JPH0722579A - Input protective circuit - Google Patents

Abstract

PURPOSE:To improve a dielectric strength between a semiconductor substrate and a resistor without increasing the thickness of an insulating film by a method wherein the resistor is formed above an electrically independent impurity region with the insulating film therebetween. CONSTITUTION:An electrically independent island-shaped P-type impurity region 15 is formed on the surface region of an N-type semiconductor substrate 10 and a resistor 17 is formed on the semiconductor substrate 10 above the P-type impurity region 15 with an insulating film there-between. A first conducting line 19 which is connected to the one end of the resistor 17 and continued to an input terminal and a second conducting line 20 which is connected to the other end of the resistor 17 and continued to an inner circuit are provided. Further, source/drain regions 14 whose one side ends are connected to the first or second conducting line 19 and 20 and other side ends are connected to a power supply potential or an earth potential and a gate electrode 13 which is laid across the source/drain regions 14 and to which a certain potential is applied are provided. With this constitution, a dielectric strength between the resistor 17 connected to the input terminal and the semiconductor substrate 10 can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input protection circuit provided at an input terminal portion of a semiconductor integrated circuit device.

[0002]

2. Description of the Related Art In an integrated circuit device such as a semiconductor memory device, an internal circuit is protected by providing an input protection circuit for preventing excessive voltage or current from being transmitted to the internal circuit. FIG. 3 is a circuit diagram of an input protection circuit using a resistor and a diode.

The input terminal 1 is composed of an aluminum electrode formed on the substrate of the device, and takes in a signal from an external device via a lead connected to this electrode. A protection resistor 2 is connected in series to the input terminal 1, and the protection resistor 2
By connecting the internal circuit to the internal circuit, the input signal is transmitted to the internal circuit via the protection resistor 2. On the internal circuit side of the protection resistor 2, a pair of diodes 3 and 4 are reversely connected to the power supply potential and the ground potential, respectively, so that the level of the input signal is compensated between the power supply potential and the ground potential. There is. That is, when the potential of the input terminal 1 becomes higher than the power source potential, the current I _{1 is made} to flow through the diode 3 to lower the potential, and conversely, when it becomes lower than the ground potential, the current I _{2 is made} to flow through the diode 4 and the potential is made lower. By pulling up, the potential of the input terminal 1 is set between the ground potential and the power supply potential. According to such an input protection circuit, even if the potential of the input terminal 1 temporarily becomes high (low) due to the influence of noise or the like, the potential fluctuation does not affect the internal circuit.

By the way, in the integrated circuit device provided with the input protection circuit as described above, if the operating power source is lowered in voltage, when it is connected to a device operating at a conventional voltage,
There is a risk that a steady current will flow through the diode that constitutes the input protection circuit, causing a malfunction. For example, when the power supply of the device in which the input protection circuit is formed is set to 3V and the device that operates with the power supply of 5V is connected, the signal applied to the input terminal 1 also has a waveform of 5V. Therefore, although the normal signal is given, the current I ₁ constantly flows from the input terminal 1 to the power supply side, the power supply potential rises, and the internal circuit malfunctions.

Therefore, in an integrated circuit device in which the operating power supply voltage can be lowered, an input protection circuit using a transistor as shown in FIG. 4 is adopted. This input protection circuit is obtained by replacing the diodes 3 and 4 of the input protection circuit of FIG. 3 with a pair of MOS transistors 5 and 6, and is provided between the internal circuit side of the protection resistor 2 and the power supply potential or the ground potential.
It is configured by connecting the S transistors 5 and 6. The MOS transistors 5 and 6 are constantly turned off by fixing the gate potential. In the case of the N-channel type, the gates are fixed to the ground potential as shown in FIG. In such an input protection circuit, when the potential difference between the potential of the input terminal 1 and the ground potential exceeds the withstand voltage between the source / drain of the MOS transistor 6, a current flows to the ground side by the punch-through operation, resulting in the input. The potential of terminal 1 is lowered. Therefore, even if the potential of the input terminal 1 rises within a range that does not exceed the withstand voltage of the MOS transistor 6, the input protection circuit does not operate, and the input terminal 1 can receive the output of a device having a different operating power supply. . On the other hand, with respect to the decrease in the potential of the input terminal 1, the MOS transistor 5 is turned on when it becomes lower than the ground potential by the threshold value of the MOS transistor 5, and a current flows from the power supply side to the input terminal 1 The potential of terminal 1 is raised.
However, the potential of the input terminal 1 rises and the difference from the ground potential is M
If it becomes smaller than the threshold voltage of the OS transistor 5, MO
The S transistor 5 is turned off, and the potential rise stops.

[0006]

In the above-mentioned input protection circuit, since the protection resistor 2 is formed by the resistor body laminated on the semiconductor substrate, it is a problem to secure the breakdown voltage between the semiconductor substrate and the resistor body. Has become. The withstand voltage can be ensured by increasing the film thickness of the insulating film interposed between the semiconductor substrate and the resistor, but increasing the film thickness lowers the step coverage. When miniaturizing, it becomes a factor that reduces the manufacturing yield.

Therefore, an object of the present invention is to secure the breakdown voltage between the semiconductor substrate and the resistor without increasing the thickness of the insulating film.

[0008]

The present invention has been made to solve the above-mentioned problems, and is characterized in that a protection resistor is connected in series between an input terminal and an internal circuit, In an input protection circuit in which a protection transistor is connected to one end of the protection resistor, an impurity region of opposite conductivity type electrically isolated from the surface region of a semiconductor substrate of one conductivity type and formed in an island shape, and the impurity region Corresponding to, a resistor formed on the semiconductor substrate via an insulating film, a first conductive line connected to one end of the resistor and connected to the input terminal, and the other end of the resistor on the other end. A second conductive line connected to the internal circuit and formed on a surface region of the semiconductor substrate, one of which is connected to the first or second conductive line and the other of which is connected to a power supply potential or a ground potential. At least a pair of sauces And the drain region, these source /
At least one gate electrode formed on the semiconductor substrate and provided with a constant potential across the drain region.

