A method for preparing a single-crystal copper thin film on a wafer

Abstract

The present application relates to the technical field of microelectronic packaging interconnection, in particular to a preparation method of single-crystal copper film on wafer. First, a 100nm Ti layer is magnetron sputtered on a silicon wafer as a barrier layer, and a 400nm Cu layer is sputtered as a seed layer, and a specific structure copper layer is prepared on the silicon wafer by adjusting the current density, plating time and plating solution composition and other plating conditions; then, the single-crystal copper structure is formed by heating for 1-4h under vacuum condition at 300-400 DEG C, thereby establishing a controllable preparation method of single-crystal copper layer on the silicon wafer. The single-crystal copper film prepared by the method has single-crystal copper interconnection circuit prepared on the wafer, which improves the conductive performance and mechanical performance of the circuit, and the single-crystal copper film preparation process can be used in microelectronic interconnection processes in the form of BGA, Flip-chip and the like.

Description

Technical Field

[0001] This invention relates to the field of microelectronic packaging interconnect technology, specifically to a method for preparing a single-crystal copper thin film on a wafer. Background Technology

[0002] Copper diffuses rapidly in SiO2, leading to severe degradation of its dielectric properties. Simultaneously, copper exhibits a strong trapping effect on charge carriers in semiconductors. Both the self-annealing effect of copper and annealing in vacuum heat treatment systems contribute to the growth and diffusion of copper grains, inevitably affecting the electrical characteristics of integrated circuit devices. Furthermore, the adhesion between copper and SiO2 is weak; therefore, an adhesion / diffusion barrier layer is typically deposited before fabricating the seed layer to prevent copper diffusion and increase adhesion between the seed layer and the substrate. Adhesion / diffusion barrier layers are generally made of materials such as Ti, TiW, Ta, TiN, and TiN. Currently, the mainstream process for fabricating the adhesion and seed layers is physical vapor deposition (PVD), followed by electroplating of the third metal layer thin film on the seed layer. The electroplating solution includes a base solution and additives. The base solution provides a favorable electroplating environment and sufficient copper ions, while the additives improve the quality and performance of the metal thin film. Electroplating can cause stress in copper films, which is why the grains of copper films grow larger after electroplating and being left for a period of time. The annealing temperature for industrial pure copper is 500-700℃, while the stress-relief annealing of copper only needs to be around 350℃.

[0003] Existing thin film preparation methods mainly include physical vapor deposition (PEV) (such as evaporation, sputtering, and ion plating) and chemical vapor deposition (CVD) (such as plasma-enhanced chemical vapor deposition and laser chemical vapor deposition). However, these methods have the following characteristics in the thin film preparation process: high temperature and high vacuum are required, the equipment is demanding and expensive, energy consumption is high, and the thin film growth rate is slow. Electroplating is fast and low-cost, but it is difficult to control the thin film growth. Therefore, it is particularly important to be able to prepare single-crystal thin films with the desired preferred orientation, addressing the problems existing in existing thin film preparation methods. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a single-crystal copper thin film on a wafer, which obtains a copper metal thin film with preferred orientation on the wafer, and forms a single-crystal electroplated copper thin film after heat treatment annealing, thereby improving the conductivity and mechanical properties of the circuit.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for preparing a single-crystal copper thin film on a wafer includes the following steps:

[0007] (1) A first metal layer thin film is provided, the first metal layer thin film is prepared by multi-target magnetron sputtering, and the material of the first metal layer thin film is one of Ti, Ta, TiN and TaN;

[0008] (2) A second metal layer thin film is provided, which is prepared by multi-target magnetron sputtering and is made of Cu.

[0009] (3) A third metal layer film is provided, the third metal layer film is prepared by electroplating, and the material of the third metal layer film is Cu;

[0010] The thickness of the first metal layer film is 100 nm, the thickness of the second metal layer film is 400 nm, the thickness of the third metal layer film is 20–100 μm, and the third metal layer film has a specific preferred orientation.

