JP6085235B2 - Manufacturing method of mechanical resonator - Google Patents

Description

  The present invention relates to a method for manufacturing a micromechanical resonator having a minute portion that mechanically vibrates.

  A micromechanical resonator is a MEMS resonator manufactured by microfabrication, and mechanically vibrates. Therefore, the micromechanical resonator is used for a detector such as pressure, stress, flow rate, temperature, or acceleration (non-patent document). Reference 1, 2, 3, 4). A typical micromechanical resonator is shown in FIG. 3C includes a GaAs substrate 301, an AlGaAs sacrificial layer 302, a GaAs or AlGaAs vibrating part forming layer 303, and the vibrating part forming layer 303 includes a support part 305 and a beam structure 306. Since there is a space between the GaAs substrate 301 and the beam structure 306, the beam structure 306 vibrates mechanically.

  FIG. 3 is a conventional manufacturing process diagram of a micro mechanical resonator using a III-V group compound semiconductor. An example using a GaAs substrate is described below.

  First, as shown in FIG. 3A, an AlGaAs sacrificial layer 302 having an Al concentration of about 65% is formed on a GaAs substrate 301, and GaAs or an AlGaAs vibrating portion having an Al concentration of 35% or less is formed on the outermost vibrating portion forming layer. Layer 303 is formed.

  Next, a fine pattern is formed by a known photolithography technique, electron beam lithography, or the like, and the opening is mesa-etched using the formed pattern as a mask, so that the AlGaAs sacrificial layer 302 and the GaAs or Al concentration of 35% or less are formed. The AlGaAs vibration part forming layer 303 is removed. In this way, a thin line structure 304 is formed on the GaAs substrate 301 as shown in FIG.

Finally, compared to GaAs or AlGaAs having an Al concentration of 35% or less, an Al concentration of about 65% is obtained by wet etching using an etching solution such as hydrofluoric acid that selectively dissolves AlGaAs having an Al concentration of about 65%. A portion exposed on the surface of the AlGaAs sacrificial layer 302 is removed. In this manner, as shown in FIG. 3C, the beam structure 306 supported by the two support portions 305 is formed on the GaAs substrate 301 so as to be separated from the GaAs substrate 301. That is, AlGaAs 302 having an Al concentration of about 65% is used as a sacrificial layer, and the sacrificial layer is partially removed to form the beam structure 306. Although the above is an example using a GaAs substrate, a similar beam structure is manufactured by the same processing method as described above, using the Si substrate as the substrate 301, SiO ₂ as the sacrificial layer 302, and Si as the vibration part forming layer 303. Is possible.

  Since the beam structure 306 manufactured in this manner is formed apart from the substrate 301, it can vibrate mechanically. By using this vibration resonance, the structure including the beam structure 306 can be used as a mechanical resonator (see Non-Patent Document 1). It is also possible to produce a membrane structure instead of the beam structure 306 using a sample having a similar structure and use it as a mechanical resonator (see Non-Patent Document 2).

  The most important index indicating the characteristics of the resonator includes a resonance frequency and a figure of merit (Q value). These mechanical resonators have higher performance index (Q value) and superior frequency characteristics because they use mechanical resonance compared to resonators with electrical circuits configured using capacitors and coils. Yes. In addition, since the resonance frequency of the mechanical resonator as described above changes depending on the force applied to the mechanical resonator, it is possible to produce a force detection element with extremely high sensitivity by detecting a change in the resonance frequency. It is possible (see Non-Patent Documents 3 and 4).

  As a method of obtaining a resonator having a high resonance frequency and a large Q, there is a method of applying tensile strain to a mechanical vibrator. When a III-V compound semiconductor is used, nitrogen is doped into the III-V compound semiconductor. A method of applying tensile strain to a mechanical vibrator using a layer as a vibration part forming layer is promising (see Patent Document 1).

