JP2010060541A - Semiconductor sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor sensor of higher reliability which can maintain airtightness with a narrow gap. <P>SOLUTION: This semiconductor sensor includes an MEMS chip, a cap chip for airtight sealing, a circuit board, and a resin member for sealing these items. The cap chip includes a jointing material ring arranged so as to surround a movable portion of the MEMS chip, a groove for the jointing material formed around inner/outer circumferences of the jointing material, and a metallization layer/insulating film on ground layer of the jointing material. The metallization layer is formed directly beneath the jointing material, the inner surface of the groove for the jointing material, and the surface externally extended to the outside of the inner surface, the insulating film is formed on the directly beneath section and the externally-extended surface not formed inside the groove for the jointing material while the metallization layer is formed on the MEMS chip. These cap chip and MEMS chip are joined to each other by the jointing material, and furthermore, the cap chip and the jointing material are electrically connected in the groove for the jointing material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a MEMS (Micro-Electro-Mechani) having a movable part.
The present invention relates to a semiconductor sensor device having a (cal Systems) chip.

MEMS technology that realizes a system having a three-dimensional microstructure on a semiconductor substrate by combining machining technology, material technology, and the like with semiconductor manufacturing process technology 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.
The semiconductor sensor device has a MEMS chip having a minute movable part. The MEMS chip is placed in a ceramic case which is an exterior. However, the ceramic case has a limit on miniaturization and it is difficult to reduce the weight. Therefore, Patent Document 1 discloses a semiconductor sensor device having a resin exterior using a resin mold technique.

In order to drive the movable part of the MEMS chip in the resin exterior, a lid that forms an appropriate gap and seals it is necessary. The MEMS assembly of Patent Document 1 is a MEM having a movable part.
The S chip and a cap chip serving as a lid for hermetically sealing the movable part are joined together. As an additional effect of this cap chip, Patent Document 2 describes an example in which, when the gap between the cap chip and the movable part of the MEMS chip is narrowed, the frequency characteristics of the movable part are controlled and the resonance is suppressed by the effect of air damping. Yes.

Patent Document 3 discloses a configuration that eliminates the cap chip being in a floating state in order to prevent the cap chip from being charged. The cap chip is made of a silicon substrate, Ti or Au is formed as a bonding film, and eutectic bonding is performed with silicon on the MEMS chip side. It is possible to realize a configuration in which the bonding portion is conductive and the cap chip and the silicon on the MEMS chip side (that is, the movable portion) are electrically connected. In addition, both the cap chip and the MEMS chip are based on silicon, and there is no difference in thermal expansion coefficient.

JP-A-10-170380 JP-A-9-178770 JP 2001-1119040 A

When the gap between the cap chip and the movable part of the MEMS chip is narrowed, problems such as unstable operation and reduced reliability due to poor airtightness occur.

The bonding disclosed in Patent Document 2 uses an anodic bonding method in which glass and silicon are directly bonded. However, the thermal expansion coefficient difference between silicon and glass is large, and in the heat shock test, cracks occur in the joints, resulting in deterioration of airtightness and breakage of the beam supporting the movable part.

In addition, when the gap (gap) between the cap chip and the movable part of the MEMS chip is narrowed, an electrostatic attractive force acts between them to displace the movable part, and the output signal of the semiconductor sensor device fluctuates. is there. The MEMS chip is molded with an insulating resin member and becomes an exterior of the semiconductor sensor device. Static electricity is generated in the resin member as the exterior due to friction generated when the semiconductor sensor device is mounted. When the cap chip is in an electrically floating state, the cap chip itself is also charged, a potential difference is generated with the movable part of the MEMS chip, and the movable part is displaced by electrostatic attraction. The strength of electrostatic attraction is inversely proportional to the distance of the gap between the cap chip and the movable part of the MEMS chip, so that the influence is particularly large when the gap is narrow.

In Patent Document 3, the eutectic bonding with good airtightness requires a thickness of about 20 μm as the Au film thickness, and the thickness of the bonding portion increases, so that there is a gap between the cap chip and the movable portion of the MEMS chip. Because it becomes wide, the original purpose cannot be achieved. Moreover, since the Au is thick, the manufacturing cost is high and it is not suitable for industrial mass production.

An object of the present invention is to solve this problem and provide a highly reliable semiconductor sensor device that maintains airtightness even when the gap between the cap chip and the movable part of the MEMS chip is narrowed.

The semiconductor sensor device of the present invention is
A MEMS chip having a movable part formed from a semiconductor substrate and one or more cap chips formed from a semiconductor substrate and hermetically sealing the movable part of the MEMS chip.
An MS assembly;
A circuit board connected by wiring to the MEMS chip;
A semiconductor sensor device comprising the circuit board and a resin member for sealing the MEMS assembly,
The cap chip serves as a bonding material disposed in a ring shape so as to surround the movable part of the MEMS chip, a bonding material groove formed at the inner and outer peripheral positions of the bonding material, and a base of the bonding material. It comprises a metallized layer and an insulating film that is the base of the metallized layer,
The metallized layer is formed on the surface directly below the bonding material, the inner surface of the bonding material groove, and the outer surface of the bonding material groove,
The insulating film is formed on the surface directly below the bonding material and on the outer surface of the bonding material groove, and is not formed on the inner surface of the bonding material groove,
The MEMS chip has a metallized layer facing the bonding material,
The cap chip and the MEMS chip are physically connected via a bonding material, and the cap chip and the bonding material are electrically connected within a bonding material groove. .

