A method for forming semi-damascus metal interconnects by cobalt electrodeposition and its structure

Abstract

This invention proposes a cobalt electrodeposition method and structure for forming semi-damascus metal interconnects. The method includes: etching vias in a SiCN / SiCO composite low-k dielectric layer and activating them with NH3 plasma to introduce surface nitrogen-active sites; preparing a cobalt seed layer on the inner surface of the vias using atomic layer deposition (ALD); applying a pulsed current using a sulfate electrolyte system to achieve bottom-up, void-free cobalt filling; removing excess cobalt layers through surface planarization to form a cobalt-dielectric layer composite structure; and finally, using the cobalt structure as a mask for reverse etching to remove the outer dielectric layer, causing the cobalt in the trenches and vias to form strip-shaped metal lines and columnar interconnects, respectively, resulting in high-density metal interconnect lines. This invention, by developing a cobalt electrodeposition method suitable for semi-damascus structures and employing a pulsed current mode and sulfate electrolyte system, significantly improves the metal layer growth rate, meeting the efficiency requirements of large-scale mass production and reducing equipment costs.

Description

Technical Field

[0001] This invention relates to the field of semiconductor integrated circuit manufacturing technology, and in particular to a cobalt electrodeposition method and structure for forming semi-damascus metal interconnects. Background Technology

[0002] Currently, ruthenium (Ru) interconnect structures are fabricated using atomic layer deposition (ALD) combined with a semi-damascus method. The core growth method of ALD is 100% step-coverage, which involves forming a uniformly thick ruthenium film (20-50 nm thick) on the sidewalls, bottom, and top of vias and trenches through layer-by-layer chemical reactions, achieving indiscriminate coverage of high aspect ratio structures (e.g., sidewall and bottom film thickness deviation < 1 nm). The specific process is as follows: First, vias are etched in a SiCN / SiCO composite low-k dielectric layer. Then, a ruthenium film is deposited using the ALD method (covering the sidewalls, bottom, and dielectric layer surface of the vias and trenches). Next, the ruthenium film on the dielectric layer surface is removed by dry etching (retaining the ruthenium within the trenches and vias) to define the metal line pattern. Air gaps are then introduced between the metal lines to reduce parasitic capacitance. Finally, SiN spacers are used to achieve self-aligned integration of the vias and underlying circuitry.

[0003] However, the ALD method has significant limitations in growth characteristics: when using the zero-valent precursor Ru(DMBD)(CO)3, the growth rate is only 0.05 nm / cycle, requiring 4000 cycles (over 6 hours) to deposit a 200 nm thick film; while the growth rate of the +2-valent precursor Ru(EtCp)2 is increased to 0.18 nm / cycle, nucleation on SiO2 substrates is significantly delayed (requiring more than 250 cycles to form a continuous film), and film discontinuities easily occur at the bottom of vias with high aspect ratios (>6:1) due to decreased uniformity of step coverage. Furthermore, the ALD process requires plasma assistance or substrate pretreatment (such as TMA modification) to maintain 100% step coverage, increasing the difficulty of method integration.

[0004] As can be seen from the above, the disadvantages of the existing technology are as follows:

[0005] 1. Extremely low deposition efficiency: The growth rate of the zero-valent precursor Ru(DMBD)(CO)3 is only 0.05 nm / cycle, and it takes 4,000 cycles to deposit a 200 nm thick film, which takes more than 6 hours. Although the growth rate of the +2-valent precursor Ru(EtCp)2 can be increased to 0.18 nm / cycle, it is still far below the mass production requirements, resulting in high equipment costs and difficulty in meeting the efficiency requirements of large-scale mass production.

[0006] 2. Poor nucleation and uniformity: The nucleation of the +2 valence precursor on the SiO2 substrate is significantly delayed, requiring more than 250 cycles to form a continuous film. Furthermore, film discontinuities are prone to occur at the bottom of vias with high aspect ratios (>6:1), leading to increased local resistance and affecting the consistency of interconnect performance.

