JP2007286007A - Method of producing thermal type flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a thermal type flow sensor capable of abolishing a level difference of semiconductor layer configuring heaters and preventing degradation of sensor properties. <P>SOLUTION: A part except for a division comprising heater pattern out of SOI layers in the SOI substrate used for formation of a thermal type flow sensor S1 is selectively oxidized to form silicon oxide film 13 around the heater pattern. In other words, the silicon oxide film 13 of almost same thickness as the heater pattern is placed around the heaters 15a and 15b corresponding to the heater pattern, the thermometers 16a and 16b measuring ambient temperature and the wiring layers 17a to 17f. Thereby, the level difference of the heater pattern can be abolished and causes of degradation of sensor properties become possible to abolish, resulting from adhesion of contaminated material at the level difference divisions and emergence of peeling due to collision by a foregin matter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a flow sensor provided with a membrane composed of a thin film portion.

  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. After the SOI layer in the SOI substrate is thinned, an impurity is doped into the SOI layer, and the SOI layer By patterning, a heater pattern composed of a resistor made of a semiconductor layer doped with impurities is formed.
Japanese Patent Laid-Open No. 2001-12985

  However, in the thermal flow sensor described in Patent Document 1, since the heater pattern is configured by patterning the SOI layer so as to insulate the periphery of each part constituting the heater pattern, there is a step in the heater pattern. Arise. For this reason, it has become a factor of deterioration of sensor characteristics, such as contaminants adhering to the stepped portion or peeling when a foreign object collides.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a thermal flow sensor that eliminates a step in a semiconductor layer constituting a heater and prevents deterioration of sensor characteristics.

  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 (11) as a buried layer, and a semiconductor layer (12) as an SOI layer. 10) a thermal flow sensor configured by using the insulating film (11) formed in the cavity (10a) in 10) as a membrane, and surrounding the semiconductor layer (12) constituting the heater pattern formed by the SOI layer Is characterized in that it is surrounded by a silicon oxide film (13) formed by selectively oxidizing the SOI layer.

  Thus, the silicon oxide film (13) is formed around the heater pattern by selectively oxidizing the portion of the SOI layer of the SOI substrate other than the portion that becomes the heater pattern. That is, the silicon oxide film (13) having the same thickness as that of the heater pattern is arranged around the heaters (15a, 15b) and the wiring layers (17a to 17f) corresponding to the heater pattern.

Therefore, it is possible to eliminate the step of the heater pattern, and it is possible to eliminate the cause of deterioration of the sensor characteristics, such as contamination adheres to the step, or peeling occurs when a foreign object collides. . For this reason, it is possible to prevent deterioration of sensor characteristics in the thermal flow sensor. In the present invention, the SOI layer is selectively oxidized around the semiconductor layer (12) constituting the heater pattern constituted by the SOI layer. The silicon oxide film (13) is surrounded by the silicon oxide film (13), and the silicon oxide film (13) protrudes further toward the insulating film (11) than the heater pattern. The second feature is that a cavity (40) is formed with a gap therebetween.

  As described above, the silicon oxide film (13) formed by selectively oxidizing the SOI layer may protrude from the heater pattern toward the insulating film (11), thereby forming the cavity (40). .

  In the first and second features of the present invention, the top surfaces of the semiconductor layer (12) and the silicon oxide film (13) may be almost the same height, but for example, a process such as polishing is performed for planarization. By doing so, it is possible to obtain a higher effect if these upper surfaces have the same height.

  The first and second features of the present invention can also be grasped as the invention of the manufacturing method. For example, in the first feature of the present invention, an insulating film (11) is formed on the surface (10a) of the silicon substrate (10), and an SOI layer is formed on the upper surface of the insulating film (11). A step of preparing an SOI substrate, and a mask (31) that covers a region where the semiconductor layer (12) forming the heater pattern in the SOI layer is to be formed and exposes the periphery of the region where the semiconductor layer (12) is to be formed are disposed. And a step of forming a silicon oxide film (13) by selectively oxidizing the exposed portion of the SOI layer using the mask as a selective oxidation prevention mask, and removing the mask (31), and then removing the semiconductor layer (12 And a step of forming a protective film (18, 20) on the upper surface of the silicon oxide film (13).

