Low-damage etching method for frequency modulation layer of resonator

Abstract

The invention discloses a low-damage etching method for a frequency modulation layer of a resonator, which comprises the following steps of: preparing a bottom electrode and a piezoelectric layer structure of the resonator on a substrate of the resonator, and carrying out photoetching treatment on the frequency modulation layer film of the resonator based on a top electrode and a frequency modulation layer film of the continuous sputtering resonator; and finally, carrying out ion beam etching on the frequency modulation layer thin film subjected to photoetching treatment to a target thickness to obtain a required frequency modulation layer pattern. According to the scheme, the frequency modulation layer of the resonator is etched based on the ion beam etching technology, etching materials are not limited, parameters in the ion beam etching process are optimized, low-speed and low-power etching is achieved, the etching effect is improved, meanwhile, the wafer yield is increased, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a low-damage etching method for a resonator frequency modulation layer. Background Art

[0002] Film Bulk Acoustic Resonator (FBAR) has the characteristics of miniaturization, high operating frequency, high power capacity and high integration, which meets the requirements of 5G communication system for RF resonators and has broad application prospects and development space. In its preparation technology, the accuracy of the device frequency and the uniformity of the frequency distribution depend on the thickness and uniformity of the piezoelectric film and the metal electrode film. At the same time, the quality and morphology of the functional layer film directly affect the performance parameters of the device such as quality factor, insertion loss and bandwidth.

[0003] The main structure of the thin film bulk acoustic wave resonator is a "sandwich" structure consisting of a bottom electrode-piezoelectric layer-top electrode. By inputting a sinusoidal signal between the two electrodes, the resonator uses the inverse piezoelectric effect to convert the input electrical signal into mechanical resonance, and then uses the piezoelectric effect to convert the mechanical resonance into an electrical signal output. At present, existing technologies have proposed using a mass load layer in the resonator to adjust the resonant frequency of the resonator. In the actual production process, when the frequency modulation layer is etched using reactive ion beam etching technology, not only will the piezoelectric layer be over-etched, affecting the accuracy of the chip frequency, but it will also cause damage to the edges of the frequency modulation layer and the piezoelectric layer. When the top electrode and passivation layer are subsequently grown, black lines will be formed on the surface due to the damage. For this situation, we use the method of continuous sputtering of the top electrode and the frequency modulation layer film, and use ion beam etching technology to pattern the frequency modulation layer.

[0004] Ion beam etching technology uses glow discharge to decompose argon gas into argon ions. The argon ions are accelerated by the anode electric field to physically bombard the sample surface, thereby achieving the purpose of etching. Its main advantages are good etching directionality and no drilling; it is physical etching, non-selective to materials, and can etch various materials; the etching rate is well controllable and the pattern resolution is high. However, ion beam etching technology also has limitations, namely the redeposition effect, that is, during the etching process, the etched particles produced cannot completely fly out of the etched groove, and some particles are redeposited on the sidewalls of the groove, forming a redeposition phenomenon. Due to the redeposition effect, when etching the resonator functional layer material, there will be etching residues on the sidewalls of the pattern, affecting the steepness of the sidewalls and the sputtering growth of the subsequent functional layer film. Existing theoretical models show that the amount of redeposited particles on the sidewalls of the etched groove pattern is related to the incident angle of the ion beam. Increasing the incident angle of the ion beam (with the ion beam incident vertically to the surface of the etched material as 0°) can reduce the redeposited residues on the sidewalls and improve the steepness of the sidewalls of the pattern. However, a larger ion beam incident angle will cause the groove bottom to open, resulting in an uneven etched surface at the bottom of the groove, which increases the difficulty of controlling the etching depth.

[0005] Therefore, in order to meet the requirements of high-precision thickness and graphic contour control of the resonator frequency modulation layer film, it is particularly important to achieve low-damage etching of the resonator frequency modulation layer. Summary of the invention

[0006] In view of the above problems, an object of the present invention is to provide a low-damage etching method for a resonator frequency modulation layer.