[0007] 3. Complexity of the method: The ALD process requires precise control of parameters such as temperature and precursor flow rate, and often requires plasma assistance or substrate pretreatment to optimize nucleation, which increases the difficulty of method integration and the risk of stability control.

[0008] 4. High material costs: Ruthenium is a precious metal, and ALD precursors are expensive, especially 0-valent precursors, which further increases the unit product manufacturing cost.

[0009] 5. Poor adaptability of the method structure: Due to the 100% step coverage characteristic of ALD, the ruthenium film will simultaneously cover the sidewalls, bottom and dielectric layer surface of the via / trench. It is necessary to additionally etch the excess ruthenium film on the dielectric layer surface and trench sidewalls (etching amount up to 10-20nm), which can easily lead to uneven ruthenium film thickness on the sidewalls (deviation > 5nm), and even cause trench narrowing (narrowing rate > 10%), affecting interconnect density. Summary of the Invention

[0010] In view of the above situation, the main objective of the present invention is to provide a cobalt electrodeposition method and structure for forming semi-damascus metal interconnects, so as to solve the above-mentioned technical problems.

[0011] This invention proposes a cobalt electrodeposition method for forming semi-damascus metal interconnects, the method comprising the following steps:

[0012] Step 1: Form a through-hole structure in the composite low-k dielectric layer composed of SiCN and SiCO by plasma etching to obtain a dielectric layer substrate with a through-hole structure;

[0013] Step 2: Perform NH3 plasma activation treatment on the surface of the dielectric layer substrate with through-hole structure to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface;

[0014] Step 3: On the inner surface of the through-hole of the activated medium layer structure with nitrogen-rich active sites, an atomic layer deposition technique is used to deposit a continuous cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor to obtain a medium layer structure with a cobalt seed layer.

[0015] Step 4: Place the dielectric layer structure with cobalt seed layer in a custom electrodeposition tank, using a sulfate electrolyte system composed of cobalt sulfate heptahydrate, citric acid, polyethylene glycol and thiourea, and apply a pulsed current; cobalt ions grow from bottom to top under the action of the pulsed electric field to form a dielectric layer structure filled with cobalt.

[0016] Step 5: Polish and reverse etch the cobalt-filled dielectric layer structure sequentially to obtain high-density metal interconnect lines.

[0017] The present invention also proposes a semi-damascus metal interconnect structure formed by cobalt electrodeposition, wherein the semi-damascus metal interconnect structure is prepared by cobalt electrodeposition as described above for forming semi-damascus metal interconnects.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention develops a cobalt electrodeposition method suitable for semi-damascus structures, employing a pulsed current mode (2-8 mA / cm²). 2 The system of sulfate electrolyte and metal layer growth rate is increased to 10-50 nm / min (more than 55 times higher than the highest rate of ALD Ru), ensuring that the time to deposit a 200 nm cobalt layer is controlled within 4-20 min, meeting the efficiency requirements of mass production and reducing equipment occupation costs.

[0020] 2. This invention optimizes the ratio of leveling agent (polyethylene glycol) to brightener (thiourea) in the electrolyte (1-5 g / L polyethylene glycol + 0.1-1 g / L thiourea), combined with continuous coverage of a 5-15 nm cobalt seed layer, to achieve void-free filling of vias and trenches with an aspect ratio of 6-8:1, control the cobalt layer thickness deviation to <3 nm, ensure the uniformity of interconnect line resistance (deviation <5%), and solve the problem of local defects caused by ALDRu nucleation delay;

[0021] 3. This invention eliminates the plasma-assisted or substrate pretreatment steps required for ALD Ru, achieving uniform cobalt deposition solely through NH3 plasma surface activation. Simultaneously, bottom-up growth avoids the trench narrowing (narrowing rate reduced from >10% to <3%) and sidewall film thickness unevenness issues caused by 100% step coverage in ALD, thus improving interconnect density. Electrodeposition parameters (temperature 40-50℃, pH=3-4) are easily controlled, reducing method integration difficulty and keeping yield loss below 3%.

