JPS626661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an MIS type (insulated gate type) semiconductor device.

In MIS type semiconductor devices, there is a tendency to make the gate insulating film thinner as the MISFET becomes finer. Therefore, the gate insulating film is extremely susceptible to electrostatic breakdown due to a small amount of current caused by external contact, making the entire device unusable, and countermeasures must be taken to prevent this.

Conventionally, as one of the countermeasures, as shown in Figure 1a, a protective MISFETM _G is provided, and when an abnormally high voltage is applied to the input pin, the protective MISFETM _G is turned on. Therefore, measures have been taken to prevent an abnormal rise in the potential of the gate of the protected MISFETM _D. To explain this protective MISFETM _G in detail, as shown in Fig. 1b, this M _G is provided in a portion where a part 2 of the electrode (aluminum) pad 1 is extended, and this extended portion (aluminum) is It is designed to form the gate of _MG . This extension part 3 and the drain region 4 of M _G are connected via a contact part 5, and the drain region 4 is extended to the vicinity of the protected MISFETM _D , and its end is connected to the gate electrode of M _D. It is connected. Figure c is M _G
FIG. This M _G uses a PSG film 8 and a silicon oxide film 10 for interlayer insulation of multilayer wiring as a gate insulating film. As a result, the threshold voltage becomes a value suitable for a protection MISFET of about 30 volts. Furthermore, this element does not require any special process and can be manufactured using a normal silicon gate MISIC manufacturing process.

By the way, with the miniaturization of MIS semiconductor devices, the size and depth of the impurity diffusion layers that form the source and drain become smaller, and the distance between the source and drain (channel length) becomes narrower. Therefore, it is no longer possible to understand this protection circuit as a lumped constant circuit, and when abnormally high voltage noise enters input pin 1, the level of the entire input line does not rise at the same time, but the level of the part near the input pin increases first. A phenomenon occurs in which the level increases only in the input pin 1, the level does not increase in other parts, and then the level gradually increases in the part far from the input pin 1. In other words, this protection circuit is essentially a distributed constant circuit as shown in Figure d, and at the moment of noise generation, a potential difference occurs between the source and drain only in the portion near input pin 1, and the potential difference occurs in that portion due to the noise. A phenomenon occurred in which the generated electric field was concentrated. Therefore, even if such a protection circuit is provided, drain junction breakdown often occurs in the portion a near the input pad.

The present invention has been made to solve such problems, and one embodiment thereof includes a protective MISFET having a gate electrode connected to an electrode pad to which an input signal is applied. An end of the drain region closer to the electrode pad is connected to the gate electrode via a contact portion, and an end of the drain region farther from the electrode pad is connected to the gate electrode of the protected MISFET. In MIS type semiconductor devices,
The drain layer has a portion where the distance between the side surface on the channel side and the side surface opposite thereto is larger on the side closer to the electrode pad, and becomes smaller as the distance from the side closer to the electrode pad increases. It is characterized by being formed as follows.

Another embodiment of the invention includes a protection MISFET having a gate electrode connected to an electrode pad to which an input signal is applied, and an end of the drain region of the protection MISFET near the electrode pad. The gate electrode is connected via a contact portion,
In an MIS type semiconductor device in which the end of the drain region on the side far from the electrode pad is connected to the gate electrode of the protected MISFET, the channel length (drain-source length) is on the side near the electrode pad. It is characterized by having a portion that is long and becomes shorter as it goes away from the side closer to the electrode pad.

Another embodiment of the invention includes a protection MISFET having a gate electrode connected to an electrode pad to which an input signal is applied, and an end of the drain region of the protection MISFET near the electrode pad and the gate. An MIS in which the electrode is connected via a contact part, and the end of the drain region far from the electrode pad is connected to the gate electrode of the protected MISFET.
The semiconductor device is characterized in that the width of the gate electrode in the portion that overlaps with the drain region increases as it moves away from the side closer to the electrode pad.

The present invention will be explained below with reference to Examples.

FIG. 2 is a layout diagram showing an embodiment of the present invention.

This MIS type semiconductor device is a protective MISFETM _G
The distance d between the side surface on the channel side of the drain layer 4 and the side surface on the opposite side thereof (hereinafter referred to as the width of the drain layer) is wider on the side closer to the part 2 of the electrode pad 1, and becomes wider as the distance from the side becomes larger. It is made to be narrower.

In other words, instead of making the width d of the drain layer of the protective MISFET uniform, the width d _a on a part of the electrode is made wider than the width of the conventional drain layer.
The width d should become narrower toward the opposite side. That is, the width d _b of the drain layer 4 at the intermediate portion b is made narrower than d _a , and the width d _c of the drain layer 4 at the side c opposite to the part of the electrode is made narrower than d a.
becomes narrower than d _b .

