CN117639697A - Method for forming bulk acoustic wave filter - Google Patents
Method for forming bulk acoustic wave filter Download PDFInfo
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- CN117639697A CN117639697A CN202210983110.9A CN202210983110A CN117639697A CN 117639697 A CN117639697 A CN 117639697A CN 202210983110 A CN202210983110 A CN 202210983110A CN 117639697 A CN117639697 A CN 117639697A
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Classifications
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- H—ELECTRICITY
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- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
- H03H2003/023—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks the resonators or networks being of the membrane type
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
The invention discloses a method for forming a bulk acoustic wave filter, which comprises the following steps: forming a piezoelectric lamination layer on the surface of the temporary substrate wafer, wherein the piezoelectric lamination layer comprises an upper electrode frequency modulation layer, a piezoelectric layer and a lower electrode layer, and the upper electrode frequency modulation layer and the lower electrode layer are respectively positioned on the opposite surfaces of the piezoelectric layer; bonding the front surface of the device wafer with the lower electrode layer and closing the first cavity; removing the temporary substrate wafer to expose the piezoelectric layer; uniformly dividing the upper electrode frequency modulation layer into N areas, and selecting at least one point in each of the N areas as a measuring point; performing first ion beam bombardment on the upper electrode frequency modulation layer to form a first upper electrode frequency modulation layer; and adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first electrode upper electrode frequency modulation layer to form a second upper electrode frequency modulation layer. The invention can improve the uniformity of the upper electrode frequency modulation layer and the qualification rate of the filter.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a method for forming a bulk acoustic wave filter.
Background
With the continuous development of wireless communication technology, in order to meet the multifunctional demands of various wireless communication terminals, terminal devices need to be able to transmit data using different carrier spectrums, and in order to support sufficient data transmission rate within a limited bandwidth, strict performance requirements are also put forward for radio frequency systems. The rf filter is an important component of the rf system and can filter out interference and noise outside the communication spectrum to meet the signal-to-noise requirements of the rf system and communication protocol. Taking a mobile phone as an example, since each frequency band needs to have a corresponding filter, tens of filters may need to be set in one mobile phone.
The film bulk acoustic wave filter is widely applied to mobile communication, and the performance requirement of the filter is higher along with the development of the mobile communication, so that the higher requirement is put on the filter manufacturing process, in general, the film bulk acoustic wave resonator comprises two film electrodes, and a piezoelectric film layer is arranged between the two film electrodes. The device performance of the filter is related to the uniformity of the thickness of the frequency modulation layer, but the uniformity of the thickness of the frequency modulation layer of the current filter is poor, so that the qualification rate of the filter is low.
Disclosure of Invention
The invention aims to provide a method for forming a bulk acoustic wave filter, which can adjust the uniformity of the thickness of a frequency modulation layer of the bulk acoustic wave filter and improve the qualification rate of the filter.
In order to achieve the above object, the present invention provides a method for forming a bulk acoustic wave filter, comprising:
providing a temporary substrate wafer, and forming a piezoelectric lamination layer on the surface of the temporary substrate wafer, wherein the piezoelectric lamination layer comprises an upper electrode frequency modulation layer, a piezoelectric layer and a lower electrode layer, and the upper electrode frequency modulation layer and the lower electrode layer are respectively positioned on the surfaces opposite to the piezoelectric layer;
providing a device wafer, wherein the front surface of the device wafer is provided with a plurality of first cavities, bonding the front surface of the device wafer with the lower electrode layer, and sealing the first cavities;
removing the temporary substrate wafer;
uniformly dividing the upper electrode frequency modulation layer into N areas, selecting at least one point in each of the N areas as a measuring point, and measuring the thickness of the upper electrode frequency modulation layer of the measuring point to obtain the thickness distribution of the upper electrode frequency modulation layer;
performing first ion beam bombardment on the upper electrode frequency modulation layer to form a first upper electrode frequency modulation layer, and measuring the thickness of the first upper electrode frequency modulation layer of a measuring point to obtain thickness distribution of the first upper electrode frequency modulation layer, wherein the thickness of the first upper electrode frequency modulation layer has first uniformity;
Calculating the ion beam bombardment rates of different measuring points according to the thickness difference of the upper electrode frequency modulation layer and the first upper electrode frequency modulation layer of the measuring points;
and adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first electrode upper electrode frequency modulation layer to form a second upper electrode frequency modulation layer, wherein the thickness of the second upper electrode frequency modulation layer has second uniformity, and the second uniformity is smaller than the first uniformity.
The invention has the beneficial effects that:
according to the invention, the surface treatment is carried out on the frequency modulation layer by adopting twice ion beam bombardment, after the first ion beam bombardment is carried out on the frequency modulation layer to form the first frequency modulation layer, the bombardment rates of different areas on the surface of the frequency modulation layer can be calculated based on the thickness changes of different measuring points on the first ion beam bombardment front and back frequency modulation layer and the first frequency modulation layer, and based on the thickness of the first frequency modulation layer which is required to be removed and the ion beam bombardment rate of each measuring point, the point-to-point type second ion beam bombardment is carried out on different areas of the first frequency modulation layer corresponding to different measuring points to form the second frequency modulation layer, so that the thickness of the corresponding area of each measuring point on the second frequency modulation layer is more approximate to or equal to the target thickness value, thereby obtaining the frequency modulation layer with more uniform thickness, and further improving the qualification rate of the filter.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a step diagram of a method for forming a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 2 to fig. 13 are schematic structural diagrams corresponding to different steps of a method for forming a bulk acoustic wave filter according to an embodiment of the present invention.
Fig. 14 is a schematic diagram showing thickness variation of a plurality of measurement points of a frequency modulation layer before and after bombardment of a second ion beam in a bulk acoustic wave filter forming method according to an embodiment of the present invention.
