JPH023302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor device having a beam structure formed on a semiconductor substrate so that at least a portion thereof can vibrate.

[Technical Background of the Invention] In detecting mechanical vibration, it is important to determine how to detect the true vibration of a vibrating part in order to ensure accuracy. To this end, a detection device that can measure even minute vibrations is required, regardless of the size or location of the vibrating part. Therefore, the present inventor has developed a device having a structure as shown in Japanese Patent Application No. 148874/1983. This device basically consists of a movable beam whose at least one end is supported on a semiconductor substrate, whose vibrating portion is approximately parallel to the surface of the substrate, and whose vibrating portion includes an integral electrode layer, and which is opposed to the movable beam. and a fixed electrode layer that is provided on the surface of the semiconductor substrate and forms a capacitor together with the electrode layer, and its operation is to reduce vibration by capacitance change of the capacitor accompanying vibration of the movable beam. It is something to detect.

[Objective and Summary of the Invention] An object of the present invention is to provide a suitable movable beam in a semiconductor device having a beam structure as described above.

In order to achieve the above object, the present invention provides a movable beam having at least one end supported on a semiconductor substrate and having a vibrating portion that integrally includes an electrode substantially parallel to the substrate; In a semiconductor device having a beam structure in which a fixed electrode is formed opposite to a vibrating part and a capacitor is formed between an electrode of a movable beam and the fixed electrode, the movable beam is resistant to alkali etch. The gist of the present invention is to have a triple structure consisting of a polysilicon film formed on the polysilicon film and a member having alkali etch resistance formed above and below the polysilicon film so that the upper layer thickness is slightly thicker than the lower layer thickness.

[Embodiments of the Invention] Examples of the invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. 1 is a movable beam provided in the form of a cantilever on a substrate 9 and has its own natural frequency, and the high concentration P ⁺ polysilicon film 3, which is resistant to alkali etch and constitutes the electrode layer, is also resistant to alkali etch. It has a triple structure sandwiched between two nitride films 5 and 7. The nitride film 5 is formed to be slightly thicker (approximately 20 Å) than the nitride film 7, as will be described later. On the other hand, a P ⁺ region 13 is formed on the substrate 9, facing the movable beam 1, with a thermally oxidized SiO ₂ film 11 interposed therebetween. The P ⁺ region 13 serves as 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, if a circuit is provided to detect the capacitance change between the movable beam 1 and the P ⁺ area 13, the movable beam 1 can be detected from the output of the circuit.
It can be determined whether a vibration corresponding to the natural frequency is added to the vibration. This capacitance change detection circuit can be integrally formed on the substrate 9. It is obvious that when the movable beam 1 is subjected to vibrations that greatly deviate from the natural frequency, the change in the capacitance of the capacitor is small because the movable beam 1 does not resonate.

Next, the manufacturing process of this semiconductor device is explained as A in FIG.
The explanation will be given according to the steps from H to H.

(A) ...First, P ⁺ regions 13, 15, 17 for the source and drain of a P-MOS FET and the fixed electrode for detecting and outputting capacitance changes are formed on the N-type Si substrate 9, A thermally oxidized SiO ₂ film having a thickness of, for example, 7000 Å is formed on the surface of the substrate 9.

(B) ...Next, the entire surface is coated, for example, by low pressure CVD method.
SiH ₄ is thermally decomposed at about 620°C to form an impurity-free polysilicon film of, for example, 1 to 3 μm, and polysilicon spacer 1 is formed by photoetching.
form 9.

(C) ...Next, apply it to the entire surface, for example, by low pressure CVD method.
NH ₃ and SiH ₂ Cl ₂ are thermally decomposed at about 750° C. to form a nitride film of about 500 Å, and then photo-etched to form an oxidation prevention film 21 for preventing oxidation of the polysilicon spacer 19.

(D) ...Thermal oxidation SiO ₂ film 11 on the gate portion and contact portion 22 of the P-MOS FET is removed by photo-etching, and thermally oxidized at 1050° C. in an oxygen atmosphere to form a gate oxide film 23. .
Then set the threshold voltage as required.
Ion implantation for Vth control is performed through the gate oxide film.

(E) ...After removing the anti-oxidation film 21 with hot phosphoric acid (150°C), the entire surface is coated with, for example, low-pressure CVD.
Forming a lower layer nitride film 7 of about 300 Å,
Furthermore, approximately 5,000
A polysilicon film of ~10,000 Å is formed, and this polysilicon is doped with boron at a high concentration by an impurity diffusion method using, for example, BBr ₃ to form a high concentration P ⁺ polysilicon film 3. Furthermore, the lower nitride film 7 is coated on the entire surface by, for example, low-pressure CVD.
The upper layer nitride film 5 is formed to be about 20 Å thicker.

Note that when the upper layer nitride film 5 is formed thicker than the lower layer nitride film 7 by the low-pressure CVD method in this way, the movable beam composed of the polysilicon film 3 and the nitride films 5 and 7 due to the intrinsic strain generated during formation. 1, it is generally known that a force that causes it to warp upwards acts (Electronics Technology Complete Book 3, published by the Industrial Research Council).
"MOS Device" (written by Iwao Tokuyama, pages 171-172).

(F)...Next, the cantilever pattern 25 is formed by plasma etching using CF ₄ , and the nide film 5 on the upper layer of the electrode extraction portion 27 is removed by photoetching.

(G) ...Next, a hole is made in the thermal oxide film of the contact part 22 by photo-etching, an Al film of 1 to 1.5 μm is formed on the entire surface by, for example, a vacuum vapor method, and electrode wirings 29 and 30 are formed by photo-etching. do.

