismuth telluride wafer, making it difficult to clean and not conducive to the subsequent nickel plating of the wafer. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a polishing liquid in view of the defects of the prior art.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a polishing liquid, comprising the following components in parts by mass: 5 to 25 parts of nano-scale abrasive particles, 0.1 to 0.5 parts of an oxidant and 74 to 94.899 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles; the polishing liquid also includes a pH regulator, and the pH regulator adjusts the pH value of the polishing liquid to 3.5-6.0.

[0008] Furthermore, it is preferred that the oxidant is nano cerium oxide particles.

[0009] Furthermore, it is preferred that the particle size of the nano-cerium oxide particles is 10-100 nm.

[0010] Furthermore, it is preferred that the particle size of the bismuth telluride particles is 30-300 nm.

[0011] Furthermore, it is preferred that the particle size of the bismuth telluride particles is 50-100 nm.

[0012] Furthermore, it is preferred that the shape structure of the bismuth telluride particles is a particle structure having at least six surfaces.

[0013] Furthermore, it is preferred that the bismuth telluride particles are a mixture of spherical particles and octahedral particles.

[0014] Furthermore, it is preferred that the mass percentage of the spherical particles in the mixture is ≥ 90%.

[0015] Furthermore, the pH value of the polishing liquid is preferably 3.8-4.5.

[0016] Furthermore, it is preferred that the pH adjuster is one or more of ammonia water, acetic acid, p-hydroxybenzoic acid, oxalic acid, citric acid, salicylic acid, succinic acid, tartaric acid and picolinic acid.

[0017] The beneficial effects of the present invention are as follows: the polishing liquid provided by the present invention provides a weak acid environment, accelerates the passivation speed of a bismuth telluride wafer, forms a passivation layer on the surface of the bismuth telluride wafer, and reduces the isotropic etching of the concave area of ​​the uneven surface; and the hardness of the bismuth telluride particles is low, and it is not easy to cause scratches on the surface of the bismuth telluride wafer, and the surface roughness of the wafer can also be reduced; in a weak acid environment, the zeta potential of the nano-scale bismuth telluride particles can be as high as 40mV or more, and the dispersibility is good, and no dispersant needs to be added, and due to the high zeta potential, it is not easy to remain on the bismuth telluride wafer, and after ultrasonic cleaning with deionized water, very few bismuth telluride particles remain on the surface; an oxidant is added to the polishing liquid, and the chemical activity of the oxidant is high, which can increase the passivation speed of the bismuth telluride wafer surface; the polishing liquid of the present invention is targeted at polishing the bismuth telluride material, improves the surface flatness, helps to reduce the overall contact resistance and thermal resistance of the bismuth telluride wafer device, and improves the performance of the ultra-fine thermoelectric material. At the same time, after using the polishing liquid, the amount of foreign impurities such as grinding particles remaining on the surface of the bismuth telluride wafer is reduced, the occurrence of problems such as difficult cleaning is avoided, and the difficulty of the cleaning process is reduced; the polishing liquid of the present invention also avoids the use of a large amount of corrosive oxidants such as hydrochloric acid, nitric acid, hydrogen peroxide, etc., thereby improving operational safety. In actual production and manufacturing, the service life of the machine can be increased to ensure the safety of the operating staff. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0019] Figure 1 is an electron microscope image of the surface of the bismuth telluride wafer of the present invention before polishing;

[0020] Figure 2 is an AFM (atomic force microscope) image of the bismuth telluride wafer surface after polishing in Example 1 of the present invention;

[0021] Figure 3 is a representative line profile of an AFM (atomic force microscope) of the bismuth telluride wafer surface after polishing in Example 1 of the present invention;

[0022] Figure 4 is an AFM (atomic force microscope) image of the bismuth telluride wafer surface after polishing in Example 2 of the present invention;

[0023] Figure 5 is a representative line profile of an AFM (atomic force microscope) of a bismuth telluride wafer surface after polishing in Example 2 of the present invention;