Japanese Patent Application No. 2012-180384

D.W.Carr, et al., "Measurement of mechanical resonance and losses in nanometer scale silicon wires", Applied Physics Letters, Vol.75, No.7, pp.920-922, 1999. J-P. Raskin, et al., "A Nobel Parameter-Effect MEMS Amplifier", Journal of Microelectromechanical Systems, Vol.9, No.4, pp.528-537, 2000. A.N.Cleland and M.L.Roukes, "A nanometre-scale mechanical electrometer", Nature, Vol.392, pp.160-162, 1998. H.L.C.Tilmans, M. Elewenspoek, and, J.H.Fluitman, Sensor and Actuators, A, 30, 35, 1998. F. Ishikawa, S. Fuyuno, K. Higashi, M. Kondow, M. Machida et al. “Direct observation of N- (group V) bonding defects in dilute nitride semiconductors using hard x-ray photoelectron spectroscopy” Appl. Phys. Lett. 98, 121915 (2011) G. Mussler, J.-M. Chauveau, A. Trampert, M. Ramsteiner, L. D. aweritz, K.H. Ploog “Nitrogen-dependent optimum annealing temperature of Ga (As, N)” Journal of Crystal Growth 267 (2004) 60-66

  Since nitrogen atom has the smallest atomic radius among group V elements, binary III-V compound semiconductor mixed crystals such as GaAs, InAs, GaSb, InSb, InP, GaP, etc., and these binary III-V compounds By doping a nitrogen atom into a ternary or higher group III-V compound semiconductor mixed crystal combined with a semiconductor mixed crystal, any of the lattice constants of the above-mentioned III-V group compound semiconductor mixed crystal can be reduced. Here, as an example, a case where GaAs in which GaAs is doped with nitrogen is used as the vibration part forming layer will be described. When GaAs is used as the substrate and GaNAs is used as the vibration part forming layer, the lattice constant of the GaNAs vibration part forming layer is smaller than that of the GaAs substrate, so that the GaNAs vibration part forming layer has tensile strain. Here, the state in which the As site of the GaNAs vibration part forming layer is replaced by one nitrogen atom is an ideal state of this nitrogen atom. Among the mixed nitrogen, ideal is the state where the As site is replaced by two nitrogen atoms, the state where the As site is replaced by both As and nitrogen, and the state where nitrogen exists between the lattices. It is known that there is nitrogen that is not mixed in the state. Nitrogen that is not in an ideal state is known to act as a trap and cause non-radiative recombination in the GaNAs vibration part forming layer (Non-Patent Documents 5 and 6). In mechanical vibrators, the nitrogen present in these non-ideal states causes the dissipation of the elastic energy of the vibrating body, thus increasing the mechanical vibrators when all of the doped nitrogen is not in the ideal state. There is a problem that the Q value becomes lower than when all the doped nitrogen is in an ideal state.

  In the above example, the explanation was made by taking GaNAs as an example. However, binary III-V compound semiconductor mixed crystals such as GaAs, InAs, GaSb, InSb, InP, and GaP and these binary III-V compound semiconductor mixed crystals are used. It is known that there is nitrogen that is mixed in a non-ideal state even if nitrogen atoms are doped into any of the combined ternary or more group III-V compound semiconductor mixed crystals. Even when an atom-doped material is used as the vibration part forming layer, there is the same problem as in the case of the GaNAs described above.

  The micromechanical resonator according to the present invention is formed by selectively etching a sacrificial layer that can be selectively etched, a vibration part forming layer using a III-V group compound semiconductor doped with nitrogen in all or part thereof, and a sacrificial layer. And a vibration part formed in the vibration part forming layer. In a nitrogen-doped group III-V compound semiconductor that forms all or part of this vibration part forming layer, if the state in which the group V site is replaced by one nitrogen is an ideal state, it exists in a non-ideal state Nitrogen that promotes dissipation of the elastic energy of the resonator reduces the Q value. Nitrogen present in these non-ideal states is extremely high by removing it by annealing when the sample is in a wafer state, during the manufacturing process of the micro mechanical resonator, or after the manufacturing process of the micro mechanical resonator is completed. A micro mechanical vibrator having a Q value can be obtained. Annealing is effective in hydrogen, but it can be performed in an inert gas such as nitrogen or argon, in a vacuum, under vacuum, under As irradiation, in an As atmosphere, in the air, or a mixture of these. Is also effective.

