KR20020029882A - The method of aoustic wave device fabrication using lcmp - Google Patents

Abstract

PURPOSE: A method for manufacturing acoustic wave device by LCMP process is provided to improve flatness of surfaces of thin films by removing minute protrusions which are formed on the surfaces of thin films. CONSTITUTION: A bottom electrode layer(10) of 1200Å through 1500Å is deposited on a silicon substrate(2). The bottom electrode layer(10) includes an aluminum(Al) film, a tungsten(W) film, a silver(Ag) film, or a molybdenum(Mo) film. The bottom electrode layer(10) is processed by an LCMP process to form a surface of an electrode layer having improved flatness. A piezoelectric thin film layer is formed on the bottom electrode layer processed by the LCMP process. The piezoelectric thin film layer includes a zinc oxide(ZnO) film(14) or an aluminum nitride(AIN) film(14). A top electrode layer(20) is formed on the piezoelectric thin film layer(14). The top electrode layer(20) has an aluminum(Al) film of 1000Å through 1300Å.

Description

Manufacturing method of elastic wave element by ELMP process method {THE METHOD OF AOUSTIC WAVE DEVICE FABRICATION USING LCMP}

The present invention relates to a method for manufacturing an acoustic wave device, and more particularly, by depositing a thin film layer on a wafer and subjecting the surface to a laser chemical mechanical planarization (CMP) process to improve the flatness of the thin film layer surface. To improve the characteristics of an acoustic wave device.

Recently, a method of using a laser for cleaning a wafer has been developed. Of course, using a laser, it is also possible to remove contaminants or fine protrusions 1 formed on the surface of the deposited thin film or to remove a part of the thin film. It is called (Laser Chemical Mechanical Planarization) process.

The present invention relates to a mobile communication component device, and more particularly, to an acoustic wave device for implementing a high frequency filter that passes only a specific high frequency component.

A conventional acoustic wave device will be described with reference to the 2001 New Technology Trend Survey Report 'Mobile Communication Components and Application Technology' Publication No. 11-1430000-000265-01 published by the Patent Office.

Recently, as the speed of the operation of the information processing apparatus and the communication apparatus is required to increase, the frequency of the signal has increased to a radio frequency. In response to such a change in frequency, a filter capable of operating at the high frequency band is required. Acoustic wave device (Acoustic Wave Device) is used for this purpose, FBAR (Film Bulk Acoustic Resonator) is one kind of these devices.

The acoustic wave device is a component that converts a communication signal, which is electromagnetic waves, to elastic waves by using piezoelectric material to extract only a wavelength of a desired frequency. There are two kinds of seismic waves currently used. One is called Surface Wave, and the other is called Bulk Wave. Surface wave acoustic wave (SAW) filter, which is widely used at present, is a surface acoustic wave (SAW) filter, which has a large insertion loss and difficulty in forming a microwave monolithic integrated circuit (MMIC). In addition, the SAW is difficult to apply the ultra-high frequency band due to the limitation of the line width, and since the electrodes having a complicated structure are arranged in a predetermined region, safety against high power cannot be ensured. In other words, the range of power handling is relatively smaller than that of the dielectric filter. As a device using the volume wave, the FBAR (FilmBulk Acoustic Resonator), which improves these shortcomings of SAW and operates at high frequency, is being actively researched by university research institutes and related companies in the United States and Japan, and prototypes have been developed for military use. In Korea, ANT Co., Ltd. is expected to enter commercialization soon.

FBAR filter is a thin film that induces resonance due to piezoelectric properties by depositing ZnO and AlN as piezoelectric materials directly on the semiconductor substrate (Si) or gallium arsenide (GaAs) by the physical vapor deposition method. It is a type of device, that is, FBAR as a filter. Compared to the dielectric filter, it can be miniaturized, has a smaller insertion loss than the surface acoustic wave device, has a wider power handling range, and uses a semiconductor wafer, thereby facilitating MMIC.

