JP2009253008A - Manufacturing method of piezoelectric device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a piezoelectric device such as an angular velocity sensor capable of enhancing reliability by further reducing a base point voltage variation in high-temperature operation. <P>SOLUTION: This manufacturing method of a piezoelectric device includes processes of: forming a lower electrode layer 33 above a wafer-like silicon substrate 30; forming a piezoelectric layer 32 on the lower electrode layer 33; forming an upper electrode layer 34 above the piezoelectric layer 32; and an adhesion layer 35 between the piezoelectric layer 32 and the upper electrode layer 34. In the process of forming the adhesion layer 35, an adhesion layer 35 formed of β-phase tungsten is formed by depositing tungsten without heating the wafer-like silicon substrate 30, and is thereafter transformed to an adhesion layer 35 formed of α-phase tungsten by heat-treating the adhesion layer 35 formed of β-phase tungsten. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a manufacturing method of a piezoelectric device used as an inertial sensor such as an angular velocity sensor used in a vehicle navigation system, attitude control, and various electric devices, a head for an inkjet printer, and the like.

  FIG. 7 is a perspective view of a detection element of an angular velocity sensor which is a kind of conventional piezoelectric device, and FIG. 8 is a cross-sectional view taken along line AA of FIG.

  The conventional angular velocity sensor includes a tuning fork type detection element 1 shown in FIG. 7 and a signal processing circuit (not shown) for calculating an angular velocity by processing a signal output from the detection element 1. As shown in FIG. 7, the detection element 1 is configured in a tuning fork type in which a pair of opposing arms 2 are connected by a connection portion 3, and the connection portion 3 is mounted on a mounting board and used. The pair of arms 2 includes a drive unit 4 for driving the arm 2, a detection unit 5 for outputting an angular velocity signal generated due to the angular velocity applied to the detection element 1, and a detection element. The monitor unit 6 for monitoring the driving state of 1 is arranged respectively. In addition, the arrangement is such that one detection unit 5 is sandwiched between the two drive units 4 in the opposing direction of the arm 2, and the monitor unit 6 is disposed near the boundary between the arm 2 and the connection unit 3. It is what is arranged.

  Further, as shown in FIG. 8, the pair of arms 2 includes a silicon substrate 9 having two layers of a silicon layer 7 and a silicon oxide layer 8 whose surface is oxidized, and the silicon substrate 9. The drive part 4 and the detection part 5 are comprised via the intermediate | middle layer 10 on the top. The driving unit 4 and the detection unit 5 are each composed of a lower electrode layer 12 and an upper electrode layer 13 with a piezoelectric layer 11 interposed therebetween, and between the piezoelectric layer 11 and the upper electrode layer 13. The adhesion layer 14 is formed on the substrate.

  The intermediate layer 10 is made of Ti, the lower electrode layer 12 is made of Pt—Ti mainly containing platinum containing titanium, and the piezoelectric layer 11 is formed of an orientation control layer 15 mainly containing lead titanate and this orientation. It consists of two layers with a PZT layer 16 made of lead zirconate titanate laminated on the control layer 15, the adhesion layer 14 is made of Ti, and the upper electrode layer 13 is made of Au (see Patent Document 1). .

  In recent years, the angular velocity sensor has been used not only in the cabin of an automobile in which a person gets on and off, but also in a very high temperature environment such as in an engine room. Therefore, the reliability of the angular velocity sensor at a high temperature is required more strongly.

  When the conventional detection element 1 having the above-described configuration is used at a high temperature such as in the vicinity of the engine, Ti that forms the adhesion layer 14 formed between the piezoelectric layer 11 and the upper electrode layer 13 of the detection element 1 Then, an interaction occurs between the piezoelectric layer 11 and the PZT layer 16, and as a result, the dielectric constant, specific resistance, and piezoelectric constant of the interface of the piezoelectric layer 11 fluctuate with time, and the detection sensitivity fluctuates. End up.

  Further, in the angular velocity sensor using the detection element 1, as shown in FIG. 9, as the operation time at high temperature (at the time of operation of 5V at 125 degrees) becomes longer, it occurs in the angular velocity sensor when the angular velocity is not applied. The base voltage, which is a voltage, varies greatly. As a result, as shown in FIG. 10, the voltage when the angular velocity is not generated varies from the base voltage to, for example, the minus side, and an error of (A) degrees occurs.

