KR20020089270A - Resonant frequency tuning of fbars by using laser beam - Google Patents

Abstract

PURPOSE: A method for tuning a resonant frequency of an FBAR(Film Bulk Acoustic Resonator) using a laser beam is provided to control thickness of a resonant portion of an FBAR by radiating a laser beam on an upper surface or a lower surface of the resonant portion of the FBAR. CONSTITUTION: A reference value is set up. A reference position of an element is set up on a wafer. A resonant frequency of a designated FBAR within the designated element is measured. The measured resonant frequency is compared with the setup resonant frequency. The resonant frequency of the designated FBAR is tuned according to the setup value. A progressive state of the tuning process for the designated element is determined. The measured object is moved to the next FBAR and the comparing process is repeated. A progressive state of the tuning process for the wafer is determined. The measured object is shifted to the next designated element. The comparing process is repeated.

Description

Resonant frequency tuning method of FBAR using laser beam {RESONANT FREQUENCY TUNING OF FBARS BY USING LASER BEAM}

Recently, with the rapid growth of the wireless mobile communication market, mobile communication terminals are becoming smaller and more functional, and information and communication parts are also being researched in order to satisfy these trends. In other words, there is a demand for miniaturization of components of information processing devices and communication devices, high speed of operation, and MMIC (Microwave Monolithic Integrated Circuit) that makes several components into one chip. Therefore, the frequency of the signal to be used has increased from the hundreds of MHz to several GHz band (Radio Frequency), and there is a need for a filter that can operate at such a high frequency band while being extremely small.

Film Bulk Acoustic Resonator (FBAR) filter is a physical vapor deposition of zinc oxide (ZnO) or aluminum nitride (AlN), a piezoelectric material, on a semiconductor wafer, that is, a silicon (Si) or gallium arsenide (GaAs) substrate. The FBAR is implemented as a filter, which is a thin film type device, which is directly deposited to a desired thickness and causes resonance due to piezoelectric properties. 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.

The FBAR has a Bragg reflection type, a membrane type, an air bridge type, and an air gap shape.

The Bragg reflection type shown in FIG. 2A forms an acoustic reflective layer by depositing a material having a large difference in acoustic impedance on a silicon wafer (Si-Wafer, hereinafter referred to as a "wafer"). Then, acoustic energy passing through the piezoelectric layer is not transmitted to the wafer direction, but is reflected from the elastic reflection layer so that efficient resonance can be generated.

The membrane form shown in FIG. 2B is a method of depositing a membrane, a silicon p ⁺ layer on the wafer by ion growth, and anisotropic etching on the opposite side of the wafer to form an etching cavity.

The airbridge form shown in FIG. 2C simplifies the device fabrication process by forming an air gap by forming a sacrificial layer on the wafer surface using a micromachining technique.

FIG. 2D shows an air gap, in which an sacrificial layer is formed by anisotropic etching of the wafer surface to form a sacrificial layer, thereby forming an air gap.

FBAR deposits a piezoelectric thin film between the two electrodes and applies electrical energy to the electrode to induce a time-varying electric field in the piezoelectric thin film layer, and the electric field is in the same direction as the thickness direction of vibration in the piezoelectric thin film which is well formed. It uses the principle of generating resonance by inducing bulk acoustic wave. The manufacturing process of the FBAR is a process of depositing a piezoelectric film (ZnO) or aluminum nitride (AIN) as a piezoelectric material on the wafer, electrode layer (Al, Cu, Pt, Au, Mo, etc.) And a step of forming an elastic reflective layer or an air gap. These thin film layers should have good adhesion, flatness and densification.

The resonance frequency of the FBAR is determined by the thickness of the upper and lower electrodes and the piezoelectric material and the physical properties of the constituent material. It is known that FBAR manufactured in a very small size on a wafer to which a general semiconductor process is applied by using a MEMS technique has a disadvantage in that the resonance frequency cannot be tuned. In addition, it is not possible to deposit thin films of the same thickness as a whole on a wafer. The thickness of the thin film according to the position on the wafer varies from several millimeters to several hundred millimeters. For this reason, the characteristics of the FBAR fabricated on the wafer vary slightly depending on the position. The above-mentioned matters are a factor of yield reduction in FBAR manufacturing.