  In the above micro mechanical resonator, the vibration part may be a beam structure having a beam, a cantilever beam structure, or a membrane.

  According to the present invention, in the fabrication of a micro mechanical resonator using a III-V group compound semiconductor doped with nitrogen in all or part of the vibration part forming layer, annealing is performed in a wafer state, during element fabrication, or after element fabrication. By performing the processing, a micro mechanical vibrator having an extremely high Q value can be obtained.

It is a schematic diagram which shows the manufacturing process of the micro mechanical resonator concerning embodiment of this invention. The resonance characteristics of the micromechanical resonator according to the embodiment of the present invention are as follows: (a) a sample without annealing, (b) a sample annealed at 500 ° C. in hydrogen, (c) a sample annealed at 600 ° C. in hydrogen, d) A graph in the case of using samples annealed at 700 ° C. in hydrogen. It is a schematic diagram which shows the manufacturing process of the conventional micro mechanical resonator.

  FIG. 1 is a schematic diagram illustrating a manufacturing process of the micro mechanical resonator according to the present embodiment. In this embodiment, GaAs is used as the substrate of the micromechanical resonator, AlGaAs is used as the sacrificial layer, and GaNAs is used as the vibration part forming layer. As shown in FIG. 1A, an AlGaAs sacrificial layer 102 containing about 65% high-concentration Al is formed on a GaAs substrate 101, and a vibrating part forming layer 103 made of GaNAs is formed on the outermost surface. For the vibration part forming layer 103, GaNAs may be used only for a part in the stacking direction, and GaAs may be used for the rest. These samples are annealed in hydrogen to remove nitrogen that is present in a non-ideal state. Next, mesa etching is performed to create a thin line structure 104 as shown in FIG. Finally, the sacrificial layer was selectively etched with hydrogen fluoride water to remove the portion exposed on the surface of the AlGaAs sacrificial layer 102, thereby supporting the sacrificial layer 105 as shown in FIG. A beam structure (vibrating portion) 106 can be formed.

  FIG. 2 shows resonance characteristics of a micromechanical vibrator manufactured using a sample in which the vibration part forming layer 103 is formed of GaNAs having a nitrogen concentration of 1%. FIG. 2A shows the structure shown in FIG. 2B after annealing the sample in hydrogen at 500 ° C. for 1 minute after the step of producing the structure shown in FIG. 2 (c) is the same as that of FIG. 2 (b), but FIG. 2 (d) is prepared when annealing is performed at 700 ° C. for 1 minute. Shows the resonance characteristics of the micromechanical vibrator. In the graph of FIG. 2, the points are experimental values, and the curves are the experimental values fitted with Lorentz functions. The Q value was calculated from the fitted Lorentz function.

  2 (a), 2 (b), 2 (c), and 2 (d), the vibration characteristics of the mechanical vibrator when the vibration portion forming layer 103 is 100 nm thick, the entire width is 10 μm, and the length is 200 μm. It is. As is apparent from FIG. 2, it can be seen that the Q value increases when annealing is performed. This is because the dissipation of the elastic energy of the mechanical vibrator is reduced by reducing NN and N-As substituted for the As site by annealing.

  The mechanical vibrator manufacturing method of the present invention is characterized in that the dissipation of elastic energy of the mechanical vibrator is reduced by performing timely annealing treatment on the group III-V compound semiconductor doped with nitrogen as described above. With respect to III-V compound semiconductors doped with nitrogen, it has been reported that the light emission characteristics are improved by annealing treatment (Non-Patent Documents 5 and 6). In this case, annealing aims to reduce non-radiative recombination centers. It is a thing. On the other hand, the annealing process in the present invention is due to the suppression of dispersion of the phonon frequency, and has a different purpose and effect from the prior art.