  In order to solve the above problems, the present inventors have examined the use of tungsten, which has extremely low reactivity with PZT, as an adhesion layer. The preparation method of the sample is as follows.

  First, after the intermediate layer 10, the lower electrode layer 12, the orientation control layer 15, and the PZT layer 16 are sequentially laminated on the wafer-like silicon substrate 9, tungsten is used as the adhesion layer 14 in a state where the silicon substrate 9 is heated to 150 ° C. The upper electrode layer 13 was laminated on the adhesion layer 14 by sputtering. FIG. 11 shows the result of measuring the crystallinity of the tungsten film after sputtering by the X-ray diffraction method. Tungsten is known to transition from a high-resistivity β-phase to a low-resistivity α-phase at about 100 ° C., and the large peak of diffraction intensity in FIG. 11 corresponds to α-phase tungsten (110). It was confirmed that the tungsten film obtained here was an α phase.

  Next, dry etching and wet etching were performed using a photolithographic method to form a drive unit 4, a detection unit 5, and a monitor unit 6 having a predetermined shape.

  Next, polarization and annealing were performed to stabilize the piezoelectric characteristics.

  Next, the wafer-shaped silicon substrate 9 was dry-etched to be processed into a plurality of tuning fork-shaped detection elements 1, and diced to be separated into individual detection elements 1.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP 2005-249645 A

  In the angular velocity sensor using the detection element having the above-described configuration, the reference voltage fluctuation amount when continuously operated at a high temperature (when operating at 125 V and 5 V) is larger than that of the conventional angular velocity sensor as shown in FIG. However, although it has been greatly improved, there has been a problem that the operation time has been rapidly increased from the point of time exceeding 2000 hours, and the reliability has been lowered.

  The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a method of manufacturing a piezoelectric device such as an angular velocity sensor that can further reduce the amount of fluctuation of the base voltage during high-temperature operation and increase the reliability. To do.

  In order to achieve the above object, the present invention has the following configuration.

  According to a first aspect of the present invention, there is provided a step of forming a lower electrode layer above a substrate, a step of forming a piezoelectric layer above the lower electrode layer, and an upper electrode above the piezoelectric layer. A step of forming a layer and a step of forming an adhesion layer between the piezoelectric layer and the upper electrode layer, wherein the step of forming the adhesion layer includes depositing tungsten without heating the substrate. After forming the adhesion layer made of β-phase tungsten by the heat treatment, the adhesion layer made of β-phase tungsten is transferred to the adhesion layer made of α-phase tungsten by heat treatment. When the adhesion layer located between the body layer and the upper electrode layer is formed, the adhesion layer made of β-phase tungsten is formed by depositing tungsten without heating the substrate. Interaction between the material constituting the upper electrode layer and tungsten constituting the upper electrode layer can be suppressed, and as a result, the amount of base voltage fluctuation during high temperature operation can be suppressed to a small level over a long period of time. In addition to providing a piezoelectric device such as an angular velocity sensor having a property, the adhesive layer made of β-phase tungsten is transferred to the adhesive layer made of α-phase tungsten by heat treatment. It has the effect that the adhesiveness with a layer can also be improved.

  According to the second aspect of the present invention, the heat treatment of the adhesion layer made of β-phase tungsten is performed in the range of 150 ° C. to 300 ° C. According to this manufacturing method, Since the heat treatment of the adhesion layer made of is performed in the range of 150 ° C. to 300 ° C., the adhesion between the adhesion layer and the piezoelectric layer can be improved, and the piezoelectric body due to the mutual reaction between the two It has the effect that progress of deterioration of the layer can be prevented.

  As described above, in the method for manufacturing a piezoelectric device of the present invention, when an adhesion layer located between the piezoelectric layer and the upper electrode layer is formed, the tungsten is deposited without heating the substrate, so that the β-phase tungsten is formed. Therefore, the interaction between the material constituting the piezoelectric layer and the tungsten constituting the upper electrode layer can be suppressed, so that the base voltage fluctuation amount at the time of high temperature operation can be reduced for a long time. Therefore, it is possible to provide a piezoelectric device such as an angular velocity sensor having high reliability at a high temperature, and by further heat-treating the adhesion layer made of β-phase tungsten, Since the adhesive layer is made of an adhesive layer, the adhesion to the piezoelectric layer can be improved. Is shall.

