JPS60500841A - integrated capacitive transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Integrated capacitive transducer The present invention provides an electrical sound source, such as a microphone, which is integrated into a semiconductor substrate containing other elements. Regarding acoustic transducers.

Due to the rapid development of integrated circuits and microelectronic devices.

Together with these circuits, they would like to form a micromicrophone that can be included in communication devices. Demand is emerging. the current.

Micromicrophones are usually of the electret type.

Such microphones typically have a variable controller that responds to vibrations in the audio band frequencies. supported on a metal plate on a printed circuit board to form a capacitor. consists of electrified) foil. Although such devices are suitable, mechanical assembly , and does not form an entirely separate element from the integrated circuit with which the device is used. ing. Microholes are integrated into semiconductor chips and formed by IC processing. They have much lower parasitic capacitance, better characteristics, are more economical to manufacture, and require less space. There are also few resources.

The main object of the present invention is to provide a microphone integrated in a semiconductor substrate. It is.

Summary of the invention This and other objects are achieved in accordance with the present invention by thinning portions of thicker semiconductor substrates. This was achieved with an electroacoustic transducer containing a thin film consisting of: Thin film is 25μm and has an area that vibrates at a frequency of at least 0.02 kHz. ing. The transducers are spaced apart to form a capacitor. Contains a pair of electrodes. One of the electrodes allows conversion between electrical and acoustic signals. The electric field between the electrodes is designed to vibrate together with the vibrating thin film.

These and other features of the invention are discussed in detail below.

FIG. 1 is a cross-sectional view of a device according to one embodiment of the invention.

FIG. 2 shows the calculated output voltage of a device according to one embodiment of the invention as a function of sound pressure level. Shown as a number on a log-log graph.

FIG. 6 is a cross-sectional view of a device according to another embodiment of the invention.

4 to 10 show the device of FIG. 3 at various stages of manufacture according to the method of the present invention. FIG.

For convenience of explanation, please note that the scale of the figures may not necessarily correspond to the actual scale. I want to be understood.

One embodiment of the microphone is shown in cross-section in FIG. only the microphone Although shown in the figure, it is an integrated circuit that has other components on other parts of the semiconductor substrate. I want people to understand that this is a good thing.

In this example, the substrate (10) is a P-type film with a uniform initial thickness of 0.38-051u. It is a recon wafer. (P-type substrate, n-type substrate depending on the requirements of other elements in the substrate) Any of the plates may be used. ) Is the silicon thin film (11) a thinned part of the substrate? It is formed from In this example, the thickness of the thin film is approximately 0.7μm, but generally the thickness is as follows: For the reasons described in , it is necessary that the thickness be in the range of 01 to 25 μm. In this example, the boron A doped (P+) region (12) is placed on the surface of the substrate to facilitate thin film formation. include. That is, region (12) is chemically etched to define the thickness of the thin film. acts as an etch stop region when applied to the back surface of the substrate. Furthermore, Since the P+ region has fairly high conductivity (approximately 103 ohms-11-1), The region can form one electrode of a capacitor. This kind of area (12) allows for misalignment during backside etching and allows for contact formation. It suffices if it extends in the lateral direction of the substrate (10) to the extent that it does. However, extending this area further It is also possible. Contacts (16) formed at the edge areas where the thin film has been removed are It serves to provide an output signal path from the membrane. Or metal Layers can also be deposited on either surface of the thin film to form electrodes. Separate request The term “electrode” also appears in the scope of research, and this electrode is defined as the thin film itself or on it. It should be understood that this is intended to include both metal electrodes formed in the same manner.

It is formed into a circular shape with a diameter of about 6M by a resist pattern (not shown). It is. The area of the thin film varies according to the criteria discussed below. used in this example The etchant used is ethylene diamine with a ratio of 17:3:8 at one temperature of 90°C. It is a mixture of pyrocatechol, pyrocatechol, and water.

polycrystalline silicon (14) or other suitable material in selected portions of the substrate other than the thin film regions. A layer of insulating material is formed.