Detailed Description
The most basic structure of the bulk acoustic wave filter is that two metal electrodes clamp a piezoelectric film, sound waves vibrate in the piezoelectric film to form standing waves, the frequency modulation range of the filter frequency is related to the thickness of a deposited material according to design, the deposited material is defined according to the frequency band of the filter, the thicker the deposited thickness is, the larger the frequency modulation range is, as different products need specific frequencies, the thickness of a frequency modulation layer which needs to be fixed is corresponding to the thickness of the frequency modulation layer, the better the uniformity of the thickness of the frequency modulation layer in a wafer is, the higher the qualification rate of the produced filter device is, the worse the uniformity of the thickness is, the frequency of a part of the filter device cannot reach a target value, and the lower the qualification rate of the filter in the wafer is.
In the existing filter manufacturing process, the deposited frequency modulation layer is required to be subjected to surface treatment due to poor uniformity of the deposited upper electrode film, and the existing process adopts primary ion beam bombardment to carry out surface treatment on the frequency modulation layer formed by deposition, but the uniformity of the frequency modulation layer obtained by primary ion beam bombardment is poor due to the fact that a machine table has deviation and film quality is different at different positions in a wafer (bombardment thickness is different at the same time)The standard deviation of the thickness of the obtained frequency modulation layer is generally equal toThe thicknesses of different areas of the frequency modulation layer in the wafer cannot basically reach the target thickness, so that the qualification rate of the filter device produced by the wafer is low.
In order to solve the above problems, a filter forming method of the present invention is described in further detail below with reference to the drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and drawings, however, it should be understood that the inventive concept may be embodied in many different forms and is not limited to the specific embodiments set forth herein. The drawings are in a very simplified form and are to non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
The terms "first," "second," and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other sequences than described or illustrated herein. Similarly, if a method described herein comprises a series of steps, and the order of the steps presented herein is not necessarily the only order in which the steps may be performed, and some of the described steps may be omitted and/or some other steps not described herein may be added to the method. If a component in one drawing is identical to a component in another drawing, the component will be easily recognized in all drawings, but in order to make the description of the drawings clearer, the specification does not refer to all the identical components in each drawing.
Examples
Fig. 1 is a step diagram showing a method for forming a frequency modulation layer of a bulk acoustic wave filter according to embodiment 1 of the present invention.
As shown in fig. 1, a method for forming a bulk acoustic wave filter includes the steps of:
A method of forming a bulk acoustic wave filter, comprising:
providing a temporary substrate wafer, forming a piezoelectric lamination layer on the surface of the temporary substrate wafer, wherein the piezoelectric lamination layer comprises an upper electrode frequency modulation layer, a piezoelectric layer and a lower electrode layer, and the upper electrode frequency modulation layer and the lower electrode layer are respectively positioned on the opposite surfaces of the piezoelectric layer;
providing a device wafer, wherein the front surface of the device wafer is provided with a plurality of first cavities, bonding the front surface of the device wafer with the lower electrode layer, and sealing the first cavities;
removing the temporary substrate wafer;
uniformly dividing the upper electrode frequency modulation layer into N areas, selecting at least one point in each of the N areas as a measuring point, and measuring the thickness of the upper electrode frequency modulation layer of the measuring point to obtain the thickness distribution of the upper electrode frequency modulation layer;
performing first ion beam bombardment on the upper electrode frequency modulation layer to form a first upper electrode frequency modulation layer, and measuring the thickness of the first upper electrode frequency modulation layer of the measuring point to obtain thickness distribution of the first upper electrode frequency modulation layer, wherein the thickness of the first upper electrode frequency modulation layer has first uniformity;
calculating the ion beam bombardment rates of different measuring points according to the thickness difference of the upper electrode frequency modulation layer and the first upper electrode frequency modulation layer of the measuring points;
And adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first electrode upper electrode frequency modulation layer to form a second upper electrode frequency modulation layer, wherein the thickness of the second upper electrode frequency modulation layer has second uniformity, and the second uniformity is smaller than the first uniformity.
In one embodiment, a method of forming a piezoelectric stack includes: forming an upper electrode frequency modulation layer on the surface of the temporary substrate wafer; forming a piezoelectric layer on the surface of the upper electrode frequency modulation layer; a lower electrode layer is formed on the piezoelectric layer.
In another embodiment, a method of forming a piezoelectric stack includes: forming a piezoelectric layer on the surface of the temporary substrate wafer; forming a lower electrode layer on the piezoelectric layer; removing the temporary substrate wafer to expose the piezoelectric layer; and forming an upper electrode frequency modulation layer with a first set thickness on the piezoelectric layer, wherein the upper electrode frequency modulation layer, the piezoelectric layer and the lower electrode frequency modulation layer form a piezoelectric lamination.
The method comprises the following steps: providing a temporary substrate wafer, and forming a piezoelectric layer on the surface of the temporary substrate wafer;
forming a lower electrode layer on the piezoelectric layer;
providing a device wafer, wherein the front surface of the device wafer is provided with a plurality of first cavities, bonding the front surface of the device wafer with the lower electrode layer, and sealing the first cavities;
Removing the temporary substrate wafer to expose the piezoelectric layer;
forming an upper electrode frequency modulation layer with a first set thickness on the piezoelectric layer, uniformly dividing the upper electrode frequency modulation layer into N areas, selecting at least one point in each of the N areas as a measuring point, and measuring the thickness of the upper electrode frequency modulation layer of the measuring point to obtain the thickness distribution of the upper electrode frequency modulation layer;
performing first ion beam bombardment on the upper electrode frequency modulation layer to form a first upper electrode frequency modulation layer, and measuring the thickness of the first upper electrode frequency modulation layer of the measuring point to obtain thickness distribution of the first upper electrode frequency modulation layer, wherein the thickness of the first upper electrode frequency modulation layer has first uniformity;
calculating the ion beam bombardment rates of different measuring points according to the thickness difference of the upper electrode frequency modulation layer and the first upper electrode frequency modulation layer of the measuring points;
and adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first electrode upper electrode frequency modulation layer to form a second upper electrode frequency modulation layer, wherein the thickness of the second upper electrode frequency modulation layer has second uniformity, and the second uniformity is smaller than the first uniformity.