On the other hand, lasers are widely used in the industrial fields such as communication, medical, processing, and the like, in particular, it is necessary to pay attention to the technology of marking by punching or stamping an object, the technology of cleaning the wafer surface. The principle of the technique is that when a laser beam is irradiated onto the material, the material absorbs the energy of the laser beam and breaks down a bond of molecules or atoms constituting the material, thereby releasing a part of the material from the body in a plasma state or a gas state. Let's do it. By using this principle of the laser, by removing some thickness of the upper or lower surface of the resonator unit 1 of the FBAR and adjusting the thickness of the resonator unit 1, the resonance frequency of the FBAR can be tuned.

The present invention relates to a resonant frequency tuning method of a FBAR (Film Bulk Acoustic Resonator). Specifically, the surface of the FBAR by irradiating a laser beam to the upper or lower surface of the resonator 1 By removing only a part of the thickness, it is intended to tune the resonance frequency of the FBAR by adjusting the thickness of the resonator 1 of the FBAR.

Figure 1a is a cross-sectional view of the laser beam is irradiated on the thin film surface.

Figure 1b is a cross-sectional view of a portion of the thin film surface is removed after the laser beam is irradiated.

Figure 2a is a cross-sectional view of the FBAR on the elastic reflection layer.

Figure 2b is a cross-sectional view of the FBAR on the membrane.

2C is a cross-sectional view of an FBAR in the form of an airbridge.

Figure 2d is a cross-sectional view of the FBAR to form an air gap by anisotropic etching.

3A is a cross-sectional view showing a common structure of FBAR.

FIG. 3B is a cross-sectional view of the upper surface removed by a portion thickness after irradiating the laser beam to the upper surface of the resonator 1 in FIG.

4 is a plan view of an element formed on a wafer;

FIG. 5A is a plan view of an element when the element on the wafer of FIG. 4 is an FBAR; FIG.

5B is a cross-sectional view taken along the line D-D 'in FIG. 5A.

FIG. 5C is a cross-sectional view taken along the line AA ′ in FIG. 5A;

5D is a cross-sectional view taken along the line A-A 'of FIG. 5A after irradiating a laser beam to the upper surface of the resonator unit 1;

6A is a plan view of an element when the element on the wafer of FIG. 4 is an FBAR filter;

FIG. 6B is a cross-sectional view taken along the line BB ′ in FIG. 6A;

6C is a cross-sectional view taken along the line B-B 'in FIG. 6A after irradiating a laser beam to the upper surface of the resonator 1 of F2 in the FBAR filter;

FIG. 6D is a circuit diagram of the FBAR filter shown in FIG. 6A. FIG.

7 is a flow chart of automatic control for tuning a resonant frequency on a wafer, in accordance with the present invention.

8 is a block diagram showing equipment for automatically tuning the resonant frequency on a wafer, in accordance with the present invention;

9 is a side view of a probe station and a detailed view of a rod for processing according to the present invention.

FIG. 10A is a plan view of an element when the element on the wafer of FIG. 4 is an FBAR duplex; FIG.

Fig. 10B is a circuit diagram of the FBAR duplex shown in Fig. 10A.

FIG. 10C is a cross-sectional view taken along the line CC ′ in FIG. 10A.

10D is a cross-sectional view taken along the line CC ′ in FIG. 10A after irradiating a laser beam to the upper surface of the resonator 1 of F2 and F4 in the FBAR duplex.

Explanation of symbols for the main parts of the drawings

One ; Resonator 2; Chuck Shifter

3; Chuck 4; Machining Rods

5; Frequency measuring probes 6; Fiber optic

7; Detecting sensor 8; Machining Rod Support

9; Chuck support 10; Bottom electrode

11; Lower electrode measurement terminal 14; Piezoelectric Thin Film Layer

20; Upper electrode 21; Upper electrode measuring terminal

30; ground

The present invention removes only a part of the thickness of the surface of the resonator unit 1 by irradiating a laser beam to the upper or lower surface of the resonator unit 1 of the FBAR. Then, since the thickness of the resonator unit 1 of the FBAR is reduced from the beginning, the resonance frequency is slightly higher than the beginning. When the laser beam is irradiated onto the material surface, the material surface receives energy from the laser beam. When the laser beam is irradiated to the surface of the material by adjusting the energy density of the laser beam, the number of pulses per second, the time for which the laser beam is irradiated, and the like, the bond of molecules or atoms constituting the material surface can be broken. Molecules or atoms leave the material surface in a plasma or gaseous state. As shown in Fig. 1A, by focusing the laser beam on the thin film surface and controlling the energy density, the number of pulses per second, and the irradiation time, the thickness of the thin film surface can be removed and adjusted to several hundreds of microseconds. FIG. 1B shows that the thin film surface region irradiated with the laser beam is removed by some thickness. The laser used at this time is selected from a KrF excimer laser, a CO ₂ laser, or a YAG laser, in addition to a laser suitable for the characteristics of the material deposited on the surface of the resonator unit 1, and the energy density of the laser beam, the number of pulses per second, and the irradiation time. You can adjust the process to implement the process.

