CN115106929A - Chemical mechanical polishing device for silicon carbide wafer - Google Patents

Abstract

The invention relates to the technical field of silicon carbide polishing, in particular to a chemical mechanical polishing device for a silicon carbide wafer, which comprises a polishing pad body, wherein an abrasive particle layer is fixed on the polishing pad body, and abrasive particles in the abrasive particle layer are uniformly distributed; the polishing solution comprises a Fenton reagent and is used for oxidizing the surface of the silicon carbide wafer; the driving device drives the silicon carbide wafer to polish on the abrasive particle layer; the electrochemical device comprises an anode and a cathode, and an electro-Fenton reaction system is formed by the anode and the cathode and a Fenton reagent in the polishing solution; polishing solution supply device. According to the invention, the polishing solution adopts a Fenton reagent and an aqueous solution, the Fenton reagent provides ferrous ions and hydrogen peroxide, the ferrous ions and the hydrogen peroxide participate in reaction and are reduced, the Fenton reagent is recycled through an electrochemical device, and then, an abrasive particle layer is deposited on the polishing pad body, and abrasive particles cannot enter the polishing solution.

Description

A chemical mechanical polishing device for silicon carbide wafers

technical field

The invention relates to the technical field of silicon carbide polishing, in particular to a chemical mechanical polishing device for silicon carbide wafers.

Background technique

The silicon carbide polishing liquid used in the prior art has an excessive burden on the environment. For example, in order to improve the dispersion stability of abrasive particles in the polishing liquid, a dispersant needs to be added to the polishing liquid. During the entire polishing process, the polishing liquid needs to be continuously replenished. However, the continuously generated polishing liquid waste liquid will eventually be discharged into the natural environment, and the production and discharge of these dispersants will inevitably cause pollution to the environment. The hardness of silicon carbide is extremely high, which requires a long polishing time. The wear of the polishing pad is a problem that cannot be ignored. The wear caused by the friction between the polishing pad and the abrasive particles makes the polishing pad need to be replaced regularly, which undoubtedly leads to an increase in processing costs.

Chinese patent CN113334242A proposes to use the Fenton method for chemical mechanical polishing of diamond wafers to improve the oxidation rate of the diamond surface. _The Fenton method is one of the advanced oxidation techniques. It uses the reaction of Fe ²⁺ and H2O2 to generate strong oxidizing hydroxyl radicals, which greatly improves the oxidation rate of the wafer surface, although _H2O2 is more environmentally friendly. , but its preparation, transportation and storage costs are high, and the traditional Fenton method needs to continuously replenish H ₂ O ₂ .

SUMMARY OF THE INVENTION

In view of the above problems, the present invention proposes a chemical mechanical polishing device for silicon carbide wafers.

The technical scheme adopted by the present invention is as follows: a chemical mechanical polishing device for silicon carbide wafers, comprising:

a polishing liquid, which includes Fenton's reagent for oxidizing the surface of the silicon carbide wafer;

A polishing pad immersed in a polishing liquid, the polishing pad has an abrasive grain layer, and the abrasive grains in the abrasive grain layer are evenly distributed;

a driving device, which drives the silicon carbide wafer and uses the abrasive grain layer for polishing;

An electrochemical device, the electrochemical device comprises an anode and a cathode, and an electro-Fenton reaction system is formed by the anode, the cathode and the Fenton reagent in the polishing solution to provide an oxidant for the polishing solution;

a polishing liquid replenishing device, the polishing liquid replenishing device adds acidic liquid to the polishing liquid;

The polishing liquid is also provided with an aeration device, the aeration device includes a blower and an aeration pipe, and the blower provides oxygen into the polishing liquid through the aeration pipe.

Optionally, the abrasive particles in the abrasive particle layer are diamond, boron carbide, silicon carbide, aluminum oxide, chromium oxide, zirconium oxide, silicon oxide, cerium oxide, iron oxide, yttrium oxide, copper oxide, and molybdenum oxide. One or more, the polishing liquid does not contain abrasive particles.

Optionally, the polishing pad includes a polishing pad body and a multi-wafer attached to the surface of the polishing pad main body, the multi-wafer includes a substrate and a polycrystalline film on the surface of the substrate, the polycrystalline film has abrasive grains.