  Also, a step of forming a cavity (10a) by etching from the surface (10a) of a silicon substrate (10) to be a support substrate, and an SOI layer forming silicon substrate (30) are prepared, and the SOI layer forming Disposing a mask that covers a region to be formed of the semiconductor layer (12) constituting the heater pattern on the surface (30a) of the silicon substrate (30) and exposes the periphery of the region to be formed of the semiconductor layer (12); The step of forming the silicon oxide film (13) by selectively oxidizing the exposed portion of the SOI layer forming silicon substrate (30) using the mask as a selective oxidation prevention mask, and the semiconductor layer after removing the mask (12) and a step of forming an insulating film (11) on the surface of the silicon oxide film (13), and attaching the surface (10a) of the silicon substrate (10) and the insulating film (11). Thus, the step of integrating the silicon substrate (10) constituting the supporting substrate and the silicon substrate for forming the SOI layer (30), and the thickness of the silicon substrate for forming the SOI layer (30) are reduced, thereby providing a heater. It can also be realized by a manufacturing method including a step of leaving only the semiconductor layer (12) and the silicon oxide film (13) constituting the pattern.

  On the other hand, regarding the second feature of the present invention, a step of forming an insulating film (11) on the surface (10a) of a silicon substrate (10) to be a supporting substrate and a silicon substrate (30) for forming an SOI layer are prepared. Covering the formation region of the semiconductor layer (12) constituting the heater pattern on the surface (30a) of the SOI layer forming silicon substrate (30), and exposing the periphery of the formation region of the semiconductor layer (12) The step (30a) of the silicon substrate for forming the SOI layer (30a) is performed by selectively oxidizing the exposed portion of the silicon substrate for forming the SOI layer (30) using the mask as a selective oxidation prevention mask. The silicon substrate constituting the supporting substrate is formed by bonding the silicon oxide film (13) and the insulating film (11) together with the step of forming the silicon oxide film (13) protruding from (10) and the SOI layer forming silicon substrate (30) are integrated, and the SOI layer forming silicon substrate (30) is thinned, whereby the semiconductor layer (12) and the silicon oxide constituting the heater pattern are formed. It can be realized by a manufacturing method including a step of leaving only the film (13).

  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 to which an embodiment of the present invention is applied, and FIG. 2 is a schematic cross-section of the thermal flow sensor S1 along the line AA in FIG. It is a figure which shows a structure.

  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 11 in which a silicon oxide film 11a, a silicon nitride film 11b, and a silicon oxide film 11c are stacked is formed on the surface 10b of the silicon substrate 10. The silicon nitride film 11b 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 11b is a film having a tensile stress, and has a thickness of, for example, about 0.05 to 0.4 μm. Further, the silicon oxide film 11c means a film having Si and O, and corresponds to, for example, SiO ₂ , SiO _x N _y containing a minute amount of N, porous silica, or the like. The silicon oxide film 11c is a film having a compressive stress, and has a thickness of about 0.01 to 1 μm, for example.

  A semiconductor layer 12 constituting a heater pattern formed by thermally diffusing impurities in the silicon layer is formed on the surface of the insulating film 11, and silicon oxide is surrounded so as to surround the semiconductor layer 12. A film 13 is formed and the periphery of the semiconductor layer 12 is insulated. The semiconductor layer 12 and the silicon oxide film 13 have substantially the same film thickness. Specifically, the semiconductor layer 12 forms heaters 15a and 15b, thermometers 16a and 16b for measuring the ambient temperature, and resistors constituting the wiring layers 17a to 17f. The heaters 15a and 15b The surroundings of the thermometers 16a and 16b and the wiring layers 17a to 17f are filled with the silicon oxide film 13.

  The silicon substrate 10, the insulating film 11, the semiconductor layer 12, and the silicon oxide film 13 configured in this way are the silicon substrate 10 as a supporting substrate, the insulating film 11 as a buried layer (BOX layer), the semiconductor layer 12 and the silicon oxide film 13. The silicon oxide film 13 is formed by selectively oxidizing portions of the SOI layer other than the heater pattern.

