JPH0634411A - Flow sensor and its manufacture - Google Patents

Abstract

PURPOSE:To easily separate a sensor chip from a wafer and to prevent the occurrence of a fault caused by dust adhering to the side face of the sensor chip even when the chip is formed to an inverted trapezoidal shape. CONSTITUTION:At the time of forming grid-shaped grooves for separating chips by plasma etching, an etching mask having such a pattern that the width of the grooves becomes wider at the parts corresponding to the four corners of the chips is used. When the chips are fitted, in addition, the side faces of the chips are surrounded with an insulating protective body provided with a slope in the flowing direction of a fluid so as to prevent the adhesion of dust contained in the fluid to the side faces of the chips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor manufacturing method and a flow sensor for measuring the flow rate of a fluid, since the resistance value of a bridge circuit formed by a thin film resistor changes as the fluid passes through. .

[0002]

2. Description of the Related Art A flow sensor chip capable of measuring a flow rate is shown in FIG. 3 when a fluid passes through a thin film resistor which is heated with a constant power consumption and the resistance value of the resistor changes. It has a structure as shown in the plan view of (a) and the sectional view of (b). That is, on the surface of the silicon substrate 1 having the cavity 6, on the underlying dielectric layer 3 formed via the stop layer 2 made of a thermal oxide film for preventing plasma damage, two upstream sides are provided. Thin film resistor
41 and 42 and downstream side thin film resistors 43 and 44, and the protective layer 5 covers them. Terminal electrodes 7 are connected to both ends of each thin film resistor. And four thin film resistors 4
A bridge circuit as shown in FIG. 4 is formed by 1, 42, 43, and 44. When a constant current flows through this circuit by the power supply 11, the temperatures of the four thin film resistors rise. When the fluid 12 flows at a right angle in the length direction on the surface of the thin film resistor, the temperature of the upstream thin film resistors 41 and 42 is greatly reduced.
The temperatures of the downstream side thin film resistors 43 and 44 do not change much. This is wired in a bridge circuit so that the output 13 becomes large, and a method of calculating the flow rate is used.

Such a flow sensor has a CV on a stop layer 2 made of a thermal oxide film on the surface of a silicon substrate 1.
The SiO ₂ layer 3 is formed by the D method or the sputtering method, a nickel film is then formed thereon by the sputtering method, and the thin film resistors 41, 42, 43, 44 on the upstream side and the downstream side are formed by the photolithography method. Pattern this thin film resistor
After covering with the protective layer 5 made of Si ₃ N ₄ , the electrode 7
Is formed, a mask is provided on the surface opposite to the substrate 1, and the cavity 6 is processed below the thin film resistor by plasma etching. Due to the processing of the cavity 6, the silicon substrate 1 does not exist below the detection portion formed of the thin film resistor,
Since only the diaphragm portion 31 of the underlying dielectric layer 3 is used, the heat flow rate is reduced, and the response speed to the fluid and the detection sensitivity are improved.

The size of the flow sensor chip is 2.5 mm
It is a corner and is manufactured by dividing a single silicon wafer, for example, having a diameter of 4 inches. In order to facilitate such division, the lattice-shaped grooves 8 are formed simultaneously with the processing of the cavity 6.

[0005]

FIG. 5 shows a mask pattern for plasma etching of a substrate, which has a rectangular opening 61 for forming the cavity 6 and a width of 40 μm for forming the groove 8.
It has openings 81 in the form of a lattice. However, even if the groove 8 is formed in this way, when the chip is divided into chips, the underlying dielectric layer 3
The diaphragm is easily damaged. To prevent this, if the width of the opening 81 is widened to facilitate the division of the wafer, the side etching of the silicon substrate 1 is large, so that the chip is cracked or the cross section of the chip becomes an inverted trapezoid.
Since the bottom surface becomes smaller, defects may occur during chip bonding and bonding. Furthermore, dust and mist in the measurement gas adhere to the side surface of the silicon substrate 1 and fly up to cause a short circuit of the bonding wire, or cause dust to adhere to the sensor portion. The adhesion of dust to the sensor unit causes a change in sensor sensitivity and the occurrence of drift. Such adhesion of dust and mist to the side surface of the base 1 is particularly remarkable when the cross section of the base 1 has an inverted trapezoidal shape.

An object of the present invention is to solve the above problems and to provide a method of manufacturing a flow sensor in which the diaphragm is less damaged when the chip is divided. Another object is to provide a flow sensor in which dust and mist are less likely to adhere to the side surface of the sensor base during use.

