Method of controlling metal protrusion in metal hybrid bond chemical mechanical polishing

Abstract

The application provides a method for controlling metal bump in metal hybrid bonding chemical mechanical polishing. The method comprises: performing a main body metal chemical mechanical polishing process; depositing a medium layer after performing the main body metal chemical mechanical polishing process; performing a metal dishing chemical mechanical polishing process to form a metal bump; and performing grinding to form a metal dishing after forming the metal bump. The application overcomes the influence of front layer thin film difference fluctuation and grinder table speed instability by breaking the traditional continuous polishing process and introducing a deposition medium layer step, combining motor torque end point capture and over polishing control, realizing accurate regulation of the size of the metal bump, and providing a consistent benchmark for subsequent accurate control of the metal dishing, thereby improving the interconnection quality and process yield of three-dimensional integrated circuit hybrid bonding.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for controlling metal protrusions in chemical mechanical polishing of metal hybrid bonding. Background Technology

[0002] 3D integrated circuit packaging is a promising advanced packaging technology in current semiconductor manufacturing. This technology achieves chip size reduction and performance improvement by stacking multiple chip layers vertically. This 3D stacking technology overcomes the physical limitations of traditional 2D packaging, bringing superior integration and performance to the semiconductor industry.

[0003] In 3D integrated circuit fabrication, metal hybrid bonding (such as typical copper hybrid bonding) is a core process for achieving interlayer electrical interconnection. Chemical mechanical polishing (CMP), as a critical preceding process affecting the final bond strength, has extremely stringent requirements on surface morphology, especially the size of metal dish-shaped recesses (typically controlled within the 20-40 angstrom range). This necessitates that the CMP process utilize advanced process control techniques to precisely regulate the degree of dish-shaped recesses.

[0004] In current chemical mechanical polishing (CMP) processes, a four-disc continuous grinding process is typically employed. The dish-shaped depression is primarily controlled through the grinding processes of the third and fourth polishing discs. Specifically, the third polishing disc removes the barrier layer, thereby forming a metal protrusion; subsequently, the fourth polishing disc is used for grinding to form the final desired metal dish-shaped depression.

[0005] However, in current processes, the third polishing disc grinding process is typically time-based for endpoint control. Due to unavoidable variations in thickness or morphology during the preceding processes, and the dynamic fluctuations in the polishing speed of the polishing machine itself, simply using time-based endpoint control is insufficient to adaptively compensate for these fluctuations, making precise control of the metal protrusion size difficult. If the morphology of the metal protrusions formed in the preceding steps is uncontrollable or unstable, subsequent processes will be unable to precisely control the final size of the metal disc-shaped depressions, severely degrading the quality of hybrid bonding, process stability, and final yield.

[0006] Therefore, there is an urgent need in this field to overcome the defects such as fluctuations in the previous process and unstable grinding speed of the machine, and to achieve precise control of the grinding endpoint and the size of the metal protrusion, so as to lay the foundation for subsequent precise control of the metal disc-shaped depression, thereby ultimately enhancing the stability and yield of the three-dimensional integrated circuit metal hybrid bonding process. Summary of the Invention

[0007] The purpose of this invention is to provide a method for controlling metal protrusions in chemical mechanical polishing of metal hybrid bonding, in order to solve the problem that in the prior art, it is difficult to accurately control the grinding endpoint and the size of metal protrusions in the continuous polishing process based solely on time control, which leads to uncontrollable subsequent metal dish-shaped depression morphology, reduced hybrid bonding quality and process stability.

[0008] To achieve the above objectives, the present invention provides a method for controlling metal protrusions during chemical mechanical polishing of metal mixed bonding, comprising:

[0009] Step 1: Perform the main metal chemical mechanical polishing process;

[0010] Step 2: After performing the aforementioned chemical mechanical polishing process on the main metal, a dielectric layer is deposited;

[0011] Step 3: Perform a metal disc-shaped recess chemical mechanical polishing process to form the metal protrusion;

[0012] Step 4: After forming the metal protrusion, grind it to form a metal disc-shaped depression.