[0022] 4. This invention reduces the manufacturing cost of a unit interconnect structure by more than 50% by taking advantage of the cost of cobalt metal (about 1 / 10 of ruthenium) and electrodeposition equipment (investment is about 1 / 4 of ALD equipment), combined with a recyclable electrolyte design.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments of the invention. Attached Figure Description

[0024] Figure 1This is a flowchart illustrating the steps of a cobalt electrodeposition method for forming semi-damascus metal interconnects proposed in this invention.

[0025] Figure 2 This is a schematic diagram of the dielectric layer structure after cobalt filling;

[0026] Figure 3 This is a schematic diagram of a cobalt-dielectric layer composite structure.

[0027] Figure 4 A schematic diagram of a semi-Damascus metal interconnect structure;

[0028] Figure 5 This is a comparison chart of the deposition efficiency of the cobalt electrodeposition method proposed in this invention and the traditional ALD method;

[0029] Figure 6 This is a comparison chart of the via filling capabilities of the cobalt electrodeposition method proposed in this invention and the traditional ALD method;

[0030] Figure 7 This is a comparison of the electrical performance of the cobalt electrodeposition method proposed in this invention and the traditional ALD method. Detailed Implementation

[0031] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0032] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0033] Example 1:

[0034] Please see Figures 1 to 4 This embodiment provides a cobalt electrodeposition method for forming a semi-damascus metal interconnect, the method comprising the following steps:

[0035] Step 1: Form a via structure with a diameter of 20 nm and an aspect ratio of 6:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure;

[0036] Step 2: The surface of the dielectric layer substrate with a through-hole structure is activated by NH3 plasma for 30s, 100W, and 50mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0037] Step 3: On the inner surface of the through-hole of the activated medium layer structure rich in nitrogen active sites, an atomic layer deposition technique is used to deposit a 5 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 150 °C and a pressure of 5 mTorr, to obtain a medium layer structure with a cobalt seed layer.

[0038] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 55 g / L cobalt sulfate heptahydrate, 20 g / L citric acid, 1 g / L polyethylene glycol, and 0.1 g / L thiourea. Apply a peak current density of 2 mA / cm² at a temperature of 40°C and a pH of 3 (adjusted with H₂SO₄). 2 A pulsed current with a duty cycle of 30% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 100 nm (e.g., Figure 2 (as shown)

[0039] Step 5: Perform surface planarization on the cobalt-filled dielectric layer structure using chemical mechanical polishing at a pressure of 2 psi to remove excess cobalt from the dielectric layer surface, retaining only the cobalt structure located inside the vias and trenches, forming a cobalt-dielectric layer composite structure (e.g., Figure 3 (as shown)

[0040] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in cobalt forming strip-shaped metal lines within the trenches and cobalt forming columnar interconnects within the vias. The strip-shaped metal lines and columnar interconnects are integrally formed, with an edge spacing of 20nm between adjacent strip-shaped metal lines, a linewidth deviation of less than 5nm, and an alignment deviation between the vias and the underlying structure of less than 5nm. This ultimately forms high-density metal interconnect lines that meet the requirements of 3nm and below process technologies (e.g., ...). Figure 4 (As shown).

[0041] Example 2:

[0042] This embodiment provides a cobalt electrodeposition method for forming a semi-damascus metal interconnect, the method comprising the following steps:

[0043] Step 1: Form a via structure with a diameter of 35 nm and an aspect ratio of 7:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure;

[0044] Step 2: The surface of the dielectric layer substrate with through-hole structure is activated by NH3 plasma for 45s, 150W, and 75mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0045] Step 3: On the inner surface of the through-hole of the activated medium layer structure rich in nitrogen active sites, an atomic layer deposition technique is used to deposit a 10 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 200 °C and a pressure of 7.5 mTorr, to obtain a medium layer structure with a cobalt seed layer.

[0046] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 85 g / L cobalt sulfate heptahydrate, 30 g / L citric acid, 3 g / L polyethylene glycol, and 0.55 g / L thiourea. Apply a peak current density of 5 mA / cm² at a temperature of 45°C and a pH of 3.5 (adjusted with H₂SO₄). 2 A pulsed current with a duty cycle of 40% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 300 nm.