Fig. 2 to 13 are schematic cross-sectional structures corresponding to the steps of the method for forming a tuning layer of a bulk acoustic wave filter according to the present embodiment, and the method for forming a tuning layer of a bulk acoustic wave filter according to the present embodiment will be described in detail with reference to fig. 2 to 13.
Referring to fig. 2, step S1 is performed to provide a temporary substrate wafer 10, and a piezoelectric layer 20 is formed on the surface of the temporary substrate wafer 10.
The temporary substrate wafer 10 may be any suitable substrate known to those skilled in the art, and may be, for example, at least one of the following materials: silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbon (SiC), silicon germanium carbon (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP), or other III/V compound semiconductors, and also include multilayer structures composed of these semiconductors, or the like, or are silicon-on-insulator (SOI), silicon-on-insulator (SSOI), silicon-on-insulator (S-SiGeOI), silicon-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), or may be double-sided polished silicon wafers (Double Side Polished Wafers, DSP), or may be ceramic substrates such as alumina, quartz, or glass substrates, or the like. In this embodiment, the material of the temporary substrate wafer 10 is silicon.
As a material of the piezoelectric layer 20, a piezoelectric material having a wurtzite crystal structure such as aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO 3), quartz (Quartz), potassium niobate (KNbO 3), or lithium tantalate (LiTaO 3), or a combination thereof can be used. When the piezoelectric layer includes aluminum nitride (AlN), the piezoelectric layer may further include at least one of rare earth metals such as scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, when the piezoelectric layer includes aluminum nitride (AlN), the piezoelectric layer may further include at least one of transition metals such as zirconium (Zr), titanium (Ti), manganese (Mn), and hafnium (Hf). The piezoelectric layer 20 may be deposited using any suitable method known to those skilled in the art, such as chemical vapor deposition, physical vapor deposition, or atomic layer deposition. In the present embodiment, the piezoelectric layer 20 is made of aluminum nitride (AlN).
As shown in fig. 3, step S2 is performed: forming a lower electrode layer 70 on the piezoelectric layer 20;
the material of the lower electrode layer 70 may be any suitable conductive material known in the art, and the conductive material may be a metal material having conductive properties, for example, a metal such as molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), chromium (Cr), titanium (Ti), gold (Au), osmium (Os), rhenium (Re), palladium (Pd), or a laminate formed of the above metals. The upper and lower electrode layers 70 may be formed by physical vapor deposition such as magnetron sputtering, evaporation, or the like, or chemical vapor deposition, physical vapor deposition, atomic layer deposition, or the like.
As shown in fig. 4, in the present embodiment, after forming the lower electrode layer 70, it further includes: the lower electrode layer 70 is patterned to form a lower electrode 71.
Before bonding the front surface of the device wafer with the lower electrode layer, the method further comprises:
performing first surface treatment on the lower electrode layer 70 to obtain an intermediate lower electrode layer;
and performing ion beam etching on the middle lower electrode layer to obtain a target lower electrode layer, wherein the standard deviation of the thickness of the target lower electrode layer in the direction vertical to the upper surface of the substrate is a second deviation value, and the second deviation value is smaller than the first deviation value.
The first surface treatment includes at least one of ion beam etching and chemical mechanical polishing treatment;
the method of performing the chemical mechanical polishing process on the lower electrode layer 70 includes at least: performing chemical mechanical polishing treatment on the lower electrode layer 70 twice or more;
the chemical mechanical polishing process performed on the lower electrode layer 70 two or more times includes:
performing a first chemical mechanical polishing treatment on the lower electrode layer 70 to obtain a first polishing layer;
performing second chemical mechanical polishing treatment on the first polishing layer to obtain an intermediate lower electrode layer;
the polishing precision of the first chemical mechanical polishing process is less than the polishing precision of the second chemical mechanical polishing process.
The thickness of the lower electrode layer 70 is h1, and the surface has a certain undulation due to the manufacturing method, etc., so that the standard deviation of the thickness of the lower electrode layer in the direction perpendicular to the upper surface of the substrate wafer is a first deviation value, typically greater than 12%, and typically 50% to 60%.
In some embodiments, the film layer prepared by the common preparation method can be directly used as the lower electrode layer 70, so as to reduce the control precision requirement on the preparation methods. The conventional film preparation method is insufficient in control accuracy of the film thickness to directly prepare the material layer with the required flatness, so that the uniformity of the film thickness of the lower electrode layer 70 is poor, and the standard deviation of the thickness is the first deviation value.
In some embodiments, the first surface treatment includes at least one of ion beam etching and chemical mechanical polishing.
In some embodiments, the thickness of the lower electrode layer 70 is greater than or equal to a first predetermined thickness, and the thickness of the target lower electrode layer is a second predetermined thickness, which is less than the first predetermined thickness.
Ion beam etching can obtain a relatively precise planarization result, so that in some embodiments, ion beam etching can be used as a final surface treatment process, and a common rapid surface treatment process, such as chemical mechanical polishing, is arranged in the preamble process to accelerate the surface treatment speed.
In some embodiments, the surface treatment method in this embodiment can be used to obtain the target bottom electrode layer close to the target thickness at last using ion beam etching.
