Electrochemical mechanical polishing method and apparatus for copper interconnect layers

Abstract

This invention provides an electrochemical mechanical polishing method and apparatus for copper interconnect layers. The method includes the following steps: providing an electrolytic cell containing polishing slurry, with a polishing pad at the bottom, and a wafer with a copper interconnect layer to be polished placed directly above the polishing pad. The wafer is fixed to a conductive backplate and serves as the anode connected to a power source as the working electrode; a reference electrode and a counter electrode are placed in the polishing slurry to form an electrolytic circuit; the power source is turned on, and a constant voltage is applied to the working electrode while mechanically polishing the copper on the wafer surface; the power source is turned off and mechanical polishing is stopped according to a preset polishing time. This invention achieves precise dynamic control of the oxidation rate and highly selective removal of the copper / barrier layer by applying a constant voltage to the working electrode; combined with the synergistic coupling of specific mechanical polishing parameters, it significantly improves process stability, repeatability, and copper removal efficiency, effectively improves wafer surface uniformity, and significantly reduces surface roughness and defect density.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, and in particular relates to an electrochemical mechanical polishing method and apparatus for copper interconnect layers. Background Technology

[0002] Chemical mechanical polishing (CMP) is a key process in semiconductor manufacturing for achieving copper interconnect planarization. It removes excess copper layers and achieves global planarization through a synergistic effect of chemical and mechanical processes, ensuring electrical isolation and high integration of multilayer wiring structures. Traditional copper CMP processes typically employ an acidic polishing slurry system using hydrogen peroxide (H2O2) as the oxidant. This system utilizes the oxidation effect of hydrogen peroxide on the copper surface to convert metallic copper into copper ions, which are then removed under mechanical polishing.

[0003] However, using hydrogen peroxide as an oxidation method has many drawbacks. Hydrogen peroxide is volatile and unstable during storage and use, and it is prone to decomposition when stored for a long time or exposed to heat or impurities. This not only causes the effective component concentration of the polishing solution to drift and the copper removal rate to be unstable and difficult to control precisely, but also poses a potential safety hazard in batch storage due to its strong oxidizing properties, increasing production and logistics management costs. In traditional high-voltage or strong oxidant environments, water electrolysis can easily occur, producing an oxygen evolution reaction. The oxygen bubbles generated by the reaction adhere to the wafer surface, hindering polishing, forming pits or causing excessively large dish-shaped depressions, which seriously affects the planarization effect. Chemical oxidation often lacks specificity and can easily oxidize both copper and the underlying barrier layer (Ta / TaN) at the same time, resulting in low selectivity and easy over-polishing of the barrier layer or damage to the dielectric layer. In addition, the treatment of hydrogen peroxide waste liquid is complicated and requires frequent replenishment to maintain the concentration.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electrochemical mechanical polishing method and apparatus for copper interconnect layers, which solves the problems of large fluctuations in copper removal rate, numerous surface defects, and low selectivity in copper / barrier layer removal in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides an electrochemical mechanical polishing method for copper interconnect layers, comprising the following steps:

[0007] An electrolytic cell is provided, the electrolytic cell contains a polishing slurry, a polishing pad is provided at the bottom of the electrolytic cell, and a wafer with a copper interconnect layer to be polished is provided directly above the polishing pad. The wafer is fixed to a conductive backplate and is connected to a power source as an anode to serve as a working electrode.

[0008] A reference electrode and a counter electrode are provided in the grinding slurry, so that the reference electrode, the counter electrode and the working electrode form an electrolytic circuit;

[0009] Turn on the power and apply a constant voltage to the working electrode to cause an electrochemical oxidation reaction of the copper on the wafer surface. At the same time, press down the polishing head to make the wafer contact the polishing pad. The polishing head drives the wafer to rotate relative to the polishing pad to mechanically polish the copper on the wafer surface to remove excess copper.

[0010] Turn off the power and stop the mechanical grinding according to the preset grinding time.

[0011] Preferably, the polishing fluid includes abrasive particles, a complexing agent, a corrosion inhibitor, and a pH adjuster, and the pH value of the polishing fluid is 2 to 7.5.

[0012] Preferably, the constant voltage applied to the working electrode has a potential range of 0.340V to 1.229V relative to the reference electrode.

[0013] Preferably, the grinding pressure of the mechanical grinding is 1~4 psi.

