CN102808150A - Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness and its preparation process - Google Patents

Abstract

A Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness and a preparation process thereof belong to the field of new materials. Under the guidance of a cluster model based on a stable solid solution, the selection and the addition of Cu film alloying elements are determined, and factors such as mixing enthalpy, cluster structure, atomic radius size and the like are comprehensively considered, so that the solid solution alloy film with high thermal stability and low chemical reaction activity is formed. The solid solution structure avoids the increase of resistivity caused by the precipitation of a large amount of solute elements; the introduction of the element Nb with large atomic radius can effectively prevent mutual diffusion between Cu and surrounding media, and the addition of Nb in proportion to the second element Ni can greatly reduce the addition of Nb, thereby greatly reducing the electron scattering effect caused by large atoms, being beneficial to stabilizing a Cu film and ensuring that the resistivity of the Cu film is influenced to the minimum. The alloy can be expected to have both diffusion barrier effect and high-temperature stability.

Description

Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness and its preparation process

technical field

The invention relates to a Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness and its preparation process. The Cu-Ni-Nb ternary alloy film uses Ni as its main alloying element, and needs to add a small amount of The third component, Nb, belongs to the field of new materials.

Background technique

Copper has low resistivity and good resistance to electromigration, and is widely used as an interconnect metal in various VLSIs. However, the diffusion of Cu and the reaction between it and the surrounding medium have always prevented it from exerting its excellent performance to the maximum. For example, Cu can react with silicon or silicon oxide at a relatively low temperature (about 200 ° C). cause damage to electronic components. In order to solve the above problems, it is necessary to add a diffusion barrier layer around the Cu wire. With the development of large-scale integrated circuits, the feature size of the device is gradually reduced, and the thickness of the diffusion barrier layer is required to be correspondingly reduced. In the scale of several nanometers, it is necessary to achieve the diffusion barrier effect and maintain high thermal stability. However, the traditional preparation process of diffusion barrier layer has encountered great difficulties. Therefore, a method for alloying the Cu seed layer before electroplating Cu wires is proposed. The feature of this method is that there is no need to prepare a special diffusion barrier layer. Certain alloying elements are selected to be added directly when sputtering the copper seed layer. The added elements The amount of Cu should be small and not combined with Cu, so that it can act as a diffusion barrier, improve thermal stability, and have no negative impact on the overall resistivity of the interconnection.

In the early research, the selected doping elements generally have a strong ability to bind oxygen, such as Mg and Al. After heat treatment, a thin passivation layer can be formed on the surface and interface of the film, compared with pure Cu film. , the binding capacity of the film-base interface is enhanced. However, the interface passivation layer formed in this way is relatively thick (about 20nm), and with the gradual reduction of chip feature size (<45nm), they have been unable to meet the development of interconnection technology.

The existing literature mainly focuses on adding insoluble metal elements with large atomic radii to copper. Due to the low solid solubility of the added metal elements, it is mainly located outside the Cu crystal lattice, grain boundaries and film defects. This can effectively reduce the resistivity increase caused by copper lattice distortion while blocking Cu diffusion and improving the thermal stability of the film. However, in actual research, it is found that the pinning effect of the precipitated second phase makes it impossible to eliminate a large number of columnar grains, dislocations and grain boundaries in the sputtered film, but instead increases the electron scattering of the copper film, which eventually leads to sputtered Cu film The resistivity cannot be reduced to the ideal range by subsequent annealing.

At present, there are few studies on the addition of Nb elements alone in Cu films. T. Mahalingam et al ^{. [2]} coated Cu films with different atomic percentages of Nb on cleaned glass sheets, among which the Cu films containing Nb2.7at.% Copper film resistivity is the lowest, but still maintains a relatively high level. It can be seen that adding Nb directly to the sputtered Cu film is not ideal.

In addition, it is difficult to determine the amount of insoluble metal elements added. If the addition amount is too small, the effect of effective diffusion barrier cannot be achieved, and if the addition amount is too large, the resistivity will increase significantly. There is a lack of theoretical guidance on how to design the amount of added elements.

Based on the above deficiencies, the present invention proposes a new dual-element co-addition alloying method based on a stable solid solution cluster model, and prepares an alloyed Cu film with low resistivity and high chemical inertness by selecting an appropriate combination of two types of elements.