[0047] Step 5: Perform surface planarization on the cobalt-filled dielectric layer structure using chemical mechanical polishing at a pressure of 3 psi to remove excess cobalt layer from the surface of the dielectric layer, retaining only the cobalt structure located inside the vias and trenches to form a cobalt-dielectric layer composite structure.

[0048] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in the cobalt forming strip-shaped metal lines in the trenches and columnar connectors in the vias. The strip-shaped metal lines and columnar connectors are integrally formed. The edge spacing between adjacent strip-shaped metal lines is 25nm, the linewidth deviation is less than 5nm, and the alignment deviation between the vias and the underlying structure is less than 5nm. This ultimately forms high-density metal interconnect lines that meet the requirements of 3nm and below process technology.

[0049] Example 3:

[0050] This embodiment provides a cobalt electrodeposition method for forming a semi-damascus metal interconnect, the method comprising the following steps:

[0051] Step 1: Form a via structure with a diameter of 35 nm and an aspect ratio of 7:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure;

[0052] Step 2: The surface of the dielectric layer substrate with a through-hole structure is activated by NH3 plasma for 60s, 200W, and 100mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0053] Step 3: On the inner surface of the through-hole of the activated medium layer structure with nitrogen-rich active sites, an atomic layer deposition technique is used to deposit a 15 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 250 °C and a pressure of 10 mTorr, thus obtaining a medium layer structure with a cobalt seed layer.

[0054] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 115 g / L cobalt sulfate heptahydrate, 40 g / L citric acid, 5 g / L polyethylene glycol, and 1 g / L thiourea. Apply a peak current density of 8 mA / cm² at a temperature of 50°C and a pH of 4 (adjusted with H₂SO₄). 2 A pulsed current with a duty cycle of 50% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 500 nm.

[0055] Step 5: Perform surface planarization on the cobalt-filled dielectric layer structure using chemical mechanical polishing at a pressure of 4 psi to remove excess cobalt layer from the surface of the dielectric layer, retaining only the cobalt structure located inside the vias and trenches to form a cobalt-dielectric layer composite structure.

[0056] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in the cobalt forming strip-shaped metal lines in the trenches and columnar connectors in the vias. The strip-shaped metal lines and columnar connectors are integrally formed. The edge spacing between adjacent strip-shaped metal lines is 25nm, the linewidth deviation is less than 5nm, and the alignment deviation between the vias and the underlying structure is less than 5nm. This ultimately forms high-density metal interconnect lines that meet the requirements of 3nm and below process technology.

[0057] Example 4:

[0058] Step 1: Form a via structure with a diameter of 20 nm and an aspect ratio of 6:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure;

[0059] Step 2: The surface of the dielectric layer substrate with a through-hole structure is activated by NH3 plasma for 30s, 100W, and 50mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0060] Step 3: On the inner surface of the through-hole of the activated medium layer structure rich in nitrogen active sites, an atomic layer deposition technique is used to deposit a 5 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 150 °C and a pressure of 5 mTorr, to obtain a medium layer structure with a cobalt seed layer.

[0061] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 55 g / L cobalt sulfate heptahydrate, 20 g / L citric acid, 1 g / L polyethylene glycol, and 0.1 g / L thiourea. Apply a peak current density of 2 mA / cm² at a temperature of 40°C and a pH of 3 (adjusted with H₂SO₄). 2 A pulsed current with a duty cycle of 30% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 100 nm.

[0062] Step 5: Perform surface planarization on the dielectric layer structure after cobalt filling. Use reactive ion etching (Cl2 / BCl3 plasma, etching rate of 30nm / min) to remove the excess cobalt layer on the surface of the dielectric layer, leaving only the cobalt structure inside the vias and trenches to form a cobalt-dielectric layer composite structure.