The potential of the movable part formed on the MEMS chip is preferably the same as the potential of the cap chip, and is preferably the same as the fixed potential outside the semiconductor sensor device. Even if the gap between the cap chip and the movable part of the MEMS chip is narrowed, electrostatic attraction does not occur in both of them, and the output of the semiconductor sensor device is stabilized. Here, the potential of the movable part formed on the MEMS chip,
When the difference from the potential of the cap chip is a certain value, although the electrostatic attraction works, there is no fluctuation, and the same effect can be obtained. Cap chip has an electrical resistivity ρ of 500Ω
A substrate of Si semiconductor of cm or less can be used, preferably ρ = 0.001 to 500
A Si semiconductor substrate having Ωcm, more preferably ρ = 5 to 20 Ωcm is used. It is preferable to have a gap of 1 to 5 μm between the MEMS chip and the cap chip.

Solder (for example, Au—Sn eutectic solder) which is a bonding material is formed on the cap chip side, and a pair of bonding material grooves are formed at positions sandwiching the solder. Further, the metallized layer is disposed not only directly under the solder but also extending outwardly on the inner surface (wall surface and bottom surface) and outer side of the bonding material groove. On one MEMS chip side, a metallized layer is formed at a position facing the bonding material on the cap chip side. When both are applied by applying weight and heating, the bonding material is crushed and simultaneously spreads on the metallized layer to form a bonded portion. The bonding material forms a fillet at the edge of the bonding material groove (corner of the groove opening) by the effect of the surface tension. This is shown in FIG. By forming the fillet 47, a hermetic seal of the joint can be realized. Also, the bonding material 40 is crushed and thinned, and the cap chip 22 and the MEM.
It is possible to narrow the gap with the movable part of the S chip 2.

The bonding material groove 31 also serves as a pocket for storing the crushed bonding member 40 so as not to leak out. When the bonding material groove 31 is not provided, the metallized layer 1 is obtained as shown in FIG.
The joint material 40 crushed from the end of 6 leaks out, causing a problem of short-circuiting with an adjacent electrode pad (49 in the figure).
When the bonding material groove 31 is present, excess bonding material 40 is accommodated in the groove and does not leak from the end of the metallized layer. In order to crush the bonding material 40 to form a thin bonding portion, it is preferable to provide the bonding material groove 31.

In the configuration of FIG. 10, since the oxide film 39 is provided as a lower layer of the metallized layer 16B, the MEMS chip and the cap chip are not electrically connected. A structure in which the oxide film 39 is not formed is produced as a reference example and bonded. As shown in FIG.
The solder as the bonding material 40 and the semiconductor substrate (for example, silicon) constituting the cap chip 22 reacted at the edge of 1 and the shape of the fillet 47 collapsed (fillet 47).
'). When the heat shock test was performed, cracks 48 were generated and the yield of hermetic sealing was reduced. The metallized layer 16B is Ni for suppressing the reaction between the Cr layer, which is an adhesion layer, and the solder.
This is a metal multilayer film composed of a layer and an Au layer with good solder wettability, and the Ni layer stops the reaction with the solder. However, since a large amount of solder gathers at the edge of the bonding material groove 31 due to surface tension, the reaction proceeds rapidly, and the Ni layer and Cr layer at the edge are melted into the solder, and the solder reaches the semiconductor substrate. And caused a reaction.

Therefore, the oxide film 39 is left on the flat portion of the cap chip 2, that is, the portion that is not the bonding material groove 31, and the insulating oxide film 3 is formed on the inner surface (wall surface and bottom surface) of the bonding material groove 31.
9 was removed. FIG. 13 shows a joining cross section in that case. The reaction between the semiconductor substrate (silicon) and the bonding material does not occur at the edge of the bonding material groove 31. On the other hand, since the insulating oxide film 39 is removed on the inner surface (wall surface and bottom surface) of the bonding material groove 31, the reaction between the semiconductor substrate and the bonding material 40 occurs, but the range is limited. Yes, it does not affect edge fillet 47 formation. Therefore, airtight sealing can be ensured. In place of the oxide film 39, a nitride film can be used.

The manufacturing process of removing the insulating oxide film or nitride film on the inner surface (wall surface and bottom surface) of the bonding material groove is easy for the following reason. Conventionally, after forming a bonding material groove on a semiconductor substrate by dry etching or wet etching technology, the insulating oxide film or nitride film is formed on the inner surface of the bonding material groove by thermal oxidation treatment or CVD film formation. did. The order of this process is changed, and the insulating oxide film or nitride film is formed on a flat semiconductor substrate by the same method, and then the insulating oxide film or the wet etching technique is used. A nitride film is opened, and a bonding material groove is formed in the semiconductor substrate. As a result, a state in which the oxide film or nitride film is removed from the inner surface of the bonding material groove can be realized. Patterning by photolithography technology is not necessary, and an increase in man-hours can be suppressed.

Electrode pads for connection to the circuit board are formed on the MEMS chip, and the electrode pads and the bonding material are electrically connected via a conductive impurity-added layer formed on the semiconductor substrate that is the base of the MEMS chip. It is desirable to be connected.

When the electrode pad and the bonding material are patterned so as to be connected by the metallization layer on the MEMS chip side, a part of the bonding material that spreads wet during bonding reaches the electrode pad,
It reacts with Au or Al of the electrode pad. In this case, wiring (bonding wire) cannot be connected to the electrode pad. In order to avoid this, a conductive impurity-added layer is formed on the semiconductor substrate, and the electrode pad and the bonding material are electrically connected through this layer so that the electrode pad is not directly connected. Thereby, the connection between the electrode pad and the wiring (bonding wire) is performed with a high yield. The impurity added layer is preferably P ⁺ -Si.