This layer has a thickness of approximately 0.75 to 2.0 μm and is formed by standard techniques such as chemical vapor deposition. is deposited. The polysilicon layer is covered with a gas that is electrostatically bonded onto the polysilicon layer. It acts as a spacing layer for the lath cover (15). glass cover has a thickness of approximately 0.06 = M, and a diameter of approximately 0.13 to 0.26 Maro hole (16) have. Top of glass cover and hole facing semiconductor before bonding A metal layer (17) is formed through it. In this example the metal is approximately 0 ．． It is a mixture of Aμ and Ni stretched to a thickness of 1 to 10 μm. In a typical example, electricity The area of the poles is approximately 80% of the area of the diaphragm.

As shown, the cover (15) has a cavity (18) that can be filled with air or other fluid. ) is bonded to the polysilicon layer (14) to form a thin film. thin film The part of the metal layer (17) on the surface of the cover facing the form the second electrode of the capacitor connected to ground.

In this way, in operating conditions, the sound waves incident on the surface of the microphone are Vibrate the microphone, thereby changing the distance between the electrodes of the capacitor.

The electrodes are biased through a load element (such as a second fixed capacitor or resistor). When applied, the change in capacitance caused by the acoustic input increases the voltage across the capacitor It appears as a change, thereby generating an electrical signal equivalent to an acoustic signal. hole (16) serves an important function in addition to allowing access to layer (17). That is, The hole allows air or other fluid to escape from the cavity, thereby or other fluid stiffness is not a factor in film motion. this air or other Without the liquid hole, the resonant frequency would be extremely high and the output signal at one communication frequency would be becomes extremely low.

If the air cavity hardness is negligible due to the pressure hole as in (16), the oscillating circle It can be shown that the energy transmitted from the shaped thin film is given by the following equation .

Here, D is the curvature index of the thin film, λ is the wavelength of the fundamental mode of energy, and T is the film of the thin film. lum tension, S is the thickness of the thin film, ρ8 is the mass per unit area of the thin film, and ω is the fundamental is the angular frequency of the mode. Thin films with free edges and completely fixed edges Assuming that the behavior is intermediate to that of a thin film with If we set λ=2.6α as a logical value, equation (1) becomes true as follows.

For an isotropic material such as silicon, the value of D is the Young's value for a thin silicon member. Based on the ratio and Poisson's ratio it is calculated as 6.136×10 dynes/−. child "(0,05o++ ~0.50ri and T(1~10x 1　For the typical value of ojo dyne/12), the first term in equation (2) is compared to the second term. All are small. Furthermore, the resonance frequency is 0.5 to 3.5kl (higher than the communication band of z) .

The microphone according to the invention thus produces a linear output as a function of the input sound wave. is configured to operate below a resonant frequency in a range that is independent of the external bias frequency. can be achieved. The following equation can be derived from equation (1).

where YaC is the output voltage, P is the amplitude of the sound wave, and vDo is the voltage applied to the capacitor. external (DC) bias, ε is the dielectric constant of the thin film, S is the thickness of the thin film, and Yo is the Plate of the capacitor where P is the cavity pressure and γ is the specific temperature and constant volume at constant pressure. (equal to 1.4 for air) and vb is the ratio of the specific temperature at the air outlet (typically 0.5 cubic inches or more) .

Figure 2 shows the calculated output voltage of the device in Figure 1 as a function of sound pressure level (SPL). It is shown in the figure, and a DC bias of about 6V is applied, and the silicon The tension of the film is 1010 dynes/.2. The curve in the figure indicates that the thickness of the thin film is 0. ．． The response is representative of a device with a thickness of 5 μm and a thin film radius of 2M. communication The normal range of sound pressure level for microphones is 50 to ID OdB SPL. can be.

Note that a significant response is generated. The device is most desirable for subsequent amplification. provides a desirable linear response. Thin film thickness, DC bias and film tension If changed, a useful linear output can be generated within this sound pressure range. but, The basic requirement is that the voltage output increases monotonically at sound pressure levels of 50-100d13 (that is, the sign of the slope does not change).

