Patent Application
20230329117
The invention relates generally to piezoelectric materials along with fabrication and use of the same.
The exceptional material properties of lithium niobate (LiNbO3) make lithium niobate an excellent material for a wide range of RF, micro-electromechanical systems (MEMS), phononic applications, and photonic applications. However, nano-scale and micro-scale devices using lithium niobate typically depend on high fidelity processing of lithium niobate films. Enhancements to the design and fabrication of lithium niobate-based devices can provide for further advancement of related technologies.
Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings in which:
The following detailed description refers to the accompanying drawings that show, by way of illustration and not limitation, various example embodiments of the invention. These embodiments are described in sufficient detail to enable those skilled in the art to practice these and other embodiments. In order to avoid obscuring embodiments of the invention, some well-known system configurations and process steps are not disclosed in detail. Other embodiments may be utilized, and structural, logical, and electrical changes may be made to these embodiments. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The following detailed description is, therefore, not to be taken in a limiting sense.
In various embodiments, procedures can be used to fabricate and measure three-dimensional (3D) piezoelectric phononic crystals. Such procedures, for example, can employ epitaxial transfer and lift off and deposition techniques to build up laminated thin film piezoelectric lithium niobate alternated with amorphous silicon. Lithium niobate, including varying stoichiometries, is herein referred to as LN. Interferometric lithograph, wet and dry fluorine electron cyclotron resonance (ECR), wet and dry chlorine electron cyclotron resonance (ECR) etching, and contact lithography, can be used to etch layer-by-layer as a structure is stacked up. Such a process can realize, but is not limited to, a pristine 3D phononic crystal at XBAND frequencies. ECR etching can include wet or dry fluorine ECR etching, wet or dry chlorine ECR etching, or combinations thereof. This structure represents the maturation of processing technology and can be the bases to impact addressing high density radio frequency (RF) systems, topological acoustics, and exotic nonlinear phononics.
Beyond disclosing a robust etching method to realize a 3D piezoelectric phononic crystal and high-quality stacked lithium niobate resonators, the present disclosure includes details regarding how to fabricate such device. Such disclosures can include, but are not limited to, the following processes: (1) near perfect etching realized by dry etching, combination chromium/aluminum (Cr/Al) hard mask, and hydrogen plasma surface treatment, and (2) epitaxial transfer and bonding. Key technical accomplishments can include optimized LN etch for vertical side walls, re-disposition, and improvement in smoothness, first pass interferometric lithography on gallium nitride (GaN), and fabricated and tested initial RF devices for filters, anisotropic focusing, and traveling wave acoustics.
LN's exceptional material properties make it an excellent material platform for a wide range of RF, micro-electromechanical systems (MEMS), phononic applications, and photonic applications. However, nanomicro scale device concepts typically depend on high fidelity processing of LN films. Herein, a highly optimized processing methodology is disclosed that can achieve a deep etch with nearly vertical and smooth sidewalls. It is demonstrated that titanium/aluminum/chromium (Ti/Al/Cr) stack works exceptionally well as a hard mask material during long plasma dry-etching. Periodically pausing the etching and chemical cleaning between cycles can be leveraged to avoid thermal effects and byproduct redeposition. To improve mask quality on X-cut and Y-cut substrates, a hydrogen (H2)-plasma treatment can be implemented to relieve surface tension by modifying the top surface atoms. Structures with etch depths as deep as 3.4 μm can be obtained in the processing, as taught herein, across a range of crystallographic orientations with a smooth sidewall and perfect or near-perfect verticality on all crystallographic facets.
LN has proven to be the material of choice for a wide range of applications due to its exceptional piezoelectric, electro-acoustical, electro-optical, and non-linear optical properties. Different crystalline orientations of LN are heavily utilized for applications in surface-acoustic-wave (SAW) resonators, optical filters, optical sensors, modulators, transducers, optical waveguides, Q-switch lasers, oscillators, and other applications.