[0007] The specific technical solution for achieving the purpose of the present invention is:

[0008] A low-damage etching method for a resonator frequency modulation layer comprises the following steps:

[0009] Step 1: preparing a bottom electrode and a piezoelectric layer structure of the resonator on a resonator substrate, and based on this, continuously sputtering a top electrode and a frequency modulation layer film of the resonator;

[0010] Furthermore, a cavity is arranged on the resonator substrate, and the material is silicon, gallium arsenide, sapphire or quartz.

[0011] Furthermore, a Bragg reflection layer is arranged on the resonator substrate.

[0012] Furthermore, the bottom electrode material is an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium.

[0013] Furthermore, the piezoelectric layer structural material is made of aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, quartz, potassium niobate or lithium tantalate;

[0014] The top electrode material is an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium;

[0015] The frequency modulation layer material is molybdenum, ruthenium, gold, aluminum, magnesium, tungsten or copper.

[0016] Step 2, performing photolithography on the frequency modulation layer film of the resonator;

[0017] Step 3, ion beam etching is performed on the frequency modulation layer film after the photolithography process to a target thickness to obtain a desired frequency modulation layer pattern;

[0018] Furthermore, the inert gas used in the etching process of the frequency modulation layer thin film includes at least one of helium, neon, argon, krypton, xenon and radon.

[0019] Furthermore, the inert gas flow rate range of the frequency modulation layer film during the ion beam etching process is 10-30 sccm.

[0020] Furthermore, the ion beam voltage used in the ion beam etching process of the frequency modulation layer film is between 200V and 500V.

[0021] Furthermore, the ion beam current used in the ion beam etching process of the frequency modulation layer thin film is between 400 mA and 500 mA.

[0022] Furthermore, during the ion beam etching process of the frequency modulation layer film, the ion beam angle ranges from 45° to 75°, and the ion beam angle is the angle between the ion beam and the normal line of the plane where the frequency modulation layer film of the resonator is located.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The scheme of the present invention etches the resonator frequency modulation layer based on ion beam etching technology, explores the influence of gas flow rate to achieve low-speed etching, and the step thickness of the frequency modulation layer after patterning is close to the product design value, without over-etching, which is more conducive to product design iteration. At the same time, the role of ion beam voltage and ion beam current is studied to achieve low-power etching, without damage to the surface of the lower structural layer film, avoiding the black line problem, and improving the wafer yield;

[0025] (2) The solution of the present invention etches the resonator frequency modulation layer based on ion beam etching technology, which has no restrictions on etching materials and has a wide range of applications;

[0026] (3) The solution of the present invention can eliminate sidewall deposition while etching the target material by adjusting the angle between the incident direction of the ion beam and the normal line of the wafer plane, thereby simplifying the process flow and improving the production efficiency of the equipment.

[0027] The present invention is further described below in conjunction with specific implementation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic flow chart of the low-damage etching method for the resonator frequency modulation layer of the present invention.

[0029] Figure 2 It is a schematic structural diagram of the thin film bulk acoustic wave resonator of the present invention.

[0030] Figure 3 This is a SEM image of the sample after etching using IBE in Example 1 of the present invention.

[0031] Figure 4 This is a SEM image of the sample step after etching using IBE in Example 1 of the present invention.

[0032] Figure 5 This is a SEM image of the sample after etching using IBE and high-voltage stripping to remove the photoresist in Example 1 of the present invention.

[0033] Figure 6 This is the step profiler test result of the sample after etching using IBE and high-voltage stripping to remove the photoresist in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] Combination Figure 1 The thin film bulk acoustic wave resonator generally includes a substrate 201, a cavity structure 202, a bottom electrode 203, a top electrode 205, a frequency modulation layer 206, and a piezoelectric layer 204 between the bottom electrode 203 and the top electrode 205. In the embodiment of the present invention, the top electrode 205 and the frequency modulation layer 206 are sputtered and grown together on the substrate 201 having the cavity structure 202, and the frequency modulation layer 206 is patterned using an ion beam etching technique, and is etched using appropriate process conditions to obtain a frequency modulation layer pattern with a target thickness removed.