[0063] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in the cobalt forming strip-shaped metal lines in the trenches and columnar connectors in the vias. The strip-shaped metal lines and columnar connectors are integrally formed. The edge spacing between adjacent strip-shaped metal lines is 20nm, the linewidth deviation is less than 5nm, and the alignment deviation between the vias and the underlying structure is less than 5nm. This ultimately forms high-density metal interconnect lines that meet the requirements of 3nm and below process technology.

[0064] Example 5:

[0065] This embodiment provides a cobalt electrodeposition method for forming a semi-damascus metal interconnect, the method comprising the following steps:

[0066] Step 1: Form a via structure with a diameter of 35 nm and an aspect ratio of 7:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure;

[0067] Step 2: The surface of the dielectric layer substrate with through-hole structure is activated by NH3 plasma for 45s, 150W, and 75mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0068] Step 3: On the inner surface of the through-hole of the activated medium layer structure rich in nitrogen active sites, an atomic layer deposition technique is used to deposit a 10 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 200 °C and a pressure of 7.5 mTorr, to obtain a medium layer structure with a cobalt seed layer.

[0069] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 85 g / L cobalt sulfate heptahydrate, 30 g / L citric acid, 3 g / L polyethylene glycol, and 0.55 g / L thiourea. Apply a peak current density of 5 mA / cm² at a temperature of 45°C and a pH of 3.5 (adjusted with H₂SO₄). 2 A pulsed current with a duty cycle of 40% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 300 nm.

[0070] Step 5: Perform surface planarization on the dielectric layer structure after cobalt filling. Use reactive ion etching (Cl2 / BCl3 plasma, etching rate of 40nm / min) to remove the excess cobalt layer on the surface of the dielectric layer, leaving only the cobalt structure inside the vias and trenches to form a cobalt-dielectric layer composite structure.

[0071] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in the cobalt forming strip-shaped metal lines in the trenches and columnar connectors in the vias. The strip-shaped metal lines and columnar connectors are integrally formed. The edge spacing between adjacent strip-shaped metal lines is 25nm, the linewidth deviation is less than 5nm, and the alignment deviation between the vias and the underlying structure is less than 5nm. This ultimately forms high-density metal interconnect lines that meet the requirements of 3nm and below process technology.

[0072] Example 6:

[0073] This embodiment provides a cobalt electrodeposition method for forming a semi-damascus metal interconnect, the method comprising the following steps:

[0074] Step 1: Form a via structure with a diameter of 50 nm and an aspect ratio of 8:1 in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, thereby obtaining a dielectric layer substrate with a via structure.

[0075] Step 2: The surface of the dielectric layer substrate with a through-hole structure is activated by NH3 plasma for 60s, 200W, and 100mTorr to obtain an activated dielectric layer structure with nitrogen-rich active sites on the surface.

[0076] Step 3: On the inner surface of the through-hole of the activated medium layer structure with nitrogen-rich active sites, an atomic layer deposition technique is used to deposit a 15 nm thick and continuously covered cobalt seed layer with bis(cyclopentadienyl)cobalt as a precursor at a temperature of 250 °C and a pressure of 10 mTorr, thus obtaining a medium layer structure with a cobalt seed layer.

[0077] Step 4: Place the dielectric layer structure with the cobalt seed layer in a custom electrodeposition tank. Use a sulfate electrolyte system consisting of 115 g / L cobalt sulfate heptahydrate, 40 g / L citric acid, 5 g / L polyethylene glycol, and 1 g / L thiourea. Apply a peak current density of 8 mA / cm² at a temperature of 50°C and a pH of 4 (adjusted with H₂SO₄). 2A pulsed current with a duty cycle of 50% is applied; cobalt ions grow in a bottom-up manner under the action of the pulsed electric field, forming a cobalt-filled dielectric layer structure with a cobalt layer thickness of 500 nm.

[0078] Step 5: Perform surface planarization on the dielectric layer structure after cobalt filling. Use reactive ion etching (Cl2 / BCl3 plasma, etching rate of 50nm / min) to remove the excess cobalt layer on the surface of the dielectric layer, leaving only the cobalt structure inside the vias and trenches to form a cobalt-dielectric layer composite structure.

