1. Field of the Invention
The present invention relates to a semiconductor mechanical sensor and Method of Manufacture of manufacturing the same, and more particularly, to an acceleration sensor or a yaw rate sensor and a method of manufacturing the same.
2. Description of the Related Art
As a semiconductor mechanical sensor such as an acceleration sensor or a yaw rate sensor, sensors using piezoelectric ceramics are in wide use for attitude control of an automobile and to prevent jitter in a commercial video camera. In addition, Japanese Patent Publication Gazette No. 3-74926 discloses that two piezoelectric resistor elements arranged in parallel to a longitudinal axis of the cantilever, and in a side-by-side configuration, detects a force which corresponds to a rotation speed. In other words, without detecting deformation due to vibration of the cantilever, only deformation due to twisting of the cantilever is detected by the piezoelectric resistor element.
However, regarding accuracy, cost, etc., existing yaw rate sensors are not satisfactory, which restricts their application to other purposes.
It is an object of the present invention to solve such a problem and to offer a semiconductor mechanical sensor having a new structure.
A further object of the present invention is to improve the S/N ratio in such a semiconductor mechanical sensor having a new structure.
A still further object of the present invention is to offer a semiconductor mechanical sensor using a beam deflection type capacity detection method and a method of manufacturing the same, and to offer a semiconductor mechanical sensor which can detect mechanical changes in two or three directions (when two such semiconductor mechanical sensors are used) and a method of manufacturing the same.
To achieve these objects, basically, a semiconductor mechanical sensor according to the present invention has a structure as follows. That is, the semiconductor mechanical sensor comprises:
In other aspect of the present invention, in addition to the above structure, the semiconductor mechanical sensor comprises: an AM modulation circuit for superimposing a signal from the physical force detect electrode onto a carrier wave; and a band pass filter for passing a signal from the AM modulation circuit whose center frequency coincides with the carrier wave.
In a further aspect of the present invention, a method of manufacturing such a semiconductor mechanical sensor comprises the steps of:
a sixth step of etching the filling material in the groove in the monocrystalline silicon substrate to thereby form the beam which has the weight.
In other words, in the semiconductor mechanical sensor according to the present invention, the weight which is formed at the tip of the beam is excited due to static electricity which is created by applying an alternating current electric power to a side wall of the substrate which faces one surface of the weight. In such a state, in the axial direction which is perpendicular to the excitation direction of the weight, a change in the capacitance value between two electrodes arranged oppositely to each other is electrically detected so that a mechanical force which acts and changes in the same direction such as a yaw rate, an acceleration or the like is detected.
More precisely, in the semiconductor mechanical sensor according to the present invention, the weight is excited by static electricity due to alternating current electric power, and in the axial direction which is perpendicular to the direction of the excitation, a change in the capacitance value between the two electrodes arranged oppositely to each other, is electrically detected. The detected signal is superimposed on the carrier wave in the AM modulation circuit so that the carrier wave is AM modulated. Further, the signal from the AM modulation circuit is passed through the band pass filter which has a center frequency which coincides with the frequency of the carrier wave.
In the following, semiconductor mechanical sensors according to embodiments of the present invention will be described with reference to the drawings.
More particularly, as clearly shown in
Thus, the sensor has a cantilever structure. In this structure, the space having the distance d2 is created by etching a layer which is predeterminedly designed to be removed by a surface micro machining technique.
In addition, the beam 3 forms a wiring region for the weight portion 4 which serves as an electrode.
In the bottom surface of the recess portion 2, at a region where the recess portion 2 faces the weight portion 4, the electrode portion 5 is formed, and a portion which faces the electrode portion 5, i.e., the weight portion 4 serves as an electrode. Further, the electrode portion 6 is formed in a surface of the inner wall of the recess portion 2 facing a side of the weight portion 4 (i.e., the upper surface of the recess portion 2 in
That is, as shown in
In other words, in the electrical circuit which is used in the present invention, the capacitor portion 7 is formed by the electrode 6 and the weight portion 4, and the oscillator 8 is connected to the weight portion 4 side of the capacitor portion 7. An impedance ZL is formed by a capacitor 9 and a resistor 10 connected to the electrode 6 side of the capacitor portion 7. A power source 11 is connected to the capacitors 9.
