JPS61283155A - Input protecting circuit of semiconductor device - Google Patents

Abstract

PURPOSE:To avoid the damage of a protecting circuit due to a breakdown of a P-N junction by forming an input protecting resistor of polysilicon wirings, and branching the input of the wirings from the midway of the connector to internal wirings to connect with a discharge transistor. CONSTITUTION:Protecting resistors R1, R2 are formed of polysilicon wirings 8, and connected with an N-type region 2 to become a drain of a protecting MOS transistor Q1 in the form of branching from the midway of the wirings 8. An input to the transistor Q1 is performed through the resistor of the wirings 8 for forming the resistors R1, R2. Thus, even if the value of the resistor R1 becomes several 100 - several kilo ohms or larger, a large current does not flow due to the breakdown of a P-N junction, but a current flowing to the transistor Q1 can be limited. Thus, the protecting circuit itself can be improved in the surge resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an input protection circuit used in a semiconductor device such as a MOSIC, and particularly to a structure of an input protection circuit with improved surge resistance.

[Conventional technology]

FIG. 4 shows a conventional input protection circuit of this kind, and FIG. 3 shows a layout configuration when this is integrated into a semiconductor device. In these figures, 1-
1 is a contact hole for connecting to a first NN region 2 formed on the input signal t-P type substrate, and this first N type region 2 has a protective resistor R1, a protective resistor R2, and a MOS transistor Q as a transistor! It constitutes the drain of the A field 3 separates the first N-type region 2, that is, the drain region of the MOS transistor Q1, from the grounded second N-type region 4 (ground region), and also serves as the gate insulating film of the MOS transistor Qt. Oxidized region, 5 is contact hole 1-2
An aluminum (A
2) Wiring, 6 is an aluminum (At) pad as a bonding pad that is wired to the input terminal, and a part of this aluminum pad 6 also serves as the gate of the Mo8 transistor Qx, forming an aluminum gate, and the gate is connected to the aluminum pad 6. It is used to apply an input signal. Note that the protective MO8 transistor Q1 has a film thickness of several thousand (1000) to tens of thousands (10000)
This element is also called a field transistor.

In such a conventional configuration, when a surge voltage of several hundred volts or more is applied to the input, the field MOS transistor Q! conducts through punch-through, discharges the surge voltage to the ground electrode, and prevents high voltage from being applied inside the semiconductor device. The function of the resistor R1 at this time is to limit the surge discharge current flowing to the field MOS transistor Q1 for discharging. This is to prevent high voltage from being transmitted inside the battery before it is discharged.

[Problem that the invention seeks to solve]

However, in the conventional protection circuit, since the protection resistor R1 is formed of the N-type region 2, if the resistance value is too large, the high voltage is removed before the surge voltage is discharged by the protection Mos transistor Qr. The PN junction between the input contact hole 1-t and the substrate breaks down, a large current flows, and as a result, aluminum penetrates into the substrate at the contact hole 1-1. Also, conversely, the protective resistance R
If 1 is too small, the current flowing through the Mo8 transistor Ql will not be restricted and a large current will flow, resulting in the aluminum penetrating into the board at the Kuko7 tact hole 1-1, destroying the protection circuit itself. Sometimes I put it away.

As described above, the conventional device has a problem in that the breakdown voltage of the protection circuit itself limits the damage resistance.

The present invention has been made to solve such problems, and an object of the present invention is to provide an input protection circuit for a semiconductor device that can improve the surge withstand voltage of the protection circuit itself.

[Means for solving problems]

An input protection circuit according to the present invention is an input protection circuit for a semiconductor device including an input protection resistor for suppressing input surges and an Mo8 transistor whose source is grounded and whose gate is applied with an input signal. It is constructed of polysilicon wiring, and is branched from the middle of the input part of the input protection resistor made of this polysilicon wiring and the connection part to the internal wiring, and is connected to the drain of the MO8 transistor.

[Effect]

In this invention, the input protection resistor is formed from a polysilicon wiring, and the Mo8 While limiting the current flowing through the transistor, it is possible to avoid destruction of the protection circuit due to breakdown of the PN junction.

〔Example〕

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 is a layout configuration diagram showing the structure of an input protection circuit according to an embodiment of the present invention, and its equivalent circuit is the same as that shown in FIG. 4. The difference in FIG. 1 from the conventional one shown in FIG. 3 is that the protective resistors R1 and R2 are formed of polysilicon wiring 8, and are branched from the middle of the polysilicon wiring 8. It is connected to the N-type region 2 which becomes the drain of the transistor Qt.

Here, 1-3 is a MO input from the branch point of the polysilicon wiring 8 through the aluminum wiring 1 and the contact hole 1-4.
This is a contact hole for branching and connecting to the N type region 2 which becomes the drain of the S transistor Q1. Also, 6-1 is M
o8 This is an aluminum wiring that also serves as the aluminum gate of the transistor Ql, and an input signal is applied to the gate. In each figure, the same reference numerals indicate the same or corresponding parts.

In this way, according to the configuration of the above embodiment, the protection MOS
By inputting the input to the transistor Qt through the resistance of the polysilicon wiring 8 forming the protective resistor RtrR2, the PN junction can be Discharging MO8 transistor Qt without large current flowing due to breakdown
Since the current flowing through can be limited, the surge withstand voltage of the protection circuit itself can be improved.

FIG. 2 shows another embodiment of the present invention, in which a branch from the polysilicon wiring layer 8B to the N-type region 2, which becomes the drain of the MOS transistor Ql, is connected between the polysilicon wiring layer and the N-type region 2. This is done through a direct (embedded +) contact hole 9 provided in the. In this embodiment as well, the same effects as in FIG. 1 can be obtained.

In addition, although the above description shows the case where a field MOS transistor is used as the protection MOS transistor Ql, the present invention is not limited to this, and a normal MOS transistor can also be used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to improve the surge withstand voltage of the protection circuit itself, which has been a problem in the past.
This has the effect of realizing an effective input protection circuit for a semiconductor device.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing the structure of an input protection circuit according to an embodiment of the present invention, FIG. 82 is a schematic block diagram showing another embodiment of the present invention, and FIG. FIG. 4 is a schematic block diagram showing the structure, and is a diagram showing the equivalent circuits of the conventional input protection circuit and the input protection circuit of the present invention. 1-1 to 1-4...contact hole, 2,4...
Nfi region, 3...Field oxidation region, 5, 6-
1. Too... Aluminum wiring, 6... Aluminum pad,
8. Conflict: Polysilicon wiring, 9. Direct (embedded) contact hole.

Claims (3)

[Claims] (1) In an input protection circuit for a semiconductor device that includes an input protection resistor that suppresses input surges and a MOS transistor whose source is grounded and whose gate is applied with an input signal, the input protection resistor is configured with polysilicon wiring. An input protection circuit for a semiconductor device, characterized in that the input protection resistor made of polysilicon wiring is branched from the middle of the input part and the connection part to the internal wiring and connected to the drain of the MOS transistor. (2) The MOS transistor is a semiconductor according to claim 1, characterized in that the field oxide region serving as a gate insulating film has a thickness of several thousand to tens of thousands of angstroms, and the gate is made of an aluminum gate. Equipment input protection circuit. (3) The branch connection from the polysilicon wiring to the drain of the MOS transistor is performed by a direct (buried) contact between the polysilicon wiring and the drain region. Input protection circuit for semiconductor devices.