JP5116945B2

Acoustic resonators

Abstract

This record has no abstract on file.

JP5116945B2, drawing sheet 1 — Sheet 1 of 1

Term

Term ended

Expired 11 August 2023, 3.1 years ago.

12 claims: 7 independent, 5 dependent

1
基材、該基材上に、直接又は一層以上の中間層の上に設けられた少なくとも一層の結晶性構造のプライマー層、該プライマー層上に設けられたほぼ滑らかな結晶性構造の電極層、及び該電極層上に設けられた圧電体層を含んでなり、 (i)該プライマー層の少なくとも一層は、第一の結晶系に属する結晶学的構造を有しており、 (ii)該電極層は、該第一の結晶系とは異なる第二の結晶系に属する結晶学的構造を有しており、かつ (iii)該プライマー層の少なくとも一層の原子間隔と該電極層の原子間隔とが、約15%以内にマッチしており、該プライマー層が20°C~100°Cで堆積されたものであり、該電極層がネオン・スパッタリングにより堆積され、次に水素プラズマで処理されたモリブデンである事を特徴とする、音響共振器。
2
基材、該基材上に、直接又は一層以上の中間層の上に設けられた少なくとも一層の結晶性構造のプライマー層、該プライマー層上に設けられたほぼ滑らかな結晶性構造の電極層、及び該電極層上に設けられた圧電体層を含んでなり、 (iv)該プライマー層の少なくとも一層は、第一の結晶系に属する結晶学的構造を有しており、 (v)該電極層は、該第一の結晶系とは異なる第二の結晶系に属する結晶学的構造を有しており、かつ (vi)少なくとも一つの方位に於いて、該プライマー層又は少なくとも該電極と接するプライマー層の原子間隔と該電極層の原子間隔とが、約15%以内にマッチしており、該プライマー層が20°C~100°Cで堆積されたものであり、該電極層がネオン・スパッタリングにより堆積され、次に水素プラズマで処理されたモリブデンである事を特徴とする、音響共振器。
3
前記電極層は、立方晶系に属する結晶学的構造を有している事を特徴とする、請求項1又は請求項2に記載された音響共振器。
4
前記プライマー層は、六方晶系、正方晶系、又は斜方晶系に属する結晶学的構造を有している事を特徴とする、請求項3に記載された音響共振器。
5
前記プライマー層は、六方晶α型チタン、インジウム、窒化アルミニウム、窒化タンタル、ケイ化タングステン、亜鉛又は炭化モリブデン、あるいは合金又は化合物から選ばれる事を特徴とする、請求項3 又は請求項4 に記載された音響共振器。
6
前記プライマー層は、約200nm以下の厚みを有している事を特徴とする、請求項1~ 5 のいずれか一項に記載された音響共振器。
7
前記プライマー層は、約100nm以下の厚みを有している事を特徴とする、請求項 6 に記載された音響共振器。
8
前記プライマー層は、約50nmの厚みを有している事を特徴とする、請求項 6 又は請求項 7 に記載された音響共振器。
9
少なくとも一層のプライマー層を 20°C~100°Cで堆積させる工程、該プライマー層の上部表面上にモリブデンを含んでいる電極層をネオン・スパッタリングにより堆積させる工程、堆積された該電極層を水素プラズマで処理する工程、及び該最上部電極層上に圧電体物質の層を堆積させる工程を含む音響共振器を形成する方法であって、該プライマー層は、六方晶α型チタン又は窒化アルミニウムを含み、その上面の原子間隔が該電極層の原子間隔と約15%以内にマッチし、かつ立方晶形態のものではない事を特徴とする、音響共振器を形成する方法。
10
少なくとも一層のプライマー層を 20°C~100°Cで堆積させる工程、該プライマー層の上部表面上にモリブデンを含んでいる電極層をネオン・スパッタリングにより堆積させる工程、堆積された該電極層を水素プラズマで処理する工程、及び該最上部電極層上に圧電体物質の層を堆積させる工程を含む音響共振器を形成する方法であって、該プライマー層の少なくとも一層は、六方晶α型チタン又は窒化アルミニウムを含み、その上面の原子間隔が該電極層の原子間隔と少なくとも一つの方位に於いて約15%以内にマッチし、かつ立方晶形態のものではない事を特徴とする、音響共振器を形成する方法。
11
前記プライマー層は、約40°Cで堆積する事を特徴とする、請求項 9又は請求項10 に記載された方法。
12
前記プライマー層及び前記電極の堆積の間に真空破壊が無い事を特徴とする、請求項 9~11のいずれか一項に記載された方法。