Since FBAR is manufactured on a wafer in a very small size using MEMS technology, the tuning process using the laser is a resonance frequency measuring device, a laser generating device and an optical system, and a probe station (probe station). It is desirable to have a system capable of controlling a computer) and the like.

An FBAR circuit, that is, an FBAR filter, an FBAR duplexer, and the like can also accurately reach the desired characteristics by tuning the resonance frequencies of the respective FBARs constituting the circuit. This is called tuning the device.

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

The FBAR, which is currently being researched or partially commercialized, has a Bragg reflection form, a membrane form, an air bridge form, an air gap form, and the like, as shown in FIGS. 2A to 2D. Common to all of them is that the electrodes 20 and 10 are formed at the upper and lower portions, and the piezoelectric thin film layer 14 is formed therebetween. The resonance includes the piezoelectric thin film layer 14 and the upper and lower electrode layers 20 and 10. When a signal of natural frequency according to the thickness of the unit 1 is applied from the outside, the FBAR resonates. At this time, the resonant frequency is approximated to f ₀ = v / 2d, where v is the velocity of the acoustic wave in the piezoelectric thin film layer 14, and d is the resonator including the piezoelectric thin film layer 14 and the upper and lower electrodes 20 and 10 ( 1) is the thickness. Therefore, if the resonant frequency f ₀ of the FBAR is 2 GHz, the thickness of the piezoelectric thin film layer 14 is zinc oxide (ZnO) is about 15825 kHz, and the thickness is 26000 kHz when the aluminum nitride (AIN).

However, the thin film process is difficult to deposit precisely to the desired thickness because the various parameters such as the temperature, the process pressure, the gas ratio, the applied power of the substrate is deposited with a margin of error.

One embodiment of tuning and manufacturing a FBAR having a resonance frequency f ₀ of 2 GHz is described. First, reference is made to the drawing shown in FIG. 3A.

When the piezoelectric thin film layer 14 is zinc oxide (ZnO), the thickness of the resonator unit 1 is 15825 when the lower electrode 10 is 1000 mV, the zinc oxide (ZnO) 14 is 13825 mV, and the upper electrode 20 is 1000 mV. However, in practice, the thin film layer is not deposited exactly as described above. Therefore, the process proceeds to approximate the thickness set during the deposition process of each thin film layer, but the deposition is performed so that the thickness of the upper electrode 20 is greater than 1000 kPa when the upper electrode 20 is deposited. Thus, if the thickness of the resonator 1 is about 16200 Å, the thickness of the upper electrode 20 is about 1375 ,, and the laser beam is irradiated onto the surface of the upper electrode 20 of the resonator 1 to remove the thickness of 375 Å. 3B, the resonator 1 has a thickness of 15825 GPa. Of course, there are several orders of magnitude error.

Even when the piezoelectric thin film layer 20 is aluminum nitride (AlN), the thickness of the resonance part 1 is adjusted in the same manner as described above.

Devices such as FBARs, FBAR filters, and FBAR duplexers are recommended to complete the tuning process in the wafer state prior to packaging.

4 shows a device (FBAR or FBAR filter or FBAR duplex) on the wafer.

FIG. 5A is a plan view when the element shown on the wafer in FIG. 4 is an FBAR. FIG. FIG. 5B is a cross-sectional view taken along the line D-D 'of FIG. 5A and shows that the measuring terminal 11 of the lower electrode, the measuring terminal 21 of the upper electrode, and the ground 30 are at the same height. This protects the frequency measuring probe 5 and makes the measurement easy when measuring the resonance frequency. FIG. 5D is a cross-sectional view of tuning a resonance frequency of one element FBAR in a wafer state, wherein the thickness of the resonance portion 1 is smaller than that of the FBAR before tuning the resonance frequency shown in FIG. 5C.

