JP2010164412A - Acceleration sensor device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor sensor device having a small, simple structure that is superior in temperature stability, more specifically, an acceleration sensor device at low cost. <P>SOLUTION: A circuit chip and a MEMS assembly are piled up on a circuit board. These components and metal wires connecting them to each other are sealed with a silicone resin having a low elastic modulus. Preferably, the circuit board is selected from among a glass epoxy resin board, an aluminum board and an LTCC board. Accordingly, it is possible to provide an acceleration sensor device having a small, simple structure that is superior in temperature stability at low cost, as compared to a structure that uses a hollow-type ceramic package. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to MEMS (Micro-Electro-Mechanical System).
ems) The present invention relates to a semiconductor sensor device having a chip, and more particularly to an acceleration sensor device having a MEMS chip having a movable part and a method of manufacturing the acceleration sensor device.

By combining semiconductor manufacturing process technology with machining technology and material technology,
The MEMS technology for realizing a system having a three-dimensional microstructure on a semiconductor substrate can be applied to a very wide range of fields. In particular, these semiconductor sensor devices used for automobiles, airplanes, portable terminal devices, toys and the like are attracting attention in the field of detecting physical quantities such as acceleration, angular velocity, and pressure.

These semiconductor sensor devices are characterized by having movable parts formed by MEMS technology. A change in the movable part is detected by a resistance change or a capacitance change of the piezoresistive element, and data processing is performed to obtain values such as acceleration, angular velocity, pressure, and the like.

Acceleration sensor devices for portable terminal devices and game consoles whose market has been expanding in recent years can relax accuracy and reliability standards compared to in-vehicle sensors, but demands for lower prices and smaller sizes are more severe. It has become. For this reason, a highly reliable but expensive hollow ceramic package is changed to a mold-type resin package that has a proven track record in semiconductors and is inexpensive, and products that support lower prices and smaller sizes are increasing.

Non-Patent Document 1 discloses a comparison of sensor characteristics when an acceleration sensor chip having the same specifications is assembled with a hollow ceramic package and a molded resin package. In a resin package that is different from a hollow package, the sensor chip is surrounded directly by resin or a lead frame, and the sensor output voltage offset variation and temperature stability are affected by the stress and temperature change from components with different thermal expansion coefficients. The decline in sex is a problem.

Furthermore, since the downsizing of the semiconductor sensor chip tends to sacrifice the symmetry of the semiconductor sensor chip itself, the above-described problem of the decrease in temperature stability becomes more conspicuous when the semiconductor sensor chip is downsized.

Patent Documents 1 and 2 apply semiconductor resin sealing technology (resin molding technology), and MEM
A semiconductor sensor device is disclosed in which the S assembly is covered with a low-elasticity resin, and the temperature stability is improved by suppressing the stress change of the sensor chip due to the temperature change.

JP-A-10-170380 JP 2000-214177 A

“Chip scale packaging of a MEMS accelerometer”, L.M. E. Felton, et al, Proc. 2004 Electric Components and Technology Conference, pp. 869-873, (2004)

Patent Document 1 discloses a structure in which a sensor chip and a circuit chip are arranged side by side on a lead frame, only the circuit chip side is resin-molded, and the sensor chip side is covered with a low elastic modulus protective resin. Although it is possible to improve the temperature stability of the semiconductor sensor device by suppressing the stress change applied to the sensor chip due to the temperature change, the two chips are arranged side by side and different resin is used for each region, so the package size is small Is difficult. In addition, the lead frame and the mold have complicated shapes, and the use of two types of sealing resins in two stages complicates the sensor device structure and the manufacturing process.

Patent Document 2 discloses a structure in which a sensor chip and a circuit chip are stacked on a lead frame, and a buffer member is disposed between the sensor chip and a mold resin that wraps the sensor chip. By suppressing the stress change applied to the sensor chip due to the temperature change, the temperature stability of the semiconductor sensor device can be improved, but a buffer member layer is provided around the chip and the outside is further resin molded, It is difficult to reduce the size of the package. Moreover, if the buffer member layer is formed stably or two types of resins are used in two stages, the sensor device structure and the manufacturing process become complicated.