At the nano-scale and micro-scale, device performance is often constrained by the fabrication quality of processed LN films. Unlike many semiconductors and dielectric materials, LN substrates are complex for processing and have been notoriously difficult to etch. Typically, in conventional processing, a long plasma dry-etch is required to obtain high-aspect ratio or deep etching profiles in LN substrates. To address such issues, a successful LN etching process is disclosed herein to manage one or more factors including substrate heating, redeposition of the etching products and mask materials, and durability of the mask materials over the etching process.
Dry etching of LN substrates has been studied by different research groups and different plasma etch conditions have been investigated to optimize the quality of the resulting structures. Fluorine (F2) based plasma sources have most commonly been used to etch LN. However, use of a fluorine-based plasma source is accompanied by the redeposition of LiF and its byproducts, which reduces the etching rate and creates unfavorable features due to local micro-masking effects. The byproducts from fluorine-based dry-etch evaporate at only at 800° C., thus remaining on the surfaces and the sidewalls of the structure. This has been reported to not only reduce the etch rate of the target material, but to also prevent obtaining vertical etching profiles. Additionally, typical mask material delaminates or are otherwise consumed during the etching process resulting in roughness on the etched structure, which can degrade performance. Degraded performance can include, for example, increased optical losses due to surface roughness. Adding argon (Ar) gas to the chemistry of the plasma etching has been reported to enhance the physical sputtering (etching) process and obtain more uniform etching profile, thus mitigating portion of these challenges during the dry etch.
To overcome the problem of redeposition of product compounds, LN concentration on the top surface should be minimized. This can be achievable, as reported in the literature, by employing a proton exchange (PE) process where some of the lithium ions are replaced by protons in the LN crystal structure. It has been shown that the PE process will significantly reduce the amount of LiF redeposition, and therefore it increases the etching rate and improves the etching profiles as well. However, the PE process is expensive, not available for all process, and time consuming, therefore, process enhancements, as taught herein, can be achieved with an alternative to replace the PE process with a cost-effective and a more available method.
In various embodiments, progress in etching different crystalline LN substrates can be provided using inductively coupled plasma (ICP). By comparing different combination of the mask materials on different LN orientations (cuts), optimum dry etch condition to obtain deep etching profiles on all orientations with smooth and vertical sidewalls is presented herein. Also demonstrated is that employing a H2-plasma treatment prior to the processing, as an alternative for PE process, overcomes delamination of the metal mask on X-cut and Y-cut LN samples and improves the quality of the etching profile.
In an inventor experiment, a standard cleaning procedure was conducted prior to a lithography process. Then, a negative photoresist (AZ® nLOF 2035) was applied to pattern the LN samples with different cuts through a contact lithography process. Single crystal LN substrates were utilized with common orientations of 128YX, 128Y, 64Y, and thin film LN on silicon (Si) substrates with the orientations of X and Y. After patterning samples, the patterned samples were cleaned in an hydrogen (H) chloride (Cl) acid solution (HCl:H2O, 1:3) and metallized in a metal evaporator. First, a hard mask with a composition having Ti, Al, and Cr was deposited. The process was followed by lift-off using a 1165 (n-methyl pyrrolidinone) solution. Then the samples were etched in a F2-based in ICP. After etching, metal masks were removed using a diluted hydrogen fluoride (HF) solution. A scanning electron microscopy (SEM) was applied to inspect and analyze the samples through the processing.
Identifying appropriate metal masks as hard mask for the etching purpose is an important, if not, crucial step for metal depositions. Some dry etch challenges such as redeposition of the mask material and the reaction products can be avoided using an appropriate metal for the processing. These challenges are more severe if the process needs to be designed to achieve deep structures on LN substrates as are desired for optical and photonic device applications.
To find an example of an optimum metal mask for a deep dry etch on LN samples, different metal combinations were tried. These metal combinations included Ti/Al (20 nm/1.3 μm) and Ti/Al/Cr (20 nm/750 nm/750 nm).