[0024] Figure 6 is an AFM (atomic force microscope) image of the bismuth telluride wafer surface after polishing in Example 3 of the present invention;

[0025] Figure 7is a representative line profile of an AFM (atomic force microscope) of a bismuth telluride wafer surface after polishing in Example 3 of the present invention;

[0026] Figure 8 is an AFM (atomic force microscope) image of the bismuth telluride wafer surface after polishing in the comparative example of the present invention;

[0027] Fig. 9 1 is a representative line profile of an AFM (atomic force microscope) of a bismuth telluride wafer surface after polishing in a comparative example of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The terms used in one or more embodiments of this specification are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of this specification. The singular forms of "one", "said" used in one or more embodiments of this specification and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0030] The present invention provides a polishing liquid, comprising the following components in parts by mass: 5 to 25 parts of nano-scale abrasive particles, 0.1 to 0.5 parts of an oxidant and 74 to 94.899 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles; the polishing liquid also comprises a pH regulator to adjust the pH value of the polishing liquid to 3.5-6.0; the amount of the pH regulator added is determined according to the target pH value, so that the pH value of the polishing liquid is 3.5-6.0.

[0031] The present invention provides a polishing liquid, which provides a weak acid environment, accelerates the passivation speed of a bismuth telluride wafer, forms a passivation layer on the surface of the bismuth telluride wafer, and reduces isotropic etching of concave areas on an uneven surface; the hardness of bismuth telluride particles is low, and it is not easy to cause scratches on the surface of the bismuth telluride wafer, and the surface roughness of the wafer can also be reduced; in a weak acid environment, the zeta potential of nano-scale bismuth telluride particles can be as high as 40mV or more, and the dispersibility is good, and no dispersant needs to be added; and due to the high zeta potential, it is not easy to remain on the bismuth telluride wafer, and after ultrasonic cleaning with deionized water, very few bismuth telluride particles remain on the surface; an oxidant is added to the polishing liquid, and the chemical activity of the oxidant is high, so the passivation speed of the bismuth telluride wafer surface can be increased; the polishing liquid of the present invention is targeted at polishing bismuth telluride materials, reduces surface flatness, helps to reduce the overall contact resistance and thermal resistance of the bismuth telluride wafer device, and improves the performance of ultrafine thermoelectric materials. At the same time, the amount of foreign impurities such as grinding particles remaining on the surface of the bismuth telluride wafer after using the polishing liquid is reduced, the occurrence of problems such as difficulty in cleaning is avoided, and the difficulty of the cleaning process is reduced; the polishing liquid of the present invention also avoids the use of a large amount of corrosive oxidants such as hydrochloric acid, nitric acid, hydrogen peroxide, etc., thereby improving operational safety. In actual production and manufacturing, the service life of the machine can be increased to ensure the safety of the operating staff.

[0032] Furthermore, the preferred oxidant is nano cerium oxide particles. Cerium oxide is a strong oxidant, and the chemical activity of cerium oxide is high, which can increase the speed of passivation of the bismuth telluride wafer surface. And the empty f orbital and d orbital of cerium in cerium oxide can form feedback bonds with the lone electrons in Bi and Te in the bismuth telluride wafer, so that cerium oxide and the surface of bismuth telluride material produce more chemical bonding, and the bonding product will be removed by mechanical force faster, thereby improving the polishing rate. Moreover, in a weakly acidic environment, the zeta potential of nano-scale cerium oxide can be as high as 40mV or more, with good dispersibility, and no dispersant needs to be added, which effectively improves the polishing rate.

[0033] Furthermore, the particle size of the nano cerium oxide particles is preferably 10-100 nm. Under this particle size, the cerium oxide particles are dispersed in the system, the chemical activity of the system is improved, and the polishing rate is further improved.

[0034] Furthermore, the particle size of the bismuth telluride particles is preferably 30-300 nm. At this particle size, the bismuth telluride particles effectively grind and polish the surface of the bismuth telluride wafer, but are not likely to scratch the surface of the bismuth telluride wafer. Furthermore, the particle size of the bismuth telluride particles is preferably 50-100 nm.

