JPH0566030B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a MOS integrated circuit, and more particularly to a MOS integrated circuit using a MOS transistor for an output buffer.

Conventionally, MOS integrated circuits that use MOS transistors for output buffers have a problem in that they are susceptible to electrostatic discharge damage, and in particular, open drain output terminals are susceptible to electrostatic discharge damage. Its destruction mode is gate destruction of the output buffer transistor.

FIG. 1 is a plan view of an example of a conventional MOS transistor.

A source region 2 and a drain region 3 are provided on a semiconductor substrate 1.
and a channel region 4 is formed therebetween. After an insulating film is deposited on the surface, contact windows 5 and 6 are formed in the source region 2 and drain region 3, respectively, and a source electrode and a drain electrode (both not shown) are formed through the windows 5 and 6. is installed. The drain electrode is then connected to the output terminal.

Now, if static electricity is applied to the drain of this MOS transistor from the output terminal, electric field concentration will occur at the corner of the drain region 3, causing breakdown of the gate insulating film. In order to prevent this gate breakdown, a design standard has been adopted in which the transistor channel width is determined from the drain junction capacitance and the gate insulating film thickness, regardless of the electrical characteristics of the output buffer. According to the design standard, the channel width is 1
It was specified that the diameter should be at least mm. In other words, since the channel width was set uniformly regardless of the magnitude of the output of the output buffer, if the output was small, the channel width would be larger than necessary, which would increase the size of the transistor, resulting in waste. It was hot.

The present invention eliminates the above-mentioned drawbacks and provides a MOS integrated circuit that has improved resistance to electrostatic breakdown by adopting a drain electrode structure that alleviates electric field concentration that occurs when static electricity is applied from an output terminal to a drain region. be.

A MOS integrated circuit of the present invention includes a source region and a drain region provided in a semiconductor substrate, a first contact window provided in the drain region and having a portion parallel to the width direction of a channel, and a first contact window provided in the drain region. a first drain electrode provided in the contact window, and a drain electrode provided in the drain region on the opposite side of the channel across the first contact window and along at least a part of the first contact window. a second contact window provided in parallel;
a second drain electrode provided in the second contact window and connected to the output terminal;
Consists of transistors.

Next, embodiments of the present invention will be described using the drawings.

FIG. 2 is a plan view of one embodiment of the present invention.

A source region 12 and a drain region 13 are provided in a semiconductor substrate 11, and a channel region 14 is formed therebetween. In this embodiment, the source region 12 and drain region 13 are comb-shaped, but this is not an essential requirement. An insulating film is deposited on the surface, and a source contact window 15 is formed in the source region 12.
A first contact window 16 having a portion (corresponding to the teeth of a comb) parallel to the width direction of the channel region 14 is formed in the drain region 13 . Further, a second contact window 17 is formed parallel to and along at least a portion of the first contact window 16 in the drain region 13 on the opposite side of the channel region 14 with the first contact window 16 interposed therebetween. In Figure 2,
A second contact window 17 is opened in parallel with an interval 18 along a portion corresponding to the comb handle portion. An ohmic contact metal such as Al is deposited and selectively removed to form a source electrode in the source contact window 15, a first drain electrode in the first contact window 16, and a second drain electrode in the second contact window 17. Two drain electrodes are provided, and the second drain electrode is connected to the output terminal.

Now, when static electricity is applied from the output terminal to the second drain electrode, the static electricity is injected into the drain region 13 through the second contact window 17. Since resistance always exists in the drain region 13 and the resistance distribution is not completely uniform, localization of current occurs. However, since the first contact window 16 is provided immediately adjacent to the window 16, and the first drain electrode of low electrical resistance such as Al is provided in the window 16,
When the localized current diffuses through the drain region 13 and reaches the first drain electrode, it is averaged and the electric field is relaxed. Therefore, the strength against gate breakage is improved. This breaking strength can be changed to some extent by setting the value of interval 18,
Breakage resistance can be improved.

As explained in detail above, according to the present invention,
The effect is significant because a MOS integrated circuit including a MOS transistor with improved breakdown resistance against gate breakdown due to static electricity can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an example of a conventional MOS transistor, and FIG. 2 is a plan view of an embodiment of the present invention. 1... Semiconductor substrate, 2... Source region, 3...
Drain region, 4... Channel region, 5... Window for source contact, 6... Window for drain contact, 11... Semiconductor substrate, 12... Source region, 13... Drain electrode, 14... Channel region , 15...source contact window, 16
...first contact window, 17...second contact window, 18...distance between the first contact window and the second contact window.

Claims (1)

[Claims] 1. A MOS integrated circuit comprising a comb-shaped drain region, a comb-shaped source region defining a channel region between the comb-shaped drain region, and a gate electrode provided on the channel region with a gate insulating film interposed therebetween. a first contact window formed continuously from a comb tooth portion to a comb handle portion of the comb-shaped drain region; a first contact window provided in the first contact window; a drain electrode provided at the comb handle portion of the comb-shaped drain region on the opposite side of the channel region across the first contact window, and at least a part of the first contact window; A MOS integrated circuit, further comprising a second contact window provided substantially parallel to the second contact window, and a second drain electrode provided in the second contact window and connected to an output terminal. circuit.