Contents of the invention

In order to overcome the deficiency of the existing non-diffusion barrier Cu film added with refractory elements, the present invention prepares a dual-element co-added ternary Cu alloy film with high chemical inertness and low resistivity.

The technical solution of the present invention is: a Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness, adding a certain atomic percentage of Ni and Nb to the Cu film, Ni as a solid solution element, and Nb as a diffusion Blocking elements; Nb and Cu have a positive mixing enthalpy of 3 kJ/mol, and Ni has a negative mixing enthalpy of -30 kJ/mol; the addition ratio of Nb/Ni maintains the atomic percentage range of 0.02~0.70%; the atomic percentage of the total amount of NiNb added 0.20~1.50%.

The preparation process of the described Cu-Ni-Nb ternary alloy film with low resistivity and high chemical inertness adopts the following steps:

(1) Preparation of alloy sputtering target, the steps are as follows:

1. Prepare materials: according to the above-mentioned Ni and Nb atomic percentages, take the value of each component, stand-by, and the purity of Ni and Nb metal raw materials is more than 99.99%;

②Smelting of Ni-Nb alloy ingots: put the metal mixture in the water-cooled copper crucible of the melting furnace, and use the method of vacuum arc melting to melt under the protection of argon. First, vacuumize to 10 ^-2 Pa, and then fill Argon gas to a pressure of 0.03±0.01MPa, the control range of the melting current density is 150±10A/cm ² , after melting, continue melting for 10 seconds, turn off the power, let the alloy cool to room temperature with the copper crucible, and then turn it over , put it back in the water-cooled copper crucible, and carry out the second smelting; the foregoing process is smelted repeatedly at least 3 times to obtain a Ni-Nb alloy ingot with uniform composition;

③Preparation of Ni-Nb alloy rods: Place Ni-Nb alloy ingots in a water-cooled copper crucible connected with negative pressure suction casting equipment, and melt the alloys by the above-mentioned vacuum arc melting method under the protection of argon, and first evacuate to 10 ^-2 Pa, then filled with argon until the air pressure is 0.03±0.01MPa, the current density used for melting is 150±10A/cm ² , after melting, continue melting for 10 seconds, power off, and open the negative pressure suction casting device at the same time, let the alloy The melt is filled into a cylindrical copper mold cavity, cooled to room temperature, and a Ni-Nb alloy rod of a certain specification is obtained;

④Preparation of alloy patches: Cut alloy rods into small alloy pieces of required thickness with a low-speed saw;

⑤Preparation of alloy sputtering target: Paste the Ni-Nb alloy sheet on the basic Cu target with a purity of 99.999% for sputtering with conductive silver glue, or directly inlay the Ni-Nb alloy sheet into a hole with a purity of 99.999% The composite alloy sputtering target is made on the basic Cu target.

(2) Preparation of multi-component co-doped Cu film, the steps are as follows:

①Cleaning of Si substrates prepared by magnetron sputtering thin films; the (100) oriented monocrystalline silicon wafers were ultrasonically cleaned with acetone, alcohol and deionized water, and then soaked in 5% HF for 2 to 3 minutes. Blow dry with _N2 and place in a vacuum chamber;

②The magnetron sputtering equipment draws a vacuum; after the sample and the target are placed in the vacuum chamber, the mechanical pump of the equipment is roughly evacuated to below 5Pa, and then the molecular pump is used for fine evacuation, and the vacuum degree is evacuated to 5.4×10 ^-4 Pa;

③ After the vacuum degree reaches the required high vacuum, fill in argon gas to a pressure of about 2Pa to let the target glow, then adjust the flow rate of argon gas to 8.0Sccm, adjust the working pressure to 0.4Pa, sputtering power 75w, and the base distance of the target is 8-12cm, the sputtering time is 25min, after the sputtering is completed, the equipment is cooled for 30min, and the ternary Cu alloy film sample is taken out.