[0013] Preferably, the metal includes at least one selected from copper, tungsten, ruthenium, aluminum, titanium, and tantalum.

[0014] Preferably, in step one, performing the chemical mechanical polishing process on the main metal includes: polishing with a first polishing pad under a first downward pressure, and polishing with a second polishing pad under a second downward pressure, wherein the first downward pressure is greater than the second downward pressure.

[0015] Preferably, in step one, polishing is performed using the first polishing pad with the first downward pressure, controlled based on the eddy current endpoint.

[0016] Preferably, in step one, polishing is performed using the second polishing disc with the second downward pressure, controlled based on the motor torque endpoint.

[0017] Preferably, in step two, the dielectric layer material includes at least one of tetraethyl orthosilicate, silicon oxide, silicon nitride, silicon oxynitride, and silicon carbonitride.

[0018] Preferably, in step two, the thickness of the dielectric layer is 200 to 400 angstroms.

[0019] Preferably, in step three, performing the metal disc-shaped recess chemical mechanical polishing process includes: controlling the grinding endpoint based on the motor torque endpoint combined with the overpolishing method to form the metal protrusion.

[0020] Preferably, in step three, performing the metal disc-shaped recess chemical mechanical polishing process includes: grinding with a third polishing disc.

[0021] Preferably, in step three, grinding with the third polishing disc to form the metal protrusion includes: removing the barrier layer located on the polishing surface.

[0022] Preferably, in step four, the grinding endpoint of forming the metal disc-shaped recess is controlled based on time.

[0023] Preferably, in step four, the depth of the metal disc-shaped recess is 20-40 angstroms.

[0024] As described above, the method for controlling metal protrusions in metal mixed-bonding chemical mechanical polishing of the present invention has the following beneficial effects:

[0025] This disclosure introduces a dielectric layer deposition step between the main grinding and dish-shaped recess grinding stages, and divides the subsequent steps into forming metal protrusions and forming metal dish-shaped recesses. This isolates the fluctuation errors in pattern density and film thickness in the preceding layer processes. By utilizing a method based on motor torque endpoint combined with over-polishing instead of purely time-based grinding control, it can adaptively compensate for machine grinding speed drift and differences in the thickness of the underlying material, achieving precise grasp of the grinding endpoint and the morphology of the metal protrusions. This method provides a highly consistent morphological reference surface for the subsequent accurate formation of dimensionally controllable metal dish-shaped recesses, improving the interconnect quality and process yield of hybrid bonding in 3D integrated circuits. Attached Figure Description

[0026] Figure 1 The diagram shows a flow chart of the method for controlling metal protrusions in chemical mechanical polishing of metal hybrid bonding according to the present invention.

[0027] Figure 2 The diagram shows a cross-sectional schematic of the wafer surface structure before polishing according to the present invention.

[0028] Figure 3 The diagram shows a cross-sectional view of the wafer surface structure after polishing with the first polishing pad according to the present invention.

[0029] Figure 4 The diagram shows a cross-sectional view of the wafer surface structure after polishing with the second polishing pad according to the present invention.

[0030] Figure 5 The diagram shows a cross-sectional view of the wafer surface structure after the deposition of the dielectric layer according to the present invention.

[0031] Figure 6 The diagram shows a cross-sectional view of the wafer surface structure after the metal protrusions are formed according to the present invention.

[0032] Figure 7 The diagram shown is a cross-sectional schematic of the wafer surface structure after forming the metal dish-shaped recess according to the present invention. Detailed Implementation

[0033] 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.