[0035] Taking into account that the nano-scale abrasive particles need to have a certain hardness and a certain contact area (grinding and polishing area) with the surface of the bismuth telluride wafer, it is further preferred that the bismuth telluride particles have a particle structure with at least six surfaces. It can be understood that the shape structure of the bismuth telluride particles is a mixture of one or more of hexahedron, heptahedron, octahedron and other particle structures with more than 6 surfaces; when the number of surfaces of the bismuth telluride particles is infinitely close to infinity, the bismuth telluride particles are spheres, or rounded structures similar to spheres.

[0036] Furthermore, the bismuth telluride particles are preferably a mixture of spherical particles and octahedral particles. The ratio of spherical particles to octahedral particles can be any ratio, and preferably the mass percentage of spherical particles in the mixture is ≥90%; the bismuth telluride particles with a spherical structure have a certain roundness, and when grinding the bismuth telluride wafer, it is not easy to cause scratches on the surface of the bismuth telluride wafer; the octahedral particles have a certain hardness, and the bismuth telluride particles with an octahedral structure are in surface contact with the bismuth telluride wafer, have a large contact area, are not easy to cause scratches on the surface of the bismuth telluride wafer, and can effectively grind and polish the surface of the bismuth telluride wafer, accelerating the polishing rate.

[0037] Furthermore, the pH value of the polishing liquid is preferably 3.8-4.5. In an acidic environment with this pH value, the passivation rate of the bismuth telluride wafer can be accelerated, and a passivation layer is easily formed on the surface of the bismuth telluride wafer, reducing the isotropic etching of the concave area of ​​the uneven surface; and the nano-scale bismuth telluride particles have a high zeta potential and good dispersibility in an acidic environment with this pH value, and no dispersant needs to be added, which is conducive to accelerating polishing and polishing surface flatness; in an acidic environment with this pH value, the zeta potential of the nano-scale bismuth telluride particles and the oxidant particles is high, and it is not easy to remain on the bismuth telluride wafer. After ultrasonic cleaning with deionized water, very few bismuth telluride particles and oxidant particles remain on the surface.

[0038] Further, the preferred pH regulator is one or more of ammonia water, acetic acid, p-hydroxybenzoic acid, oxalic acid, citric acid, salicylic acid, succinic acid, tartaric acid and picolinic acid. Here, the addition of the pH regulator is to make the system environment in a weak acid environment, and the input amount of the pH regulator is determined according to the target pH value; when an acidic acid regulator is used in excess (the excess here refers to the deviation from the target pH, which is acidic), an ammonia solution can be used for callback.

[0039] The present invention is further explained below through specific examples.

[0040] Example 1

[0041] A polishing liquid comprises the following components in parts by mass: 5 parts of nano-scale abrasive particles, 0.1 parts of oxidant cerium oxide particles (particle size is 30-50nm) and 94.899 parts of water, wherein the nano-scale abrasive particles are spherical bismuth telluride particles with a particle size of 30-50nm; the polishing liquid also comprises a pH adjuster, wherein acetic acid is selected as the pH adjuster and ammonia water is used for fine adjustment, and the pH adjuster adjusts the pH value of the polishing liquid to 3.5.

[0042] The above components are mixed, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer. The existing polishing method and existing polishing instrument are used during polishing, which will not be repeated here; the surface (electron microscope) of the bismuth telluride wafer before polishing is as follows Figure 1 As shown in the figure, the wire cutting marks are very obvious and the surface roughness is very large. The AFM (atomic force microscope) image after polishing is as follows Figure 2 As shown, Figure 3 It is a representative line profile diagram of the AFM (atomic force microscope) after the surface of the bismuth telluride wafer is polished; the following data are obtained by analysis: the polishing rate is 100nm / min, and the surface roughness is 70.8nm. It can be seen from the figure and the data that the polishing rate of the polishing liquid in this embodiment is fast, and the polishing effect and flatness are good. The surface roughness of the wafer is significantly reduced after polishing, and there are no obvious scratches on the wafer surface.