In the above technical solution, Ni is selected as the main alloying element, which is completely miscible with Cu, and an appropriate amount of large atomic radius diffusion barrier element Nb is added to prepare a Cu-Ni-Nb film, and the resistivity and thermal stability of the alloy Cu film are measured. Since the alloying elements are completely dissolved or most of them are dissolved in the Cu lattice, the Cu film has high thermal stability and low chemical reactivity, avoiding the increase in resistivity caused by the large precipitation of solute elements. ; The introduction of Nb, a large atomic radius element, can effectively block the interdiffusion between Cu and the surrounding medium, and the proportional addition of the second component Ni can greatly reduce the amount of Nb added, thereby reducing the large The electron scattering effect caused by the atoms themselves is beneficial to stabilize the Cu film while ensuring that its resistivity is minimally affected. Such alloys can be expected to have both diffusion barrier effect and high temperature stability.

The advantages of the present invention are: 1. The selection and addition of alloying elements in the Cu film without a diffusion barrier layer are all carried out under the guidance of theory, and the solid solution element Ni Alloyed Cu films co-added with diffusion barrier element Nb. ②Double element co-added Cu alloy film has the characteristics of a stable solid solution. After annealing at 400℃/40h, the resistivity of the grain growth in the film remains at a low level, and the grain grows quickly during the annealing process, which can be greatly improved. The increased electron scattering effects such as dislocations and grain boundaries are eliminated, so that the resistivity is maintained at a low level. ③The addition of the diffusion barrier element Nb is greatly reduced, which can be reduced to 0.01at % (0.03wt %), which will greatly reduce the electron scattering caused by the large atoms themselves, which is conducive to stabilizing the Cu film while maintaining it. The resistivity is minimally affected.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with technical solutions.

The preparation process steps are described below taking the composition of Cu _99.68 Ni _0.29 Nb _0.03 (atomic percent) [Cu _99.69 Ni _0.27 Nb _0.04 (weight percent)] as an example:

The first step, preparation of combined alloy target

Material preparation: According to the Ni and Nb components in the design composition, weigh the value of each component and wait for use. The purity of Ni and Nb metal raw materials is required to be above 99.99%;

Melting of Ni-Nb alloy ingots: put the metal mixture in the water-cooled copper crucible of the arc melting furnace, and use the non-consumable arc melting method to melt under the protection of argon, first vacuumize to 10 ^-2 Pa, Then fill in argon until the pressure is 0.03±0.01MPa, and the control range of the melting current density is 150±10A/cm ² . After melting, continue to melt for 10 seconds, then cut off the power, let the alloy cool down to room temperature with the copper crucible, and then Turn it over, put it in the water-cooled copper crucible again, and carry out the second smelting, so that the smelting is repeated at least 3 times to obtain a Ni-Nb alloy ingot with uniform composition;

Preparation of Ni-Nb alloy rods: Place Ni-Nb alloy ingots in a water-cooled copper crucible connected with negative pressure suction casting equipment, melt the alloys by non-consumable arc melting under the protection of argon, and first evacuate to 10 ^-2 Pa, then fill it with argon until the pressure is 0.03±0.01MPa, the current density used for melting is 150±10A/cm ² , after melting, continue melting for 10 seconds, turn off the power, and turn on the negative pressure suction casting device at the same time, The air pressure difference is 0.01±0.005MPa, and the alloy melt is filled into the cylindrical copper mold cavity, cooled to room temperature, and a Ni-Nb alloy rod with a diameter of 3mm and other specifications is obtained;

Preparation of the alloy patch: the alloy rod was cut into small pieces of alloy with a thickness of about 1 mm with a low-speed saw.

Preparation of the alloy sputtering target: Paste the Ni-Nb alloy sheet on the basic target for sputtering—a Cu target with a purity of 99.999%—with conductive silver glue to make a combined alloy sputtering target.

The second step, Si substrate cleaning prepared by magnetron sputtering thin film

The (100) oriented monocrystalline silicon wafer is ultrasonically cleaned with acetone, alcohol and deionized water, then immersed in 5% HF for 2 to 3 minutes, dried with _{N2 and} placed in a vacuum chamber.

The third step, magnetron sputtering equipment vacuum

After the sample is placed in the vacuum chamber, the mechanical pump of the equipment is roughly evacuated to below 5 Pa, and then the molecular pump is used for fine evacuation, and the vacuum degree is evacuated to 5.4×10 ^-4 Pa.