Independent claims12

54 paragraphs, as filed

The present invention relates to acoustic resonators and methods of forming such devices. In particular, but not limited to, the present invention relates to a molybdenum (Mo) electrode on which, for example, a piezoelectric layer of aluminum nitride (AlN) is deposited. Such a structure is a good indication of the characteristics of acoustic resonators formed on silicon wafers. Acoustic resonators are used as RF filters and resonators such as bulk elastic wave (BAW) or film bulk elastic wave resonator (FBAR), and the term "acoustic resonator" is all such. Widely used to cover various devices and other types that use similar structures. In such devices, for example, a crystalline aluminum nitride piezoelectric layer is located between at least two electrodes. Apply high frequency voltage to the structureApplyThe piezoelectric layer is then believed to vibrate in the permissible vibration mode at the selected frequency, resulting in a bandpass filter or frequency stabilization.

Molybdenum has the advantage of lower acoustic loss due to its higher stiffness compared to other electrode metals such as Al, Pt, Au and Ti, so as a lower electrode, for example FBAR devices Used in class. The benefits associated with lower acoustic loss in MoA higher Q factor in devices, Q determines the speed at which the filter turns on and off.

One of the major requirements for good performance in FBAR devices is the pre-selected crystallographic aspects.InOf the locking curveFWHM (full width half maximum)Preferably 2 ° or lessIs, AlN membraneInA sharp {0002} texture. It is known that the texture of the AlN film strongly depends on both the roughness and texture of the underlying electrode on which the AlN film is deposited. A smooth underlayer with a sharp texture is the best possible combination.

In UK Patent Application Publication No. 2 349 392, Applicants describe the use of hydrogen atoms in plasma before, during, or after depositing the underlying electrodes. And it resulted in improved quality of the aluminum nitride layer subsequently deposited on the electrode. At that time, the process was not well understood and, as a result, not optimized. In US Pat. No. 6,060,818 (US-B-6,060,818), molybdenum was well collimated by polishing the surface of the phosphorus-doped silica glass (PSG) layer to a mirror finish. -collimated) It has been shown that membranes can be deposited. This disclosure is then highly textured, "despite the fact that the mirror finish on the PSG layer does not contain a crystalline structure that" seeds "the piezoelectric layer." Highly textured C-axis piezoelectric layerIs the basis ofI will describe the matter further. The PSG layer in this disclosure is a sacrificial layer, which is subsequently wet etched to create a cavity. The chemical mechanical polishing process and subsequent cleaning are complex and costly. Therefore, an improved method of depositing the lower electrode, which is suitable as a surface on which the piezoelectric layer is deposited, but does not require polishing of the sacrificial layer under the electrode layer and / or the underlay in direct contact. There is a request. From research, Applicants have found that the lower layer or multiple layers beneath the electrode layer not only is smooth at the interface with the electrode layer, but also fulfills two functions, that is, one matches the electrode layer. Interatomic spacing, and the other is buffering the lower electrode from the substrate beneath or at least partially crystallographicSeparated intoHe insisted that it was also necessary to fulfill the two functions of doing.