To one end of the impedance ZLI the impedance matching means 12, comprising an operational amplifier, is connected at a point a which is created by a change in the capacitance value of the capacitor portion 7. Here, an alternating current voltage source VS (=V·sin ωSt) shown in
The output of the impedance matching means 12 of
The clock signal generation means 17 is comprised of a voltage adjustor 18, two comparators 19 and 20, power sources 21 and 22, a NOR gate 23, a resistor 24 and a capacitor 25. In the clock signal generation means 17, sample-and-hold periods T1 and T2 shown in
The sample-and-hold circuit 26 is formed by two operational amplifiers 27 and 28, switches 29, 30, 31 and 32 and capacitors 33, 34, 47 and 48. In the sample-and-hold periods T1 and T2 shown in
The differential amplifier circuit 35 is formed by operational amplifiers 36, 37 and 38, resistors 39, 40, 41, 42, 43, 44 and 45 and a power source 46. From an output value available from the sample-and-hold circuit 26, a difference between peak values during the sample-and-hold periods T1 and T2 is calculated (i.e., A in
At the output terminal of the operational amplifier 38, a sensor output Vout is obtained.
Next, functions of a semiconductor mechanical sensor having a construction as explained above will be described with reference to
As shown in
Between the electrode 5 and the weight portion (electrode) 4 of
F
E=∈0·S·VS2/2d2 (1)
In the direction Z, a displacement as defined by Equation 2 below is generated.
where ∈0 is a dielectric constant, S is a facing area of the electrodes, d is a distance between the electrodes, L is the length of the beam, Lm is the length of the weight portion 4, IZ is a secondary moment of area of the beam 3 in the Z-axis direction, and E is a Young's modulus.
Differentiating Equation 2 by time t, the velocity VZ vibrates as:
V
Z
=dD
Z
/dt (3)
At this stage, with a rotational angular velocity X applied to the axis X which is perpendicular to the axis Z, the Coriolis effect Fc defined by
Fc=2mVZω (4)
is created in the axis-Y direction.
In Equation 4, m is the mass of the weight portion 4.
Due to the Coriolis effect Fc, a displacement DY which is expressed by Equation 5 below is generated in the Y-axis direction.
where IY is a secondary moment of area in the axis-Z direction. Hence, a capacitance between the electrodes CY is expressed by Equation 6 below.
where Sy is the faced area or the electrodes and dy is the distance between the electrodes.
Due to a change in the value Cy, a voltage Vω defined by Equation 7 is created at the output terminal (output voltage) Vout.
In other words, the output Vω changes in accordance with the rotational angular velocity ω and the angular velocity ω is calculated as the change in the value Vω.
Next, a description will be given of now the signal is processed in the circuit with reference to
The input waveform applied to the weight portion 4 is a sinusoidal wave as shown in
The most largely deformed portions of the input waveform of the capacitor portion 7 during the sample-and-hold periods T1 and T2 shown in
Next, we assume that an acceleration of a frequency fa (in the direction Y) is applied as a disturbance noise. Here, if the relation
fa<<2πωS (8)
holds, with respect to the input waveform shown in
In the processing in the circuit shown in
Further, since the frequency component is even smaller for displacement due to temperature, Eq. 8 holds satisfactorily.
In this manner, in a sensing operation, the processing circuit cancels most noises interfering with detection or the angular velocity. Hence, the angular velocity is detected accurately.
In addition, in the electrical circuit as above according to the present invention, since a deformed waveform of the beam due to acceleration and a deformed waveform of the beam due to a yaw rate are different from each other and clearly distinguishable from each other, the semiconductor mechanical sensor according to the present invention can be used as both an acceleration sensor and a yaw rate sensor, as well as for other sensors.