In some embodiments, the first chemical mechanical polishing process corresponds to rough polishing and the second chemical mechanical polishing process corresponds to fine polishing. The rough polishing can achieve rapid thinning of the lower electrode layer 70, shortens the time spent in the entire polishing process, and obtains a standard deviation value of the thickness of the first polishing layer smaller than the first deviation value but not reaching the second deviation value requirement. The fine polishing can further optimize the standard deviation of the thickness of the obtained intermediate electrode layer on the basis of the rough polishing, and further approach the second deviation value requirement.
In some embodiments, the thickness of the first polishing layer is 0.3 to 0.47 times the initial thickness of the lower electrode layer 70, the thickness of the intermediate electrode layer is 0.57 to 0.75 times the thickness of the first polishing layer, and the thickness of the target electrode layer is 0.84 to 0.96 times the thickness of the intermediate electrode layer.
In some embodiments, the abrasive particles in the slurry used in the first chemical mechanical polishing process have a smaller particle size than the abrasive particles in the slurry used in the second chemical mechanical polishing process. In general, an alumina slurry may be selected during the first chemical mechanical polishing process and a diamond slurry may be selected during the second chemical mechanical polishing process. The particle sizes of the grinding particles of the two grinding liquids meet the requirements. Wherein the particle size of the abrasive particles of the alumina abrasive liquid is 50nm to 200nm, and the particle size of the abrasive particles of the diamond abrasive liquid is 5 to 100nm.
In addition, the alumina grinding fluid has excellent removal rate for hard base materials, sapphire substrates and the like, and can be used for carrying out quick rough grinding on the surface of the initial lower electrode layer under the condition that other structures are not formed on the surface of the initial lower electrode layer, so that the overall polishing speed is increased.
In some embodiments, the initial electrode layer 102 is subjected to a first chemical mechanical polishing process using a grinding wheel having a rotational speed of 100 to 110 revolutions per minute, the grinding fluid including an alumina grinding fluid for 10 to 15 minutes at a grinding pressure of 1 to 1.5Mpa, thereby obtaining a thickness of 6000 to 1.5Mpa Is included in the polishing layer 1021.
In some embodiments, the first polishing layer 1021 is subjected to a second chemical mechanical polishing process using a grinding wheel having a rotation speed of 70 to 80 rpm, and the polishing liquid comprises a diamond polishing liquid having a polishing time of 5 to 6 minutes and a polishing pressure of 0.8 to 1Mpa, thereby obtaining a thickness of 4000 to 1MpaIs provided, the intermediate electrode layer 1022 of (a).
The first chemical mechanical polishing process is a rough polishing process, and a thicker initial electrode layer needs to be polished, so that the polishing time is longer, the polishing pressure is larger, and the polishing rotating speed is faster. The second chemical mechanical polishing process is a fine grinding process, and the standard deviation of the thickness of the first polishing layer is smaller than that of the initial electrode layer, so that the thickness of the first polishing layer to be removed is thinner, the grinding time is shorter, the grinding pressure is smaller, and the grinding rotating speed is slower.
The thickness of the initial bottom electrode layer which is removed by grinding can be effectively controlled by adopting the twice chemical mechanical polishing treatment, the excessive initial electrode layer which is removed as a whole can not be caused by adopting only the rough grinding treatment, the time required by grinding to the target bottom electrode layer can also be effectively controlled, and the overlong time spent by grinding to the target bottom electrode layer can not be caused by adopting only the fine grinding treatment.
In some embodiments, ion beam lithography is provided using an ion beam tool. The parameters of the ion beam machine include: the radio frequency power (RF power) of the Ion Beam Source (Ion Beam Source) is 63 to 66W, the electron Beam voltage (Beam voltage) is 1305 to 1310V, the Ion current (Ion current) is 8 to 11mA, and the acceleration voltage (Accelerator voltage) is 145 to 153V; the neutralizer emission current (Neutralizer Emission current) is 26 to 32mA; the ion beam intensity (Ion beam intensity) is 5-6 mA/CM2, and under the parameters of the ion beam, the ions provided by the ion beam machine can meet the current density requirement, the ion energy requirement and the etching angle requirement.
Based on the above-mentioned machine parameters, the current density, ion energy and angle range of the ion beam etching target film layer can be made to be within the required range.
In one embodiment, the intermediate bottom electrode layer is ion beam etched. In some embodiments, at least one of bulk bombardment or zone bombardment or point bombardment may be used to etch the intermediate bottom electrode layer using an ion beam, so that the surface of the intermediate bottom electrode layer may be partially etched to a predetermined thickness, and finally, the thickness requirement of the target electrode layer is met, so that the thickness uniformity of the target electrode layer is better.
As shown in fig. 5, step S3 is performed: providing a device wafer 80, wherein the front surface of the device wafer 80 is provided with a plurality of first cavities 81, bonding the front surface of the device wafer 80 with the lower electrode layer 71, and closing the first cavities 81;
the device wafer 80 in this embodiment includes only the plurality of first cavity 81 structures formed in the front surface. In other embodiments, device structures such as mos devices and conductive interconnect structure layers may also be included within device wafer 80.
In one embodiment, before bonding the front surface of the device wafer 80 to the lower electrode layer 71, the method further comprises: a portion of the target lower electrode layer is removed to form a mass-loaded structure (not shown) at an edge region of the target lower electrode layer.
Removing a portion of the target electrode layer to form a mass-loaded structure at an edge region of the target electrode layer includes the steps of:
forming a patterned mask layer on the surface of the target lower electrode layer, wherein the patterned mask layer covers the area to be formed with the mass load structure; and removing part of the target lower electrode layer from the surface of the target lower electrode layer exposed out of the patterned mask layer along the downward direction of the surface of the target lower electrode layer, taking the target lower electrode layer covered by the patterned mask layer as a mass load structure, wherein the standard deviation of the thickness of the rest part of the surface of the exposed target lower electrode layer in the direction vertical to the upper surface of the substrate is smaller than a first deviation value.