[0035] Combination Figure 2 Specifically, a low-damage etching method for a resonator frequency modulation layer comprises the following steps:

[0036] Step 1: Prepare the bottom electrode 203 and piezoelectric layer 204 structure of the resonator on the resonator substrate 201, and continuously sputter the top electrode 205 and frequency modulation layer 206 thin film of the resonator based on the structure;

[0037] The cavity structure 202 is disposed on the resonator substrate 201 , and the substrate 201 may be made of silicon, gallium arsenide, sapphire or quartz.

[0038] A Bragg reflection layer may also be arranged on the resonator substrate.

[0039] In this embodiment, the bottom electrode 203 may be made of an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium.

[0040] Furthermore, the structural material of the piezoelectric layer 204 can be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), quartz (Quartz), potassium niobate (KNbO3) or lithium tantalate (LiTaO3), or it can be a rare earth element doped material containing a certain atomic ratio of the above materials.

[0041] The top electrode 205 material may be an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium;

[0042] The frequency modulation layer 206 can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten or copper.

[0043] Step 2, performing photolithography on the frequency modulation layer 206 thin film of the resonator;

[0044] Step 3, ion beam etching is performed on the frequency modulation layer 206 film after the photolithography process to a target thickness to obtain the desired frequency modulation layer 206 pattern;

[0045] Specifically regarding the parameters of ion beam etching, the inert gas used in the etching process of the frequency modulation layer thin film includes at least one of helium, neon, argon, krypton, xenon, and radon.

[0046] The inert gas flow rate range of the frequency modulation layer film during the ion beam etching process is 10-30 sccm.

[0047] The ion beam voltage used in the ion beam etching process of the frequency modulation layer film is between 200V and 500V.

[0048] The ion beam current used in the ion beam etching process of the frequency modulation layer film is between 400 mA and 500 mA.

[0049] In addition, during the ion beam etching process of the frequency modulation layer film, the ion beam angle ranges from 45° to 75°, where the ion beam angle is the angle between the ion beam and the normal line of the plane where the frequency modulation layer film of the resonator is located.

[0050] In order to clearly describe the technical solution and the effects achieved by the present invention, the technical solution of the present invention is clearly explained below in combination with the accompanying drawings and specific embodiments of the present invention, so that technical personnel in the field can implement the invention without performing creative work. The structure shown in the accompanying drawings is not the entire actual structure but only a part of the actual structure. It should be noted that all other embodiments made by ordinary technical personnel in the field on the basis of the embodiments of the present invention without performing creative work should fall within the protection scope of the present invention.

[0051] The following examples are only for better explanation of the present invention, but the content of the present invention is not limited to the application in the examples. Therefore, those skilled in the art can make non-essential modifications to the implementation scheme based on the above invention content and apply it to other embodiments, which is still within the protection scope of the present invention. In addition, the experimental methods without specific conditions in the following examples should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the expressions in the text are not specially explained, they are only used for distinction and have no other meanings.

[0052] Example 1

[0053] Step 1, sputtering a layer with a thickness of The AlN piezoelectric layer 204 and Mo top electrode 205 and frequency modulation layer 206;

[0054] Step 2, transferring the wafer after the photolithography of the frequency modulation layer 206 thin film to an ion beam etching device for etching process, during the etching process, using 10sccm Ar, ion beam voltage of 200V, ion beam current of 400mA, sample stage tilt angle of 60°, and stop etching after the target thickness is reached;

[0055] Step 3: Take out the wafer and carry out subsequent process operations.

[0056] SEM of samples etched with IBE is shown in Figure 3 Before etching, the thickness of the piezoelectric layer AlN is about The thickness of metal Mo is After IBE process, see Figure 4 , etched about The target material. After that, the photoresist is removed by high-voltage stripping, and the remaining Mo metal film thickness is about Left and right, such as Figure 5 As shown, it is consistent with the etching design value.