In the MEMS assembly, the movable part of the MEMS chip is preferably hermetically sealed by being sandwiched between two cap chips. The base bodies of the two cap chips are electrically connected to the bonding material, respectively, and are electrically connected to the circuit board or the wiring board by wiring through the electric circuit and electrode pads formed on the MEMS chip. Is preferred. The base of the MEMS chip and the cap chip facing the MEMS chip are set to the same potential as the potential of the movable part, and more preferably the same potential as Vcc of the electric circuit of the movable part.

Even if the gap between the cap chip and the movable part of the MEMS chip is narrowed, it is possible to provide a highly reliable semiconductor sensor device that maintains airtightness.

Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not necessarily limited by these embodiment.

[Embodiment 1]
The acceleration sensor device of the present invention comprises a MEMS chip (sensor chip) having a movable part, and an upper cap chip that hermetically seals at least the movable part in the sensor chip and a lower cap chip formed of a MEMS assembly formed of a lower cap chip. Fixed on the circuit board fixed on the wiring board, the sensor chip, the circuit board, the circuit board, and the wiring board are connected by wiring, and the circuit board on the wiring board, the wiring, and the MEMS assembly are sealed with a resin member. It is a semiconductor sensor device.

When acceleration is applied to the sensor chip from the outside, an electric circuit formed by a piezoresistive element or the like formed on the movable part converts the acceleration from the outside into a current or a voltage and outputs it. Since the change in output is very small, an element (amplifier circuit or the like) that amplifies the output is formed on the circuit board. When the piezoresistive element is affected by temperature, it is preferable to mount a temperature correction circuit or the like.

The MEMS assembly includes a sensor chip, an upper cap chip, and a lower cap chip.
Have an element as a component. The sensor chip and the upper cap chip, and the sensor chip and the lower cap chip are bonded to each other at a bonding portion.

The sensor chip includes a movable part that is displaced from the outside by acceleration, a conversion element for converting the displacement of the movable part into an electric signal, an electric circuit, a beam and a support frame for supporting the movable part so as to be displaceable, a sensor chip, and an upper A cap chip joint, a sensor chip and a lower cap chip joint, and an electrode pad are included as components. These joints and separation grooves described later can be formed by using a photolithographic technique, wet etching, and dry etching techniques.

The sensor chip facing surface side of the upper cap chip has a joint portion fixed to the sensor chip and an opening portion (separation groove) of the electrode pad as components. The sensor chip is bonded to the upper cap chip and the lower cap chip to obtain a MEMS assembly. Specifically, since the bonding is performed in a substrate state in which a plurality of chips are formed, a plurality of upper cap chips are connected. is there. This is separated by etching or polishing and separated into individual pieces to obtain an upper cap chip. By making the separation groove deep, the upper cap chip can be separated into pieces by a short etching or polishing process. These junctions and separation grooves can be formed by using photolithography technology, wet etching, and dry etching technology.

The sensor chip facing surface side of the lower cap chip has a joint portion fixed to the sensor chip as a constituent element. The joint portion can be formed by using a photolithography technique, wet etching, and dry etching technique.

A conductive bonding material such as a low melting point metal is formed at the bonding portion. Using a bonding material, the sensor substrate and the upper cap substrate are fixed to each other, and the sensor substrate and the lower cap substrate are fixed to each other for hermetic sealing. The bonding material is formed using techniques such as lift-off, ion milling, etching, and plating.

As a material constituting the conductive bonding material, A known as a solder material for mounting electronic components
u-20 to 37.6Sn, Au-90Sn, Sn-9Zn, Sn-3.5Ag, Sn-
3Ag-0.5Cu, Pb-5Sn, Pb-10Sn, Sn-37Pb, Sn-57B
It is preferable to use any of i. Au-90Sn contains 90% by mass of Sn,
An alloy having a composition in which the balance is gold and inevitable impurities. Since the bonding material wets and spreads when heated and melted, it is preferable to form a metallized layer as a base of the bonding material. The metallized layer is preferably a multilayer film in which an adhesive layer with the base layer, a protective layer for preventing solder from reaching the adhesive layer, and a layer with high solder wettability are stacked from the base side. When the underlayer is a Si oxide film, the adhesive layer with the underlayer is preferably a metal such as Cr, Ti, or W. As the protective layer, Ni, Cu, Pt, Pd, or the like, which has a slow reaction rate with solder, is preferable. As the layer having high solder wettability, Au having a high reaction speed with solder is preferable. The multi-layer metallized layer is formed by sputtering, vapor deposition, electrolytic plating or electroless plating, lift-off, milling,
A desired pattern is formed by etching.

The bonding material is preferably formed on both the sensor chip side and the upper cap chip side, but may be formed on only one of them. Further, the bonding material is preferably formed on both the sensor chip side and the lower cap chip side, but may be formed on only one of them. However, the metallized layer is preferably formed on both the sensor chip side and the upper cap chip side and formed on both the sensor chip side and the lower cap chip side in order to react with the bonding material.

When the surface of the bonding material is oxidized, the bonding material may not spread out. In order to prevent this, it is preferable to form a material that is not easily oxidized, such as Au, on the surface.

It is preferable that a groove (hereinafter referred to as a bonding material groove) is formed so as to surround the bonding material. When viewed from above, the bonding material is formed in a ring shape, and a ring-shaped bonding material groove is formed on the inner periphery and outer periphery of the bonding material. The metallized layer is disposed not only directly below the bonding material, but also on the wall surface, bottom surface, and outer surface of the bonding material groove. The bonding material melts and spreads wet on the metallized layer. However, by forming a fillet at the edge of the bonding material groove (the corner of the groove opening), hermetic sealing can be realized with a high yield. Moreover, the groove | channel for joining materials ensures sufficient volume (cross-sectional area) that a joining material does not leak out of a groove | channel.