In any of the above-described methods, the structure of the sensor device becomes complicated, so that analysis such as stress simulation becomes complicated. Also, the manufacturing process itself becomes complicated,
Corresponding to inexpensive parts for consumer use becomes difficult in terms of cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object thereof is to provide a semiconductor sensor device having a simple structure, a small size, and excellent temperature stability, more specifically, an acceleration sensor device at low cost. I have to.

The acceleration sensor device of the present invention includes a MEMS acceleration sensor chip (hereinafter, referred to as a MEMS acceleration sensor chip having a movable part).
MEMS chip) and a cap chip that seals at least the movable part of the MEMS chip.
An EMS acceleration sensor assembly (hereinafter referred to as a MEMS assembly) is formed, and the MEMS is formed on a wiring board.
A circuit chip for controlling the output from the MS chip and the MEMS assembly are stacked, and the MEMS chip, the circuit chip, and the circuit chip and the wiring board are connected by metal wires, and are stacked on the wiring board. The circuit chip, the MEMS assembly and the metal wire are sealed with a silicon-based resin.

The MEMS chip is a silicon substrate or SOI (Silicon On Insul).
ator) The movable part is formed by fine processing of the substrate, and the cap chip is MEM.
Preferably, the S chip is formed of silicon having the same thermal expansion coefficient. The bonding between the MEMS chip and the cap chip is one of anodic bonding, low melting point material bonding (including low melting point metal bonding, eutectic bonding, low melting point glass bonding, resin bonding, etc.), diffusion bonding, and surface activation bonding. Although it is possible to use a method, industrially, it is preferable to use a low-melting-point material joint such as an Au—Sn alloy from the viewpoint of the reliability of the manufacturing process. In the low-melting-point material bonding, the chips are aligned via the low-melting-point material, and then the low-melting-point material is melted by applying heat and pressure, and the chips are bonded to each other. In the low melting point material bonding, since the low melting point material flows into the gap generated by the undulation of the MEMS chip and the cap chip, the gap is filled and the airtightness can be improved. It is not necessary to force the substrate to swell by applying a large pressure, and the risk of damaging the cap chip or the like is small, which is preferable for joining the MEMS chip and the cap chip. In order to make the space in the MEMS assembly vacuum (under reduced pressure) or to fill and hermetically with dry nitrogen or inert gas, bonding is performed under a vacuum (depressurized) atmosphere or under dry nitrogen or inert gas atmosphere. preferable. By sealing the movable part of the MEMS chip with a cap chip, the movable part of the MEMS chip is shielded from the environmental atmosphere, and an acceleration sensor device with good environmental resistance can be obtained.

When acceleration is applied to the acceleration sensor device from the outside, an electric circuit formed by a resistance element, a capacitance element, etc. formed on the movable part of the MEMS chip generates an acceleration force from the outside, such as current, voltage, capacitance, etc. Convert to physical quantity and output. Since the change in the output physical quantity is very small, it is preferable to include a circuit chip on which an element (amplifier circuit or the like) that amplifies the output is formed. When the element is affected by temperature, it is preferable to form a temperature correction circuit or the like on the circuit chip.

When a MEMS chip and a circuit chip are stacked on a lead frame and transfer molded with an epoxy resin as in general resin sealing of a semiconductor, the sensor output voltage is affected by the stress received from the component and its temperature change. Offset variation and temperature stability may be reduced. Moreover, in the transfer mold using a solid tablet-like resin, generally a pressure of around 80 kg / cm ² is required to press the resin into the mold.
Since residual stress is generated in the sealing resin and sensor chip, it is not a preferable method. In order to prevent the MEMS chip from being affected by changes in the stress of surrounding components with respect to changes in environmental temperature, it is ideal to match all the thermal expansion coefficients of the components. Is possible. In order to suppress the influence of the stress change on the temperature change as much as possible, it is effective to reduce the difference in thermal expansion coefficient between the constituent materials and to reduce the elastic modulus of the surrounding constituent materials (particularly the sealing resin). As a specific sealing resin, it is preferable to use a silicon-based resin having a low elastic modulus.

The acceleration sensor device of the present invention is characterized in that the wiring board is a glass epoxy resin board.

