CN104183570B - Near-zero-eddy-current-loss interconnection line and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of radio frequency devices, and provides a near-zero-eddy-current-loss interconnection line and a preparation method of the near-zero-eddy-current-loss interconnection line. The near-zero-eddy-current-loss interconnection line comprises a substrate and an interconnection line body arranged on the surface of the substrate. The interconnection line body is a periodical composite superlattice film structure formed by stacking metallic copper thin film layers and ferromagnetic metal thin film layers alternately, wherein each metallic copper thin film layer is 50-1000 nm thick, each ferromagnetic metal thin film layer is 20-500 nm thick, ferromagnetic metal is alloy composed of magnetic metal and copper, and the periodicity of the periodical composite superlattice film structure is 5-200. The metallic copper is used as raw materials of the interconnection line body, so that the cost is low. The superlattice film structure is adopted, so that the interconnection line is simple in structure and easy to make, reduces stress caused by lattice mismatch and is low in resistivity. Near-zero effective magnetic conductivity is realized through frequency band selection, so that no obvious skin effect is caused when the thickness ranges from 10 micrometers to 100 micrometers. The interconnection line is prepared through a metal electrochemistry alternating deposit method in a multi-period and alternate electroplating mode, so that the difficulty and cost of the preparation process are reduced. The near-zero-eddy-current-loss interconnection line and the preparation method of the near-zero-eddy-current-loss interconnection line are suitable for the radio frequency devices.

Description

A near-zero eddy current loss interconnection wire and its preparation method

technical field

The invention relates to the technical field of radio frequency devices, in particular to an ultra-low eddy current loss radio frequency interconnection wire and a preparation method thereof, in particular to a near zero eddy current loss interconnection wire for radio frequency devices and a preparation method thereof.

Background technique

In the field of radio frequency device technology, on-chip integrated devices such as micro-inductors, microstrip lines, and coplanar waveguides all require patterned thin films as interconnect lines, while copper is often used as the preparation material for interconnect lines in traditional devices. However, due to the skin effect, electromagnetic waves will cause eddy currents inside the copper conductor, and the distribution of the current on the cross-section of the conductor is no longer uniform. Increased power. In order to facilitate the description of the skin effect, a skin depth, the critical depth δ, is introduced, and the current density at this depth is exactly 1/e times the surface current density:

$\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}{{\mathrm{<span\; class="notranslate">\; \&pi;f\&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}}$

Wherein, f is the frequency, μ ₀ μ _r is the magnetic permeability (H/m), σ is the electrical conductivity (S/m), for general metal materials such as copper, its relative magnetic permeability μ _r is 1, Therefore, the magnetic permeability is the vacuum magnetic permeability μ ₀ =4π×10 ^-7 H/m. Therefore, in the preparation of high-frequency devices (especially radio-frequency devices), in order to increase the skin depth, metal materials with higher conductivity such as silver are often used as interconnect lines, but because silver is a noble metal, it will greatly increase the thickness of the interconnect lines. cost of the final device. A near-zero eddy current loss interconnection wire with low cost and low resistivity, and even near-zero effective magnetic permeability in a specific frequency band and its preparation method have not been reported so far.

Contents of the invention

The technical problem to be solved by the present invention is to provide an interconnection wire with low cost and near-zero eddy current loss in a specific frequency band and its preparation method, which can effectively eliminate the eddy current loss of metal copper as an interconnection wire in a specific frequency band.

The technical solution adopted by the present invention to solve its technical problems is:

A near-zero eddy current loss interconnection line, including a substrate substrate and an interconnection line on the surface of the substrate substrate; the interconnection line is a periodic layer formed by laminating metal copper thin film layers and ferromagnetic metal thin film layers. Composite superlattice film structure; wherein, the thickness of each metal copper film layer is 50-1000nm, and the thickness of each ferromagnetic metal film layer is 20-500nm; the ferromagnetic metal is an alloy formed of magnetic metal and copper; The period number of the periodic composite superlattice film structure is 5-200.

Specifically, the total thickness of the interconnection line is in the range of 10-100 μm.

