JP2007309914A - Method of manufacturing physical quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a physical quantity sensor capable of preventing a membrane from breaking because of becoming too thin. <P>SOLUTION: The buried layer of the SOI substrate (Silicon On Insulator) used for forming a thermal flowrate sensor is not only constituted with one layer of SiO<SB>2</SB>but also a silicon nitride membrane 11 arranged on the surface 10b of the silicon substrate 10. Thereby, at the time of etching the silicon substrate 10, the silicon nitrate membrane 11 is functioned as an etching stopper, therefore the silicon oxide membrane 12 is prevented from being eliminated. Thereby, the thinning of the membrane caused by the being etched of the silicon oxide membrane 12 can be prevented, and breakage caused by the too much thinning the membrane can be prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a physical quantity sensor provided with a membrane composed of several layers of films.

  Conventionally, Patent Document 1 discloses a thermal flow sensor using a heating resistor and a resistance temperature detector. The thermal flow sensor detects the flow rate of the fluid to be measured by installing a heating resistor in the fluid to be measured and detecting the amount of heat released from the heating resistor taken by the fluid to be measured by the temperature measuring resistor. In such a thermal flow sensor, a membrane is provided as a thin film portion that can reduce contact with the substrate and suppress heat transfer to the substrate by forming a recess or a cavity in the substrate. The responsiveness of the thermal flow sensor is enhanced by arranging a heating resistor and a resistance temperature detector on the membrane.

The thermal flow sensor disclosed in Patent Document 1 is manufactured using an SOI (Silicon on insulator) substrate, and the lowermost layer of the membrane is made of SiO ₂ that constitutes a buried layer (BOX layer) in the SOI substrate. ing.
Japanese Patent Laid-Open No. 2001-12985

However, in the thermal flow sensor described in Patent Document 1, the lowermost layer of the membrane is composed of only one SiO ₂ layer constituting the buried layer of the SOI substrate. When anisotropic etching is performed using KOH or the like to form the recess, SiO ₂ is also etched. Therefore, there arises a problem that the membrane becomes too thin and breaks.

  Here, the above problem has been described by taking a thermal flow sensor as an example, but the same problem as described above also occurs with respect to other physical quantity sensors using a membrane.

  An object of this invention is to provide the manufacturing method of the physical quantity sensor which can prevent that a membrane becomes thin too much and breaks in view of the said point.

  In order to achieve the above object, in the present invention, a silicon substrate (10) is formed using an SOI substrate having a supporting substrate, an insulating film (13) as a buried layer, and a semiconductor layer (14) as an SOI layer. 10) In the method of manufacturing a physical quantity sensor in which the insulating film (13) formed in the cavity (10a) in 10) is used as a membrane, the insulating film (13) is formed of a silicon nitride film (11) and the silicon as an SOI substrate. Preparing a layered structure including at least two silicon oxide films (12) disposed on the semiconductor layer (14) side of the nitride film (11), and etching the silicon substrate (10) in the SOI substrate; Thus, the method includes a step of forming a cavity (10a) in the silicon substrate (10).

  In this manner, the buried layer of the SOI substrate used for forming the thermal flow sensor is not formed by only one layer of the silicon oxide film (12), but closer to the silicon substrate (10) side than the silicon oxide film (12). The silicon nitride film (11) is also provided. Therefore, when the silicon substrate (10) is etched, the silicon nitride film (11) functions as an etching stopper, and the silicon oxide film (12) can be prevented from being removed. For this reason, it is possible to prevent the membrane from being thinned due to the etching of the silicon oxide film (12), and it is possible to prevent the membrane from becoming too thin and cracking.

For example, the silicon nitride film (11) included in the insulating film (13) can be formed using Si ₃ N ₄ or Si-rich Si _x N _y .

  Such a silicon nitride film (11) is preferably formed as a film having tensile stress. By doing in this way, it becomes possible to make the average stress of the whole film | membrane which comprises a membrane become a tensile stress, and it can make it difficult for a membrane to buckle and to be damaged.

  The silicon nitride film (11) may be formed by forming the silicon nitride film (11) on the surface (10b) of the silicon substrate (10) or the surface (10b) of the silicon substrate (10). ) May be performed by forming a silicon nitride film (11) at a predetermined depth in the silicon substrate (10) by performing heat treatment after ion implantation of nitrogen ions.

On the other hand, for example, it is possible to form a silicon oxide film contained in the insulating film (13) using any of SiO _x N _y and porous silica containing SiO _2, N minutely (12).

  In this case, regarding the formation of the silicon oxide film (12), the upper surface of the silicon nitride film (11) formed on the surface (10b) of the silicon substrate (10) or the silicon substrate (30) for forming the SOI layer. This may be performed by forming a silicon oxide film (12) on the surface (30a) of the silicon substrate, or by performing heat treatment after ion implantation of oxygen ions from the surface (10b) of the silicon substrate (10). This may be performed by forming a silicon oxide film (12) at a position of the depth determined in (10).

  For example, the step of preparing an SOI substrate includes a step of forming a silicon nitride film (11) on the surface (10b) of a silicon substrate (10) to be a support substrate, and a silicon substrate for an SOI layer for forming an SOI layer ( 30), and a step of forming the silicon oxide film (12) on the surface (30a) of the SOI layer silicon substrate (30) and the silicon nitride film (11) and the silicon oxide film (12) are bonded together. Thus, a step of integrating the silicon substrate (10) serving as the support substrate and the silicon substrate for SOI layer (30), and a step of forming the SOI layer by thinning the silicon substrate for SOI layer (30). It is performed by the process including.

  In this case, hydrogen ions are implanted at a depth corresponding to the thickness of the SOI layer from the surface (30a) of the SOI layer silicon substrate (30), and then heat treatment is performed to implant hydrogen ions. By dividing the SOI layer silicon substrate (30) at the position, the SOI layer can be formed.

  In the physical quantity sensor manufacturing method described above, for example, the semiconductor layer (14) disposed in the membrane is the heater (15a, 15b), and the physical quantity is based on the temperature change of the heater (15a, 15b) due to the fluid flow. It can apply as a manufacturing method of the thermal type flow sensor (S1) which detects the flow volume of fluid.

  In addition, the wiring layer (41) is disposed above the semiconductor layer (14) and has a plurality of contacts serving as contact points with the semiconductor layer (14), and in the membrane above the wiring layer (41). An infrared absorption film (43) disposed, and of the contacts between the wiring layer (41) and the semiconductor layer (14), a contact in the membrane is a hot contact, and a contact outside the membrane is a cold contact, absorbing infrared rays. When the film (43) is irradiated with infrared rays, the amount of infrared rays is detected as a physical quantity based on the electromotive force caused by the temperature difference between the hot junction and the cold junction generated as the temperature of the infrared absorption film (43) rises. It can also be applied as a manufacturing method of the infrared sensor (S2).

  Moreover, the gas sensitive film which changes resistance value by reaction with the wiring layer (51) arrange | positioned in the upper layer of a semiconductor layer (14), and the measurement object gas arrange | positioned in the membrane above the wiring layer (51). The resistance value of the gas sensitive film (53) can be detected through the pad portions (51a, 51b) electrically connected to the gas sensitive film (53) in the wiring layer (51). The wiring layer (51) is configured to allow current to flow through the semiconductor layer (14) through the pad portions (51c, 51d) electrically connected to the semiconductor layer (14), and allows current to flow through the semiconductor layer (14). As a physical quantity, the temperature of the gas sensitive film (53) in the membrane is increased by heating and the gas sensitive film (53) reacts with the target gas to change the resistance value of the gas sensitive film (53). Gas cell that detects the amount of target gas It can also be applied as a method for manufacturing a support (S3).

  In addition, the wiring layer (61) disposed on the semiconductor layer (14) and electrically connected to the semiconductor layer (14), and the cavity (10a) are disposed on the back surface of the silicon substrate (10). ) As a pressure reference chamber, and the semiconductor layer (14) disposed in the membrane is used as a gauge resistance, based on a change in the resistance value of the semiconductor layer (14) due to the displacement of the membrane due to the pressure. It can also be applied as a manufacturing method of a pressure sensor (S4) that detects pressure as a physical quantity.