If the sealing resin is simply made of low elastic resin, the main terminals may move due to external force or thermal cycle after soldering, because the independent elastic terminals are restrained by the low elastic resin.
There is a possibility of causing problems such as a change in the offset of the sensor output voltage and a wire breakage at the wire joint with respect to the stress change transmitted to the EMS element.

By replacing the lead frame with a wiring substrate of a glass epoxy resin substrate, the movement of the main terminal can be fixed by the substrate. As a result, even if the sealing resin is a low-elasticity resin, problems such as offset changes in the sensor output voltage and wire breakage can be solved.

Furthermore, the acceleration sensor device of the present invention is characterized in that the wiring board is an alumina or LTCC board.

The thermal expansion coefficient of the glass epoxy resin substrate is about 14 × 10 ⁻⁶ / ° C., whereas the thermal expansion coefficient of the alumina substrate or the LTCC substrate is about 7 × 10 ⁻⁶ / ° C., which is closer to the MEMS chip. In addition, the alumina substrate and the LTCC substrate do not need to consider the influence of the swelling of the substrate itself due to humidity, and can obtain more stable characteristics than the glass epoxy resin substrate. In general, the member cost is slightly higher than that of the glass epoxy resin substrate, but it is possible to provide an acceleration sensor device having more stable characteristics than the glass epoxy resin substrate and less expensive than the hollow ceramic package.

Furthermore, in the manufacturing method of the acceleration sensor device of the present invention, a MEMS acceleration sensor assembly having a movable part and a cap chip that seals at least the movable part of the MEMS acceleration sensor chip are formed, and the MEMS acceleration sensor assembly is formed on the wiring board. Stacking a circuit chip for controlling output from the MEMS acceleration sensor chip and the MEMS acceleration sensor assembly, connecting the MEMS acceleration sensor chip, the circuit chip, the circuit chip, and the wiring board with metal wires, respectively. The circuit chip, the MEMS acceleration sensor assembly, and the metal wire stacked on the wiring board are sealed with a silicon-based resin using a printing method or a potting method.

In transfer molding, which is a general resin sealing method for semiconductor packages, it is necessary to apply a pressure of around 80 kgf / cm ² when injecting resin into a mold to prevent bubbles from remaining. This mold pressure is not a problem in resin sealing of normal semiconductor chips,
In a MEMS chip that detects a minute stress change such as an acceleration sensor, an influence on characteristics such as a change in offset is unavoidable. By forming the resin by printing or potting, the influence of the mold pressure described above can be avoided, and a sensor device with more stable characteristics can be provided.

As in the present invention, a circuit chip and a MEMS assembly are stacked on a wiring board and sealed with a silicon resin having a low elastic modulus together with a metal wire for connecting them, and the wiring board is preferably a glass epoxy resin board or an alumina board. By using the LTCC substrate, an acceleration sensor device having a simple structure, a small size, and excellent temperature stability can be provided at a lower cost than a structure using a hollow ceramic package.

It is a perspective view of the MEMS chip used for the Example. It is the perspective view and exploded view of the MEMS assembly used for the Example. It is a semi-perspective view of the acceleration sensor device used in the example. It is A-A 'sectional drawing of the acceleration sensor apparatus of FIG. FIG. 4 is a B-B ′ sectional view of the acceleration sensor device of FIG. 3. It is a top view which shows the wiring board used for the Example. It is a top view which shows the example of another wiring board which can be used for the acceleration sensor apparatus of this invention. It is a figure which shows the characteristic change with respect to the temperature change of the acceleration sensor apparatus used for the Example.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals are used for the same parts and parts.

Example 1
The acceleration sensor device of the present embodiment will be specifically described with reference to FIGS. FIG. 1 is a perspective view of a MEMS chip 2 used in this embodiment. The MEMS chip 2 is a piezoresistive element 1
3, 14, 15, wiring (omitted), electrode pad 24, joint portion 20, beam portion 12, weight portion 11, support frame portion 10, and the like.