  Further, the semiconductor layer 12 and the silicon oxide film 13 are covered with an insulating film 18 made of BPSG or the like and a silicon nitride film 20. The insulating film 18 and the silicon nitride film 20 protect the surface of the thermal flow sensor S1. In addition, pads 19 a to 19 f made of aluminum or the like are electrically connected to desired locations of the semiconductor layer 12 through contact holes formed in predetermined portions of the insulating film 18 and the silicon nitride film 20. Then, the wires 21a to 21f are bonded to the pads 19a to 19f so that they are electrically connected to a control circuit provided outside the thermal flow 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, and heater temperature rises in connection with this.

  At this time, the heat of the heaters 15a and 15b is taken away by the air flow. There is a difference in how heat is taken away depending on the air flow rate. The current is adjusted on the control circuit side so that the heaters 15a and 15b always have a constant temperature. The flow rate is calculated using the change in the current value at this time as a signal. Further, depending on the direction of flow, there is a difference in how heat is taken away by the two heaters 15a and 15b. That is, the upstream side is more deprived of heat than the downstream side, and more current is required. From the difference between the two, the flow direction can be detected simultaneously with the flow rate. Each of the thermometers 16a and 16b is used for detecting a reference environmental temperature.

  For example, assume that air flows from the direction of the white arrow in FIG. Here, as described above, the heater 15a of the heaters 15a and 15b is deprived of much heat. Therefore, if the control circuit keeps the temperature (resistance value) of the heater 15a constant, the energization amount to the heater 15a is increased. On the contrary, since the air warmed by the heat generated by the heater 15a passes over the heater 15b, the heat radiation amount is reduced, and the energization amount to the heater 15b is reduced.

Therefore, the control circuit can detect the air flow rate and the flow direction based on the energization amount to the heater 15a and the heater 15b.
The heaters 15a and 15b referred to here are heating resistors whose resistance values change with temperature, and also have the function of a temperature sensitive resistor. That is, the temperature is kept constant by replacing the resistance values of the heaters 15a and 15b. For this reason, if a resistance value change due to stress (piezoresistance effect) occurs, the temperature cannot be maintained correctly, which causes an error.

  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 600 μm is used as the silicon substrate 10.

  Then, by oxidizing the surface 10b of the silicon substrate 10 to form a silicon oxide film 11a with a thickness of about 0.2 to 0.7 μm, LP-CVD (low pressure CVD) is formed on the upper surface of the silicon oxide film 11a. The silicon nitride film 11b is deposited by, for example, about 0.05 to 0.4 μm by the method. At this time, these film formation conditions are set so that the silicon nitride film 11b becomes a film having tensile stress. Most of the silicon nitride film 11b, silicon oxide film 11c, insulating film 18 and silicon nitride film 20 constituting the membrane are configured as films having compressive stress. However, when the compressive stress acts, the membrane is easily damaged. It has been known. For this reason, the membrane is not easily damaged by making the silicon nitride film 11b a film having a tensile stress.

  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, a silicon oxide film 11c is formed on the surface 30a (and the back surface 30b) of the silicon substrate 30 by thermal oxidation, for example, about 0.01 to 1 μm.

  Then, the two silicon substrates 10 and 30 are integrated by bonding the silicon nitride film 11b on the surface 10b side of the silicon substrate 10 and the silicon oxide film 11c on the surface 30a side of the silicon substrate 30 together. Specifically, the silicon nitride film 11b and the silicon oxide film 11c are overlapped so that no voids (voids) are formed between them, and heat treatment is performed at a high temperature of 1000 ° C. or higher. Thereby, an SOI substrate is formed in which the insulating film 11 constituting the buried layer is constituted by the silicon nitride film 11b and the silicon oxide film 11c.

[Step shown in FIG. 3B]
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. After that, after implanting donor impurities (for example, P, As, Sb, etc.) or acceptor impurities (for example, B, Al) into the SOI layer at, for example, about 1 × 10 ¹⁹ to 1 × 10 ²¹ cm ^−3. The semiconductor layer 12 is formed by performing an activation heat treatment.

  Here, impurities are doped by ion implantation, but originally donor impurities (for example, P, As, Sb, etc.) and acceptor impurities (for example, B, Al, etc.) are grown during the growth of the silicon crystal when the silicon substrate 30 is formed. ) Is doped, it is not necessary to perform ion implantation here.