[0034] For methods to control metal protrusions during chemical mechanical polishing of mixed metal bonds, please refer to [reference needed]. Figure 1 It includes the following steps:

[0035] The manufacturing process of integrated circuit devices typically includes front-end, mid-end, and back-end processes. The method for controlling the metal 105 bumps in the chemical mechanical polishing of metal hybrid bonding can be integrated into the wafer-level interconnect structure of back-end processes or advanced packaging processes.

[0036] Please refer to the reference. Figure 2 Before polishing, the wafer's surface structure contains a multilayer dielectric structure with different materials and functions, specifically including a first dielectric layer 101, a second dielectric layer 102 disposed above the first dielectric layer 101, and a third dielectric layer 103 disposed above the second dielectric layer 102. Extending and penetrating trenches or vias are formed in the multilayer dielectric structure, and a barrier layer 104 and a metal layer 105 are sequentially deposited on the sidewalls and bottom.

[0037] The first dielectric layer 101 typically serves as the main interlayer insulation structure. Its material may include carbon-doped silicon oxide, porous silicate glass, or a polymeric material with extremely low dielectric constant. It primarily reduces parasitic capacitive coupling and RC delay effects between adjacent conductive interconnects. The second dielectric layer 102 often serves as an etch stop layer or a penetration-proof capping layer. Its material can be replaced with dense silicon carbonitride, silicon nitride, silicon carbide, or silicon oxynitride. This layer possesses high physical hardness and chemical resistance, providing a precise longitudinal depth control reference in the preceding double damask patterned aperture process. The third dielectric layer 103 serves as the outermost planarization interface layer. Its material may include tetraethyl orthosilicate oxide, undoped silicate glass, or a silicon-rich oxide film. The third dielectric layer 103 not only provides a highly flat and hydrophilic direct mating surface in subsequent hybrid bonding thermal annealing processes but also acts as a buffer medium for the grinding rate in current chemical mechanical polishing processes. By setting up a layered dielectric structure with stepped distribution of materials and hardness, the global polishing rate and the final wafer surface morphology can be more precisely adjusted by utilizing the differences in the grinding selectivity of each layer material for a specific polishing slurry formulation.

[0038] It should be understood that the above description of the stacked dielectric structure including the first dielectric layer 101, the second dielectric layer 102, and the third dielectric layer 103 is for illustrative purposes only and does not constitute a rigid limitation. In other embodiments, the dielectric layer structure can be flexibly adjusted according to the parasitic capacitance tolerance and mechanical strength requirements of specific process nodes, for example, configured as a single dielectric layer, a two-layer stacked dielectric, or a composite dielectric system containing more layers. For example, in a streamlined process, only the main insulating layer and the surface bonding dielectric layer can be provided, omitting the intermediate etch stop layer; conversely, when facing complex multiple exposure morphologies or special thermal expansion stress control requirements, additional photolithographic anti-reflective coatings, stress relaxation buffer layers, or moisture-proof isolation layers can be inserted between each main dielectric layer. Regardless of the specific number of layers and stacking arrangement, as long as it can provide effective electrical isolation and physical support substrate for internal conductive interconnects, it can be seamlessly connected to and benefit from the chemical mechanical polishing morphology control method disclosed in this invention.

[0039] The barrier layer 104 serves a dual purpose of diffusion blocking and physical adhesion in the wafer interconnect structure. Its materials may include tantalum, tantalum nitride, titanium, titanium nitride, tungsten nitride, or a composite stack of the aforementioned materials, such as a combination of a lower layer of pure titanium and an upper layer of titanium nitride, or a bilayer stack of tantalum nitride and pure tantalum. The barrier layer 104 can be conformally coated onto the inner wall of the trench using physical vapor deposition, chemical vapor deposition, or atomic layer deposition processes with high step coverage. This barrier layer 104 not only blocks the electromigration and thermal diffusion of conductive atoms within the metal layer 105 into the surrounding multilayer dielectric network, preventing capacitor breakdown or device short-circuit failure; simultaneously, the barrier layer 104 also acts as an interface adhesion layer, significantly enhancing the physical adhesion between the metal layer 105 and the interfaces of the various dielectric layers 101, 102, and 103.