When using semiconductors such as silicon, it is important to choose the thickness of the thin film. It will be understood that this is a key point. This is mainly because the input frequency is usually o5~ greater than other materials used in microphones that vary in the 3.5kHz range It is said that silicon has a Young's modulus of (approximately 0.67 x 1012 dynes/-2). This is due to the fact that Maximum thickness when used as a communication microphone is considered to be 2.5 μm in order for the thin film to be sufficiently sensitive to acoustic input. It is. At the same time, the thin film must be thick enough to provide mechanical strength. I have to throw it. For this reason, the minimum α thickness is considered to be 0.1 μm. There is. Furthermore, as pointed out earlier, it is desirable to have a roughly linear output, so The area of the thin film is also an important factor. Surface in the range of 0.01 to 16n2 It is believed that a thickness within the ranges stated above will give satisfactory results. external The preferred spacing between the electrodes of a capacitor that is not supplied with bias is during operation. In order to generate a sufficient output (at least 100μ■) without the electrode contacting the Must be a 5-2.5μ door.

FIG. 3 shows another embodiment of the invention that is more easily integrated. Figure 1 element Elements corresponding to children are numbered the same. The glass cover is layered (17) at least one insulating layer providing mechanical stiffness in addition to the mechanical stiffness provided by the Note that (24) has been replaced by In this example the layer is approximately Boron nitride with a thickness of 10 μm. Air holes (25) are formed in the insulating layer. There is.

Figures 4-10 show a typical sequence for manufacturing a microphone. These stairs Each is compatible with the VLS I circuit process. microphone Although only shown, other circuit elements may be formed on the same substrate.

The starting material is typically a single crystal <IQQ> in the form of a wafer as shown in Figure 4. It's silicon. substrate so that a thin film can later be formed by an etch-stop technique. for a particular dopant, except that high dopant densities in the bulk of There are no requirements regarding the presence or density of punts. Etching alignment from front to back ( eg holes drilled through the substrate).

The surface layer (12) has an impurity concentration of about 102012+-3 and a depth of about 0.5 μm. Boron implantation of 8XID 151112 and 115k to give Formed in the substrate by eV energy. This implantation is a substrate This can be done simultaneously with the formation of the source/drain regions of the transistor therein.

A SiO2 layer (not shown) prevents implantation into undesired areas of the substrate. It can be used to prevent after implantation.

The structure is typically heated at a temperature of 1000° C. for 15 minutes in a non-oxidizing atmosphere.

At this point in the process all support circuitry has been formed on the top layer of the metal. , a protective layer (such as phosphorous-doped glass, hereinafter referred to as P-glass) contact pads to the metal, i.e. in areas where contact to metal is later required as a connection It is assumed that the circuit is formed on a circuit that has an opening at .

If necessary, remove the protective layer of P glass while processing other areas of the substrate. It can also be provided above the microphone area.

As shown in Figure 4, the spacing layer (14), in this example silicon nitride, is Deposited and formed by standard techniques to define thin film regions. This step is holes in the layer (14) in areas (not shown) requiring contact to metal in the supported support circuit; It can be opened.

This layer has a thickness of approximately 0.65 μm.

Other insulating layers can also be used that can act as masks for later applied etchants. can be used.

Next, as shown in FIG. Deposited and formed. In this example the layer is deposited by chemical vapor deposition to a thickness of approximately 1.2 μm. It is.

Phosphorus formed using chemical etching with buffered HP solution and standard etching techniques. It is a doped glass (P glass). P-glass is also used in the interconnect area of support circuits. area and contact pads. Next, as shown in Figure 6, for example, P glass is Covered with resist and etched by reactive ion etching or plasma techniques. averaged using the standard technique of grading.

Next, as shown in the cross-sectional view of Fig. 7 and the plan view of Fig. 8, the upper electrode of the capacitor is (17) is deposited and prescribed.

In this example the electrode material was deposited by chemical vapor deposition, doped with phosphorus, and etched with standard photolithography. Polycrystalline silicon patterned by layer provides mechanical stiffness It is necessary to have a sufficient thickness (approximately 1.5 μrIL). in a subsequent process Other conductors may be used if they are not etched. In Figure 8, electrodes are added. It can be seen that they are shaped like spokes to provide mechanical rigidity. support times Interconnections to the tracks are also formed during patterning of the electrodes (17).

As shown in Figure 9, another insulating layer (24) is provided on both major surfaces of the wafer (10). is deposited in This layer serves as a mask layer on the lower surface for forming a thin silicon film. act as a cover layer for the microphone on the top surface. . In this example, the layer is chemical vapor deposited boron nitride to a thickness of approximately 10 μm. The layer is Initially formed on the upper surface by photo-etching using plasma etching, P Provide a hole (25) leading to the glass fissure.

