JP2013160706A - Flow detector and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a sensor element by obtaining a flow detector which has excellent resistance to stress.SOLUTION: In a flow detector 1, a heating element 5 and an inlet-air temperature detection body 6 are provided on a front face side of a silicon wafer 51, and a rear face protection film 4 is provided on a rear face side of the silicon wafer. A cavity 2 formed by etching the rear face protection film and the silicon wafer is provided below the heating element on the rear face side of the silicon wafer.

Description

  The present invention relates to a flow rate detection device for measuring an inflow air amount of an internal combustion engine and a manufacturing method thereof.

  As a flow rate detection device used for measuring the amount of air flowing into an internal combustion engine, there is a flow rate detection device using a temperature-dependent resistor. In such a flow rate detection device, a sensor element including a heating element and an intake air temperature detection body is used. The sensor element measures the flow rate or flow rate of the fluid based on the heat transfer phenomenon from the heating element or the portion heated by the heating element to the fluid. Specifically, control is performed such that the temperature of the heating element is higher than the temperature detected by the intake air temperature detection body, and a voltage corresponding to the amount of heat radiated from the heating element to the fluid is captured as an output.

  In a flow rate detection device using a temperature-dependent resistor, a cavity that is a detection unit is formed by wet etching. At that time, if there is a pinhole on the wafer surface where the opening for providing the cavity is formed, there is a problem that the shape of the cavity is disturbed due to, for example, the etchant entering. For example, Patent Document 1 discloses a technique for preventing such disturbance of the cavity, and protective films formed by thermal oxidation are provided on both surfaces of the wafer.

  Further, in a flow rate detection apparatus having a micromachining (hereinafter referred to as MEMS) microstructure on the wafer surface, a cutting and separating process called dicing for cutting individual sensor elements from the wafer is performed. In a normal dicing process, the wafer is fixed on a dicing stage (chuck table) of the dicing apparatus by suction or the like with the sensor element forming surface side facing up. After mounting a thin disc-shaped cutting blade called a dicing blade on the flange, the wafer is cut by rotating at high speed on a dicing area (hereinafter referred to as “dicing line”) on the sensor element forming surface. Divide into sensor elements.

  At the time of this cutting, water is sprayed onto the cutting part and the dicing blade in order to suppress frictional heat generated by the cutting and to wash away fine debris (cutting chips) of the wafer. Since MEMS is a three-dimensional microstructure, it is vulnerable to direct external force and easily damaged. In order to alleviate this, there is also a method of cutting by reducing the amount of pure water sprayed.

  However, when the amount of water sprayed is reduced, a part of the cutting waste remains on the sensor element without being washed away. For this reason, problems such as cutting scraps on the sensor element affecting the element operation, and affecting the contact strength by fouling the pad portion to be wire-bonded occur. Moreover, even if the amount of water sprayed and the pressure are reduced, it cannot be said that the breakage of the fine structure can be reliably prevented. In this connection, for example, Patent Document 2 discloses that an adhesive tape is applied to the wafer surface for the purpose of reliably protecting the fine structure.

JP 11-295127 A JP 2004-349416 A

  In the wafer with a double-sided thermal oxide film as in Patent Document 1, the disturbance of the cavity shape due to small pits generated from scratches can be reduced, but cannot be completely eliminated. Also, for example, if scratches or indentations caused by contact with the metal chuck occur on the backside thermal oxide film forming the cavity, tetramethylammonium hydroxide (hereinafter referred to as TMAH) or potassium hydroxide (hereinafter referred to as KOH). In the wet silicon etching process using chemicals, there was a problem that the chemical solution penetrated from scratches or indentations on the back surface, resulting in rectangular etching traces called etch pits and disordered cavity shapes.

  Moreover, according to an aspect like patent document 2, film peeling and a chip | tip by dicing on the wafer surface side can be reduced, and the influence of cutting water can be reduced. However, the following problems still remain with respect to the wafer back surface.

  In other words, in the half-cut method in which a dicing tape is applied for the purpose of preventing the sensor elements separated by dicing from being scattered, cut to several tens of μm before the backmost outer surface, and then physically separated for each element, Since the separation is forcibly caused by the cut generated when the cutting is stopped immediately before, a large chip occurs in the section cut by expanding. Therefore, the end surface on the back side of the wafer is the most rough, and the silicon wafer is still likely to be chipped or cracked.