The fourth step, sputtering process

After the vacuum degree reaches the required high vacuum, fill in argon gas to a pressure of about 2Pa to let the target glow, then adjust the argon gas flow rate to 8.0 sccm, adjust the working pressure to 0.4Pa, sputtering power 75W, and the target base distance is about 10cm. The substrate is neither heated nor artificially cooled during sputtering. The sputtering time is 25 minutes. After the sputtering is completed, the equipment is cooled for 30 minutes, and the Cu alloy film sample is taken out. The thickness of the film was measured to be about 350nm by a step meter. In order to prevent the sample from being oxidized, after the sputtering of the sample is completed, do not take it out as soon as possible, and take out the sample after the equipment cools down for half an hour.

The fifth step, annealing

Vacuum annealing is adopted, the vacuum degree is better than 7×10 ^-4 Pa, the heating rate is about 1°C/s, and it is naturally cooled when the temperature is lowered. First, anneal at 400°C, 500°C, and 600°C for 1 hour respectively. Further perform long-time cycle annealing at 500° C.: 10 hours as one cycle, and perform 4 cycles of long-time annealing for a total of 40 hours.

Step 6. Analysis

The EPMA-1600 electron probe analyzer from Shimadzu Corporation of Japan was used to monitor the composition of the film, and the German Bruker D8 discover thin film X-ray diffractometer (XRD) and Philips TechnaiG2 transmission electron microscope were used to analyze the microstructure of the film. The sheet resistance of the Cu-Ni-Nb film before and after annealing was measured by a double-electrometer four-probe tester.

The contents of Cu, Ni and Nb in the film were analyzed by EPMA as follows: 99.68 at.%, 0.29 at.%, 0.03 at.%. The atomic ratio of Ni and Nb is 12:1.2. The total doping amount in the Cu film is 0.32 at.%. The final composition of the alloy is Cu _99.68 Ni _0.29 Nb _0.03 (atomic percent) Cu _99.69 Ni _0.27 Nb _0.04 (weight percent).

The XRD results show that the Cu-Ni-Nb film was annealed at 400°C, 500°C, and 600°C for 1 hour, and Cu was the main diffraction peak. After 40 hours of long-term vacuum annealing at 400°C, there was still only the diffraction peak of Cu, which was not detected. The diffraction peaks of the Cu-Si compound indicate that the Cu-Ni-Nb film has excellent thermal stability. In addition, comparing the X-ray diffraction spectra before and after annealing, it can be found that: 1. The half-maximum width of the Cu diffraction peak is obviously reduced, and the crystal grains are obviously grown. This is different from the simple addition of Nb, Ru and other elements that are immiscible with copper: Nb, Ru and other elements are precipitated in the copper film and become the second phase that hinders the growth of the grain. Therefore, studies have shown that the sputtered copper film The columnar crystal structure can be maintained to a higher temperature, and the annealed grains do not grow significantly. A large amount of residual stress cannot be recovered during the grain merger growth, and the excessive grain boundaries make the resistivity of this binary Cu alloy film very high. 2. After annealing at different temperatures and times, the Cu peak position did not move significantly, which indicated that the lattice constant remained stable. Both of these phenomena indicate that the added elements are not precipitated from the copper lattice during the annealing process, and the structure of a stable solid solution is maintained.

The results of transmission electron microscopy show that the Cu alloy film in the sputtered state is mainly columnar crystals with a width of about 20-30nm, and there is an intrinsic silicon oxide amorphous layer with a thickness of ~3nm at the interface between the film and the substrate. The cross-sectional sample after 500℃/40h annealing shows that the interface between the film and the substrate remains flat, uniform, without holes, and no Cu-Si compound is formed. At the same time, the intrinsic interface amorphous layer is thickened to ~5nm, columnar The structure disappears, and the grains gradually grow into large grains, which is consistent with the XRD results.

As shown in Attached Table 1, the resistivity of Cu-Ni-Nb film showed a trend of first decreasing and then increasing with the increase of annealing temperature. After ℃/1h annealing, the resistivity increased slightly, about 2.74μΩ-cm. The commonly used stability detection temperature is 500°C, and the resistivity remains at a low level after annealing for 40 hours, about 2.77 μΩ-cm. Therefore, the solid solution Cu alloy film under the guidance of this cluster model effectively protects the continuity of the Cu layer, blocks Cu-Si interdiffusion, and ensures its excellent electrical properties.