  In the present embodiment, the micro mechanical vibrator using GaNAs as the vibration part forming layer has been described. However, binary III-V compound semiconductor mixed crystals such as GaAs, InAs, GaSb, InSb, InP, and GaP, and their two When nitrogen is doped into a ternary or more group III-V compound semiconductor mixed crystal combined with a group III-V compound semiconductor mixed crystal, the nitrogen is mixed in a non-ideal state as in the case of GaNAs by annealing treatment. Therefore, it is clear that the same effect as that of the present embodiment can be obtained.

  In the present embodiment, the case where annealing is performed from 500 ° C. to 700 ° C. is shown. However, since the sample surface hardly deteriorates up to 850 ° C., the case where annealing is performed at a temperature up to 850 ° C. It is clear that the same effect can be obtained.

  In the present embodiment, the case where the annealing treatment is performed in hydrogen is shown. However, by performing the surface treatment of the sample, it is possible to perform the annealing treatment in various atmospheres other than in hydrogen. Ideal for annealing in typical inert gas atmospheres, arsenic atmospheres, vacuums, air, and inert gases such as hydrogen and nitrogen, arsenic, and atmospheres of all or part of air It is clear that the same effect as that of the present embodiment can be obtained because nitrogen mixed in the state can be reduced.

  Further, in this embodiment, the annealing process is performed after the step of manufacturing the structure of FIG. 1A, and then the step of manufacturing the structure of FIG. 1B is performed, but the structure of FIG. 1B is manufactured. In the case where the annealing process is performed after the process and then the process of manufacturing the structure of FIG. 1C is performed, and the annealing process is performed after the process of manufacturing the structure of FIG. It is clear that is obtained.

DESCRIPTION OF SYMBOLS 101 GaAs substrate 102 AlGaAs sacrificial layer 103 GaNAs vibration part formation layer 104 Fine wire structure 105 Support part 106 Beam structure (vibration part)
301 GaAs substrate 302 AlGaAs sacrificial layer 303 GaAs or AlGaAs vibrating part forming layer 304 Fine wire structure 305 Supporting part 306 Beam structure (vibrating part)

Claims (7)

On a substrate, forming a sacrificial layer,
Forming a vibration part forming layer including a group III-V compound semiconductor doped with nitrogen on the sacrificial layer;
Forming a vibration part in the vibration part forming layer;
And a step of removing a portion exposed on the surface of the sacrificial layer by etching, and
A method for manufacturing a mechanical resonator, further comprising a step of annealing the substrate on which the sacrificial layer and the vibration part forming layer are formed.   2. The method for manufacturing a mechanical resonator according to claim 1, wherein the sacrificial layer includes a binary III-V compound semiconductor mixed crystal of GaAs, InAs, GaSb, InSb, InP, and GaP and a binary III-V group thereof. A method comprising any one of a ternary or more group III-V compound semiconductor mixed crystal in which compound semiconductor mixed crystals are combined.   3. The method for manufacturing a mechanical resonator according to claim 1, wherein annealing is performed at 500 to 850.degree. In the method for manufacturing a mechanical resonator according to any one of claims 1 to 3, wherein the step of annealing, between the step of forming a pre-Symbol vibration section forming layer and the step of forming the vibrating portion, or, The method is performed either between the step of forming the vibrating portion and the step of removing, or after the step of removing.   5. The method for manufacturing a mechanical resonator according to claim 1, wherein the annealing is performed in a hydrogen atmosphere, an inert gas atmosphere, an arsenic atmosphere, a vacuum, or in the air. Any one of these, or the method of performing in the atmosphere which mixed any two or more. In the method for manufacturing a mechanical resonator according to any one of claims 1 to 5, wherein the vibration section forming layer is a Group III-V compound semiconductor partially doped with nitrogen in the laminating direction, the vibration section forming layer The remaining portion is a group III-V compound semiconductor not doped with nitrogen.   7. The method of manufacturing a mechanical resonator according to claim 1, wherein the vibration part has a beam structure or a membrane structure.

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