FBAR deposits a piezoelectric thin film between two electrodes and applies electrical energy to the electrode to induce an electric field that changes in time in the piezoelectric layer, and the electric field is formed in the same direction as the thickness vibration direction in the piezoelectric thin film which is well formed. It uses the principle of generating resonance by inducing a bulk acoustic wave. The manufacturing process of the FBAR is a process of depositing a piezoelectric film (Piezoelectric Film) of the piezoelectric material ZnO, AlN on Si or GaAs substrate, forming an electrode layer of Al, Cu, Pt, Au, Mo, etc., It may be divided into a step of forming an elastic reflective layer. These thin film layers should have good adhesion, flatness and densification.

The FBAR has a membrane form, an air gap form, and a Bragg reflection form.

The membrane type is a method of depositing a membrane, a silicon p ⁺ layer on an Si substrate by an ion growth method, and anisotropic etching on an opposite side of the Si substrate to form an etching cavity. This method has problems such as troublesome process, weakness of the device itself, and loss of acoustic wave energy.

The air gap form simplifies the device fabrication process by forming a sacrificial layer on a silicon surface substrate using micromachining techniques. This method also has a problem of causing many defects due to the weakness of the element itself when cutting into individual elements.

The Bragg reflection type forms an Acoustic Reflecting Layer by depositing a material having a large difference in Acoustic Impedance on a Si substrate in a layer. Then, acoustic energy passing through the piezoelectric layer is not transmitted toward the substrate, but is reflected from the reflective layer, thereby generating efficient resonance. This method saves manufacturing time and has the advantage of realizing an external shock resistant device.

The operation principle of the FBAR is to use the thickness vibration of the piezoelectric thin film layer. In order to accurately extract the desired frequency and minimize signal loss, the thickness control of the piezoelectric thin film layer and the electrode layer must be accurate, and the surface flatness is also a very important factor. However, when depositing another thin film layer on the wafer or on the thin film layer in the FBAR manufacturing process, it is very difficult to produce a completely flat surface of the thin film layer. Deposition of the thin film layer produces fine protrusions on its surface, making it difficult to form the same thickness entirely on the wafer. For these reasons, the electrical characteristics of the resonator, namely selectivity Q and insertion loss, which are necessary for manufacturing FBAR, are difficult to reach the target level.

The present invention improves the flatness of the surface of the thin film layers by removing the fine protrusions 1 formed on the surface of the thin film by LCMP process in the process of forming a thin film layer such as a piezoelectric thin film layer and an electrode layer during the manufacturing process of the acoustic wave device. This is to improve the characteristics of the acoustic wave element.

1A is a cross-sectional view before processing, showing the LCMP process principle.

1B is a cross-sectional view after the process, showing the LCMP process principle.

FIG. 2A is a cross-sectional view and a detailed view of a bottom electrode layer formed on a substrate (before LCMP processing). FIG.

Figure 2b is a cross-sectional view and a detailed view of the bottom electrode layer formed on the substrate (after the LCMP process)

3A is a cross-sectional view of an acoustic wave element constructed on a substrate.

Fig. 3B is a sectional view of an acoustic wave element having a protective film formed on a substrate.

4A is a cross-sectional view showing a piezoelectric layer, a Miss Matching Zone, and a silicon oxide film (or bottom electrode layer) before LCMP processing.

4B is a cross-sectional view showing a piezoelectric layer, a Miss Matching Zone, and a silicon oxide film (or bottom electrode layer) after LCMP processing.

5 is a cross-sectional view of an elastic reflection layer formed on a substrate.

6 is a cross-sectional view of the acoustic wave device on the elastic reflection layer.

7 is a cross-sectional view of an acoustic wave element in which a protective film is formed on an elastic reflection layer.

8 is a cross-sectional view of an acoustic wave element in which a membrane is formed.

9 is a cross-sectional view of an acoustic wave element in which an air gap is formed.

10 is a cross-sectional view of an acoustic wave element in which a space layer is formed by anisotropic etching.

