CN114411233A - A kind of method for rapidly preparing (100) single crystal copper - Google Patents

Abstract

The invention provides a method for rapidly preparing (100) single crystal copper, which is characterized in that while annealing is carried out on a (111) preferred orientation nanometer twin crystal Cu film, an electric field is applied to the film and the film is kept for a certain time, so that crystal grains of the film grow rapidly, and finally the (111) preferred orientation nanometer twin crystal Cu is converted into (100) preferred orientation single crystal Cu. The method of the invention obviously improves the production efficiency of the single crystal Cu, and the prepared single crystal Cu with the (100) preferred orientation and large grain size has the advantages of excellent mechanical property, oxidation resistance, electromigration resistance, thermal stability and the like. The preparation method of the (100) single crystal copper is simple, efficient, low in cost, good in compatibility with the existing microelectronic packaging process and very suitable for large-scale industrial production.

Description

A kind of method for rapidly preparing (100) single crystal copper

technical field

The invention relates to the technical field of microelectronics manufacturing, in particular, to a method for rapidly preparing (100) single crystal copper.

Background technique

Copper (Cu) is currently the most widely used conductor material in microelectronic packaging technology, and is used in Under Bump Metallization (UBM), Redistribution Layer (RDL), chip interconnects and wires Wait. With the development of semiconductor technology, microelectronic packaging technology continues to develop in the direction of miniaturization, and advanced three-dimensional system-in-package puts forward new requirements for the Cu interconnect material used. With the reduction in size and the increase in density, the current density in the microelectronic packaging structure increases, the heat dissipation capacity is weakened, and electromigration failure and high temperature failure are more likely to occur; at the same time, with the reduction of bump size, the intermetallic compounds in the microbump The number of grains of Intermetallic Compound (IMC) and UBM also continues to decrease, even with only one grain, so the anisotropic characteristics of IMC and UBM will be more prominent, which may lead to early failure of micro-bumps and reduced reliability. Traditional polycrystalline Cu cannot solve the above problems, so new materials are needed to fully replace polycrystalline Cu widely used in microelectronic packaging technology.

Single crystal copper has a single preferred orientation, which eliminates the grain boundary structure as a diffusion channel, so it has better anti-electromigration properties than polycrystalline copper; at the same time, single crystal copper does not undergo grain growth and recrystallization, and has more Crystalline Cu has better thermal stability; in addition, the IMC grains formed by the reaction between UBM and solder alloy also have a preferred orientation, which can reduce the formation of Kirkendall voids and improve the reliability of micro-solder joints; Single crystal copper also has the advantages of excellent mechanical properties and low resistivity. Therefore, single crystal Cu is an ideal material for UBM, RDL, and wires in microelectronic packaging technology. In industry, single-crystal Cu is generally prepared by methods such as the Bridgman method to control the solidification process of molten metal. However, it is difficult to obtain thin-film structures with fine patterns such as UBM and RDL required in microelectronic packaging technology by this method. At the same time, the high temperature of the casting process will cause serious thermal damage to the semiconductor device, so it has important engineering practical value to develop a single crystal Cu preparation method suitable for microelectronic packaging.

In the prior art, the method for preparing single crystal Cu in the microelectronic packaging technology is mainly as follows:

International Patent Application Publication No. WO2020006761 discloses a method for preparing (100) single-crystal Cu thin film by electrodeposition. ) single crystal Cu thin films. However, the plating solution used in this method contains a variety of additives. On the one hand, the composition is complex, which makes it difficult to guarantee the stability of the plating solution. On the other hand, the additives will remain in the Cu film as impurities, affecting the film properties. The high stirring speed of the plating solution can only be achieved by using a rotating disk electrode. The electroplating area of the rotating disk electrode is very small, which makes it difficult to deposit large-area (100) single-crystal Cu thin films with this method, and the low efficiency is not suitable for industrialization. In addition, the single crystal Cu grains obtained by this method are about 10-20 μm, which means that there are still many grain boundaries, thus affecting its electrical conductivity, mechanical properties and electromigration resistance.

There is also a technology to obtain (100) single crystal Cu pillars or films by subjecting the prepared nanotwinned Cu pillars or films with (111) preferred orientation to high temperature annealing for a long time. However, semiconductor chips and devices cannot withstand long-term high-temperature annealing, which will cause serious thermal damage; and excessive annealing time will cause problems such as warping of chips and substrates; in addition, long process time will also increase process costs and increase production efficiency. Low. Therefore, it is not economical for industrial production.

In summary, the existing single crystal Cu preparation methods suitable for microelectronic packaging technology have problems such as complex preparation equipment, large thermal damage, and low quality of the single crystal obtained, making it difficult for single crystal Cu to be applied in microelectronic packaging technology on a large scale. Therefore, it is necessary to provide a method for preparing single crystal Cu with simple preparation device, little influence on chips and devices, high efficiency and high quality, so that single crystal Cu can be applied in the field of microelectronics manufacturing.

SUMMARY OF THE INVENTION

According to the above-mentioned technical problems such as the complexity of the single crystal Cu preparation method in the existing microelectronic packaging technology, the low quality of the manufactured single crystal and the large thermal damage, a method for rapidly preparing (100) single crystal copper is provided. . The present invention mainly generates stress and strain in the nano-twinned Cu in the (111) direction under the action of the electric current by applying an electric field during the annealing process of the nano-twinned Cu in the (111) preferred orientation, and promotes the crystal grains in the (100) direction in the Among them, nucleation and growth, to rapidly form (100) preferentially oriented single crystal Cu. This method significantly accelerates the conversion rate of (111) nanotwinned Cu to (100) single crystal Cu at lower process temperatures with electric current as an additional energy input.

The technical means adopted in the present invention are as follows:

A method for rapidly preparing (100) single crystal copper, characterized in that a (111) nano-twinned Cu with a preferred orientation is provided, and while the nano-twinned Cu is annealed, a current is directly/indirectly applied to it The density is kept for a certain period of time, so that the grains grow rapidly and transform into (100) preferred orientation, and finally the (111) preferred orientation of nano-twinned Cu is transformed into (100) preferred orientation of single crystal Cu.

Further, the method specifically includes the following steps:

Step 1: provide a nano-twinned Cu, the grains are columnar and have a (111) preferred orientation;

Step 2: connecting the nano-twinned Cu described in Step 1 with a current source to form a complete path;

Step 3: Heat and anneal the nano-twinned Cu connected to the wires described in step 2, and at the same time directly/indirectly apply a certain DC or pulse current to maintain a constant temperature and current density for a period of time until the nano-twinned Cu is All of them are converted into single crystal Cu; wherein, the single crystal Cu is formed by the rapid growth of crystal grains during the annealing process of nano-twinned Cu, and has a single (100) preferred orientation.

The single-crystal Cu is formed by the rapid growth of crystal grains during the annealing process of nano-twinned Cu. Under the condition that other conditions remain unchanged, the higher the applied current density, the faster the nano-twinned Cu forms single-crystal Cu. .

The direct/indirect application of current means that the nano-twinned Cu can be directly connected to the current source through the wire, or the nano-twinned Cu can be used as UBM to form a metallurgical connection with the UBM on the other side with solder, and then the current can be connected to the current through the wire. source connected.

Further, the current density is defined as I/S, where I is the current value passing through the nano-twinned Cu, and S is the cross-sectional area of the nano-twinned Cu perpendicular to the current direction.

Further, the direction of the current is parallel, perpendicular or at any angle to the (111) crystal plane of the nano-twinned Cu.

Further, the current density value of the current is 1×10 ³ to 5×10 ⁵ A/cm ² , preferably 5×10 ³ to 10 ⁵ A/cm ² .

