ESD protection device

The present application is a continuation of PCT/JP2014/054403 filed Feb. 25, 2014, which claims priority to JP Application No. 2013-126659, filed Jun. 17, 2013, and JP Application No. 2013-079978, filed Apr. 5, 2013, the entire contents of each of which are incorporated herein by reference.

The present invention relates to an ESD protection device which protects an electronic circuit from surge such as electrostatic discharge.

Various electronic devices include ICs. In order to protect the ICs from surge caused by ESD (electrostatic discharge), an ESD protection device as described in, for example, Patent Document 1 is connected to input/output parts of the ICs. Patent Document 1 discloses an ESD protection device with an integrated circuit formed on a semiconductor substrate, thereby achieving the reduction in size for ESD protection devices.

Patent Document 1: JP 2008-507124 W.

However, when a semiconductor substrate is exposed in an ESD protection device with an integrated circuit formed on the semiconductor substrate as in Patent Document 1, there is a possibility that a phenomenon will be caused in which the semiconductor substrate comes into contact with an outer conductor to cause ESD or noise current to flow through the semiconductor substrate into the integrated circuit, and further flow through a circuit (signal line) with the ESD protection device connected thereto.

Therefore, an object of the present invention is to provide an ESD protection device which can suppress the influence of external noise, etc.

The present invention characteristically includes: a semiconductor substrate with an ESD protection circuit formed; a first metallic film formed on a first surface of the semiconductor substrate, and electrically connected to a first input/output terminal of the ESD protection circuit; a second metallic film formed on the first surface of the semiconductor substrate, and electrically connected to a second input/output terminal of the ESD protection circuit; a rewiring layer formed on the first surface of the semiconductor substrate, which electrically connects the first metallic film and a first external electrode and electrically connects the second metallic film and a second external electrode; and an insulating resin film formed on a second surface of the semiconductor substrate.

In this configuration, the semiconductor substrate is protected with the insulating resin film, and thus, even when the semiconductor substrate comes into contact with an outer conductor, no noise (current) will flow in through the semiconductor substrate.

The insulating resin film is preferably a film of thermoplastic resin.

In this configuration, for example, in the case of separating individual ESD protection devices from a wafer by cutting with a dicer, the insulating resin film can flow out to side surfaces of the semiconductor substrates by heat in cutting with a dicer, and protect not only the second surface of the semiconductor substrates, but also the side surfaces.

The insulating resin film has multiple layers formed, and among the multiple layers, at least one layer closer to the semiconductor substrate is preferably a thermosetting resin.

In this configuration, even when the insulating resin film is melted by heat in cutting with a dicer to produce parts reduced in film thickness, the thermosetting resin can prevent the semiconductor substrate from being exposed.

The insulating resin film preferably has the same thickness as a resin layer included in the rewiring layer.

In this configuration, warpage can be suppressed which is caused under the influence of heat shrinkage of the semiconductor substrate, and the semiconductor substrate can be precisely cut with a dicer.

According to the present invention, the protection of the semiconductor substrate with the insulating resin film can prevent the semiconductor substrate from coming into contact with an outer conductor to cause noise (current) to flow in through the semiconductor substrate.

FIG. 1 is a front cross-sectional view of an ESD protection device according to an embodiment.

FIG. 2A is a diagram illustrating the planar configuration of an ESD protection circuit formed on a Si substrate.

FIG. 2B is a circuit diagram of an ESD protection circuit.

FIG. 3A is a diagram illustrating the pathway of current flowing through an ESD protection device.

FIG. 3B is a diagram illustrating the pathway of current flowing through an ESD protection device.

FIG. 4 is a schematic diagram illustrating cut sections of an ESD protection device, which are obtained when an insulating resin film is thermoplastic.

FIG. 5 is a cross-sectional view of an ESD protection device obtained when multiple layers of insulating resin films are formed.

FIG. 6 is a front cross-sectional view of another example of an ESD protection device according to an embodiment.

FIG. 7A is a diagram illustrating an example of connecting an ESD protection device according to an embodiment.

FIG. 7B is a diagram illustrating an example of connecting an ESD protection device according to an embodiment.

FIG. 1 is a front cross-sectional view of an ESD protection device according to the present embodiment. The ESD protection device 1 is a CSP (Chip Size Package) type device, where a rewiring layer 20 including multiple resin layers, etc. is formed on a Si substrate 10 configured to have an ESD protection circuit 10 A including a diode and a zener diode. While the Si substrate 10 corresponds to a semiconductor substrate according to the present invention, the semiconductor substrate according to the present invention is not limited to any Si substrate, but may be a GaAs substrate or the like.

FIG. 2A is a diagram illustrating the planar configuration of the ESD protection circuit 10 A formed in the Si substrate 10 , whereas FIG. 2B is a circuit diagram of the ESD protection circuit 10 A. The Si substrate 10 is a p-type substrate, at the surface thereof, a p-type epitaxial layer is formed, n wells and p wells are sequentially formed in the p-epitaxial layer, and the wells and a p-type diffusion layer or an n-type diffusion layer form diodes and zener diodes in the Si substrate 10 .

In the present embodiment, diodes D 1 a , D 1 b , D 3 a , D 3 b are formed at the surface of the Si substrate 10 . Further, diodes D 2 , D 4 and a zener diode Dz are formed in the thickness direction of the Si substrate 10 . The respective elements form the circuit shown in FIG. 2B . It is to be noted that in FIG. 2B , the diodes D 1 a , D 1 b are expressed as one diode D 1 , whereas the diodes D 3 a , D 3 b are expressed as one diode D 3 .

The diodes D 1 , D 2 formed are aligned in the forward direction and connected in series, whereas the diodes D 3 , D 4 are aligned in the forward direction and connected in series. In addition, the diodes D 1 , D 2 and diodes D 3 , D 4 connected in series are each aligned in the forward direction, and connected in parallel with the zener diode Dz. Furthermore, the zener diode Dz is formed between the forming positions of the diodes D 1 , D 4 , and between the forming positions of the diodes D 2 , D 3 . The connection point between the diodes D 1 a , D 1 b and diode D 2 formed serves as a first input/output terminal of the ESD protection circuit 10 A, which is connected to an Al pad (hereinafter, referred to as a pad) P 1 formed on the Si substrate 10 . In addition, the connection point between the diodes D 3 a , D 3 b and diode D 4 formed serves as a second input/output terminal of the ESD protection circuit 10 A, which is connected to an Al pad (hereinafter, referred to as a pad) P 2 formed on the Si substrate 10 . The pads P 1 , P 2 correspond to a first metallic film and a second metallic film according to the present invention.

The rewiring layer 20 formed on the surface layer of the Si substrate 10 includes a SiN protection film (not shown) formed on the surface of the Si substrate 10 , and a resin layer 21 covering the SiN protective film, so as to partially cover the pads P 1 , P 2 . The SiN protection film is formed by sputtering, and the resin layer 21 is formed by spin coating with an epoxy (or polyimide) solder resist. The SiN protection film and the resin layer 21 have openings (contact holes) formed for exposing parts of the pads P 1 , P 2 .

Layers of Ti and Cu are formed in the contact holes and on regions around the contact holes, and the layers constitute interlayer wirings 21 A, 21 B. Columnar in-layer electrodes 22 A, 22 B are formed partially on the surfaces of the interlayer wirings 21 A, 21 B. The in-layer electrodes 22 A, 22 B are built in a resin layer 23 composed of an epoxy (or polyimide) resin.

The surfaces of the in-layer electrodes 22 A, 22 B have metal plated films 23 A, 23 B such as Ni/Au or Ni/Sn formed. The metal plated films 23 A, 23 B are electrically connected to the in-layer electrodes 22 A, 22 B. The ESD protection device 1 is mounted on a mother board so that the metal plated films 23 A, 23 B serve as a surface connected to the mother board such as a printed wiring board. In addition, in the present embodiment, the metal plated film 23 A is connected to a terminal electrode for signal line of the mother board, whereas the metal plated film 23 B is connected to a terminal electrode for grounding.

On the rear surface (the surface on the side opposite to the surface with the rewiring layer 20 formed) of the Si substrate 10 , an insulating resin film 30 is formed by applying a solder resist such as an epoxy resin with a resistivity of 1 MΩ·cm, for example. The formation of the insulating resin film 30 can prevent external current from affecting the ESD protection device 1 . The principle for operation of the ESD protection device 1 will be described below as well with reference to FIGS. 2 and 3 .

FIGS. 3A and 3B are diagrams illustrating the pathway of current flowing through the ESD protection device 1 . It is to be noted that the illustration of the rewiring layer 20 is omitted in FIG. 3A .

As described above, the pad P 1 leading to the first input/output terminal of the ESD protection circuit 10 A is connected to a signal line, whereas the pad P 2 leading to the second input/output terminal is connected to the ground. The surge current from the signal line to the pad P 1 flows from the diode D 1 and the zener diode Dz through the diode D 4 to the pad P 2 , as shown by the pathway of a dashed line in FIGS. 3A and 3B . Then, the current is discharged from the pad P 2 to the ground for a mother board with the ESD protection device 1 connected thereto.

As described above, the respective elements of the ESD protection circuit 10 A are formed in the Si substrate 10 as a p-type substrate. For this reason, if an outer conductor comes into contact with the Si substrate 10 of the ESD protection device 1 without the insulating resin film 30 formed, there is a possibility that a current Iout will flow into the Si substrate 10 from the outer conductor. In this case, there is a possibility that the current Iout will flow from the diodes D 2 , D 4 into the pads P 1 , P 2 as shown in FIG. 3B , and flow from there into the signal line. In this case, the function of the ESD protection device 1 will be damaged, such as discharge of surge current from the signal line to the ground. According to the present invention, the formation of the insulating resin film 30 on the Si substrate 10 can prevent the current Iout from flowing into the Si substrate 10 .

It is to be noted that the ESD protection device 1 is bidirectional, and for example, when surge current is input from the pad P 2 , the current is discharged from the pad P 1 to the ground through the diode D 3 , the zener diode Dz, and the diode D 2 .

In addition, the insulating resin film 30 has the same thickness as the rewiring layer 20 . The ESD protection device 1 is formed (chipping) by cutting integrated circuits formed on a silicon wafer with a dicer. If the insulating resin film 30 is not formed, there is a possibility that the silicon wafer will be pulled to the rewiring layer 20 to cause warpage when the insulating resin film 30 is subjected to curing, thereby resulting in failure to cut the silicon wafer in a horizontal position with a dicer. Therefore, the formation of, on the rear surface of the Si substrate 10 , the insulating resin film 30 which has almost the same thickness and the same material as the rewiring layer 20 can suppress warpage of the silicon wafer, and cut the silicon wafer in a horizontal position with a dicer. In addition, the insulating resin film 30 can prevent the Si substrate 10 from being subjected to chipping. It is to be noted that the thickness of the insulating resin film 30 is not limited to the same thickness as the rewiring layer 20 .

This insulating resin film 30 may be thermoplastic, and in this case, the influence of the current Iout may be further suppressed. FIG. 4 is a schematic diagram illustrating cut sections of the ESD protection device 1 , which are obtained when the insulating resin film 30 is thermoplastic. When the ESD protection device 1 is formed (chipping) by cutting the integrated circuits formed on the silicon wafer with a dicer, the insulating resin films 30 hang over side surfaces of the Si substrates 10 by heat generation in the case of the cutting with a dicer, as shown in FIG. 4 . Thus, the insulating resin film 30 can insulate and protect not only the rear surfaces of the Si substrates 10 , but also the side surfaces.

In addition, multiple layers of insulating resin films may be formed on the rear surface of the Si substrate 10 . FIG. 5 is a cross-sectional view of an ESD protection device obtained when multiple layers of insulating resin films are formed. In this example, a thermosetting resin 31 is formed on the rear surface of the Si substrate 10 , and further, a thermoplastic resin 32 is formed. In this case, even when the thermoplastic resin 32 is melted by heat in cutting with a dicer to produce parts reduced in film thickness, the thermosetting resin 31 can prevent the Si substrate 10 from being exposed.

It is to be noted that three or more layers of insulating resin films may be formed. In this case, at least one layer closer to the Si substrate 10 is preferably a thermosetting resin, in order to prevent the Si substrate 10 from being exposed.

FIG. 6 is a front cross-sectional view of another example of the ESD protection device 1 according to the present embodiment. The ESD protection device 1 A has, as in FIG. 1 , the Si substrate 10 with the ESD protection circuit 10 A configured, and a rewiring layer 40 formed on the Si substrate 10 .