Explanation of symbols for the main parts of the drawings

One ; Protrusion 12; Shield

2 ; Silicon substrate 14; Zinc oxide

4 ; Silicon oxide film 20; Top electrode

6; Tungsten film

7; Elastic reflective layer

10; Bottom electrode

The method of manufacturing the acoustic wave device according to the present invention for achieving the above object is as follows.

The first step is to form a bottom electrode layer, which is a thin film layer, on the substrate.

Second, a second step of LCMP process the bottom electrode (Bottom Electrode) layer surface.

The third step is to form a piezoelectric thin film layer by depositing a piezoelectric material with an appropriate thickness on the bottom electrode (Bottom Electrode) layer surface subjected to the LCMP process.

Fourth, a fourth step of forming a top electrode layer on the piezoelectric thin film layer. As described above, the acoustic wave device of the present invention can be manufactured by providing four steps.

In order to further improve the characteristics of the acoustic wave device, it is preferable to form an acoustic reflecting layer between the substrate and the bottom electrode layer in the first step to prevent loss of acoustic energy. An acoustic reflective layer is an odd layer or layer of a material having a first acoustic impedance on a substrate and a material having a second acoustic impedance different from that of the material. It is preferable to alternately form and form so that it may become an even layer. At this time, whenever each thin film layer of the acoustic reflecting layer is further formed, an LCMP process is performed on the upper surface of each layer to improve the flatness of the surface of each thin film layer.

The elastic reflection layer may be formed of an odd layer or an even layer by alternating a silicon oxide (SiO ₂ ) film and a tungsten (W) film. Of course, even if not a silicon oxide (SiO ₂ ) film or tungsten (W) film, two different materials with an acoustic impedance difference may be alternately stacked.

The bottom electrode thin film forming the bottom electrode layer is any one of a gold (Au) film, an aluminum (Al) film, a tungsten (W) film, a silver (Ag) film, a molybdenum (Mo) film and an indium (In) film. The thin film constituting the top electrode layer may be any one of a gold (Au) film, an aluminum (Al) film, and a tungsten (W) film. The piezoelectric material may be zinc oxide (ZnO) or aluminum nitride (AlN). Is preferable.

It is preferable to further form a silicon oxide film (SiO ₂ ) as a protective film between the bottom electrode layer and the piezoelectric thin film layer or between the piezoelectric thin film layer and the top electrode layer as a protective film to prevent resonance frequency variation of the device from external temperature change.

Another method for further improving the characteristics of the acoustic wave device is to form a space layer under the bottom electrode layer in the first step process. Then, since the material constituting the acoustic wave device and the air constituting the space layer have a large difference in acoustic impedance from each other, the space layer acts like an elastic reflection layer to prevent loss of acoustic energy. You can do it.

Meanwhile, the LCMP process is a process of removing the minute protrusions 1 and the contaminants on the surface of the thin film layer or removing a portion of the thin film by irradiating laser light to the surface of the thin film layer. As shown in Fig. 1A, when the laser beam is irradiated onto the thin film surface, the projection 1 has a large surface area, and this part uses the principle that this part is first removed by evaporation with temperature rise. When the thin film layer, which is the bottom electrode 10, is formed on the silicon substrate 2, as shown in FIG. 2A, the surface of the thin film is not flat and fine protrusions are generated. The LCMP process may improve the roughness of the thin film surface and improve the flatness by 30 to 50% as shown in FIG. 2B. Therefore, when the LCMP process is performed on the surface of each thin film layer, the projections generated on the surface of the thin film layer are removed and the flatness of the surface is improved. Can be reduced. When the reflective layer is formed, the LCMP process is performed on the surface of the thin film layer constituting the reflective layer, thereby improving the reflection coefficient of the reflective layer and minimizing the loss of acoustic energy. The laser used is preferably a KrF excimer laser, and the LCMP process may be performed by adjusting the energy density and repetition rate of the laser beam according to the characteristics of the material constituting the thin film.

