Diamond CMP polishing device assisted by photocatalysis and electrochemistry

Abstract

The invention belongs to the technical field of semiconductor manufacturing, and particularly relates to a photocatalysis and electrochemistry assisted diamond CMP (Chemical Mechanical Polishing) device, a polishing head is rotatably arranged above a polishing table, a step groove of the polishing table is filled with a polishing solution, and a negative electrode and a polishing pad are arranged on the upper step surface of the step groove; an ultraviolet light source is arranged on the lower step face of the step groove, a plurality of to-be-polished diamond wafers at the bottom of the polishing head can make friction contact with the polishing pad, and a part of the circular track where the diamond wafers are located is located over the ultraviolet light source. The core of the device is that the negative electrode, the boron-doped diamond positive electrode and the polishing solution form an electrolysis loop, and efficient electrochemical auxiliary polishing is achieved. And the ultraviolet light source adopts an immersed design and directly irradiates the polishing solution and the wafer, so that the ultraviolet light acting effect is remarkably improved. The device has the advantages of high hydroxyl radical generation efficiency, continuous and stable chemical reaction, high reaction controllability and the like, and effectively solves the technical problems of low diamond polishing efficiency and poor consistency.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor manufacturing, and specifically relates to a photocatalytic and electrochemically assisted diamond CMP Polishing device. Background Art

[0002] Diamond has extremely high thermal conductivity, excellent dielectric breakdown strength, outstanding electron mobility, ultra-wide band gap and extremely low thermal expansion coefficient, which makes it show great application potential in the semiconductor field and is an ideal material for the manufacture of electronic and optical equipment. Diamond wafer materials need to have extremely high surface integrity, including low surface roughness, no scratches, microcracks, dislocations and residual stress and other surface or subsurface damage to ensure its excellent operating performance. However, the interatomic carbon-carbon bond energy of diamond is extremely high, and it hardly reacts chemically with any acid or alkali reagent at room temperature. In addition, its extremely high hardness makes the surface treatment of diamond wafers difficult.

[0003] Chemical Mechanical Polishing ( CMP ) is a mature process for obtaining ultra-smooth and ultra-low damage surfaces on semiconductor materials. It mainly uses the strong oxidizing effect of hydroxyl radicals. These free radicals are usually generated by chemical reactions, such as Fenton reaction, Fenton-like reaction or ultraviolet photocatalysis, or directly generated by chemical reagents, such as hydrogen peroxide or oxidant decomposition. CN113334242B The Chinese patent uses hydrogen peroxide to decompose hydroxyl radicals, and uses ultraviolet light to promote the oxidation of the diamond wafer surface. However, the hydroxyl radicals generated by this method have low generation efficiency, poor reaction sustainability, and difficulty in controlling the rate, resulting in chemical instability. In addition, the ultraviolet light source of the device is arranged outside the polishing disk. The ultraviolet light needs to pass through the rotating quartz glass polishing disk, and then through the polishing liquid before acting on the diamond surface. The propagation path of ultraviolet light is long, and it passes through more media, so the effect will be weakened. For diamond wafers with high hardness, brittleness, strong chemical inertness, and difficult oxidation, the existing polishing process has a technical bottleneck of low efficiency. Summary of the invention

[0004] The present invention provides a photocatalytic and electrochemically assisted diamond CMPThe polishing device is provided with a step groove on the top of the polishing table, and the negative electrode and the polishing pad are provided on the upper step surface of the step groove. The positive electrode is made of boron-doped diamond material, and is connected to an external power supply to form an electrolysis circuit to electrolyze the polishing liquid. Compared with other common positive electrodes, the boron-doped diamond electrode has a unique sp³ hybrid structure and hole conductivity characteristics introduced by boron doping, so that it can still maintain stable electrochemical activity in a strong oxidizing environment, so that it can achieve efficient and stable generation of hydroxyl radicals by itself during the electrocatalytic process without relying on other chemical additions. In addition, by adjusting the applied potential and current density, the generation rate of hydroxyl radicals can be precisely controlled. In addition, by setting the ultraviolet light source on the lower step surface of the step groove, the ultraviolet light source is immersed in the polishing liquid, and the polishing liquid and diamond wafer are directly irradiated, which greatly reduces the loss of ultraviolet light and improves the effect of ultraviolet light. Moreover, the device achieves precise control of process parameters through optimized design, ensuring that each diamond wafer obtains equal process conditions during processing. By adjusting the speed and pressure of the polishing head, the UV irradiation time of all wafers can be kept strictly consistent. Based on the design of the electrolytic circuit, the uniformity of the electrochemical reaction time of each wafer is achieved. This multi-parameter coordinated control mechanism significantly improves the quality consistency of diamond wafer surface treatment and effectively solves the problem of processing consistency in traditional polishing processes.