Optionally, the polycrystalline film is formed by depositing abrasive grains on the surface of the substrate using an electrochemical co-deposition technique, a chemical vapor deposition technique or a glue-coating thermosetting technique.

Optionally, the grain size of the abrasive grains of the polycrystalline film ranges from 0 to 400 nm, and the surface roughness of the polycrystalline film ranges from 0 to 200 nm.

Optionally, the Fenton reagent includes ferrous ions and H ₂ O ₂ , the concentration of ferrous ions ranges from 100 to 1200 mg/L, and the molar ratio of H ₂ O ₂ : Fe ² + ranges from 4:1 to 8 :1.

Optionally, the driving device includes a driving source, a telescopic mechanism and a silicon carbide wafer, the driving source is connected to the telescopic mechanism, the telescopic mechanism is connected to the silicon carbide wafer, and the driving source is used for the rotation of the silicon carbide wafer. Power is provided, and the telescopic mechanism provides power for the reciprocating motion of the silicon carbide wafer.

Optionally, the polishing pad includes a polishing pad body and a colloidal abrasive grain layer on the surface of the polishing pad body, the polishing pad body is a felt pad or a polymer felt pad, the surface of which has fibers, and the abrasive grain layer is semi-solid The colloid, the semi-solid colloid includes colloid and abrasive particles, and the abrasive particles are uniformly distributed in the colloid.

Optionally, the polishing liquid replenishing device further includes a peristaltic pump, a conduit and an acid source, the acid source provides the conduit with acidic liquid, and the peristaltic pump controls the cross-sectional area of the conduit, thereby controlling the amount of acidic liquid in the conduit. flow speed.

Optionally, the acidic solution is one or more of nitric acid, hydrochloric acid, phosphoric acid, metaphosphoric acid, oxalic acid, citric acid, malic acid, and tartaric acid.

The beneficial effects of the invention are as follows: the polishing liquid adopts Fenton's reagent, and the Fenton reagent provides ferrous ions and hydrogen peroxide. After the participation of ferrous ions and hydrogen peroxide in the reaction is reduced, the cycle of the Fenton's reagent is realized through an electrochemical device. It is not necessary to continuously replenish hydrogen peroxide; secondly, the abrasive grain layer is deposited on the body of the polishing pad, and the abrasive grains will not enter the polishing liquid. The polishing liquid can be recycled, which is truly green and environmentally friendly. At the same time, the polishing liquid replenishing device adds acidic liquid to the Fenton reagent solution at a certain speed, and adds oxygen to the polishing liquid through a blower to prevent iron hydroxide flocculation in the polishing liquid. It can also speed up the transformation efficiency of substances in the polishing liquid.

Description of drawings:

1 is a schematic structural diagram of a chemical mechanical polishing device for silicon carbide wafers in an embodiment of the present invention;

Fig. 2 is the structural representation that the ventilation groove is arranged on the aeration pipe in the embodiment of the present invention;

FIG. 3 is a schematic structural diagram of disposing an abrasive grain layer on a polishing pad body in an embodiment of the present invention.

The reference numbers in the figure are:

1. Power source; 2. Metal disc; 3. Polishing pad body; 4. Polishing liquid; 5. Frame; 6. Silicon carbide wafer; 7. Counterweight; 8. Peristaltic pump; 9. Catheter; 10. Acidic liquid; 11, cathode; 12, anode; 13, power supply; 14, blower; 15, aeration pipe; 16, abrasive layer; 17, polishing tank body; 18, driving source; 19, sealing ring.