[0014] Preferably, during mechanical grinding, grinding fluid is also supplied to the grinding pad, and the flow rate of the grinding fluid is 100~300mL / min.

[0015] Preferably, the grinding head drives the wafer to rotate relative to the grinding pad at a speed of 60~120 rpm.

[0016] Preferably, the preset grinding time is 50s to 150s.

[0017] Preferably, before fixing the wafer to the conductive backplane, a pretreatment step is further included, specifically, rinsing the wafer with deionized water to remove surface particles and drying it with nitrogen gas.

[0018] The present invention also provides an electrochemical mechanical polishing apparatus for implementing the above-described electrochemical mechanical polishing method for copper interconnect layers, characterized in that the apparatus comprises:

[0019] An electrolytic cell for containing grinding fluid;

[0020] An electrochemical control unit includes a power source, a reference electrode, a counter electrode, and a conductive backplate. The conductive backplate is connected to a wafer, which serves as the working electrode. The reference electrode and the counter electrode are both immersed in a polishing slurry and together with the working electrode, they form an electrolytic circuit.

[0021] The polishing unit includes a polishing pad, a polishing head, and a pressure applying mechanism. The polishing pad is disposed at the bottom of the electrolytic cell. The polishing head is fixedly connected to the wafer through the conductive back plate and drives the wafer to rotate. The pressure applying mechanism is used to make the wafer contact the polishing pad and apply pressure.

[0022] A liquid supply system for delivering polishing fluid to the surface of the polishing pad.

[0023] Preferably, the device includes a control module connected to the power supply, which is used to control the potential of the working electrode relative to the reference electrode and monitor the current density of the electrolysis circuit.

[0024] As described above, the electrochemical mechanical polishing method and apparatus for copper interconnect layers of the present invention have the following beneficial effects:

[0025] This invention uses a polishing slurry as both an electrolyte and a polishing solution, completely replacing the traditional CMP's reliance on hydrogen peroxide. This reduces raw material costs and process safety risks from the source, effectively avoiding process instability caused by fluctuations in hydrogen peroxide concentration, and enhancing the safety and long-term stability of the process. By applying a constant voltage of 0.340V~1.229V to the working electrode, an electrochemical oxidation reaction is induced on the copper surface of the wafer, maximally suppressing oxygen evolution reaction on the anode surface, achieving precise dynamic control of the oxidation rate and highly selective removal of the copper / barrier layer. Electrochemical oxidation forms a uniform oxide film on the copper surface, which is then removed by mechanical polishing, avoiding mechanical scratches caused by directly polishing metallic copper. The synergistic coupling of specific mechanical polishing parameters significantly improves process stability, repeatability, and copper removal efficiency, effectively improving wafer surface uniformity and significantly reducing surface roughness and defect density. Furthermore, the device in this invention ensures wafer conductivity stability through a conductive backplate integrated into the polishing head, and, in conjunction with a three-electrode electrolysis circuit and a control module for real-time monitoring and feedback of potential and current density, further enhances the controllability and reliability of the process. Attached Figure Description

[0026] Figure 1 The diagram shown is a flow chart of the electrochemical mechanical polishing process for the copper interconnect layer in a specific embodiment of the present invention.

[0027] Figure 2 The diagram shown is a structural schematic of the electrochemical mechanical grinding device in a specific embodiment of the present invention.

[0028] Component designation explanation

[0029] 10 Electrolytic cell 11 Reference electrode 12 counter electrode 20 Abrasive pad 30 wafer 31 conductive adhesive 32 conductive backplate Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0032] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0033] Please see Figures 1-2 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0034] This invention provides an electrochemical mechanical polishing method for copper interconnect layers, comprising the following steps:

[0035] S1. An electrolytic cell 10 is provided, the electrolytic cell 10 contains a polishing liquid, a polishing pad 20 is provided at the bottom of the electrolytic cell 10, a wafer 30 with a copper interconnect layer to be polished is provided directly above the polishing pad 20, the wafer 30 is fixed to a conductive backplate 32 and is connected to a power source as an anode to serve as a working electrode.

[0036] S2. A reference electrode 11 and a counter electrode 12 are provided in the grinding fluid so that the reference electrode 11, the counter electrode 12 and the working electrode form an electrolytic circuit.