FIG. 6A is a plan view when the element shown on the wafer of FIG. 4 is an FBAR filter, where F1 is FBAR connected in series on a circuit and F2 is FBAR connected in parallel. Since the measuring terminal 11 of the lower electrode, the measuring terminal 21 and the ground 30 of the upper electrode are exposed to the upper surface, the resonance frequency can be measured for each FBAR.

FIG. 10A is a plan view when the device shown on the wafer of FIG. 4 is an FBAR duplex, where F1 is FBAR connected in series in a circuit, F2 is FBAR connected in parallel, and a reception filter Rx Where F3 is FBAR connected in series in circuit and F4 is FBAR connected in parallel. In addition, since the measuring terminal 11 of the lower electrode, the measuring terminal 21 and the ground 30 of the upper electrode are exposed on the upper surface, the resonance frequency can be measured for each FBAR.

In order to tune the resonant frequency, first, the equipment to tune the resonant frequency of the FBAR must be provided.

8 is a block diagram showing equipment for automatically tuning the resonant frequency in a wafer state. It is equipped with a laser generator, optical system, frequency measuring device, probe station (a device capable of surface treatment of FBAR in a wafer state), and a computer so that the devices can be controlled by one system.

The devices function as follows.

The probe station assists in measuring the resonant frequency of each FBAR in the device in the wafer state, and simultaneously processes the surface of the resonator 1 of the FBAR directly with a laser beam through the processing rod 4. As a device capable of doing this, the structure of the probe station is shown in FIG. According to FIG. 9, the chuck 3 is positioned at the lower part of the chuck moving device 2, and the chuck 3 is positioned at the upper part of the chuck moving device by the chuck support 9, and the chuck 3 is horizontally positioned by the chuck moving device 2. The chuck 3 is a device that can fix the wafer horizontally by using a vacuum or the like. The upper part of the chuck has a processing rod 4 (frequency measuring probe) 5) and an optical fiber 6 for transmitting a laser beam and a sensor 7 for element detection are built in the rod support 8. The laser generator generates a laser suitable for processing the upper material of the resonator unit 1 of the FBAR (adjusting the energy density and the number of pulses per second), and the optical system uses the generated laser beam for processing the probe station through the lens and the optical fiber. It serves to deliver to the rod (4). The frequency measuring device receives the signal measured from the frequency measuring probe 5 in the processing rod 4, measures the resonance frequency, and transmits information about the resonance frequency to a computer. The computer receives information about the resonant frequency of the FBAR from the frequency measuring device, and compares the resonant frequency set as a reference, and controls the laser generator to generate a laser beam suitable for resonant frequency tuning. Information is collected from the sensing sensor 7 to control the chuck 3 through the chuck moving device 2.

After the automatic tuning equipment as described above, a flow chart shown in FIG. 7 is programmed and installed in a computer.

The flowchart shown in FIG. 7 is as follows.

The first step of setting defaults,

A second step of setting the reference position of the element on the wafer,

A third step of measuring the resonant frequency of the designated FBAR in the designated device,

A fourth step of comparing and determining the measured resonance frequency with the set resonance frequency;

The fifth step of tuning the resonance frequency of the designated FBAR to the set value;

A sixth step of determining whether to continue the tuning process of the designated device;

The seventh step of moving the measurement target to the next designated FBAR and executing again from the third step,

The eighth step of judging whether to continue the tuning process of the wafer;

The ninth step of moving the measurement target to the next designated element and executing again from the third step,

In accordance with the first to ninth steps described above, resonant frequency tuning of FBARs in each device on the wafer is automatically controlled. In the first step, by default, the appropriate energy density of the laser beam, the number of pulses per second, according to the material deposited on the upper surface of the resonator 1, and tuning each target FBAR in the device to the target resonance frequency value This step is to set the target device to be tuned and input it to the computer. In the first step, it is preferable that information on the reaction between the laser beam and a substance is documented, stored in a computer, and recalled when necessary. The second step is to move the chuck 3 under the control of the computer to position the first tuning target element and the machining rod 4 and to align the wafer for the tuning process. The third step is to measure the resonant frequency by contacting the measuring terminal of the designated FBAR by moving the frequency measuring probe 5 embedded in the processing rod 4 downward (may move the chuck 3 upward). to be. Step 4 compares and analyzes the set resonance frequency value and the measured resonance frequency value. If the measured resonance frequency value is equal to the set resonance frequency value, tuning is not necessary. Therefore, the fourth step is performed, and the measured resonance frequency value is set. If it is less than the resonant frequency value, tuning is required to execute the fifth step. In the fifth step, tuning is performed by controlling the thickness of the laser beam by controlling the irradiation time of the laser beam to irradiate the upper portion of the resonator unit 1. The sixth step causes the eighth step to be performed when there are no more measurement targets in the designated device, and the seventh step if the measurement targets remain. In the eighth step, if the device to be measured is no longer on the wafer, the tuning is completed on the wafer, and if the measurement object remains, the ninth step is executed.