  Although the case where the silicon substrate 30 is polished by CMP or the like has been described as an example here, the SOI layer may be formed by smart cut. For example, after the silicon oxide film 11c is formed on the surface 30a of the silicon substrate 30, hydrogen ions are implanted from above the silicon oxide film 11c. The implantation depth of hydrogen ions by ion implantation at this time is set to be equal to the thickness of the SOI layer (semiconductor layer 12). That is, if the SOI layer has a thickness of 1 μm, for example, the hydrogen ion implantation depth is also set to 1 μm. Then, by performing heat treatment, an SOI layer having a desired film thickness can be formed by dividing the silicon substrate 30 at a position where hydrogen ions are implanted.

[Step shown in FIG. 3 (c)]
After performing a step of removing phosphorous glass formed on the surface of the semiconductor layer 12 when the impurities are thermally diffused, for example, a silicon nitride film 31 is disposed on the surface of the semiconductor layer 12 as a mask, and photoetching is performed. A portion of the silicon oxide film 31 other than the heater pattern, that is, a portion corresponding to a region where the silicon oxide film 13 is to be formed is removed.

  Then, by performing selective oxidation using the silicon nitride film 31 as an anti-oxidation mask, the portion not covered with the silicon oxide film 31 is oxidized, and then the silicon nitride film 31 is removed. At this time, the heat treatment time and temperature at the time of selective oxidation are set so that the semiconductor layer 12 is completely oxidized to the deepest portion of the portion to be oxidized, that is, the position reaching the silicon oxide film 11c. Accordingly, the heaters 15a and 15b corresponding to the heater pattern, the thermometers 16a and 16b for measuring the environmental temperature, and the wiring layers 17a to 17f are left unoxidized, and the heaters 15a and 15b and the thermometers 16a and 16b and The periphery of the wiring layers 17 a to 17 f is filled with the silicon oxide film 13.

  At this time, when the step is formed by the selective oxidation to increase the thickness of the silicon oxide film 13 as compared with the portion of the semiconductor layer 12 constituting the heater pattern, before the silicon nitride film 31 is removed, By using the silicon nitride film 31 as an etching mask and etching the silicon oxide film 13 by an increase in film thickness after oxidation, the step can be further reduced. However, the step due to the increase in film thickness generated here is sufficiently smaller than the step of the heater pattern itself, that is, the step corresponding to the film thickness of the SOI layer as in the prior art. You don't have to.

[Step shown in FIG. 4 (a)]
In order to stabilize the surface of the semiconductor layer 12, the surface of the semiconductor layer 12 is slightly oxidized as necessary, and then the BPSG layer is deposited to form the insulating film 18. Subsequently, the surface step is flattened by performing an annealing process as necessary, and then the protective film is formed 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. A silicon nitride film 20 is deposited. This makes it possible to increase the thickness of the membrane, prevent damage when dust mixed in the air collides with the membrane, and suppress deformation of the membrane in response to air pressure fluctuations, resulting in poor 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.

  Subsequently, contact holes are formed in the insulating film 18 and the silicon nitride film 20 by a photoetching process. Then, after depositing aluminum, the pads 19a to 19f are formed by patterning the aluminum by a photoetching process. Here, aluminum is patterned to form the pads 19a to 19f. However, the lead wiring may be configured.

[Step shown in FIG. 4B]
A silicon nitride film 21 serving as a mask for etching the silicon substrate 10 is formed by LP-CVD or the like. And the part corresponding to the formation position of the opening part 10d of the silicon substrate 10 among the silicon nitride films 21 is opened by the photoetching process.

[Step shown in FIG. 4 (c)]
By performing anisotropic etching using the silicon nitride film 21 as a mask from the exposed portion until the silicon oxide film 11a is exposed using, for example, KOH, an opening 10d is formed in the silicon substrate 10; The cavity 10a is configured. 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 heater pattern is obtained by selectively oxidizing the portion of the SOI layer of the SOI substrate used for forming the thermal flow sensor S1 other than the portion that becomes the heater pattern. A silicon oxide film 13 is formed around the periphery of the substrate. That is, the silicon oxide film 13 having substantially the same thickness as the heater pattern is arranged around the heaters 15a and 15b corresponding to the heater pattern, the thermometers 16a and 16b for measuring the environmental temperature, and the wiring layers 17a to 17f. I am doing so.