[0079] Step 6: Using a cobalt-dielectric layer composite structure, a self-aligned mask is created. Reverse etching is performed using a Cl2 / BCl3 / O2 mixed plasma (volume ratio 3:1:0.2) at a radio frequency power of 200W, a gas pressure of 15mTorr, and an etching rate of 40nm / min until the SiCN / SiCO composite low-k dielectric layer surrounding the cobalt structure is completely removed. This results in the cobalt in the trenches forming strip-shaped metal lines and the cobalt in the vias forming columnar connectors. The strip-shaped metal lines and columnar connectors are integrally formed. The edge spacing between adjacent strip-shaped metal lines is 30nm, the linewidth deviation is less than 5nm, and the alignment deviation between the vias and the underlying structure is less than 5nm. Finally, high-density metal interconnect lines that meet the process requirements of 3nm and below are formed.

[0080] To verify the effectiveness and superiority of the cobalt electrodeposition method proposed in this invention, a systematic comparative experimental scheme was designed to evaluate the advantages of the cobalt electrodeposition method (Examples 1-3) proposed in this invention over the existing atomic layer deposition (ALD) ruthenium method in terms of deposition efficiency.

[0081] Please see Figure 5 This invention conducted deposition kinetic experiments on existing technologies (atomic layer deposition (ALD) ruthenium method, using the +2 valence precursor Ru(EtCp)2) and Examples 1 to 3 of this invention to evaluate their deposition efficiency. Figure 5 As shown, the performance gap is already apparent within the first 5 minutes of deposition: existing technologies, limited by the inherent mechanism of cycle-by-cycle reaction, can only increase the thickness to 1.5 nm; while the three embodiments of this invention, thanks to the high-speed bulk phase growth advantage of electrodeposition, have achieved thicknesses of 77.5 nm, 91 nm and 109 nm respectively, achieving a lead of orders of magnitude.

[0082] Meanwhile, as deposition time extends to critical points in industrial production, the performance gap widens further: existing technologies require over 1 hour to deposit a target thickness of 200nm, severely restricting production line cycle time; while Example 1 of this invention achieves the same result in just 5.7 minutes, and Examples 2 and 3 further reduce the time to 4.8 minutes and 4.1 minutes, respectively. This significant efficiency improvement demonstrates that the cobalt electrodeposition method provided by this invention is not a gradual improvement on the traditional ALD method, but rather a fundamental methodological revolution that replaces "surface layer-by-layer reaction" with "electrodeposition bulk phase growth," setting a new benchmark for large-scale mass production efficiency in semiconductor manufacturing.

[0083] Please see Figure 6 This invention evaluates the high aspect ratio via filling capability of existing technologies (atomic layer deposition (ALD) ruthenium method, using the +2 valence precursor Ru(EtCp)2) and Examples 1-3 of this invention, to verify the method window and reliability of this invention in high-density interconnect applications. Figure 6 As shown, when the aspect ratio of the via is 6:1, the traditional ALD method has a step coverage rate of 82% due to the limitations of precursor delivery and the problem of nucleation delay, and the filling quality has declined significantly. However, the step coverage rate of the three embodiments of the present invention is maintained above 97% (97% in Embodiment 1, 98% in Embodiment 2, and 98% in Embodiment 3), and the filling quality remains perfect.

[0084] As the structural complexity increases to an aspect ratio of 8:1, the performance gap undergoes a qualitative change: the step coverage of the traditional ALD method plummets to 55%, and the fill quality score is only 4 points (discontinuous at the bottom), making it impossible to form a reliable electrical connection; while the method of the present invention has extremely significant advantages. The step coverage of Example 3 is still as high as 97%, and Examples 1 and 2 also reach 94% and 96% respectively, and their fill quality scores are all maintained at an excellent level of 9-10 points.