As described above, in the above example of the present invention, the beam structure is formed in a portion of the silicon substrate 1 (semiconductor substrate) spaced away from the silicon substrate 1, and an alternating current electric power is applied to a wall surface of the substrate which faces one surface of the weight which is formed at the tip of the beam, so as to deflect the weight by static electricity. In the axial direction perpendicular to the direction of the excitation of the weight, the electrodes 6 are disposed in a facing relation on the wall surfaces of the substrate facing the one surface of the weight and the surface of the beam. A change in the capacitance value between the facing electrodes is electrically detected so that mechanical forces which act in the same direction, i.e., an acceleration or a yaw rate, is detected. Thus, the semiconductor mechanical sensor has a new structure.
The present invention is not limited to the example above. For example, as shown in
As hereinabove described in detail, the present invention provides a semiconductor mechanical sensor which has a new structure.
Incidentally, the semiconductor mechanical sensor structure as above has an inconvenience that in amplifying a signal of the sensing part, noise (e.g., thermal noise, 1/f noise) is also amplified, which makes it difficult to improve the S/N ratio.
As a result of study devoted to solving this problem, the inventor of the present invention has come to the conclusion that the problem can be solved if the semiconductor mechanical sensor described above further comprises an AM modulation circuit for superimposing a signal from the physical force detecting electrode onto a carrier wave, and a band pass filter for passing a signal from the AM modulation circuit whose center frequency coincides with the carrier wave.
In the following, an embodiment of a circuit structure of the example above according to the present invention will be described with reference to the drawings.
In
In addition, one side surface of the weight 55 (the top surface in
On the other hand, one side surface of the weight 56 (the top surface in
Thus, the illustrated sensor has a cantilever structure. In this structure, the distance d1 is created by etching a layer which is predeterminedly designed to be removed, by a surface micro machining technique.
In
In an inner wall surface of the recess portion 52 where the recess portion 52 faces the weights 55 and 56 (i.e., in the lower surface of the recess portion 52 in.
In addition, in this structure, the electrodes 57, 58, 59, 60, 61, 62, 63, 64, 159 and 160 are insulated from each other.
A capacitor Cs+ is created by the electrodes 59 and 57, a capacitor Cs− is created by the electrodes 60 and 58, a capacitor Cd+ is created by the electrodes 159 and 61, a capacitor Cd− is created by the electrodes 64 and 66, a capacitor Ce+ is created by the electrodes 65 and 63, and a capacitor Ce− is created by the electrodes 160 and 62.
The beams 53 and 54 form wiring regions for the electrodes 59 (61, 65) and 60 (62, 66), respectively.
For clarity of explanation, although the electrodes 59, 61 and 65 are described as different electrodes, they are one and the same electrode (same potential). Likewise, although described as different electrodes for clarity of explanation, the electrodes 60, 62 and 66 are one and the same electrodes (same potential).
The processing circuit of the sensor comprises an oscillator 67, a sensing part 68, a differential amplifier 69, a band pass filter 70, a sample-and-hold circuit 71 and a subsequent stage amplifier 72.
A capacitor Cr of
The capacitors Ce+ and Ce− drive the weights 55 and 56 by static electric force Fe. The capacitors Cs+ and Cs− are capacitors for detecting the amount of displacement of the weights 55 and 56 in the Z-axis direction due to the Coriolis effect Fc.
The capacitors Cd+ and Cd− shown in
Next, the structure shown in
The oscillator 67 has an oscillation frequency of 10 KHz and provides a voltage (alternating current electric power) for driving the weights 55 and 56 and a signal (carrier wave) to the capacitors Cs+ and Cs−. The resistor R applies a bias voltage to any one of connection portions between the capacitors Cs− or Cs+ and Crs, and has a resistance R>>1/Cr. By applying a bias, each one of the resistors R makes subsequent signal processing possible.