In some embodiments, ion beam etching is performed on the surface of the target bottom electrode layer exposed to the patterned mask layer to remove a portion of the target bottom electrode layer.
In this embodiment, the thickness of the removed portion of the target lower electrode layer is on the order of 10 nm, and it is difficult to achieve such thinning accuracy with a general polishing process, so that the target lower electrode layer is partially removed with ion beam etching that can achieve the process requirements to achieve the required processing accuracy.
In some embodiments, the mask layer is a photomask layer, and the patterning of the photomask layer may be achieved by exposing the photomask layer.
In some embodiments, the top surface of the mass-loaded structure has a height difference from the top surface of the target lower electrode layer in the area after the removed portion, which may be set according to actual use needs. The width of the mass-loaded structure can be set according to the actual use requirements.
In some embodiments, the mass-loaded structure is in the form of a rectangular ring disposed around a central region of the piezoelectric stack and along a peripheral edge of the substrate. In practice, the specific shape of the mass-loaded structure may also be set as desired.
As shown in fig. 6, step S4 is performed: removing the temporary substrate wafer 10, exposing the piezoelectric layer 20;
the temporary substrate wafer 10 may be removed by a mechanical polishing, chemical mechanical polishing, or CMP process, or the like.
As shown in fig. 7, step S5 is performed: forming an upper electrode frequency modulation layer 30 with a first set thickness on the piezoelectric layer, wherein the upper electrode frequency modulation layer 30, the piezoelectric layer 20 and the lower electrode frequency modulation layer form a piezoelectric lamination, the upper electrode frequency modulation layer 30 is uniformly divided into N areas, at least one point is selected as a measuring point in each of the N areas, and the thickness of the upper electrode frequency modulation layer of the measuring point is measured to obtain the thickness distribution of the upper electrode frequency modulation layer;
in this embodiment, the upper electrode frequency modulation layer 30 includes an upper electrode layer on the piezoelectric layer 20 and a frequency modulation layer on the upper electrode layer; the material of the frequency modulation layer is the same as that of the upper electrode layer, and the frequency modulation layer is formed in the process of forming the upper electrode layer, and comprises molybdenum;
specifically, the upper electrode frequency modulation layer 30 may have a single layer structure with the same material, that is, the upper electrode layer and the frequency modulation layer are formed at the same time, and the material of the upper electrode frequency modulation layer 30 may be any suitable conductive material known in the art, and the conductive material may be a metal material having conductive properties, for example, made of one of molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), chromium (Cr), titanium (Ti), gold (Au), osmium (Os), rhenium (Re), palladium (Pd), or a stack formed of the above metals. The upper electrode frequency modulation layer 30 may be formed by physical vapor deposition such as magnetron sputtering, evaporation, or the like, or chemical vapor deposition, physical vapor deposition, atomic layer deposition, or the like.
In the present embodiment, the upper electrode tuning layer 30 is preferably formed on the piezoelectric layer 20 by a deposition process, the upper electrode tuning layer 30 is preferably made of metallic molybdenum (Mo), and the initial thickness (first set thickness) of the upper electrode tuning layer 30 is formed to beIn general, the thickness uniformity of the upper electrode FM layer 30 formed by deposition is +.>Thickness uniformity refers to the magnitude of the deviation of the actual thickness from the target thickness.
The method for forming the upper electrode frequency modulation layer 30 may also be: a metal layer is formed on the piezoelectric layer 20 through a deposition process, and then the metal layer is surface-treated through a CMP process to form the upper electrode frequency modulation layer 30 of a first set thickness.
In other embodiments, the materials of the frequency modulation layer and the upper electrode layer are different, that is, the upper electrode frequency modulation layer 30 is a dual-layer structure including the upper electrode layer and the frequency modulation layer, the frequency modulation layer is a dielectric layer separately formed on the upper electrode layer, and the material of the dielectric layer may be aluminum nitride or the like.
This step also requires obtaining the thickness profile of the upper electrode tuning layer 30 after forming the upper electrode tuning layer 30. The specific method for obtaining the thickness distribution of the frequency modulation layer comprises the following steps:
the upper electrode fm 30 is uniformly divided into N regions, and at least one point is selected as a measurement point in each of the N regions, and the thickness of the upper electrode fm 30 at the measurement point is measured to obtain the thickness distribution of the upper electrode fm 30.
Preferably, 400 measurement points capable of covering the upper electrode tuning layer can be uniformly selected on the upper electrode tuning layer 30, and an actual thickness value (first thickness value) of each measurement point position is obtained. The thickness value of each measurement point may be obtained by an ion beam tool APC (advanced process control ) system.
Referring to fig. 7 and 8, step S6 is performed: performing first ion beam bombardment on the upper electrode frequency modulation layer 30 to form a first upper electrode frequency modulation layer 40, and measuring the thickness of the first upper electrode frequency modulation layer 40 of the measuring point to obtain thickness distribution of the first upper electrode frequency modulation layer 40, wherein the thickness of the first upper electrode frequency modulation layer 40 has first uniformity;
wherein performing a first ion beam bombardment of the upper electrode frequency modulation layer 30 comprises:
and performing first ion beam bombardment on the upper electrode frequency modulation layer 40 according to a first removal thickness set value to form a first upper electrode frequency modulation layer 40, wherein the first removal thickness set value is smaller than the thickness required to be removed of the whole upper electrode frequency modulation layer 30.