[0037] S3. Turn on the power and apply a constant voltage to the working electrode to cause the copper on the surface of the wafer 30 to undergo an electrochemical oxidation reaction. At the same time, press down the polishing head to make the wafer 30 contact the polishing pad 20. The polishing head drives the wafer 30 to rotate relative to the polishing pad to mechanically polish the copper on the surface of the wafer 30 to remove excess copper.

[0038] S4. Based on the preset grinding time, turn off the power and stop the mechanical grinding.

[0039] Specifically, this invention uses a polishing slurry as both an electrolyte and a polishing solution, completely replacing the traditional CMP's reliance on hydrogen peroxide. This reduces raw material costs and process safety risks from the source, effectively avoiding process instability caused by fluctuations in hydrogen peroxide concentration, and enhancing the safety and long-term stability of the process. By applying a constant voltage of 0.340V~1.229V to the working electrode, the copper on the wafer 30 surface undergoes an electrochemical oxidation reaction, maximally suppressing oxygen evolution on the anode surface, achieving precise dynamic control of the oxidation rate and highly selective removal of the copper / barrier layer. The use of electrochemical oxidation... The process involves forming a uniform oxide film on the copper surface, which is then removed by mechanical grinding, avoiding mechanical scratches caused by directly grinding metallic copper. The synergistic coupling of specific mechanical grinding parameters significantly improves process stability, repeatability, and copper removal efficiency, effectively improving the surface uniformity of wafer 30 and drastically reducing surface roughness and defect density. Furthermore, the device in this invention ensures the conductivity stability of wafer 30 by integrating a conductive backplate 32 into the grinding head. Combined with a three-electrode electrolysis circuit and control module for real-time monitoring and feedback of potential and current density, the controllability and reliability of the process are further enhanced.

[0040] See Figure 1 and Figure 2 The electrochemical mechanical polishing method for copper interconnect layers will be described in detail below.

[0041] First, step S1 is performed, providing an electrolytic cell 10 containing a polishing slurry. A polishing pad 20 is provided at the bottom of the electrolytic cell 10, and a wafer 30 with a copper interconnect layer to be polished is provided directly above the polishing pad 20. The wafer 30 is fixed to a conductive backplate 32 and is connected to a power source as an anode to serve as a working electrode.

[0042] Specifically, the polishing slurry contained in the electrolytic cell 10 also serves as the electrolyte. This polishing slurry does not contain hydrogen peroxide or other oxidants. The polishing slurry completely submerges the conductive backplate 32 used to fix the wafer 30. In a specific example, the conductive backplate 32 is integrated below the polishing head. The conductive backplate 32 is fixedly connected to the wafer 30 by conductive adhesive 31 to ensure the conductivity stability of the wafer 30. The wafer 30 is connected to the positive terminal of the power supply through the conductive backplate 32 as a working electrode. The power supply here is a DC power supply.

[0043] In a specific embodiment of the present invention, the wafer 30 involved is a wafer 30 with a copper interconnect layer. The wafer 30 includes a semiconductor substrate, an interlayer dielectric layer formed on the substrate, and trench and via structures patterned in the dielectric layer. A barrier layer and a copper seed layer are sequentially formed within the trenches and vias, and a copper interconnect structure is formed by electroplating. After electroplating, the surface of the wafer 30 is covered with an excess copper layer higher than the dielectric layer. This excess copper needs to be removed by a chemical mechanical polishing (CMP) process, ensuring that the copper remains only within the trenches and vias, forming a flat surface. Since the barrier layer is formed between the copper interconnect structure and the dielectric layer, during the CMP process, after the copper is removed, the barrier layer is exposed on the surface of the wafer 30. The polishing parameters need to be adjusted to achieve highly selective removal of the barrier layer material relative to the copper.

[0044] As an example, the polishing fluid includes abrasive particles, a complexing agent, a corrosion inhibitor, and a pH adjuster, and the pH value of the polishing fluid is 2 to 7.5.