Detailed ways:

The present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1 , the present invention discloses a chemical mechanical polishing device for silicon carbide wafers, which is used to solve the harm to the environment caused by the pollutants produced by polishing, including:

Polishing liquid 4, which includes Fenton's reagent for surface oxidation of silicon carbide wafer 6;

The polishing pad body 3 immersed in the polishing liquid 4, the abrasive grain layer 16 is fixed on the polishing pad body 3, and the abrasive grains in the abrasive grain layer 16 are evenly distributed;

a driving device, which drives the silicon carbide wafer 6 and uses the abrasive grain layer 16 for polishing;

An electrochemical device, the electrochemical device comprises an anode and a cathode, and an electro-Fenton reaction system is formed by the anode, the cathode and the Fenton reagent in the polishing solution to provide an oxidant for the polishing solution;

A polishing liquid replenishing device, the polishing liquid replenishing device adds the acidic liquid 10 to the polishing liquid 4, and the adding speed of the acidic liquid 10 is controllable;

The polishing liquid is also provided with an aeration device, the aeration device includes a blower and an aeration pipe, and the blower provides oxygen into the polishing liquid through the aeration pipe.

In the embodiment of the present invention, the chemical mechanical polishing device for silicon carbide wafers includes a frame 5, a polishing tank body 17, a polishing liquid 4, a polishing pad body 3, a driving device, an electrochemical device, a polishing liquid replenishing device, and an aeration device, The polishing tank body 17 is installed on the frame 5, the polishing liquid 4 is located in the polishing tank body 17, and the driving device, the electrochemical device, the polishing liquid replenishing device and the aeration device are all installed on the frame.

Fenton's reagent refers to a strong oxidizing system composed of hydrogen peroxide and ferrous ions. The chemical reaction in polishing liquid 4 is Fe ²⁺ +H ₂ O ₂ +H ⁺ →Fe ³⁺ +H ₂ O+ OH·, the hydroxyl radical in the formula has strong oxidizing property, and is used for oxidizing the surface of the silicon carbide wafer 6 to form silicon oxide which is easy to grind.

When configuring Fenton's reagent, the content of ferrous ion is in the range of 100-1200mg/L, the source of ferrous ion is ferrous sulfate and ferrous chloride, and the molar ratio of H ₂ O ₂ : Fe ²⁺ is in the range of 4:1— 8:1.

In this embodiment, the ferrous ion content is 800 mg/L, and the molar ratio of H ₂ O ₂ : Fe ²⁺ is 5:1.

When the electrochemical device works, a reaction occurs between the anode 12 and the cathode 11, wherein the reaction formula of the anode is Fe ²⁺ +H ₂ O ₂ +H ⁺ →Fe ³⁺ +H ₂ O+OH·, and the reaction formula of the cathode is O ₂ +2H ⁺ +2e ^- →H ₂ O ₂ , Fe ³⁺ +e ^- →Fe ²⁺ , the electro-Fenton reaction system regenerates H ₂ O ₂ , and changes Fe ³⁺ into Fe ²⁺ , realizing Fenton Recycling of reagents.

The acidic liquid is added to the polishing liquid 4 through the polishing liquid replenishing device to increase the H ⁺ in the polishing liquid, which can increase the production speed of H ₂ O ₂ and prevent the production of flocs such as ferric hydroxide. At the same time, adding oxygen into the polishing liquid 4 can increase the production speed of H ₂ O ₂ and realize the cyclic use of Fenton's reagent.

In another embodiment, the polishing liquid further includes Na ₂ FeO ₄ , and Na ₂ FeO ₄ under acidic conditions has strong oxidizing properties, which can oxidize C in silicon carbide, and Na ₂ FeO ₄ is reduced to Fe ³⁺ , Fe ²⁺ , which accelerates the polishing efficiency of silicon carbide. And the generated Fe ²⁺ becomes a catalyst for the Fenton reaction, generates OH radicals with strong oxidizing properties, rapidly oxidizes C of silicon carbide, and further accelerates the polishing efficiency of silicon carbide. At the same time, the electro-Fenton reaction system is used to convert the generated Fe ³⁺ into Fe ²⁺ , so as to realize the recycling of the Fenton reagent. Since the oxidizing ability of the polishing solution added with Na ₂ FeO ₄ is greater than that of Fenton's reagent, it is beneficial to polish the uneven silicon carbide wafer in the early stage, and the subsequent use of Fenton's reagent to continuously polish the silicon carbide wafer is beneficial to improve the polishing uniformity and polishing quality.