Through the above experimental analysis, taking Ni and Nb as co-alloying elements as a typical example, the following results can be drawn: In the scheme of the present invention, the cluster model of stable solid solution alloy is used, and the mixing enthalpy, cluster structure and atomic size are comprehensively considered. Factors, the scheme of co-alloying with Cu miscible elements Ni and diffusion barrier elements is selected, and Cu alloy films without diffusion barrier layers can be prepared. By ensuring the alloy ratio and content, we have obtained high chemical inertness that can meet the needs of the industry. and Cu alloy film with low resistivity.

Attached table 1 Cu _99.68 Ni _0.29 Nb _0.03 film resistivity changes under different annealing conditions

Claims (2)

1. one kind has low-resistivity and high chemically inert Cu-Ni-Nb ternary alloy film, it is characterized in that: in the Cu film, add the Ni and the Nb of certain atomic percent, Ni is as solid solution element, and Nb is as the diffusion barrier element; Nb and Cu are positive enthalpy of mixing 3 kJ/mol, are negative enthalpy of mixing-30 kJ/mol with Ni; It is 0.02 ~ 0.70% that the adding proportion of Nb/Ni keeps the atomic percent proportional range; The atomic percent that NiNb adds total amount is 0.20 ~ 1.50%.

2. the preparation technology with low-resistivity and high chemically inert Cu-Ni-Nb ternary alloy film according to claim 1, it is characterized in that: it adopts the following step:

(1) preparation alloy sputtering target, its step is following:

1. get the raw materials ready: according to Ni recited above, Nb atomic percent, take by weighing each constituent element value, for use, the purity of Ni, Nb raw metal is more than 99.99%;

2. the melting of Ni-Nb alloy pig: the compound of metal is placed in the water jacketed copper crucible of smelting furnace, adopts the method for vacuum arc melting under the protection of argon gas, to carry out melting, at first be evacuated to 10 ^-2Pa, charging into argon gas to air pressure then is 0.03 ± 0.01MPa, the span of control of melting current density is 150 ± 10A/cm ², after the fusing, continuing 10 seconds of melting again, outage lets alloy be cooled to room temperature with copper crucible, then with its upset, places again in the water jacketed copper crucible, carries out the melting second time; Aforementioned process melt back at least 3 times obtains the uniform Ni-Nb alloy pig of composition;

3. the preparation of Ni-Nb alloy bar: the Ni-Nb alloy pig is placed in the water jacketed copper crucible that is connected with negative pressure suction casting equipment, under argon shield,, at first be evacuated to 10 with above-mentioned vacuum arc melting method molten alloy ^-2Pa, charging into argon gas to air pressure then is 0.03 ± 0.01MPa, the used current density of melting is 150 ± 10A/cm ², after the fusing, continuing 10 seconds of melting again, the negative pressure absorbing and casting device is opened in outage simultaneously, lets alloy melt charge in the cylindrical, copper model cavity, is cooled to room temperature, obtains the Ni-Nb alloy bar of certain specification;

4. the preparation of alloy paster: the alloy small pieces that alloy bar are cut into desired thickness with the low speed saw;

5. the preparation of alloy sputtering target: using conductive silver glue that the Ni-Nb alloy slice is sticked on the used purity of sputter is on the 99.999% basic Cu target, and perhaps the Ni-Nb alloy slice directly being mounted to foraminous purity is to process the combined alloy sputtering target material on the 99.999% basic Cu target.

(2) the polynary codoped Cu film of preparation, its step is following:

1. the Si substrate of magnetron sputtering film preparation cleans; The monocrystalline silicon piece of (100) orientation earlier through acetone, alcohol and deionized water ultrasonic cleaning, is put into 5% HF then and soaked 2～3 minutes, adopt N ₂Put into Vakuumkammer after drying up;

2. magnetron sputtering equipment extracting vacuum; After sample and target were all put into Vakuumkammer, the plant machinery pump slightly was evacuated to below the 5Pa, adopted molecular pump to carry out essence then and vacuumized, and vacuum tightness is evacuated to 5.4 * 10 ^-4Pa;

3. after vacuum tightness reaches required high vacuum, charge into argon gas to the air pressure 2Pa, let the target build-up of luminance; Regulate argon flow amount then to 8.0Sccm, operating air pressure modulation 0.4Pa, sputtering power 75w; Target-substrate distance is 8-12cm, and sputtering time is 25min, after sputter finishes; Apparatus cools 30min takes out ternary Cu alloy firm sample.