Specifically, the magnetic metal is one or more of iron, nickel or cobalt.

In order to prepare the above-mentioned near-zero eddy current loss interconnection wire, the technical solution adopted is: a preparation method of a near-zero eddy current loss interconnection wire, comprising the following steps:

A. sputter barrier layer on silicon substrate substrate, and sputter copper seed layer on barrier layer;

B. Use photoresist to perform thick photolithography on the seed layer to expose the interconnection line pattern;

C. Based on the electrochemical alternate deposition method, use the electrochemical deposition solution to alternately electroplate periodically alternately laminated metal copper thin film layers and ferromagnetic metal thin film layers on the interconnection line pattern; D. Rinse the silicon substrate substrate and dry it After removing the photoresist;

E. Remove the barrier layer and the copper seed layer other than the interconnection pattern.

Specifically, Step A is specifically to use magnetron sputtering to sputter a layer of 50nm metal titanium layer as a barrier layer on the silicon substrate, and then sputter a 200nm copper seed layer on the metal titanium layer.

Preferably, the photoresist in step B is AZ4620 photoresist.

Preferably, there are steps between steps B and C:

B1. Use a plasma cleaning machine for 50 seconds to remove the organic bottom film and sticky dirt in the graphic area of the interconnection line;

B2. Soak the silicon substrate with 5% dilute sulfuric acid for 1 min.

Specifically, in step C, alternate electroplating is performed using a multi-potential constant voltage method.

Preferably, in step E, a solution with a volume ratio of 98% H ₂ SO ₄ :30% H ₂ O ₂ :H ₂ O=5ml:1ml:100ml is used to remove the copper layer at a rate of 300nm/min, and 5% HF is used The solution removes the titanium layer within 2-4s.

The beneficial effects of the present invention are: the use of metal copper as the raw material of the interconnection line, the cost is low, the superlattice film structure is adopted, the structure is simple, easy to realize, the stress caused by the lattice mismatch is reduced, and the resistivity is low, the most important The most important thing is that the frequency band can be selected to achieve near-zero effective magnetic permeability, so the thickness can be 10-100 μm without obvious skin effect; the interconnection line is prepared by multi-cycle alternating electroplating by metal electrochemical alternate deposition method, which reduces the difficulty and cost of the preparation process , increasing the design freedom. The invention is applicable to radio frequency devices.

Description of drawings

Fig. 1 is the periodic composite superlattice film structure schematic diagram in the interconnection line of the present invention;

Fig. 2 is the change trend of sheet resistance of superlattice multilayer film with frequency under different periods;

Fig. 3 is the variation trend of the square resistance of the superlattice film with frequency under different thickness ratios;

Wherein, 1 is a metal copper thin film layer, 2 is a ferromagnetic metal thin film layer, and 3 is a substrate substrate.

detailed description

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, a kind of near-zero eddy current loss interconnection line of the present invention comprises substrate substrate 3 and the interconnection line on the surface of substrate substrate 3, and described interconnection line is made of metal copper film layer 1 and A periodic composite superlattice film structure formed by laminating ferromagnetic metal thin film layers 2; wherein, the thickness of each metal copper thin film layer 1 is 50-1000 nm, and the thickness of each ferromagnetic metal thin film layer 2 is 20-500 nm; The ferromagnetic metal is an alloy formed of magnetic metal and copper; the period number of the periodic composite superlattice film structure is 5-200.

The superlattice thin film structure is a multilayer film that is alternately grown by two different materials in thin layers of several nanometers to tens of nanometers and maintains strict periodicity. It is a specific form of layered fine composite structure. The interconnection line of the present invention adopts a superlattice thin film structure, that is, a structure formed by a plurality of metal copper thin film layers 1 and ferromagnetic metal thin film layers 2 alternately superimposed on each other.