The differential amplifier 69 amplifies a difference voltage between inputs (capacitors Cs+ and Cs−. The band pass filter 70 has a center frequency of 10 KHz which coincides with the frequency of the carrier wave. In addition, the band pass filter 70 attenuates signals other than those having a predetermined frequency band (near the center frequency). In this example, the band pass filter 70 is formed by a switched-capacitor filter (S.C.F.).
The sample-and-hold circuit 71 (detector circuit) demodulates a signal which is AM modulated as will be described later. An operational amplifier 73 and resistors 74 and 75 form a reference voltage for use within the processing circuit. The subsequent stage amplifier 72 amplifies a detected signal. The subsequent stage amplifier 72 may be omitted.
In this example, the electrodes 57, 58, 59 and 60 form a yaw rate detecting electrode while the oscillator 67 and the differential amplifier 69 form an AM modulation circuit.
Next, the functions of a semiconductor mechanical sensor having the construction described above will be described.
When the oscillator 67 applies a voltage VIN (=VCM·cos ωct) to the capacitors Ce− and Ce+, static electric force Fe as defined by Equation 9 below is created.
Fe=(∈0S/2a2)·VIN2 (9)
where
Due to the static electric force Fe, the weights 55 and 56 are displaced in the Y-axis direction. Assuming that the amounts of the displacements are Dy, the relationship shown in Equation 10 is created.
Dy=KFe (10)
where K: a constant which is determined by the cantilever. Here, it is to be noted that the weights 55 and 56 move in different directions.
From Eqs. 9 and 10, where the velocities in the Y-axis direction of the weights 55 and 56 are Vy55 and Vy56, respectively, the following equation (11) is obtained.
V
y55
=−V
y56
=K·(∈0S/4a2)·VCM2·2ωc·sin 2ωct (11)
At this stage, if the axis X is the rotation axis, and when the weight is rotated with respect to the axis X rotates at the angular velocity ω, Coriolis effect Fc55=2mVy55ω, F56=2mVy56ω are created at the axis z.
As a result, the weights 55 and 56 are displaced in the Z-axis direction. Assuming that the displacements are Dz55 and Dz56,
D
z55
=L
55
·F
c55
D
z56
=L
56
·F
c56 (12)
where L55, L56 are constants which are determined by the cantilever.
If the weights 55 and 56 and the cantilever are formed to have the same dimensions, L55 L56, and hence, |Dz55|=|Dz56|=Δd.
In other words, the capacitance values of Cs+ and Cs− are
C
s+=(∈0·S)/(d+Δd)
C
s−=(∈0·S)/(d−Δd) (13)
Hence, an output Vpre of the differential amplifier 69 is
V
pre
=V
IN
·{C
S+/(CS++Cr)−CS−/(CS−+Cr)}·AV1≈VIN(—Δd/2d)·AV1 (14)
where VA1 is an amplification factor of the differential amplifier 67.
From Eqs. 11 and 12, Δd is
Δd=L55·2m·K(∈0·S/4a2)·VCM2·2ωc·ω·sin 2ωct (15)
On the other hand, from Eqs. 14 and 15,
V
pre
=AV1·VCM3·L55·2m·K(∈0·S/4a2)·ωc·ω·(sin ωct+sin 3ωct) (16)
In Eq. 16, VCM3·L55·2m·K(∈0·S/4a2)·ωc on the right side is a constant which is determined by the structure of the cantilever and a condition of the input voltage. From Eq. 16, it is understood that the value Vpre indicates a voltage which is in proportion to the angular velocity X which is to be detected. The value Vpre is expressed as a voltage output which is AM modulated to the frequency of the input signal fIN=ωc/2π and a frequency which is triple the same.