[0045] Specifically, the abrasive particles in the polishing slurry can be silica abrasives, accounting for 3 wt% by mass; the complexing agent is used to form a complex with oxidized copper ions, the corrosion inhibitor is used to inhibit copper corrosion in non-polishing areas, and the pH adjuster is used to maintain the pH of the polishing slurry. In a specific embodiment of the present invention, the abrasive particles used are silica abrasives, accounting for 3 wt% by mass; the complexing agent is glycine with a molar concentration of 0.1 M; the corrosion inhibitor is BTA (benzotriazole) with a molar concentration of 0.01 M; and the pH adjuster is used to adjust the pH of the polishing slurry to 2~7.5, such as 2, 3, 4, 5, 6, 7, 7.5, etc. BTA has an excellent corrosion inhibition effect on copper in a neutral environment, while having little effect on the Ta / TaN barrier layer. Combined with electrochemical oxidation occurring only at the contact point, copper removal is much faster than the removal of the barrier layer. Preferably, the pH of the polishing slurry is 7.5. As an example, before fixing the wafer 30 to the conductive backplate 32, a pretreatment step is also included, specifically, rinsing the wafer 30 with deionized water to remove surface particles and drying it with nitrogen.

[0046] Specifically, the conductive backplates 32 between wafers 30 are connected by conductive adhesive 31 to ensure the conductivity stability of wafers 30. However, there are no excessive restrictions on the thickness of conductive adhesive 31, conductive backplate 32, and the material of conductive backplate 32, as long as they meet the actual needs.

[0047] Next, step S2 is performed, in which a reference electrode 11 and a counter electrode 12 are placed in the polishing slurry, so that the reference electrode 11, the counter electrode 12 and the working electrode form an electrolytic circuit.

[0048] For details, please refer to Figure 2The working electrode, counter electrode 12, and reference electrode 11 form two independent circuits to achieve precise control and measurement of the electrochemical reaction. The working electrode and counter electrode 12 constitute a current circuit. A voltage is applied in this circuit to drive the oxidation reaction of copper on the surface of the working electrode, while the counter electrode 12 undergoes the opposite electrode reaction, thus forming a complete closed loop. The working electrode and reference electrode 11 constitute a potential measurement circuit. The reference electrode 11 has an extremely stable and known potential. The precise potential of the working electrode is obtained by monitoring the potential difference between the working electrode and the reference electrode 11.

[0049] In a specific embodiment of the present invention, the counter electrode 12 and the reference electrode 11 are both independent electrodes and are physically isolated from the polishing pad 20 and do not contact each other; preferably, the counter electrode 12 is a platinum electrode and the reference electrode 11 is a saturated calomel electrode (SCE).

[0050] Next, step S3 is executed: the power is turned on, and a constant voltage is applied to the working electrode to cause an electrochemical oxidation reaction of the copper on the surface of the wafer 30. At the same time, the polishing head is pressed down to bring the wafer 30 into contact with the polishing pad 20. The polishing head drives the wafer 30 to rotate relative to the polishing pad 20 to mechanically polish the copper on the surface of the wafer 30 to remove excess copper.

[0051] Specifically, electrochemical oxidation is used to form a uniform oxide film on the copper surface, which is then removed by mechanical polishing, avoiding mechanical scratches caused by directly polishing metallic copper. Simultaneously, the synergistic coupling of specific mechanical polishing parameters significantly improves process stability, repeatability, and copper removal efficiency, effectively improving the surface uniformity of wafer 30 and substantially reducing surface roughness and defect density. In a specific embodiment of the invention, the polishing head used for mechanical polishing integrates a conductive backplate 32, which is fixedly connected to the back of wafer 30 via conductive adhesive 31. The polishing head drives the rotation of wafer 30, presses down to bring wafer 30 into contact with polishing pad 20, and applies a certain pressure. Under this pressure, wafer 30 rotates relative to polishing pad 20, thereby mechanically polishing away the oxide film formed on the copper interconnect layer. As an example, the constant voltage applied to the working electrode has a potential range of 0.340V to 1.229V relative to the reference electrode 11.

[0052] Specifically, the constant voltage applied to the working electrode relative to the potential of the reference electrode 11 can be any value in any range, such as 0.340V, 0.500V, 0.600V, 0.800V, 1.000V, 1.150V, or 1.229V. A constant voltage within this range can drive the copper on the wafer 30 to undergo an electrochemical oxidation reaction, while simultaneously suppressing the oxygen evolution reaction of water, thus avoiding the formation of pits or causing excessively large dish-shaped depressions.

[0053] As an example, the grinding pressure of the mechanical grinding is 1~4 psi.