[0005] The device comprises a polishing table and a polishing head, wherein the polishing head is rotatably arranged above the polishing table; a step groove is arranged on the top of the polishing table, wherein polishing liquid is contained in the step groove, a negative electrode and a polishing pad are arranged on the upper step surface of the step groove in sequence from bottom to top, and an ultraviolet light source is arranged on the lower step surface of the step groove; a boron-doped diamond positive electrode and a plurality of diamond wafers to be polished are arranged at the bottom of the polishing head, wherein the plurality of diamond wafers to be polished are distributed on a circular track and can be in frictional contact with the polishing pad, wherein the circular track, the boron-doped diamond positive electrode and the polishing head are coaxially arranged, and a part of the circular track is located directly above the ultraviolet light source; the negative electrode and the boron-doped diamond positive electrode are both connected to an external power source through a conductive slip ring, and form an electrolysis circuit with the polishing liquid; and the ultraviolet light source is also connected to an external power source through a conductive slip ring to form a power supply circuit.

[0006] In a specific embodiment, the polishing table is cylindrical, the step groove is an annular step groove with a low center and high surroundings, the negative electrode is an annular negative electrode matching the upper step surface of the annular step groove, the polishing pad is an annular polishing pad matching the upper step surface of the annular step groove, and the polishing table is rotatable.

[0007] In a specific embodiment, it also includes a base plate and a support column, wherein a first motor is disposed on the base plate and is transmission-connected to the polishing table, a second motor is disposed on the support column and is transmission-connected to the polishing head, and the support column is disposed on the base plate.

[0008] In a specific embodiment, the polishing liquid contains a conductive medium and a composite photocatalyst, wherein the conductive medium is hydrochloric acid or sodium hydroxide, and the composite photocatalyst is PS / CeO 2 -TiO 2 , ZIF-8 , CNTs-TiO 2 , PMMA / SiO 2 - B , PS / CeO 2 A combination of one or more materials.

[0009] In a specific embodiment, the negative electrode is fixed to the upper step surface of the step groove by screws, and the negative electrode is a platinum electrode.

[0010] In a specific embodiment, the polishing pad is bonded to the negative electrode, and the polishing pad is provided with a plurality of through holes.

[0011] In a specific embodiment, the plurality of through holes are distributed in a honeycomb array.

[0012] In a specific embodiment, a transparent lampshade is further provided on the lower step surface of the step groove, and the ultraviolet light source is provided in the transparent lampshade.

[0013] In a specific embodiment, the boron-doped diamond positive electrode is bonded to the bottom of the polishing head by conductive adhesive.

[0014] In a specific embodiment, the diamond wafer to be polished is bonded to the bottom of the polishing head by paraffin wax.

[0015] The present invention has at least the following beneficial effects: 1. Boron-doped diamond is used as the anode material to electrolyze the polishing liquid. Compared with other common positive electrodes, the use of boron-doped diamond positive electrode can achieve continuous and stable generation of a large number of hydroxyl free radicals, making the hydroxyl free radical generation efficiency high, the reaction sustainability good, and the reaction rate easy to control.

[0016] 2. By setting a step groove on the top of the polishing table, the ultraviolet light source can be integrated on the polishing table and immersed in the polishing liquid to directly irradiate the polishing liquid and diamond wafer, which greatly reduces the loss of ultraviolet light and improves the effect of ultraviolet light.

[0017] 3. By distributing a number of diamond wafers to be polished on a circular track coaxial with the polishing head, and a part of the circular track is located directly above the ultraviolet light source, the diamond wafers to be polished are alternately subjected to mechanical polishing and ultraviolet light catalysis as the polishing head rotates, thereby making each diamond wafer receive the same ultraviolet light irradiation time, mechanical polishing time, and electrolytic reaction time, which greatly improves the consistency of the surface treatment effect of the diamond wafer. Moreover, the ultraviolet light can irradiate the entire diamond wafer, improving the effect of the ultraviolet light.