  Hereinafter, an angular velocity sensor which is a kind of piezoelectric device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view of a detection element of an angular velocity sensor which is a kind of piezoelectric device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line BB in FIG.

  As shown in FIG. 1, an angular velocity sensor that is a type of piezoelectric device according to an embodiment of the present invention processes a tuning fork type detection element 21 and a signal output from the detection element 21 to calculate an angular velocity. A signal processing circuit (not shown), and the detection element 21 is configured in a tuning fork type in which a pair of opposing flexible arms 22 are connected by a connecting portion 23, and the connection The unit 23 is used by being mounted on a mounting board. The pair of arms 22 includes a drive unit 24 for driving the arms 22, a detection unit 25 for outputting an angular velocity signal generated due to an angular velocity applied to the detection element 21, and a detection element. The monitor unit 26 for monitoring the driving state 21 is disposed. Further, the arrangement is such that one detection unit 25 is sandwiched between the two drive units 24 in the opposite direction of the arm 22, and the monitor unit 26 is disposed near the boundary between the arm 22 and the connection unit 23. It is what is arranged. Further, a signal line portion 27 (including an electrode pad and the like) that extends the drive portion 24, the detection portion 25, and the monitor portion 26 is disposed.

  Further, as shown in FIG. 2, the pair of arms 22 includes a silicon substrate 30 having two layers of a silicon layer 28 and a silicon oxide layer 29 whose surface is oxidized, and the silicon substrate 30. The drive part 24 and the detection part 25 are comprised via the intermediate | middle layer 31 on the top. The driving unit 24 and the detecting unit 25 are each composed of a lower electrode layer 33 and an upper electrode layer 34 with a piezoelectric layer 32 interposed therebetween, and between the piezoelectric layer 32 and the upper electrode layer 34. The adhesion layer 35 is formed.

  The intermediate layer 31 is made of Ti, the lower electrode layer 33 is made of Pt—Ti containing platinum containing titanium as a main component, and the piezoelectric layer 32 is formed of an alignment control layer 36 containing lead titanate as a main component and this alignment. The adhesive layer 35 is made of tungsten and the upper electrode layer 34 is made of Au. The piezoelectric layer 37 is made of a lead-containing piezoelectric material laminated on the control layer 36. Examples of the orientation control layer 36 include lanthanum magnesium-added lead titanate and lanthanum-added lead titanate. Examples of the piezoelectric layer 37 made of a piezoelectric material containing lead include PZT and PLZT.

  When the X axis, the Y axis, and the Z axis orthogonal to each other are taken as shown in FIG. 1, when an AC signal is applied to the drive unit 24 of the detection element 21, the arm 22 vibrates in the X axis direction. At this time, when an angular velocity around the Z-axis is generated, a Coriolis force in the Y-axis direction is generated, and the arm 22 is bent in the Y-axis direction. An angular velocity signal can be obtained by detecting this bending by the detection unit 25.

  Next, a method for manufacturing the detection element 21 will be described.

  First, an intermediate layer 31 is formed by sputtering Ti on a wafer-like silicon substrate 30 having a silicon oxide layer 29 on the surface.

  Next, the lower electrode layer 33 is formed on the intermediate layer 31 by simultaneously sputtering using Ti and Pt as targets.

  Next, the orientation control layer 36 is formed on the lower electrode layer 33 by sputtering lanthanum-added lead titanate or lanthanum magnesium-added lead titanate.

  Next, the piezoelectric layer 37 is formed by sputtering PZT on the orientation control layer 36.

  Next, an adhesion layer 35 made of β-phase tungsten is formed on the piezoelectric layer 37 by vapor deposition using tungsten as a target (hereinafter referred to as sputtering). In order to form this β-phase tungsten, it is necessary to keep the temperature of the wafer-like silicon substrate 30 below the transition temperature from the β-phase to the α-phase (about 100 ° C.). In this case, in one embodiment of the present invention, sputtering is performed without heating the wafer-like silicon substrate 30. At this time, the temperature of the silicon substrate 30 rises to about 60 ° C. by the radiant heat of the sputtering. To do. Then, after the adhesion layer 35 made of β-phase tungsten is formed, heat treatment is performed in a sputtering apparatus at 180 ° C. for 2 hours in a vacuum. By this heat treatment, β-phase tungsten is transferred to α-phase tungsten having a lower specific resistance. In addition, it is desirable to perform this heat processing within the range of 150 to 300 degreeC so that it may become clear also from the reason mentioned later.