In order to explain this observation, it is hypothesized that both crystal orientation and the stress due to the transferring LN film on Si substrate play an important role on atomic bonding between metals and top surface of LN. Therefore, a surface treatment seems appropriate to improve the quality of the Ti/Al/Cr metal mask on X-cuts and Y-cuts. Researchers have performed similar treatment to engineer crystal properties of the LN using proton implantation. Here, a H2-plasma treatment (H2: 30 sccm, pressure: 15 mTorr, RF power: 150 W, ICP power: 300 W, DC bias: 53V) was employed in an ICP chamber prior to the lithography and metallization in order to imitate the effect of proton treatment on the LN substrate.
After obtaining high quality metal mask on LN cuts, the procedure included a plasma dry etch using F2-based chemistry ICP. Previous research on etching LN revealed that formation of niobium fluoride (NbF5) becomes volatile at temperatures around 200° C., while the lithium fluoride (LiF) byproducts will remain on the sidewalls and the surfaces that lower downs the etching rate of the LN.
It is clearly demonstrated that the etching profile with the Cr mask stacked on Al worked as a better mask since the surface roughness and redeposition underneath the sidewalls are omitted and also the verticality is nearly maintained as illustrated in
Table 1 lists the etch rates and the obtained depths for all the cuts using CF3/Ar (1:1) plasma dry etch. The etching rate may vary depending on the crystal orientations that may include properties of local neighborhood atoms, and may vary depending on the role of the dangling and surface bonds. As seen in Table 1, the etching rates are nearly the same, but 64Y and 128Y cuts present slightly lowering etch rate compared to the other cuts.
An optimum ICP dry etch process to obtain a deep etching profile in LN substrate with minimum roughness and vertical sidewalls has been disclosed. Combination of CHF3/Ar (1:1) gases were used to etch all LN substrates. The plasma etching characteristics of different orientations of LN samples were studied under various metal masks. The stack of Ti/Al/Cr metals found to be the best mask material for all cuts i.e., 128YX, 128Y, 64Y, X-, and Y-cuts as it removed all the redeposition and micro-masking issues during the dry etch process. However, to achieve the same quality of metal mask, X-cut and Y-cut samples were treated with H2-Plasma. It is assumed that the plasma treatment will mitigate surface stress on the transferred LN film due to the Si substrate and also can modify the surface structures by replacing Li-ion with protons. Likewise, periodic interruptions were included in a plasma dry etch recipe followed by a chemical cleaning between each cycle to avoid thermal effect and minimize byproduct redeposition during the long etching process. Microstructures with etch depths as deep as 3.4 μm were achieved using this method with a smooth sidewall and perfect verticality, which is promising for fabrication of optical devices where high-aspect ratio structures are required.
Processing and examining LN structures, as discussed herein, can lead to understanding the stress-strain effect on different cuts of LN. Such processing techniques can lead to building a multilayer phononic crystal structure. LN on Al2O3 ca be used followed by lapping to enable repeated epitaxial growth to build up a phononic structure. Compositions such as GaN may possibly be used. Such processing techniques may be used in the fabrication of resonators and testing and characterization of opto-mechanical devices.
Variations of method 2400 or methods similar to method 2400 can include a number of different embodiments that may be combined depending on the application of such methods and/or the architecture of systems including a piezoelectric material in which such methods are implemented. Such variations can include forming the mask as a hard mask and applying a hydrogen-plasma treatment to the hard mask prior to using the inductively coupled plasma dry etch. The hard mask can be a metal mask.
Variations of method 2400 or methods similar to method 2400 can include the etching being performed by using periodic interruptions to the etching followed by a chemical cleaning between each cycle of the etching. Variations can include forming the patterned structure in the piezoelectric material having vertical sidewalls. The vertical sidewalls can deviate from ninety degrees by five degrees or less. Variations can include the piezoelectric material to include lithium niobate. The lithium niobate can be structured on a silicon substrate.
Variations of method 2500 or methods similar to method 2500 can include a number of different embodiments that may be combined depending on the application of such methods and/or the architecture of systems including a lithium niobate crystal in which such methods are implemented. Such variations can include the metal mask having a composition of one or more of titanium, aluminum, or chromium. Such variations can include the ICP dry etch using one or more fluoride-based chemistries. The one or more fluoride-based chemistries can include one or more of sulfur hexafluoride or trifluoromethane.
