Bragg Acoustic Reflecting Layer Structure and Manufacturing Method and Solid-State Mounted Resonator

Abstract

Disclosed is a method for fabricating a Bragg acoustic wave reflection structure, comprising: fabricating a reflective layer group formed by sequentially stacking a first dielectric layer and a second dielectric layer on a substrate; performing ion implantation on the second dielectric layer in the reflective layer group To increase the acoustic impedance of the second dielectric layer. Also disclosed is a Bragg acoustic wave reflective layer structure manufactured by the above method, the Bragg acoustic wave reflective layer structure has a flat reflective layer, and a solid assembly resonator comprising the Bragg acoustic wave reflective layer structure, which also includes a Bragg acoustic wave Bottom electrode layer, piezoelectric layer and top electrode layer on reflective layer. The process of the Bragg acoustic wave reflective layer structure does not need to use etching and CMP processes, and the cost is greatly reduced. The ion implantation process is used to prepare a high-quality high-acoustic impedance dielectric reflective layer, and the non-implanted area suppresses the parasitic capacitance due to its insulation. Produced, and can obtain reflective layers for high and ultra-high frequency acoustic wave resonators.

Description

technical field [0001] The application relates to the field of communication devices, and mainly relates to a Bragg acoustic wave reflection layer structure, a manufacturing method thereof, and a solid-state assembled resonator. Background technique [0002] With the increasingly crowded electromagnetic spectrum and the increase of frequency bands and functions of wireless communication equipment, the electromagnetic spectrum used by wireless communication has grown rapidly from 500MHz to above 5GHz. Therefore, there is a demand for RF front-end modules with high performance, low cost, low power consumption, and small size. also growing. The filter is one of the RF front-end modules, which can improve the transmitted and received signals, and is mainly composed of multiple resonators connected through a topology network structure. Baw (Bulk Acoustic Wave) is a bulk acoustic wave resonator. The filter composed of it has the advantages of small size, strong integration abilit...

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Problems solved by technology

According to F=v / λ, v is the sound velocity of the sound wave in the piezoelectric layer. For example, the velocity in AlN under certain process conditions is 9400m / s, and λ is twice the thickness h of the resonator film, that is, λ=2h. The thickness includes For electrodes and piezoelectric layers, the higher the frequency, the smaller the wavelength, the lower the thickness of the Bragg reflective layer that needs to be processed, especially when processing ultra-high frequency devices, such as 6Ghz-20Ghz, the thickness of the Bragg reflective layer is 0.1175μm- 0.33571μm, when the frequency range is 100GHz-10THz, the thickness of the Bragg reflective layer is 0.28nm-28.37nm. At this time, the reflective layer is very thin, and the existing process methods cannot make high-quality Bragg reflective layers

After the frequency of the device exceeds 6Ghz, the preparation of the reflective layer is facing more and more challenges. When the thickness of the reflective layer film is less than 200nm, the difficulties brought about by this process begin to appear. The reflective layer film is 100nm or even smaller. It is impossible to achieve mass production. , yield and process cost verification restrict the technical development of such devices

When the high acoustic impedance layer is metal, its processing must be etched, and its overlapping shadow with the resonator is not allowed to exceed the working area of ​​the resonator. If it exceeds, it will cause parasitic formation between the electrodes and the high acoustic impedance layer when they are connected outwards. capacitance, causing the device not to function properly

The bottom electrode extension forms parasitic capacitance with the metal reflective layer (even all metal reflective layers in the vertical direction), which affects device performance

[0004] In the prior art, there are the following problems when processing the Bragg reflective layer: when using CVD to process the dielectric film or PVD to process the metal film to 100nm or below, the stress and uniformity cannot be guaranteed, the product consistency is poor, and the process is unstable, which will lead to Bragg reflection. The reflection effect of the layer becomes worse, lower than 90% or even 80%, making the resonator unable to work normally, or even completely ineffective; this problem also exists when the MoCVD method is used to process dielectric or metal thin films, and the temperature of the process is higher, usually 800 ℃, the stress control and uniformity are even worse; CMP cannot guarantee the uniformity of the process when grinding the dielectric thin film <100nm. The effect will deteriorate sharply or even fail completely; methods such as ALD and MBE can process some dielectric and technical materials, but metal films still need to be etched, and the etching process will cause roughness between the reflective layer interfaces (for example, after etching the metal and then Deposit the dielectric layer, and then CMP can no longer be used to make up for the over-etching defects caused by etching metal, because CMP cannot guarantee uniformity and cannot be applied anymore), the reflection effect of the reflective layer will deteriorate sharply or even fail completely

Low Acoustic Impedance Layer Prepared SiO by CVD 2 Thin film and high acoustic impedance layer are deposited and etched by PVD method. After multiple layers are completed alternately, piezoelectric electrodes and piezoelectric layers are processed above this area to form an effective resonance area. This solution faces technical bottlenecks at high frequencies and cannot produce high Thin films with uniformity and good stress control cannot be used in CMP process, and the etching of high acoustic impedance layer will also cause the interface between the reflective layers to be rough, so it is impossible to process high-quality resonator reflective layers

Also in some existing technologies, the high and low acoustic impedance reflective layer is trapped in the substrate, which effectively suppresses the parasitic capacitance generated by the top / bottom electrode extending outside the effective area, but the making of the reflective layer requires multiple CMP (chemical mechanical Polishing) processing, the reflective layer of high-frequency devices is <100 nanometers in thickness. At this time, CMP is not compatible, and it is difficult to prepare a high-quality reflective layer, or the film thickness uniformity after CMP processing is poor, which deteriorates the Bragg reflective layer. The reflection effect of bulk acoustic wave, when the high acoustic impedance layer is etched, also leads to the morphology problem at the interface of high and low acoustic impedance. Both factors will lead to the deterioration of the reflection effect, the failure of the resonator, and the decrease of the Q value. Bottleneck, unable to process high-quality resonators

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