The contact pad (not shown) is opened again. Only one hole is shown in Figure 9. However, it should be understood that one can obtain a large number of holes, for example between each spoke of an electrode. . [See Silk Figure 8].

The layer (24) on the lower surface is then etched by photolithography and plasma etching. The silica on the back surface aligned with the area on the front surface defining the thin film region shown in Figure 9. It is patterned by exposing the pattern to light. Of course, the cover on the upper surface and The masks on the upper and lower surfaces do not have to be of the same material, but in the example shown here You can save steps. Other insulating materials compatible with the process may also be used or Either side surface can be used.

Next, as shown in Figure 10, the air cavity (18) is made of silicon (12) * or P glass fiber (20) without affecting layers (14), (17) and (24) ) is formed by applying and removing an etchant through the hole (25).

An example of an etchant that can be used is buffered HF acid. This etching also applies to electrodes. (17) is kept embedded in the cover layer (24). Also shown in Figure 10. As shown, the silicon thin film (11) uses the layer (24) as an etching mask. formed by etching the wafer from the bottom surface using It will be done. One technique is to first perform rapid etching through most of the basics (e.g. (For example, HNO, and HFf7) using a 90:10 solution).

Subsequently, an etchant is added that stops at the boundary of the high concentration layer (12). The latter The chant is ethylenediamine.

It may be a mixture of pyrocatechol and water. In most cases, two layers (24) are used. It is desirable to leave it on the back surface of the substrate. However, if necessary, the bottom layer (24 ) are removed with an etchant, while the top layer (24) is removed with photoresist or other suitable material. protected by a suitable mask, thereby obtaining the structure of FIG.

Another method of manufacturing the microphone is to use 5I02 for the spacing layer (14). are doing. The electrode (17) containing the hole pattern is then unpatterned 5i A thick boron nitride layer (2o) is formed on the o2 layer followed by deposition. next A hole is formed through the boron nitride layer, aligned with the hole in the electrode. The lower layer of 5i02 is It is then removed by applying an etchant through the hole. air cavity (18) The horizontal size is determined by the degree of etching, not by photoetching as shown above. It will be done.

Furthermore, the radius of the thin film can be controlled in the vicinity of the desired thin film parameters on the semiconductor surface. This is done by providing a boron-diffused ring. This annular ring To prevent lateral over-etching of the semiconductor during thin film formation It is diffused deeper into the semiconductor than region (12).

FIG./ Sound pressure level (d8) 0 Submission of translation of written amendment (Article 184-7, Paragraph 1 of the Patent Act) io month 24, 1982 Manabu Shiga, Commissioner of the Patent Office ■Display of patent application PCT/US84100219 2. Name of the invention Integrated capacitive transducer 3. Patent applicant Address: New York, 10022, United States.

New York, Madison Avenue 550 name American Telephone 3-2-3 Marunouchi, Chiyoda-ku, Tokyo. Fuji Building 208 Room 5, Amendment Submission date June 22, 1984 6. List of attached documents 1 translation of the written amendment 1 The scope of the claims 1. It has a pair of electrodes spaced apart to form a capacitor, and the One of the poles is movable with respect to the other, allowing conversion between electrical and acoustic signals In order to do this, the electric field between the electrodes changes the capacitance in response to the oscillating thin film. In electroacoustic transducers that are configured to vibrate together.

Said thin film (11) comprises a thin part of a thicker semiconductor substrate (1o), said thin film having a small (both 0.02k) (area that vibrates at frequency z and thickness of 2.5μm or less An electroacoustic transducer characterized by having:

2. In the device according to claim 1.

Thin film: (11) and an electrode capable of vibrating in the surface of the semiconductor (10) within the thin film region. An electroacoustic transducer characterized in that it has a region of high electrical conductivity (12) in sa.

3. In the device according to claim 1.

An electroacoustic transducer, wherein the semiconductor includes silicon.

4. In the device according to claim 1.

The voltage output of the capacitor has a sound and pressure level in the range of 50 to 100 dB. An electroacoustic transducer characterized by increasing monotonically as the .