In this embodiment, the range of the target thickness value of the upper electrode frequency modulation layer isThe total bombardment thickness of the upper electrode frequency modulation layer to be removed is +.>The first set removal thickness of the first ion beam bombardment is preferably
After the first ion beam bombardment is completed, step S7 is performed: according to the thickness difference of the upper electrode frequency modulation layer 30 and the first upper electrode frequency modulation layer 40 of the measuring points, the ion beam bombardment rates of different measuring points are calculated, specifically:
acquiring a first thickness value of the upper electrode frequency modulation layer 30 and a second thickness value (actual thickness value) of the first upper electrode frequency modulation layer 40 of each measurement point;
and calculating the ion beam bombardment rate of each measuring point according to the first thickness value, the second thickness value and the first ion beam bombardment duration.
In this embodiment, the first ion beam bombardment is to bombard the upper electrode fm layer 30 with a uniform bombardment duration, that is, the residence time of the ion beam in the area where each measurement point is located is the same, so that the thickness difference between the first thickness value and the second thickness value of each measurement point on the upper electrode fm layer 30 before and after the first ion beam bombardment can be calculated, and then the quotient of the thickness difference and the first ion beam bombardment duration can be calculated, so as to obtain the bombardment rate of the ion beam at each measurement point.
As shown in fig. 8 and 9, step S8 is performed: and adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first upper electrode frequency modulation layer 40 to form a second upper electrode frequency modulation layer 50, wherein the thickness of the second upper electrode frequency modulation layer 50 has second uniformity, and the second uniformity is smaller than the first uniformity.
Wherein, the second ion beam bombardment is performed on the first electrode frequency modulation layer 40, which comprises:
calculating the thickness value of the residual electrode frequency modulation layer 40 on the first electrode of each measuring point to be removed according to the second thickness value and the target thickness value;
calculating the residence time of the ion beam bombarding the corresponding area of each measuring point according to the thickness value and the ion beam bombardment rate of the first upper electrode frequency modulation layer 40 which are required to be removed;
and respectively performing second ion beam bombardment on the first upper electrode frequency modulation layer 40 of each measuring point corresponding region according to the stay time of each measuring point corresponding region to form a second upper electrode frequency modulation layer 50.
The difference value between the second thickness of a certain measuring point and the target thickness is the thickness which is required to be removed; the quotient of the thickness value to be removed of the rest of the measuring points and the bombardment speed of the ion beam corresponding to the measuring points is the bombardment time required by the second bombardment of the measuring points, the bombardment time of each measuring point is calculated, the ion beam is controlled to stay at different measuring points for corresponding time respectively through an ion beam machine table, the thickness of the rest of the area where each measuring point is located to be removed is bombarded, namely the thickness of the area where each measuring point is located is enabled to reach or basically reach the target thickness value by adopting point-to-point bombardment.
It should be noted that, in this embodiment, the first ion beam bombardment and the second ion beam bombardment are performed by the same ion beam machine, and the process parameters of the ion beam machine for performing the first ion beam bombardment and the second ion beam bombardment are the same. Preferably, the process parameters of the ion beam machine for performing the first ion beam bombardment and the second ion beam bombardment include:
radio frequency power range: 60-100W;
electron beam voltage range: 1300-1600V;
ion current range: 5-15A;
acceleration voltage range: 100-150V;
neutralizer emission current range: 10-40 mA;
ion beam intensity range: 5-10 mA/CM 2
In this embodiment, the ion beam machine preferably performs the first ion beam bombardment and the second ion beam bombardment at a time interval of less than 24 hours.
Because the variable length deviation of the ion beam machine along with the use time can be gradually larger, the problem that the filter qualification rate is low due to inaccurate bombardment thickness of the frequency modulation layer caused by deviation of the ion beam machine can be avoided by controlling the time interval of two ion beam bombarding to be smaller than 24 hours.
In one specific example, a thickness of grown on the piezoelectric layer isUniformly selecting 400 different measuring points on the upper electrode frequency modulation layer, and recording the actual thickness value of each measuring point;
2) And optimizing the thickness uniformity of the upper electrode frequency modulation layer by adopting a mode of bombarding the upper electrode frequency modulation layer twice by an ion beam machine.
Wherein the target thickness isTotal bombardment thickness->The thickness of the first ion beam bombardment is set toControlling the residence time of the ion beam according to the film quality at different positions to reach the bombarding thickness +.>The ion beam bombardment is carried out by adopting the technological parameters of the ion beam machine.
As shown in fig. 13, first ion beam bombardment is performed to cut down the upper electrode fm 30 and optimize the uniformity of the upper electrode fm in the wafer to obtain a first fm 40; acquiring thickness distribution data of different measurement points to obtain thickness deviation of the first frequency modulation layer 40 as follows
According to the actual change of the thickness of each measuring point of the upper electrode frequency modulation layer before and after the bombardment of the first ion beam and the bombardment time length, calculating the bombardment rate of different measuring points;
then, according to the required different reduction thicknesses of each measurement point in each wafer and the ion beam bombardment rates of different points of the machine, the first upper electrode frequency modulation layer 40 is subjected to point-to-point ion beam bombardment to form a second upper electrode frequency modulation layer 50 with uniform thickness, and finally each measurement point of the second upper electrode frequency modulation layer 50 is equal to the target thickness Thickness variation of +.>
Compared with the existing primary ion beam bombardment surface treatment method, the method provided by the invention has the advantages that the bombardment thickness is precisely controlled according to the data obtained by the primary ion beam bombardment, the secondary ion beam bombardment is performed to prepare the high-uniformity upper electrode frequency modulation layer, and the thickness uniformity of the upper electrode frequency modulation layer is improved to beAnd further, the qualification rate of the filter device produced subsequently is effectively improved.
As shown in fig. 10, in this embodiment, after forming the second upper electrode frequency modulation layer, the method further includes: the second upper electrode frequency modulation layer 50 is patterned to form an upper electrode 51.
As shown in fig. 11, in this embodiment, after forming the upper electrode, it may further include:
step S9: providing a cap wafer 90, wherein the front surface of the cap wafer 90 is provided with a plurality of second cavities 91;
the front side of the cap wafer 90 is bonded to a piezoelectric stack that encloses the second cavity 91 to form a plurality of resonator elements including: a first cavity 81, a lower electrode 71, a piezoelectric layer and an upper electrode 51 which are sequentially stacked above the first cavity 81, and a second cavity 81 above the upper electrode 51.
As shown in fig. 12 to 13, after bonding the front surface of the cap crystal, 90 to the piezoelectric stack, step S10 is further included: :
Forming a through silicon via 84 on the back surface of the device wafer 80, the through silicon via 84 exposing the electrical connection portions of the upper electrode 51 and the lower electrode 71;
an electrical connection structure 85 is formed within the through silicon via 84, the electrical connection structure 85 being used for electrical extraction of the upper electrode 51 and the lower electrode 71.
In this embodiment, the device wafer 80 includes a substrate 82 and a supporting layer 83 formed on the substrate, through-silicon vias 84 penetrating the substrate 82 and the supporting layer 83 may be formed by a TSV process, the electrical lead-out structure 85 may be a conductive plug (copper pillar) made of copper material, and the electrical connection portion between the upper electrode 51 and the lower electrode 71 may be a bonding pad (not shown), and the electrical lead-out structure 85 is connected to the bonding pad. The electrical lead-out structure 85 may be formed by electroplating or deposition processes.
After the electrical lead-out structures are formed, a re-wiring layer may also be formed on the back side of the device wafer 80 to enable electrical connection of the filter to external circuitry.
It should be noted that fig. 2 to 13 only show an exemplary structure forming process of a bulk acoustic wave resonator unit, which is a wafer level process in this embodiment, so that the resonator unit formed finally has a plurality of resonator units.
The above description is only illustrative of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, and any alterations and modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the appended claims.
Claims (19)
1. A method of forming a bulk acoustic wave filter, comprising:
providing a temporary substrate wafer, and forming a piezoelectric lamination layer on the surface of the temporary substrate wafer, wherein the piezoelectric lamination layer comprises an upper electrode frequency modulation layer, a piezoelectric layer and a lower electrode layer, and the upper electrode frequency modulation layer and the lower electrode layer are respectively positioned on the surfaces opposite to the piezoelectric layer;
providing a device wafer, wherein the front surface of the device wafer is provided with a plurality of first cavities, bonding the front surface of the device wafer with the lower electrode layer, and sealing the first cavities;
removing the temporary substrate wafer;
uniformly dividing the upper electrode frequency modulation layer into N areas, selecting at least one point in each of the N areas as a measuring point, and measuring the thickness of the upper electrode frequency modulation layer of the measuring point to obtain the thickness distribution of the upper electrode frequency modulation layer;
performing first ion beam bombardment on the upper electrode frequency modulation layer to form a first upper electrode frequency modulation layer, and measuring the thickness of the first upper electrode frequency modulation layer of a measuring point to obtain thickness distribution of the first upper electrode frequency modulation layer, wherein the thickness of the first upper electrode frequency modulation layer has first uniformity;
calculating the ion beam bombardment rates of different measuring points according to the thickness difference of the upper electrode frequency modulation layer and the first upper electrode frequency modulation layer of the measuring points;
And adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing second ion beam bombardment on the first electrode upper electrode frequency modulation layer to form a second upper electrode frequency modulation layer, wherein the thickness of the second upper electrode frequency modulation layer has second uniformity, and the second uniformity is smaller than the first uniformity.
2. The method of forming a bulk acoustic wave filter according to claim 1, wherein the upper electrode tuning layer comprises an upper electrode layer on the piezoelectric layer and a tuning layer on the upper electrode layer;
the material of the frequency modulation layer is the same as that of the upper electrode layer, the frequency modulation layer is formed in the process of forming the upper electrode layer, and the material of the frequency modulation layer comprises molybdenum;
or the material of the frequency modulation layer is different from that of the upper electrode layer, the frequency modulation layer is a dielectric layer formed on the upper electrode layer, and the material of the dielectric layer comprises aluminum nitride.
3. The method of claim 1, wherein the gas used for the first ion beam bombardment and the second ion beam bombardment comprises an inert gas.
4. The method of claim 1, wherein the performing a first ion beam bombardment on the upper electrode tuning layer comprises:
And performing first ion beam bombardment on the upper electrode frequency modulation layer according to a first removal thickness set value to form the first upper electrode frequency modulation layer, wherein the first removal thickness set value is smaller than the thickness required to be removed of the whole upper electrode frequency modulation layer.
5. The method of forming a bulk acoustic wave filter according to claim 4, wherein calculating ion beam bombardment rates of different measurement points according to a thickness difference between the upper electrode tuning layer and the first upper electrode tuning layer of the measurement points comprises:
acquiring a first thickness value of the upper electrode frequency modulation layer and a second thickness value of the first upper electrode frequency modulation layer of each measuring point;
and calculating the ion beam bombardment rate of each measuring point according to the difference value between the first thickness value and the second thickness value and the duration of the first ion beam bombardment.