[0011] The wafer, the first metal layer film, the second metal layer film and the third metal layer film assembly are annealed in a vacuum heat treatment system at a temperature of 300-400°C for 1-4 hours.

[0012] After annealing, the grains of the second and third metal layers become larger, the grain orientation of the third metal layer exhibits a preferred orientation, and single crystals appear in the third metal layer.

[0013] The method for preparing a single-crystal copper thin film on a wafer includes the following steps:

[0014] Step 1: The first metal layer film is prepared by sputtering, and the material of the first metal layer film is Ti;

[0015] Step 2: The second metal layer film is prepared by sputtering, and the second metal layer film is Cu;

[0016] Step 3: Electroplating is performed on the second metal layer film to form a four-layer structure combination of wafer, first metal layer film, second metal layer film, and third metal layer film;

[0017] Step 4: Perform vacuum annealing heat treatment on the assembly formed in Step 3. Heat to a certain temperature and set the required heating time to ensure the assembly from Step 3 is fully annealed. The vacuum annealing heat treatment process parameters are as follows: vacuum degree is 10. -4 ~10 -7 Pa, temperature range of 300-400℃, heat preservation time of 1-4h;

[0018] During the annealing process in the composite, a second metal layer film grows on the first metal layer film, and a third metal layer film grows and recrystallizes on the second metal substrate; the thickness of the first metal layer film is 100 nm, the thickness of the second metal layer film is 400 nm, and the thickness of the third metal layer film is 20–100 μm.

[0019] In the method for preparing a single-crystal copper thin film on a wafer, step two involves preparing the third metal layer film using a specific electroplating system, electroplating time, current, and additives. The electroplating solution consists of 200 g / L CuSO4·H2O, 50 g / L 98 wt% sulfuric acid, and Cl... - 40 ppm of electroplating additives and water; the electroplating additives are one or more of the following: 5-20 ppm sodium dipropane sulfonate (SPS), 20-60 ppm polyethylene glycol (PEG400), and 5-40 ppm gelatin; the electroplating process parameters are as follows: current density is 1-18 A / dm³. 2 The electroplating time is 10–240 min, and the stirring speed is 300–600 r / min.

[0020] In the method for preparing single-crystal copper thin films on wafers, in step four, the assembly formed in step three is subjected to vacuum heat treatment until the second metal layer film and the third metal layer film are completely recrystallized and grown.

[0021] The method for preparing single-crystal copper thin films on wafers has the same relationship between coating thickness and annealing time.

[0022] In the method for preparing a single-crystal copper thin film on a wafer, step three involves electroplating with a current density of 1–5 A / dm². 2 The electroplating time is 120–240 min; in step four, the vacuum annealing temperature is 300–350℃ and the annealing time is 120–180 min.

[0023] In the method for preparing a single-crystal copper thin film on a wafer, step three involves electroplating with a current density of 5–10 A / dm². 2 The electroplating time is 60-120 min; in step four, the vacuum annealing temperature is 300-350℃ and the annealing time is 150-220 min.

[0024] In the method for preparing a single-crystal copper thin film on a wafer, step three involves electroplating with a current density of 10–15 A / dm². 2 The electroplating time is 30-60 min; in step four, the vacuum annealing temperature is 320-400℃ and the annealing time is 120-240 min.

[0025] In the method for preparing a single-crystal copper thin film on a wafer, step three involves electroplating with a current density of 15–18 A / dm². 2 The electroplating time is 10-30 min; in step four, the vacuum annealing temperature is 350-400℃ and the annealing time is 120-240 min.