Hereinafter, a specific embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First step; As shown in FIG. 2A, an aluminum (Al) film is deposited at 1200 to 1500 占 으로 with a bottom electrode (Bottom Electrode 10) layer on the silicon substrate 2. When the surface of the bottom electrode layer is observed under a scanning microscope, it can be seen that the surface is not flat and fine protrusions are formed. This is shown in the detail of FIG. 2A.

In addition to the aluminum (Al) film, any one of tungsten film W, silver film Ag, molybdenum (Mo) film, and indium film (In) may be used as the bottom electrode layer 10.

Second step; When the bottom electrode layer is subjected to the LCMP process, as shown in FIG. 2B, an electrode layer having improved surface flatness can be formed.

Third step; A zinc oxide (ZnO) film 14 or an aluminum nitride (AlN) film 14, which is a piezoelectric thin film layer, is formed on the bottom electrode layer subjected to the LCMP process. In this case, the piezoelectric thin film layer 14 may be deposited using a physical vapor deposition method.

LCMP process treatment of the deposited surface of the piezoelectric thin film layer 14 is preferable for improving the characteristics of the acoustic wave device.

The thickness d of the piezoelectric thin film layer 14 may be obtained according to the relational expression d = v / 2f ₀ . Where v is the elastic wave velocity in the constituent material of the piezoelectric thin film layer, and f ₀ is the center band frequency. Therefore, when the piezoelectric thin film layer is the zinc oxide (ZnO) film 14 when the center band frequency f ₀ of the acoustic wave device is 2 GHz, the thickness is about 15825 kHz.

The fourth step; The top electrode layer 20 is formed on the piezoelectric thin film layer 14. As the top electrode layer 20, an aluminum (Al) film is deposited at 1000 to 1300 μs. The thin film of the top electrode layer 20 may be a gold (Au) film or a tungsten (W) film in addition to the aluminum (Al) film.

The method for manufacturing an acoustic wave device of the present invention comprises four steps as described above.

A cross-sectional view of the acoustic wave device manufactured by the above method is shown in FIG. 3A.

In order to further improve the characteristics of the acoustic wave device, first, consideration should be given to preventing resonance frequency fluctuations from external temperature changes, and preventing loss of elastic waves generated in the piezoelectric thin film layer. Hereinafter, the method will be described in detail.

First, a method of preventing resonance frequency variation from external temperature change is as follows.

In the second step process of the present invention, after the LCMP process of the bottom electrode layer 10 to form a silicon oxide (SiO ₂ ) film 12, which is a protective film 12 on the bottom electrode layer 10 to about 1000 산화, the silicon oxide The zinc oxide (ZnO) film 14 or the aluminum nitride (AlN) film 14, which is a piezoelectric thin film layer, may be formed on the (SiO ₂ ) film 12 in the third step of the present invention.

In this process, the LCMP process is performed on the upper surfaces of the silicon oxide (SiO ₂ ) film 12 as the protective film and the zinc oxide (ZnO) film 14 or the aluminum nitride (AlN) film 14 as the piezoelectric film layer, respectively. good.

As a result, the flatness of the upper surface of the silicon oxide (SiO ₂ ) film 12 as the protective film is improved, so that it is easy to deposit the zinc oxide (ZnO) film 14 or the aluminum nitride (AlN) film 14 as the piezoelectric thin film layer. And piezoelectric properties are also improved. The reason is that if the flatness of the silicon oxide (SiO ₂ ) film 12 is good, seeds can be easily formed at low temperatures during the deposition of the piezoelectric thin film layer, and the C-axis orientation is further improved. On the other hand, during the deposition of the piezoelectric thin film layer, a region which does not have a C-axis orientation and thus does not have piezoelectricity is formed on the interface with the lower layer, which is referred to as a mismatching zone. The piezoelectric thin film layer is composed of the mismatching zone and the piezoelectric layer having a good C-axis orientation and piezoelectricity. When depositing the piezoelectric thin film layer, it is very important to secure the piezoelectric layer to realize the characteristics of the acoustic wave device. When the piezoelectric thin film layer is a zinc oxide (ZnO) film, before and after the LCMP process is shown in Figs. 4A and 4B. Comparing these two figures, it can be seen that after the LCMP process, the mismatching zone becomes thin, thus further securing a piezoelectric layer.