Variations of method 2500 or methods similar to method 2500 can include applying a hydrogen-plasma treatment to the metal mask prior to applying the inductively coupled plasma dry etch. Variations can include using periodic interruptions to the etching followed by a chemical cleaning between each cycle of the etching.
Variations of method 2500 or methods similar to method 2500 can include forming the patterned structure in the lithium niobate with the lithium niobate forming the patterned structure having vertical sidewalls. The vertical sidewalls can deviate from ninety degrees by five degrees or less.
Variations of method 2500 or methods similar to method 2500 can include forming the metal mask by spin coating a photoresist on the lithium niobate and forming a pattern in the photoresist using photolithography. A metallization can be formed according to the pattern and the photoresist of the pattern can be removed.
Wide bandgap, enhanced piezoelectric responses, high electromechanical coupling, and low dielectric permittivity are some of the outstanding properties that have made scandium aluminum nitride (ScxAl1-xN) a promising material in multiple applications. One of the major challenges in device fabrication including ScxAl1-xN is its resistivity to etch, specifically with the higher scandium concentration. Herein, a developed experimental approach of a wet etching process by using tetramethyl ammonium hydroxide (TMAH) followed by high temperature annealing is disclosed. This approach can maintain uniformity of etching in lower as well as higher scandium concentrations. In this disclosure, presentation is made of experimental results of etching approximately 730 nm of ScxAl1-xN (x=12.5%, 20%, 40%) thin films, where it can be observed that the etching rate reduces with the increase of scandium content. Nevertheless, in this work by the inventors, sidewall verticality (85°˜90°) for all the concentrations has been successfully maintained in experiments. As shown by the experimental outcomes, the etching procedure can be advantageous in the fabrication of acoustic, photonic, and piezoelectric devices.
Group III-V materials are getting notable attraction for their diverse applications in MEMS, piezoelectric transducers, resonators, RF acoustic devices. Due to some of its promising qualities and simplicity of process integration, aluminum nitride (AlN) is widely employed in piezoelectric MEMS devices. AlN can be doped with other metals to enrich its piezoelectric properties and ensure more efficient coupling, which leads to the success of ScxAl1-xN based integrated photonic circuits and optical waveguides. Previous researchers have used first-principles analysis to determine that the wurtzite structure of ScxAl1-xN(Sc-IIIA-N) alloys can be fabricated, and it might have a more significant piezoelectric coefficient value in comparison with AlN. This more significant piezoelectric coefficient value was proved that by measuring co-sputtered ScxAl1-xN films, indicating a peak coefficient of 27.6 pC/N and a higher piezoelectric response compared to AlN. Furthermore, according to the experiments of other researchers, the electromechanical coupling coefficient (kt2) value of scandium doped AlN can be improved by up to 15%. As noted in the literature, utilizing ScxAl1-xN thin film with increased scandium concentration offers a great opportunity for the fabrication of high-frequency and wideband acoustic wave filters. However, the ScxAl1-xN thin film becomes increasingly resistant to etching as the scandium concentration (x) rises, especially when using reactive ion etching (RIE) or inductively coupled plasma (ICP) etching. In the past two decades, substantial research has been performed on ScxAl1-xN to understand its material features, growth, characterization, how different etching can be used for device manufacture.