For ferromagnetic metals, due to the existence of ferromagnetic resonance, when the applied frequency is higher than the resonance frequency, its magnetic permeability is negative. For the superlattice structure thin film in the present invention, because there is coupling effect, overall relative magnetic permeability can be expressed as:

${\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}$

Among them, _tN and _tF are the thicknesses of the metal copper thin film layer 1 and the ferromagnetic metal thin film layer 2 respectively, and μ _rF is the relative magnetic permeability of the ferromagnetic metal. It can be seen from the above formula that since μ _rF is negative in a specific frequency band, by adjusting the relative thickness of the metal copper film layer 1 and the ferromagnetic metal film layer 2, the relative permeability of the superlattice film in a specific frequency band can be realized According to the above formula, when the relative magnetic permeability is zero, the skin depth is infinite, and the eddy current loss caused by this is almost zero.

The ferromagnetic metal is an M-Cu alloy which is close to copper (Cu) in lattice constant and lattice type, and M is a magnetic metal, specifically iron (Fe), nickel (Ni) or cobalt (Co). Its purpose is as follows: firstly, the magnetic element alloy can provide high-frequency negative magnetic permeability; secondly, the M-Cu alloy layer and the Cu layer have good lattice matching, which can reduce the interface stress and create conditions for thick film plating; thirdly , the resistivity of M-Cu alloy is close to that of Cu, and the higher the degree of lattice matching, the lower the energy loss of electrons when they are transported at the interface, which is beneficial to reduce the overall resistivity of the superlattice film; finally, select these three magnetic elements Forming an alloy with Cu avoids the introduction of other elements, and the properties of the ferromagnetic alloy can be adjusted only by changing the content of Cu, which reduces the process difficulty of superlattice preparation and provides greater flexibility for interconnect lines used in different frequency bands. degrees of freedom.

Figure 2 shows the variation trend of the sheet resistance of the superlattice multilayer film with frequency under different periods. Among them, the total thickness of the film is 6 μm, the ferromagnetic metal film layer here is a CoCu layer, the ratio of Cu layer to CoCu layer is 3:1, and the period numbers of the periodic composite superlattice film structure are 50, 30, 14 and 8, respectively. It can be seen from the figure that at a frequency of about 8.9GHz, the sheet resistance has an obvious minimum value, and at this time the real part of the magnetic permeability corresponding to the magnetic spectrum is -3, considering t _Cu : t _CoCu = 3 , according to the above formula, it can be seen that the overall relative magnetic permeability μ _av =0 of the superlattice. In addition, it can be seen from the figure that the larger the period and the thinner the thickness of each layer, the smaller the minimum value, which indicates that the larger the period, the stronger the coupling effect, making the resistance smaller.

As shown in Figure 3, the square resistance of the superlattice film changes with frequency under different thickness ratios (the thickness ratio of the Cu layer to the CoCu layer decreases from 5 to 1). It can be seen from the figure that the thicker the metal copper thin film layer 1 is than the ferromagnetic metal thin film layer, the smaller the frequency of occurrence of the minimum value of resistance. Therefore, in practical applications, different application requirements can be met by changing the period and thickness ratio.

In practical applications, on the basis of obtaining the magnetic spectrum of the ferromagnetic metal film, the change trend of the square resistance of the multilayer film with frequency can be obtained by calculating the surface impedance, and then the design can be improved to realize the magnetic permeability of the interconnection line in the selected frequency band tends to zero, while the skin depth is infinite.

Considering the cost and the realization effect, the total thickness of the interconnection is in the range of 10-100 μm. Compared with the existing interconnection of the same length, the resistance of the interconnection of the present invention is greatly reduced, and the eddy current loss is close to zero.

The method for preparing the above-mentioned near-zero eddy current loss interconnection wire comprises the following steps:

