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JPS6055655

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DESCRIPTION JPS6055655
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
semiconductor device having a beam structure in which at least a part is vibratably formed on a
semiconductor substrate. "Technical background of the invention" In the detection of mechanical
vibration, it is important how to detect the vibration of the true vibration part in order to ensure
its accuracy. For that purpose, a detection device is required which can measure even if the
vibration is fine regardless of the size and the place of the vibration part. Therefore, the present
inventor has previously developed an apparatus having a structure as shown in Japanese Patent
Application No. 57-148874. In this apparatus, basically, at least one end is supported on a
semiconductor substrate, a vibrating portion is substantially parallel to the substrate surface, and
a movable beam including an electrode layer integrally with the vibrating portion, and the
movable beam facing the movable beam And a fixed electrode layer provided on the surface of
the semiconductor substrate and forming a capacitor with the electrode layer, and the operation
is to detect the vibration by the capacitance change of the capacitor accompanying the vibration
of the movable beam. It is a thing. OBJECTS AND SUMMARY OF THE INVENTION It is an object
of the present invention to provide a movable beam suitable for a semiconductor device having a
beam structure as described above. In order to achieve the above object, the present invention is
directed to a movable beam having a vibrating portion having at least one end supported on a
semiconductor substrate and integrally including an electrode substantially parallel to the
substrate, and a movable beam on the semiconductor substrate In a semiconductor device having
a beam structure having a fixed electrode formed opposite to a vibrating portion and having a
capacitor formed between an electrode of the movable beam and the fixed electrode, the beam
The gist of the present invention is to form a triple structure of a polysilicon film formed to be
etchable and a member having alkali etching resistance formed on the upper and lower sides of
the polysilicon film. DETAILED DESCRIPTION OF THE INVENTION The present invention will be
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described in detail below with reference to the drawings. FIG. 1 shows an embodiment of the
present invention. Reference numeral 1 denotes a movable beam provided on the substrate 9 in
the form of a cantilever beam and having a unique natural frequency, and the alkali etch resistant
high concentration P + polysilicon film 3 constituting the electrode layer is also alkali etch
resistant The nitride film 5, 7 is a triple structure sandwiched by five. On the other hand, the
substrate 9 faces the movable beam 1 and thermally oxidized S! The P + region 13 is formed via
the 02 film 11. The P ? region 13 is a fixed electrode layer, and forms a capacitor with the high
concentration P + polysilicon film 3 of the movable beam 1. Therefore, when the movable beam 1
resonates, the distance between the movable beam 1 and the P + region 13 changes, and the
capacitance of the capacitor changes accordingly.
Therefore, a circuit for detecting a change in capacitance between the movable beam 1 and the P
+ region 13 is provided (if it is determined from the output of the circuit whether the vibration
corresponding to the natural frequency is applied to the movable beam 1) it can. The capacitance
change detection circuit can be integrally formed on the substrate 9. In addition, since the
movable beam 1 does not resonate at the lift table where the vibration that largely deviates from
the natural imaging motion frequency to the movable beam 1 is over 71 G, it is obvious that the
capacity change of the capacitor is small. Next, the manufacturing process of this semiconductor
device will be described according to (A> to (1-1) in FIG. (A) First of all, P + fJ1 or 13.15.17 for
detection and output of capacitance change, for example, P-MOS FET for drain and the fixed
electrode for detecting and outputting capacitance change to the substrate 9 of N-type S1. A
thermal oxidation 3i02 film, for example, 7000 A is formed on the surface of the substrate 9. (B)
иии Next, 3iH + is thermally decomposed at about 620 ░ C. by low pressure CVD, for example, to
form a polysilicon layer containing no impurity of 1 to 3 ?m, for example, on the entire surface,
and a polysilicon spacer 19 is formed by photoetching. Form (C) ... Next, NH3 and 5i) -12c ? 2
are thermally decomposed at about 750 ░ C. by low pressure CVD, for example, to form a nitride
film of about 500 A on the entire surface, and photoetching is performed to form polysilicon. An
anti-oxidation film 21 is formed to prevent the oxidation of the spacer 19. (D) Remove the
thermal oxidation 5tO2tlQ11 of the gate portion of the P-MO8 FET and the contact portion 22 by
7 etching, for example, thermally oxidize in a 1050 ░ C. oxygen atmosphere to form the gate
oxide film 23 . Thereafter, ion implantation for controlling the threshold voltage vth is performed
through the gate oxide film as required. 4- (E)... After removing the anti-oxidation film 21 with
hot phosphoric acid (150 ░ C.), a low-layer nitride film 7 of about 30 OA is formed on the entire
surface by, eg, low pressure CVD. For example, a polysilicon film of about 5000 to 10000 A is
formed by low pressure CVD, and high concentration P + polysilicon film 3 is formed by doping
this polysilicon with a high concentration of boron by an impurity diffusion method using BBr 3,
for example. Further, the nitride film 5 in the upper layer which is about 2 OA thicker than the
nitride film 7 in the lower layer is formed on the entire surface by, eg, low pressure CVD. (F)...
Next, the cantilever pattern 25 is formed by plasma etching using CF4, and the nitride layer Il! In
the upper layer of the electrode lead-out portion 27 is formed by photoetching.