Further, the atmosphere conditions of the annealing process are vacuum, inert gas protection, nitrogen protection or air atmosphere.

Further, in the annealing process, the annealing temperature is 125-275°C, preferably 150-180°C, or 225-250°C. At a lower temperature, the thermal stress in the semiconductor device is small, and problems such as warping, cracking or tearing caused by thermal stress are not easy to occur; at the same time, the atomic activity weakens with the decrease of temperature, which can effectively avoid the atomization in the semiconductor device. Diffusion-induced failure.

Further, the annealing time, that is, the time for maintaining a constant temperature and current, is 5-25 minutes, preferably 10-20 minutes, and reducing the annealing time can effectively reduce thermal damage to the semiconductor device.

Further, the nano-twinned Cu is prepared on a metal substrate or a non-metal substrate by direct current or pulse electroplating, and its shape is not particularly limited, and can be columnar, linear, thin-film, irregular, etc., Its area is 1-10 ⁷ μm ² , and its thickness is 0.1-100 μm, preferably 20-80 μm.

The nano-twinned Cu columnar crystals have an average diameter of greater than 3 μm, have high-density twin boundaries, and the spacing between the twin boundaries is 1-100 nm, preferably 10-50 μm. Wherein, the nano-twinned Cu substrate material can be silicon, glass, quartz, printed circuit board, metal and alloy thereof, but is not particularly limited.

Further, in the connection process of step 2, the nano-twinned Cu and the wires may be connected by soldering, clamped by metal clamps, etc., and the connection methods used are not limited to the above methods.

Further, the single crystal Cu has a single (100) preferred orientation, and its average grain size is greater than 50 μm.

Compared with the prior art, the present invention has the following advantages:

In the present invention, during the annealing process of nano-twinned Cu, an electric field is applied to the nano-twinned Cu as an additional energy input, and the current is applied to promote crystal grain transformation. To achieve the same effect, reduce the process temperature and reduce the process time. When the material is subjected to a large current (current density greater than 1×10 ³ A/cm ² ), stress and strain will be generated inside the material, and the magnitude of the stress and strain also increases with the increase of the current density. These stresses and On the one hand, the strain increases the internal energy of the material, making it easier for grain growth and detwining, thereby reducing the temperature required for the transformation of nanotwinned Cu into single crystal Cu during the annealing process; More defects such as vacancies and dislocations provide nucleation sites for new grains, and more nucleation sites shorten the time for single-crystal Cu grains to grow and replace all nano-twinned Cu grains. It should be pointed out that although the greater the current applied during the annealing process, the stronger the effect of promoting the transformation of nanotwinned Cu to single crystal Cu, the current density cannot be increased indefinitely, when the current density is greater than 5×10 ⁵ A /cm ² , the directional migration of atoms caused by the current will cause pores to appear in the microstructure of Cu, so the current density value selected in the present invention is 10 ³ -5×10 ⁵ A/cm ² .

The method provided by the invention realizes the rapid preparation of single crystal Cu suitable for electronic packaging, and the thermal damage to semiconductor chips and devices is small during the process; the production efficiency of preparing single crystal Cu is high; the prepared single crystal Cu has (100 ) direction, and has a large grain size, with good mechanical properties, oxidation resistance, electromigration resistance and thermal stability. preferential orientation of intercompounds and inhibition of Kirkendall pores.

In summary, the method provided by the present invention overcomes the disadvantages of the prior art, such as large thermal damage, low single crystal quality, and poor economy, so that single crystal Cu can be quickly prepared at a lower process temperature, which is very suitable Preparation of metallization layer, redistribution layer, chip interconnection or wire, etc. under the bump of single crystal Cu material.

The method of the invention is simple, efficient, low in cost, and has good compatibility with the current microelectronic packaging process, and is very suitable for large-scale industrial production.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is an X-ray diffraction (XRD) detection result of nanotwinned Cu used in Examples 1 and 2 of the present invention.