5. In the device according to claim 1.

An electroacoustic transformer characterized in that the voltage output of the capacitor is approximately linear. Juicer.

6. In the device according to claim 1.

The thin film vibrates in response to sound waves having a frequency of 0.5 to 3.5 kl (z). An electroacoustic transducer characterized in that it is made as follows.

Z. In the device according to claim 1.

The area of the thin film is in the range of 0.01 to 1.0'ff12. Electro-acoustic transducer.

8. In the device according to claim 1.

Electricity, characterized in that the output voltage of the capacitor is at least 100 μV. acoustic transducer.

9. In the device according to claim 1.

The other capacitor electrode is fixed and shaped on the semiconductor substrate outside the area of the thin film. The insulating layer (24) is formed on the spacer layer (14) formed on the insulating layer (24). the law of nature.

Electroacoustic device characterized in that the cavity (18) is formed by an insulating layer and a thin film. transducer.

10. In the device according to claim 1.

The other capacitor electrode is a space formed on the semiconductor substrate (10) in the area of the thin film. It is formed on a glass bar (15) formed on a layer (14).

An electromagnetic device characterized in that a cavity (18) is formed by the force bar and the thin film. acoustic transducer.

11. The device according to claim 9 or 10.

characterized in that air holes are provided to allow air to escape from the cavity Electro-acoustic transducer.

12. The device according to claim 1.

The thin film includes a thin portion of a thinner silicon substrate.

The thin film has a frequency of 0.5 to 3.5 kHz incident on one of its surfaces. The thickness ranges from 0.1 to 2.5 μm, and the thickness ranges from 0.01 to 1 μm, which vibrates in response to sound waves. ．． It has an area in the range of O5m2.

is formed to vibrate with a thin film (11) that changes in response to sound waves. Characteristic electroacoustic transducer.

13. Forming an electroacoustic transducer including a capacitor and a vibrating semiconductor thin film The method includes: forming a highly electrically conductive region in the first major surface of the semiconductor; form a region.

A scan of a pattern that includes a thin film and exposes a semiconductor region that forms a cavity above the semiconductor region. A pacing layer is formed on the first surface.

forming an insulating layer over the exposed area to fill the cavity; Form a flat surface with layers.

depositing an electrode over a portion of the spacing layer and insulating layer;

depositing a layer of a cover over the electrode, spacing layer and insulating layer; forming an opening through the layer to the insulating layer;

removing the insulating layer from the cavity to create an air gap between the electrode and the semiconductor surface; Formed.

A mask layer with a pattern that exposes the area containing the thin film is placed on the opposite main surface of the semiconductor. Formed into.

The semiconductor region exposed by the mask is etched to form a region with high conductivity. Electroacoustic technology characterized by stopping etching and forming a thin film. How to form a transducer.

14. In the method according to claim 16.

The electrode has outwardly extending spokes overlying the insulating layer and the spacing layer. a pattern comprising a hub on an insulating layer.

15. The method according to claim 13.

The spacing layer includes silicon nitride and the insulating layer includes phosphorous-doped glass. , the electrode contains polycrystalline silicon, and the cover layer and mask layer contain boron nitride. Patent featuring international search report Continuation of page 1 [Phase] Int, CI, 4 Identification symbol Internal reference number H04R311006733 -5D Priority claim [Phase] 198 Group January 20 [Phase] United States (US) ■52268:■ Inventor: William Tortusa.

the law of nature 0 shots Akira Potato, Tommy Leroy, USA 07901 Ni 72 Bath I Avenue, Summit, New Jersey United States 08807 New Jersey, Bridgewater Penn Row Do 1171

Claims (1)