The bonding material groove may be formed on the sensor chip side, the upper cap chip side, or the lower cap chip side. Further, when the bonding material is formed only on one side, it may be formed on either the sensor chip side, the upper cap chip side, or the lower cap chip side. In either case, since the fillet is formed at the edge of the bonding material groove (the corner of the groove opening) when bonded, hermetic sealing can be realized with a high yield.

An underlayer that does not easily react with the bonding material is preferably formed on the underlayer of the metallized layer. For example, when the bonding material is Au-20 to 37.6Sn and the substrate of the sensor chip, the upper cap chip, and the lower cap chip is silicon, the bonding material and the substrate react by an eutectic reaction of Au-Si, and after bonding There arises a problem that the thickness of the joint portion varies, or a crack occurs in the joint portion to deteriorate the airtightness. In order to prevent this, it is effective to form an oxide film (such as a silicon oxide film) or a nitride film (such as a silicon nitride film) as a base for the metallized layer. A silicon oxide film and a silicon nitride film are particularly useful because they have high adhesion and can be easily formed.

When a silicon oxide film or a silicon nitride film is used as the material for the base layer, since it is insulative, the movable part of the sensor chip and the upper cap chip and the lower cap chip are in an electrically floating state. In this state, due to the influence of external static electricity, the resin member is charged and the upper cap chip and the lower cap chip are also charged, and the movable part of the sensor chip is displaced to cause the output fluctuation of the semiconductor sensor device. In order to prevent this, it is preferable to remove the silicon oxide film or silicon nitride film in the bonding material groove and form a metallized layer thereon. The reaction between the substrate and the bonding material occurs in the groove, but the range is limited, and the thickness of the bonding portion does not vary and the bonding portion does not crack. In this structure, the “upper cap chip or lower cap chip substrate”, “upper cap chip or lower cap chip metallization layer”, “bonding material”, and “sensor chip metallization layer” all have the same potential. When the metallized layer of the sensor chip is connected to the movable part of the sensor chip through the opening of the silicon nitride film, the “upper cap chip substrate” and the “movable part of the sensor chip” have the same potential, and the output fluctuation is reduced. Can be suppressed.

After aligning the sensor chip substrate on which a plurality of sensor chips are formed, the upper cap substrate on which a plurality of upper cap chips are formed, and the lower cap substrate on which a plurality of lower cap chips are formed, pressurization and Join by heating. Since the bonding material flows in the gap formed by the undulation of the sensor chip substrate, the upper cap substrate, and the lower cap substrate, the gap can be filled and airtightness can be improved. For this reason, since it is not necessary to correct the undulation of the substrate by applying a large pressure, the risk of damaging the upper cap substrate or the like is reduced. In order to keep the space in the MEMS assembly in a vacuum (under reduced pressure) or to fill and air-tight with dry nitrogen or inert gas, it is preferable to join in a vacuum (depressurized) atmosphere or in a dry nitrogen or inert gas atmosphere. .

The upper cap substrate and the lower cap substrate are thinned by wet etching or polishing,
After separating the upper cap substrate into pieces, the MEMS assembly substrate can be cut with a diamond grindstone to obtain a MEMS assembly. MEMS assembly substrate is separated into pieces, and MEMS
To make an assembly, cut with a wet etching or diamond grinding wheel (dicing)
Is used.

Using a die attach film on the wiring board (lead frame), the circuit board (I for detection)
C) is adhered. Further, the MEMS assembly is bonded on the circuit board (detection IC) with a die attach film.

Between the MEMS assembly and the circuit board, or between the circuit board and the wiring board, a fine metal wire (
Connect with wire). The connection between the electrode pad and the metal fine wire can be performed by ultrasonic welding or solder welding. Instead of the connection by the metal fine wire, the connection by a solder ball or a ball bond can also be used. The wiring board is a printed circuit, a lead frame, or the like. The wiring board has a main terminal as an electrode corresponding to an electric circuit formed on the sensor chip.

In order to seal the MEMS assembly, the circuit board, the wiring board, and the wire with a resin, a thermosetting resin such as an epoxy resin, a silicon resin, or a phenol resin can be used. As a molding method, a potting method using a liquid resin or a transfer molding method using a powder resin can be used. In the transfer molding method, a MEMS assembly, a circuit board, a wiring board, and a wire are integrated into a mold, and a resin molded in a tablet shape is loaded into a pod of a molding machine, and an extrusion part of the pod is attached. The resin is softened by heating, and the softened resin in the pod is pressed into the mold by a plunger (pressing mechanism). After the resin is cured in the mold, the resin mold product is taken out from the mold to obtain a semiconductor sensor device. In the potting method, a MEMS assembly, a circuit board, a wiring board, and a wire are integrated into a mold, a liquid resin is poured into the mold, the resin is cured, and then the resin mold product from the mold. To obtain a semiconductor sensor device.

Hereinafter, an acceleration sensor device as a semiconductor sensor device of the present invention is shown in FIGS.
This will be described in more detail using. Therefore, the sensor chip substrate is described as a term synonymous with the acceleration sensor chip substrate, and the sensor chip is described as a term synonymous with the acceleration sensor chip.
FIG. 1 is an exploded perspective view of the acceleration sensor chip 2, the upper cap chip 22, and the lower cap chip 23.
FIG. 2 is a semi-transparent top view showing the resin package assembly structure of the acceleration sensor, that is, the acceleration sensor device 1. The resin member on the upper cap side of the wiring board 26 is seen through.
FIG. 3 is a cross-sectional view showing the structure of the acceleration sensor device 1.
FIG. 4 is a diagram for explaining a manufacturing process of the acceleration sensor device 1.