The polishing pad includes a polishing pad body 3 and an abrasive particle layer 16 located on the surface of the polishing pad body 3 . In this embodiment, the abrasive grain layer 16 is a polycrystalline wafer attached to the surface of the polishing pad body 3 . The polycrystalline wafer includes a base and a polycrystalline film on the surface of the base, and the polycrystalline film has abrasive grains.

The substrate is one of a metal substrate, a silicon dioxide substrate, a sapphire substrate, a diamond substrate, and a polyester fiber board, and the grinding is made by electrochemical co-deposition technology, chemical vapor deposition technology or glue-coating thermosetting technology. The particles are deposited on the surface of the substrate, forming the polycrystalline film.

The abrasive particles are one or more of diamond, boron carbide, silicon carbide, aluminum oxide, chromium oxide, zirconium oxide, silicon oxide, cerium oxide, iron oxide, yttrium oxide, copper oxide, and molybdenum oxide. The grain size range of the crystal film is 0-400 nm, the surface roughness of the polycrystalline film is 0-200 nm, and the silicon carbide wafer is ground by using the polycrystalline film.

Since the abrasive grain layer of the polishing pad is fixed on the polishing pad, in this embodiment, the polishing liquid 4 does not contain abrasive grains, and no waste liquid is generated, and the polishing liquid can be recycled.

In another embodiment, the formation of the abrasive grain layer 16 is to deposit the abrasive grains on the polishing pad body 3 using a glue-coating thermosetting technology, and use an intermediate medium polyester fiber board to directly adhere the polyester fiber board to the polishing pad body 3, Abrasive particle layer 16 is formed by coating alumina particles on a polyester fiberboard.

In another embodiment, the polishing pad body is a felt pad or a polymer felt pad, the surface of which has fibers, and the abrasive particle layer is a semi-solid colloid, and the semi-solid colloid includes colloid and abrasive particles. The abrasive particles are uniformly distributed in the colloid.

Specifically, pour the alginate sodium salt solution into the container, add abrasive particles to it, and stir the abrasive particles and the alginate sodium salt solution to make the abrasive particles evenly distributed in the alginate sodium salt solution, and then add the abrasive particles to the alginate sodium salt solution. The sodium alginate aqueous solution of the abrasive grains is dropped into the calcium chloride aqueous solution to form sodium alginate and calcium chloride solutions, and the liquids in the sodium alginate and calcium chloride solutions have weak fluidity and are in a colloidal state;

The prepared colloid is coated on the surface of the polishing pad body, and the abrasive particles in the colloid are evenly distributed on the surface of the polishing pad body;

The polishing pad body and the colloid are heated together, and the polishing pad body coated with the colloid is dried. During the drying process, a heavy object is pressed on the surface of the polishing pad body to make the colloid on the surface of the polishing pad body evenly distributed. The surface of the pad body forms colloidal abrasive particles.

The polishing pad body is a felt pad or a polymer felt pad, and its model is Suba ^TM , STT711 ^TM or Pellon ^TM . The surface of the felt pad or polymer felt pad is a microstructure of fibers, and the semi-solid jelly will not penetrate into the polishing pad. The inner layer of the pad body, and the compression degree and hardness of the polishing pad body are moderate. After the polishing pad is made, the silicon carbide wafer is ground by the abrasive particles on it, so as to reduce the damage to the polishing pad body. And because the body of the polishing pad is a felt pad with a tiny structure of fibers, when the colloidal solution of sodium alginate and calcium chloride meets the fibers, the adsorption is tighter, and the adhesion between the surface of the polishing pad and the semi-solid colloid is increased. During the process, the semi-solid colloid is not easy to fall off, so that the polished surface can be semi-fixed without affecting the recycling of the polishing liquid.

In this embodiment, the drive device includes a drive source 18 and a telescopic mechanism. The drive source 18 includes a first motor. The telescopic mechanism includes an electric telescopic rod, a counterweight 7 and a silicon carbide wafer 6. The output end of the first motor It is connected with the electric telescopic rod, the electric telescopic rod is connected with the counterweight 7, the counterweight 7 is connected with the silicon carbide wafer 6, and the first motor provides power for the rotation of the silicon carbide wafer 6, and the electric telescopic The rods power the reciprocating motion of the silicon carbide wafer 6 .

