CN101630946A - Film bulk acoustic resonator (FBAR) and preparation method thereof - Google Patents

Abstract

The invention discloses a thin-film bulk acoustic resonator and a preparation method thereof. The thin-film bulk acoustic resonator is composed of an integrated substrate, an acoustic wave reflection layer and a sandwich piezoelectric stack. The substrate is composed of an FBAR The integrated circuit chip for signal processing and the passivation layer deposited on the integrated circuit chip and whose surface is polished, the acoustic wave reflection layer and the sandwich piezoelectric stack are located on the passivation layer surface of the substrate. The thin film bulk acoustic resonator of the present invention does not occupy additional silicon chip area, can greatly reduce the chip area and cost, and has a simple and reliable structure, which is convenient for sensing, and the FBAR and the processing circuit are connected through interconnection holes, which can reduce the reflection of radio frequency signals , can be used in the single-chip integrated design of various radio frequency systems and micro mass sensing systems.

Description

A thin film bulk acoustic resonator and its preparation method

technical field

The invention relates to the technical field of microelectronics, in particular to a film bulk acoustic resonator FBAR and a manufacturing method thereof.

Background technique

Wireless communication is developing towards high communication frequency, high transmission rate, high-intensity multiplexing and high integration. At present, semiconductor technology can fully integrate active devices into a chip, but passive frequency devices cannot be integrated, which seriously restricts the development of RFIC. Passive components are mainly multiplexers, filters, resonators and matching LC networks. Resonators can form multiplexers, filters, oscillators, etc. A wireless transceiver requires multiple resonators to form multiplexers, VCO and RF filter. Therefore, the integration of the basic unit resonator is the key to the problem. At present, wireless communication requires higher-capacity data transmission in a narrow frequency band. For example, the duplexer in the code division multiple access (CDMA) frequency band requires a very steep square coefficient and isolation, and a new generation of multi-channel input and output ( MIMO) To achieve multi-I/O communication in a very narrow channel, a multiplex filter with excellent filtering characteristics is required, and a VCO with low noise and low power consumption requires a high-Q resonator; this requires a high-Q value , low temperature coefficient, and low loss resonators to realize these demanding filters, duplexers, and oscillators. In short, finding a high-Q resonator that can be integrated has become the key to RFIC integration technology, and it is also a hot research topic for major multinational companies.

At present, radio frequency filters are mainly dielectric filters and surface acoustic wave (SAW) filters that cannot be integrated. Although the former has good performance, it is too bulky. The latter has low power capacity and operating frequency, large insertion loss and temperature coefficient, and low Q value. It is difficult to meet the comprehensive performance of frequency selection characteristics, integration and low power consumption required by RF systems. Micro-Electro-Mechanical Systems (MEMS) technology development, especially the appearance of Film Bulk Acoustic Resonator (FBAR) has brought dawn to single-chip integrated high-performance RFIC. FBAR is a bulk acoustic wave (BAW) device with a very simple structure. It is usually composed of a sandwich piezoelectric stack fabricated on a silicon substrate. The sandwich piezoelectric stack is composed of a lower electrode, a piezoelectric film and an upper electrode. Standing wave resonance is formed by reflection in the sandwich structure of the lower electrode, the piezoelectric film, and the upper electrode.

FBAR has the advantages of high operating frequency, excellent performance in the radio frequency band, potential compatibility with semiconductor processes, and good power carrying capacity. It is considered to be the most promising GHz radio frequency front-end solution that can be fully integrated on chips. Its excellent filtering characteristics, low insertion loss and low temperature coefficient make it have an important application prospect in the field of ultra-low power RF front-end. At the same time, due to its high sensitivity (Q>1200), FBAR is also used as a micromass sensor and is widely used in the fields of chemistry and biology. Due to the broad application prospects of FBAR, its integration research has received more and more attention. At present, there are mainly two integration strategies: hybrid integration and monolithic integration. Hybrid integration is to manufacture the FBAR circuit and the original integrated circuit on two mutually independent substrates, and then bond the two together with metal wires to form a complete circuit, so that the MEMS process of FBAR and the CMOS process of the signal processing circuit can be Completed separately, regardless of its process compatibility. Using this method to integrate FBAR as an oscillator can refer to "A 300uW 1.9GHz CMOS Oscillator Utilizing Micromachined Resonators" (IEEE J.Solid-State Circuit, Jul.2003, vol.38, pp1271-1274) by BPOtis et al. The firmness is not high, and it is not suitable for mass production of products. The monolithic integration method is to fabricate the FBAR and the FBAR signal processing integrated circuit on a silicon chip, use the CMOS process to realize the FBAR signal processing integrated circuit, and then use the post-CMOS process to realize the FBAR, and connect them through metal wiring. In 1993, this technology was disclosed in U.S. Patent No. 5,260,596. Although the area is smaller than the hybrid integration method using different substrates, because the FBAR and CMOS circuits are fabricated and interconnected on the same substrate plane, the process is complicated and the area is not large. would decrease too much. In 2005, there were reports on the implementation of FBAR integration based on this technology, which can be found in "Integration of high-Q BAW resonators and filters above IC" by MADubois et al. (IEEE International Solid-State Circuits Conference, Digest of Technical Papers.2005, pp 392- 393) and "A SiGe: CBiCMOS WCDMA Zero-IF RF Front-End Using an Above-IC BAW Filter" by JF Carpentier et al. (IEEE International Solid-State Circuits Conference, Digest of Technical Papers. 2005, pp 394-395). In 2008, the patent document WO 2008/101646A1 proposed a monolithic integration technology, which is to invert the FBAR, use a metal layer to support the electrical contact of the CMOS circuit, and form an air gap structure. This method can further reduce the chip area, but still requires Two sets of different processes prepare FBAR and CMOS circuits separately, and this method uses a support structure, the reliability is not high enough, and the yield rate will be relatively low. The above integration technologies all require a single silicon chip area for manufacturing FBAR, which is fabricated on a single silicon chip, and FBAR generally has an area of 1-5×10 ⁴ um ² , which is too large and expensive for silicon integrated circuits. high.