A. sputter barrier layer on silicon substrate substrate, and sputter copper seed layer on barrier layer;

A variety of existing methods can be used to realize the sputtering of the seed layer. In order to effectively improve the adhesion and prevent the interdiffusion between the copper seed layer and the silicon of the substrate, the method of magnetron sputtering can be used first on the substrate. A 50nm titanium (Ti) layer is grown on the chip. At the same time, because copper is difficult to etch, it cannot be deposited and then etched like the traditional metal aluminum. Therefore, it is necessary to etch the circuit pattern first, and then deposit and electroplate the circuit. However, electroplating needs to conduct electricity, so it is necessary to cover a layer of copper seed layer on the surface of the barrier layer to conduct electricity. When the power is added between the periodic composite superlattice film structure (anode) and the silicon wafer (cathode), the metal of the anode The elements react to convert into metal ions and electrons, and the cathode also reacts, and the copper ions on the surface of the seed layer near the cathode combine with electrons to form copper plated on the surface of the seed layer. Eventually the wiring is formed, so another 200nm of copper needs to be grown as a seed layer. B. Use thick glue AZ4620 to perform thick glue photolithography on the seed layer to expose the interconnection line pattern;

Positive photoresist AZ4620 is widely used in microfabrication, usually in the i-line spectral range, and has the advantages of high resolution, large aspect ratio, and small absorption coefficient.

C. Based on the metal electrochemical alternate deposition method, the electrochemical deposition liquid is used to alternately electroplate periodically alternately laminated metal copper thin film layers and ferromagnetic metal thin film layers on the interconnection line pattern to form a superlattice thin film structure;

Taking the ferromagnetic metal as the alloy formed by the magnetic metal cobalt and copper as an example, the formulation of the electrochemical deposition solution includes CoSO ₄ .7H ₂ O, CuSO ₄ .5H ₂ O, H ₃ BO ₃ , LFT-930Mu cylinder opener, LFT-930A brightener and LFT-930B brightener. The ratio of Co ²⁺ to Cu ²⁺ in the electrochemical deposition solution is very important. If there is too much Cu ²⁺ , the content of Co ²⁺ will be difficult to control when electroplating ferromagnetic metal thin film layers; if Co ²⁺ If the content is too much, it will be very slow or difficult to electroplate copper. In the present invention, the formula of Co ²⁺ :Cu ²⁺ =25:1 is adopted. The function of H ₃ BO ₃ in the chemical deposition solution is to adjust the pH value, and the pH value of the above formula is 3. LFT-930Mu opener, LFT-930A brightener and LFT-930B brightener are used to improve the flatness and brightness of the film, reduce defects, make the quality higher and the resistivity lower. In addition, electroplating baths with Ni ²⁺ or Fe ²⁺ can also be used.

The invention adopts a metal electrochemical alternate deposition method to prepare a multilayer film formed by alternately stacking metal copper thin film layers and ferromagnetic metal thin film layers. Since Co ²⁺ is more noble than copper element, there are different deposition states in the voltammetry curves. When the voltage is low enough, the reduction rate of Cu ²⁺ is very fast at this time, and the reduction rate of Co ²⁺ is very slow, so basically all deposited is Cu; and when the voltage is high, it is the reduction of Co ²⁺ at this time The maximum point of the potential, so that only the reduction of Co ²⁺ occurs at the cathode. Therefore, by changing the potential, films with different compositions can be obtained; by changing the plating time, films with different thicknesses can be obtained.

In the following, the superlattice film structure composed of deposited Co-Cu ferromagnetic metal and Cu is taken as an example to describe the process of alternate electroplating using the multi-potential constant voltage method in detail. Using the constant voltage method, when the deposition voltage is -1V, the composition of the film is Co _0.68 Cu _0.32 , and has good magnetic properties, which can be used as the required magnetic layer. Alternate electroplating adopts multi-potential constant voltage method, in which potential 1 is set to -0.5V to deposit Cu layer, and potential 2 is set to -1V to deposit Co _0.68 Cu _0.32 layer. Multilayer films with different thickness ratios can be obtained by changing the residence time of different potentials. A multi-period structure can be obtained by alternately changing the potential through programming control time.

D. Rinse the silicon substrate substrate, and remove the photoresist after drying;

Specifically, after the electroplating is completed, rinse and dry with deionized water, and then dissolve and remove the photoresist with acetone.