[0026] The idea behind this invention is:

[0027] This invention, after electrodeposition, performs annealing by controlling vacuum and temperature. This releases residual stress from the electrodeposition process while providing thermal stress to promote grain growth and recrystallization, thereby achieving the purpose of preparing single crystals. In integrated circuits, the interconnect delay problem caused by excessively high capacitance and resistance of copper interconnects is becoming increasingly serious. The electrical performance of metal interconnects has become an important factor affecting the development of integrated circuits. Excessive resistance of copper interconnects increases the power consumption of integrated circuits and exacerbates interconnect delays, reducing reliability and ultimately leading to failure. This invention first magnetron sputters a 100nm Ti layer as a barrier layer and a 400nm Cu layer as a seed layer on a silicon wafer. By controlling the electroplating conditions such as current density, electroplating time, electroplating solution composition, and additives, a copper thin film with a specific structure is electroplated on the silicon wafer. Then, under vacuum conditions of 300–400℃, it is heated for 1–4 hours to form a single-crystal copper structure, thus establishing a controllable preparation method for single-crystal copper layers on silicon wafers. The copper single-crystal thin film prepared by the method of the present invention has fewer grain boundaries, avoiding more electron diffraction, resulting in lower resistivity and higher thermal conductivity than polycrystalline copper. At the same time, the mechanical properties of single-crystal copper are also superior to those of polycrystalline copper.

[0028] The advantages and beneficial effects of this invention are as follows:

[0029] 1. This invention proposes a method for preparing single-crystal copper thin films by electrodeposition in microelectronic interconnects. After sequentially sputtering a 100nm Ti barrier layer and a 400nm Cu seed layer on a wafer, a copper metal thin film is electrodeposited on the seed layer by electroplating. This copper metal thin film, after testing, exhibits a specific preferred orientation. Upon heat treatment, the copper film becomes single-crystal, significantly improving its mechanical properties and conductivity.

[0030] 2. The single-crystal copper fabrication process of this invention can be used in microelectronic interconnection processes such as ball grid arrays (BGA) and flip-chip. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the combined structure formed in step three of the first technical solution of the present invention.

[0032] Figure 2 This is a tissue morphology diagram from Embodiment 1 of the present invention. Detailed Implementation

[0033] The described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0034] like Figure 1 As shown, the method for preparing single-crystal copper thin films on Si wafers according to the present invention can be implemented through the following specific process steps:

[0035] Step 1: Prepare a barrier layer of metallic Ti, wherein the metallic Ti is sputtered on a Si wafer with a thickness of 100 nm;

[0036] Step 2: Prepare a polycrystalline Cu seed layer, wherein the polycrystalline Cu is sputtered on a Si wafer with a thickness of 400 nm;

[0037] Step 3: Cut the Si wafer and its barrier and seed layers into 1cm × 1.5cm pieces as samples. Use these samples as cathodes. Select an electroplating solution with the following composition: CuSO4·H2O 200g / L, 98wt% sulfuric acid 50g / L, and Cl... - Using 40 ppm of sodium dithiosulfate (e.g., NaCl, HCl) and the remainder water, with phosphorus-containing copper (e.g., phosphor bronze, tin phosphor bronze, etc.) as the anode, appropriate additives are selected and added to the electroplating solution (one or more of the following: 5-20 ppm sodium dithiosulfate dipropane sulfonate (SPS), 20-60 ppm polyethylene glycol (PEG400), and 5-40 ppm gelatin). The electroplating process parameters are as follows: current density is 1-18 A / dm³. 2 The electroplating time is 10–240 min, and the stirring speed is 300–600 r / min. A copper thin film of 20–100 μm is electroplated on the seed layer. The copper thin film has a specific preferred orientation, which is (220).

[0038] Step 4: The Si wafer, Ti barrier layer, Cu seed layer, and electroplating layer are combined to form a four-layer assembly. This assembly is then placed in an ultrasonic cleaner and cleaned with deionized water.

[0039] Step 5: Perform vacuum heat treatment on the assembly processed in Step 4, selecting a vacuum level of 10. -4 ~10 -7 Pa, annealing temperature is 300-400℃, annealing time is 1-4h, furnace cooling, so that the electroplated layer forms a copper metal single crystal thin film (Singlecrystal copper).

[0040] The present invention will now be further described with reference to specific embodiments.