  Also, due to the improvement of dicing accuracy and the strength of the dicing tape, the through-cut (full-cut) method that cuts the entire wafer is the mainstream at present, but the processing stress is covered with the dicing tape even if through-cutting. Chipping occurs on the back surface. In particular, when the sensor element is assembled to the base material, bending stress to the sensor element is generated in the fixing part via the adhesive, so that even if the sensor element as a whole has a low stress concentration, chipping of the cut end face In addition, stress exceeding the theoretical tensile strength is applied to the tip of the part where the crack is generated, and the element is broken with apparently small stress, which affects the reliability of the sensor element. With the recent trend toward downsizing of sensor elements for the purpose of improving detection sensitivity and the like, the above-mentioned influence can be said to be more prominent because the fixing part of the sensor element is becoming thinner and more easily broken. In the through-cut method, the dicing tape may be excessively cut and the tape may be torn when expanded, resulting in chip displacement. Therefore, it cannot be said that effective measures are taken on the back surface of the wafer with respect to these dicing problems.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the reliability of the sensor element by obtaining a flow rate detection device having good resistance to stress stress. .

  In order to achieve the above-described object, the flow rate detection device of the present invention is provided with a heating element and a temperature detection body on the front surface side of the semiconductor wafer, and a back surface protection film is provided on the back surface of the semiconductor wafer, A cavity formed by etching the back surface protective film and the semiconductor wafer is provided on the back surface side of the semiconductor wafer and below the heating element.

  ADVANTAGE OF THE INVENTION According to this invention, the tolerance with respect to stress-like stress can be made favorable, and the reliability of a sensor element can be improved.

(A) is a top view of the sensor element in Embodiment 1, (b) is a cross-sectional structure figure at the time of cutting out the A-A 'site | part of (a). (A) is the figure which looked at a part of the sensor element before the division | segmentation of the sensor element in Embodiment 1 from the back, (b) is a cross section of the sensor element in the BB 'line of (a). FIG. It is the figure which showed typically the processing state which reaches after the division | segmentation before the division | segmentation of the sensor element in this Embodiment 1. FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment in which the present invention is implemented as a flow rate detection device for measuring an inflow air amount of an internal combustion engine will be described based on the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

Embodiment 1 FIG.
The flow rate detection device used in the first embodiment is a flow rate inspection device having a sensor element 3 in which a cavity 2 is formed by partially removing the back side of a semiconductor wafer whose front and back sides are thermally oxidized. A thin film (back surface protective film 4) for protecting the back surface side of the sensor element 3 is formed on the back surface excluding the cavity 2 of the sensor element 3 for the purpose of suppressing chipping and cracks in the cross section of the sensor element during dicing.

  Hereinafter, the structure and manufacturing process of the sensor element 3 according to the first embodiment will be described with reference to FIGS. FIG. 1A is a plan view of a sensor element 3 according to an embodiment of the present invention, and FIG. 1B is a cross-sectional structural view when a portion AA ′ in FIG. 1A is cut out. ing. FIG. 2A is a view of a part of the sensor element 3 before the sensor element is divided from the back according to the embodiment of the present invention, and the dotted line indicates the dicing line 11. FIG. 2B is a cross-sectional view of the sensor element 3 taken along the line BB ′ of FIG. 2A, schematically showing the wafer surface 12 side as the upper side in the drawing. The dotted line indicates the dicing line 11.

  The flow rate detection device 1 includes a sensor element 3 cut out, for example, from a silicon wafer (semiconductor wafer) 51 having a thickness of 0.5 mm into a long side of 12 mm and a short side of 3 mm. As shown in FIG. 1, a heating element 5 and an intake air temperature detection body (temperature detection body) 6 are formed on the front side of the sensor element 3. The heating element 5 is connected to an electrode 7a for electrical connection with the outside via a lead portion, and the intake air temperature detecting body 6 is connected to an electrode 7b via a lead portion.

  The sensor element 3 has a cavity 2 with the back surface partially removed, and has a thin film portion 8 on which a heating element 5 is formed above the cavity 2. Note that the vertical direction is set based on the vertical direction of the paper surface of FIGS. 1A and 2A and FIG. 3 described later. On the back surface side of the sensor element 3, a back surface protective film 4 which is a silicon film is formed as a so-called solid film. The back surface protective film 4 is present around the diaphragm opening of the cavity 2 on the back surface of the silicon wafer 51 and on the back surface side of the thermal oxide film 13.