  Therefore, it is possible to eliminate the step of the heater pattern, and it is possible to eliminate the cause of deterioration of the sensor characteristics, such as contamination adheres to the step, or peeling occurs when a foreign object collides. . For this reason, deterioration of the sensor characteristics in the thermal flow sensor S1 can be prevented.

(Second Embodiment)
A second embodiment of the present invention will be described. In the first embodiment, the silicon oxide film 11a, the silicon nitride film 11b, and the silicon oxide film 11c are formed between the silicon substrate 10 and the SOI layer in the step shown in FIG. Although the insulating film 11 is formed by the above, as shown in the sectional view of FIG. 5A, the SOI layer is formed on the silicon nitride film 11b without forming the silicon oxide film 11c. good.

  In this case, the cross-sectional configuration of the completed thermal flow sensor S1 is as shown in FIG. 5B, the insulating film 11 is composed of the silicon oxide film 11a and the silicon nitride film 11b, and the membrane is the silicon oxide film 11a and silicon nitride. The film 11b, the semiconductor layer 12, the silicon oxide film 13, the insulating film 18 and the silicon nitride film 20 are formed.

  In this structure, the surface 10b of the silicon substrate 10 serving as the support substrate is oxidized to form the silicon oxide film 11a, and the surface 30a of the silicon substrate 30 for forming the SOI layer is subjected to the LP-CVD method. For example, the silicon nitride film 11b is formed by bonding them together.

(Third embodiment)
A third embodiment of the present invention will be described. In the thermal flow sensor S1 of this embodiment, the silicon oxide film 11c is not formed on the base of the heater pattern as in the first embodiment, and the lower portion of the heater pattern is a hollow portion. And it is set as the structure which abolished the cavity 10a and the silicon nitride film 21 with which the thermal type flow sensor S1 of 1st Embodiment was equipped. Regarding other parts, the thermal flow sensor S1 of the present embodiment is the same as that of the first embodiment.

  6A and 6B are cross-sectional views showing a part of the manufacturing process of the thermal flow sensor S1 of the present embodiment. Hereinafter, with reference to these drawings, a method of manufacturing the thermal flow sensor S1 of the present embodiment will be described.

  First, in the step shown in FIG. 6A, the silicon oxide film 11a and the silicon nitride film 11b are formed on the surface 10b of the silicon substrate 10 by the same method as in the step shown in FIG.

  Next, as the silicon substrate 30 for forming the SOI layer, one originally doped with impurities is prepared, or a silicon substrate 30 before doping is prepared, and impurities are ion-implanted into the surface 30a. Although not shown, after a silicon nitride film, for example, is disposed on the surface 30a of the silicon substrate 30 as an anti-oxidation mask, a portion other than the heater pattern in the silicon nitride film, that is, the silicon oxide film 13 is formed by photoetching. The part corresponding to the planned area is removed.

  Subsequently, selective oxidation (so-called LOCOS oxidation) using the silicon nitride film as an anti-oxidation mask is performed to oxidize the portion not covered with the silicon nitride film, and then the silicon nitride film is removed. Accordingly, the heaters 15a and 15b corresponding to the heater pattern, the thermometers 16a and 16b for measuring the environmental temperature, and the wiring layers 17a to 17f are left unoxidized, and the heaters 15a and 15b and the thermometers 16a and 16b and The periphery of the wiring layers 17 a to 17 f is filled with the silicon oxide film 13. At this time, the heat treatment time and temperature at the time of selective oxidation are set so that the oxidized portion of the semiconductor layer 12 enters more than the thickness of the SOI layer from the surface 30a and sufficiently protrudes from the surface 30a. Yes.

  6B, the upper surface of the silicon oxide film 13 formed on the silicon substrate 30 is bonded to the upper surface of the silicon nitride film 11b formed on the silicon substrate 10, and the silicon substrate 10 and the silicon substrate 30 are integrated. Make it. Thereby, since the silicon oxide film 13 protrudes from the surface 30a (one surface of the heater pattern) of the silicon substrate 30, the heater pattern and the silicon nitride film 11b are separated from each other, and the cavity 40 is formed between them. The Thereafter, the silicon substrate 30 is thinned by polishing or the like and left by the thickness of the SOI layer, so that only the heater pattern and the silicon oxide film 13 surrounding the heater pattern are left.

  Regarding the subsequent steps, the thermal flow sensor S1 of the present embodiment is completed by performing the steps shown in FIG. 4A described in the first embodiment.

  Even if it does in this way, since it can prevent a level | step difference from being formed in a heater pattern, the effect similar to 1st Embodiment can be acquired. Furthermore, since the cavity 40 can be formed below the heater pattern, the film (heater pattern, insulating film 18 and silicon nitride film 20) above the cavity 40 including the heater pattern can be used as a membrane. Therefore, the steps of FIGS. 4B and 4C of the first embodiment need not be performed. Therefore, it is possible to simplify the manufacturing process of the thermal flow sensor S1. Further, even if the silicon nitride film 11b is formed on the upper surface of the heater portion 12 and the oxide film 13, the same effect can be obtained.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. In the thermal flow sensor S1 of the present embodiment, a cavity portion 10a is formed in advance with respect to the silicon substrate 10, and a membrane is constituted by a film above the cavity portion 10a. The silicon nitride film 21 provided in the thermal flow sensor S1 of the first embodiment is abolished. Regarding other parts, the thermal flow sensor S1 of the present embodiment is the same as that of the first embodiment.

  7A and 7B are cross-sectional views illustrating a part of the manufacturing process of the thermal flow sensor S1 of the present embodiment. Hereinafter, with reference to these drawings, a method of manufacturing the thermal flow sensor S1 of the present embodiment will be described.

  First, in the step shown in FIG. 7A, the silicon substrate 10 is prepared, a mask is arranged on the surface 10b of the silicon substrate 10, and then a cavity formation scheduled position in the mask is opened. Thereafter, a portion of the silicon substrate 10 exposed from the mask is deepened by dry etching or the like to form a cavity 10 a in the silicon substrate 10.

  On the other hand, the silicon oxide film 13 is formed on the surface 30a of the silicon substrate 30 by selective oxidation by the same method as the process shown in FIG. Accordingly, the heaters 15a and 15b corresponding to the heater pattern, the thermometers 16a and 16b for measuring the environmental temperature, and the wiring layers 17a to 17f are left unoxidized, and the heaters 15a and 15b and the thermometers 16a and 16b and The periphery of the wiring layers 17 a to 17 f is filled with the silicon oxide film 13.

  Subsequently, the silicon oxide film 13 formed on the surface 30a side of the silicon substrate 30 and the silicon nitride film used in the selective oxidation are removed by polishing or the like to expose the heater pattern. Thereafter, the insulating film 11 is formed by sequentially forming the silicon oxide film 11c, the silicon nitride film 11b, and the silicon oxide film 11a on the heater pattern.

  7B, the surface 10b of the silicon substrate 10 and the upper surface of the insulating film 11 formed on the silicon substrate 30 are bonded together so that the silicon substrate 10 and the silicon substrate 30 are integrated. As a result, the cavity portion 10a formed in the silicon substrate 10 causes the heater pattern and the silicon substrate 10 to be separated from each other in this portion, leaving the cavity portion 10a therebetween. Thereafter, the silicon substrate 30 is thinned by polishing or the like and left by the thickness of the SOI layer, so that only the heater pattern and the silicon oxide film 13 surrounding the heater pattern are left.

  Regarding the subsequent steps, the thermal flow sensor S1 of the present embodiment is completed by performing the steps shown in FIG. 4A described in the first embodiment.

  Even if it does in this way, since it can prevent a level | step difference from being formed in a heater pattern, the effect similar to 1st Embodiment can be acquired. Furthermore, the cavity 10a can be formed below the heater pattern, and the film (heater pattern, insulating film 18 and silicon nitride film 20) above the cavity 10a including the heater pattern can be used as a membrane. Therefore, the steps of FIGS. 4B and 4C of the first embodiment may not be performed. Therefore, it is possible to simplify the manufacturing process of the thermal flow sensor S1.

(Other embodiments)
In each of the above embodiments, the structure of each part can be changed as appropriate, and is not limited to that shown in each of the above embodiments. For example, as the configuration of the insulating film 11, the case where the three-layer structure of the silicon oxide film 11a, the silicon nitride film 11b, and the silicon oxide film 11c or the two-layer structure of the silicon oxide film 11a and the silicon nitride film 11b is adopted has been described. The insulating film 11 may be a single-layer film or may have a multilayer structure including more than three layers.

  Further, as described in the first embodiment, in the second to fourth embodiments, the silicon substrate 30 used for forming the SOI layer may be thinned by smart cut.

  Further, for example, as shown in the cross-sectional view of the thermal flow sensor S1 shown in FIG. 8, the structure including the cavity 40 as in the third embodiment and the cavity 10a as in the fourth embodiment are provided. It is good also as a structure which combined the structure.

  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.

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 the thermal type flow sensor S1 concerning 2nd Embodiment of this invention, (a) is sectional drawing of the SOI substrate used for manufacture of the thermal type flow sensor S1, (b) shows to (a). It is thermal type flow sensor S1 sectional drawing manufactured using the SOI substrate. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 concerning 3rd Embodiment of this invention. It is sectional drawing which shows the manufacturing process of thermal type flow sensor S1 concerning 4th Embodiment of this invention. It is sectional drawing of thermal type flow sensor S1 shown in other embodiment.

Explanation of symbols

10 ... Silicon substrate, 10a ... Cavity, 10b ... Front surface, 10c ... Back surface,
10d ... opening, 11 ... insulating film, 11a ... silicon oxide film,
11b ... silicon nitride film, 11c ... silicon oxide film, 12 ... semiconductor layer,
13 ... Silicon oxide film, 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 ... hollow part, S1 ... thermal flow sensor.

Claims (8)