Like other group III-V materials, ScxAl1-xN can be etched by dry or wet etching techniques. One of the known dry etching approaches is ion beam etching, which can be physical or chemical and can result in etched surfaces for ScxAl1-xN with a smooth surface and a suitable etch rate. Table 1 lists some outcomes of dry etching attempts of ScxAl1-xN considering sidewall verticality and etch rate. Researchers have tried ICP etching with thick S1818 photoresist (PR) as an etch mask with promising results, in which they demonstrated how RF power might control the sample's plasma etching energy, and demonstrated that the energy of the Cl2/boron trichloride (BCl3)/N2 plasma enhances the sidewall angle of Sc0.06Al0.94N sample etching. Other researchers have demonstrated that the reactive ion beam etching (RIBE) process of ScxAl1-xN etching is superior to ion beam etching (IBE) in terms of etching rate, selectivity, sidewall angle (73°), and a smooth surface free of roughness. The ScxAl1-xN etching rate and selectivity degrade when the identical beam parameters are used without the reactive gas. On the other hand, other researchers presented the design, manufacture, and characterization of Sc0.20Al0.80N thin films based on piezoelectric micromachined ultrasound transducers (PMUTs) using RIE as an etching process, where these researchers claimed that the etched layer has good verticality and concluded that increasing the scandium concentration would enhance PMUT performance. Other researchers attempted ICP etching using Ar rather than the more commonly used nitrogen, in which their etch rate is comparably lower. Furthermore, other researchers successfully fabricated a lamb wave resonator with a quality factor of around 1000 with Sc0.22Al0.78N, in which they have demonstrated a reasonable etching rate (130 nm/min), and promising verticality (77°). They also concluded that the primary reactive etching gas Cl2 increases the anisotropy of the etching process. However, as reported in other publications, as the dry etching process is mainly Cl2/BCl3 based, performing dry etching of ScxAl1-xN is an ineffective process due to ScCl3's poor volatility. In other reports, it is noted that it takes more etching power and ion bombardment to get the etching rate back to a considerable level. Moreover, other researchers have reported that it was found that excessive etching into the bottom layer might have a risk concern and a lower etching rate as well as high-power consumption are the fundamental causes of poor selectivity to various mask materials, which has accelerated the wet etching trials in the research community.
Due to the different experimental conditions, it is not easy to draw any conclusive comment about the wet etching from prior research works; nonetheless, some older experimental outcomes are presented here, demonstrating promising results as shown in the table of
In this disclosure, a wet etching process using a TMAH solution for etching ScxAl1-xN thin films is presented, introducing an intermediary thermal annealing process, which can be demonstrated using the procedures of
Experiments of a wet process, disclosed herein, included thin film deposition of SiO2, application of lithography, preparation of a nickel (Ni) mask and lift-off of the Ni mask, high temperature annealing, ICP etching of the SiO2 layer, and TMAH wet etching. ScxAl1-xN samples for the experiments were grown sputter-coated in a physical vapor deposition system. With this method, the ScxAl1-xN thin film contains abnormally oriented grains (AOG) which makes the surface highly rough, as can be seen in
After the silicon-dioxide deposition, lithography was conducted using a MLA 150 Advanced Maskless Aligner from Heidelberg Instruments. During the process, AZ5214E photoresist (PR) was used at 5000 rpm in the spin coating process, which created a thickness of approximately 1.2 to 1.4 microns. The samples were pre-baked at 110° C. for 4 minutes and then exposed with 405 nm UV light at 135 mJ/cm2. Finally, the samples were developed in a AZMIF-300 for approximately 45 to 50 seconds and rinsed in diluted water.
With SiO2 utilized as the mask layer for ScxAl1-xN etching, another mask layer was used to etch SiO2 layer first. An e-beam evaporation was used to deposit 100 nm of Ni, which will serve as a mask to etch SiO2 layer. During the Ni-metallization process, the base chamber pressure and evaporation pressure were maintained at 3.3×10−7 Torr and 1.2×10−6 Torr, respectively. The deposition process was performed at 0.5 Å/s to ensure a smooth Ni surface. Afterwards, the deposited samples were soaked in acetone solution for 15 mins for lifting off the photoresist and opening space for SiO2 layer etching. At a later processing, all the samples were rinsed with acetone, IPA, and DI water.
An ICP etching method was used to etch down the SiO2 layer. Initially, a chamber cleaning process was performed for 10 mins, where 50 sccm of O2 was used with 30 mTorr chamber pressure. Later, a fluorine-based ICP process was performed for 1 min 50 s. CHF3 (45 sccm) and O2 (5 sccm) gases were used as the primary etchants during the process, where ICP, RF power, and chamber pressure were set at 400 W, 100 W, and 5 mTorr, respectively. There will be some Ni still existing after ICP process, but this is not significant as it will be removed later during the wet etching and HF cleaning process.