In addition, LCMP process treatment of the upper surface of the zinc oxide (ZnO) film or the aluminum nitride (AlN) film 14, which is a piezoelectric thin film layer, improves the flatness of the thin film surface, which occurs between the piezoelectric thin film layer and the top electrode layer. Scattering of acoustic energy can be reduced. As a result, it is possible to improve the characteristics of the acoustic wave device by reducing the loss of acoustic energy generated in the piezoelectric thin film layer between the two electrode layers.

Second, a method for preventing the loss of the acoustic wave energy generated in the piezoelectric thin film layer is as follows.

That is, the acoustic reflection layer is formed between the substrate and the bottom electrode layer to prevent the loss of acoustic energy, or the space layer is formed under the bottom electrode layer to act as the elastic reflection layer. It is desirable to prevent the loss of acoustic energy.

First, the acoustic reflective layer may be configured as follows.

In a first step process of the present invention, referring to FIG. 5, a silicon oxide (SiO ₂ ) film 4 having a first elastic impedance on the silicon substrate 2 and a second, larger than the first elastic impedance, are provided. The tungsten (W) film 6 having elastic impedance is alternately deposited. That is, the silicon oxide (SiO ₂ ) film 4 and the tungsten (W) film 6 are deposited to form a pair sequentially, and the uppermost layer is deposited on the silicon oxide (SiO ₂ ) film 4. It deposits and forms the elastic reflection layer 7 which has an odd layer as a whole. The elastic impedance is larger in the tungsten (W) film 6 than in the silicon oxide (SiO ₂ ) film 4. Here, it is preferable to perform an LCMP process on the upper surface of each layer every time each thin film layer is formed. Then, since the flatness of the surface of the thin film layer is improved, the adhesion between the films is enhanced and the stresses between the films are alleviated. In addition, since the scattering of acoustic energy is minimized, the reflection coefficient can be increased. In this case, the substrate is not limited to the silicon substrate 2 as in the present embodiment, and substrates of various materials such as gallium arsenide (GaAs), glass, quartz, sapphire, and the like may be used. The deposition of the silicon oxide (SiO ₂ ) film 4 and the tungsten (W) film 6 may be performed using a physical vapor deposition method. Of course, it can also be formed by chemical vapor deposition (Chemical Vapor Deposition). The elastic reflection layer 7 may be variously formed as an odd layer or an even layer by repeatedly depositing according to the characteristics of the acoustic wave device. In this embodiment, the elastic reflective layer 7 having a seven-layer structure is formed. The thickness of the silicon oxide (SiO ₂ ) film 4 and the thickness of the tungsten (W) film 6 satisfy the relationship of λ / 4 when the wavelength of the acoustic wave is λ .

Next, there are three methods for forming a space layer under the bottom electrode layer.

First, in the first step process of the present invention, by depositing a silicon p ⁺ layer on the silicon surface substrate by the ion growth method and anisotropic etching the opposite surface of the silicon surface to form an etching cavity (space) Then, the bottom electrode layer is formed on the silicon p ⁺ layer to perform the second, third and fourth steps of the present invention. The silicon p ⁺ layer here is called a membrane. 8 is a cross-sectional view of the acoustic wave device manufactured by the above method.

Second, in the first step of the present invention, after forming a sacrificial layer (ZnO) on the silicon substrate, a thin film is formed on the sacrificial layer, the thin film is a silicon oxide (SiO ₂ ) film or silicon nitride (SiN) It is preferable to deposit a film by a CVD method, and a bottom electrode layer is formed on the thin film to remove the sacrificial layer after the second, third, and fourth steps of the present invention to form a space layer.