FIG. 1 b) is a perspective view of the acceleration sensor chip 2. The left figure is the front side and the right figure is the back side. Piezoresistive elements 13, 14, 15, wiring (not shown), electrode pad 24, joint 20, beam 12, weight 11, support frame on the surface side of sensor chip 2 (left figure) 10 etc. are formed. Four beam portions 12 extending from the support frame portion 10 support the weight portion 11. The joint portion 20 is formed in a ring shape on the support frame portion 10 so as to surround the beam portion 12 and the weight portion 11. Piezoresistive elements 13, 14, and 15 are formed on the beam portion 12,
The distortion generated in the beam portion 12 due to the displacement of the weight portion 11 is converted into an electric signal.

The acceleration sensor chip 2 is manufactured by SOI (Silicon on Insul) having a silicon plate of about 400 μm thickness and a silicon oxide layer of several μm and a silicon layer of about 6 μm.
attor) substrate was used. Photoresist patterns were formed in the shape of the piezoresistive elements 13, 14 and 15 on the surface on the silicon layer side. Boron is implanted into the silicon layer by ion implantation at 1 to 3 × 10 18 atoms / cm 3 to form the piezoresistive elements 13, 14, and 15.
Wirings connected to the piezoresistive elements 13, 14, and 15 were formed using a metal sputtering and dry etching apparatus. The silicon layer and the silicon plate were processed using a photolithographic technique and a dry etching apparatus to form a beam portion 12 formed in 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, it was immersed in an aqueous solution of hydrofluoric acid and ammonium fluoride, and the silicon oxide layer was removed by wet etching. Dry etching is SF6, oxygen gas and C4
This was performed in a plasma in which F8 gas was alternately introduced. A large number of acceleration sensor chips 2 were produced on one SOI substrate to obtain an acceleration sensor substrate 2 ′.

After the piezoresistive elements 13, 14, 15, wirings, and electrode pads 24 are formed, a silicon nitride film is laminated thereon by CVD (thickness: 0.1 μm), and then the silicon nitride film on the electrode pads 24 is photolithography. Removed by technique, etching. Next, the electrode pad 24 and the region to be the joint are opened by lift-off, and then Cr (thickness 0.05 μm) -Ni (
A laminated film was formed in the order of 0.4 μm thickness) −Au (0.5 μm thickness). Next, the photoresist and the metal film other than the electrode pad 24 and the joint 20 were removed. By this step, the metallized layer 16 is formed on the electrode pad 24 and the bonding portion 20.

On the back surface side (right figure) of the acceleration sensor chip 2, the joint portion 2 so as to surround the weight portion 11.
8 is formed. After opening the joint 28 on the surface of the silicon substrate by lift-off, Cr (thickness 0.05 μm) -Ni (thickness 0.4 μm) -Au (thickness 0.
A laminated film was formed in the order of 5 μm). Next, the photoresist and the metal film other than the joint portion 28 were removed. By this step, the metallized layer 16 is formed at the joint portion 28.

FIG. 1 a) is a perspective view of the upper cap chip 22. A joint portion 33 is formed on the surface (right diagram) on the side facing the surface of the acceleration sensor chip 2. The joint portion 33 is formed at a position facing the joint portion 20 of the acceleration sensor chip 2. Bonding portion 33 is metallized layer 1
6. It is comprised by the groove | channel for joining materials, and a joining material (not shown). Multiple upper cap tips 22
The upper cap substrate 22 ′ is formed with a separation groove 32 at a position facing the electrode pad of the acceleration sensor chip 2. In the subsequent back grinding process, the upper cap chip 22 is separated into pieces by thinning it to the depth of the separation groove.

The separation groove 32 is formed by dry etching, but is not limited to this. As another embodiment, the silicon oxide film is processed by wet etching using a hydrogen fluoride-based solution, and the silicon is processed by wet etching using a potassium hydroxide aqueous solution or TMHA (tetramethylammonium hydroxide aqueous solution). Replaced. In any case, the separation groove 32 has a depth of 100 μm or more.

FIG. 1 c) is a perspective view of the lower cap chip 23. A joint portion 34 is formed on a surface (right diagram) on the side facing the back surface of the acceleration sensor chip 2. The joint 34 is formed at a position facing the joint 28 of the acceleration sensor chip 2. Joint 34 is metallized layer 1
6. It is comprised by the groove | channel for joining materials, and a joining material (not shown). A plurality of lower cap chips 23 are formed on the lower cap substrate 23 '.

The acceleration sensor substrate 2 ′ is in the state of a substrate, and the upper cap substrate 22 ′ and the lower cap substrate 2
3 '(FIG. 4b)), the upper cap substrate and the lower cap substrate are shaved by 300 μm by back grinding (that is, the thickness of the upper cap substrate and the lower cap substrate is 100 μm).
And the MEMS assembly substrate 45 in which the upper cap substrate 22 ′ is divided by the separation groove 32, that is, the upper cap substrate and the lower cap substrate are thinned (FIG. 4c)).

As another embodiment, the MEMS assembly substrate 45 is immersed in a 40 wt% potassium hydroxide aqueous solution heated to 67 ° C., and the upper cap substrate and the lower cap substrate are etched by 300 μm to obtain a thinned MEMS assembly substrate 45. .

Die attach film (upper DAF) 6 on the lower cap substrate side of the MEMS assembly substrate 45
1a was affixed, and dicing was performed with a dicing line 90 shown by a one-dot chain line in FIG. 4c) to obtain a MEMS assembly 21 separated into individual pieces (FIG. 4d)).