(H) ...Next, the entire surface is coated with approximately
Pyrolyze _SiH4 and _PH3 at 400℃, e.g. thickness
A PSG film with a thickness of 1.2 μm is formed, and a protective film 31 is formed on areas other than the bonding pad and movable beam area by photoetching. And finally,
Strong alkaline aqueous solution (e.g. ethylenediamine +
Etch the entire surface using a mixture of pyrocatechol and water as an etching solution. As a result, the polysilicon spacer 19 to which no boron is added is etched at a speed of about 50 μm/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 movable beam 1, contains boron at a high concentration, it is hardly etched from the lateral direction, and the movable beam can be manufactured with high precision.

In addition, in this etching process, as mentioned above, a force is applied to the movable beam 1 that causes it to warp upward, so it should be noted that the movable beam 1 may stick to the substrate surface during the steps from etching to washing and drying. It can be prevented.

Note that the shape of the movable beam 1 can be freely created by photo etching in the process shown in FIG. Alternatively, an elongated hole may be opened in the center in the length direction of the movable beam 1, and during the final process of etching with a strong alkaline aqueous solution, a strong alkaline aqueous solution may be allowed to penetrate through the hole.
It is also possible to shorten the etching time for the polysilicon spacer 19 immediately below.

Specific examples of applications of the semiconductor device formed in this manner include knocking detection in automobile engines, acceleration sensors, and tachometers. In other words, when detecting knocking, vibrations of about 7KHz are generated from the engine when knocking occurs.
This knocking detection can be performed if the movable beam 51 is formed so that its natural frequency is 7 KHz. On the other hand, in applications such as acceleration sensors and tachometers, semiconductor devices are arranged so that force is applied in a vertical direction to the horizontal portion of the movable beam 1 due to acceleration or centrifugal force, and changes in capacitance due to acceleration or centrifugal force are detected. Just do it like this.

FIG. 3 shows another embodiment of the present invention, which is characterized in that the support portion of the movable beam 1 is reinforced by the formation and arrangement of high concentration P ⁺ polysilicon spacers 33.

The manufacturing process of the semiconductor device of this embodiment will be explained below with reference to C and C' in FIG. Note that since steps A, B, C to (H) in FIG. 2 described above are the same steps, their explanation will be omitted. In addition, the same reference numerals as in FIGS. 1 and 2 indicate the same items.

(C) _... After completing the process shown in _{FIG .}
is thermally decomposed at approximately 750°C to form a lower layer nitride film 7 of approximately 500 Å, and on top of this, SiH ₄ is thermally decomposed at approximately 400°C by, for example, atmospheric pressure CVD, and approximately
A SiO ₂ film with a thickness of 7000 Å is formed, and the SiO ₂ film on the reinforcing portion of the movable beam is removed by photoetching to form an ion implantation microphone 35. Boron is then ion-implanted using, for example, acceleration energy.
Inject 3×10 ¹⁶ pieces/cm ² at 100 KeV to form polysilicon spacers 33 in 19 unmasked polysilicon spacers.

(C') ...Next, the ion implantation mask 35 is etched with dilute hydrofluoric acid, and the oxidation prevention film 21 that prevents the high concentration P ⁺ polysilicon spacer 33 and the polysilicon spacer 19 from being oxidized is formed by photo-etching. . After that, Figure 2D
After the steps ~H, the polysilicon spacer 19 is finally etched with a strong alkaline aqueous solution. At this time, the high concentration ^P5 polysilicon spacer 33 is doped with boron at a high concentration, so the etching rate for the strong alkaline aqueous solution is low. Since it is extremely small, it remains and a semiconductor device as shown in FIG. 3 is formed.

Therefore, by reinforcing the support part of the movable beam and eliminating the rise of the movable beam, the strength against lateral forces is increased and problems such as the movable beam breaking during etching or washing are suppressed. As a result, it is possible to expect an improvement in yield in forming movable beams.

[Effects of the Invention] As explained above, according to the present invention, there is provided 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 the semiconductor substrate. A semiconductor device having a beam structure having a fixed electrode formed on the top facing a vibrating part of a movable beam, and forming a capacitor between the electrode of the movable beam and the fixed electrode. By creating a triple structure of a polysilicon film formed to have alkali etch resistance and a member having alkali etch resistance formed above and below the polysilicon film, the upper layer thickness is slightly thicker than the lower layer thickness. A force is applied to the movable beam that causes it to warp upward. As a result, when forming a movable beam,
To provide a semiconductor device having a movable beam which is free from sticking to a substrate particularly in the process of washing and drying from the end of an etching process, can be expected to improve the yield in forming the movable beam, and has a suitable movable beam as a result. Can be done.

[Brief explanation of drawings]

1 is a 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 sectional view of a semiconductor device showing another embodiment of the invention. 4 are manufacturing process diagrams of the semiconductor device of FIG. 3. Explanation of the symbols representing the main parts of the figure: 1...Movable beam, 3...P ⁺ polysilicon film, 5, 7...Nitride film, 9...Substrate, 13...P ⁺ region.

Claims (1)

[Claims] 1. A movable beam having at least one end supported on a semiconductor substrate and having a vibrating part that integrally includes an electrode substantially parallel to the substrate, and a fixed electrode formed on the semiconductor substrate to face the vibrating part of the movable beam. In a semiconductor device, the movable beam has a polysilicon film formed to have alkali etch resistance, and an alkali etch resistant film in which the upper layer thickness is slightly thicker than the lower layer thickness above and below the polysilicon film. 1. A semiconductor device having a beam structure, characterized in that it has a triple structure with a member having a beam structure.