  The wiring layer (61) is disposed above the semiconductor layer (14) and electrically connected to the semiconductor layer (14), and the insulating film (13) formed in the cavity (10a) is provided on the insulating layer (13). The semiconductor layer (14) having a weight portion (10e) provided therein and having a semiconductor layer (14) disposed in the membrane as a gauge resistance, and acceleration as a physical quantity based on a change in resistance value of the semiconductor layer (14) due to the displacement of the membrane due to acceleration. It can also be applied as a method of manufacturing an acceleration sensor (S5) that detects

  Further, the wiring layer (61) disposed on the semiconductor layer (14) and electrically connected to the semiconductor layer (14), and disposed on the back surface of the silicon substrate (10), the cavity (10a) ) As a pressure reference chamber, and a weight portion (10e) provided to be separated from the pedestal (63) in the insulating film (13) formed in the hollow portion (10a), A composite sensor (S6) that uses the semiconductor layer (14) disposed in the membrane as a gauge resistance and detects pressure or acceleration as a physical quantity based on a change in resistance of the semiconductor layer (14) due to displacement of the membrane due to pressure or acceleration. It can also be applied as a manufacturing method.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
FIG. 1 is a diagram showing a schematic plan configuration of a thermal flow sensor S1 as a physical quantity sensor to which an embodiment of the present invention is applied, and FIG. 2 is a thermal flow sensor along the line AA in FIG. It is a figure which shows schematic sectional structure of S1.

  The thermal flow sensor S1 is formed based on, for example, a silicon substrate 10 having a plate thickness of 400 μm or 600 μm. A cavity 10a is formed in the silicon substrate 10, and a membrane is formed at a site where the cavity 10a is formed.

  As shown in FIG. 2, the cavity 10 a is formed so as to penetrate the front surface 10 b and the back surface 10 c of the silicon substrate 10. Specifically, the cavity 10a is configured as a recess that is recessed from the back surface 10c side of the silicon substrate 10 toward the front surface 10b side with the back surface 10c side of the silicon substrate 10 being an opening 10d.

Further, as shown in FIG. 2, an insulating film 13 in which a silicon nitride film 11 and a silicon oxide film 12 are stacked is formed on the surface 10 b of the silicon substrate 10. The silicon nitride film 11 here means a film containing Si and N, and corresponds to, for example, Si ₃ N ₄ or Si-rich Si _x N _y . The silicon nitride film 11 is a film having tensile stress, and has a thickness of, for example, about 0.05 to 0.5 μm. Further, the silicon oxide film 12 means a film containing Si and O. For example, SiO ₂ , SiO _x N _y containing minute amounts of N, porous silica, and the like are applicable. The silicon oxide film 12 is a film having a compressive stress, and has a thickness of about 0.01 to 1 μm, for example.

  A semiconductor layer 14 formed by thermally diffusing impurities in the silicon layer is patterned on the surface of the insulating film 13, and the semiconductor layer 14 is used to measure the heaters 15a and 15b and the environmental temperature. Resistors constituting the thermometers 16a and 16b and the wiring layers 17a to 17f are formed.

  The silicon substrate 10, the insulating film 13, and the semiconductor layer 14 thus configured are formed using an SOI substrate in which the silicon substrate 10 is a supporting substrate, the insulating film 13 is a buried layer, and the semiconductor layer 14 is an SOI layer. It is.

  Further, the semiconductor layer 14 is covered with an insulating film 18 made of BPSG or the like, and is electrically connected to pads 19a to 19f made of aluminum or the like through contact holes formed in predetermined portions of the insulating film 18. Yes.

  Further, a silicon nitride film 20 is formed on the surface of the insulating film 18 so as to cover almost the entire area of the silicon substrate 10, and the surface of the thermal flow sensor S1 is protected. Openings are formed in portions of the silicon nitride film 20 corresponding to the pads 19a to 19f, and wires 21a to 21f are bonded to the pads 19a to 19f through the openings, so that a thermal flow rate is obtained. It is electrically connected to a control circuit provided outside the sensor S1.

  A silicon nitride film 21 is formed on the back side of the silicon substrate 10. An opening is formed in the silicon nitride film 21, and an opening 10d of the silicon substrate 10 is formed through the opening.

  With such a structure, the thermal flow sensor S1 is configured.

  Next, an example of the operation when the flow rate of air, which is the fluid to be measured, is detected by such a thermal flow sensor S1 will be described.

  The heaters 15a and 15b are driven by a control circuit (not shown) and controlled so as to be 200 ° C. higher than the environmental temperature measured by the thermometers 16a and 16b, for example. Specifically, current flows from the control circuit to the heater 15a through the wires 21b and 21c, the pads 19b and 19c and the wiring layers 17b and 17c, and the heater through the wires 21d and 21c, the pads 19d and 19e and the wiring layers 17d and 17e. A current is passed through 15b. Thereby, each heater 15a, 15b comprised by the predetermined | prescribed line | wire width is heated.

  In the measurement of the environmental temperature, the resistance value of each thermometer 16a, 16b varies according to the environmental temperature. , 17b, and a change in the amount of current accompanying a change in the resistance value of the thermometer 16b is input to the control circuit through the wires 21e, 21f, the pads 19e, 19f, and the wiring layers 17e, 17f, respectively. Thereby, the temperature of each position of each thermometer 16a, 16b is detected by the control circuit side.

  Therefore, on the control circuit side, the amount of current flowing through each heater 15a, 15b is feedback-controlled so that the temperature becomes 200 ° C. higher than the environmental temperature detected by each thermometer 16a, 16b.

  For example, assume that air flows from the direction of the white arrow in FIG. Here, as described above, the heated heaters 15a and 15b are deprived of heat due to the flow of air, and the temperature is lowered, but the heater 15b on the downstream side of the air flow passes through the heater 15a on the upstream side. When heated, the heated air contacts the downstream heater 15b, so that only a little heat is taken away and the temperature drop is small. In this way, the way in which the heaters 15a and 15b are deprived of heat depends on the air flow rate.

  Therefore, the control circuit increases the energization amount to each of the heaters 15a and 15b so that the heater 15a and the heater 15b are always 200 ° C. higher than the environmental temperature, and based on the energization amount, the air flow rate is increased. And the direction of flow can be detected.

  Next, a manufacturing method of the thermal flow sensor S1 shown in the present embodiment will be described with reference to a manufacturing process diagram shown in FIG.

[Step shown in FIG. 3 (a)]
First, a silicon substrate 10 serving as a supporting substrate made of single crystal silicon is prepared. For example, a 6-inch wafer having a plane orientation of (100) and a thickness of about 400 μm or 600 μm is used as the silicon substrate 10. At this time, the cavity 10a is not yet formed in the silicon substrate 10.

[Step shown in FIG. 3B]
A silicon nitride film 11 and a silicon nitride film 21 are formed by deposition on the front surface 10b and the back surface 10c of the silicon substrate 10 by LP-CVD (low pressure CVD), for example, about 0.05 to 0.5 μm. At this time, these film formation conditions are set so that the silicon nitride film 11 and the silicon nitride film 21 become films having tensile stress. Most of the silicon nitride film 11, silicon oxide film 12, insulating film 18, and silicon nitride film 20 constituting the membrane are configured as films having compressive stress, but when the compressive stress is applied, the membrane is bent and damaged. It is known to be easier. For this reason, by making the silicon nitride film 11 a film having a tensile stress, the membrane is bent and hardly damaged.

At this time, the silicon nitride film 11 may be made of Si ₃ N ₄ , but is preferably Si-rich Si _x N _y . That is, since the tensile stress of Si ₃ N ₄ is too high as about 1200 MPa, if it is formed thick, cracks may occur in the silicon nitride film 11 itself made of Si ₃ N ₄ . Therefore, even if Si ₃ N ₄ is thick, it can be formed only up to about 0.2 μm in one deposition and up to about 0.5 μm in a plurality of depositions (forming Si ₃ N ₄ by a plurality of depositions). The generation of cracks can be suppressed even if the film is formed thick, so that it is preferable to carry out the deposition multiple times when depositing at a thickness of 0.2 μm or more. In addition, when Si ₃ N ₄ is formed thick, there is a problem that slip occurs on the surface 10b in the vicinity of the outer edge of the silicon substrate 10 where the tensile stress of the silicon nitride film 11 increases. In contrast, Si _x N _y of Si-rich it is possible to reduce the tensile stress from the Si ₃ N _4, it thicker than Si ₃ N _4. For this reason, even if the total film thickness of the membrane is increased, the average stress of the entire film can be made the tensile stress. Such Si-rich Si _x N _y is formed by the LP-CVD method, for example, and depends on the formation temperature (700 to 900 ° C.) and the gas flow rate ratio (SiH ₂ Cl ₂ / NH ₃ ratio≈0.3 to 8). The amount of Si rich can be controlled, and a desired tensile stress can be obtained.

  The silicon nitride film is formed by the LP-CVD method so that the average stress of the entire film constituting the membrane becomes a tensile stress (preferably a tensile stress of 20 MPa or more), but the silicon nitride film is formed. If there is a step on the surface, there are problems such as peeling or cracking of the silicon nitride film. However, as described here, by forming the silicon nitride film 11 on the planar surface 10b of the silicon substrate 10, the silicon nitride film 11 is not peeled off or cracked.

[Steps shown in FIGS. 3C and 3D]
On the other hand, a silicon substrate 30 constituting an SOI layer made of single crystal silicon is prepared. For example, the same silicon substrate 10 can be used. Then, the silicon oxide film 12 is formed on the front surface 30a (and the back surface 30b) of the silicon substrate 30 by thermal oxidation, for example, about 0.01 to 1 μm.

At this time, the silicon oxide film 12 may be composed of SiO _2, when the SiO _x N _y (silicon oxynitride), it is possible to lower the compressive stress than SiO _2. As described above, the average stress of the entire film constituting the membrane needs to be a tensile stress. By using the silicon oxide film 12 as SiO _x N _y , a film having a compressive stress as compared with the case of using SiO ₂ can be obtained. Can be thicker. This makes it possible to increase the total film thickness of the membrane, prevent damage to the membrane when dust mixed in the gas collides with the membrane, and suppress deformation of the membrane due to air pressure fluctuations. The deterioration of accuracy can also be prevented. Such SiO _x N _y is formed by, for example, a plasma CVD method.

Even if the silicon oxide film 12 is made of porous silica instead of SiO ₂ , the compressive stress can be made lower than that of SiO ₂ . Furthermore, since the thermal conductivity can be reduced by using porous silica, in addition to the above effects, the heaters 15a and 15b constituting the heating resistor can be controlled to the same temperature with a small amount of power, and power saving can be achieved. It becomes. Such porous silica is formed by, for example, organic SOG (Spin On Glass) O ₂ ashing. Note that the organic SOG indicates that a part of the Si—O bond of the main network is terminated with a methyl group.

[Step shown in FIG. 3 (e)]
By bonding the silicon nitride film 11 on the surface 10b side of the silicon substrate 10 and the silicon oxide film 12 on the surface 30a side of the silicon substrate 30, the two silicon substrates 10 and 30 are integrated. Specifically, the silicon nitride film 11 and the silicon oxide film 12 are overlapped so that voids (voids) are not formed between them, and heat treatment is performed at a high temperature of 1000 ° C. or higher. As a result, an SOI substrate in which the insulating film 13 constituting the buried layer is formed by the silicon nitride film 11 and the silicon oxide film 12 is formed.

[Step shown in FIG. 3 (f)]
The SOI substrate is formed by polishing the silicon substrate 30 by CMP (Chemical Mechanical polishing) or the like and reducing the thickness to, for example, 0.2 to 2 μm. Thereafter, after oxidizing the surface of the SOI layer as necessary, donor impurities (for example, P, As, Sb, etc.) or acceptor impurities (for example, B, Al), for example, 1 × 10 ¹⁹ to After ion implantation so as to have a concentration of about 1 × 10 ²¹ cm ⁻³ , the semiconductor layer 14 is formed by performing activation heat treatment. As for the activation heat treatment, when a heat treatment step is performed later, it may be performed only when the diffusion of impurities and the electrical activation are insufficient in the heat treatment.

  Although the impurity is doped here by ion implantation, a doping method that does not perform ion implantation, such as a phosphorus deposit, may be used, or a donor impurity (originally during silicon crystal growth when the silicon substrate 30 is formed). For example, if the atmosphere is doped with P, As, Sb, etc. or acceptor impurities (for example, B, Al), the ion implantation is not necessary here, and the manufacturing process can be simplified. Can also be obtained.

[Step shown in FIG. 4 (a)]
After performing a step of removing the silicon oxide film formed on the surface of the semiconductor layer 14 before ion-implanting impurities, the semiconductor layer 14 is patterned. Thus, the heaters 15a and 15b, the thermometers 16a and 16b for measuring the environmental temperature, and the wiring layers 17a to 17f are configured. At this time, for the heaters 15a and 15b, for example, the line width is set to about 10 μm. The patterning of the semiconductor layer 14 is performed by etching. However, since the silicon oxide film 12 is formed as a base of the SOI layer, the silicon nitride film 11 is prevented from being etched during etching. Can do. For this reason, the strength of the membrane to be formed later can be prevented from being lowered.

[Step shown in FIG. 4B]
In order to stabilize the surface of the semiconductor layer 14, the surface of the semiconductor layer 14 is slightly oxidized as necessary, and then the BPSG layer is formed by deposition to form the insulating film 18. Subsequently, an annealing process is performed to flatten the surface level difference, and then a contact hole is formed in the insulating film 18 by a photoetching process. And after forming aluminum by deposition, the pads 19a-19f are formed by patterning aluminum by a photo-etching process. Here, aluminum is patterned to form the pads 19a to 19f. However, the lead wiring may be configured.

[Step shown in FIG. 4 (c)]
A silicon nitride film 20 serving as a protective film is formed by deposition on the entire surface of the silicon substrate 10 on the surface 10b side by a plasma CVD method or the like with a film thickness of about 3.2 μm, for example. As a result, the pads 19a to 19f made of aluminum can be protected, the membrane can be made thicker, damage when dust mixed in the air collides with the membrane, and the pressure of the air can be prevented. Since the deformation of the membrane with respect to fluctuations can be suppressed, deterioration of measurement accuracy can also be prevented. Although the case where both the silicon nitride film 20 and the insulating film 18 are formed has been described here, one of these functions as a protective film.

  Then, the pads 19a to 19f are exposed by opening predetermined positions of the silicon nitride film 20 by a photoetching process. Thereafter, a passivation annealing process is performed.

[Step shown in FIG. 4 (d)]
A predetermined portion of the silicon nitride film 21 is opened by a photoetching process. Then, the silicon substrate 10 is anisotropically etched from the exposed portion using the silicon nitride film 21 as a mask to form the opening 10d in the silicon substrate 10, thereby forming the cavity 10a. At this time, since the plane orientation of the silicon substrate 10 is (100), the opening 10d is formed in a shape as shown in FIG. Thereby, the thermal flow sensor S1 of this embodiment shown in FIGS. 1 and 2 is completed.

As described above, in the thermal flow sensor S1 of the present embodiment, the buried layer of the SOI substrate used for forming the thermal flow sensor S1 is not composed of only one layer of SiO ₂ , but the surface of the silicon substrate 10 The silicon nitride film 11 arranged at 10b is also provided. For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. For this reason, it is possible to prevent the membrane from being thinned by etching the silicon oxide film 12, and it is possible to prevent the membrane from being too thin and cracking.

(Second Embodiment)
A second embodiment of the present invention will be described. In the first embodiment, in the process shown in FIG. 3B, not only the silicon nitride film 11 on the front surface 10b of the silicon substrate 10 but also the silicon nitride film 21 on the back surface 10c is formed at the same time. You may form in a process. For example, the silicon nitride film 21 may be formed after the step of FIG.

  However, since the silicon nitride film 11 has a tensile stress as described above, the silicon substrate 10 may be warped by the tensile stress of the silicon nitride film 11. For this reason, if the silicon nitride film 21 is formed simultaneously with the formation of the silicon nitride film 11 as in the first embodiment, warping of the silicon substrate 10 can be suppressed. Further, as compared with the case where the silicon nitride film 11 and the silicon nitride film 21 are separately formed as described above, it is possible to simplify the manufacturing process by forming them in the same process as in the first embodiment described above. An effect is also obtained.

(Third embodiment)
A third embodiment of the present invention will be described. The thermal flow sensor S1 of the present embodiment is obtained by changing the configuration of the insulating film 13 with respect to the first embodiment, and is otherwise the same as that of the first embodiment, and therefore only different parts will be described.

5A is a cross-sectional view of the thermal flow sensor S1 of this embodiment, and FIG. 5B is a cross-sectional view of an SOI substrate used for forming the thermal flow sensor S1 of FIG. 5A. is there. As shown in FIGS. 5A and 5B, a silicon oxide film 22 having a thickness of, for example, 0.02 to 1 μm is disposed between the surface 10b of the silicon substrate 10 and the silicon nitride film 11, An insulating film 13 corresponding to a buried layer in the SOI substrate is composed of a silicon oxide film 22, a silicon nitride film 11, and a silicon oxide film 12. The silicon oxide film 22 means a film containing Si and O. For example, SiO ₂ , SiO _x N _y containing minute amounts of N, porous silica, and the like are applicable.

  Thus, the insulating film 13 may have a three-layer structure of the silicon oxide film 22, the silicon nitride film 11, and the silicon oxide film 12. Further, since the silicon nitride film 11 is a film having a tensile stress, when the silicon nitride film 11 is directly formed on the surface 10b of the silicon substrate 10, the surface of the silicon nitride film 11 near the outer edge where the tensile stress increases. Although slip may occur in 10b, the formation of such a slip can be prevented by forming the silicon oxide film 22 under the silicon nitride film 11.

  However, in the case of such a structure, as shown in FIG. 5B, the silicon oxide film 22 is also etched during the etching for forming the opening 10d in the silicon substrate 10. Since the silicon nitride film 11 is present, it is not etched too much and the membrane is not damaged.

  FIG. 6 is a cross-sectional view showing the manufacturing process of the thermal flow sensor S1 of the present embodiment. In the manufacturing process of the thermal flow sensor S1 of this embodiment, the process before forming the SOI substrate is different from the first embodiment, but the process after forming the SOI substrate is the first implementation. Since the configuration is exactly the same, only the process before forming the SOI substrate is shown here.

  In the step shown in FIG. 6A, after the silicon substrate 10 described in the step shown in FIG. 3A is prepared, the silicon substrate 10 is formed by thermal oxidation or the like in the subsequent step shown in FIG. 6B. A silicon oxide film 22 is formed on the surface 10b. Then, silicon nitride films 11 and 21 are formed on the upper surface of the silicon oxide film 22 and the back surface 10c of the silicon substrate 10 by a method similar to the process shown in FIG.

  In the steps shown in FIGS. 6C and 6D, the silicon oxide film 12 is formed on the surface 30a of the silicon substrate 30 by the same method as the steps shown in FIGS. 3C and 3D described above. . 6E, the silicon nitride film 11 formed on the upper surface of the silicon oxide film 22 in the silicon substrate 10 and the surface in the silicon substrate 30 by the same method as the process shown in FIG. The silicon oxide film 12 on the 30a side is bonded. Thereafter, in the step shown in FIG. 6F, the semiconductor layer 14 is formed by polishing and thinning the silicon substrate 30.

  When the silicon oxide film 22 is formed by thermal oxidation in the process shown in FIG. 6B, a silicon oxide film is also formed on the back surface 10c of the silicon substrate 10. Even if etching is performed to form the opening 10d in the silicon substrate 10 to be performed in a later step, the silicon nitride film 21 is not removed so much.

(Fourth embodiment)
In the third embodiment, the silicon oxide film 22 and the silicon nitride film 11 are formed on the surface 10b of the silicon substrate 10 in the step shown in FIG. 6B. However, in the step shown in FIG. 6D, the silicon oxide film 12, the silicon nitride film 11, and the silicon oxide film 22 are laminated in order, and the surface 10b of the silicon substrate 10 and the silicon oxide film 22 are bonded together. It is also possible. In this case, a silicon nitride film or a silicon oxide film is also formed on the back surface 30b of the silicon substrate 30, but these are removed by polishing performed in the step shown in FIG. no problem.

(Fifth embodiment)
A fifth embodiment of the present invention will be described. In the first embodiment, the silicon substrate 30 is thinned by polishing in the step shown in FIG. 3F. However, in the present embodiment, the silicon substrate 30 is thinned by a method different from the first embodiment. To do.

  FIG. 7 is a cross-sectional view showing the manufacturing process of the thermal flow sensor S1 of the present embodiment. In the manufacturing process of the thermal flow sensor S1 of this embodiment, the process before forming the SOI substrate is different from the first embodiment, but the process after forming the SOI substrate is the first implementation. Since the configuration is exactly the same, only the process before forming the SOI substrate is shown here.

  In the steps shown in FIGS. 7A and 7B, silicon nitride films 11 and 21 are formed on the front surface 10b and the back surface 10c of the silicon substrate 10 by the same method as the steps shown in FIGS. Form.

  On the other hand, in the step shown in FIG. 7C, the silicon substrate 30 is prepared similarly to the step shown in FIG. 3C, and in the subsequent step shown in FIG. 7D, the surface 30a of the silicon substrate 30 is formed. After the silicon oxide film 12 is formed, hydrogen ions are implanted from above the silicon oxide film 12. The implantation depth of hydrogen ions by ion implantation at this time is made equal to the thickness of the SOI layer (semiconductor layer 14). If the SOI layer has a thickness of 1 μm, for example, the implantation depth of hydrogen ions The thickness is also set to 1 μm.

  Thereafter, in the step shown in FIG. 7E, the silicon nitride film 11 formed on the upper surface of the silicon oxide film 22 in the silicon substrate 10 and the surface in the silicon substrate 30 by the same method as the step shown in FIG. The silicon oxide film 12 on the 30a side is bonded. At this time, since the heat treatment performed for bonding is set to 1000 ° C. or higher, the silicon substrate 30 is cracked at the position where the hydrogen ions are implanted (smart cut). Thus, an SOI layer having a desired film thickness can be formed without using polishing.

(Sixth embodiment)
A sixth embodiment of the present invention will be described. In the first embodiment, the SOI substrate is basically configured by bonding the silicon substrate 10 and the silicon substrate 30 through the insulating film 13, but this embodiment is different from the first embodiment. An SOI substrate is formed by the method.

  FIG. 8 is a cross-sectional view showing the manufacturing process of the thermal flow sensor S1 of the present embodiment. In the manufacturing process of the thermal flow sensor S1 of this embodiment, the process before forming the SOI substrate is different from the first embodiment, but the process after forming the SOI substrate is the first implementation. Since the configuration is exactly the same, only the process before forming the SOI substrate is shown here.

  In the step shown in FIG. 8A, the silicon substrate 10 as shown in FIG. 3A is prepared. Thereafter, oxygen ions and nitrogen ions are implanted from the surface 10 b side of the silicon substrate 10. At this time, oxygen ions are implanted from the position 10 μm deep from the surface 10 b to the position deeper than the silicon oxide film 12 in consideration of the film thickness of the SOI layer. Nitrogen ions are implanted from the deepest position where oxygen ions are implanted to a position deeper than the thickness of the silicon nitride film 11.

In the step shown in FIG. 8B, thereafter, a donor impurity (for example, P, As, Sb, etc.) or an acceptor impurity (for example, P, As, Sb, etc.) up to a surface layer portion in the silicon substrate 10, specifically, a depth corresponding to the SOI layer. , B, Al) are ion-implanted to a concentration of about 1 × 10 ¹⁹ to 1 × 10 ²¹ cm ^−3, for example, and then heat treatment is performed at a high temperature of 1000 ° C. or more to activate the impurities. Then, oxygen ions and nitrogen ions are reacted with silicon in the silicon substrate 10. Thereby, the silicon nitride film 11 and the silicon oxide film 12 are formed, and the SOI layer is formed, thereby completing the SOI substrate.

Thus, it is possible to form an SOI substrate using a single silicon substrate 10. In this way, the number of silicon substrates can be reduced and the manufacturing process for forming the SOI substrate can be simplified, so that the sensor manufacturing cost can be reduced.



(Seventh embodiment)
A seventh embodiment of the present invention will be described. In the first to sixth embodiments, the case where one embodiment of the present invention is applied to the thermal flow sensor S1 as a physical quantity sensor has been described. However, in the present embodiment, one embodiment of the present invention is applied to a thermopile infrared sensor. The case of applying will be described.

  FIG. 9 is a sectional view of the thermopile type infrared sensor S2 of the present embodiment. As shown in this figure, similarly to the first to sixth embodiments, the thermopile infrared sensor S2 of this embodiment also has a silicon substrate 10 as a supporting substrate, an insulating film 13 as a buried layer, and a semiconductor layer 14 as an SOI layer. The silicon substrate 10 is formed using an SOI substrate, and a cavity 10a is formed in the silicon substrate 10. A membrane is formed at a site where the cavity 10a is formed.

  Also in this embodiment, the semiconductor layer 14 is formed by thermally diffusing impurities in the silicon layer. An interlayer insulating film 40 made of, for example, BPSG is formed above the semiconductor layer 14, and a wiring layer 41 made of, for example, Al is formed. The contact in which the wiring layer 41 is formed on the interlayer insulating film 40 The semiconductor layer 14 is brought into contact with the hole.

  A protective film 42 made of, for example, TEOS is formed on the wiring layer 41 and the interlayer insulating film 40. In the protective film 42, an opening 42a for forming a pad by partially exposing the wiring layer 41 is formed.

  Furthermore, an infrared absorption film 43 made of, for example, carbon paste is formed on the protective film 42 only in the membrane. As described above, the wiring layer 41 is in contact with the semiconductor layer 14. Specifically, the wiring layer 41 is in contact with the semiconductor layer 14 below the infrared absorption film 43 inside the membrane and outside the membrane. It has been made. Of these contacts, the one located below the infrared absorption film 43 is a hot contact, and the one outside the membrane is a cold junction.

  In the thermopile infrared sensor S2 having such a configuration, when infrared rays are irradiated, the infrared absorption film 43 absorbs the infrared rays and generates heat. The heat is transferred to the hot junction, and the temperature of the hot junction rises, so that a thermoelectromotive force is generated between the cold junction. For this reason, the thermopile type infrared sensor S2 can detect the amount of infrared rays based on the thermoelectromotive force generated between the hot junction and the cold junction. At this time, since the hot junction is inside the membrane and the cold junction is outside the membrane, the temperature rises efficiently for the hot junction, and the temperature rise associated with the temperature rise of the hot junction can be reduced for the cold junction It becomes. In addition, since the semiconductor layer 14 is made of single crystal silicon instead of polycrystalline silicon, a low resistance value and a high thermoelectromotive force can be obtained even with the same impurity concentration, and further, there are no grain boundaries, resulting in variation in characteristics. It is also possible to obtain an effect of reducing the amount of material.

  Then, the manufacturing method of thermopile type infrared sensor S2 of this embodiment is demonstrated with reference to the manufacturing-process figure of thermopile type infrared sensor S2 shown in FIG.

[Step shown in FIG. 10A]
First, after preparing the SOI substrate described in the first to sixth embodiments, for example, the SOI substrate formed by the process of FIG. 3 of the first embodiment, in order to make the semiconductor layer 14 have a desired resistance value, Donor impurities (P, As, Sb) and acceptor impurities (B, Al) are ion-implanted and doped so that the impurity concentration is about 1 × 10 ¹⁶ to 1 × 10 ²¹ / cm ³ . The technique at this time may be the same as the process shown in FIG.

[Step shown in FIG. 10B]
The semiconductor layer 14 is patterned by etching. Thus, the semiconductor layer 14 is extended from the inside of the membrane to the outside of the membrane so that a portion that is a contact point with the wiring layer 41, that is, a hot contact point or a cold contact point is formed.

[Step shown in FIG. 10 (c)]
After the semiconductor layer 14 is thermally oxidized as necessary, an interlayer insulating film 40 made of BPSG is formed by a CVD method, and heat treatment is performed. Thereby, the level | step difference of the semiconductor layer 14 can be smoothed. Here, the interlayer insulating film 40 is formed of BPSG, but may be formed of an oxide film other than BPSG. Thereafter, the interlayer insulating film 40 is etched to open a contact hole. Furthermore, after Al is formed on the interlayer insulating film 40, the wiring layer 41 including a hot contact point, a cold contact point, and a portion to be a pad is formed by patterning the Al.

[Step shown in FIG. 10 (d)]
A protective film 42 made of TEOS is formed on the wiring layer 41 and the interlayer insulating film 40. Then, an opening 42 a is formed at a location corresponding to the portion of the protective film 42 that becomes the pad of the wiring layer 41. Although the protective film 42 is formed here by TEOS, it may be formed by an oxide film or a nitride film other than TEOS.

  Then, a silicon nitride film 20 is formed on the back surface of the SOI substrate by a CVD method. This film may be a silicon oxide film, but the silicon nitride film 20 is preferred because it functions as a mask for etching with KOH. After a region where the cavity 10a of the silicon substrate 10 is to be formed is opened by etching in the silicon nitride film 20, the cavity 10a is formed by performing anisotropic etching with KOH using the silicon nitride film 20 as a mask. To do. Thereby, a membrane is comprised. Finally, an infrared absorption film 43 made of carbon paste is formed on the protective film 42, and this is then patterned and left only in the membrane. Thereby, the thermopile type infrared sensor S2 shown in FIG. 9 is completed.

The thermopile infrared sensor S2 of the present embodiment described above also includes a silicon nitride film 11 disposed on the surface 10b of the silicon substrate 10 without forming the buried layer of the SOI substrate by only one layer of SiO _2. Yes. For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. Thereby, it is possible to obtain the same effect as in the first embodiment.

(Eighth embodiment)
An eighth embodiment of the present invention will be described. This embodiment demonstrates the case where one Embodiment of this invention is applied with respect to a gas sensor as a physical quantity sensor. The structure of the gas sensor is substantially the same as that of the thermopile type infrared sensor S2 described in the seventh embodiment, and therefore, different parts will be mainly described.

  11 and 12 are views showing the gas sensor S3 of the present embodiment, FIG. 11 is a sectional view of the gas sensor S3, and FIG. 12 is a top layout view of the gas sensor S3. As shown in FIG. 11, as in the first to seventh embodiments, the gas sensor S3 of this embodiment also includes an SOI substrate in which the silicon substrate 10 is a supporting substrate, the insulating film 13 is a buried layer, and the semiconductor layer 14 is an SOI layer. The silicon substrate 10 is formed with a cavity 10a, and a membrane is formed at the site where the cavity 10a is formed.

  An interlayer insulating film 50 made of, for example, BPSG is formed above the semiconductor layer 14, and a wiring layer 51 made of, for example, Al is formed, and a contact hole in which the wiring layer 51 is formed in the interlayer insulating film 50. Through the semiconductor layer 14.

A protective film 52 made of, for example, TEOS is formed on the wiring layer 51 and the interlayer insulating film 50. The protective film 52 is formed with an opening 52a for forming a pad by partially exposing the wiring layer 51 and an opening 52b for allowing contact with a gas sensitive film 53 described later. Yes. Further, a gas sensitive film 53 made of, for example, tin oxide (which can detect CO, NO _x , hydrogen, etc.) is formed on the upper layer of the protective film 52 so as to include the inside of the membrane. As shown in FIG. 12, the gas-sensitive film 53 is formed so as to cover the membrane, and is electrically connected to the wiring layer 51 on both sides of the semiconductor layer 14 below the gas-sensitive film 53, and the pad portion. By connecting external terminals to 51a and 51b, a current can be passed through the wiring layer 51, and the resistance value of the gas sensitive film 53 can be detected. In addition, pad portions 51c and 51d constituted by a part of the wiring layer 51 are also connected to the semiconductor layer 14, and by connecting an external terminal to the pad portions 51a and 51b, a current is passed through the semiconductor layer 14, A thinned portion in the membrane of the semiconductor layer 14 can be heated.

  In the gas sensor S3 having such a configuration, a current is passed through the semiconductor layer 14 through the wiring layer 51 to raise the temperature of the gas sensitive film 53 formed in the membrane, thereby causing an oxidation or reduction reaction with the target gas in the atmosphere. Make it. Thereby, since the resistance value of the gas sensitive film 53 is changed, the amount of the target gas can be detected by detecting the resistance value of the gas sensitive film 53 through the pad portion of the wiring layer 51. At this time, since the gas sensitive film 53 is in the membrane, the temperature can be increased efficiently. Note that the temperature rise is managed based on the resistance value of the semiconductor layer 14, but since the semiconductor layer 14 is made of single crystal silicon instead of polycrystalline silicon, a high resistance temperature coefficient (TCR) Thus, temperature measurement can be performed accurately. In addition, even with respect to the change in resistance over time that occurs at high temperatures, it is possible to obtain a gas sensor S3 in which single crystal silicon is less stable than polycrystalline silicon and can be used stably. It is also possible to obtain an effect of reducing the amount of material.

  FIG. 13 is a manufacturing process diagram of the gas sensor S3 of the present embodiment. The processes shown in FIGS. 13A to 13D are basically the same as those of the thermopile type infrared sensor S2 described above. The interlayer insulating film 50 instead of the interlayer insulating film 40 and the wiring layer instead of the wiring layer 41 are used. 51, the wiring layer 52 instead of the protective film 42, and the gas sensitive film 53 instead of the infrared absorption film 43 are formed, and the pattern layout of each film is different. In order to reduce the contact resistance between the gas sensitive film 43 and the wiring layer 51 or to prevent mixing, a thin film may be formed on the wiring layer 52 as necessary.

The gas sensor S3 of the present embodiment described above is also configured to include the silicon nitride film 11 disposed on the surface 10b of the silicon substrate 10 without forming the buried layer of the SOI substrate by only one layer of SiO ₂ . For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. Thereby, it is possible to obtain the same effect as in the first embodiment.

  In addition, although the example of the gas sensor which detects the resistance value change of the gas sensitive film | membrane 53 was described here, it is applicable also to the gas sensor of another detection principle.

(Ninth embodiment)
A ninth embodiment of the present invention will be described. This embodiment demonstrates the case where one Embodiment of this invention is applied with respect to a pressure sensor as a physical quantity sensor. Note that the structure of the pressure sensor is substantially the same as that of the thermopile type infrared sensor S2 described in the seventh embodiment, and therefore, different parts will be mainly described.

  14 and 15 are views showing the pressure sensor S4 of the present embodiment, FIG. 14 is a sectional view of the pressure sensor S4, and FIG. 15 is a schematic top view layout diagram of the pressure sensor S4. As shown in FIG. 11, as in the first to eighth embodiments, the pressure sensor S4 of this embodiment is also an SOI substrate in which the silicon substrate 10 is a supporting substrate, the insulating film 13 is a buried layer, and the semiconductor layer 14 is an SOI layer. A cavity 10a is formed in the silicon substrate 10, and a membrane is formed at the site where the cavity 10a is formed.

  As shown in FIG. 15, the semiconductor layer 14 is made of single crystal silicon having a (001) plane orientation, and a plurality of gauge resistors used for pressure detection are provided by a portion of the semiconductor layer 14 disposed in the membrane. Composed. For example, a plurality of gauge resistors are connected to a Wheatstone bridge, and the longitudinal direction of each gauge resistor is a <110> direction, and the longitudinal direction is a direction in which current flows to the gauge resistor (that is, a direction in which a resistance value is measured). The Each gauge resistor is arranged at the edge of the membrane.

  Further, an interlayer insulating film 60 made of, for example, BPSG is formed above the semiconductor layer 14, and a wiring layer 61 made of, for example, Al is formed. The wiring layer 61 is formed on the interlayer insulating film 60. The semiconductor layer 14 is brought into contact with the contact hole.

  A protective film 62 made of, for example, TEOS is formed on the wiring layer 61 and the interlayer insulating film 60. In the protective film 62, an opening 62a for forming a pad by partially exposing the wiring layer 61 is formed. Furthermore, a base glass 63 for constituting a reference pressure chamber that closes the cavity 10a below the membrane is joined to the back surface of the SOI substrate by anodic bonding.

  In the pressure sensor S4 having such a configuration, when a pressure to be measured is applied to the membrane, the membrane is displaced according to a differential pressure between the applied pressure and the pressure in the reference pressure chamber, and accordingly, the gauge Since the resistance value of the resistance changes due to the piezoresistance effect, the pressure can be detected by detecting the resistance value of the gauge resistance through the pad portion of the wiring layer 61. At this time, since the membrane can be constituted by the cavity 10a where the silicon substrate 10 does not remain as in the present embodiment, extremely low pressure measurement is possible (for example, 1 atm or less at full scale). It is also suitable for downsizing. Further, by making the semiconductor layer 14 a single crystal silicon instead of a polycrystalline silicon, a high piezoresistance effect can be obtained, and furthermore, since there are no grain boundaries, variation in characteristics (such as an offset voltage) is reduced. It can also be obtained.

  FIG. 16 is a manufacturing process diagram of the pressure sensor S4 of the present embodiment. The processes shown in FIGS. 16A to 16E are basically the same as those of the thermopile type infrared sensor S2 described above. The interlayer insulating film 60 is used instead of the interlayer insulating film 40, and the wiring layer is used instead of the wiring layer 41. 61, forming a wiring layer 62 instead of the protective film 42 is different. Then, after the cavity 10a is formed using the silicon nitride film 20 as a mask (step of FIG. 16E), the silicon nitride film 20 is removed, and the base glass 63 is bonded to the back surface of the SOI substrate by anodic bonding. The pressure sensor S4 is completed.

The pressure sensor S4 of the present embodiment described above is also configured to include the silicon nitride film 11 disposed on the surface 10b of the silicon substrate 10 without forming the buried layer of the SOI substrate by only one layer of SiO ₂ . For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. Thereby, it is possible to obtain the same effect as in the first embodiment.

(10th Embodiment)
A tenth embodiment of the present invention will be described. This embodiment demonstrates the case where one Embodiment of this invention is applied with respect to an acceleration sensor as a physical quantity sensor. Note that the structure of the acceleration sensor is substantially the same as that of the pressure sensor S4 described in the ninth embodiment, and thus different parts will be mainly described.

  FIG. 17 is a cross-sectional view of the acceleration sensor S5 of the present embodiment. As shown in FIG. 17, as in the first to seventh embodiments, the acceleration sensor S5 of the present embodiment is also an SOI substrate in which the silicon substrate 10 is a supporting substrate, the insulating film 13 is a buried layer, and the semiconductor layer 14 is an SOI layer. It is formed using. A cavity 10a is formed in the silicon substrate 10, and a membrane is formed at a portion where the cavity 10a is formed, but a weight 10e is formed by leaving the silicon substrate 10 at the center of the membrane. ing. Further, the base glass 63 provided in the pressure sensor S4 is eliminated. The other configuration is the same as that of the pressure sensor S4 described in the ninth embodiment, and a plurality of gauge resistors are configured by the semiconductor layer 14. The top surface layout of the semiconductor layer 14 is also the pressure sensor shown in FIG. It is the same as S4.

  In the acceleration sensor S5 having such a configuration, when acceleration occurs, when a stress due to the inertia of the weight portion 10e is applied to the membrane, the membrane is displaced according to the applied stress, and accordingly, the resistance of the gauge resistance Since the value changes due to the piezoresistive effect, the acceleration can be detected by detecting the resistance value of the gauge resistance through the pad portion of the wiring layer 61. Thereby, the same effect as in the ninth embodiment can be obtained. The manufacturing method of the acceleration sensor S5 of the present embodiment is almost the same as the manufacturing process of the pressure sensor S4 shown in FIG. 16, and it is only necessary to change the pattern of the cavity portion 10a in order to form the weight portion 10e. .

The acceleration sensor S5 of the present embodiment described above also includes a silicon nitride film 11 disposed on the surface 10b of the silicon substrate 10 without forming the buried layer of the SOI substrate by only one layer of SiO ₂ . For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. Thereby, it is possible to obtain the same effect as in the first embodiment.

(Eleventh embodiment)
An eleventh embodiment of the present invention will be described. This embodiment demonstrates the case where one Embodiment of this invention is applied with respect to the composite sensor which integrated the pressure sensor and the acceleration sensor as a physical quantity sensor. Note that the structure of the composite sensor is substantially the same as that of the pressure sensor S4 described in the ninth embodiment, and therefore different parts will be mainly described.

  FIG. 18 is a cross-sectional view of the composite sensor S6 of the present embodiment. As shown in FIG. 18, as in the first to seventh embodiments, the composite sensor S6 of this embodiment also has an SOI substrate in which the silicon substrate 10 is a supporting substrate, the insulating film 13 is a buried layer, and the semiconductor layer 14 is an SOI layer. It is formed using. The silicon substrate 10 is formed with a cavity 10a, and a membrane is formed at a portion where the cavity 10a is formed. Like the acceleration sensor S5 of the tenth embodiment, the silicon substrate 10 is formed at the center of the membrane. The weight part 10e is comprised by leaving. Further, the semiconductor layer 14 constitutes a plurality of gauge resistors. And the base glass 63 is provided in the back surface of SOI substrate similarly to pressure sensor S4 of 9th Embodiment. A counterbore (concave portion) 63a is formed at a location corresponding to the weight portion 10e in the pedestal glass 63, and the structure does not hinder the displacement of the weight portion 10e. Other structures are the same as those of the pressure sensor S4 described in the ninth embodiment.

  A composite sensor S6 having such a configuration may be used. The operation principle of the composite sensor S6 is the same as that of the pressure sensor S4 and the acceleration sensor S5. In addition, the manufacturing method of the acceleration sensor S5 of the present embodiment also uses a base glass 63 in which a counterbore 63a is formed, and the pattern of the cavity portion 10a is a pattern that can form the weight portion 10e. It may be the same as the manufacturing process of the pressure sensor S4 shown in FIG.

Also in the composite sensor S6 of the present embodiment described above, the buried layer of the SOI substrate without configuring the single layer of SiO _2, silicon nitride film disposed on the surface 10b of the silicon substrate 1011 it is also configured to include. For this reason, when the silicon substrate 10 is etched, the silicon nitride film 11 functions as an etching stopper, and the silicon oxide film 12 can be prevented from being removed. Thereby, it is possible to obtain the same effect as in the first embodiment.

  In the above, the counterbore 63a is provided on the base glass 63 of the composite sensor S6 so that the weight part 10e can be displaced. However, as shown in FIG. 19, the tip of the weight part 10e is separated from the base glass 63. It is good also as such a structure. Such a structure reduces the area of the region left in the position corresponding to the weight 10e in the silicon nitride film 20 used as a mask when forming the cavity 10a, and anisotropically etches the silicon substrate 10 with KOH. The silicon nitride film 20 in that region may not be removed by side etching at that time.

(Other embodiments)
In each of the above embodiments, a method for manufacturing an SOI substrate has been described. However, what has been described here is merely an example, and the methods described in each embodiment may be combined. For example, in the sixth embodiment, the case where the silicon nitride film 11 and the silicon oxide film 12 are formed by ion implantation of both nitrogen ions and oxygen ions has been described. The layer may be formed by deposition. In the first embodiment, the silicon oxide film 12 is formed on the surface 30a of the silicon substrate 30 as shown in FIG. 3D. However, the surface of the silicon nitride film 11 formed on the silicon substrate 10 is formed on the surface. The silicon substrate 30 may be bonded after the silicon oxide film 12 is directly formed.

  In the first embodiment, the silicon oxide film 12 is formed on the surface 30a of the silicon substrate 30 as shown in FIG. 3D. However, in the step shown in FIG. It is also possible to form the silicon nitride film 11 on the silicon oxide film 12 formed on the surface 30a and bond the surface 10b of the silicon substrate 10 and the silicon nitride film 11 together. In this case, a silicon nitride film or a silicon oxide film is also formed on the back surface 30b of the silicon substrate 30, but these are removed by polishing performed in the step shown in FIG. no problem.

  In the above-described embodiment, the heaters 15a and 15b have been described by taking as an example the configuration in which the heating resistor and the resistance temperature detector of Patent Document 1 are combined. However, the heating resistor and the resistance temperature detector are separated. It may be configured as a body.

  Moreover, in each said embodiment, although the cavity part 10a was formed by etching from the back surface 10c side of the silicon substrate 10, you may form the cavity part 10a by etching from the surface 10b side. For example, FIG. 20 is a cross-sectional view when the cavity 10a is formed from the surface 10b side of the silicon substrate 10 with respect to the thermal flow sensor S1 of the first embodiment. As shown in this figure, after forming the membrane and each component to be disposed thereon, a hole 70 is formed that penetrates through the membrane and reaches the surface 10b of the silicon substrate 10. Then, by performing isotropic etching, for example, through the hole 70, the cavity 10a can be formed. Also in this case, since the silicon nitride film 11 serves as an etching stopper, it is possible to obtain the same effects as in the above embodiments.

  In the seventh to eleventh embodiments, the case where the SOI substrate shown in FIG. 3 is used as an example has been described. However, the SOI substrate shown in FIGS. 6 to 8 may be used.

  Furthermore, in the above description, a physical quantity sensor has been described as an example of a semiconductor device having a thin film (membrane) structure. However, as long as it has a thin film structure using single crystal silicon, it is not limited to a physical quantity sensor. Absent. For example, the present invention may be applied to a thin film structure used as a simple heater.

It is a figure which shows schematic plan structure of thermal type flow sensor S1 concerning 1st Embodiment of this invention. It is a figure which shows schematic sectional structure of the thermal type flow sensor S1 along the AA line in FIG. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 shown in FIG. 1 and FIG. FIG. 4 is a cross-sectional view showing a manufacturing process of the thermal flow sensor S <b> 1 following FIG. 3. It is a figure regarding thermal type flow sensor S1 concerning a 3rd embodiment of the present invention, (a) is a sectional view of thermal type flow sensor S1, and (b) is formation of thermal type flow sensor S1 of (a). It is sectional drawing of the SOI substrate to be used. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 shown in FIG. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 concerning 5th Embodiment of this invention. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 concerning 6th Embodiment of this invention. It is sectional drawing of the thermopile type infrared sensor S2 concerning 7th Embodiment of this invention. It is a manufacturing-process figure of the thermopile type infrared sensor S2 shown in FIG. It is sectional drawing of gas sensor S3 concerning 8th Embodiment of this invention. FIG. 12 is a top layout view of the gas sensor S3 shown in FIG. 11. It is a manufacturing process figure of gas sensor S3 shown in FIG. It is sectional drawing of pressure sensor S4 concerning 9th Embodiment of this invention. FIG. 15 is a top layout view of the pressure sensor S4 shown in FIG. FIG. 15 is a manufacturing process diagram for the pressure sensor S4 shown in FIG. 14; It is sectional drawing of acceleration sensor S5 concerning 10th Embodiment of this invention. It is sectional drawing of composite sensor S6 concerning 11th Embodiment of this invention. It is sectional drawing which showed the modification of compound sensor S5. It is sectional drawing of thermal type flow sensor S1 shown in other embodiment of this invention.

Explanation of symbols

10 ... Silicon substrate, 10a ... Cavity, 10b ... Front surface, 10c ... Back surface,
10d ... opening, 11 ... silicon nitride film, 12 ... silicon oxide film, 13 ... insulating film,
14 ... Semiconductor layer, 15a, 15b ... Heater, 16a, 16b ... Thermometer,
17a to 17f ... wiring layer, 18 ... insulating film, 19a to 19f ... pad,
20 ... silicon nitride film, 21 ... silicon nitride film, 21a-21f ... wire,
22 ... Silicon oxide film, 30 ... Silicon substrate, 30a ... Front surface, 30b ... Back surface,
40, 50, 60 ... interlayer insulating film, 41, 51, 61 ... wiring layer,
42, 52, 62 ... protective film, 43 ... infrared absorbing film, 53 ... gas sensitive film,
63: Pedestal glass, S1: Thermal flow sensor, S2: Infrared sensor, S3: Gas sensor,
S4: Pressure sensor, S5: Acceleration sensor, S6: Composite sensor.