A circuit board (detection IC) 25 for amplifying a signal from the acceleration sensor chip 2 and correcting temperature is fixed on a wiring board (lead frame) 26 having a thickness of 125 μm by a die attach film (lower DAF) 61b. . A plurality of wiring boards 26 were prepared in an arrayed state.
The MEMS assembly 21 separated on the circuit board 25 is attached to a die attach film (upper DAF).
) 61a (FIG. 4e)). Die attach film (upper DAF) used in this process
) Is the upper DAF 61a attached before the dicing step in FIG.

The electrode pad 24 of the MEMS assembly 21 and the electrode pad (24 ′) of the circuit board 25, and the electrode pad 24 ′ and the wiring board 26 of the circuit board 25 are each a gold bare wire having a diameter of 25 μm using an ultrasonic bonder. 27 (FIG. 4f)).

The structure in which the MEMS assembly 21, the circuit board 25, and the wiring board 26 were assembled was molded so as to be covered with an epoxy resin (mold resin) 29 using a transfer molding method. As a result, the configuration shown in the sectional view of FIG. 3 was obtained. In order to suppress the influence of environmental temperature changes in the completed acceleration sensor device 1, the thermal expansion coefficient of the epoxy resin (mold resin) 29 used in the transfer mold is the thermal expansion of silicon, which is the main component of the MEMS assembly 21. It is desirable to be close to the coefficient. In the acceleration sensor device of the present invention, a resin having a thermal expansion coefficient of about 6 × 10 −6 / ° C. was used.

The transfer molding operation was performed according to the following procedure and conditions. The structure in which the MEMS assembly 21, the circuit board 25, and the wiring board 26 were assembled was held at a predetermined position in the molding die. A resin molded in a tablet shape is loaded into a pod of a molding machine, the extruded portion of the pod is heated to soften the resin, and the softened resin in the pod is pressed into the mold by a plunger (pressing mechanism). A resin at 175 ° C. was pressed into the mold at a pressure of 5 MPa. Molding time is 2
Minutes. After the resin is cured in the mold, the resin molded product is taken out from the mold (FIG. 4g).
)), And the acceleration sensor device 1 was obtained by dicing into pieces (FIG. 4h)). A mold that can obtain 50 acceleration sensor devices 1 in one transfer molding operation was used.

The structure of the joint portion of the MEMS assembly 21 will be described in more detail. FIG. 5 is a cross-sectional view showing a joint portion before the upper cap chip 22, the sensor chip 2, and the lower cap chip 23 are joined. A silicon nitride film 35 that is an insulator is formed on the silicon layer 36 on the surface of the sensor chip 2, and a metallized layer 16 </ b> A is formed on the silicon nitride film 35 so as to connect the bonding portion 20 and the electrode pad portion 24. Part of the silicon nitride film 35 is opened by dry etching to form an opening 41, and the metallized layer 16A is in contact with and electrically connected to the silicon layer 36.

Two ring-shaped bonding material grooves 31 are formed in a concave shape in the bonding portion 33 of the upper cap chip 22. Subsequently, a silicon oxide film 39 is formed on a planar portion other than the inner surface (side surface and bottom surface of the groove) of the bonding material groove 31. Further, the metallized layer 16 </ b> B is disposed so as to extend to the portion sandwiched between the bonding material grooves 31, the wall surface, the bottom surface, and the outside of the bonding material grooves 31. Further, a bonding material 40 is formed in a portion sandwiched between the bonding material grooves 31.

The upper cap chip 22 is manufactured using a silicon substrate with t = 400 μm. First, the silicon substrate was heat-treated to form a silicon oxide film 39 (thickness 0.5 μm), and a resist pattern for the bonding material groove 31 was formed on one surface thereof. The silicon oxide film 39 at the resist opening is removed by dry etching, followed by SF6 gas, oxygen gas, and C4F8.
Silicon was removed by dry etching in a plasma in which a gas mixture was alternately introduced to form a bonding material groove 31 having a depth of 8 to 15 μm.
An Au—Sn alloy solder was formed as a bonding material 40 between the two bonding material grooves by a thickness of 5 μm by electrolytic plating. Further, an Au film 44 (with a thickness of 0.
1 μm) was formed. Cr (thickness 0.05 μm) as the base of Au—Sn alloy solder—
A film formed by stacking and forming Ni (thickness 0.4 μm) -Au (thickness 0.2 μm) in this order by sputtering and patterning by ion milling was used as a metallized layer 16B.

A metallized layer 16A (Cr (thickness 0.05 μm) -Ni (thickness 0.4 μm) -Au (thickness 0.5 μm)) is formed on the sensor chip 2 at a position facing the bonding material 40. A silicon nitride film 35 was formed under the metallized layer 16A.

The upper cap chip 22 and the lower cap chip 23 produced as described above and the sensor chip 2 were appropriately aligned and joined by applying weight and heating to obtain a MEMS chip. At this time, bonding is performed in a substrate state. The bonding material 40 is melted and crushed, and at the same time, an alloying reaction occurs between the metallized layer 16B on the upper cap chip 22 side and the metallized layer 16A on the sensor chip 2 side, and the integrated alloy becomes the metallized layer 16 electrically. It becomes the same potential. The silicon that is the base of the upper cap chip 22 is in contact with the metallized layer 16 at the inner surface of the bonding material groove 31, and the silicon layer 36 of one sensor chip 2 is metallized layer 16 through the opening 41 of the silicon nitride film. These are at the same potential. The weight part 11 which is a movable part is composed of a silicon layer 36, a silicon oxide film 38, and a silicon plate 37 of an SOI substrate. Of these, only the silicon layer 36 is at the same potential as the silicon that is the base of the upper cap chip 22, and the silicon plate 37 is in a floating state. However, the electrostatic attractive force with the upper cap chip 22 is strong between the silicon layer 36 having a short distance and hardly acting with the silicon plate 37 having a long distance. Therefore, a sufficient effect can be expected even in the present embodiment in which only the silicon layer 36 of the weight portion 11 has the same potential.

