JP4276118B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device including an electrostatic breakdown protection element, and more particularly to a semiconductor device including an electrostatic breakdown protection element that is not damaged even when a large current flows.

  In general, semiconductor devices are easily damaged by static electricity. For this reason, an electrostatic breakdown protection element is generally provided between the input / output electrode and the internal circuit (see Patent Document 1).

An example of this type of electrostatic breakdown protection element is shown in FIG. In FIG. 2A, 1 is a P-type semiconductor substrate, 2 is an N ⁺ type buried layer constituting a part of the collector region, 3 is a P ⁺ type buried layer constituting a part of the isolation region, N-type epitaxial layer, 5 is a LOCOS oxide film, 6 is a P-type diffusion layer that forms an isolation region together with P ⁺ -type buried layer 3, and 7 is an N-type that forms part of a collector region together with N ⁺ -type buried layer 2 The reference numeral 8 denotes a P-type base region, 9 denotes an N-type emitter region, 10 denotes an oxide film, 11 denotes an interlayer insulating film, 12a and 12b denote aluminum wirings, and 13 denotes a P ⁺ -type diffusion layer.

The electrostatic breakdown protection element shown in FIG. 2A is formed simultaneously with the NPN bipolar transistor constituting the internal circuit. First, in order to form the N ⁺ type buried layer 2 constituting a part of the collector region and the P ⁺ type buried layer 3 constituting a part of the isolation region on the P type semiconductor substrate 1, ions are implanted and diffused. I do. Thereafter, an N type epitaxial layer 4 is grown, and an N ⁺ type buried layer 2 and a P ⁺ type buried layer 3 are formed. Impurity ions are implanted from the surface of the N-type epitaxial layer 4 to form a P-type diffusion layer 6 that reaches the previously formed P ⁺ -type buried layer 3, thereby forming an isolation region. After the LOCOS oxide film 5 is formed, impurity ions are implanted into the region where the collector region is to be formed, and an N-type collector region 7 reaching the N ⁺ -type buried layer 2 formed earlier is formed, thereby forming a collector region. Next, an oxide film 10 is formed on the surface. Impurity ions are implanted into the base region formation planned region to form the P-type base region 8. Similarly, impurity ions are implanted into the emitter region formation planned region through the oxide film 10 to form the N-type emitter region 9. In order to form a base extraction region connected to the P-type base region 8, impurity ions are implanted to form a P ⁺ -type diffusion layer 13. After forming the interlayer insulating film 11, the oxide film 10 on the N-type collector region 7, the N-type emitter region 9, and the P ⁺ -type diffusion layer 13 is removed, and an aluminum wiring 12 a connected to the N-type collector region 7, P-type An aluminum wiring 12b connected to the base region 8 and the N-type emitter region 9 is formed. The aluminum wiring 12a is connected to the power supply voltage potential (Vcc), and the aluminum wiring 12b is connected to the ground potential to complete the electrostatic protection element.

In the electrostatic breakdown protection element having such a structure, when a strong negative voltage is applied to the aluminum wiring 12a connected to the N-type collector region 7, the order of the PN junction between the N-type epitaxial layer 4 and the P ⁺ -type diffusion layer 13 is increased. A current flows in the direction, and the electric charge is discharged to the side of the aluminum wiring 12b grounded by short-circuiting the P ⁺ -type diffusion layer 13 and the N-type emitter region 9. In this case, the PN junction has forward characteristics, the breakdown current of the electrostatic protection element is sufficiently large, and even if a large current flows through the PN junction, the electrostatic protection element is not destroyed.

On the other hand, FIG. 2B shows current-voltage characteristics when a strong positive voltage is applied to the aluminum wiring 12a connected to the N-type collector region. Unlike the case where the negative voltage is applied, the reverse current of the PN junction gradually increases as the applied voltage increases, and the reverse current flows into the N ⁺ -type buried layer 2. The potential of the base region 8 rises. When this potential reaches the voltage V2 that causes the avalanche breakdown phenomenon of FIG. 2B, the NPN bipolar transistor is turned on at that moment, and a large current flows between the P ⁺ -type diffusion layer 13 and the N-type epitaxial layer 4. Passes, and the electric charge is discharged to the ground.
JP 2001-144191 A

  In the electrostatic breakdown protection element having the structure shown in FIG. 2A, the resistance value around the N-type emitter region 9 is high and current does not easily flow. Therefore, when an avalanche breakdown phenomenon occurs and a large current passes, high heat is generated in the current path around the N-type emitter region 9 and the electrostatic breakdown protection element is destroyed. In order to prevent the destruction of the electrostatic discharge protection element, even if the emitter area is increased, the resistance value around the N-type emitter region 9 is high, the current does not flow easily, and the breakdown of the electrostatic discharge protection element cannot be prevented. . Therefore, an object of the present invention is to provide a semiconductor device including an electrostatic breakdown protection element that does not break down even when a large current is generated.