[0018] 4. By combining electric field, light field and chemical mechanical polishing and their synergistic effects, the efficient, stable and controllable generation of hydroxyl radicals is achieved, thereby improving the surface treatment efficiency and quality of diamond wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a partial cross-sectional schematic diagram of an embodiment of the present invention.

[0020] Figure 2 It is an overall structural diagram of an embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram of the local structure of an embodiment of the present invention.

[0022] Figure 4 Schematic diagram of the structure of the annular polishing pad in an embodiment of the present invention.

[0023] Figure 5 This is an electron microscope image of the surface of a diamond wafer before treatment in an embodiment of the present invention.

[0024] Figure 6 This is an electron microscope image of the surface of a diamond wafer after being processed in an embodiment of the present invention.

[0025] Reference numerals: base plate 1, support column 2, L A support plate 3, a first motor 4, a polishing table 5, a right-angle support plate 6, a second motor 7, a polishing head 8, an annular negative electrode 9, an annular polishing pad 10, a through hole 11, an ultraviolet light source 13, a boron-doped diamond positive electrode 14, a diamond wafer 15, a conductive slip ring 16, a polishing liquid 18, and a power supply 19. DETAILED DESCRIPTION

[0026] See also Figure 1-Figure 4 The present invention provides a photocatalytic and electrochemically assisted diamond CMPThe polishing device comprises a base plate 1 and a support column 2. An L-shaped support plate 3 is arranged on the base plate 1. L A first motor 4 is arranged on the support plate 3, and the output shaft of the first motor 4 is connected to a step shaft through an elastic coupling, and the step shaft is connected to the step shaft through a tapered roller bearing. LThe support plate 3 is rotatably connected, and a polishing table 5 is installed on the step shaft, so that the polishing table 5 can be driven to rotate by the first motor 4. The support column 2 is arranged on the base plate 1, and a right-angle support plate 6 is detachably connected to the support column 2 by bolts. A second motor 7 is arranged on the right-angle support plate 6. The output shaft of the second motor 7 is rotatably connected to the right-angle support plate 6 through a tapered roller bearing, and is connected to a polishing head 8 through an elastic coupling. The polishing head 8 is arranged above the polishing table 5, so that the polishing head 8 can be driven to rotate by the second motor 7, thereby realizing the rotation of the polishing head 8 relative to the polishing table 5. The polishing table 5 is cylindrical, and the top of the polishing table 5 is provided with an annular step groove with a low center and high surroundings, and the polishing liquid 18 is sprayed into the annular step groove through an external polishing liquid nozzle. The upper step surface of the annular step groove is sequentially provided with an annular negative electrode 9 and an annular polishing pad 10 from bottom to top. The annular negative electrode 9 is fixed to the upper step surface of the annular step groove by screws to ensure its stability. The annular negative electrode 9 adopts a platinum electrode. The annular polishing pad 10 is bonded to the annular negative electrode 9 for easy disassembly and assembly. The annular polishing pad 10 is provided with a plurality of through holes 11, which are distributed in a honeycomb array. A transparent lampshade (not shown in the figure) is provided on the lower step surface of the annular step groove, and an ultraviolet light source 13 is provided in the transparent lampshade, which is made of quartz glass. A boron-doped diamond positive electrode 14 and a plurality of diamond wafers 15 to be polished are provided at the bottom of the polishing head 8. The boron-doped diamond positive electrode 14 is bonded to the center of the bottom of the polishing head 8 by conductive glue. The plurality of diamond wafers 15 to be polished are distributed on a circular track, bonded to the bottom of the polishing head 8 by paraffin wax, and can be in friction contact with the annular polishing pad 10, so as to realize multi-station simultaneous processing. The right-angle support plate 6 on the support column 2 is detachably connected by bolts, so that the right-angle support plate 6, the second motor 7 and the polishing head 8 can be disassembled as a whole, and then the diamond wafers 15 to be polished can be disassembled. The circular track, the boron-doped diamond positive electrode 14 and the polishing head 8 are coaxially arranged, and a part of the circular track is located directly above the ultraviolet light source 13. The polishing liquid 18 completely immerses the annular negative electrode 9, the annular polishing pad 10, the transparent lampshade, the ultraviolet light source 13, the boron-doped diamond positive electrode 14 and the diamond wafer 15. The annular negative electrode 9 and the boron-doped diamond positive electrode 14 are both connected to an external power supply 19 through a conductive slip ring 16 connected to a conductive wire, and form an electrolysis circuit with the polishing liquid 18. The ultraviolet light source 13 is also connected to an external power supply 19 through a conductive slip ring 16 connected to a conductive wire (not shown in the figure) to form a power supply circuit. The polishing liquid 18 contains a conductive medium and a composite photocatalyst. The conductive medium is hydrochloric acid, so that the annular negative electrode 9 and the boron-doped diamond positive electrode 14 can be connected through the polishing liquid 18 to form an electrolysis circuit. The composite photocatalyst is PS / CeO 2 -TiO 2By adding the composite photocatalyst of the high specific surface area porous material, the ultraviolet catalytic effect can be enhanced, and hydroxyl radicals can be generated more efficiently. By setting the annular polishing pad 10 with holes, the hydroxyl radicals generated by electrolysis can quickly reach and act on the surface of the diamond wafer.