When the acceleration sensor device 1 was manufactured using the MEMS assembly 21 manufactured as described above, it was possible to perform a stable operation with little influence of external static electricity. For example, even when the charged resin rod was brought close to the acceleration sensor device 1, there was almost no output fluctuation.

Although a reaction layer of silicon and the bonding material 40 was observed on the inner surface of the bonding material groove 31, the region was small. Fillets were also formed at the edges of the bonding material groove 31 and the airtightness was good. Further, the bonding material 40 was thinly crushed, the gap between the movable part of the sensor chip 2 and the cap chip could be 2 μm, and a sufficient air damping effect could be obtained. Moreover, even if an excessive impact was applied, the beam was not broken, and a highly reliable acceleration sensor device could be obtained. In FIG. 5, the constituent member of the joint 20 (on the upper cap side of the sensor) corresponds to the metallized layer 16A. Constituent members of the joining portion 33 (upper cap) are the metallized layer 16B, the joining member 40, the joining member groove 31, the Au film 44, and the silicon oxide film 3.
It corresponds to 9. The component of the joint 28 (the lower cap side of the sensor) is the metallized layer 1
It corresponds to 6C. Constituent members of the joining portion 34 (lower cap) correspond to the metallized layer 16D, the joining member 40, the joining member groove 31, the Au film 44, and the silicon oxide film 39.

FIG. 6 is a cross section of the joint portion of the comparative example. A silicon oxide film 39 is also formed on the inner surface of the bonding material groove 31 of the upper cap chip 22. Further, the silicon nitride film 35 of the sensor chip 2 has no opening 41, and the electrode pad 24 and the metallized layer of the joint 20 are insulated. In the case of this comparative example, the silicon that is the base of the upper cap chip 22 and the silicon layer of the sensor chip 2 are electrically insulated.

When the acceleration sensor device 1 was manufactured using the MEMS assembly 21 manufactured as described above, a problem that the output value was not stabilized due to the influence of external static electricity occurred. For example, when the charged resin rod was brought close to the acceleration sensor device, the output value changed.

FIG. 7 is a cross section of a joint portion of another comparative example. There is no silicon oxide film 39 on both the inner surface and the flat portion of the bonding material groove 31 of the upper cap chip 22, and the metallized layer 1 is formed on the silicon of the base.
6B is formed. Further, the silicon nitride film 35 of the sensor chip 2 is not provided, and the silicon layer 3
A metallized layer 16 </ b> A is formed on 6.

In the case of this comparative example, although the silicon that is the base of the upper cap chip 22 and the silicon layer 36 of the sensor chip 2 are electrically connected, the bonding material groove 31 is used in the heat shock test.
As a result, cracks developed from the edges of the film, and the hermetic seal was broken. The heat shock test was performed under the conditions of −45 to 85 ° C., holding for 20 minutes, temperature change time within 5 minutes, and 500 cycles.

Further, as another comparative example of the present invention, a Cu layer (between the Cr layer and the Ni layer of the metallized layer)
When the joining portion was formed with the inserted structure (thickness: 0.3 μm), the gap between the movable portion of the sensor chip 2 and the cap chip could be 2.6 μm. Even in this comparative example, a sufficient air damping effect could be obtained. Thus, the thickness of the junction could be adjusted by sandwiching the Cu layer. Since the Cu layer has low film stress and good adhesion with Cr and Ni,
It is suitable as a junction thickness adjusting layer. In addition, by controlling the load and heating during bonding,
The thickness of the joint could be controlled and the same effect could be obtained.

[Embodiment 2]
Another embodiment of the present invention will be described with reference to FIG. FIG. 8 is a cross-sectional view showing a joint portion before the upper cap chip 22, the sensor chip 2, and the lower cap chip 23 of the second embodiment are joined. The silicon layer 36 and the silicon oxide film 38 directly under the opening 41 of the silicon nitride film 35 were also removed, and the metallized layer 16A was formed with the silicon plate 37 exposed. As a result, the metallized layer 16A, the silicon plate 37 of the support frame 10 and the silicon layer 36 have the same potential. In addition, the silicon layer 36 and the silicon oxide film 38 immediately below the opening 41 ′ of the silicon nitride film 35 are also removed from the weight part 11, and the metal plate 16 </ b> A is exposed with the silicon plate 37 exposed.
Formed. As a result, the metallized layer 16A, the silicon plate 37 of the weight 11 and the silicon layer 36 have the same potential. The structure of the upper cap chip 22 is the same as that of the first embodiment.

Similarly to the lower cap chip 23, the upper cap chip 22 is set to the same potential as the silicon plate 37 of the sensor chip 2 through the metallized layer 16 </ b> B on the inner surface of the bonding material groove 31. With this structure, the silicon that is the base of the upper cap chip 22, the silicon layer 36 of the sensor chip 2 and the silicon plate 37 of the support frame 10 and the weight part 11, and the silicon that is the base of the lower cap chip 23 all have the same potential. .

When the acceleration sensor device 1 was manufactured using the MEMS assembly 21 manufactured as described above, it was possible to perform a stable operation with little influence of external static electricity. For example, even when the charged resin rod was brought close to the acceleration sensor device 1, there was almost no output fluctuation.

The upper cap chip 22 having a large area in contact with the resin member 29 is most affected by the external static electricity. On the other hand, since the lower cap chip 23 has a small area in contact with the resin member 29, its influence is small. However, when the gap between the weight part 11 and the lower cap chip 23 facing the weight part 11 is narrow, the electrostatic attractive force is low. It becomes stronger and the output fluctuation becomes larger. In the present embodiment, the weight portion 11 and the silicon that is the base of the lower cap chip 23 have the same potential, and it is possible to suppress fluctuations in the output.