  Next, a manufacturing method of the flow rate detection device, that is, a manufacturing process of the sensor element will be described with reference to FIG. FIG. 3 schematically shows a processed state from before to after the division of the sensor element 3 according to the embodiment of the present invention. 3 is shown as a cross section taken along line A-A ′ of FIG. 1A, as in FIG. 1B. 3 are described briefly. (A) is a state after forming the wafer surface side, (b) is a state after opening the electrode pads, and (c) is a state after forming the back surface protective film. , (D) is a state after processing of the cavity, and (e) is a diagram showing a mode of split processing of the sensor element. Hereinafter, detailed description of each illustrated state will be given.

  The process leading to the state of FIG. 3A will be described. First, a double-sided mirror-polished silicon wafer 51 having thermal oxide films 13 on both front and back surfaces is prepared. In the first embodiment of the present invention, the wafer having a thickness of 625 μm and the thermal oxide film 13 having a thickness of 500 nm is used.

  Then, an insulating support film 9 made of silicon nitride, silicon oxide film or the like having a thickness of 1 μm or more is formed on the surface of the silicon wafer 51 (surface of the thermal oxide film 13 on the wafer surface 12 side) by sputtering or CVD ( Chemical Vapor Deposition).

  Next, the heating element 5 made of a heat-sensitive resistance film such as silicon or platinum is formed on the support film 9 by a method such as vapor deposition or sputtering to a thickness of 500 nm, for example. Further, the surface protective film 10 is formed by the same method as the support film 9.

  Sputtering applied to the support film 9 and the surface protective film 10 includes, for example, a target made of silicon nitride (SiN) or silicon oxide (SiO2) and a Si (silicon) target used for reactive sputtering. It is also possible to form an insulating film. In Embodiment 1 of the present invention, reactive sputtering is used in which nitrogen gas is introduced using a Si target in order to increase the deposition rate. CVD includes atmospheric pressure CVD, low pressure CVD, plasma CVD, etc., and the film forming temperature is about 300 to 400 ° C. Examples of the special material gas include monosilane and disilane, and the nitride film is formed using ammonia gas, and the oxide film is formed using nitrous oxide or oxygen gas. There is a TEOS-CVD method as a method of providing a silicon oxide film. The CVD method is excellent in step coverage as compared with sputtering, and has good stress controllability, so that it is applied to various devices. The support film 9 and the surface protection film 10 are preferably formed by CVD with excellent step coverage, because an insulating film can be formed with a smaller film thickness and a dense film can be formed.

  A current path pattern is formed on the heating element 5 by using a well-known patterning method such as photolithography, wet etching, or dry etching using silicon, platinum, or the like. Although not shown in FIG. 3, the intake air temperature detection body 6 made of a heat-sensitive resistance film such as silicon or platinum is also formed in the same manner as the heating element 5. Next, as shown in FIG. 3B, the surface protective film 10 on the electrode 7b is removed in order to make electrical connection to the outside by a method such as wire bonding with respect to the electrode 7b.

  Next, as shown in FIG. 3C, the back surface protective film 4 is formed on the thermal oxide film 13 on the back surface side of the wafer 51. The back surface protective film 4 is provided by sputtering, and the film thickness is, for example, in the range of 1 μm to several tens of μm.

  Thereafter, as shown in FIG. 3D, the back surface protection film 4 and the thermal oxide film 13 are sequentially subjected to photolithography, and isotropically performed by dry etching with a mixed gas of CF4 (carbon tetrafluoride) and oxygen, for example. After etching holes are formed by conducting reactive etching, for example, resist ashing using a technique such as resist plasma ashing, dipping in a bath heated with TMAH or KOH, and performing wet etching, FIG. A cavity 2 having a trapezoidal cross section as shown in d) is formed below the heating element 5. In this way, a plurality of sensor elements 3 are formed on the silicon wafer 51.

  Next, the dicing line 11 is cut with a dicing saw to obtain the sensor element 3 as shown in FIG.

  According to the first embodiment as described above, at the time of dicing, the cavity 2 is formed after the back surface protective film 4 made of, for example, carbon or silicon is provided on the back surface of the wafer as shown in FIG. Furthermore, by performing dicing, the occurrence of physical contact scratches such as chucks is suppressed, and the formation of etch pits and cavities are reduced, and even if the back surface protective film 4 is chipped or cracked, It is possible to suppress the occurrence of large chips and cracks in the thermal oxide film 13 on the back surface side and the inside of the silicon wafer 51. That is, the back surface protective film 4 functions as a film that covers the scratches on the back surface of the wafer when the cavity is formed, and as a buffer film on the back surface of the wafer when dicing. Thereby, the weakening at the time of the diaphragm pressurization by the local stress concentration produced when a sensor element is assembled | attached to a support body etc. can be suppressed. Further, for example, by applying a silicon nitride film (SiN) or a silicon oxide film (SiO 2) to the back surface protective film 4, it can be used as a protective film for anisotropic etching by TMAH or KOH.