[0041] Example 1

[0042] like Figure 1As shown, a 4-inch diameter Si wafer was used to sequentially fabricate a titanium / copper conductive layer (titanium barrier layer and copper seed layer) on the Si wafer surface using magnetron sputtering. The thicknesses of the titanium barrier layer and the copper seed layer were 100 nm and 400 nm, respectively. The electroplating solution consisted of 200 g / L CuSO4·H2O, 50 g / L 98 wt% sulfuric acid, 40 ppm NaCl, electroplating additives (10 ppm SPS, 50 ppm PEG, 15 ppm gelatin), and water. The sample was used as the cathode, phosphor bronze as the anode, and the current density was 5 A / dm³. 2 The stirring speed was 300 rpm, the electroplating time was 2 hours, and the copper film thickness was approximately 100 μm. After electroplating, the sample was ultrasonically cleaned in deionized water for 3 minutes. After drying, the sample was placed on a vacuum heating stage and evacuated to a pressure of 1 × 10⁻⁶. -7 After Pa, heat to 300℃ at a heating rate of 100℃ / min and hold for 3 hours. After the time is up, turn off the heating switch and allow the furnace to cool, thus obtaining single-crystal copper for microelectronic interconnect circuits.

[0043] like Figure 2 As shown, after annealing, the grains of the second and third metal layers become larger, the grain orientation of the third metal layer has a preferred orientation, and single crystals appear in the third metal layer.

[0044] Example 2

[0045] like Figure 1 As shown, a titanium / copper conductive layer (titanium barrier layer and copper seed layer) was sequentially fabricated on the surface of a 4-inch Si wafer using magnetron sputtering. The thicknesses of the titanium barrier layer and the copper seed layer were 100 nm and 400 nm, respectively. The electroplating solution consisted of 200 g / L CuSO4·H2O, 50 g / L 98 wt% sulfuric acid, 40 ppm NaCl, electroplating additives (50 ppm PEG, 15 ppm gelatin), and water. The sample was used as the cathode, phosphor bronze as the anode, and the current density was 5 A / dm³. 2 The stirring speed was 400 rpm, the electroplating time was 60 min, and the copper film thickness was approximately 80 μm. After electroplating, the sample was ultrasonically cleaned in deionized water for 3 min. After drying, the sample was placed on a vacuum heating stage and evacuated to a pressure of 1 × 10⁻⁶. -6 After Pa, the temperature was increased to 350℃ at a rate of 100℃ / min and held for 2.5 hours. After the time was up, the heating switch was turned off and the furnace was cooled to obtain twinned copper for microelectronic interconnect circuits. No large grains were observed, and the structure remained twinned.

[0046] Example 3

[0047] like Figure 1As shown, a 4-inch diameter Si wafer was used. Titanium / copper conductive layers (titanium barrier layer and copper seed layer) were sequentially fabricated on the Si wafer surface using magnetron sputtering. The thicknesses of the titanium barrier layer and the copper seed layer were 100 nm and 400 nm, respectively. The electroplating solution consisted of 200 g / L CuSO4·H2O, 50 g / L 98 wt% sulfuric acid, 40 ppm HCl, electroplating additives (50 ppm PEG, 15 ppm gelatin), and water. The sample was used as the cathode, tin-phosphor bronze as the anode, and the current density was 15 A / dm³. 2 The stirring speed was 500 rpm, the electroplating time was 30 min, and the copper film thickness was approximately 50 μm. After electroplating, the sample was ultrasonically cleaned in deionized water for 3 min. After drying, the sample was placed on a vacuum heating stage and evacuated to a pressure of 1 × 10⁻⁶. -5 After Pa, the temperature was increased to 400℃ at a rate of 100℃ / min and held for 2 hours. After the time was up, the heating switch was turned off and the furnace was cooled to obtain twinned copper for microelectronic interconnect circuits. No large grains appeared, and the structure remained twinned.