E. Remove the barrier layer and the copper seed layer other than the interconnection pattern.

Specifically, a solution with a volume ratio of 98% H ₂ SO ₄ :30% H ₂ O ₂ :H ₂ O=5ml:1ml:100ml is used to remove the copper layer at a rate of 300nm/min, and a 5% HF solution is used in the The 50nm titanium layer can be removed within 2-4 seconds without affecting the CoCu/Cu multilayer film.

Preferably, before electrochemical deposition, also need to carry out two-step seed layer pretreatment, therefore, also have step between step B and step C:

B1. Use a plasma cleaning machine, such as using an oxygen plasma O ₂ Plasma base film for 50s to remove the organic base film and sticky dirt in the pattern area of the interconnection line;

B2. Soak the silicon substrate with 5% dilute sulfuric acid for 1 min to remove the oxide film formed on the copper layer in oxygen plasma and air.

The near-zero eddy current loss interconnection wire for radio frequency devices generated by the above method can effectively eliminate the eddy current loss when copper is used as the interconnection wire in a specific frequency band. By changing different potentials, it is convenient and precise to control the thickness and composition of each layer in the multilayer film, so that the frequency band of the interconnection line can be adjusted conveniently, greatly reducing the preparation time and cost, and has great application prospects in radio frequency devices and integrated circuits. .

Claims (9)

1. a kind of near zero eddy current loss interconnection line, comprise the interconnection line of substrate substrate (3) and substrate substrate (3) surface, it is characterized in that, described interconnection line is made of metallic copper film layer ( 1) and the ferromagnetic metal thin film layer (2) are laminated to form a periodic composite superlattice thin film structure; wherein, the thickness of each metal copper thin film layer (1) is 50-1000nm, and each ferromagnetic metal thin film layer (2) The thickness is 20-500nm; the ferromagnetic metal is an alloy formed of magnetic metal and copper; the period number of the periodic composite superlattice film structure is 5-200. 2 . The near-zero eddy current loss interconnection wire according to claim 1 , wherein the total thickness of the interconnection wire is in the range of 10-100 μm. 3. The near-zero eddy current loss interconnection wire according to claim 1, wherein the magnetic metal is one or more of iron, nickel or cobalt. 4. A preparation method of a near-zero eddy current loss interconnection wire, characterized in that, comprising the following steps: A. sputter barrier layer on silicon substrate substrate, and sputter copper seed layer on barrier layer; B. Use photoresist to perform thick photolithography on the seed layer to expose the interconnection line pattern; C. Based on the electrochemical alternate deposition method, the electrochemical deposition liquid is used to alternately electroplate periodically alternately stacked metal copper thin film layers and ferromagnetic metal thin film layers on the interconnection line pattern; D. Rinse the silicon substrate substrate, and remove the photoresist after drying; E. Remove the barrier layer and the copper seed layer other than the interconnection pattern. 5. The preparation method of a kind of near-zero eddy current loss interconnection wire as claimed in claim 4, is characterized in that, step A is specifically the method for adopting magnetron sputtering, sputtering a layer of 50nm on the silicon substrate substrate A metal titanium layer as a barrier layer, and then a 200 nm copper seed layer is sputtered on the metal titanium layer. 6. The method for preparing a near-zero eddy current loss interconnection wire as claimed in claim 5, wherein the photoresist in step B is AZ4620 photoresist. 7. The preparation method of a kind of near-zero eddy current loss interconnection wire as claimed in claim 6, it is characterized in that, there are steps between steps B and C: B1. Use a plasma cleaner for 50 seconds to remove the organic base film and dirt in the graphic area of the interconnection line; B2. Soak the silicon substrate with 5% dilute sulfuric acid for 1 min. 8. The method for preparing a near-zero eddy current loss interconnection wire as claimed in claim 6, characterized in that, in step C, the multi-potential constant voltage method is used for alternate electroplating. 9. A method for preparing a near-zero eddy current loss interconnection wire as claimed in claim 8, characterized in that, in step E, a volume ratio of 98% H ₂ SO ₄ :30% H ₂ O ₂ :H ₂ O is used =5ml:1ml:100ml solution removes the copper seed layer at a rate of 300nm/min, and uses 5% HF solution to remove the metal titanium layer within 2-4s.