[0057] In addition, the samples were characterized using a step profiler, e.g. Figure 6 As shown, the height of the step is about This is consistent with the SEM results, and no obvious sidewall residues appear on both sides of the step.

[0058] Example 2

[0059] Step 1, sputtering a layer with a thickness of The AlN piezoelectric layer 204 and Mo frequency tuning layer 206 and top electrode 205;

[0060] Step 2, transferring the wafer after the photolithography of the frequency modulation layer 206 thin film to an ion beam etching device for etching process, during the etching process, using 14sccm Ar, ion beam voltage of 500V, ion beam current of 500mA, sample stage tilt angle of 75°, and stop etching after the target thickness is reached;

[0061] Step 3: Take out the wafer and carry out subsequent process operations.

[0062] Example 3

[0063] Step 1, sputtering a layer with a thickness of The AlN piezoelectric layer 204 and A Mo top electrode 206 and a frequency modulation layer 205;

[0064] Step 2, transferring the wafer after the photolithography of the frequency modulation layer 205 thin film to an ion beam etching device for etching process, during the etching process, using 14sccm Ar, ion beam voltage of 200V, ion beam current of 400mA, sample stage tilt angle of 45°, and stop etching after the target thickness is reached;

[0065] Step 3: Take out the wafer and carry out subsequent process operations.

[0066] The scheme of the present invention etches the frequency modulation layer of the resonator based on ion beam etching technology, controls the parameters in the etching process, and explores the influence of gas flow rate to achieve low-speed etching. The step thickness of the frequency modulation layer after patterning is close to the product design value, and there is no over-etching of thickness, which is more conducive to product design iteration. At the same time, the role of ion beam voltage and ion beam current is studied to achieve low-power etching. The surface of the thin film of the lower structural layer is not damaged, the black line problem is avoided, and the wafer yield is improved.

[0067] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A low-damage etching method for a resonator frequency modulation layer, characterized in that: The following steps are involved: Step 1: preparing a bottom electrode and a piezoelectric layer structure of the resonator on a resonator substrate, and based on this, continuously sputtering a top electrode and a frequency modulation layer film of the resonator; Step 2, performing photolithography on the frequency modulation layer film of the resonator; Step 3: Perform ion beam etching on the frequency modulation layer film after the photolithography process to a target thickness to obtain a desired frequency modulation layer pattern.

2. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The inert gas used in the etching process of the frequency modulation layer film in step 3 includes at least one of helium, neon, argon, krypton, xenon and radon.

3. The low damage etching method for the resonator frequency modulation layer according to claim 2, characterized in that: The inert gas flow rate range of the frequency modulation layer film in step 3 during the ion beam etching process is 10-30 sccm.

4. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The ion beam voltage used in the ion beam etching process of the frequency modulation layer film in step 3 is between 200V and 500V.

5. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The ion beam current used in the ion beam etching process of the frequency modulation layer film in step 3 is between 400 mA and 500 mA.

6. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The low-damage etching method for the frequency modulation layer of a resonator according to claim 1 is characterized in that, during the ion beam etching process of the frequency modulation layer film in step 3, the ion beam angle range is 45-75°, and the ion beam angle is the angle between the ion beam and the normal of the plane where the frequency modulation layer film of the resonator is located.

7. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: A cavity is arranged on the resonator substrate, and the material is silicon, gallium arsenide, sapphire or quartz.

8. The low-damage etching method for the resonator frequency modulation layer according to claim 7, characterized in that: A Bragg reflection layer is arranged on the resonator substrate.

9. The low-damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The bottom electrode material in step 1 is an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium.

10. The low damage etching method for the resonator frequency modulation layer according to claim 1, characterized in that: The piezoelectric layer structure material in step 1 is aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, quartz, potassium niobate or lithium tantalate; The top electrode material is an alloy of one or more of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium or chromium; The frequency modulation layer material is molybdenum, ruthenium, gold, aluminum, magnesium, tungsten or copper.

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