[0027] During operation, the power supply 19, the first motor 4, the second motor 7 and the ultraviolet light source 13 are started, the annular negative electrode 9 and the boron-doped diamond positive electrode 14 are connected through the polishing liquid 18, the polishing liquid 18 is electrolyzed, and a large number of hydroxyl radicals are generated. At the same time, the polishing head 8 and the polishing table 5 rotate in the opposite direction, and a number of diamond wafers 15 to be polished are mechanically polished by friction with the polishing pad under the drive of the second motor 7. The diamond wafers 15 rotate to be located directly above the ultraviolet light source 13 and are irradiated by ultraviolet light, which further promotes the generation of hydroxyl radicals. By combining the electric field, the light field and the chemical mechanical polishing, and acting synergistically, the efficient, stable and controllable generation of hydroxyl radicals is achieved, and the surface treatment efficiency and quality of the diamond wafers 15 are improved. Boron-doped diamond is used as the anode material to electrolyze the polishing liquid 18. Compared with other ordinary positive electrodes, the use of the boron-doped diamond positive electrode 14 can achieve continuous and stable generation of a large number of hydroxyl radicals, so that the hydroxyl radical generation efficiency is high, the reaction continuity is good, the reaction rate is easy to control, and the boron-doped diamond material itself is basically not consumed. By providing an annular step groove on the top of the polishing table 5, the ultraviolet light source 13 can be integrated on the polishing table 5 and immersed in the polishing liquid 18, directly irradiating the polishing liquid 18 and the diamond wafer 15, greatly reducing the loss of ultraviolet light and improving the effect of ultraviolet light. By distributing a number of diamond wafers 15 to be polished on a circular track coaxial with the polishing head 8, and a part of the circular track is located directly above the ultraviolet light source 13, the number of diamond wafers 15 to be polished are alternately mechanically polished and ultraviolet catalyzed as the polishing head 8 rotates, so that each diamond wafer 15 is irradiated with ultraviolet light for a consistent time, mechanically polished for a consistent time, and electrolytic reaction time, which greatly improves the consistency of the surface treatment effect of the diamond wafer 15. Moreover, the ultraviolet light can irradiate the entire diamond wafer 15, improving the effect of ultraviolet light.

[0028] See also Figure 5-Figure 6 , Figure 5 This is an electron microscope image of the surface of a diamond wafer before treatment in an embodiment of the present invention. Figure 6 This is an electron microscope image of the surface of a diamond wafer after being processed in an embodiment of the present invention. From the comparison of the two images, it can be seen that the surface treatment quality of the diamond wafer processed by the device is higher and the treatment effect is better.