The foregoing has referred to a detected signal alone. However, noise may be generated by circuit elements of the differential amplifier 69 when a signal is processed in the differential amplifier 69, and noise may be introduced into the power source system from outside. These noises are also amplified by the differential amplifier 69. Hence, from Eq. 16,
V
pre
=AV1·VCM3·L55·2m·K(∈0·S/4a2)·ωc·ω·(sin ωct+sin 3ωct)+AV1·VN (17)
Thus, AV1·VN is created which expresses a noise which degrades the S/N ratio of the angular velocity ω to be detected.
To deal with this, as shown in Eq. 17, signal data concerning the angular velocity to be detected, is AM modulated by a certain modulator and passed through the band pass filter 70, having a center frequency fc=ωc2π, whereby the S/N ratio is improved.
Assume that an output of the band pass filter 70 having 5c=ωc/2π is VBPF,
V
BPF
=AV1·VCM3·L55·2m·K(∈0·S/4a2)·ωc·ω·sin ωct+AV1·VN(fc) (18)
The value VBPF is expressed as shown in Eq. 18, and therefore, only AV1·VN(fc), i.e., an noise component whose frequency component is equal to fc is left. Hence,
AV1·VN>>AV1·VN(fc) (19)
Thus, an output which is in proportion to the angular velocity ω and which has a high S/N ratio is obtained. By processing this output in the sample-and-hold circuit 71 (detector circuit) if necessary, an output Vout which is in proportion to the angular velocity ω is obtained as below.
V
out
≈AV1·VCM3·L55·2m·K(∈0·S/4a2)·ωc·ω (20)
This output is amplified, if necessary, in the subsequent stage amplifier 72.
As described above, in the present embodiment, the oscillator 67 and the differential amplifier 69 (AM modulation circuit) superimpose signals from the electrodes 57, 59 and 58, 60 (yaw rate detect electrodes) on a carrier wave, and a signal from the differential amplifier 69 is passed through the band pass filter 70 which has a center frequency which coincides with that of the carrier wave. Hence, in processing a signal by the differential amplifier 69, even if noise is generated in a circuit element of the differential amplifier 69 when a signal is processed in the differential amplifier 69 and other noise is introduced into the power source system from outside, these noises are removed. That is, noise (e.g., a thermal noises, a 1/f noise) is deemphasized and therefore the S/N ratio is improved.
As described above, the present embodiment provides an improved S/N ratio.
However, with respect to a semiconductor mechanical sensor such as the semiconductor yaw rate sensor above which is movable in two directions, the example described above is insufficient in terms of structure. To manufacture the sensor, an efficient manufacturing method for a high productivity has not been proposed yet.
To deal with this, in addition to the examples described above, the present invention offers a semiconductor mechanical sensor which has an optimum structure and methods of efficiently manufacturing the semiconductor mechanical sensors according to the examples described above. That is, according to an other example of the present invention, a semiconductor mechanical sensor comprises: a thin monocrystalline silicon substrate which is joined onto a substrate through an insulation film; a beam which is formed in the monocrystalline silicon substrate and which has a weight; a first electrode which is formed in one surface of said weight and a wall surface which corresponds to said weight surface; and a second electrode which is formed in one surface of the weight and a wall surface which corresponds to the weight surface in an axial direction of the weight which is perpendicular to the electrode, and either one of the electrodes is preferably formed on the major surface of the monocrystalline silicon substrate in parallel with the monocrystalline silicon substrate.
Further, all electrode contacting portions are preferably formed on the same surface of the thin monocrystalline silicon substrate.
Describing the semiconductor mechanical sensor according to the present invention in more detail, the semiconductor mechanical sensor has a structure in which a plurality of groove portions 201 are formed in the tip portion 139 of a weight portion 139, an electrode is disposed on an inner wall portion of each of groove portions 201, and a fixed member 202 extends in each groove portion 201 and an other electrode is disposed on a side surface portion which faces the inner wall portion of the groove portion of the weight portion 4 of the fixed member 202.
In this example, a first electrode and a second electrode which is disposed in an axial direction perpendicular to the first electrode detect a mechanical quantity which is applied to a beam having a weight.