[0040] In some embodiments, metal 105 includes at least one of copper, tungsten, ruthenium, aluminum, titanium, and tantalum. These conductive metals possess excellent carrier transport characteristics and can serve as signal transmission lines, heat dissipation channels, or structural supports in microelectromechanical systems (MEMS) within wafer stacked structures. The deposition process of metal layer 105 can be performed using physical vapor deposition, chemical vapor deposition, or electrochemical plating. When using electroplating, a step of pre-forming an extremely thin seed layer at the bottom of the via and on the surface of the barrier layer 104 may be included. The seed layer material may be the same as or different from the main metal 105 material to guide uniform nucleation and pore-free growth of metal grains. Multiple layers of composite stacks of different metals may also be nested within the conductive metal structure to control the distribution of thermal expansion stress.

[0041] Step 1: Perform the main metal chemical mechanical polishing process.

[0042] In some embodiments, step one, performing the chemical mechanical polishing process on the main metal, includes: polishing with a first polishing pad under a first downward pressure, and polishing with a second polishing pad under a second downward pressure, wherein the first downward pressure is greater than the second downward pressure. The surface of the polishing pad is typically covered with a polishing pad containing polyurethane or other microporous polymer materials. During polishing operation, a polishing slurry distribution module continuously supplies the polishing pad with an abrasive slurry containing abrasive particles and chemical additives; the abrasive particles can be replaced with silica, alumina, or cerium dioxide particles.

[0043] Please refer to Figure 3 The first stage, with its higher pressure and higher rotation speed, primarily targets the rapid stripping of large metal layers (105mm+) covering the wafer surface, thereby reducing overall equipment uptime. Please refer to [link / reference needed]. Figure 4 The second stage switches to lower pressure, using a polishing pad with a softer microporous structure to smooth out surface micro-scratches or stress damage areas caused by the high pressure in the first stage.

[0044] In some embodiments, in step one, polishing is performed using a first polishing pad with a first downward pressure, controlled based on the eddy current endpoint. An eddy current sensing module is embedded below the first polishing pad. It analyzes the continuous thickness information of the metal layer 105 thin film by emitting a high-frequency alternating magnetic field onto the wafer and detecting changes in the induced eddy currents. When the measured thickness of the metal layer 105 reaches a preset safety threshold, the control unit issues a command to interrupt the polishing operation. In addition to eddy current detection, the monitoring system can also integrate an optical reflectance spectroscopy system or an acoustic emission sensor to improve the accuracy of remaining thickness identification and prevent excessively fast polishing rates from causing penetrating wear to the underlying third dielectric layer 103.

[0045] In some embodiments, in step one, polishing is performed using a second polishing pad with a second downward pressure, controlled based on the motor torque endpoint. As the second-stage soft polishing gradually reaches its bottom and exposes the barrier layers 104 of different materials, the dynamic friction coefficient of the polishing interface undergoes a transient change. The control system records the operating current and torque fluctuation characteristic curves of the servo motor driving the polishing pad or polishing head in real time. By capturing the slope peak of this curve as a characteristic signal of the alternation of different thin film materials, this monitoring method can accurately identify the moment when the metal layer 105 is completely removed and the barrier layer 104 is just exposed.

[0046] Step 2: After performing the main metal chemical mechanical polishing process, deposit the medium layer 106.