6. The method of forming a bulk acoustic wave filter according to claim 5, wherein adjusting the bombardment time of each region according to the bombardment rates of different measurement points and the target thickness of the upper electrode frequency modulation layer, and performing the second ion beam bombardment on the first upper electrode frequency modulation layer comprises:
calculating the thickness value of the electrode frequency modulation layer on the first electrode of each measuring point, which is required to be removed, according to the second thickness value and the target thickness value;
Calculating the residence time of the ion beam bombarding the corresponding area of each measuring point according to the thickness value and the ion beam bombardment rate of the first upper electrode frequency modulation layer which are required to be removed;
and respectively carrying out second ion beam bombardment on the first upper electrode frequency modulation layer of the corresponding area of each measuring point according to the residence time of the corresponding area of each measuring point to form the second upper electrode frequency modulation layer.
7. The method of any one of claims 1-6, wherein the first ion beam bombardment and the second ion beam bombardment are performed by a same ion beam tool, and wherein the process parameters of the ion beam tool performing the first ion beam bombardment and the second ion beam bombardment are the same.
8. The method of claim 7, wherein the ion beam tool performs the first ion beam bombardment and the second ion beam bombardment less than 24 hours apart.
9. The method of claim 7, wherein the process parameters of the ion beam tool to perform the first ion beam bombardment and the second ion beam bombardment comprise:
Radio frequency power range: 60-100W;
electron beam voltage range: 1300-1600V;
ion current range: 5-15A;
acceleration voltage range: 100-150V;
neutralizer emission current range: 10-40 mA;
ion beam intensity range: 5-10 mA/CM 2 。
10. The method of forming a bulk acoustic wave filter according to claim 1, wherein the method of forming a piezoelectric stack comprises:
forming an upper electrode frequency modulation layer on the surface of the temporary substrate wafer; forming a piezoelectric layer on the surface of the upper electrode frequency modulation layer; a lower electrode layer is formed on the piezoelectric layer.
11. The method of forming a bulk acoustic wave filter according to claim 1, wherein the method of forming a piezoelectric stack comprises:
forming a piezoelectric layer on the surface of the temporary substrate wafer;
forming a lower electrode layer on the piezoelectric layer;
providing a device wafer, wherein the front surface of the device wafer is provided with a plurality of first cavities, bonding the front surface of the device wafer with the lower electrode layer, and sealing the first cavities;
removing the temporary substrate wafer to expose the piezoelectric layer;
and forming an upper electrode frequency modulation layer with a first set thickness on the piezoelectric layer, wherein the upper electrode frequency modulation layer, the piezoelectric layer and the lower electrode frequency modulation layer form a piezoelectric lamination.
12. The method for forming a bulk acoustic wave filter as recited in claim 11, wherein,
forming an upper electrode frequency modulation layer of a first set thickness on the piezoelectric layer comprises:
forming the upper electrode frequency modulation layer with the first set thickness on the piezoelectric layer through a deposition process;
or forming a metal layer on the piezoelectric layer through a deposition process, and performing surface treatment on the metal layer through a CMP process to form the upper electrode frequency modulation layer with the first set thickness.
13. The method of forming a bulk acoustic wave filter according to claim 1, further comprising, after forming the second upper electrode tuning layer:
and patterning the second upper electrode frequency modulation layer to form an upper electrode.
14. The method of forming a bulk acoustic wave filter according to claim 13, further comprising, after forming the upper electrode:
providing a cap wafer, wherein the front surface of the cap wafer is provided with a plurality of second cavities;
bonding the front side of the cap wafer with a second upper electrode tuning layer of the piezoelectric stack, the piezoelectric stack closing the second cavity to form a plurality of resonator units, the resonator units comprising: the piezoelectric device comprises a first cavity, a lower electrode, a piezoelectric layer, an upper electrode and a second cavity, wherein the lower electrode, the piezoelectric layer and the upper electrode are sequentially stacked above the first cavity, and the second cavity is arranged above the upper electrode.
15. The method of forming a bulk acoustic wave filter according to claim 14, further comprising, after bonding the front side of the cap wafer to the piezoelectric stack:
forming a through silicon via on the back surface of the device wafer, wherein the through silicon via exposes the upper electrode and the electric connection part of the lower electrode;
and forming an electric connection structure in the through silicon via, wherein the electric connection structure is used for electrically leading out the upper electrode and the lower electrode.
16. The method of forming a bulk acoustic wave filter according to claim 1, further comprising, prior to bonding the front side of the device wafer to the lower electrode layer:
and patterning the lower electrode layer to form a lower electrode.
17. The method of forming a bulk acoustic wave filter according to claim 1, further comprising, prior to bonding the front side of the device wafer to the lower electrode layer:
performing first surface treatment on the lower electrode layer to obtain an intermediate lower electrode layer;
and performing ion beam etching on the middle lower electrode layer to obtain a target lower electrode layer, wherein the standard deviation of the thickness of the target lower electrode layer in the direction vertical to the upper surface of the substrate is a second deviation value, and the second deviation value is smaller than the first deviation value.
18. The method of forming a bulk acoustic wave filter according to claim 17, further comprising, prior to bonding the front side of the device wafer to the lower electrode layer:
and removing part of the target lower electrode layer to form a mass loading structure at the edge area of the target lower electrode layer.
19. The method of forming a bulk acoustic wave filter according to claim 17, wherein the first surface treatment comprises at least one of ion beam etching and chemical mechanical polishing treatment;
the method for carrying out chemical mechanical polishing treatment on the lower electrode layer at least comprises the following steps: performing chemical mechanical polishing treatment on the lower electrode layer for more than two times;
the chemical mechanical polishing treatment of the lower electrode layer for more than two times comprises:
performing first chemical mechanical polishing treatment on the lower electrode layer to obtain a first polishing layer;
performing second chemical mechanical polishing treatment on the first polishing layer to obtain the middle lower electrode layer;
the polishing precision of the first chemical mechanical polishing process is less than the polishing precision of the second chemical mechanical polishing process.
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