Now, a semiconductor mechanical sensor having such a structure according to the present invention will be described with reference to
As shown in
In
The sense electrode 113 detects excitation of the weight 139, based on an output signal which is generated in response to excitation of the weight 139, and feedback control is performed to thereby achieve predetermined excitation of the weight 139. That is, the movable electrode 112 and the sense electrode 113 form electrodes for excitation feedback.
As shown in
As shown in
In this embodiment, a groove is formed by the recess portion 115 and the trench 116.
On the major surface of the monocrystalline silicon substrate 101 including an inner wall of the trench 116, an n+ type diffusion layer 117 is formed which will be then covered with an SiO2 film 118 by thermal oxidization.
Following this, as shown in
The surface of the polysilicon film 119 is then polished using the SiO2 film 118 as a stopper to smooth the surface of the polysilicon film 119. At this stage, the surfaces of the polysilicon film 119 and the SiO2 film 118 are preferably smoothed.
Then, in the surfaces, an SiO2 film 120 is formed to a thickness of about 0.3 to 2 μm by a CVD method or other suitable method, and a bottom contact 121 is formed at a predetermined location for electrical connection with the n+ type diffusion layer 117.
Further, an n+ polysilicon 122 doped with As and P (phosphorus) is formed to a thickness of 0.2 to 1 μm which will serve as an electrode pattern and a shield layer.
Next, a BGSP film 123 which serves as an insulation film, for instance, is formed to a thickness of 0.2 to 1 μm in the surface. The surface of the BGSP film 123 is then polished and flattened.
On the other hand, as shown in
Following this, as shown in
An IC board and other devices (not shown) are them formed in the region of the monocrystalline silicon substrate 101 by a known method, and an aluminum wire, a passivation film and a pad window (these elements are not shown) are formed as well.
Next, as shown in
In the semiconductor mechanical sensor fabricated in this manner, the thin monocrystalline silicon substrate 101 is joined onto the monocrystalline silicon substrate 110 through the SiO2 film 111, and in the monocrystalline silicon substrate 101, the cantilever 102 which has the weight 139 is formed at the tip. Further, in one surface of the weight 139 (the bottom surface in
That is, an alternating current electric power is applied to the excitation electrode (i.e., the n+ type diffusion layer 117 and the n+ type polysilicon 122) to create static electricity and the weight is excited by the static electricity. Under this condition, the yaw rate detecting electrode (i.e., the n+ type diffusion layer 117 of the weight 139 side and the n+ type diffusion layer 117 on the side of the wall surface of the monocrystalline silicon substrate 101), for example, detects a change in an electrical capacitance in the axial direction which is perpendicular to the direction of the excitation of the weight 139, whereby a change in a physical quantity which acts in the same direction, such as a yaw rate, is detected.
Thus, in this embodiment, the recess portion 115 and the trench 116 are formed as a groove of a predetermined depth in the major surface of the monocrystalline silicon substrate 101 to thereby form the cantilever 102 which has the weight 139 (first step). In inner walls of the recess portion 115 and the trench 116 which surround a substrate surface region which serves as the weight 139 and the weight 139, a pair of electrodes are formed facing each other on the opposite sides of the trench 116 in the direction of the surface of the substrate (a left-to-right direction in
As a result, the semiconductor mechanical sensor comprises the thin monocrystalline silicon substrate 101 which is joined onto the monocrystalline silicon substrate 110 through the SiO2 film 111 (insulation film), the cantilever 102 which is formed in the monocrystalline silicon substrate 101 and which has the weight 139, the movable electrode 112 which is formed in one surface of the weight 139 and a wall surface which corresponds to the same, the excitation electrode 114 (first electrode), the movable electrode 112 of the weight 139, the projections 103 to 105 which are formed one surface of the weight 139 and a wall surface which corresponds to the same in the axial direction which is perpendicular to the excitation electrode 114, and the fixed electrodes 133 to 138 (second electrode).
Either one of the electrodes, namely, the movable electrode 112 or the excitation electrode 114 is formed parallel to the major surface of the monocrystalline silicon substrate 101.