The MEMS chip 2 includes a silicon plate having a thickness of about 400 μm, a silicon oxide layer of several μm, and a thickness of about 6 μm.
It was manufactured using an SOI substrate having an m silicon layer. Photoresist is patterned in the shape of the piezoresistive elements 13, 14 and 15 on the surface on the silicon layer side, and boron is added to the silicon layer.
Piezoresistive elements 13, 14, and 15 were formed by implanting ˜3 × 10 ¹⁸ atoms / cm ³ . Wirings connected to the piezoresistive elements 13, 14, and 15 were formed using metal sputtering and a dry etching apparatus. The silicon layer and the silicon plate were processed using a photolithography and dry etching apparatus to form a beam portion 12 formed on the silicon layer and a weight portion 11 formed from the silicon layer to the silicon plate. The silicon oxide layer functions as an etching stopper during dry etching of silicon. Since only silicon is dry etched, the silicon plate is dry etched but the silicon oxide layer remains. After dry etching, the silicon oxide layer was removed by wet etching by dipping in an aqueous solution of hydrofluoric acid or ammonium fluoride. Dry etching was performed in plasma in which SF ₆ , oxygen mixed gas and C 4 F 8 gas were alternately introduced. A number of acceleration sensor chips were produced on one wafer.

After forming the piezoresistive elements 13, 14, 15, the wiring, and the electrode pad 24 of the MEMS chip 2, silicon nitride is laminated thereon by CVD (thickness 0.1 μm), and then the silicon nitride on the electrode pad is formed. It was removed by photolithography and etching. Next, after opening the electrode pad 24 and the joint portion with a photoresist, Cr (thickness 0.1 μm) -Ni (
A laminated film was formed in the order of thickness 0.2 μm) -Au (thickness 0.5 μm).

An Au—Sn alloy film having a thickness of 3 to 5 μm as a bonding material was formed on the bonding portion 20 by vacuum deposition. During film formation, portions other than the joint 2 were protected with a photoresist, and the pattern was formed by removing the photoresist after film formation. Although not shown in FIG.
Were formed on both the piezoresistive element surface of the MEMS chip 2 and the opposite surface.

In this embodiment, the Au—Sn alloy film is formed at the joint, but the present invention is not limited to this as long as it is a joining material that can join the upper cap 22 and the lower cap 23 and does not affect the characteristics of the MEMS chip 2. Other low melting point metals or resin bonding materials may be used.

FIG. 2 is a perspective view and an exploded view of the MEMS assembly 21 used in this embodiment. MEMS
The assembly 21 was produced by joining the upper cap chip 22 and the lower cap chip 23 to the MEMS chip 2 via the joint portion 20.

The upper cap 22 and the lower cap 23 have a depth of 15 on a silicon chip having a thickness of about 400 μm.
A μm drive control groove 31 and a joint 2 are formed. The drive control groove 31 was formed by anisotropic wet etching of an opening formed by applying a photoresist with a 40 wt% potassium hydroxide aqueous solution at a temperature of 67 ° C. The joint portion 20 was formed on the outer peripheral portion of the drive control groove 31 by the same method as the joint portion of the MEMS chip 2.

The formation method of the drive suppression groove | channel 30 is not limited to said wet etching. It is also possible to apply dry etching in plasma in which SF ₆ , oxygen mixed gas and C ₄ F ₈ gas are alternately introduced.

The MEMS chip 2 and the upper cap chip 22 and the lower cap chip 23 were joined by applying a load of 10 kN from above and below the chip in a nitrogen gas atmosphere and heating to a temperature at which the Au—Sn alloy film was melted. . By this bonding, the movable part of the MEMS chip 2 is sealed in a space between the upper cap chip 22 and the lower cap chip 23 to form the MEMS assembly 21. The movable part is previously formed by the upper cap chip 22 and the lower cap. MEM of chip 23
Since the drive suppression groove 30 is formed on the surface facing the S chip 2, it can operate freely.

FIG. 3 is a semi-transparent perspective view showing the assembly structure of the acceleration sensor device 1 used in this embodiment.
4 and 5 are cross-sectional views showing the structure of the acceleration sensor device 1. First, the circuit chip 25
Is fixed to the wiring board 26 via the lower bonding layer 31b, and the MEMS assembly 21 is bonded to the upper bonding layer 31a.
It fixed to the circuit chip 25 via this. Next, the electrode pad 24 of the MEMS chip 2 and the electrode pad 24 ′ of the circuit chip 25, and the electrode pad 24 ′ of the circuit chip 25 and the wiring board 26
The main terminal 26 a was connected by a metal wire 27. Finally, the circuit chip 25, the MEMS assembly 21, and the metal wire 27 stacked on the wiring substrate 26 were sealed with a silicon-based resin 29.