  Next, the upper electrode layer 34 is formed by sputtering Au on the adhesion layer 35.

  FIG. 3 shows the results of measuring the crystallinity of the tungsten film after the film formation by sputtering and before the heat treatment by the X-ray diffraction method. The lower data in FIG. 3 shows the crystallinity of the tungsten film of the present invention. As is clear from FIG. 3, no peak corresponding to α-phase tungsten (110) appears, Since peaks corresponding to β-phase tungsten (200) and (210) appear, it can be seen that the tungsten film obtained here is β-phase. The upper data in FIG. 3 shows the crystallinity of the tungsten film formed with the substrate temperature set at 150 ° C., and the data in FIG. 11 is reproduced for comparison.

  Next, using a photolithographic method, first, dry etching is performed to form a drive unit 24, a detection unit 25, a monitor unit 26 having a predetermined shape, and a signal line unit 27 that is extended and routed. At this time, a part of the signal line part 27 is not completely etched, and the drive part or the like is electrically connected to the ground through the part.

  Next, wet etching is performed to remove a part of the signal line portion 27 to form the signal line portion 27 having a predetermined shape.

  Next, polarization treatment and annealing treatment are performed to stabilize the piezoelectric characteristics.

  Next, the wafer-shaped silicon substrate 30 is dry-etched to be processed into a plurality of tuning-fork-shaped detection elements 21, and diced to be separated into individual detection elements 21.

  As shown in FIG. 4, the angular velocity sensor using the detection element 21 maintains the base voltage fluctuation amount at a low level even when the operation time at the time of high temperature operation (at 125 V and 5 V operation) becomes long. In other words, since the base voltage fluctuation amount during high-temperature operation can be suppressed to a small level over a long period of time, an angular velocity sensor having high reliability at high temperatures can be obtained.

  The reason why the reference voltage fluctuation amount of the angular velocity sensor according to the embodiment of the present invention constructed and manufactured as described above can be kept at a low level even during a long time high temperature operation is as follows. It is thought that.

  In order to stabilize the angular velocity sensor characteristics, it is necessary to suppress the mutual reaction between the adhesion layer 35 made of tungsten and the piezoelectric layer 37 made of PZT in contact therewith and to maintain the adhesion. When the substrate is heated when the adhesion layer 35 is formed by sputtering, the piezoelectric layer 37 simultaneously receives high energy given to the vapor deposition particles by sputtering and thermal energy from the substrate. As a result, it becomes impossible to suppress the interaction between the piezoelectric layer 37 and the tungsten constituting the adhesion layer 35, and the deterioration of the sensor characteristics is accelerated.

  On the other hand, in the embodiment of the present invention, when the adhesion layer 35 made of tungsten is formed by sputtering, the wafer-like silicon substrate 30 is not heated, so that the piezoelectric layer 37 is configured. The interaction between the material and tungsten constituting the adhesion layer 35 can be suppressed, and only the heating is performed after the film formation to improve the adhesion, so that the adhesion with the material constituting the piezoelectric layer 37 is improved. The adhesiveness can be enhanced while suppressing the interaction with tungsten constituting the layer 35. This is considered to stabilize the sensor characteristics.

  Next, a preferable temperature range of the heat treatment performed after the adhesion layer 35 is formed will be described.

  FIG. 5 shows the relationship between the heat treatment temperature after the adhesion layer 35 is formed and the maximum polarization amount of the piezoelectric layer 32, where the maximum polarization amount is a state where a voltage is applied to the piezoelectric layer 32. Is the maximum amount of polarization (dipole moment per unit volume). As can be seen from FIG. 5, when the heat treatment temperature exceeds 300 ° C., the maximum polarization is greatly reduced. This indicates that the tungsten constituting the adhesion layer 35 and the PZT constituting the piezoelectric layer 37 in the piezoelectric layer 32 interact with each other and the deterioration of the piezoelectric layer 32 proceeds. For this reason, it is desirable that the heat treatment temperature be 300 ° C. or lower.

  FIG. 6 shows the experimental results showing the relationship between the heat treatment temperature after the adhesion layer 35 is formed and the adhesion between the adhesion layer 35 and the piezoelectric layer 37 in the piezoelectric layer 32. In this experiment, an adhesion layer 35 heat-treated at various temperatures was prepared, and a marking line was drawn on the film of the adhesion layer 35 using a diamond indenter. Is performed by peeling off the film. As is apparent from FIG. 6, when the heat treatment temperature is 100 ° C. or less, the adhesion layer 35 is largely peeled off from the marking line, and in this case, it can be seen that the adhesion is insufficient. For this reason, it is desirable that the heat treatment temperature be 150 ° C. or higher.