Further, all electrode contacting portions are formed on the same surface of the thin monocrystalline silicon substrate 101.
Thus, the semiconductor mechanical sensor comprises the thin monocrystalline silicon substrate 101 joined to the monocrystalline silicon substrate 110 through the SiO2 film 111, the cantilever 102 which is formed in the monocrystalline silicon substrate 101 and which has the weight 139 at the tip, the excitation electrode which is formed in one surface of the weight 139 and a wall surface of the monocrystalline silicon substrate 110 facing the weight, the excitation electrode creating static electricity and exciting the weight when an alternating current electric power is applied thereto, and the detecting electrode which is formed in one surface of the weight 139 and a wall surface of the monocrystalline silicon substrate 110 facing the weight in the axial direction which is perpendicular to the direction of excitation of the weight 139, the detecting electrode detecting a change in an electrical capacitance and hence a change in a physical quantity which acts in the same direction.
In this manner, processes are performed stably and a device which is stable and accurate is manufactured without contamination by using a surface micro machining technique, without performing a thermal treatment and a photolithographic process during a wafer forming process, especially during fabrication of an IC circuit, in a condition where a wafer recess portion, a through hole and the like have been already formed.
Although the foregoing has described the present embodiment in relation to the case where the excitation electrode and the sense electrode are buried in the substrate, the sense electrode may be omitted to reduce cost, in which case, the silicon substrate as it is may be used as the excitation electrode, unlike the structure described above.
In addition, although the electrodes which are formed parallel to the wafer surface are used as the sense electrode and the excitation electrode and the electrodes which are disposed in the vertical direction are used as the fixed electrodes for detecting the Coriolis effect, in the present embodiment, the opposite is also possible. That is, one of the fixed electrodes which are disposed in the vertical direction in the silicon substrate 101 may be used as the excitation electrode, and the other one of the fixed electrodes may be used as the sense electrode for performing feedback, while the electrodes which are formed parallel to the wafer surface may be used as electrodes for detecting the Coriolis effect.
Further, as the polysilicon film 119 for filling the recess portion 115 and the trench 116 (i.e., a polycrystalline silicon film), an amorphous silicon film or a silicon film in which a polycrystalline portion and an amorphous portion are mixed may be used.
Next, still another example of the present invention will be described with reference to
This example is intended to further increase output as compared with the preceding example and to prevent destruction of the beam by excessive shock and the like.
In the example of
In processes similar to those of the above example, polishing and flattening of the surface as shown in
Following this, a resist 126 of
Next, using the resist 126 as a mask, the SiO2 film 118 is removed by wet etching, for example, which primarily uses hydrofluoric acid as an etchant, followed by removal of the resist 126.
In the following, for clarity of explanation, an enlarged view of a portion of the sensor part B of
As shown in
Next, as shown in
Further, the surface is treated with a TMAH (tetramethylammoniumhidroxide) solution. At this stage, in a peripheral portion, an IC circuit and the like are formed (not shown).
Thereafter, as shown in
Then, as shown in
In this manner, a sensor which comprises a movable portion (cantilever) which is entirely surrounded by an electrode and a stopper is obtained. In such a structure, when the weight portion is excited in a direction which is perpendicular to the substrate, as shown in
As described above, in the present example, since the stopper member 130 is disposed above the cantilever 102, output is further increased, as compared with the above example, and destruction of the cantilever by excessive shock and the like is prevented.