In short, realizing simple integration and reducing the silicon area occupied by FBAR are the key technologies to reduce its cost. Therefore, there is a need for an FBAR integration process, which can realize the monolithic integration of the FBAR and the existing original integrated circuit process, with small chip area and high structural reliability.

Contents of the invention

The present invention provides a film bulk acoustic resonator (FBAR) structure and its integrated manufacturing method. The film bulk acoustic resonator of the present invention does not occupy additional silicon chip area, can greatly reduce the chip area and cost, and has a simple and reliable structure, which is convenient for transmission. Sense, FBAR and processing circuit are connected through interconnection holes, which can reduce the reflection of radio frequency signals, and can be used in single-chip integrated design of various radio frequency systems and micro mass sensing systems.

A thin film bulk acoustic resonator is composed of an integrated substrate, an acoustic wave reflection layer and a sandwich piezoelectric stack. The substrate is composed of an integrated circuit chip capable of FBAR signal processing and deposited on the integrated circuit chip And the surface is composed of a polished passivation layer, the acoustic wave reflection layer is located on the polished surface of the passivation layer of the substrate, and the sandwich piezoelectric stack is located on the surface of the acoustic wave reflection layer.

The integrated circuit chip in the sandwich piezoelectric stack and the substrate is connected by an interconnection via hole, and a conductive medium (such as tungsten, etc.) is poured into the interconnection via hole to realize the sandwich piezoelectric stack and the integrated circuit chip in the substrate circuit connection.

In order not to affect the normal operation of the thin-film bulk acoustic resonator, the position of the interconnection holes should avoid the piezoelectric working area of the sandwich piezoelectric stack.

The position between the acoustic reflection layer and the sandwich piezoelectric stack only needs to be arranged according to the prior art. The main difference between the film bulk acoustic resonator of the present invention and the prior art is that the substrate used is an integrated circuit chip capable of FBAR signal processing , and the surface of the integrated circuit chip is passivated and polished, and the chip and the piezoelectric stack are connected by interconnection via technology.

The present invention also provides a method for manufacturing the thin film bulk acoustic resonator, comprising the following steps:

(1) Utilize the existing technology to make an integrated circuit chip capable of FBAR signal processing (can be under the premise of ensuring its function, select a chip of various process types), deposit a passivation layer on the surface of the integrated circuit chip, The material of the passivation layer is silicon dioxide, borosilicate glass, phosphosilicate glass, silicon nitride or photosensitive resin, with a thickness of 0.1-100um. The deposition of the passivation layer can be completed by existing technologies such as low-pressure chemical vapor deposition equipment. Then, the surface of the passivation layer is polished by chemical mechanical polishing (CMP) to obtain a substrate.

The photosensitive resin is polyimide photosensitive resin, benzocyclobutene photosensitive resin or epoxy photosensitive resin;

(2) On the surface of the polished passivation layer of the substrate, an acoustic wave reflection layer and a sandwich piezoelectric stack are sequentially formed.

The advantages of the thin film bulk acoustic resonator of the present invention are:

(1) FBAR, as a frequency-related functional device that cooperates with integrated circuits, is located on top of the original integrated circuit, which can greatly reduce the area of the entire circuit and increase the degree of integration;

(2) Using contact hole technology to realize interconnection, eliminating the need for bonding wires, reducing interconnection parasitics, and improving circuit performance. Interconnection holes are used to connect FBAR and integrated circuits, which reduces the mutual interference of radio frequency signals;

(3) The passivation layer protects the integrated circuit part, especially for the monolithically integrated FBAR sensor;

(4) Strong mechanical fastness, simple and reliable structure, convenient for sensing, very suitable for high-performance radio frequency or sensing system applications in harsh environments.