[Embodiment 3]
Another embodiment of the present invention will be described with reference to FIG. FIG. 9 is a cross-sectional view showing a joint portion before the upper cap chip 22, the sensor chip 2, and the lower cap chip 23 of the third embodiment are joined. A metallized layer 16A is separately formed on the electrode pad 24 and the joint 20 of the sensor chip 2, and is in contact with the silicon layer 36 through openings 41 and 41 '' of separate silicon nitride films. The silicon layers immediately below the opening are connected to each other by a conductive layer doped with boron at a high concentration, and the electrode pad 24 and the metallized layer 16A of the joint 20 are electrically connected. The configuration of the upper cap chip 22 is the same as that of the first embodiment.

When the upper cap chip 22 and the sensor chip 2 are joined, the silicon that is the base of the upper cap chip 22 has the same potential as the silicon layer 36 of the sensor chip 2. This MEMS
When the acceleration sensor device 1 was manufactured using the assembly, the influence of static electricity from the outside was small and stable operation was possible.

This embodiment is effective when the reaction rate between the metallized layer and the bonding material is high. For example, Au of the metallized layer 16 has good solder wettability and reacts very quickly with the Au—Sn alloy as the bonding material. When the electrode pad 24 and the metallized layer 16 of the joint part 20 are connected as in the first embodiment, when the upper cap chip 22 and the sensor chip 2 are joined, it reacts to Au of the metallized layer 16 of the electrode pad part 24. End up. In this case, it will become a defect which cannot perform the wire bonding of a post process. In the present embodiment, since the metallized layer 16 is separately formed on the electrode pad 24 and the bonding part 20, Au of the metallized layer 16 of the electrode pad 24 does not react with the Au—Sn alloy. Can be eliminated.

It is a disassembled perspective view of a MEMS assembly. It is a semi-transparent perspective view of an acceleration sensor device. It is sectional drawing which shows the structure of an acceleration sensor apparatus. It is a figure explaining the manufacturing process of an acceleration sensor apparatus. It is sectional drawing which shows the structure of the MEMS assembly of one Embodiment of this invention. It is sectional drawing which shows the structure of the MEMS assembly of one Embodiment of a comparative example. It is sectional drawing which shows the structure of the MEMS assembly of one Embodiment of a comparative example. It is sectional drawing which shows the structure of the MEMS assembly of one Embodiment of this invention. It is sectional drawing which shows the structure of the MEMS assembly of one Embodiment of this invention. It is sectional drawing which shows the mode of the junction part of a comparative example. It is sectional drawing which shows the mode of the junction part of a comparative example. It is sectional drawing which shows the mode of the junction part of a comparative example. It is sectional drawing which shows the mode of the junction part of one Embodiment of this invention.

Explanation of symbols

1 Acceleration sensor device,
2 Acceleration sensor chip (sensor chip),
2 'acceleration sensor board (sensor board),
10 Support frame,
11 weight,
12 Beam part,
13 X-axis piezoresistive element, 14 Y-axis piezoresistive element,
15 Z-axis piezoresistive element,
16 Metallized layer,
16A 16B 16C 16D Metallized layer,
20 joints,
21 MEMS assembly,
22 upper cap chip, 22 'upper cap substrate,
23 lower cap chip, 23 'lower cap substrate,
24 24 'electrode pads,
25 Circuit board (IC for detection),
26 Wiring board (lead frame),
27 wires,
28 joints,
29 resin members,
31 Groove for bonding material,
32 separation groove,
33 joints,
34 joints,
35 silicon nitride film,
36 silicon layer,
37 Silicon plate,
38 Silicon oxide film (sensor chip),
39 Silicon oxide film (cap chip),
40 bonding material,
41 41 'opening of silicon nitride film,
44 Au film,
45 MEMS assembly substrate,
47 fillet, 47 'collapsed fillet,
48 cracks, 49 leaked joint material,
50 A gas pool remaining in the groove for the joining member,
61a Upper DAF (upper die attach film),
61b Lower DAF (upper die attach film),
90 dicing line,
90 'dicing line

Claims (2)

A MEMS chip having a movable part formed from a semiconductor substrate and one or more cap chips formed from a semiconductor substrate and hermetically sealing the movable part of the MEMS chip.
An MS assembly;
A circuit board connected by wiring to the MEMS chip;
A semiconductor sensor device comprising the circuit board and a resin member for sealing the MEMS assembly,
The cap chip serves as a bonding material disposed in a ring shape so as to surround the movable part of the MEMS chip, a bonding material groove formed at the inner and outer peripheral positions of the bonding material, and a base of the bonding material. It comprises a metallized layer and an insulating film that is the base of the metallized layer,
The metallized layer is formed on the surface directly below the bonding material, the inner surface of the bonding material groove, and the outer surface of the bonding material groove,
The insulating film is formed on the surface directly below the bonding material and on the outer surface of the bonding material groove, and is not formed on the inner surface of the bonding material groove,
The MEMS chip has a metallized layer facing the bonding material,
The cap chip and the MEMS chip are physically connected via a bonding material, and the cap chip and the bonding material are electrically connected within a bonding material groove. Semiconductor sensor device. Electrode pads for connection to the circuit board are formed on the MEMS chip, and the electrode pads and the bonding material are electrically connected via a conductive impurity-added layer formed on the semiconductor substrate that is the base of the MEMS chip. The semiconductor sensor device according to claim 1, wherein the semiconductor sensor device is connected.

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