In this way, when abnormally high voltage noise is applied between the input pad 1 and the semiconductor substrate, the width d of the part side a of the electrode pad of the drain layer 4, which is the part where electric field concentration is most likely to be applied, can be reduced. Since _a is wide, the resistance of that part becomes smaller. Therefore, the distributed resistance r' on the side near the input of the distributed constant circuit on the input side of the protective MISFETM _G is small, which speeds up the progression of the noise voltage and prevents the electric field from concentrating locally. be done. As a result, it is possible to prevent the bond from breaking on one side of the electrode. And this
By making the width of the drain layer 4 of MISFETM _G narrower from one side of the electrode to the other side, it is possible to prevent the drain junction capacitance from becoming unnecessarily large. The distributed capacitance c' of the constant circuit is also reduced, preventing the noise voltage from slowing down and preventing electric field concentration more effectively. Note that in such a drain, the resistance increases as the distance from a part of the electrode increases; however, if the resistance of the part of the electrode is small, the effect of the present invention can be fully obtained; This is not a problem if the resistance on the opposite side is slightly larger; on the contrary, making the resistance larger as you move away from one part of the electrode makes the electric field more uniform across the channel. It is preferable to join the group.

FIG. 3 shows another embodiment of the invention.

This MIS type semiconductor device is a protective MISFETM _G
Distance between source and drain (channel length L)
is wide on one side a of the electrode pad and narrows toward the opposite side, and the width d of the drain layer 4 is made uniform.

In other words, the channel length L of the protective MISFET
Rather than making it uniform, some side a of the electrode pad
The channel length is longer than the conventional channel length, and becomes shorter toward the opposite side. By doing this, even if abnormally high voltage noise is added between the electrode pad 1 and the semiconductor substrate and the electric field between the source and drain becomes high on a part of the electrode side a, that part will remain in the channel. Since the length is long, the potential gradient at each part does not become very high.
Then, by making the channel length L shorter in a portion where a lower electric field is applied, the potential gradient is made generally uniform in all portions. Therefore, when the protective MISFETM _G is turned on, current is prevented from concentrating locally, and destruction of the protective MISFETM _G can be prevented. In addition, since the width d of the drain layer is made minimum and uniform as in the conventional case, increasing the junction area, that is, increasing the distributed capacitance in the distributed constant circuit, can be restricted. Therefore, it is possible to prevent the noise voltage from decreasing in speed. This also becomes a factor in preventing electric field concentration.

FIG. 4 shows still another embodiment of the present invention.

In this embodiment, the channel length is not uniform;
There is no difference from the embodiment shown in FIG. 3 in that the channel length L _a at the part side a of the electrode is longer than the channel length L _b at the middle part b, but the channel length L _b at the middle part b is the same as the embodiment shown in FIG. This embodiment differs from the embodiment shown in FIG. 3 in that the channel length L _c on the opposite side c of the part of the electrode is the same length.

Since the part where the channel length L needs to be particularly long is the part close to the electrode, it is not necessarily necessary to form a shape in which the channel length gradually becomes shorter over the entire width direction a to b to c of the channel. As in this embodiment, the channel length is gradually shortened only in a portion close to the electrode,
Even if the channel length in other parts is made uniform, the effects unique to the present invention can be obtained.

In the embodiments shown in FIGS. 5 and 6, the side surface of the source 6 on the channel side is sloped so that the channel length becomes shorter as it progresses from the electrode side to the opposite side. With this embodiment, as in the embodiments shown in FIGS. 3 and 4, it is possible to prevent a portion where the potential gradient is abnormally high from occurring on the side near the electrode, and to prevent local concentration of current. Therefore, it is possible to prevent damage caused by

The present invention can be applied to general MIS type semiconductor devices having gate protection circuits.

[Brief explanation of the drawing]

Figures 1 a to d relate to conventional examples, where a is a circuit diagram showing the protection circuit, b is a layout diagram of the protection MISFET section, c is a cross-sectional view showing the structure of the protection MISFET, and d is the input side of the protection circuit. FIG. 2 to 6 are layout diagrams showing each embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Electrode pad, 2... Part of electrode pad (extension opening), 3... Aluminum gate electrode, 4... Drain, 5... Contact part, 6... Source, 7... SiO ₂
Film, 8...PSG film, 9...p-type semiconductor substrate, 10...
_SiO2 film.

Claims (1)

[Scope of Claims] 1. An electrode pad formed on a semiconductor substrate to which an input signal is applied, a protected MISFET to which the input signal is supplied via the electrode pad, and a drain region thereof connected via a contact portion. and a protective MISFET that is coupled to the electrode pad and turns on in response to the abnormal voltage so as to protect the protected MISFET from the abnormal voltage applied to the electrode pad, and the protective MISFET is connected to the drain of the protective MISFET. 1. A MIS type semiconductor device characterized in that the width of the region is widened on the side close to the electrode pad and narrowed on the side remote from the electrode pad. 2. An electrode pad formed on a semiconductor substrate to which an input signal is applied, a protected MISFET to which the input signal is supplied via the electrode pad, and a drain region thereof coupled to the electrode pad via a contact portion. and a protective MISFET that turns on in response to the abnormal voltage so as to protect the protective MISFET from the abnormal voltage applied to the electrode pad, and the protective MISFET has a channel region whose width is equal to that of the electrode pad. An MIS type semiconductor device characterized in that the side closer to the electrode pad is longer and the side farther from the electrode pad is shorter.