A silicon substrate (10) having a cavity (10a) formed thereon;
On the surface (10b) side of the silicon substrate (10), an insulating film (11) formed to cover the cavity (10a);
A semiconductor layer (12) forming a heater pattern including heaters (15a, 15b) and wiring layers (17a-17f) formed on the insulating film (11);
The silicon substrate (10) is formed using an SOI substrate having a supporting substrate, the insulating film (11) as a buried layer, and the semiconductor layer (12) as an SOI layer. 10a) a thermal flow sensor configured with the insulating film (11) formed in 10a) as a membrane,
The periphery of the semiconductor layer (12) constituting the heater pattern constituted by the SOI layer is surrounded by a silicon oxide film (13) formed by selectively oxidizing the SOI layer. Thermal flow sensor. The thermal flow sensor according to claim 1, wherein the semiconductor layer (12) and the silicon oxide film (13) have the same thickness. A silicon substrate (10);
An insulating film (11) formed on the surface (10b) side of the silicon substrate (10);
A semiconductor layer (12) forming a heater pattern including heaters (15a, 15b) and wiring layers (17a-17f) formed on the insulating film (11);
A thermal flow sensor formed using an SOI substrate in which the silicon substrate (10) is a supporting substrate, the insulating film (11) is a buried layer, and the semiconductor layer (12) is an SOI layer;
The periphery of the semiconductor layer (12) constituting the heater pattern constituted by the SOI layer is surrounded by a silicon oxide film (13) formed by selectively oxidizing the SOI layer, and the silicon oxide film Since (13) protrudes to the insulating film (11) side from the heater pattern, the insulating film (11) and the heater pattern are separated from each other to form a cavity (40). A thermal flow sensor characterized by that. The thermal flow sensor according to any one of claims 1 to 3, wherein the upper surfaces of the semiconductor layer (12) and the silicon oxide film (13) have the same height. A silicon substrate (10) having a cavity (10a) formed thereon;
On the surface (10b) side of the silicon substrate (10), an insulating film (11) formed to cover the cavity (10a);
A semiconductor layer (12) forming a heater pattern including heaters (15a, 15b) and wiring layers (17a-17f) formed on the insulating film (11);
The silicon substrate (10) is formed using an SOI substrate having a supporting substrate, the insulating film (11) as a buried layer, and the semiconductor layer (12) as an SOI layer. 10a) is a method of manufacturing a thermal flow sensor comprising the insulating film (11) formed in 10a) as a membrane,
Preparing the SOI substrate in which the insulating film (11) is formed on the surface (10a) of the silicon substrate (10) and the SOI layer is formed on the upper surface of the insulating film (11); ,
Disposing a mask (31) that covers a region to be formed of the semiconductor layer (12) constituting the heater pattern in the SOI layer and exposes a periphery of the region to be formed of the semiconductor layer (12);
Forming a silicon oxide film (13) by selectively oxidizing the exposed portion of the SOI layer using the mask as a selective oxidation prevention mask;
Forming a protective film (18, 20) on the upper surface of the semiconductor layer (12) and the silicon oxide film (13) after removing the mask (31). Method for manufacturing a flow sensor. A silicon substrate (10);
An insulating film (11) formed on the surface (10b) side of the silicon substrate (10);
A semiconductor layer (12) forming a heater pattern including heaters (15a, 15b) and wiring layers (17a-17f) formed on the insulating film (11);
A method of manufacturing a thermal flow sensor using an SOI substrate in which the silicon substrate (10) is a supporting substrate, the insulating film (11) is a buried layer, and the semiconductor layer (12) is an SOI layer,
Forming the insulating film (11) on the surface (10a) of the silicon substrate (10) to be the support substrate;
Preparing the SOI layer forming silicon substrate (30), covering a region to be formed of the semiconductor layer (12) constituting the heater pattern in the surface (30a) of the SOI layer forming silicon substrate (30); Disposing a mask that exposes the periphery of a region where the semiconductor layer (12) is to be formed;
Silicon that protrudes from the surface (30a) of the SOI layer forming silicon substrate (30) by selectively oxidizing the exposed portion of the SOI layer forming silicon substrate (30) using the mask as a selective oxidation preventing mask. Forming an oxide film (13);
The step of integrating the silicon substrate (10) constituting the support substrate and the silicon substrate for forming the SOI layer (30) by bonding the silicon oxide film (13) and the insulating film (11) together. When,
And thinning the SOI layer forming silicon substrate (30) to leave only the semiconductor layer (12) and the silicon oxide film (13) constituting the heater pattern. A method for manufacturing a thermal flow sensor. A silicon substrate (10) having a cavity (10a) formed thereon;
On the surface (10b) side of the silicon substrate (10), an insulating film (11) formed to cover the cavity (10a);
A semiconductor layer (12) forming a heater pattern including heaters (15a, 15b) and wiring layers (17a-17f) formed on the insulating film (11);
The silicon substrate (10) is formed using an SOI substrate having a supporting substrate, the insulating film (11) as a buried layer, and the semiconductor layer (12) as an SOI layer. 10a) is a method of manufacturing a thermal flow sensor comprising the insulating film (11) formed in 10a) as a membrane,
Forming the cavity (10a) by etching from the surface (10a) of the silicon substrate (10) to be the support substrate;
Preparing the SOI layer forming silicon substrate (30), covering a region to be formed of the semiconductor layer (12) constituting the heater pattern in the surface (30a) of the SOI layer forming silicon substrate (30); Disposing a mask that exposes the periphery of a region where the semiconductor layer (12) is to be formed;
Forming a silicon oxide film (13) by selectively oxidizing the exposed portion of the SOI layer forming silicon substrate (30) using the mask as a selective oxidation prevention mask;
Forming the insulating film (11) on the surfaces of the semiconductor layer (12) and the silicon oxide film (13) after removing the mask;
By bonding the surface (10a) of the silicon substrate (10) and the insulating film (11), the silicon substrate (10) constituting the support substrate and the silicon substrate for forming the SOI layer (30) are bonded. Integrating the process;
And thinning the SOI layer forming silicon substrate (30) to leave only the semiconductor layer (12) and the silicon oxide film (13) constituting the heater pattern. A method for manufacturing a thermal flow sensor. The step of forming the insulating film (11) includes polishing the silicon oxide film (13) and the mask, removing the mask, and planarizing the silicon oxide film (13) to thereby form the semiconductor layer (12). The method of manufacturing a thermal flow sensor according to claim 7, further comprising:

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