Claims (18)

A silicon substrate (10) having a cavity (10a) formed thereon;
On the surface (10b) side of the silicon substrate (10), an insulating film (13) formed to cover the cavity (10a);
A semiconductor layer (14) formed on the insulating film (13),
It is formed using an SOI substrate in which the silicon substrate (10) is a supporting substrate, the insulating film (13) is a buried layer, and the semiconductor layer (14) is an SOI layer, and the cavity ( In the method of manufacturing a physical quantity sensor configured by using the insulating film (13) formed in 10a) as a membrane,
As the SOI substrate, the insulating film (13) includes at least two layers of the silicon nitride film (11) and a silicon oxide film (12) disposed closer to the semiconductor layer (14) than the silicon nitride film (11). Preparing a layered structure including:
Etching the silicon substrate (10) of the SOI substrate to form the cavity (10a) in the silicon substrate (10). The step of preparing the SOI substrate includes a step of forming the silicon nitride film (11) included in the insulating film (13) using Si ₃ N ₄ or Si-rich Si _x N _y. The method for manufacturing a physical quantity sensor according to claim 1. The method of manufacturing a physical quantity sensor according to claim 2, wherein in the step of forming the silicon nitride film (11), the silicon nitride film (11) is formed as a film having a tensile stress. The step of forming the silicon nitride film (11) is a step of forming the silicon nitride film (11) on the surface (10b) of the silicon substrate (10). Manufacturing method of physical quantity sensor. In the step of forming the silicon nitride film (11), after ion implantation of nitrogen ions from the surface (10b) of the silicon substrate (10), heat treatment is performed, whereby a predetermined depth of the silicon substrate (10) is determined. The method of manufacturing a physical quantity sensor according to claim 2 or 3, wherein the silicon nitride film (11) is formed at a predetermined position. In the step of preparing the SOI substrate, the silicon oxide film (12) included in the insulating film (13) is formed using any one of SiO ₂ , SiO _x N _y containing minute amounts of N ₂ and porous silica. 6. The method of manufacturing a physical quantity sensor according to claim 1, further comprising a step. The step of forming the silicon oxide film (12) includes an upper surface of the silicon nitride film (11) formed on the surface (10b) of the silicon substrate (10) or a silicon substrate (for forming the SOI layer). The method of manufacturing a physical quantity sensor according to claim 6, wherein the silicon oxide film (12) is formed on a surface (30a) of (30). In the step of forming the silicon oxide film (12), oxygen ions are implanted from the surface (10b) of the silicon substrate (10), and then heat treatment is performed, whereby a predetermined depth of the silicon substrate (10) is determined. The method of manufacturing a physical quantity sensor according to claim 6, wherein the silicon oxide film (12) is formed at a predetermined position. The step of preparing the SOI substrate includes:
Forming the silicon nitride film (11) on the surface (10b) of the silicon substrate (10) to be the support substrate;
Providing an SOI layer silicon substrate (30) for forming the SOI layer, and forming the silicon oxide film (12) on a surface (30a) of the SOI layer silicon substrate (30);
Bonding the silicon nitride film (11) and the silicon oxide film (12) to integrate the silicon substrate (10) serving as the support substrate and the silicon substrate for the SOI layer (30);
The physical quantity sensor according to claim 1, further comprising a step of forming the SOI layer by thinning the silicon substrate for the SOI layer (30). Production method. Implanting hydrogen ions from the surface (30a) of the SOI layer silicon substrate (30) to a position corresponding to a depth corresponding to the film thickness of the SOI layer;
The step of dividing the SOI layer silicon substrate (30) at a position where the hydrogen ions are implanted by performing a heat treatment, and forming the SOI layer is included. Manufacturing method of physical quantity sensor. The method of manufacturing a physical quantity sensor according to any one of claims 1 to 10, wherein the semiconductor layer (14) is made of single crystal silicon. The physical quantity sensor uses the semiconductor layer (14) disposed in the membrane as a heater (15a, 15b), and based on the temperature change of the heater (15a, 15b) accompanying the flow of the fluid, The method of manufacturing a physical quantity sensor according to any one of claims 1 to 11, wherein the physical quantity sensor (S1) detects a flow rate. The physical quantity sensor is disposed above the semiconductor layer (14), and has a wiring layer (41) having a plurality of contacts serving as contact points with the semiconductor layer (14), and the wiring layer in the membrane. An infrared absorption film (43) disposed above (41), and the contact in the membrane among the contacts of the wiring layer (41) and the semiconductor layer (14) is a hot contact, When the infrared absorption film (43) is irradiated with infrared rays using a contact point outside the membrane as a cold contact point, a temperature difference between the hot contact point and the cold contact point that occurs as the temperature of the infrared absorption film (43) increases. The method of manufacturing a physical quantity sensor according to any one of claims 1 to 11, wherein the physical quantity sensor is an infrared sensor (S2) that detects the amount of the infrared rays as a physical quantity based on an electromotive force caused by the. The physical quantity sensor has a resistance value due to a reaction between a wiring layer (51) disposed above the semiconductor layer (14) and a measurement target gas disposed above the wiring layer (51) in the membrane. The gas-sensitive film (53) through a pad portion (51a, 51b) electrically connected to the gas-sensitive film (53) in the wiring layer (51). ) Can be detected, and current can flow through the semiconductor layer (14) through the pad portions (51c, 51d) of the wiring layer (51) electrically connected to the semiconductor layer (14). The temperature of the gas-sensitive film (53) in the membrane is raised by flowing an electric current through the semiconductor layer (14) to heat the gas, and the gas-sensitive film (53) reacts with the target gas to Gas sensitive membrane (53 By changing the resistance value method of manufacturing a physical quantity sensor according to any one of claims 1 to 11, characterized in that said a physical quantity as a gas sensor for detecting the amount of the target gas (S3). The physical quantity sensor is disposed on an upper layer of the semiconductor layer (14), and is disposed on a back surface of the silicon substrate (10), a wiring layer (61) electrically connected to the semiconductor layer (14). The pedestal (63) having the cavity (10a) as a pressure reference chamber, the semiconductor layer (14) disposed in the membrane as a gauge resistance, and the membrane accompanying displacement of the membrane due to pressure The method of manufacturing a physical quantity sensor according to any one of claims 1 to 11, wherein the physical quantity sensor is a pressure sensor (S4) that detects the pressure as the physical quantity based on a change in resistance value of the semiconductor layer (14). . The physical quantity sensor has a wiring layer (61) disposed on the semiconductor layer (14) and electrically connected to the semiconductor layer (14), and is formed in the cavity (10a). The semiconductor layer (14) having a weight portion (10e) provided in the insulating film (13), the semiconductor layer (14) disposed in the membrane as a gauge resistance, and accompanying the displacement of the membrane due to acceleration 12. The method of manufacturing a physical quantity sensor according to claim 1, wherein the physical quantity sensor is an acceleration sensor (S <b> 5) that detects the acceleration as the physical quantity based on a change in resistance value. The physical quantity sensor is disposed on an upper layer of the semiconductor layer (14), and is disposed on a back surface of the silicon substrate (10), a wiring layer (61) electrically connected to the semiconductor layer (14). Thus, the pedestal (63) having the cavity (10a) as a pressure reference chamber and the insulating film (13) formed in the cavity (10a) are provided so as to be separated from the pedestal (63). Based on a change in resistance value of the semiconductor layer (14) due to displacement of the membrane due to pressure or acceleration, the semiconductor layer (14) having a weight portion (10e) and having a gauge resistance as the semiconductor layer (14) disposed in the membrane The method of manufacturing a physical quantity sensor according to any one of claims 1 to 11, wherein the physical quantity is a composite sensor (S6) that detects the pressure or the acceleration as the physical quantity. A silicon substrate (10) having a cavity (10a) formed thereon;
On the surface (10b) side of the silicon substrate (10), an insulating film (13) formed to cover the cavity (10a);
A semiconductor layer (14) formed on the insulating film (13),
The silicon substrate (10) is formed using an SOI substrate having a supporting substrate, the insulating film (13) as a buried layer, and the semiconductor layer (14) as an SOI layer. The insulating film (13) formed in the cavity (10a) is configured as a membrane,
In the SOI substrate, the insulating film (13) includes at least two layers of the silicon nitride film (11) and a silicon oxide film (12) disposed closer to the semiconductor layer (14) than the silicon nitride film (11). A laminated structure including
The physical quantity sensor, wherein the cavity (10a) is formed by etching the silicon substrate (10) in the SOI substrate using the silicon nitride film (11) as a stopper.

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