In the above description, the silicon wafer 51 with the thermal oxide film 13 is used. However, a film may be formed by TEOS-CVD as an alternative to the thermal oxide film 13, for example. Further, an aluminum oxide film or a nitride film may be used as the insulating film of the support film 9 or the surface protective film 10. Further, a silicon insulating film and an aluminum-based insulating film may be used for either the support film 9 or the surface protective film 10.

  In addition to platinum, the heating element 5 may be made of silicon, an alloy containing silicon, nickel, an alloy containing nickel, chromium, or chromium, thereby providing a required line width pattern. In addition, it is desirable to apply a relatively hard material such as an alumina-based oxide film, a nitride film, or a carbon film to the back surface protective film 4.

  The cavity 2 is provided by utilizing anisotropic etching of silicon. For example, the cavity 2 may be formed by physical etching such as deep etching or milling by ICP-RIE (reactive ion etching of dielectric coupling method). .

  Further, the above description has been made using the silicon wafer 51 that has been subjected to double-sided mirror polishing. However, for example, the sensor element 3 may be formed of the silicon wafer 51 that is a single-sided mirror. In this case, the heating element 5, the support film 9, and the surface protection film 10 are provided on the mirror polished surface, and the cavity 2 is provided on the rough surface on the rough surface side to form the sensor element 3.

  Further, although the back surface protective film 4 is formed after the electrode pad opening in FIG. 3B, it may be formed between the formation of the wafer surface in FIG. 3A and the electrode pad opening in FIG. Absent. In this case, there is an advantage that it is possible to obtain a buffering effect against physical contact damage such as a chuck on the back surface of the wafer.

Embodiment 2. FIG.
As the second embodiment of the present invention, the back surface protective film can be formed as follows. That is, in the second embodiment, when the back surface protective film 4 is formed by sputtering, the back surface protective film 4 is formed as a porous thin film, for example, by increasing the argon pressure to increase the porosity of the thin film. To do.

  According to this, the back surface protective film 4 is formed with a recess for improving the compatibility with the adhesive, and the compatibility with the adhesive is improved, so that the excess adhesive is applied to the surface of the sensor element 3 and the cavity 2. An effect of suppressing the protrusion can be expected.

  Although the contents of the present invention have been specifically described with reference to the preferred embodiments, various modifications can be made by those skilled in the art based on the basic technical idea and teachings of the present invention. It is self-explanatory.

  For example, the back surface protective film can be formed by CVD instead of sputtering.

  DESCRIPTION OF SYMBOLS 1 Flow rate detection apparatus, 2 Cavity, 4 Back surface protective film, 5 Heat generating body, 6 Intake air temperature detection body (temperature detection body), 13 Thermal oxide film, 51 Silicon wafer (semiconductor wafer).

Claims (8)

A heating element and a temperature detector are provided on the surface side of the semiconductor wafer,
A back surface protective film is provided on the back surface of the semiconductor wafer,
A cavity formed by etching the back surface protective film and the semiconductor wafer is provided on the back surface side of the semiconductor wafer and below the heating element.
Flow rate detection device. At least the back surface of the semiconductor wafer has a thermal oxide film,
The back surface protective film is provided on the back surface of the thermal oxide film,
The flow rate detection device according to claim 1. The thermal oxide film is a silicon oxide film,
The back surface protective film is a silicon film, an alumina-based oxide film, a nitride film, or a carbon film.
The flow rate detection device according to claim 2.   4. The flow rate detection device according to claim 1, wherein the back surface of the semiconductor wafer is a mirror-polished mirror surface or a rough surface.   The flow rate detection device according to any one of claims 1 to 4, wherein the back surface protective film is a porous thin film. A heating element and a temperature detector are provided on the front side of the semiconductor wafer, and a back surface protective film is provided on the back side of the semiconductor wafer,
After providing the back surface protective film, a cavity is formed by etching the back surface protective film and the semiconductor wafer on the back surface side of the semiconductor wafer and below the heating element.
A method for manufacturing a flow rate detection device.   The method for manufacturing a flow rate detection device according to claim 6, wherein the back surface protective film is formed by sputtering.   The method for manufacturing a flow rate detection device according to claim 6, wherein the back surface protective film is formed by CVD.

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