This space layer is called an air gap. 9 is a cross-sectional view of the acoustic wave device manufactured by the above method.

Third, in the first step of the present invention, after etching by anisotropic etching on a silicon substrate, a sacrificial layer (ZnO) is formed on the etched portion and a bottom electrode layer is formed thereon. After the third step is executed, the sacrificial layer is removed after the top electrode layer is formed in the fourth step to form a space layer. 10 is a cross-sectional view of the acoustic wave device manufactured by the above method.

As described above, in the present invention, in depositing the piezoelectric material zinc oxide (ZnO) 14 or aluminum nitride (AlN) 14 between two electrode layers, the surface of each thin film layer is subjected to an LCMP process to provide flatness. By securing, acoustic wave energy is effectively concentrated between electrode layers, and the resonance is efficiently produced.

As described above, according to the present invention, in the process of forming the electrode layer or the piezoelectric thin film layer during fabrication of the acoustic wave device, the following effects can be obtained by improving the flatness of the surface of the thin film layer by performing LCMP process on the thin film surface.

First, the mismatching zone formed at the interface of the bottom electrode layer in the piezoelectric thin film layer can be made thinner than the conventional one. As a result, the thickness of the piezoelectric layer can be easily secured and the C-axis orientation can be easily secured.

Second, since the flatness of the thin film boundary surface is improved, the scattering of acoustic energy may be reduced, thereby minimizing the loss of acoustic energy.

Third, it can strengthen the adhesion between the membrane and relieve stress.

Fourth, the reflection coefficient can be increased when the elastic reflection layer is formed.

Therefore, it is possible to manufacture a device having a characteristic that is more improved than the conventional Q value and insertion loss.

Claims (8)

Forming a bottom electrode layer on the substrate; Performing a LCMP treatment on the bottom electrode layer surface; Forming a piezoelectric thin film layer on the surface of the bottom electrode layer subjected to the LCMP process; And a fourth step of forming a top electrode layer on the piezoelectric thin film layer. The method of claim 1, wherein the first step comprises forming an odd layer or an even layer of a material having a first elastic impedance on the substrate and a material having a second elastic impedance having a different impedance value from the material. A method of manufacturing an acoustic wave device, characterized in that to form a bottom electrode layer on the elastic reflecting layer after the step of alternately stacked to form an acoustic reflecting layer (Acoustic Reflecting Layer). The bottom electrode layer of claim 1, wherein the first step comprises depositing a silicon P ⁺ layer on the silicon substrate by ion growth, forming an etching cavity on the opposite side of the silicon substrate by anisotropic etching, and then forming a bottom electrode layer on the silicon P ⁺ layer. A method of manufacturing an acoustic wave element, characterized in that to form a. The method of claim 1, wherein after forming the sacrificial layer on the silicon substrate, the first step is to form a thin film on the sacrificial layer, the bottom electrode layer is formed on the thin film, and the fourth step is a top electrode on the piezoelectric thin film layer. And forming a space layer by removing the sacrificial layer after the formation of the elastic wave element. The method of claim 1, wherein after etching the silicon substrate by anisotropic etching, a sacrificial layer is formed on the etched portion to form a bottom electrode layer thereon, and the fourth step includes forming a top electrode layer on the piezoelectric thin film layer. And removing the sacrificial layer to form a space layer. The method of manufacturing an acoustic wave device according to claim 1, further comprising a process of LCMP processing the surface of the piezoelectric layer after the third step process. The protective film according to claim 1 or 2 or 3 or 4 or 5, wherein after the second step process, a protective film for preventing fluctuations in the resonance frequency of the device from external temperature change is placed on the bottom electrode layer. And forming a surface and subjecting the surface to LCMP. The method of claim 2, wherein each of the thin film surfaces of the acoustic reflective layer is subjected to LCMP process.