[0048] In this invention, the electroplating apparatus consists of a power supply with adjustable current and a magnetic stirrer with adjustable rotation speed. A vacuum heat treatment system is employed, which allows for adjustment of the vacuum level. The thickness of the metal layer thin film (barrier layer, seed layer), current density, additives, electroplating time, vacuum level, heating temperature, and heating time are the most significant factors affecting the orientation and growth of the copper metal thin film; other factors have a relatively minor impact. During electroplating, the grain orientation of the third metal layer thin film changes with the film thickness, and the annealing time and temperature also change with the thickness of the electroplated film.

Claims

1. A method for preparing a single-crystal copper thin film on a wafer, characterized in that, Includes the following steps: (1) A first metal layer thin film is provided, the first metal layer thin film is prepared by multi-target magnetron sputtering, and the material of the first metal layer thin film is one of Ti, Ta, TiN and TaN; (2) A second metal layer film is provided, which is prepared by multi-target magnetron sputtering and is made of Cu. (3) Provide a third metal layer film, which is prepared by electroplating and is made of Cu; The thickness of the first metal layer film is 100 nm, the thickness of the second metal layer film is 400 nm, the thickness of the third metal layer film is 20~100 µm, and the third metal layer film has a specific preferred orientation, which refers to (220). The wafer, the first metal layer film, the second metal layer film and the third metal layer film assembly are annealed in a vacuum heat treatment system at a temperature of 300~400℃ for 1~4h. After annealing, the grains of the second and third metal layers become larger, the grain orientation of the third metal layer exhibits a preferred orientation, and single crystals appear in the third metal layer. The third metal layer thin film was prepared using a specific electroplating system, electroplating time, current magnitude, and additives; the electroplating solution consisted of CuSO4·H2O 200 g / L, 98 wt% sulfuric acid 50 g / L, and Cl... - 40 ppm of electroplating additives and water; the electroplating additives are one or more of the following: 5-20 ppm sodium dipropane sulfonate (SPS), 20-60 ppm polyethylene glycol (PEG400), and 5-40 ppm gelatin; the electroplating process parameters are as follows: stirring speed is 300-600 r / min; current density during electroplating is 1-5 A / dm³. 2 The electroplating time is 120~240 min; the vacuum annealing temperature is 300~350℃, and the annealing time is 120~180 min; or, the current density during electroplating is 5~10 A / dm³. 2 The electroplating time is 60~120 min; the vacuum annealing temperature is 300~350℃, and the annealing time is 150~220 min; or, the current density during electroplating is 10~15 A / dm³. 2 The electroplating time is 30-60 min; the vacuum annealing temperature is 320-400℃, and the annealing time is 120-240 min; or, the current density during electroplating is 15-18 A / dm³. 2 The electroplating time is 10~30min; the vacuum annealing temperature is 350~400℃, and the annealing time is 120~240min.

2. The method for preparing a single-crystal copper thin film on a wafer according to claim 1, characterized in that, Includes the following steps: Step 1: The first metal layer film is prepared by sputtering, and the material of the first metal layer film is Ti; Step 2: The second metal layer film is prepared by sputtering, and the second metal layer film is Cu; Step 3: Electroplating is performed on the second metal layer film to form a four-layer structure combination of wafer, first metal layer film, second metal layer film, and third metal layer film; Step 4: Perform vacuum annealing heat treatment on the assembly formed in Step 3. Heat to a certain temperature and set the required heating time to ensure the assembly from Step 3 is fully annealed. The vacuum annealing heat treatment process parameters are as follows: vacuum degree is 10. -4 ~10 - 7 Pa, temperature range of 300~400℃, heat preservation time of 1~4h; During the annealing process in the composite, a second metal layer film is grown on the first metal layer film, and a third metal layer film is grown and recrystallized on the second metal substrate; the thickness of the first metal layer film is 100 nm, the thickness of the second metal layer film is 400 nm, and the thickness of the third metal layer film is 20~100 µm.

3. The method for preparing a single-crystal copper thin film on a wafer according to claim 2, characterized in that, In step four, the composite formed in step three is subjected to vacuum heat treatment until the second and third metal layer films are completely recrystallized and grown.

Images