[0085] When faced with ultra-high aspect ratio structures of 10:1, the traditional ALD method is almost ineffective (step coverage of 25%), while Embodiment 3 of the present invention can still maintain a step coverage of 95%. The step coverage difference of more than 70 percentage points and the near-perfect filling quality retention capability prove that the cobalt electrodeposition method provided by the present invention is not a simple optimization of the existing method, but a fundamental breakthrough in the metallization capability of high aspect ratio structures through the synergistic technical route of "NH3 plasma activation + cobalt seed layer + pulse electrodeposition", which provides a foundation for advancing the semi-damascus method to below 3nm and even more advanced technology nodes.

[0086] It should be noted that the step coverage is: film thickness at the bottom of the via / film thickness at the top of the via × 100%. The step coverage quantifies the film thickness uniformity in high aspect ratio structures, and 100% indicates perfect uniformity.

[0087] exist Figure 6 In the control group, a conventional atomic layer deposition method was used with Ru(EtCp)2 precursor.

[0088] Experimental group 1: The cobalt electrodeposition method of Example 1 of this invention was used, with specific parameters including: via diameter 20 nm, NH3 plasma activation time 30 s, cobalt seed layer thickness 5 nm, and pulse current density 2 mA / cm². 2 Duty cycle 30%;

[0089] Experimental group 2 employed the cobalt electrodeposition method described in Example 2 of this invention, with specific parameters including: via diameter 35 nm, NH3 plasma activation time 45 s, cobalt seed layer thickness 10 nm, and pulsed current density 5 mA / cm². 2 Duty cycle 40%;

[0090] Experimental group 3: The cobalt electrodeposition method of Example 3 of this invention was used, with specific parameters including: via diameter 50 nm, NH3 plasma activation time 60 s, cobalt seed layer thickness 15 nm, and pulse current density 8 mA / cm². 2 Duty cycle 50%.

[0091] Please see Figure 7 This invention compares the electrical performance of traditional atomic layer deposition (ALD) ruthenium methods with those of Examples 1-3 of this invention to evaluate their applicability in metal interconnect technology. Figure 7 As shown, when the aspect ratio of the via is 5:1, the equivalent interconnect resistivity of the traditional ALD method has risen to 13.3 μΩ·cm due to the difficulty of precursor adsorption at the bottom of the via and the delay in nucleation; while the resistivity of the three embodiments of the present invention is stable below 8.3 μΩ·cm (Embodiments 2 and 3 are even lower than 8 μΩ·cm).

[0092] As interconnect structures are further miniaturized to the more challenging 8:1 aspect ratio, the performance gap widens dramatically: the resistivity of the conventional ALD method soars to 20.5 μΩ·cm, an increase of over 57%; in contrast, the embodiments of the present invention, thanks to their unique bottom-up filling mechanism, maintain excellent and stable electrical performance—the resistivity of Example 3 is only 7.9 μΩ·cm, with almost no degradation, while the resistivities of Examples 1 and 2 are only 8.5 μΩ·cm and 8.9 μΩ·cm, respectively.

[0093] The resistivity difference of up to 12.6 μΩ·cm fully demonstrates that the cobalt electrodeposition method provided by this invention is not a simple optimization of method parameters, but rather a fundamental solution to the reliability problem of metal filling under high aspect ratio structures through the synergistic effect of cobalt electrodeposition and pulsed current, surface activation and other technologies. It achieves a qualitative leap from "difficult to fill" to "perfect filling", laying a solid foundation for high-density, high-performance interconnects in 3nm and below processes.

[0094] It should be understood that although the steps in the flowcharts of the various embodiments of the present invention are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the various embodiments may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.