[0047] In some embodiments, in step two, please refer to the reference. Figure 5The dielectric layer 106 material includes at least one of tetraethyl orthosilicate, silicon oxide, silicon nitride, silicon oxynitride, and silicon carbonitride. After grinding in step one, the dielectric layer 106 is deposited to cover the entire surface of the wafer. This dielectric layer 106 serves as a barrier buffer layer that interrupts the conventional continuous polishing process and can be prepared by plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition, or high-density plasma chemical vapor deposition. Using tetraethyl orthosilicate as a reaction precursor and supplementing it with oxidants such as oxygen or ozone can generate a dense and uniform oxide protective film. Alternatively, fluorinated silicon glass, carbon-doped silicon glass, or porous organosilicon polymers can also be introduced as the dielectric layer 106 material. By adjusting the mixing flow rate ratio of different precursor gases, the density and surface hydrophilicity of the dielectric layer 106 can be flexibly controlled, providing a uniform reaction substrate for subsequent precise shaping.

[0048] In some embodiments, in step two, the thickness of the dielectric layer 106 is 200 to 400 angstroms, for example, 300 angstroms. Controlling the thickness of the dielectric layer 106 within this process window allows for the precise conformal coverage and smoothing of residual microstructure undulations on the wafer surface, filling in local depressions. Simultaneously, this specific thickness range prevents the accumulation of excessive residual tensile or compressive stress within the film, mitigating the potential risk of film cracking or warping during subsequent multiple thermal cycling processes.

[0049] Step 3: Perform a metal disc-shaped recess chemical mechanical polishing process to form a metal 105 protrusion.

[0050] In some embodiments, in step three, please refer to the reference. Figure 6 The chemical mechanical polishing (CMP) process for metal disc-shaped recesses includes: controlling the grinding endpoint based on the motor torque endpoint combined with over-polishing methods to form metal protrusions 105. This stage of the process is mainly used to reshape the local morphology at the interface between the metal and the dielectric. The control system continuously monitors the servo motor torque parameters, and when it detects a sudden torque change signal indicating that a large area of ​​the dielectric layer 106 has been ground away, exposing the underlying structure, it marks the arrival of the main polishing endpoint. Subsequently, the control unit automatically starts and executes the over-polishing procedure based on a pre-established material removal rate feedback model. Please refer to [reference needed]. Figure 6 Over-polishing completely removes the surface dielectric layer 106, and simultaneously peels off a portion of the thickness of the bottom third dielectric layer 103 and barrier layer 104, resulting in a micro-protrusion morphology where the surface of the internal metal 105 is slightly higher than the surrounding remaining dielectric layer 102. Over-polishing can be achieved by fine-tuning the pH of the polishing slurry or reducing the polishing head speed, relying on the chemical complexation reaction of the polishing slurry supplemented by slight mechanical polishing. The over-polishing stage can also introduce a polishing slurry formulation rich in specific corrosion inhibitors to slow down the chemical etching rate of the metal 105, thus making it easier to control the height of the protrusion.

[0051] In some embodiments, step three, performing the metal disc recess chemical mechanical polishing process includes: grinding with a third polishing pad.

[0052] In some embodiments, step three, using a third polishing pad to grind and form the metal 105 protrusion, includes removing the barrier layer 104 located on the polishing surface. Since the barrier layer 104 typically has high hardness, removing it not only removes the conductive barrier material covering the metal but also utilizes the difference in polishing selectivity between the barrier layer 104, the metal 105, and the surrounding dielectric layer to the current polishing slurry formulation. By adjusting the concentration ratio of oxidant to complexing agent in the polishing slurry, the removal rate of the barrier layer 104 and the surrounding dielectric is controlled to be higher than that of the metal 105, thereby causing the surrounding material to recede, and the more corrosion-resistant conductive protrusion morphology inside is naturally revealed.

[0053] Step 4: After forming the metal 105 protrusion, grind it to form the metal 105 disc-shaped recess.

[0054] In some embodiments, in step four, please refer to the reference. Figure 7 The grinding endpoint is controlled based on time, forming a 105-shaped disc-shaped indentation in the metal. For example... Figure 7 As shown, a fourth polishing pad is used for grinding. Through mechanical friction of the polishing pad and slight corrosion of the chemical solution, the surface of metal 105 exhibits a slight concavity relative to the plane of the outer second dielectric layer 102. During this finishing stage, the polishing slurry composition and the downward processing pressure are adjusted to a soft polishing mode with extremely low mechanical wear. The grinding time can be dynamically compensated and corrected by the wafer batch management control system based on online measurement data fed back from the preceding measurement equipment.