[0043] Example 2

[0044] A polishing liquid comprises the following components in parts by mass: 25 parts of nano-scale abrasive particles, 0.5 parts of oxidant cerium oxide particles (particle size is 10-30nm) and 74.5 parts of water, wherein the nano-scale abrasive particles are spherical bismuth telluride particles with a particle size of 50-100nm; the polishing liquid also comprises a pH regulator, wherein acetic acid is selected as the pH regulator and ammonia water is used for fine adjustment, and the pH regulator adjusts the pH value of the polishing liquid to 5.

[0045] The above components are mixed, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer; the surface (electron microscope) of the bismuth telluride wafer before polishing is as follows Figure 1 As shown, the AFM (atomic force microscope) image after polishing is as follows Figure 4 As shown, Figure 5 The following is a representative line profile of the AFM (atomic force microscope) of the bismuth telluride wafer surface after polishing; the following data are obtained by analysis: the polishing rate is 615nm / min, and the surface roughness is 30.2nm. It can be seen from the figure and data that the polishing liquid of this embodiment has a fast polishing rate and a good polishing effect. After polishing, the surface roughness of the wafer is low, the flatness is good, and there are no obvious scratches on the wafer surface.

[0046] Example 3

[0047] A polishing liquid comprises the following components in parts by mass: 10 parts of nano-scale abrasive particles, 0.5 parts of oxidant cerium oxide particles (particle size is 50-100nm) and 89.5 parts of water, wherein the nano-scale abrasive particles are spherical bismuth telluride particles with a particle size of 50-100nm; the polishing liquid also comprises a pH regulator, wherein acetic acid is selected as the pH regulator and ammonia water is used for fine adjustment, and the pH regulator adjusts the pH value of the polishing liquid to 4.

[0048] The above components are mixed, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer; the surface (electron microscope) of the bismuth telluride wafer before polishing is as follows Figure 1 As shown, the AFM (atomic force microscope) image after polishing is as follows Figure 6 As shown, Figure 7 The following is a representative line profile of the AFM (atomic force microscope) of the bismuth telluride wafer surface after polishing. The following data are obtained by analysis: the polishing rate is 415nm / min, and the surface roughness is 1.3nm. It can be seen from the data that the polishing liquid of this embodiment has a fast polishing rate and a good polishing effect. After polishing, the surface roughness of the wafer is low, the flatness is good, and there are no obvious scratches on the wafer surface.

[0049] Example 4

[0050] A polishing liquid comprises the following components in parts by mass: 20 parts of nano-scale abrasive particles, 0.3 parts of oxidant cerium oxide particles (particle size is 30-50nm) and 79.3 parts of water, wherein the nano-scale abrasive particles are hexahedral bismuth telluride particles with a particle size of 100-300nm; the polishing liquid also comprises a pH regulator, wherein acetic acid is selected as the pH regulator and ammonia water is used for fine adjustment, and the pH regulator adjusts the pH value of the polishing liquid to 6.

[0051] The above components are mixed, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer; the following data are obtained by analysis: the polishing rate is 390nm / min, and the surface roughness is 5.9nm. It can be seen from the data that the polishing liquid of this embodiment has a fast polishing rate and a good polishing effect. After polishing, the surface roughness of the wafer is low, the flatness is good, and there are no obvious scratches on the wafer surface.

[0052] Example 5

[0053] A polishing liquid comprises the following components in parts by mass: 12 parts of nano-scale abrasive particles, 0.4 parts of oxidant cerium oxide particles (particle size is 30-50nm) and 87.6 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles with a particle size of 50-100nm, which are a mixture of bismuth telluride particles with an octahedral structure and bismuth telluride particles with a spherical structure; the polishing liquid also comprises a pH regulator, wherein acetic acid is selected as the pH regulator and ammonia water is used for fine adjustment, and the pH regulator adjusts the pH value of the polishing liquid to 4.5.