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Remove 5 (G) ... Next, a hole is formed in the thermal oxide film of the contact portion 22 by
photoetching, and an A coating film of 1 to 1.5 ?m is formed on the entire surface by, for
example, vacuum evaporation. Form .30. (H) .... Next, 5il-14 and PH3 are pyrolyzed on the entire
surface by, eg, atmospheric pressure CVD at about 400 ░ C to form, for example, a PSG film
having a thickness of 1.2 ?m, and bonding by photoetching. A protective film 31 is formed other
than on the pad and movable beam region. Finally, the whole is etched with a strong alkaline
aqueous solution (for example, a mixed solution of ethylene diamine + pyrocatechol + water) as
an etching solution. Thereby, the polysilicon spacer 19 to which boron is not added is etched at a
speed of about 50 ?l / hour, and the semiconductor device shown in FIG. 1 is completed. At this
time, since the high concentration P + polysilicon film 3 which is the main material of the
variable beam 1 contains high concentration of boron, it is hardly etched from the lateral
direction, and the movable beam can be manufactured with high accuracy. The shape of the
movable beam 1 can be freely made by photoetching in the process of FIG. 2 (F). For example,
the shape of the movable beam 1 should be shifted from the center in the length direction to the
tip side. Alternatively, an elongated hole is opened at the center of the movable beam 1 in the
lengthwise direction, and a strong alkaline aqueous solution is permeated from the hole into the
etching solution with the strong aqueous Alrica solution in the final step. It is also possible to
shorten the etching time of the As a specific application example of the semiconductor device
formed in this way, it can be applied to knocking detection of an automobile engine, an
acceleration sensor, and a tachometer. That is, in knocking detection, vibration of about 7 K)-1 z
is generated from the engine at the time of knocking occurrence, so if the movable beam 51 is
formed to have a natural frequency of 7 KHz, the knocking can be detected. . On the other hand,
in the application of the acceleration sensor or tachometer, the semiconductor device is disposed
such that a force is applied in the vertical direction to the horizontal portion of the movable beam
1 by J: acceleration or centrifugal force. Should be detected. FIG. 3 shows another embodiment of
the present invention, characterized in that the supporting portion of the movable beam 1 is
reinforced by the formation arrangement of the high concentration P + polysilicon spacer 33. 7Hereinafter, the manufacturing process of the semiconductor device of this embodiment will be
described with reference to (C) and (C-) of FIG.
In addition, since (A), (B), (D) thru | or (I ') of FIG. 2 mentioned above are the same processes, the
description is abbreviate | omitted. The same reference numerals as in FIGS. 1 and 2 indicate the
same components. (C) ииииииии After completing ? ? shown in FIG. 2 (B), NH3 and Sf 1-12012 are
thermally decomposed at about 750 ░ C., for example, by a low pressure CVD method to form a
lower layer of about 50 OA. A nitride film 7 is formed, SiH 4 is pyrolyzed thereon at about 400 ░
C. by, for example, atmospheric pressure CVD to form a SiO 2 film of about 700 OA, and a
reinforcing part of the movable beam is formed by photoetching. The 5i02 film is removed to
form an ion implantation microphone 35. Then, 3 О 10 5 / cm 2 of boron is implanted at an
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acceleration energy of, for example, 100 KeV by ion implantation to form polysilicon spacers 33
in the unmasked polysilicon spacers 19. (C1... Next, the ion implantation mass 8-35 is etched
with dilute hydrofluoric acid, and further, the antioxidation film 21 for preventing the oxidation
of the high concentration P + polysilicon spacer 33 and the polysilicon spacer 19 by
photoetching Form. Thereafter, through the steps of FIG. 2D to (1-1), the polysilicon spacer 19 is
finally etched with a strong alkaline aqueous solution. At this time, the high concentration P +
polysilicon spacer 33 has a high concentration of boron. Since the etching rate with respect to
the strongly alkaline aqueous solution is extremely small because it is doped, the semiconductor
device as shown in FIG. 3 is formed. Therefore, since the supporting portion of the movable beam
is reinforced in this way and the rising of the movable beam is eliminated, the strength against
lateral force is increased, and it is possible to suppress the problem that the movable beam is
broken during etching or washing with water, Thus, with regard to the formation of the movable
beam, an improvement in yield can be expected. [Effects of the Invention] As described above,
according to the present invention, a movable beam having a vibrating portion at least one end of
which is supported on a semiconductor substrate and integrally includes an electrode
substantially parallel to the substrate, and the semiconductor substrate In the semiconductor
device, there is provided a beam structure having a fixed structure formed on the upper surface
of the movable beam opposite to a vibrating portion of the movable beam and having a capacitor
formed between the movable beam and the fixed electrode. The triple structure of the polysilicon
film formed to be alkali-etch resistant and the member having alkali-etch resistance formed on
the upper and lower sides of the polysilicon film has the following effects. ? @ @ In order to
form a movable beam later, polysilicon around the movable beam may be etched with an alkaline
etching solution, but etching of polysilicon with an alkaline etching solution does not use
anisotropy, and from all directions Since the etching proceeds, the movable beam can be formed
in a short time (for example, about 2 hours for a movable beam having a width of 100 ?m)
regardless of the length of the movable beam.
? Low cost aluminum and PSG II i with some etching rates for alkaline etching solutions due to
the short etching time! Can be used as an electrode material and a protective film material,
respectively, so that the semiconductor device is inexpensive. (2) Since no anisotropy is used in
etching, it is not necessary to provide ultra-high precision reference sides (orientation flats) on
the wafer to set the direction of each side of the etching window pattern, which facilitates
manufacture. Thus, the movable beam can be formed with high precision in manufacturing.
[0002]
Brief description of the drawings
[0003]
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1 is a cross sectional view of a semiconductor device showing one embodiment of the present
invention, FIG. 2 is a manufacturing process diagram of the semiconductor device of FIG. 1, and
FIG. 3 is a cross section of the semiconductor device showing another embodiment of the present
invention FIG. 4 is a manufacturing process diagram of the semiconductor device of FIG.
(Description of reference numerals representing major parts of the figure) 1 ... movable beam 3 ...
P + polysilicon film 5.7 ... nitride film 9 ... substrate 3 ... P + area
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