[0009]

According to the present invention, the resistor is formed on the electrically independent impurity region via the insulating film, so that the resistor is formed by the depth of the impurity region in addition to the film thickness of the insulating film. Since the substantial distance between the semiconductor substrate and the semiconductor substrate is increased, the breakdown voltage between the semiconductor substrate and the resistor is increased.

[0010]

1 is a plan view showing the structure of an input protection circuit of the present invention, and FIG. 2 is a sectional view taken along line XX of FIG. A potential-fixed P-type diffusion layer 11 serving as an element formation region is formed in the surface region of the N-type semiconductor substrate 10, and a gate made of polycrystalline silicon is formed on the diffusion layer 11 via a thin oxide film 12. The electrode 13 is formed. In diffusion layer 11, source / drain regions 14 into which N-type impurities have been implanted are formed using gate electrode 12 as a mask, and N-channel type MOS transistor is formed together with gate electrode 13. In addition, the semiconductor substrate 1 adjacent to the diffusion layer 11
In the surface region of 0, an electrically independent P-type diffusion layer 15 is formed.
Is formed, and a resistor 17 made of polycrystalline silicon is formed on the diffusion layer 15 through an oxide film 16 thickly formed by a selective oxidation method. The resistor 17 is formed so as to be within the range of the diffusion layer 15 formed on the semiconductor substrate 10. The diffusion layer 15 and the resistor 17 are the same as the diffusion layer 11 in the element formation region and the gate electrode 13 of the MOS transistor, and are formed by the same process.

Then, an interlayer insulating film 18 is formed on the semiconductor substrate 10 so as to cover the gate electrode 13 and the resistor 17, and various aluminum wirings 19 to 22 are formed on the interlayer insulating film 18. The aluminum wiring 19 forming the input terminal is connected to the resistor 1 through the contact hole 23.
A signal applied to the input terminal is applied to the resistor 17, which is connected to one end of the resistor 7. The aluminum wiring 20 connected to the internal circuit is connected to the other end of the resistor 17 through the contact hole 24 to transmit the signal input from the input terminal to the internal circuit, and through the contact hole 25, the source / source of the protection MOS transistor. Drain region 14
Connected to. The aluminum wiring 21 to which the ground potential is applied is connected to the MOS through the contact holes 26 and 27.
It is connected to one of the source / drain regions 14 of the transistor and the gate electrode 13, and fixes the gate and source potentials of the MOS transistor to the ground potential. Further, the aluminum wiring 22 to which the power supply potential is applied is connected to the other of the source / drain regions 14 of the MOS transistor through the contact hole 28 and fixes the potential of the drain of the MOS transistor to the power supply potential.

According to the above structure, the resistor 17 serves as a protective resistor, and the gate electrode 13 and the source / drain region 14 are provided.
The MOS transistor is connected between the protection resistor and the power supply potential or the ground potential to form an input protection circuit as shown in FIG. Here, the resistor 17 is the oxide film 1
6 and the diffusion layer 15 separate from the semiconductor substrate 10, the breakdown voltage is increased by the depth of the diffusion layer 15 in addition to the breakdown voltage of the oxide film 16.

In the above embodiments, the semiconductor substrate 10 is N-type and the MOS transistor is N-channel type. However, the conductivity type of the semiconductor substrate 10 and the MOS transistor is P-type. It doesn't matter.
However, when the MOS transistor is P-type, the potential applied to the gate needs to be the power supply potential. Further, the MOS transistor connected between the power supply potential and the ground potential may be connected to the input terminal side of the resistor 17.

[0014]

According to the present invention, the breakdown voltage between the protective resistor connected to the input terminal and the semiconductor substrate can be improved, and the reliability of the device can be improved. In addition, since the thickness of the insulating film that insulates between the protective resistor and the semiconductor substrate can be reduced, the step coverage is improved and the manufacturing yield can be prevented from lowering.

[Brief description of drawings]

FIG. 1 is a plan view showing a structure of an input protection circuit of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a circuit diagram of an input protection circuit using a diode.

FIG. 4 is a circuit diagram of an input protection circuit using a MOS transistor.

[Explanation of symbols]

 1 Input Terminal 2 Protection Resistor 3, 4 Diode 5, 6 MOS Transistor 10 Semiconductor Substrate 11, 15 P-type Diffusion Layer 12, 16 Oxide Film 13 Gate Electrode 14 Source / Drain Region 17 Resistor 18 Interlayer Insulating Film 19-22 Aluminum Wiring 23 to 28 contact holes

Claims (1)

[Claims] 1. In an input protection circuit in which a protection resistor is connected in series between an input terminal and an internal circuit, and a protection transistor is connected to one end of the protection resistor, an electric field is formed on a surface region of a semiconductor substrate of one conductivity type. Oppositely-conducting impurity regions formed independently in an island shape, and a resistor formed corresponding to the impurity regions on the semiconductor substrate via an insulating film,
A first conductive line connected to one end of the resistor and continuous to the input terminal, a second conductive line connected to the other end of the resistor and connected to the internal circuit, and a surface region of the semiconductor substrate. And at least one pair of source / drain regions connected to the first or second conductive line and the other connected to the power supply potential or the ground potential, and the source / drain regions. An input protection circuit, comprising: at least one gate electrode formed on a semiconductor substrate and supplied with a constant potential.