Applicants have found a way to achieve this. Therefore, in one feature of the present invention,IncludingAn acoustic resonator is provided. that is, Base material,TheOn the substrate, Directly orOne or more intermediate layersuponToProvisionAt least one moreAlmostCrystalline primer layer,TheOn the primer layerProvisionWasAlmostSmoothAlmostCrystalline electrode layer, as well asTheOn the electrode layerProvisionPiezoelectric layer And、 (i)ThePrimerLayerAt least one layer, firstofIt has a crystallographic structure belonging to a crystalline system and has a crystallographic structure. (ii)TheThe electrode layer isThefirstCrystalsystemWhat isDifferent secondofIt has a crystallographic structure belonging to the crystal system and has a crystallographic structure.And (iii) In at least one orientationThePrimerLayerAt least one layerAtomic distanceWhenTheDistance between atoms in the electrode layerWhenBut matches within about 15% Characterized by things. From another feature, the present invention has the following:IncludingIt is in the acoustic resonator. that is, Base material,TheOn the substrate, Directly orOne or more intermediate layersuponToProvisionAt least one moreAlmostCrystalline primer layer,TheOn the primer layerProvisionWasAlmostSmoothAlmostCrystalline electrode layer, as well asTheElectrode layerProvided on topPiezoelectric layerIncluding (vi) PrimerLayerAt least one layer, firstofHas a crystallographic structure belonging to the crystalline system、 (vii)TheThe electrode layer isThefirstCrystalsystemWhat isDifferent secondofIt has a crystallographic structure belonging to the crystal system and has a crystallographic structure.And (viii) In at least one directionThePrimer layer or at leastTheWith electrodesTouchPrimer layerAtomic distanceWhenTheDistance between atoms in the electrode layerWhenBut matches within about 15% Characterized by things. For clarity, the conductive layer on which the piezoelectric layer is deposited is referred to as the "electrode", whether or not the conductive layer acts as a current carrier on its own or in conjunction with the conductive underlayer. .. Aluminum nitride is well known as the piezoelectric layer and is shown herein as an example, but other piezoelectric materials used include zinc oxide (ZnO) and lead zirconate titanate (PZT). Including. The underlying substrate is, for example, an acoustic mirror layer or an amorphous layer (which may in some cases be a sacrificial layer that is partially or completely removed during the next processing step) or smooth. It may include some other layer that creates the surface. The surface on which the electrode structure is deposited is likely to have little or no crystallographic elements, and therefore the primer layer is poorly or irregularly crystalline in the underlying substrate. It is selected so that it has a crystalline structure so that no different structure is duplicated in the electrode layer, but it has a different crystalline system from the crystalline system of the electrode. Thus, the primer layer has a different crystallographic structure with respect to the electrode layer in order to reduce any tendency of the primer layer to the amorphous or irregular properties of the substrate replicated with the electrode layer. And are selected to have the property of having good (ie, within about 15%) interatomic spacing matching between the primer layer and the electrode layer. In one example, a single primer layer comprises a single primer layer between the substrate and the lower electrode layer that provides both applied functions. Alternatively, it has a lower primer layer selected to have a crystallographic structure different from the crystallographic structure of the electrode layer, and an upper primer layer selected to have interatomic distances matched to the electrode layer. There may be more than one primer layer. In one example, the single primer layer has a crystallographic structure belonging to the hexagonal system, and the electrode layer has a crystallographic structure belonging to the cubic system. For example, the electrode layer may be formed of molybdenum (cubic system), and the primer layer may be selected from, for example, aluminum nitride or hexagonal α-titanium. The primer layer may be an alloy or compound of elements, stoichiometric or non-stoichiometric substances. The molybdenum electrode layer may be in substantial elemental form, or alloyed with other elements or combined in another way. In an alternative electrode system, the electrode layer is any suitable metal in cubic form.sexIt may be made of a material (eg, an alloy or compound such as tungsten, silicon, aluminum, copper, gold, nickel, platinum, tantalum, or TiW), and the primer layer may have a different crystalline form (eg, eg). It may be formed of a tetragonal, orthorhombic, or hexagonal) layer or multiple layers, and may be an element, compound, or alloy. Such layers are, for example, titanium (titanium is dimorphic).sexIt is unusual in that it is (dimorphic) and α-type hexagonal. ), Indium, aluminum nitride, tantalum nitride, tungsten silicate, zinc, and molybdenum carbide. The applicant has found that multiple layers of thick (thicker) primers tend to reduce the texture quality of the electrode layer, so the primer layer is preferably about 200 nm or less, more preferably about 100 nm or less. And, conveniently, it has a thickness of about 50 nm. In certain situationsA single primer layer may be provided on the base material, a single electrode layer is provided on the primer layer, and a piezoelectric material is further provided on the single electrode layer. Also, it is provided on the base material.There is a multi-layer structureAlsoGood. In another feature, the present invention performs the following steps.IncludingA method of forming an acoustic resonator is provided. The process is The process of depositing the primer layer,TheA step of depositing an electrode layer containing molybdenum on the upper surface of the primer layer, as well as Step of depositing a layer of piezoelectric material on the top electrode layer AndTheThe primer layer is in at least one orientationIt contains a nearly crystalline substance, the interatomic distance of which matches the interatomic distance of the electrode layer within about 15%, andIt is characterized in that it is not in the cubic form. In some embodiments, the deposition of the primer layer is performed at a substrate temperature of less than about 100 ° C, and 20-100 ° C may be a suitable range. It may also be preferable to have no vacuum fracture between the deposition of the primer layer and the deposition of the electrode layer. In some situations, it may not always be possible to use multiple layers of primers or deviate from the molybdenum electrode. For example, an acoustic resonator may have an acoustic mirror underneath the lower electrode that makes it difficult to perform the above techniques. Therefore, further attempts were made to improve the crystallographic texture of the piezoelectric material formed on the lower electrode without a primer layer. However, it should be noted that the techniques developed as a result of those studies may also be used in combination with the primer layer structure described above. Therefore, in a further feature of the present invention,IncludingAn acoustic resonator is provided. that is, Base material,TheDirectly on the substrate orTheIndirectly on one or more intermediate layers on the substrateProvisionElectrode layer containing molybdenum andTheOn the electrode layerProvisionLayer of piezoelectric material soAhRi,TheMolybdenum electrode layerIs the LordAccumulated by neon sputtering processAndElectrode layerIs waterIt is characterized by being processed with plain plasma. Applicants will find that sputtering molybdenum onto a substrate with a gas that is not mass-matched to the target material will result in a smoother electrode surface with improved FWHM. I insisted on saying that. Studies conducted with argon and krypton have implied that this hypothesis is true. This is because the molybdenum electrodes deposited on the substrate using argon as the sputtering gas had a smoother appearance than those deposited using krypton. However, further by the applicantthe study(work) showed that the FWHM on the molybdenum surface decreases when argon is used, but the FWHM deteriorates when neon (atomic weight 20) is used. However, quite surprisingly, the FWHM of the piezoelectric material (aluminum nitride) deposited on molybdenum using neon sputtering is significantly improved if the electrode layer is treated with hydrogen plasma, and really, It has been found that the tests show excellent FWHM results, which are better than those obtained using argon sputtering. In another feature, the present invention performs the following steps.IncludingA method of forming an acoustic resonator is provided. The process is Directly on the substrateContactIndirectly on one or more intermediate layers on the substrateToElectrode layer containing ribdenProvisionFor this purpose, a neon sputtering process and a process using a molybdenum target, With hydrogen plasmaTheThe process of processing the electrode layer andTheA layer of piezoelectric material on the electrode layerProvisionProcess Is. The piezoelectric material may conveniently include aluminum nitride. Hydrogen plasma treatment uses frequencies in the range of about 180 KHz to about 27.12 MHz and ranges from about 0.5 to about 10 KW for 200 mm diameter substrates.Electric powerIt may be carried out using a parallel plate reactor and a hydrogen pressure in the range of about 1 to about 10 Torr. Further features, the present invention provides an electrode layer.Is crystallographicallyDifferentAndHas an interatomic spacing that matches within about 15% of the interatomic spacing of the electrode layer in at least one orientationIncluding choosing a layer, Select a primer layer for the lower electrode layer in the acoustic resonatorBuIn the way. The primer layer may include two or more layers, and different crystallographic structures may be in the lower layer. Although the invention has been described above, it applies to any combination of inventions described or later described in the appended claims. The present invention may be implemented in various ways, and specific embodiments are described herein through examples with reference to FIGS. 1-3.

Experiments were performed by first depositing a primer layer under the Mo film to see if a primer layer could promote the growth of a fully textured Mo film. The results are summarized in Table 1.

In Table 1, the heading "atomic mismatch" is used to indicate the percentage difference in interatomic spacing of the primer layers on the surface corresponding to the surface with respect to the molybdenum layer deposited on the primer layer. .. For example, hexagonal crystals may have very different interatomic distances shown at the same time, depending on the orientation of the crystals. This is further discussed, especially with regard to titanium.

Primer layers are Mo (atomic distance of molybdenum, aMoSelected based on interatomic spacing matches with = 2.725 Å), where the primers were non-cubic in crystalline as well as crystalline morphology. This is a good primer layer for Mo, aTa2N= Tantalum nitride, aluminum nitride and titanium with interatomic spacing of 3.05 Å, especiallyTo sixSquare αOf the moldTitanium was implied.

Titanium is dimorphicsexSo, it exists in both hexagonal and cubic forms, and depending on the deposition conditions, hexagonal form titanium may indicate its crystal orientation in one of the two crystal forms. Placing titanium at a higher temperature, eg, a substrate temperature of 400 ° C, created (Equation 1) orientations with significantly different atomic distances on the crystal plane, but at lower temperatures (typically less than 100 ° C). ), For example, depositing titanium at a substrate temperature of 40 ° C created a {0002} orientation. This was found to create an inferior molybdenum electrode layer.

As a further comparison with materials with poor crystallinity matching, molybdenum nitride was also attempted, as was the extremely smooth but non-crystalline amorphous SiON layer.

The results from these experiments are that the primer layer is crystalline, has different crystallography to the electrode layer, and has close atomic distance matching, eg, matching within about 15% to the electrode layer. The selection identifies how to select a primer layer that produces a well-textured lower electrode layer in the acoustic resonator.

It can be seen that AlN deposited on Mo (FWHM = 1.84 °) with good orientation also has good orientation (FWHM = 1.10 °). It seems that there is a direct relationship between the well-oriented Mo electrode layer and the well-oriented AlN piezoelectric layer deposited on it. Also noteworthy is that thick primer layers tend to reduce the quality of the Mo texture. It is considered that this is because the thick primer layers are coarser.

Quite naturally, the Nitrided Mo primer layers with poor interatomic spacing matching with Mo showed poor Mo texture. The extremely smooth amorphous SiON primer also showed a poor Mo texture.

It is hypothesized that good piezoelectric electrode layers may also be formed on a stack structure consisting of, for example, hexagonal titanium, cubic aluminum, with a cubic molybdenum layer on top. This stack structure will provide the required change in crystallography between the lower titanium and the overlying aluminum (from hexagonal to cubic in this example). In such a structure, multiple layers of primers with an upper electrode layer greater than 1,000 Å and typically 2,000 Å thick, each layer is typically 150 Å thick and typically Would have a total thickness of less than 500 Å. This example is shown to demonstrate the generality of the invention, and the upper aluminum and molybdenum layers can be considered together as electrodes because they are both conductive. And, in practice, a single conductive layer should never exceed a thickness of 1,000 Å if the film thickness is increased to a thickness suitable for several layers to perform this function.

Atomic force microscopy (AFM) and FWHM studies were performed on the AlN (50 nm) / Mo (180 nm) stack. And a photomicrograph of such a structure is shown in FIG. The rms roughness is 0.50 nm. The FWHM of Mo is 2.4 ° and the FWHM of AlN is 1.22 °. The z-axis is 5 nm.

Perhaps due to the design of the acoustic mirror under the bottom electrode, it may not always be possible to use primer layers or deviate from the Mo electrode. Therefore, additional experiments were performed to improve the AlN texture on the molybdenum bottom electrode without a primer layer.

The sputtering process utilizes rare gas ions that collide with the target. Sputtering efficiency is improved by using a sputtering gas that matches the mass of the target atom. So, for example, the difference seen between Ar and Kr efficiencies is probably due to the efficiency of energy transfer between Mo and sputtering gas atoms. Energy transfer between Kr and Mo (Et= 0.99) is the energy transfer (E) between Ar and Mo due to a better mass match between Kr (atomic weight 80) and Mo (atomic weight 96).tHigher than = 0.83). Therefore, Mo atoms sputtered with Kr will have lower energies than Mo atoms sputtered with Ar. This explains the significant differences in the roughness of the Argon and krypton-deposited Mo films (FIGS. 2 and 3) and the differences in the next AlN texture formed on these films.

This implies that a smoother layer of aluminum nitride may be achieved by sputtering the lower molybdenum electrode with a sputtering gas that is poorly mass matched to the target material. Therefore, this provides a higher residual energy level for the target material to be sputtered when it reaches the wafer surface (although there is a loss of sputtering efficiency).

Therefore, the experiment was performed on a molybdenum electrode layer deposited on the insulator in argon, krypton and neon, and then aluminum nitride was sputtered onto this molybdenum layer. In addition, for some experiments, hydrogen plasma treatment was performed on the Mo lower electrode layer before sputtering the aluminum nitride layer. The hydrogen treatment chamber was a narrowly spaced parallel plate reactor with RF at 13.56 MHz applied to the upper shower head. Best results were obtained with a power of 2 kW and a hydrogen pressure of 4 Torr. These experiments are summarized in Table 2.

Surprisingly, the best AlN FWHM results are obtained by hydrogen plasma treating the Mo underlay, which shows the worst FWHM. This is totally unexpected, and by hydrogenating the neon-deposited Mo, the worst Mo base is transformed into the best Mo base by a considerable margin.

The process window for hydrogen plasma processing has been found to be fairly broad with respect to the overall tendency to improve the FWHM results of AlN for higher powers and pressures (smaller angles). It was. Within the range of 0.5-2 kW of power applied to the 200 mm wafer and 0.5-4 Torr hydrogen pressure, good results were obtained, along with the best results under 2 kW and 4 Torr conditions.

In contrast, the low frequency RF of 356KHz,Attempted to replace RF at 13.56MHz frequency,AlN FWHM angle with respect to process time increased to 150 secondsDoes not change,Blistering Mo membranes for longer process timesAccompanied.. The electrodes were closely spaced (less than 30 mm) in the plasma reactor used. Lower pressures and frequencies are associated with increased energy at the bombardmentShi, Experimental evidence is low energy levelIncrease inThe best result can be obtained by the added magnetic flux.

In all cases, it is preferred to deposit an electrode layer on the surface of the primer layer (multiple layers) without exposure of the surface to the atmosphere, and this is commercially available from Applicants. For multi-chamber "cluster" type single wafer sputtering systems such as the Sigma sputtering system, or similar systems such as Endura available from Applied Materials Inc. It is obtained in the best condition.

It has been shown that the quality of the piezoelectric layer deposited on the electrode layer can be dramatically improved by selecting an appropriate primer layer. This is the latest content with further experimental results.

All molybdenum deposits mentioned above are standardClosely coupled(close coupled) (45 mm throw) Performed in a magnetron sputtering chamber. However, the Ultra® spatter chamber (commercially available from Trikon Technologies Inc.) with a 430 mm source-to-base material distance and magnetic coil, and described in WO 02/11176. When used for molybdenum deposition on a suitable primer layer, the FWHM angle of the molybdenum electrode and the layer of aluminum nitride piezoelectric material to be deposited nextImprovementIt has been found to do. This is the case where the primer layer is not used at allNot seen inIt's a surprising result, and thisImprovementThe reason for this is still not understood, but it will be explained as follows.

The confinement of the magnetic coil has the effect of increasing the plasma density at the target and, as a result, is sputtered to the coil at 1350 amp turns.TaIncreases the degree of ionization of a substance from about 5% to about 20-25%. Prolonging the distance from the source to the substrate (at least 5 times greater than the standard) pulls the substrate away from the target plasma, resulting in the substrate.WhatIt has the effect of reducing the impact of. Even in the absence of applied substrate bias, the wafer will typically be negatively self-biased in the 10 eV range, resulting in some impact from the ionized gas and / or material being sputtered. The long throw chamberinevitablyWith poor material efficiency (1/10 deposition rate on substrate), no requirement for step coverage (because the cavities are flat), and no primer layer under the electrodes. There is no improvement in the FWHM angle. For these reasons, the long throw chamber is a bookUseAll known requirements ofHas been avoided from(contra-indict),Usually not selected for experimentation.. The results are summarized in Table 3.

Titanium was "cold" deposited (nominal 40 ° C). The standard (45 mm source-to-base material distance) values correspond directly to the values in Table 1 and differ only within the range of experimental results.

The following experiments were performed as shown in Table 2 to determine in more detail the conditions for depositing the preferred {0002} and (Equation 2) textures of titanium. XRD measurements on a Ti film deposited at 400 ° C showed that the texture had a very faint {0002} peak (Equation 3). The {0002} texture in Ti is needed to promote the growth of well-oriented Mo films. It was found that further cold deposition of the Ti film would promote the growth of the {0002} texture. Deposition at low temperatures requires a cooling step, as the wafers are heated in a heat station to degas before sputtering. This was achieved experimentally by backfilling the titanium chamber with argon in order to increase the thermal conductivity to the wafer chuck. More precisely, it is an electrostatic wafer clamping as well as a wafer backside gas. It may be achieved by suitable clamping / cooling such as pressurisation). The Ti film was then deposited at 100 ° C and 40 ° C to promote the {0002} texture. The results are shown in Table 4.

The following conclusions can be drawn from the results shown in Table 4. The {0002} texture of Ti is more effective than the (Equation 4) texture in promoting a good Mo texture, and the wafer is during Ti deposition to obtain the {0002} texture at Ti. It needs to be medium cold, and the AlN texture is improved by improvements with the Mo texture.

As already shown, the reason for the effect of Ti seeds and especially {0002} seeds is to match the interatomic spacing of the seeds with the interatomic spacing of the electrodes.

The lattice constants and interatomic distances on the relevant planes for Ti, Mo and AlN are shown in the table below. It can be seen from Table 5 that the lattice match at Mo on the {110} plane, which is the preferred texture at Mo, is better with the {0002} textured Ti seed. This explains the better Mo FWHM seen on cold-deposited Ti films below 100 ° C.

Tungsten has the best atomic match with Mo and is therefore a candidate for use as a seeding layer for well textured Mo films. However, the texture of the as-deposited W film (without "seeding" or primer layers) is inadequate (FWHM> 10.0 °) (similar to Mo), so tungsten is It cannot be used in this respect. This inadequate texture will be replicated in the covering Mo membrane. In contrast, Ti textures are not the only factor affecting Mo textures, but can deposit Ti with a FWHM of less than 4.5 °. It is found that the Ti texture improves with increasing film thickness of the Ti primer layer, while the quality of Mo (and AlN) texture decreases with increasing film thickness of the Ti primer layer. The FWHM of {0002} Ti is 4.5 ° for a 15 nm thick Ti film and 3.52 ° for a 100 nm thick Ti film. The deterioration of Mo texture quality with increasing thickness of Ti primer is probably due to the coarsening of Ti film with increasing thickness.

Therefore, the desired primer has close interatomic spacing matching with the electrode layer and is well textured and smooth as deposited. The optimum thickness of the titanium primer layer is shown in Table 6. In general, the best electrodes for resonators will be cubic, and the best primer layers will be hexagonal in crystalline form.

A Ti film with a texture (Equation 5) with a very faint {0002} peak was deposited at 400 ° C. The {0002} texture at Ti is needed to promote the growth of well-oriented Mo films. The Mo film is 500 nm thick, andElectric powerWas deposited at 200 ° C. in an Ultra chamber with a powered coil. The AlN membrane was 1.5 μm thick and deposited at 400 ° C.