The rewiring layer 40 formed on the surface layer of the Si substrate 10 includes a SiN (or SiO 2 ) protection film 41 formed on the surface of the Si substrate 10 so as to partially cover peripheral edges of the pads P 1 , P 2 , and a resin layer 42 covering the SiN protective film 41 and the pads P 1 , P 2 . The SiN protection film 41 is formed by sputtering, and the resin layer 42 is formed by spin coating with an epoxy (or polyimide) solder resist. The resin layer 42 has contact holes formed for exposing parts of the pads P 1 , P 2 .

Ti/Cu/Ti electrodes 43 A, 43 B are formed in the contact holes and on regions around the holes. The Ti/Cu/Ti electrodes 43 A, 43 B have planar parts opposed to the surface of the Si substrate 10 , and have electrical connection to the pads P 1 , P 2 through the contact holes of the resin layer 42 . The Ti/Cu/Ti electrodes 43 A, 43 B serve as current pathways for surge current (ESD current) through the ESD protection device 1 A.

External electrodes 44 A, 44 B of Au/Ni are formed partially on the planar parts of the Ti/Cu/Ti electrodes 43 A, 43 B. The parts of the Ti/Cu/Ti electrodes 43 A, 43 B, on which the external electrodes 44 A, 44 B are formed, are etched to have Cu exposed, and the exposed Cu parts are selectively plated with the external electrodes 44 A, 44 B. The external electrodes 44 A, 44 B serve as terminal electrodes for input/output terminals of the ESD protection device 1 , and correspond to, for example, the metal plated films 23 A, 23 B shown in FIG. 1 .

The rewiring layer 40 includes a resin layer 46 further formed on the resin layer 42 . The resin layer 46 is, for example, a layer of low-dielectric-constant epoxy resin (or a polyimide resin, a liquid crystal polymer, or the like). It is to be noted that the Ti/Cu/Ti electrodes 43 A, 43 B have Ti as a surface layer, and thus have a joint strength between the Ti/Cu/Ti electrodes 43 A, 43 B and the resin layer 46 . This resin layer 46 has openings 46 A, 46 B formed for exposing parts of the external electrodes 44 A, 44 B.

On the rear surface of the Si substrate 10 , an insulating resin film 50 is formed by applying a solder resist such as an epoxy resin with a resistivity of 1 MΩ·cm, for example. The insulating resin film 50 has the same thickness as the rewiring layer 40 .

The formation of the insulating resin film 50 can prevent external current from affecting the ESD protection device 1 A. In addition, the formation of the insulating resin film 50 can suppress warpage of the silicon wafer during manufacture.

FIGS. 7A and 7B are diagrams illustrating examples of connecting the ESD protection device 1 according to the present embodiment. The ESD protection device 1 is mounted on an electronic device. Examples of the electronic device include laptop PCs, tablet terminals, cellular phones, digital cameras, and portable music players.

FIG. 7A shows an example of connecting the ESD protection device 1 between a single line connecting an I/O port 100 and an IC 101 to be protected, and GND. The I/O port 100 is, for example, a port to which an antenna is connected. The ESD protection device 1 according to the present embodiment is bidirectional, and any of the first input/output terminal and second input/output terminal may serve as an input terminal. For example, when the first input/output terminal is treated as an input terminal, the first input/output terminal is connected to the signal line, whereas the second input/output terminal is connected to the GND.

FIG. 7B shows an example of connecting the ESD protection devices 1 between single lines connecting a connector 102 and an IC 101 , and a GND line. The signal lines in this example are, for example, high-speed transmission lines (differential transmission lines), and the ESD protection device 1 is connected between each of the multiple signal lines and the GND line.

As described above, for the ESD protection device 1 according to the present embodiment, the formation of the insulating resin film 30 on the Si substrate 10 can prevent the Si substrate 10 from coming into contact with an outer conductor to cause noise (current) to flow through the Si substrate 10 into the signal line.

1 , 1 A ESD protection device

10 Si substrate

10 A ESD protection circuit

20 rewiring layer

21 resin layer

21 A, 21 B interlayer wiring

22 A, 22 B in-layer electrode

23 resin layer

23 A metal plated film (first external electrode)

23 B metal plated film (second external electrode)

30 insulating resin film

31 thermosetting resin

32 thermoplastic resin

40 rewiring layer

41 SiN protection film

42 resin layer

43 A, 43 B Ti/Cu/Ti electrode

44 A, 44 B external electrode

46 resin layer

46 A, 46 B opening

50 insulating resin film

P 1 pad (first metallic film)

P 2 pad (second metallic film)

D 1 to D 4 diode

Dz zener diode