[0055] In some embodiments, in step four, the depth of the dish-shaped recess of metal 105 is 20-40 angstroms. When two independent wafers with such shallow dish-shaped recesses of metal 105 are aligned face-to-face and subjected to high-temperature annealing in an oven, the conductive metal material undergoes significant volume expansion due to heat. The aforementioned micro-recessed depth space is precisely sufficient to accommodate the additional volume overflow caused by the thermal expansion of the metal material, allowing the surfaces of the mating metal 105 ends to be tightly pressed and adhered to each other at the interface, thereby inducing the mutual diffusion and fusion of metal atoms to form a continuous and low-impedance complete lattice interconnect. This structural design alleviates the lateral destructive compressive tensile stress exerted on the surrounding insulating dielectric layer by the excessive thermal expansion of metal 105, prevents micro-cracks in the insulating layer or physical peeling defects at the bonding interface, thereby improving the electromigration resistance and mechanical connectivity of the three-dimensional interconnect node.

[0056] 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.

[0057] 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. A method for controlling metal protrusions in chemical mechanical polishing of mixed metal bonding, characterized in that, At least including: Step 1: Perform the main metal chemical mechanical polishing process; Step 2: After performing the aforementioned chemical mechanical polishing process on the main metal, a dielectric layer is deposited; Step 3: Perform a metal disc-shaped recess chemical mechanical polishing process to form the metal protrusion; Step 4: After forming the metal protrusion, grind it to form a metal disc-shaped depression.

2. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 1, characterized in that: The metal includes at least one of copper, tungsten, ruthenium, aluminum, titanium, and tantalum.

3. The method for controlling metal protrusions in chemical mechanical polishing of mixed metal bonding according to claim 1, characterized in that: In step one, performing the chemical mechanical polishing process on the main metal includes: polishing with a first polishing pad under a first downward pressure, and polishing with a second polishing pad under a second downward pressure, wherein the first downward pressure is greater than the second downward pressure.

4. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 3, characterized in that: In step one, the first polishing pad is used to polish the material with the first downward pressure, and the polishing is controlled based on the eddy current endpoint.

5. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 3, characterized in that: In step one, polishing is performed using the second polishing pad with the second downward pressure, controlled based on the motor torque endpoint.

6. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 1, characterized in that: In step two, the dielectric layer material includes at least one of tetraethyl orthosilicate, silicon oxide, silicon nitride, silicon oxynitride, and silicon carbonitride.

7. The method for controlling metal protrusions in chemical mechanical polishing of mixed metal bonding according to claim 1, characterized in that: In step two, the thickness of the dielectric layer is 200 to 400 angstroms.

8. The method for controlling metal protrusions in chemical mechanical polishing of mixed metal bonding according to claim 1, characterized in that: In step three, the chemical mechanical polishing process for the metal disc-shaped depression includes: controlling the grinding endpoint based on the motor torque endpoint combined with the over-polishing method to form the metal protrusion.

9. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 1, characterized in that: In step three, the metal disc-shaped recess chemical mechanical polishing process includes grinding using a third polishing disc.

10. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 9, characterized in that: In step three, grinding with the third polishing disc to form the metal protrusion includes removing the barrier layer located on the polishing surface.

11. The method for controlling metal protrusions in chemical mechanical polishing of metal mixed bonding according to claim 1, characterized in that: In step four, the grinding endpoint is controlled based on time to form the metal disc-shaped recess.

12. The method for controlling metal protrusions in chemical mechanical polishing of mixed metal bonding according to claim 1, characterized in that: In step four, the depth of the metal disc-shaped recess is 20-40 angstroms.

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