In this embodiment, a die attach film (DAF) is formed on the upper bonding layer 31a and the lower bonding layer 31b.
However, a die attach paste may be used.

In this embodiment, a flat glass epoxy resin substrate is used for the wiring substrate 26. As a result, it was possible to sufficiently secure the bonding area of the circuit chip corresponding to the die pad, which is difficult to secure an area in a small package using a lead frame. Further, in this example, a glass epoxy resin substrate corresponding to FR-5 having a high heat resistant temperature was used in consideration of wire bondability. The thermal expansion coefficient of the glass epoxy resin substrate was about 14 × 10 ⁻⁶ / ° C. in the plane direction, and the elastic modulus was about 27 GPa.

Further, by using the flat wiring substrate 26, the physical properties of the substrate base material are dominant in the deformation of the wiring substrate 25. The flat wiring board 26 has a smaller deformation anisotropy in the XY direction of the board as compared with the lead frame, and is preferable for stabilizing the temperature characteristics. this is,
Even if the secondary mounting substrate is deformed due to temperature when the acceleration sensor device is secondarily mounted by solder, the MEMS is used.
This means that the influence of external force on the chip 2 is reduced, which can be said to be effective for stabilizing the temperature characteristics after the secondary mounting. In particular, in an acceleration sensor device sealed with a flexible silicon-based resin, the influence of external force on the MEMS chip 2 is further reduced, and the effect of stabilizing temperature characteristics becomes remarkable.

In addition, in the combination of the silicon resin and the lead frame, individual leads are easily moved by an external force, so that a load is applied to the metal wire 27 that connects the electrode pad 24 ′ of the circuit chip 25 and the main terminal 26 a of the wiring substrate 26, and is easily disconnected. Become. By using the flat wiring board 26 fixed so that the leads do not move individually, such disconnection of the metal wire 27 can be avoided.

In addition, in a lead frame of a small package, it is difficult in terms of layout to secure a sufficient die pad area to which the circuit chip is bonded. However, in the case of the flat wiring substrate 26, the entire back surface of the circuit chip 25 is bonded to the wiring substrate. can do. Thereby, since the whole joining surface of the wiring board 26 and the circuit chip 25 can be flattened, the generation of bubbles at the time of joining can be reduced, and at the same time, the thermal expansion coefficient of the joining surface can be made uniform. You can also. For this reason,
This is preferable because the influence of the external force on the MEMS chip 2 with respect to the temperature change of the acceleration sensor device can be stabilized, and the correction of the circuit chip 25 can be facilitated by stabilizing the sensor output voltage.

A ceramic substrate such as an alumina substrate or LTCC is more advantageous than the glass epoxy resin substrate for the wiring substrate 26 because it has a thermal expansion coefficient closer to that of the MEMS chip 2. It is also necessary to consider compatibility with components.

FIG. 6 is a top view showing the wiring board 26 used in this embodiment. The main terminals 26a formed on the front and back of the substrate base material 26b are electrically connected by Cu plating through the through holes 26c, and the main terminals 26a are covered with a resist 26c except for the portions necessary for connection. It is.

The wiring board 26 used in this embodiment may be a wiring board as shown in the top view of FIG. The wiring board of FIG. 7 is made flat by eliminating the wiring pattern of the circuit chip joint portion by connecting the main terminals 26a formed on the front and back of the substrate base material 26b with a castellation structure (end face electrode). As in the case of the wiring substrate of FIG. 7, if the wiring pattern is not arranged in the region where the circuit chip is bonded, no resist is required, and the configuration of the laminated material can be simplified. In addition, the influence of external force on the MEMS assembly due to thermal deformation of the wiring board can be stabilized, and the change in characteristics of the acceleration sensor device with respect to the temperature change can be further stabilized.