[0029] Of course, in other embodiments, the polishing table 5 can also be set to be fixed, that is, the first motor 4 is not started, or the first motor 4 is directly omitted. A plurality of polishing heads 8 can be provided, and the plurality of polishing heads 8 are evenly arranged along the circumference of the polishing table 5, so as to process more diamond wafers 15 at one time, greatly improve the processing efficiency, and ensure that the polishing table 5 is evenly stressed without deviation. The conductive medium in the polishing liquid 18 can be sodium hydroxide, and the composite photocatalyst in the polishing liquid 18 can be ZIF- 8 , CNTs-TiO 2 , PMMA / SiO 2 -B , PS / CeO 2 One or more combinations of these materials can also achieve the purpose of the present invention.

[0030] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A photocatalytic and electrochemically assisted diamond CMP The polishing device is characterized in that The invention comprises a polishing table (5) and a polishing head (8), wherein the polishing head (8) is rotatably arranged above the polishing table (5); a step groove is arranged on the top of the polishing table (5), a polishing liquid (18) is contained in the step groove, a negative electrode and a polishing pad are arranged on the upper step surface of the step groove in order from bottom to top, and an ultraviolet light source (13) is arranged on the lower step surface of the step groove; a boron-doped diamond positive electrode (14) and a plurality of diamond wafers (15) to be polished are arranged at the bottom of the polishing head (8), and a plurality of diamond wafers (15) to be polished are arranged at the bottom of the polishing head (8). ) are distributed on a circular track and can be in frictional contact with the polishing pad, the circular track, the boron-doped diamond positive electrode (14) and the polishing head (8) are coaxially arranged, and a part of the circular track is located directly above the ultraviolet light source (13); the negative electrode and the boron-doped diamond positive electrode (14) are both connected to an external power source (19) through a conductive slip ring (16), and form an electrolytic circuit with the polishing liquid (18); the ultraviolet light source (13) is also connected to an external power source (19) through a conductive slip ring (16) to form a power supply circuit.

2. The photocatalytic and electrochemically assisted diamond according to claim 1 CMP The polishing device is characterized in that The polishing table (5) is cylindrical, the step groove is an annular step groove with a low center and high peripheries, the negative electrode is an annular negative electrode (9) matching the upper step surface of the annular step groove, the polishing pad is an annular polishing pad (10) matching the upper step surface of the annular step groove, and the polishing table (5) is rotatable.

3. The photocatalytic and electrochemically assisted diamond according to claim 2 CMP The polishing device is characterized in that It also comprises a base plate (1) and a support column (2), wherein a first motor (4) is arranged on the base plate (1), and the first motor (4) is connected to the polishing table (5) in a transmission manner, and a second motor (7) is arranged on the support column (2), and the second motor (7) is connected to the polishing head (8) in a transmission manner, and the support column (2) is arranged on the base plate (1).

4. The photocatalytic and electrochemically assisted diamond according to claim 1 or 3 CMP The polishing device is characterized in that The polishing liquid (18) contains a conductive medium and a composite photocatalyst, wherein the conductive medium is hydrochloric acid or sodium hydroxide, and the composite photocatalyst is PS / CeO 2 -TiO 2 , ZIF-8 , CNTs-TiO 2 , PMMA / SiO 2 -B , PS / CeO 2 A combination of one or more materials.

5. The photocatalytic and electrochemically assisted diamond according to claim 3 CMP The polishing device is characterized in that The negative electrode is fixed on the upper step surface of the step groove by screws, and the negative electrode is a platinum electrode.

6. The photocatalytic and electrochemically assisted diamond according to claim 3 CMP The polishing device is characterized in that The polishing pad is bonded to the negative electrode, and the polishing pad is provided with a plurality of through holes (11).

7. The photocatalytic and electrochemically assisted diamond according to claim 6 CMP The polishing device is characterized in that The plurality of through holes (11) are distributed in a honeycomb array.

8. The photocatalytic and electrochemically assisted diamond according to claim 1 or 3 CMP The polishing device is characterized in that A transparent lampshade is also provided on the lower step surface of the step groove, and the ultraviolet light source (13) is arranged in the transparent lampshade.

9. The photocatalytic and electrochemically assisted diamond according to claim 1 CMP The polishing device is characterized in that The boron-doped diamond positive electrode (14) is bonded to the bottom of the polishing head (8) via conductive adhesive.

10. The photocatalytic and electrochemically assisted diamond according to claim 1 CMP The polishing device is characterized in that The diamond wafer (15) to be polished is bonded to the bottom of the polishing head (8) by paraffin wax.

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