2 is a backscattered electron diffraction (EBSD) photograph of the nanotwinned Cu used in Examples 1 and 2 of the present invention.

FIG. 3 is a schematic diagram of Embodiment 1 of the present invention.

FIG. 4 is a schematic diagram of Embodiment 2 of the present invention.

FIG. 5 is a photograph of the single crystal Cu obtained in Example 1 of the present invention after being etched by argon ions.

6 is an EBSD photograph of the single crystal Cu obtained in Example 1 of the present invention.

FIG. 7 is the XRD detection result of the single crystal Cu obtained in Example 2 of the present invention.

FIG. 8 is an EBSD photograph of the single crystal Cu obtained in Example 2 of the present invention.

9 is a photograph of the single crystal Cu obtained in Example 2 of the present invention after being etched by a focused ion beam (FIB).

FIG. 10 is the XRD detection result of the annealed nano-twinned Cu obtained in the comparative example.

FIG. 11 is the EBSD photograph of the nanotwinned Cu obtained in the comparative example after annealing.

In the figure: 10, substrate; 20, (111) preferentially oriented nano-twinned Cu; 30, solder bumps; 40, under bump metallization (UBM).

Detailed ways

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the invention unless specifically stated otherwise. Meanwhile, it should be understood that, for convenience of description, the dimensions of various parts shown in the accompanying drawings are not drawn in an actual proportional relationship. Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the authorized specification. In all examples shown and discussed herein, any specific values should be construed as illustrative only and not limiting. Accordingly, other examples of exemplary embodiments may have different values. It should be noted that like numerals and letters refer to like items in the following figures, so once an item is defined in one figure, it does not require further discussion in subsequent figures.

Example 1

As shown in Figure 3, a method for rapidly preparing (100) single crystal copper of the present invention can be realized by the following specific process steps:

Step 1: Provide a nano-twinned Cu 20 (as shown in Figures 1 and 2), which has high-density twin boundaries, columnar grains and a (111) preferred orientation, and the average diameter of the columnar grains is 8 μm. The nano-twinned Cu is prepared on the substrate 10 by means of direct current or pulse electroplating, and the substrate is rolled polycrystalline Cu. The thickness of the nano-twinned Cu is 30 μm.

Step 2: The nano-twinned Cu described in Step 1 is used as UBM to form metallurgical connection with solder 30 and UBM 40 on the other side to form an assembly, and then the assembly is connected to a current source to form a complete path.

Step 3: heating the assembly described in Step 2 to 225° C., while applying a direct current to the nano-twinned Cu, so that the current density through the nano-twinned Cu is 1×10 ⁴ A/cm ² , And the current direction is perpendicular to the surface of the nano-twinned Cu, that is, perpendicular to the (111) plane of the nano-twinned Cu, and the above-mentioned temperature and current density are maintained for 15min, and the nano-twinned Cu is completely transformed into single-crystal Cu. .

As shown in Figures 5 and 6, the formed single crystal Cu has a (100) preferred orientation, and its grain size is >50 μm.

Example 2

As shown in Figure 4, a method for rapidly preparing (100) single crystal copper of the present invention can be realized by the following specific process steps:

Step 1: Provide a nano-twinned Cu 20, which has high-density twin boundaries, the grains are columnar and have a (111) preferred orientation, and the average diameter of the columnar grains is 8 μm. The nano-twinned Cu is prepared on the substrate 10 by a method of direct current or pulse electroplating, and its shape is a strip. The thickness of the nano-twinned Cu is 30 μm.

Step 2: Connect the nano-twinned Cu described in Step 1 with a current source to form a complete path.