The silicon-based resin 29 has a small product (α × E) of the thermal expansion coefficient α and the elastic modulus E in order to reduce the influence of the environmental temperature change in the acceleration sensor device 1, and the thermal expansion coefficient itself is the same as that of the MEMS assembly 21. It is preferable to be close to silicon which is a main constituent member. In this example, a SiO ₂ filler is mixed with black silicon resin to lower the thermal expansion coefficient, the thermal expansion coefficient after curing is about 170 × 10 ⁻⁶ / ° C., and the elastic modulus is about 5 MPa. System resin 29 was used.

In this embodiment, the silicon resin 29 is formed by a printing method. The circuit chip 25 and the MEMS assembly 21 stacked on the wiring substrate 26 were fixed on the stage of a printing machine, and the resin paste was applied and formed through a mask that determines the printing area and thickness. 15 for printing
Batch printing was performed using 225 sensors in rows and 15 columns as printing units. Since bubbles were entrained in the resin after printing, the resin was thermally cured in a clean oven after defoaming for 20 minutes with a vacuum defoamer. The thermosetting conditions were 175 ° C. × 30 minutes.

FIG. 8 is a diagram showing a characteristic change with respect to a temperature change in the acceleration sensor device 1 of the present embodiment. The characteristic change is indicated by an acceleration conversion value of the output voltage offset with respect to the acceleration in the direction perpendicular to the MEMS chip 2. As a comparative example, the same MEMS assembly 25 and circuit chip 25 as in the example were fixed to the lead frame via the same upper bonding layer 31a and lower bonding layer 31b as in the example, and epoxy resin was sealed by transfer molding. The evaluation result of the acceleration sensor device is also shown.

In the acceleration sensor device using the lead frame and the epoxy resin as a comparative example, the acceleration conversion value of the offset with respect to the temperature change is about 3.5 mg / ° C., whereas the glass epoxy resin substrate and the silicon resin are used. The acceleration sensor device is about 1/7 of about 0.5 mg / ° C.
As a result, it was confirmed that the acceleration sensor device was excellent in temperature stability. This result is considered to be the effect that the stress propagating to the MEMS chip 2 due to the temperature change can be reduced by using the combination of the glass epoxy resin substrate and the silicon resin.

1 acceleration sensor device,
2 acceleration sensor chip,
10 Support frame,
11 weight,
12 Beam part,
13, 14, 15 piezoresistive element,
20 joints,
21 MEMS assembly,
22 Upper cap tip,
23 Lower cap tip,
24, 24 'electrode pads,
25 circuit chips,
26 Wiring board,
26a main terminal,
26b base material,
26c through hole,
26d resist,
27 metal wire,
29 Mold resin,
30 Drive suppression groove,
31a upper bonding layer,
31b Lower joining layer.

Claims (4)

A MEMS acceleration sensor assembly having a movable part and a cap chip that seals at least the movable part of the MEMS acceleration sensor chip to form a MEMS acceleration sensor assembly, and a circuit chip for controlling an output from the MEMS acceleration sensor chip on a wiring board And the MEMS
The acceleration sensor assembly is stacked, the MEMS acceleration sensor chip, the circuit chip, and the circuit chip and the wiring board are connected to each other by metal wires, and the circuit chip and the MEMS acceleration sensor stacked on the wiring board are stacked. An acceleration sensor device, wherein the assembly and the metal wire are sealed with a silicon-based resin. The acceleration sensor device according to claim 1, wherein the wiring substrate is a glass epoxy resin substrate. The acceleration sensor device according to claim 1, wherein the wiring board is an alumina or LTCC board. A circuit chip for forming a MEMS acceleration sensor assembly with a MEMS acceleration sensor chip having a movable part and a cap chip for sealing at least the movable part of the MEMS acceleration sensor chip, and controlling an output from the MEMS acceleration sensor chip on a wiring board And the MEMS acceleration sensor assembly, the MEMS acceleration sensor chip, the circuit chip, and the circuit chip and the wiring board are respectively connected by metal wires, and the circuit chip and the MEMS stacked on the wiring board are connected to each other. A method of manufacturing an acceleration sensor device, comprising: sealing an acceleration sensor assembly and the metal wire with a silicon-based resin using a printing method or a potting method.

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