In order to solve the above-described object, the present invention provides a semiconductor substrate on which a one-conductivity type epitaxial layer is formed, the one-conductivity type buried layer between the semiconductor substrate and the epitaxial layer, and the surface of the epitaxial layer. A collector region composed of a diffusion layer of one conductivity type reaching the buried layer, a base region composed of a diffusion region of reverse conductivity type formed on the surface of the epitaxial layer, and a conductivity type formed on the surface of the base region An electrostatic breakdown protection element comprising an emitter region composed of a diffusion region, a first electrode connecting the emitter region and the base region, and a second electrode connected to the collector region, in the semiconductor device to be protected from electrostatic breakdown, the base region in contact with the disposed so as to surround the emitter region, the base region impurity concentration rather higher than, partially pre In contact with the epitaxial layer comprises a heavily doped region of the one conductivity type, wherein, when the first electrode and the voltage applied between the second electrode is increased, the epitaxial and the high concentration region of the electrostatic discharge protection element When an electric current is passed through a PN junction composed of a layer, the applied potential between the first electrode and the second electrode further increases, and the potential applied to the base region increases, the electrostatic breakdown protection element A current is passed through a PN junction formed by the emitter region and the base region.

  In the semiconductor device of the present invention, when a large positive voltage is applied to the collector region, the voltage rises until avalanche breakdown occurs, and a current flows through the PN junction composed of the base region and the emitter region. The structure does not occur. As a result, it is possible to prevent destruction of the electrostatic breakdown protection element due to heat. Further, since no high heat is generated, the value of the current flowing between the PN junctions can be increased.

In the electrostatic breakdown protection element of the present invention, as described above, in the vicinity of the emitter region, a large current can flow between the high concentration region and the emitter region with respect to a rapid potential change such as static electricity. high high-concentration region impurity concentration than the base region, enclose take emitter region, a portion is placed in contact with the epitaxial layer. Hereinafter, the present invention will be described in detail.

FIG. 1 shows a cross-sectional view in which an electrostatic breakdown protection element according to the present invention is formed of an NPN bipolar transistor. The electrostatic breakdown protection element according to the present invention can be formed as follows. First, impurity ions are implanted on the P-type semiconductor substrate 1 to form an N ⁺ -type buried layer 2 constituting a part of the collector region and a P ⁺ -type buried layer 3 constituting a part of the isolation region. . Thereafter, the N-type epitaxial layer 4 is grown to a thickness of about 5 μm. A P-type diffusion layer 6 connected to the previously formed P ⁺ -type buried layer 3 is formed, and an element isolation layer is formed. Further, a LOCOS oxide film 5 is formed on the surface of the N type epitaxial layer 4. Thereafter, an N type collector region 7 reaching the N ⁺ type buried layer 2 is formed. Next, the P-type base region 8 is formed.

After forming the oxide film 10 on the exposed surface, the N-type emitter region 9 is formed. Next, a P + type high concentration impurity layer 14 is formed. The high-concentration impurity layer 14 is formed so as to surround the periphery of the N-type emitter region 9, with the end portion disposed around 1 μm away from the end portion of the N-type emitter region 9. The part of the high concentration impurity layer 14, placed in contact with the N-type epitaxial layer 4 of the N-type collector region 7 side.

  Thereafter, an interlayer insulating film 11 is formed on the entire surface, and the surfaces of the N-type collector region 7, the high-concentration impurity layer 14, and the N-type emitter region 9 are exposed, and aluminum wirings 12a and 12b connected to the respective surfaces are formed. The aluminum wiring 12a is connected to the power supply voltage potential (Vcc), and the aluminum wiring 12b is connected to the ground potential, thereby completing the electrostatic breakdown protection element.

  The semiconductor device including the electrostatic breakdown protection element as described above has a forward characteristic of the PN junction between the N-type epitaxial layer 4 and the high-concentration impurity layer 14 when an excessive negative voltage is applied to the aluminum wiring 12a. Discharge charge to ground.

  Further, when an excessive positive voltage is applied to the aluminum wiring 12a, the electrical characteristics shown in FIG. That is, since the PN junction between the N-type epitaxial layer 4 and the high-concentration impurity layer 14 is in the opposite direction, the depletion layer spreads and no current flows. However, when the voltage V1 is reached due to the avalanche breakdown phenomenon, a reverse current flows through the PN junction. When the flowing current gradually increases, a reverse current flows into the N-type buried layer 2 and the potential of the P-type base region 8 rises due to a voltage drop. With this potential increase, the NPN transistor is turned on, and a reverse current flows through the NPN junction composed of the N-type epitaxial layer 4, the high-concentration impurity layer 14, the P-type base region 8, and the N-type emitter region 9, and the aluminum wiring 12a A large current can flow through the aluminum wiring 12b, and the charge is discharged to the ground.