Generally, during any ICP process, the ions generated by the plasma bombardment and the etched surface transfer kinetic energy. Moreover, it creates significant surface damage, in which lateral etching occurs for further etching. As a consequence, an intermediary process before ScxAl1-xN etching, is implemented that can remove the impurities of the grains as well as repair the damaged ions. Researchers have demonstrated that, high temperature thermal annealing process could be a prospective solution to the challenge. Thus, after the SiO2 mask has been defined, the samples were placed in a high-temperature annealing furnace chamber in a nitrogen atmosphere and annealed for 1 hr at 650° C. Researchers have demonstrated that there is a possibility of damaging the ScxAl1-xN during annealing process due to the high compressive stress produced by the annealing, which might be linked with the lattice parameters of the corresponding ScxAl1-xN film. Thus, in the experiments disclosed herein, a slow temperature gradient of 20° C./min was used for ramping up the process and cooling down the samples, as well as using a minimal nitrogen gas flow of approximately 40 sccm to 45 sccm to ensure the mechanical stability of the samples.
The recent success of KOH based wet etching process of ScxAl1-xN (x=12.5%) results in poor verticality of approximately 55′ to about 65′ for Sc0.20Al0.80N, and Sc0.40Al0.60N, while on the other hand, other researchers have demonstrated that TMAH could be used as a wet chemical etchant for Sc0.20Al0.80N. In the experiments disclosed herein, 25% concentrated TMAH (TMAH:Water in 1:3 ratio) solution was used at approximately 78° C. to 82° C. to etch ScxAl1-xN (x=12.5%, 20%, 40%) layer. In these experiments, the etching rate of Sc0.125Al0.875N, Sc0.20Al0.80N, and Sc0.40Al0.60N was found to be approximately 365 nm/min, 243 nm/min, and 81 nm/min, respectively. It was observed that the etching rate is significantly lower compared to the etching rate presented for AlN of 1500 nm/min in the literatures. Similar to other group III-V materials, ScxAl1-xN is expected to form oxides compound while reacting with TMAH [N(CH3)4+OH−]. During the wet etch process of ScxAl1-xN, when it mixes with the TMAH solution, nitride forms separately by Al and Sc, and thereafter, AlN and ScN react, where, generally, oxides and amphoteric substance are produced. The following chemical reactions are expected to happen during the wet etching process disclosed herein:
The formation of the scandium hydroxide residues occurs at a temperature of less than 85° C., and it slows down the etching process of ScxAl1-xN. During the chemical reaction process, other components such as CH4, NO, and NO2 can be formed as well, usually at higher temperatures greater than 300° C. Thus, in the experiments disclosed herein, the temperature of the TMAH solution was kept at 80° C. during the etching process in order to have fine control of the etching rates. Hydroxides that eventually remain on the sample as shown in
The experiments and processing approaches herein developed a process to etch ScxAl1-xN layer with a vertical sidewall that will be valid for a wide range of concentrations of scandium into AlN. In several research publications, it is reported that the etch rate decreases with the increase of scandium concentration, and the verticality of the side walls decreases. Several etching processes shown in the table of
Selecting a suitable hard mask was another challenge. Researchers demonstrated that Mo/SiO2/SiNx could be used as etching mask for TMAH-based etching of ScxAl1-xN, and it does not make any significant difference in the etching performance. Since SiO2 deposition is comparatively much more accessible, and well-established from experience in Si processing, the experiments disclosed herein moved forward with SiO2. During the wet etching process, the 25% TMAH solution was heated to 80° C. and then immersed the ScxAl1-xN samples in the solution.