[0054] A grinding pressure is applied to the wafer 30 using a pressure-applying mechanism, making its magnitude controllable. In a specific embodiment of the present invention, the grinding pressure of mechanical grinding may include any value within the range of 1psi, 1.5psi, 2psi, 3psi, 3.5psi, 4psi, etc., and can be adjusted according to actual conditions.

[0055] As an example, during mechanical grinding, grinding fluid also needs to be supplied to the grinding pad 20, and the flow rate of the grinding fluid is 100~300mL / min.

[0056] In a specific embodiment of the present invention, a liquid supply system is used to deliver polishing liquid to the surface of polishing pad 20. During the mechanical polishing process, the flow rate of the polishing liquid can include any value within the range of 100mL / min, 150mL / min, 200mL / min, 250mL / min, 300mL / min, etc. The polishing liquid here is the same as the polishing liquid pre-contained in the electrolytic cell 10, and serves as both polishing liquid and electrolyte.

[0057] As an example, the grinding head drives the wafer 30 to rotate relative to the grinding pad 20 at a speed of 60~120 rpm.

[0058] Specifically, the wafer 30 rotates relative to the polishing pad 20, while the polishing pad 20 remains stationary. The rotational speed of the wafer 30 relative to the polishing pad 20 is equivalent to the polishing rate, which can include any value within a range such as 60rpm, 80rpm, 100rpm, 110rpm, or 120rpm. The specific value can be adjusted according to actual needs.

[0059] Finally, perform step S4, and according to the preset grinding time, turn off the power and stop the mechanical grinding.

[0060] As an example, the preset grinding time is 50s to 150s.

[0061] Specifically, the preset grinding time can be any value within the range of 50s, 60s, 80s, 100s, 120s, 140s, 150s, etc., and can be adjusted according to the actual situation. In addition, during the electrochemical mechanical polishing process, it is also necessary to monitor the current density, which directly reflects the oxidation rate of copper. By monitoring the current, the polishing status can be judged in real time. If the barrier layer is worn through, the current will change abruptly.

[0062] In a specific embodiment of the present invention, after turning off the power and stopping the mechanical grinding, the grinding head is lifted, the wafer 30 is unloaded and immediately rinsed with deionized water and dried.

[0063] See Figure 2The present invention also provides an electrochemical mechanical polishing apparatus for implementing the above-mentioned electrochemical mechanical polishing method for copper interconnect layers. It should be noted that the above-mentioned electrochemical mechanical polishing method for copper interconnect layers can be performed using this apparatus, but other feasible apparatuses can also be used for electrochemical mechanical polishing, and it is not limited to this apparatus here.

[0064] The electrochemical mechanical polishing apparatus of this invention includes:

[0065] Electrolytic cell 10, wherein the electrolytic cell 10 is used to contain grinding fluid;

[0066] An electrochemical control unit includes a power source, a reference electrode 11, a counter electrode 12, and a conductive backplate 32. The conductive backplate 32 is connected to a wafer 30, which serves as the working electrode. The reference electrode 11 and the counter electrode 12 are both immersed in a polishing slurry and form an electrolytic circuit with the working electrode. The wafer 30 is connected to the anode of the power source through the conductive backplate 32, the counter electrode 12 is connected to the cathode of the power source, and the reference electrode 11 is connected in parallel with the working electrode.

[0067] The polishing unit includes a polishing pad 20 (not shown in the figure), a polishing head, and a pressure applying mechanism (not shown in the figure). The polishing pad 20 is disposed at the bottom of the electrolytic cell 10. The polishing head is fixedly connected to the wafer 30 through the conductive back plate 32 and drives the wafer 30 to rotate. The pressure applying mechanism is used to make the wafer 30 contact the polishing pad 20 and apply pressure.

[0068] A liquid supply system is provided for supplying polishing fluid to the surface of the polishing pad 20.

[0069] As an example, the device includes a control module connected to the power supply for controlling the potential of the working electrode relative to the reference electrode 11 and monitoring the current density of the electrolysis circuit.

[0070] Specifically, the control module can be an electrochemical workstation, which is electrically connected to the three electrodes through the electrochemical workstation structure and controls the potential of the working electrode relative to the reference electrode 11. At the same time, it monitors the current density of the electrolytic reflux. The current density directly reflects the oxidation rate of copper. By monitoring the current density, the polishing status can be judged in real time.