Step 3: Heating the nano-twinned Cu connected to the wire in step 2 to 160 ° C, and applying a pulse current to the nano-twinned Cu at the same time, T _on /T _off is 1, and the frequency is 200 Hz, so that the The current density of nano-twinned Cu is 1×10 ⁵ A/cm ² , and the current direction is parallel to the surface of the nano-twinned Cu, that is, parallel to the (111) plane of the nano-twinned Cu, keeping the above constant. At the temperature and current density of 15min, the nano-twinned Cu was all transformed into single-crystal Cu.

As shown in Fig. 7, Fig. 8 and Fig. 9, the formed single crystal Cu has a (100) preferred orientation, and its grain size is >50 μm.

Comparative ratio

In this comparative example, no current is applied to the nano-twinned Cu, that is, only heating is performed for annealing. The annealing temperature is 300 °C, and the annealing time is 1 h. Other steps, materials and process conditions are the same as those in Example 2. The result (111) is the preferred orientation. The nanotwinned Cu was not transformed into (100) single crystal Cu, as shown in Figures 10 and 11.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (10)

1. A method for rapidly preparing (100) single crystal copper is characterized in that a (111) preferentially oriented nano-twin crystal Cu is provided, annealing is carried out on the nano-twin crystal Cu, a current is directly/indirectly applied to the nano-twin crystal Cu and is kept for a certain time, crystal grains of the nano-twin crystal Cu grow rapidly and are converted into (100) preferentially oriented single crystal Cu, and finally the (111) preferentially oriented nano-twin crystal Cu is converted into the (100) preferentially oriented single crystal Cu.

2. The method for the rapid production (100) of single-crystal copper according to claim 1, characterized in that it comprises in particular the following steps:

the method comprises the following steps: providing a nanometer twin crystal Cu, wherein crystal grains are columnar and have (111) preferred orientation;

step two: connecting the nano twin crystal Cu of the step one with a current source to form a complete path;

step three: and (2) heating the nano-twin crystal Cu of the connected wire in the step two for annealing, simultaneously directly/indirectly applying a certain direct current or pulse current, and keeping constant temperature and current density for a period of time until the nano-twin crystal Cu is completely converted into single crystal Cu, wherein the single crystal Cu is formed by rapid growth of crystal grains in the annealing process of the nano-twin crystal Cu and has single (100) preferred orientation.

3. The method for rapidly preparing (100) single-crystal copper according to claim 1 or 2, wherein the current density is defined as I/S, I is a current value passing through the nano-twin Cu, and S is a sectional area of the nano-twin Cu perpendicular to a current direction.

4. The method for rapidly preparing (100) single crystal copper according to claim 3, wherein the current direction is parallel to, perpendicular to or at any angle with respect to the (111) crystal plane of the nano twin crystal Cu.

5. The method for rapid production (100) of single-crystal copper according to claim 4, characterized in that the current density value of the current is 1 x 10³～5×10⁵A/cm²。

6. The method for rapid production (100) of single-crystal copper according to claim 1 or 2, characterized in that the annealing process atmosphere conditions are vacuum, inert gas blanket, nitrogen blanket or air atmosphere.

7. The method for rapidly preparing (100) single crystal copper according to claim 6, wherein the annealing temperature is 125-275 ℃ during the annealing process.

8. The method for rapid production (100) of single-crystal copper according to claim 7, wherein the annealing time, that is, the time for maintaining the constant temperature and current density, is 5 to 25 min.

9. The method for rapidly preparing (100) single crystal copper according to claim 1 or 2, wherein the nano twin crystal Cu is prepared on a metal substrate or a non-metal substrate by a direct current or pulse plating method, and the area of the nano twin crystal Cu is 1-10%⁷μm²The thickness is 0.1 to 100 μm; the average diameter of the nano twin Cu columnar crystal is larger than 3 mu m, the nano twin Cu columnar crystal has a high-density twin boundary, and the twin boundary spacing is 1-100 nm.

10. The method for rapid production (100) of single-crystal copper according to claim 1 or 2, characterized in that the single-crystal Cu has a single (100) preferred orientation with an average grain size of more than 50 μ ι η.

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