  As described above, in one embodiment of the present invention, the step of forming the lower electrode layer 33 above the wafer-like silicon substrate 30 and the step of forming the piezoelectric layer 32 above the lower electrode layer 33; A step of forming an upper electrode layer 34 above the piezoelectric layer 32 and a step of forming an adhesion layer 35 between the piezoelectric layer 32 and the upper electrode layer 34 to form the adhesion layer 35. The step of forming the adhesion layer 35 made of β-phase tungsten by evaporating tungsten without heating the wafer-like silicon substrate 30 and then heat-treating the adhesion layer 35 made of β-phase tungsten by α When the adhesion layer 35 located between the piezoelectric layer 32 and the upper electrode layer 34 is formed, it is transferred to the adhesion layer 35 made of phase tungsten. Since the adhesion layer 35 made of β-phase tungsten is formed by evaporating tungsten without heating the recon substrate 30, the material of the piezoelectric layer 37 that constitutes a part of the piezoelectric layer 32 and the upper electrode layer 34 can suppress the interaction with the tungsten constituting this, and the amount of fluctuation of the base voltage during high-temperature operation can be suppressed to a small level over a long period of time. In addition to providing a piezoelectric device, the adhesive layer 35 made of β-phase tungsten is transferred to the adhesive layer 35 made of α-phase tungsten by heat treatment. The effect that the adhesiveness with the piezoelectric layer 37 which comprises can also be improved is acquired.

  In addition, the manufacturing method of the piezoelectric device in one embodiment of the present invention can be applied to a manufacturing method of an inertial sensor including an angular velocity sensor and a head for an ink jet printer.

  The method for manufacturing a piezoelectric device such as an angular velocity sensor according to the present invention has an effect that the reliability under high temperature use can be improved, and in particular, the piezoelectric device such as an angular velocity sensor obtained by this manufacturing method. The device is useful when applied to vehicles and various electric devices.

The perspective view of the detection element of the angular velocity sensor which is 1 type of the piezoelectric device in one embodiment of this invention BB sectional view of FIG. Characteristic diagram showing X-ray diffraction measurement result after deposition of adhesion layer in the same angular velocity sensor Characteristic diagram showing time-dependent change in reference voltage fluctuation at high temperature of the angular velocity sensor Characteristic diagram showing the relationship between the heat treatment temperature and the maximum polarization amount of the adhesion layer of the same angular velocity sensor The figure which shows the relationship between the heat processing temperature of the upper contact | glue layer of the same angular velocity sensor, and adhesiveness The perspective view of the detection element of the angular velocity sensor which is a kind of the conventional piezoelectric device AA line sectional view of FIG. Characteristic diagram showing time-dependent change in reference voltage fluctuation at high temperature of the angular velocity sensor Characteristic diagram showing change in output voltage with respect to change in angular velocity of the same angular velocity sensor Characteristic diagram showing X-ray diffraction measurement results when an adhesion layer made of tungsten is formed with the substrate heated to 150 ° C. The characteristic diagram which shows the time-dependent change of the amount of fluctuation of the base voltage at the high temperature when the adhesion layer made of tungsten is formed with the substrate heated to 150 ° C.

Explanation of symbols

30 Silicon substrate 32 Piezoelectric layer 33 Lower electrode layer 34 Upper electrode layer 35 Adhesion layer 36 Orientation control layer 37 Piezoelectric layer

Claims (2)

Forming a lower electrode layer above the substrate; forming a piezoelectric layer above the lower electrode layer; forming an upper electrode layer above the piezoelectric layer; and the piezoelectric layer; A step of forming an adhesion layer between the upper electrode layer and the step of forming the adhesion layer after forming an adhesion layer made of β-phase tungsten by depositing tungsten without heating the substrate. A method for manufacturing a piezoelectric device, wherein the adhesion layer made of β-phase tungsten is transferred to the adhesion layer made of α-phase tungsten by heat treatment. The method for manufacturing a piezoelectric device according to claim 1, wherein the heat treatment of the adhesion layer made of β-phase tungsten is performed within a range of 150 ° C to 300 ° C.