  In particular, according to the present invention, since the high-concentration impurity layer 14 can reduce the resistance around the N-type emitter region 9, a high-resistance portion is not generated around the P-type base region 8. The P-type base region 8 around the emitter region 9 does not reach a high temperature. In addition, since the high-concentration impurity layer 14 is disposed so as to surround the N-type emitter region 9, current does not concentrate. As a result, element destruction due to heat can be prevented.

  In this embodiment, the dimension between the N-type emitter region 9 and the high-concentration impurity layer 14 is 1 μm, but the N-type emitter region 9 and the high-concentration impurity layer 14 are not in contact with each other and the resistance does not increase. It can be set as appropriate. Further, the voltage V1 of the electrostatic breakdown protection element, the current value flowing through the PN junction between the N-type epitaxial layer 4 and the high-concentration impurity layer 14, and the PN junction between the P-type base region 8 and the N-type emitter region 9 are A desired value can be set by appropriately setting the impurity concentration, size, and the like of the semiconductor region.

  For example, in the electrostatic breakdown protection element having the characteristics shown in FIG. 1B, the N-type epitaxial layer 4 has a specific resistance of 5 Ω · cm, a thickness of 5 μm, an emitter size of 6 μm × 50 μm, and a high-concentration impurity layer 14. Although the case where the width is 4 μm is shown, the current value that can be passed through the electrostatic breakdown protection element can be increased by increasing only the emitter width.

  In addition, it was confirmed that when the width of the high concentration impurity layer 14 is 2 μm, the breakdown current (current value leading to breakdown) of the electrostatic breakdown protection element decreases and varies as compared with the case of 4 μm. Specifically, when the width of the high-concentration impurity layer 14 is 4 μm, the average breakdown current is 2.5 A and the variation is 1.12%. When the width is 2 μm, the average breakdown current is 1.98 A and the variation is 9.2. Confirmed to be 62%. Therefore, when the voltage V1 is large, the width of the high-concentration impurity layer 14 needs to be widened and set to a width where variations and the like are small.

  In the present invention, the high-concentration impurity layer 14 needs to be disposed so as to surround the entire periphery of the N-type emitter region 9 so that the current can be more dispersed. That is, when the formation conditions such as the emitter size and the width of the high-concentration impurity layer are the same, and the case where the high-concentration impurity layer is disposed so as to surround the periphery of the emitter region is compared with the case where it is disposed only on the collector region side. It was confirmed that the former average breakdown current was 2.5 A and the variation was 1.12%, but the latter average breakdown current was decreased to 1.68 A and the variation was increased to 12.5%. Because.

It is a figure explaining one Example of the semiconductor device of this invention. It is a figure explaining this kind of conventional semiconductor device.

Explanation of symbols

1: P type semiconductor substrate, 2: N ⁺ type buried layer, 3: P ⁺ type buried layer, 4: N type epitaxial layer, 5: LOCOS layer, 6: P type diffusion layer, 7: N type collector region 8: P-type base region, 9: N-type emitter region, 10: oxide film, 11: insulating oxide film, 12a, 12b: aluminum wiring, 13: P ⁺ type diffusion layer, 14: high-concentration impurity layer

Claims (1)

One conductivity type buried layer between the semiconductor substrate and the epitaxial layer, and one conductivity type diffusion reaching the buried layer from the surface of the epitaxial layer on the semiconductor substrate on which the one conductivity type epitaxial layer is formed A collector region composed of layers, a base region composed of a reverse conductivity type diffusion region formed on the surface of the epitaxial layer, an emitter region composed of a one conductivity type diffusion region formed on the surface of the base region, and In a semiconductor device that includes an electrostatic breakdown protection element including a first electrode that connects an emitter region and the base region and a second electrode that is connected to the collector region, and protects an internal circuit from electrostatic breakdown.
The base region in contact and arranged to surround said emitter region, said base region impurity concentration rather higher than, part is in contact with the epitaxial layer comprises a heavily doped region of the one conductivity type,
When an applied voltage between the first electrode and the second electrode rises, a current is passed through a PN junction constituted by the high concentration region of the electrostatic breakdown protection element and the epitaxial layer,
When the potential applied between the first electrode and the second electrode is further increased and the potential applied to the base region is increased, the emitter region and the base region of the electrostatic breakdown protection element are configured. A semiconductor device characterized by passing a current through a PN junction.

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