That is, in the present example, in the first step, a groove of a predetermined depth is formed in the major surface of the monocrystalline silicon substrate to thereby form the beam which has the weight. In the second step, a pair of electrodes are formed which faced each other on the opposite sides of the groove in a substrate surface region and an inner wall of the groove which surrounds the weight in the direction of the surface of the substrate, while the first electrode is formed in a substrate surface region which will serve as the weight in a direction which is perpendicular to the surface of the substrate. In the third step, the groove is filled with a filling material and an electrode which faces the first electrode through the filling material is formed, and the major surface of the monocrystalline silicon substrate is smoothed. Next in the fourth step, the major surface of the monocrystalline silicon substrate and the silicon substrate are joined to each other. In the fifth step, the back surface side of the monocrystalline silicon substrate 101 is polished by a predetermined amount to thereby make the monocrystalline silicon substrate thin. Lastly, in the sixth step, the filling material is etched from the back surface side of the monocrystalline silicon substrate, whereby the beam which has the weight is formed. As a result, the semiconductor mechanical sensor according to the present invention is completed.
It is to be noted that the present invention is not limited to the embodiments described above. Rather, two pairs of the sensor units may be arranged in directions perpendicular to each other in order to detect yaw rates in the two axial directions. Further, the present invention is not limited to a cantilever. The present invention is also not limited to detection of a yaw rate. For instance, the excitation electrode of the embodiments above may be replaced with an electrode which detects a capacitance of displacement in an up-to-down direction so that the present invention is applied to a mechanical sensor which is capable of detecting displacements in two directions.
As heretofore described in detail, the present invention creates effects by which a yaw rate sensor of the beam excitation type capacity detection method and a method of manufacturing the same are obtained, and a semiconductor mechanical sensor which can detect movement in two or three directions and a method of manufacturing the same are obtained.
Number | Date | Country | Kind |
---|---|---|---|
4-223072 | Aug 1992 | JP | national |
4-273202 | Oct 1992 | JP | national |
5-77151 | Apr 1993 | JP | national |
This application is a divisional of U.S. patent application Ser. No. 12/215,884 filed Jun. 30, 2008 which is a divisional of U.S. patent application Ser. No. 11/210,006 (U.S. Pat. No. 7,407,827) filed Aug. 23, 2005 which is a divisional of Ser. No. 11/062,935 (U.S. Pat. No. 7,040,165) filed Feb. 22, 2005 which is a divisional of Ser. No. 10/899,729 (U.S. Pat. No. 6,938,486) filed on Jul. 27, 2004 which is a divisional of Ser. No. 10/358,691 (U.S. Pat. No. 6,868,727) filed on Feb. 5, 2003 which is a divisional of Ser. No. 09/947,409 (U.S. Pat. No. 6,550,331) filed on Sep. 7, 2001 which is a divisional of Ser. No. 09/749,693 (U.S. Pat. No. 6,463,803) filed on Dec. 28, 2000 which is a divisional of Ser. No. 08/834,129 (U.S. Pat. No. 5,872,024) filed on Apr. 14, 1997 which is a divisional of Ser. No. 08/508,170 (U.S. Pat. No. 5,627,318) filed on Jul. 27, 1995 which is a divisional of Ser. No. 08/109,504 (U.S. Pat. No. 5,461,916) filed on Aug. 20, 1993. This application claims the benefit of JPSN 5-77151, filed Apr. 2, 1993; JPSN 4-273202 filed Oct. 12, 1992; JPSN 4-223072 filed Aug. 21, 1992. The disclosures of the above applications are incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
Parent | 12215884 | Jun 2008 | US |
Child | 12381356 | US | |
Parent | 11210006 | Aug 2005 | US |
Child | 12215884 | US | |
Parent | 11062935 | Feb 2005 | US |
Child | 11210006 | US | |
Parent | 10899729 | Jul 2004 | US |
Child | 11062935 | US | |
Parent | 10358691 | Feb 2003 | US |
Child | 10899729 | US | |
Parent | 09947409 | Sep 2001 | US |
Child | 10358691 | US | |
Parent | 09749693 | Dec 2000 | US |
Child | 09947409 | US | |
Parent | 08834129 | Apr 1997 | US |
Child | 09749693 | US | |
Parent | 08508170 | Jul 1995 | US |
Child | 08834129 | US | |
Parent | 08109504 | Aug 1993 | US |
Child | 08508170 | US |