An embodiment in which the resonant frequency of the FBAR in the device is tuned in the wafer state by the tuning device of FIG. 8 and the above-described automatic control method is described below.

In the wafer station of FIG. 9, the wafer on which the device process is completed in the wafer state is placed and the default value is input to the computer. Here, the default value is first, information on the laser beam, that is, the energy density of the laser beam according to the material deposited on the resonator 1 of the FBAR, the number of pulses per second setting, and second, the number of FBAR to be tuned in the device And the target resonance frequency setting by tuning for each FBAR. Third, the order of elements to be tuned. After entering the default value and starting execution, the sensor 7 embedded in the machining rod 4 transmits the wafer information to the computer, and the computer moves the chuck 3 so that the machining rod 4 can be tuned first. The wafer is positioned at the top of the wafer, and the wafer is aligned to facilitate the tuning process. The computer controls the chuck 3 to move upward and bring the frequency measuring probe 5 embedded in the machining rod 4 into contact with the designated FBAR measurement terminal in the designated element. Alternatively, the chuck 3 may be fixed, and the frequency measuring probe 5 in the machining rod 4 may be moved downward to contact the designated FBAR measurement terminal. The frequency measuring device transmits the resonant frequency value of the designated FBAR to the computer, and the computer determines whether or not to tune with the input set resonant frequency value. When tuning, the laser generator is controlled to reach the upper surface of the resonance section 1 of the FBAR through the optical fiber 6 embedded in the processing rod 4, and tuning is performed. When the tuning of the designated FBAR is not necessary or the tuning is completed, the chuck 3 is moved downward, and then the chuck 3 is horizontally moved to move the machining rod 4 to the next measurement target FBAR. Here, the measuring rod 5 may be moved upward without moving the chuck 3 downward, and then the chuck 3 may be horizontally moved to move the processing rod 4 to the next measurement target FBAR.

In the same manner as described above, when the resonant frequency tuning of the FBAR for one device is completed, the processing rod 4 is moved to the next tuning target device, and the resonant frequency tuning of the FBARs in the device is performed again. All specified devices on the wafer are tuned.

As described above, if FBAR, FBAR filter, FBAR duplex, etc. are manufactured in a microminiature on a wafer by a general semiconductor process using MEMS technology, it is difficult to manufacture all devices manufactured on the wafer in the thin film process to have the same characteristics. As a result, the yield is lowered and the economy is lost. According to the present invention, a tuning step is performed for each device, so that all devices manufactured on the wafer can be manufactured to have almost the same characteristics, thereby overcoming the problem of reduced yield. Therefore, it is possible to secure economic feasibility and to benefit the high frequency field of the communication component industry.

Claims (4)

In the method of tuning the resonant frequency of the FBAR Resonance frequency tuning method of the FBAR, characterized in that by tuning the resonant frequency of the FBAR by adjusting the thickness of the resonator (1) by removing only a part of the thickness of the upper surface of the resonator (1) using a laser beam. The resonance frequency tuning method of an FBAR according to claim 1, wherein the resonance frequency of the FBAR constituting the element is tuned to each element on the wafer in the wafer state. In tuning the resonant frequency of the FBAR, The first step of setting defaults, A second step of setting the reference position of the element on the wafer, A third step of measuring the resonant frequency of the designated FBAR in the designated device, A fourth step of comparing and determining the measured resonance frequency with the set resonance frequency; The fifth step of tuning the resonance frequency of the designated FBAR to the set value; A sixth step of determining whether to continue the tuning process of the designated device; The seventh step of moving the measurement target to the next designated FBAR and executing again from the third step, The eighth step of judging whether to continue the tuning process of the wafer; The ninth step of moving the measurement target to the next designated element and executing again from the third step, Method for automatically controlling the tuning made of a FBAR. In tuning the resonant frequency of the FBAR using a laser beam, FBAR resonant frequency, characterized in that the laser generator and the optical system, frequency measuring device, probe station, computer can be configured as one system as shown in Figure 8 to automatically tune the resonant frequency of the FBAR Tuning device.