Once etching starts, it can be visually seen that the ongoing chemical reactions create bubbles around the solution. Generally, once the whole ScxAl1-xN layer is etched, the sample color changes. For Sc0.20Al0.80N, it only took 3 minutes to etch a 730 nm thick layer, ensuring an etch rate of 243 nm/min with approximately 870 to 900 vertical sidewalls, as shown in
The same TMAH concentration and temperature were applied during the etching process of Sc0.40Al0.06N and Sc0.125Al0.875N and the results are shown in
As the scandium concentration increases, usually the undercut (lateral) etching increases, but in the works disclosed herein were successful to reduce the lateral etching resulting in an undercut layer of less than 400 nm. See
N(CH3)4+OH−+HF→(CH3)4+F−+H2O (5)
In the works disclosed herein, a diluted HF of approximately 3% to 5% was used to remove the SiO2 hard mask. As shown in
The following provides features of the disclosed experiments discussed above:
In the work disclosed herein, an efficient process was successfully developed that is capable ensuring good vertical sidewalls of etching ScxAl1-xN (x=12.5%, 20%, 40%) as well as reducing the amount of undercuts. The inventors have also analyzed the prospective reasons behind the factors that affect verticality during etching and demonstrated how the annealing process significantly improves the surface damage by reducing the ion-bombardment effect, which prevents lateral etching. As noted in the literature, the scandium content increases, the more difficult it is to etch in the presence of AOGs and formation of residues. Furthermore, the impact of high-temperature annealing may lead to optimizing the etching process for successful device fabrication. Finally, with the process disclosed herein ensuring vertical sidewalls, thus this process or variations thereof can be applied in the fabrication of piezoelectric devices like ring resonators, contour resonators, lamb wave resonators, RF filters, transducers, MEMS devices, photonics integrated circuits, and other similar devices.
Variations of method 3200 or methods similar to method 3200 can include a number of different embodiments that may be combined depending on the application of such methods and/or the architecture of systems including a piezoelectric material in which such methods are implemented. Such variations can include annealing the patterned first mask before wet etching the piezoelectric material. Variations can include patterning the first mask using an inductively coupled plasma dry etch to etch the first mask.
Variations of method 3200 or methods similar to method 3200 can include the piezoelectric material being a ScxAl1-xN film and the first mask being a silicon oxide mask. The second mask can include nickel. Variations of method 3200 or methods similar to method 3200 can include wet etching the piezoelectric material by using tetramethyl ammonium hydroxide.
In various embodiments, an apparatus can comprise a piezoelectric material as a functional component. The piezoelectric material can have vertical sidewalls, where the vertical sidewalls deviate from ninety degrees by fifteen degrees or less. The deviation from ninety degrees can be by five degrees or less. The deviation from ninety degrees can be between approximately three degrees to about five degrees.
Variations of such an apparatus and its features, as taught herein, can include a number of different embodiments and features that can be combined depending on the application of such apparatus, the format of such apparatus, and/or the architecture in which such apparatus are implemented. Variations of such apparatus can include characteristics of the piezoelectric material being defined by an ICP dry etch process applied to the piezoelectric material. Variations of such apparatus can include the piezoelectric material being lithium niobate or ScxAl1-xN. The apparatus can be a component in a radio frequency system, a MEMS, a phononic system, or a photonic system.
An inductively coupled plasma dry etch process can obtain a deep etching profile in a piezoelectric material, such as lithium niobate, with minimum roughness and substantially vertical sidewalls. In addition, quality metal masks can be achieved by employing a hydrogen-plasma treatment prior to the processing steps. Periodic interruption steps can be included in the plasma dry etch procedure followed by a chemical cleaning between each cycle to avoid thermal effect and minimize byproduct redeposition during the long etching process. Additionally, a deep etching profile in a piezoelectric material, such as a ScxAl1-xN film, can be attained with minimum roughness and substantially vertical sidewalls using wet etching and a patterned mask, where the patterned mask is formed using another mask. The patterned mask can be annealed before wet etching the piezoelectric material.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Upon studying the disclosure, it will be apparent to those skilled in the art that various modifications and variations can be made in the devices and methods of various embodiments of the invention. Various embodiments can use permutations and/or combinations of embodiments described herein. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is to be understood that the above description is intended to be illustrative, and not restrictive, and that the phraseology or terminology employed herein is for the purpose of description.
This application claims priority under 35 U.S.C. 119(e) from U.S. Provisional Application Ser. No. 63/330,103, filed 12 Apr. 2022, which application is incorporated herein by reference in its entirety.
This invention was made with government support under DE-NA0003525 awarded by Department of Energy-Sandia National Labs. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63330103 | Apr 2022 | US |