Table 1 shows that the AlN primer layer is more effective than Ti in promoting the growth of Mo membranes with good orientation. This further implies that atomic matching between the primer and the electrode is not the only factor affecting the electrode texture. The better texture and smoothness of the AlN seed may outweigh the better atomic matching between Ti and Mo.

Additional experiments were performed (at a 45 mm source to substrate distance) to clarify the role of the primer layer texture in influencing the Mo texture. Poorly oriented AlN membranes can be deposited by excluding the degassing step prior to AlN deposition. It can be seen that the AlN film having good orientation is a better primer layer than the AlN film having poor orientation. This may be due to the improved smoothness, as AFM studies show that well-textured Mo films are smoother than poorly textured films.

Tungsten is another metal of interest when applied to lower electrodes in BAW devices. It can be seen from Table 5 that W has good atomic matching with Ti and AlN, and therefore Ti and AlN primer layers have also been studied for W films.

It can be seen from the above table that both the Ti and AlN primer layers improve the W texture. As demonstrated by Mo, AlN is more effective than Ti in improving W (and AlN) textures.

<figref num="1">FIG. 1 is an atomic force microscope (AFM) photograph of an electrode structure including an electrode layer of molybdenum deposited on a primer layer of aluminum nitride deposited on a substrate.</figref>

<figref num="2">FIG. 2 is a scanning electron micrograph (SEM) of a molybdenum film deposited using argon as the sputtering gas.</figref>

<figref num="3">FIG. 3 is an SEM micrograph of a molybdenum film deposited using krypton as a sputtering gas.</figref>

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Citations
Document	Relation	Office
JP2000332569A	Cites	Japan
JP11260835A	Cites	Japan
JP2002374145A	Cites	Japan
JP200276824A	Cites	Japan
JP11346140A	Cites	Japan
JP2000232334A	Cites	Japan
JP2002180106A	Cites	Japan
JP2001274650A	Cites	Japan
WO01018273A1	Cites	World Intellectual Property Organization (WIPO)
JP2002185042A	Cites	Japan
JP60103709A	Cites	Japan
JP200464786A	Cites	Japan

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Document	Office	Kind	Date
0218762	United Kingdom	A	2002-08-13
0218762	United Kingdom	A	2002-08-13
02187623	United Kingdom	–	2002-08-13
40272802	United States of America	P	2002-08-13
40272802	United States of America	P	2002-08-13
60402728	United States of America	–	2002-08-13
0227981	United Kingdom	A	2002-11-30
0227981	United Kingdom	A	2002-11-30
02279818	United Kingdom	–	2002-11-30
0303504	United Kingdom	W	2003-08-11
0303504	United Kingdom	W	2003-08-11
2002402728	–	–	–
2002200218762	–	–	–
2002200227981	–	–	–
2003003504	–	–	–
GB20020018762	–	–	–
GB20020027981	–	–	–
US20020402728P	–	–	–
WO2003GB03504	–	–	–

Members17

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Document	Office	Kind
WO2004015862A2	World Intellectual Property Organization (WIPO)	A2	2004-02-19
AU2003252992A1	Australia	A1	2004-02-25
US2004061415A1	United States of America	A1	2004-04-01
WO2004015862A3	World Intellectual Property Organization (WIPO)	A3	2004-10-14
GB0501682D0	United Kingdom	D0	2005-03-02
GB2406582A	United Kingdom	A	2005-04-06
US2005099099A1	United States of America	A1	2005-05-12
DE10393038T5	Germany	T5	2005-07-28
US6944922B2	United States of America	B2	2005-09-20
JP2005536098A	Japan	A	2005-11-24
US2005269900A1	United States of America	A1	2005-12-08
US7141913B2	United States of America	B2	2006-11-28
US7327073B2	United States of America	B2	2008-02-05
JP2010161781A	Japan	A	2010-07-22
JP5074540B2	Japan	B2	2012-11-14
JP5116945B2This record	Japan	B2	2013-01-09
DE10393038B4	Germany	B4	2013-11-07

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