[0071] To better understand the electrochemical mechanical polishing method and apparatus for copper interconnect layers in this invention, the following description refers to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0072] The grinding object in the following embodiments is a 12-inch wafer 30 with a copper interconnect layer and a Ta / TaN barrier layer. The initial copper film thickness deposited on the surface of the wafer 30 is 10000 Å (i.e. 1 μm). Before grinding, the wafer 30 is rinsed with deionized water to remove surface particles and dried with nitrogen.

[0073] Example 1

[0074] This embodiment provides an electrochemical mechanical polishing method for copper interconnect layers, including the following steps:

[0075] S1. An electrolytic cell 10 is provided, the electrolytic cell 10 contains a polishing slurry, a polishing pad 20 is provided at the bottom of the electrolytic cell 10, and a wafer 30 with a copper interconnect layer to be polished is provided directly above the polishing pad 20. The wafer 30 is fixed to a conductive backplate 32 and is connected to a power source as an anode to serve as a working electrode. The polishing slurry comprises colloidal silica abrasive (mass concentration of 3wt%), glycine with a molar concentration of 0.1M, BTA with a molar concentration of 0.01M, and a pH adjuster. The pH value of the polishing slurry is 7.5, and no hydrogen peroxide is used in the polishing slurry.

[0076] S2. A reference electrode 11 and a counter electrode 12 are provided in the polishing slurry, so that the reference electrode 11, the counter electrode 12 and the working electrode form an electrolytic circuit; wherein, the counter electrode 12 is a platinum sheet and the reference electrode 11 is a saturated calomel electrode (SCE).

[0077] S3. Turn on the power and apply a constant potential of +0.8V (vs. SCE) to the working electrode to cause an electrochemical oxidation reaction of copper on the surface of wafer 30 to form an oxide layer. The monitored current density is 2.5mA / cm². At the same time, press down the polishing head to bring wafer 30 into contact with polishing pad 20. The polishing head drives wafer 30 to rotate relative to polishing pad 20 to mechanically polish the copper on the surface of wafer 30 to remove excess copper. The polishing pressure is 1.5psi, the rotation speed of wafer 30 relative to polishing pad 20 is 93rpm, and the flow rate of polishing fluid delivered to polishing pad 20 during mechanical polishing is 200mL / min.

[0078] S4. Grind for 60 seconds, then turn off the power and stop mechanical grinding.

[0079] Comparative Example 1

[0080] This comparative example provides a mechanical polishing method for copper interconnect layers. The difference from Example 1 is that a conventional CMP mechanical polishing machine is used, without an electrochemical module, and the polishing slurry consists of: colloidal silica abrasive (mass concentration of 3 wt%), glycine (molar concentration of 0.1 M), BTA (0.01 M), hydrogen peroxide (mass concentration of 0.5 wt%), and a pH adjuster, and the pH value of the polishing slurry is 7.5; other aspects are the same as in Example 1, and will not be described in detail here.

[0081] After unloading the milled wafers 30 from Example 1 and Comparative Example 1, rinsing them immediately with deionized water and drying them, their performance was tested, including the copper material removal rate, the selectivity of the barrier layer removal rate, the butterfly-shaped depression, the number of particles, and the surface roughness. The specific results are shown in Table 1 below.

[0082] Table 1. Performance data of wafers after electrochemical mechanical polishing in Example 1 and performance data of wafers after mechanical polishing in Comparative Example 1.

[0083] Testing items Example 1 Comparative Example 1 Copper material removal rate 6500 Å / min 6000 Å / min Barrier layer removal rate selectivity (Cu:Ta) >200:1 150:1 Disc-shaped depression 280Å 280Å Number of particles 5ea 35ea Surface roughness (Ra) 1.2nm 2.8nm

[0084] As shown in Table 1, while maintaining the same butterfly-shaped recess (i.e., planarization capability), Example 1 exhibits a higher copper removal rate, higher copper selectivity for the barrier layer, effectively prevents damage from excessive grinding, significantly reduces surface particle defects, and substantially optimizes the surface roughness of wafer 30, thereby improving interconnect reliability. In other words, the method in Example 1 effectively solves the problems of uneven oxidation, poor copper selectivity for the barrier layer, and high defect rates in traditional CMP processes, achieving high performance and high stability in copper interconnect planarization.