[0054] The above components are mixed, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer; the following data are obtained by analysis: the polishing rate is 527nm / min, and the surface roughness is 8.9nm. It can be seen from the data that the polishing liquid of this embodiment has a fast polishing rate, good polishing effect, good flatness, and the surface roughness of the wafer after polishing is low, the flatness is good, and there are no obvious scratches on the wafer surface.

[0055] Example 6

[0056] A polishing liquid comprises the following components in parts by mass: 18 parts of nano-scale abrasive particles, 0.2 parts of oxidant cerium oxide particles (particle size is 30-50nm) and 81.8 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles with a spherical structure and a particle size of 30-50nm; the polishing liquid also comprises a pH regulator, wherein acetic acid is selected as the pH regulator and ammonia water is used for fine adjustment, and the pH regulator adjusts the pH value of the polishing liquid to 3.8.

[0057] The above components are mixed evenly, and the mixed polishing liquid is used to polish the surface of the bismuth telluride wafer; the polishing rate is 298nm / min, and the surface roughness is 19.9nm. From the data, it can be seen that the polishing rate of the polishing liquid in this embodiment is fast and the polishing effect is good. After polishing, the surface roughness of the wafer is low, the flatness is good, and there are no obvious scratches on the wafer surface.

[0058] Comparative Example

[0059] A commercial polishing liquid is purchased and contains 5% (mass percentage) silicon oxide. The pH value of the polishing liquid is 9.

[0060] The polishing liquid of the comparative example is used to polish the surface of the bismuth telluride wafer; the AFM (atomic force microscope) image of the bismuth telluride wafer surface after polishing is as follows: Figure 8 As shown, Fig. 9 This is a representative line profile diagram of the AFM (atomic force microscope) of the bismuth telluride wafer surface after polishing; the following data were obtained through analysis: the polishing rate is 362nm / min, and the surface roughness is 98.7nm. It can be seen from the figure and data that the surface roughness of the wafer is relatively high after polishing, and there are obvious scratches on the wafer surface.

[0061] It can be seen from the embodiments and comparative examples of the present invention that the polishing liquid of the present invention has a better polishing effect on the bismuth telluride wafer, the surface roughness of the bismuth telluride wafer is significantly reduced, and the polishing speed is faster.

[0062] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A polishing liquid for polishing bismuth telluride wafers ， It is characterized in that The polishing liquid comprises the following components in parts by mass: 5 to 25 parts of nano-scale abrasive particles, 0.1 to 0.5 parts of an oxidant, and 74 to 94.899 parts of water, wherein the nano-scale abrasive particles are bismuth telluride particles; the oxidant is nano-cerium oxide particles; the polishing liquid also comprises a pH regulator, and the pH regulator regulates the pH value of the polishing liquid to 3.5-6.

0.

2. The polishing liquid according to claim 1, characterized in that The particle size of the nano cerium oxide particles is 10-100 nm.

3. The polishing liquid according to claim 1, characterized in that The particle size of the bismuth telluride particles is 30-300 nm.

4. The polishing liquid according to claim 3, characterized in that The particle size of the bismuth telluride particles is 50-100 nm.

5. The polishing liquid according to claim 1, characterized in that The bismuth telluride particles have a particle structure having at least six surfaces.

6. The polishing liquid according to claim 5, characterized in that The bismuth telluride particles are a mixture of spherical particles and octahedral particles.

7. The polishing liquid according to claim 6, characterized in that The mass percentage of the spherical particles in the mixture is ≥90%.

8. The polishing liquid according to claim 1, characterized in that: The pH value of the polishing liquid is 3.8-4.

5.

9. The polishing liquid according to claim 1, characterized in that The pH regulator is one or more of ammonia water, acetic acid, p-hydroxybenzoic acid, oxalic acid, citric acid, salicylic acid, succinic acid, tartaric acid and picolinic acid.

Images