In this embodiment, under the gravity of the counterweight 7, the silicon carbide wafer 6 is kept stable when the silicon carbide wafer 6 is rotated.

In this embodiment, the polishing pad body 3 is connected with a power source 1, and the power source 1 includes a second motor, which provides power for the rotation of the polishing pad body 3, and the lower end of the polishing pad body 3 is fixedly connected There is a metal disc 2, the metal disc 2 is connected with the rotating shaft, the rotating shaft is connected with the output end of the second motor, and a sealing ring 19 is arranged between the rotating shaft and the polishing groove body 17. The bottom is sealed to prevent the leakage of polishing liquid 4.

The power source 1 and the drive source 18 are located on both sides of the polishing pad body 3. Through the parameter design of the first motor, the second motor and the electric telescopic rod, when the surface of the silicon carbide wafer 6 is in contact with the abrasive grain layer 16, The abrasive grain layer 16 polishes the surface of the silicon carbide wafer 6, and the rotational speed of the polishing pad body 3 is 40-100 rpm, the rotational speed of the silicon carbide wafer 6 is 30-100 rpm, and the polishing pressure is 70-130 kgf.

In this embodiment, the electrochemical device further includes a power source 13, the power source 13 is a DC power source, the positive and negative electrodes of the DC power source are respectively connected to the anode 12 and the cathode 11, and the material of the cathode 11 is selected from mercury electrodes, graphite electrodes, One or more of carbon felt, activated carbon fiber, foamed glass carbon, and carbon nanotubes, and the material of the anode 12 is selected from one or more of mercury electrodes, graphite electrodes, titanium electrodes, platinum electrodes, and iron electrodes .

In this embodiment, the cathode 11 and the anode 12 are both made of graphite, the electrode area is 100 cm ² , the distance between the cathode 11 and the anode 12 is 1-10 cm, and the current density of the DC power supply is 2-40 mA/cm ² .

In this embodiment, the distance between the cathode 11 and the anode 12 is 3 cm, and the current density of the DC power supply is 20 mA/cm 2 .

In this embodiment, the polishing liquid replenishing device further includes a peristaltic pump 8 , a conduit 9 and an acid source. The acid source provides the polishing liquid with an acidic liquid 10 through the conduit 9 , and the peristaltic pump 8 controls the transverse direction of the conduit 9 . The cross-sectional area is controlled, so as to control the flow rate of the acidic liquid 10 in the conduit 9, thereby controlling the addition amount of the acidic liquid in the polishing liquid.

The acidic liquid is one or more of nitric acid, hydrochloric acid, phosphoric acid, metaphosphoric acid, oxalic acid, citric acid, malic acid and tartaric acid.

In this embodiment, the acidic liquid is an oxalic acid aqueous solution, the pH range of the oxalic acid aqueous solution is 2-4, and the flow rate of the oxalic acid aqueous solution is 0.1-1 ml/min under the control of the peristaltic pump 8 .

In this embodiment, the aeration device includes a blower 14 and an aeration pipe 15, the blower 14 is installed on the side wall of the frame 5, the output end of the blower 14 is connected to the aeration pipe, and the blower 14 passes through the aeration pipe Oxygen is supplied into the polishing liquid 4 , and the oxygen reacts with the polishing liquid 4 to increase the production speed of H ₂ O ₂ , which is used for rapidly oxidizing the surface of the silicon carbide wafer 6 .

The air flow of the blower 14 is 0.1-10 L/min.

In this embodiment, the aeration pipe 15 is arranged under the metal plate 2 , the oxygen generated by the aeration pipe 15 is transported upward from the bottom of the polishing tank 17 , the oxygen reacts with the polishing liquid 4 , and the aeration pipe 15 reacts with the acid liquid 10 . In the same vertical plane, oxygen can quickly come into contact with the acidic liquid 10 .

And as shown in FIG. 2 , the aeration pipe 15 is provided with a plurality of aeration ports to increase the contact area between the oxygen and the polishing liquid 4 and increase the reaction rate of the oxygen and the polishing liquid 4 .