[Claims] 1. It has a pair of electrodes spaced apart to form a capacitor, and the One of the poles is in a moving state with respect to the other, and the electric field between the electrodes fluctuates, producing electrical signals and sound. One of the electrodes is in a movable state with respect to the other to allow during the electrical sound signal. In acoustic transducers. The thin film including the thin part of the thicker semiconductor substrate (10) has a thickness of less than 25 μm. , and an area that vibrates at a frequency of at least 0.02k)lz. . one of the electrodes (12) is configured to vibrate together with the thin film (11); As a result, the electric field between the electrodes changes in relation to the vibrating membrane, causing electrical and acoustic signals to be generated. An electroacoustic transducer characterized in that it allows conversion between 2. In the device according to claim 1. The transducer is a microphone and one of the electrodes (12) is connected to the membrane. The film vibrates with the thin film so that the capacitance changes in response to the input acoustic signal. An electroacoustic transducer characterized in that it is formed in the shape of a sea urchin. 3. In the device according to claim 1. An electrode that can vibrate together with the thin film (11) is located in the surface of the semiconductor (10) in the thin film region. An electroacoustic transducer characterized by having a region of high conductivity (12). -Sa. 4. In the device according to claim 1. An electroacoustic transducer, wherein the semiconductor includes silicon. 5. In the device according to claim 2. The voltage output of the capacitor has a sound pressure level in the range of 50 to 1'00 dB. An electroacoustic transducer characterized in that the transducer increases monotonically as the transducer increases. 6. In the device according to claim 5. An electroacoustic transformer characterized in that the voltage output of the capacitor is approximately linear. Juicer. Z. In the device according to claim 2. The thin film vibrates in response to sound waves having a frequency of 0.5 to 3.5 kHz. An electroacoustic transducer characterized in that it is made by: 8. In the device according to claim 7. The area of the thin film is 0.01 to 1. CI (characterized by being in the range of m2) Electro-acoustic transducer. 9. In the device according to claim 2. An electric sound characterized in that the output voltage of the capacitor is at least 100 μV. Hibiki transducer. 10. In the device according to claim 1. The other capacitor electrode is fixed and shaped on the semiconductor substrate outside the area of the thin film. The insulating layer (24) is formed on the spacer layer (14) formed on the insulating layer (24). the law of nature. Electroacoustic device characterized in that the cavity (18) is formed by an insulating layer and a thin film. transducer. 11. Del as described in claim 1 (X, 1 on the chair). The other capacitor electrode was formed on the semiconductor substrate (10) outside the thin film area. formed on the glass cover (15) formed on the spacer layer (14). characterized in that a cavity (18) is formed by the cover and the thin film. Electroacoustic transducer. 12. In the device according to claim 10 or 11. characterized in that air holes are provided to allow air to escape from the cavity Electro-acoustic transducer. 13. The device according to claim 1 (held at ℃ on a chair). The thin film includes a thin portion of a thinner silicon substrate. The thin film receives a sound having a frequency of 0.5 to 3.5 J (z) incident on one of its surfaces. vibrates in response to waves, has a thickness in the range of 0.1 to 2.5 μm, and has a thickness of 0.01 to i; It has an area in the range of "ocm". One of the electrodes (12) has a sound pressure level of 50 to 100 dB. Capacitance capacitance should be adjusted to produce a voltage output of at least 100 μ■ that increases monotonically with increasing voltage. - It is formed to vibrate with the thin film (11) that changes in response to sound waves. Characteristic electroacoustic transducer. 14. Forming an electroacoustic transducer including a capacitor and a vibrating semiconductor thin film The method includes forming a highly conductive region in the first major surface of the two-handed conductor. form a region. A scan of a pattern that includes a thin film and exposes a semiconductor region that forms a cavity above the semiconductor region. A pacing layer is formed on the first surface. forming an insulating layer over the exposed area to fill the cavity; form a flat surface with. depositing an electrode over a portion of the spacing layer and insulating layer; A cover layer is deposited over the electrode, spacing layer and insulating layer, and a cover layer is passed through the cover layer. and forming an opening reaching the insulating layer. removing the insulating layer from the cavity to create an air gap between the electrode and the semiconductor surface; form. A mask layer with a pattern that exposes the area containing the thin film is placed on the opposite main surface of the semiconductor. Formed into. The semiconductor region exposed by the mask is etched to form a region with high conductivity. Electro-acoustic technology characterized by stopping etching and forming a thin film. How to form a transducer. 15. In the method according to claim 14. The electrode has outwardly extending spokes overlying the insulating layer and the spacing layer. a pattern comprising a hub on an insulating layer. 16. In the method according to claim 14. The spacing layer includes silicon nitride and the insulating layer includes phosphorous-doped glass. , the electrode contains polycrystalline silicon, and the cover layer and mask layer contain boron nitride. A method characterized by: