JPH03196677A - Semiconductor device - Google Patents

Abstract

PURPOSE:To maintain electrostatic withstand voltage without deteriorating response characteristics of input first-stage circuit, by forming gate oxide film of MOS FET which forms input protective circuit and input first-stage circuit in such a way that the gate oxide-film is thicker than gate oxide film of other internal MOS FET. CONSTITUTION:Gate oxide film of MOS FETs 5' and 6' forming input protective circuit 9, and MOS FETs 12' and 13' forming input first-stage circuit are thicker than those of MOS FETs 14 and 15 and the like forming other internal circuits 11. By thickening gate oxide film of an MOS FET forming input protective circuit 9 and input first-stage circuit 10, electrostatic withstand voltage of gate oxide film is increased. Therefore, electrostatic withstand voltage property can be maintained without increasing resistances of resistors 1 and 2, and stray capacitances 3 and 4 of the input protection circuit 9, and high speed characteristics of the internal circuit 11 is maintained since gate oxide films of other internal circuits 11 is thin. By this, electrostatic withstand voltage property can be maintained without reducing response characteristics of the input first-stage circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to a semiconductor device provided with measures against electrostatic damage of MOSFET.

[Conventional technology]

Recently, semiconductor integrated circuits have been increasing in capacity and speed at the same time. In order to achieve higher speeds, the gate oxide film thickness is becoming thinner and thinner due to the need to increase charging and discharging capabilities. However, in general, as the thickness of the gate oxide film becomes thinner, electrostatic discharge damage becomes more likely to occur.

Therefore, an input first stage circuit 9 shown in FIG. 3 has conventionally been used as a countermeasure against static damage using this type of metal oxide semiconductor (MOS) field effect transistor (CFET). In FIG. 3, a polysilicon resistor 1, a diffusion layer resistor 2, a parasitic capacitance such as a diffusion layer 3.4, and an N-type MO8FET 5.6
is shown.

Further, including the diode 7, it becomes an input first stage circuit 9, to which the pad 8 is connected. The next input first stage circuit 10 has C.
There is MO8-FET12.13, and the internal circuit 11 has C
There is MO8-FET 14.15.

Now, the drain of MOSFET5 is at power supply potential VK.

The gates are connected to the ground potential G, respectively, and the MOSFE
The source and gate of T6 are connected to ground potential GK. Resistance 1.2 and parasitic capacitance 3.4 are both used to suppress peak voltage when surge voltage such as static electricity is input, and N-type MO8FET 5.6 suppresses the charge of surge voltage to MOSFET. This is to release the power supply potential V or ground potential GK by breakdown.

As mentioned above, the basic idea of an input protection circuit is to suppress the peak of surge voltage and provide an escape route for charges, so the thinner the gate oxide film, the larger the resistance 1.2, the parasitic capacitance 3, 4 must be increased.

[Problem to be solved by the invention]

As mentioned above, in the conventional example, when the gate oxide film becomes thin, the input protection circuit 9 and the input first stage circuit 100M08FET
The risk of gate destruction will increase. So, input security: I! #If the parasitic capacitance 3.4 and resistance 1.2 in the circuit 9 are increased, #voltage resistance can be improved, but the input first stage circuit 1
The waveform to be input to 0 is parasitic capacitance i3.4 and resistance 1
．． 2, the response of the input first stage circuit 9 becomes worse.

An object of the present invention is to provide a semiconductor device with improved electrostatic withstand voltage without degrading the response characteristics of the input first stage circuit.

[Means to solve the problem]

The structure of the semiconductor device of the present invention is such that a gate oxide film of a MOSFET constituting an input/output circuit connected to a pad on a semiconductor substrate is formed thicker than a gate oxide film of other MOSFETs on the substrate. It is characterized by

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a semiconductor device according to an embodiment of the present invention.

In FIG. 1, the difference between this embodiment and the conventional example shown in FIG.
', 6', and MOSF constituting the input first stage circuit 10
The gate oxide film of the ETs 12' and 13' is thicker than that of the MOSFETs 14, 15, etc. that constitute the other internal circuits 11. In FIG. 1, the difference in the thickness of the gate oxide film is expressed by the difference in the notation of (MOSFET). In FIG. 1, the resistance to gate oxide film breakdown due to static electricity is improved by making the gate oxide films of the MOSFETs constituting the input protection circuit 9° and the input first stage circuit 10 thicker than other MOSFETs.

Therefore, the input protection circuit 9 has a resistance 1.2 and a parasitic capacitance 3.
4, and the gate oxide film of the other internal circuits 11 is made thin, so the high speed performance of the internal circuits 11 is not lost. of course,
In Figure 1, input protection times A! i! The gate oxide film may be thickened only in a part of the MOSFET constituting I9 or the input first stage circuit 10.

By the way, in the manufacturing method of making the gate oxide film thicker or thinner, first the input protection circuit 9 or the input first stage circuit 1 is
The thickness of the gate oxide film used for internal circuits other than the MO8FET that constitutes the input protection circuit 9 is thermally grown to a specified thickness, and then photoresist is applied.
Alternatively, if the photoresist is removed only from the MOSFET portion that constitutes the input first stage circuit 10, and thermal growth is performed at that point, the gate oxide film will grow and become thicker only where the photoresist is removed. do.

FIG. 2 is a circuit diagram showing a semiconductor device according to another embodiment of the present invention.

In FIG. 2, in this embodiment, the signal from the internal circuit @20 passes through the output transistors 22 and 23 and is output from the output pad 21. The output transistor 19'ta connected to the output terminal: MO8FET22.
The gate oxide film of 23 is the other internal MO5FET 24
, 25, 26, and 27. Therefore, the output transistor 1 connected to the output terminal
9, the resistance to gate oxide film breakdown due to static electricity can be improved.

As described above, the semiconductor device of the embodiment of the present invention is a semiconductor device including a MOSFET formed on a semi-fluid substrate, and includes a MOSFET that constitutes an input protection circuit connected to an input terminal or an input first stage circuit, or a MOSFET connected to an output terminal. The difference is that the gate oxide film of the MOSFET that constitutes the output transistor is thicker than that of other internal MOSFETs.

〔Effect of the invention〕

As explained above, the present invention provides a method for replacing the gate oxide film of a MOSFET that constitutes an input protection circuit connected to an input terminal and an output terminal, or an input first stage circuit or an output transistor with a gate oxide film of another internal MO8F or ET. Making the button thicker has the effect of maintaining voltage resistance against electrostatic damage without increasing resistance or capacitance.

Of course, in the present invention, the other internal circuits are made by thinning the gate oxide film, so high speed can be maintained.

Diode, 8... Input pad, 21...
・Output pad, 1...Polysilicon resistor, 2...
...Diffused layer resistance.

Claims (1)

[Claims] The gate oxide film of the MOSFET constituting the input/output circuit connected to the pad on the semiconductor substrate is connected to the other M on the substrate.
A semiconductor device characterized by being formed thicker than a gate oxide film of an OSFET.