[0095] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A cobalt electrodeposition method for forming a semi-damascene metal interconnect, characterized by, The method comprises the following steps: Step 1, forming a via structure in a composite low-k dielectric layer composed of SiCN and SiCO by plasma etching, to obtain a dielectric layer substrate with a via structure; Step 2, performing NH3 plasma activation treatment on the surface of the dielectric layer substrate with a via structure, to obtain an activated dielectric layer structure with a surface rich in nitrogen active sites; Step 3, depositing a continuous cobalt seed layer on the inner surface of the via of the activated dielectric layer structure with a surface rich in nitrogen active sites by atomic layer deposition technology, using bis(cyclopentadienyl) cobalt as a precursor, to obtain a dielectric layer structure with a cobalt seed layer; Step 4, placing the dielectric layer structure with a cobalt seed layer in a customized electrodeposition tank, using a sulfate electrolyte system composed of cobalt sulfate heptahydrate, citric acid, polyethylene glycol and thiourea, and applying a pulse current; Cobalt ions grow from bottom to top under the action of a pulse electric field, to obtain a dielectric layer structure filled with cobalt; Step 5, sequentially performing polishing and reverse etching treatment on the dielectric layer structure filled with cobalt, to obtain high-density metal interconnection lines; In the process of obtaining high-density metal interconnection lines, the following sub-steps are specifically included: Performing surface planarization treatment on the dielectric layer structure filled with cobalt, using chemical mechanical polishing or reactive ion etching, to remove the excess cobalt layer on the surface of the dielectric layer, and only keep the cobalt structure inside the via and trench, to form a cobalt-dielectric layer composite structure; Using the cobalt-dielectric layer composite structure as a self-aligned mask, performing reverse etching treatment using Cl2 / BCl3 / O2 mixed plasma, until the SiCN / SiCO composite low-k dielectric layer around the cobalt structure is completely removed, so that the cobalt in the trench forms a strip-shaped metal line, and the cobalt in the via forms a columnar connecting body, and the strip-shaped metal line and the columnar connecting body are integrally formed.

2. The cobalt electrodeposition method for forming semi-damascene metal interconnects of claim 1 wherein, In the process of obtaining the dielectric layer substrate with a via structure in step 1, the diameter of the via is 20-50 nm, and the aspect ratio of the via is 6:1-8:

1.

3. The cobalt electrodeposition method for forming semi-damascene metal interconnects of claim 2, wherein, In the process of obtaining the activated dielectric layer structure with a surface rich in nitrogen active sites in step 2, the NH3 plasma activation treatment is performed for 30-60 s, the power is 100-200 W, and the gas pressure is 50-100 mTorr.

4. The cobalt electrodeposition method for forming semi-damascene metal interconnects of claim 3, wherein, In the process of obtaining the dielectric layer structure with a cobalt seed layer in step 3, the deposition temperature is 150-250℃, the gas pressure is 5-10 mTorr, and the thickness of the cobalt seed layer is 5-15 nm.

5. The cobalt electrodeposition method for forming semi-damascene metal interconnects of claim 4, wherein, In the process of obtaining the medium layer structure filled with cobalt in the step 4, the concentration of cobalt sulfate heptahydrate is 55-115 g / L, the concentration of citric acid is 20-40 g / L, the concentration of polyethylene glycol is 1-5 g / L, the concentration of thiourea is 0.1-1 g / L, the peak current density is 2-8 mA / cm 2 , the duty cycle is 30-50%, and the thickness of the cobalt layer in the medium layer structure filled with cobalt is 100-500 nm.

6. The cobalt electrodeposition process for forming semi-damascene metal interconnects of claim 1 wherein, In the process of obtaining the cobalt-dielectric layer composite structure, the pressure of chemical mechanical polishing is 2-4 psi, and the reactive ion etching uses Cl2 / BCl3 plasma, and the etching rate is 30-50 nm / min.

7. The cobalt electrodeposition method for forming semi-damascene metal interconnects of claim 6, wherein, In the process of obtaining high-density metal interconnection lines, the volume ratio of Cl2 / BCl3 / O2 mixed plasma is 3:1:0.2, the radio frequency power is 200-300 W, the gas pressure is 15-25 mTorr, the etching rate is 40-60 nm / min, the edge distance between adjacent strip-shaped metal lines is 20-30 nm, the line width deviation is less than 5 nm, and the alignment deviation between the via and the lower structure is less than 5 nm.

8. A semi-damascene metal interconnect structure formed by a cobalt electrodeposition process, characterized by, The semi-damascene metal interconnection structure is prepared by the cobalt electrodeposition method for forming semi-damascene metal interconnection according to any one of claims 1 to 7.

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