[0085] In summary, this invention utilizes a polishing slurry as both an electrolyte and a polishing solution, completely replacing the traditional CMP's reliance on hydrogen peroxide. This reduces raw material costs and process safety risks from the source, effectively avoiding process instability caused by fluctuations in hydrogen peroxide concentration, and enhancing the safety and long-term stability of the process. By applying a constant voltage of 0.340V~1.229V to the working electrode, an electrochemical oxidation reaction occurs on the copper surface of the wafer, maximally suppressing oxygen evolution reaction on the anode surface, achieving precise dynamic control of the oxidation rate and highly selective removal of the copper / barrier layer. Electrochemical oxidation forms a uniform oxide film on the copper surface, which is then removed by mechanical polishing, avoiding mechanical scratches caused by directly polishing metallic copper. The synergistic coupling of specific mechanical polishing parameters significantly improves process stability, repeatability, and copper removal efficiency, effectively improving wafer surface uniformity and drastically reducing surface roughness and defect density. Furthermore, the device in this invention ensures wafer conductivity stability through a conductive backplate integrated into the polishing head, and, in conjunction with a three-electrode electrolysis circuit and control module for real-time monitoring and feedback of potential and current density, further enhances the controllability and reliability of the process. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0086] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electrochemical mechanical polishing method for copper interconnect layers, characterized in that, Includes the following steps: An electrolytic cell is provided, the electrolytic cell contains a polishing slurry, a polishing pad is provided at the bottom of the electrolytic cell, and a wafer with a copper interconnect layer to be polished is provided directly above the polishing pad. The wafer is fixed to a conductive backplate and is connected to a power source as an anode to serve as a working electrode. A reference electrode and a counter electrode are provided in the grinding slurry, so that the reference electrode, the counter electrode and the working electrode form an electrolytic circuit; Turn on the power and apply a constant voltage to the working electrode to cause an electrochemical oxidation reaction of the copper on the wafer surface. At the same time, press down the polishing head to make the wafer contact the polishing pad. The polishing head drives the wafer to rotate relative to the polishing pad to mechanically polish the copper on the wafer surface to remove excess copper. Turn off the power and stop the mechanical grinding according to the preset grinding time.

2. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: The polishing fluid includes abrasive particles, complexing agent, corrosion inhibitor and pH adjuster, and the pH value of the polishing fluid is 2 to 7.

5.

3. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: The constant voltage applied to the working electrode has a potential range of 0.340V to 1.229V relative to the reference electrode.

4. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: The grinding pressure of the mechanical grinding is 1~4 psi.

5. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: During mechanical grinding, grinding fluid also needs to be supplied to the grinding pad, and the flow rate of the grinding fluid is 100~300mL / min.

6. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: The grinding head drives the wafer to rotate relative to the grinding pad at a speed of 60~120 rpm.

7. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: The preset grinding time is 50s to 150s.

8. The electrochemical mechanical polishing method for copper interconnect layers according to claim 1, characterized in that: Before fixing the wafer to the conductive backplane, a pretreatment step is also included, specifically, rinsing the wafer with deionized water to remove surface particles and drying it with nitrogen gas.

9. An electrochemical mechanical polishing apparatus for implementing the electrochemical mechanical polishing method for copper interconnect layers according to any one of claims 1 to 8, characterized in that, The device includes: An electrolytic cell for containing grinding fluid; An electrochemical control unit includes a power source, a reference electrode, a counter electrode, and a conductive backplate. The conductive backplate is connected to a wafer, which serves as the working electrode. The reference electrode and the counter electrode are both immersed in a polishing slurry and together with the working electrode, they form an electrolytic circuit. The polishing unit includes a polishing pad, a polishing head, and a pressure applying mechanism. The polishing pad is disposed at the bottom of the electrolytic cell. The polishing head is fixedly connected to the wafer through the conductive back plate and drives the wafer to rotate. The pressure applying mechanism is used to make the wafer contact the polishing pad and apply pressure. A liquid supply system for delivering polishing fluid to the surface of the polishing pad.

10. The electrochemical mechanical grinding apparatus according to claim 9, characterized in that: The device includes a control module connected to the power supply, which is used to control the potential of the working electrode relative to the reference electrode and monitor the current density of the electrolysis circuit.

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