[0007]

In order to achieve the above object, the present invention provides a mask on the back surface of a substrate having upstream and downstream thin film resistors on the surface through an underlying dielectric layer. In the method of manufacturing a flow sensor, a lattice-like groove is formed by providing a cavity below the thin-film resistor and a lattice-like groove for dividing the substrate into a sensor base by etching from the opening of the mask. For this purpose, the width of the mask opening is partially widened. Then, it is effective that the widened portion includes the intersection points of the lattice. Further, in the flow sensor of the present invention, it is assumed that the side surface of the sensor base body having the thin film resistor on the surface thereof is surrounded by the insulating protective body having the inclined surface in the fluid passage direction.

[0008]

By not widening the width of the groove for facilitating the division of the chip but widening it partly, the damage of the diaphragm during the dicing is reduced and the damage of the chip is reduced. On the other hand, by enclosing the side surface of the chip with a protective body having an inclined surface that does not obstruct the flow of fluid,
Even if the measurement fluid is allowed to flow for a long time, it becomes difficult for dust and mist to adhere to the side surface of the sensor substrate, and the obstacles due to the adhered dust and mist are eliminated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a mask pattern for plasma etching used in one embodiment of the first aspect of the present invention, which is for dividing into a lattice shape surrounding an opening 61 for forming the cavity 6 shown in FIG. An opening 81 for forming the groove 8 is formed, and a wide opening 82 having a width of 100 μm is formed in the vicinity of the intersection. Using this mask, the stop layer 2, the underlying dielectric layer 3, the thin film resistors 41 to 44, and the protective layer 5 are formed.
Plasma etching is performed from the back surface side of the silicon wafer of μm. The stop layer 2 serves to prevent plasma damage at that time. The large opening 61 is etched until the diaphragm of the underlying dielectric layer 3 is formed, and the etching from the narrow opening 81 reaches a depth of about 200 μm.
However, since the etching from the wide opening portion 82 becomes deeper than that, the division becomes easy when the wafer is thereafter made into chips by braking. The wide openings 82 may be formed not only in the four corners of the chip as described above but also in other portions as long as the chip itself is not broken.

FIGS. 2 (a) and 2 (b) show a second embodiment of the present invention. As can be seen from FIG. 2 (b) which is a sectional view taken along the plane B of FIG. 2 (a), the base of the sensor chip is shown. The silicon substrate 1 supporting the dielectric layer 3 has an inverted trapezoidal cross-sectional shape by plasma etching, and a protective body 9 surrounds the periphery thereof.
The protector 9 is made of epoxy resin and has a roof-like structure having inclined surfaces 91 and 92 in the direction in which the fluid 12 flows. The fluid 12 flows along the inclined surfaces 91 and 92, and even if dust and mist are mixed with the fluid, the fluid 12 flows left and right on the surface without adhering to the side surface of the chip.
Does not adhere to the surface of 31. The protector may be made of ceramics.

[0011]

As described above, according to the present invention, the dividing groove formed at the same time as the plasma etching for forming the diaphragm structure is partially widened, so that the substrate can be divided into the base body more easily than before. It was possible to prevent the damage of the diaphragm portion or the cracking of the substrate and improve the yield.

Further, according to the present invention, by enclosing the side surface of the substrate with an insulating protective body having an inclined surface that does not impede the flow of fluid, dust and mist do not adhere to the side surface, and the bonding wire is short-circuited. It was possible to prevent changes in sensor sensitivity and the occurrence of drift due to contamination of the sensor and the sensor.

[Brief description of drawings]

FIG. 1 is a plan view of a plasma etching mask used in an embodiment of the present invention.

2A and 2B show a protector according to an embodiment of the present invention, in which FIG. 2A is a mounting view, and FIG.

FIG. 3 shows a flow sensor chip, (a) is a plan view,
(b) is a sectional view taken along the line AA of (a).

FIG. 4 is a circuit diagram of a detection circuit of a flow sensor.

FIG. 5 is a plan view of a conventional plasma etching mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Stop layer 3 Underlying dielectric layer 31 Diaphragm part 41 Upstream side thin film resistor 42 Upstream side thin film resistor 43 Downstream side thin film resistor 44 Downstream side thin film resistor 5 Protective layer 6 Cavity 61 Cavity mask opening 81 Groove mask opening 82 Wide opening 9 Protective body 91 Sloping surface 92 Sloping surface 12 Fluid

Claims (3)

[Claims] 1. A mask is provided on the back surface of a substrate having upstream and downstream thin film resistors with an underlying dielectric layer on the front surface, and a mask is provided below the thin film resistor by etching from the opening of the mask. In a method of manufacturing a flow sensor for forming a lattice-shaped groove for dividing a cavity and a substrate into a sensor base, a width of a mask opening for forming the lattice-shaped groove is partially widened. Flow sensor manufacturing method. 2. The method for manufacturing a flow sensor according to claim 1, wherein the portion of which the width is wide includes an intersection of lattices. 3. A flow sensor characterized in that a side surface of a sensor substrate having a thin film resistor on the surface of which is provided with an underlying dielectric layer is surrounded by an insulating protective body having an inclined surface in a fluid passage direction. .