Description of drawings

Fig. 1 is the top view schematic diagram of the integrated structure of the solid-state assembly type FBAR adopting the Bragg reflection layer of the present invention;

Fig. 2 is a schematic cross-sectional view of the integrated structure of the solid-state assembled FBAR using the Bragg reflective layer of the present invention.

Detailed ways

Referring to FIG. 1 , a schematic top view of an integrated structure of an FBAR using a Bragg reflection layer according to the present invention, and FIG. 2 is a schematic cross-sectional view of an integrated structure of an FBAR using a Bragg reflection layer according to an embodiment of the present invention.

The FBAR in the figure includes a substrate 110 , an acoustic wave reflection layer on it and a sandwich piezoelectric stack 111 , and the acoustic wave reflection layer in the figure is composed of a layer of low acoustic impedance film 104 and a layer of high acoustic impedance film 105 .

The substrate 110 is composed of an integrated circuit chip 109 capable of FBAR signal processing and a passivation layer 106 deposited on the integrated circuit chip 109 and whose surface is polished.

The sandwich piezoelectric stack includes an upper electrode 101 , a lower electrode 103 and a piezoelectric layer 102 .

The sandwich piezoelectric stack 111 and the integrated circuit 109 in the substrate realize circuit communication through the interconnection via hole 107 and the interconnection via hole 108 filled with conductive medium tungsten.

When FBAR of the present invention is made, at first be to use CMOS technology to manufacture the integrated circuit chip 109 that can carry out FBAR signal processing on the silicon wafer, adopt the low pressure chemical vapor deposition equipment (LPCVD) to plate the thick 50um on the integrated circuit chip 109 then Oxygen passivation layer 106 (silicon nitride), then chemical mechanical polishing (CMP) is carried out to passivation layer 106, the upper surface is polished smooth, and the substrate 110 of the FBAR integrated structure of the present invention is formed at this moment, and the smoothness of the substrate 110 surface The property affects the reflection of sound waves on the surface, the smoother and smoother the Q value of FBAR is, the higher it will be.

Then, on the surface of the substrate 110 , a pair of Bragg acoustic reflection layers of the FBAR, that is, a low acoustic impedance film 104 and a high acoustic impedance film 105 , is sequentially fabricated.

The low acoustic impedance film 104 is made of aluminum (Al) and prepared by DC magnetron sputtering method, and the high acoustic impedance film 105 is made of SiO ₂ and prepared by LPCVD method.

Next, the FBAR sandwich structure piezoelectric stack 111 is to be fabricated on the Bragg reflective layer, including the upper electrode 101, the piezoelectric layer 102, and the lower electrode 103. The upper and lower electrodes are made of aluminum (Al) electrodes and DC sputtering method is used. For preparation, the material of the piezoelectric layer 102 can be selected from aluminum nitride (AlN) and prepared by radio frequency magnetron reactive sputtering.

Finally, the interconnection via hole 107 and the interconnection via hole 108 are made, and the upper electrode 101 and the lower electrode 103 of the FBAR are respectively connected with the integrated circuit 109 by using tungsten plug technology, so as to realize the complete function of the monolithic integrated system.

The integrated FBAR of the present invention has strong integrated mechanical fastness, simple and reliable structure, is convenient for sensing, is applied to radio frequency or sensing systems, and has good adaptability to various complex environments.

Claims (6)

1. A thin film bulk acoustic resonator is characterized in that it is composed of an integrated substrate, an acoustic reflection layer and a sandwich piezoelectric stack. The substrate is composed of an integrated circuit chip that can process FBAR signals and The passivation layer is deposited on the integrated circuit chip and its surface is polished, the acoustic wave reflection layer is located on the polished surface of the substrate passivation layer, and the sandwich piezoelectric stack is located on the surface of the acoustic wave reflection layer. 2. The thin film bulk acoustic resonator according to claim 1, characterized in that the sandwich piezoelectric stack and the integrated circuit chip in the substrate are connected by interconnection holes. 3. A method for manufacturing a thin-film bulk acoustic resonator, comprising the steps of: (1) making an integrated circuit chip capable of FBAR signal processing, after depositing a passivation layer on the surface of the integrated circuit chip, the surface of the passivation layer is polished to obtain a substrate; (2) An acoustic wave reflection layer and a sandwich piezoelectric stack are sequentially formed on the surface of the polished passivation layer of the substrate. 4. The manufacturing method according to claim 3, wherein the material of the passivation layer is silicon dioxide, borosilicate glass, phosphosilicate glass, silicon nitride or photosensitive resin. 5. The manufacturing method according to claim 3, wherein the passivation layer has a thickness of 0.1-100um. 6. The manufacturing method according to claim 4, wherein the photosensitive resin is polyimide photosensitive resin, benzocyclobutene photosensitive resin or epoxy photosensitive resin.

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