As shown in FIG. 3 , in this embodiment, the polishing pad body 3 and the abrasive grain layer 16 are fixed together. When using the abrasive grain layer 16 to grind the silicon carbide wafer 6 , the abrasive grains in the abrasive grain layer 16 will not be removed from polishing The pad body 3 will not cause pollution to the polishing liquid.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of patent protection of the present invention. Any equivalent structural transformation made by using the contents of the description and accompanying drawings of the present invention can be directly or indirectly used in other related technical fields. All are similarly included in the protection scope of the present invention.

Claims (10)

1. a silicon carbide wafer chemical mechanical polishing device, is characterized in that, comprises: a polishing liquid, which includes Fenton's reagent for surface oxidation of the silicon carbide wafer; A polishing pad immersed in a polishing liquid, the polishing pad has an abrasive grain layer, and the abrasive grains in the abrasive grain layer are evenly distributed; a driving device, which drives the silicon carbide wafer and uses the abrasive grain layer for polishing; An electrochemical device, the electrochemical device comprises an anode and a cathode, and an electro-Fenton reaction system is formed by the anode, the cathode and the Fenton reagent in the polishing solution to provide an oxidant for the polishing solution; a polishing liquid replenishing device, the polishing liquid replenishing device adds acidic liquid to the polishing liquid; The polishing liquid is also provided with an aeration device, the aeration device includes a blower and an aeration pipe, and the blower provides oxygen into the polishing liquid through the aeration pipe. 2 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the abrasive grains in the abrasive grain layer are diamond, boron carbide, silicon carbide, aluminum oxide, chromium oxide, zirconia, One or more of silicon oxide, cerium oxide, iron oxide, yttrium oxide, copper oxide, and molybdenum oxide, and the polishing liquid does not contain abrasive particles. 3 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the polishing pad comprises a polishing pad body and a multi-wafer attached to the surface of the polishing pad body, and the multi-wafer comprises a base and a A polycrystalline film on the surface of a substrate, the polycrystalline film having abrasive grains. 4 . A chemical mechanical polishing device for silicon carbide wafers according to claim 3 , wherein the abrasive particles are deposited on the surface of the substrate by using electrochemical co-deposition technology, chemical vapor deposition technology or glue-coating thermosetting technology to form the the polycrystalline film. 5 . The chemical mechanical polishing device for silicon carbide wafers according to claim 3 , wherein the abrasive grain size of the polycrystalline film ranges from 0 to 400 nm, and the surface roughness of the polycrystalline film is 0 nm. 6 . ~200nm. 6 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the Fenton reagent comprises ferrous ions and H ₂ O ₂ , and the concentration of ferrous ions ranges from 100 to 1200 mg/L. 7 . , the molar ratio of H ₂ O ₂ : Fe ²⁺ ranges from 4:1 to 8:1. 7 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the driving device comprises a driving source, a telescopic mechanism and a silicon carbide wafer, the driving source is connected with the telescopic mechanism, and the The telescopic mechanism is connected with the silicon carbide wafer, the driving source provides power for the rotation of the silicon carbide wafer, and the telescopic mechanism provides power for the reciprocating motion of the silicon carbide wafer. 8 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the polishing pad comprises a polishing pad body and a colloidal abrasive particle layer located on the surface of the polishing pad body, and the polishing pad body is 8 . Felt pads or polymer felt pads have fibers on the surface, and the abrasive grain layer is a semi-solid colloid, the semi-solid colloid includes colloid and abrasive grains, and the abrasive grains are uniformly distributed in the colloid. 9 . The chemical mechanical polishing device for silicon carbide wafers according to claim 1 , wherein the polishing liquid replenishing device further comprises a peristaltic pump, a conduit and an acid source, and the acid source provides an acidic liquid for the conduit. 10 . , the peristaltic pump controls the cross-sectional area of the conduit, thereby controlling the flow rate of the acidic liquid in the conduit. 10. A chemical mechanical polishing device for silicon carbide wafers according to claim 9, wherein the acidic solution is one of nitric acid, hydrochloric acid, phosphoric acid, metaphosphoric acid, oxalic acid, citric acid, malic acid, and tartaric acid or more.

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