JPH06295591A - Semiconductor integrated circuit device - Google Patents

Abstract

PURPOSE:To manufacture through a simple process a semiconductor integrated circuit that is provided with a plural number of stable clamp voltage with few variation, by using a p-n junction diode, which is formed on a polycrystal Si film on an insulating film, in a voltage clamping circuit so as to be an electrically forward direction. CONSTITUTION:For example, two pieces of p-n junction diode 3 are serially connected, and three sets of the combination in which a switch MOSFE 5 is parallelly connected to the serially connected p-n diodes 3 are serially connected in this case. In addition, to one end of these serially connected three sets, a Zener diode 1 is serially connected. Furthermore, to one end of these serially connected three sets, a Zener diode 1 is connected serially and in a reverse direction to the p-n junction diode 3. One terminal on the diode 1 side of the voltage clamping circuit thus formed is connected to the output of a high voltage generating circuit, and the terminal of the opposite side is connected to a grounding potential. Thus, the plural number of stable clamp voltage with a simple manufacturing process and few manufacturing variation are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit device and, more particularly, to a technique effectively applied to a high voltage generating circuit (booster circuit) of an EEPROM.

[0002]

2. Description of the Related Art EEPROM having a built-in high voltage generation circuit
For semiconductor integrated circuit devices such as, various products have hitherto been released and are known.

In such an EEPROM or the like, a normal logic circuit such as its address decoder has + 5V or +3.3.
A power supply voltage such as V is used, and a relatively high voltage such as + 9V or + 15V is required to write or erase the memory cell. Since the internal high voltage generating circuit alone cannot output the required voltage accurately, a voltage clamp circuit composed of a Zener diode or the like is used.

Early products such as EEPROMs having a built-in high voltage generation circuit have a high voltage of 1 for writing and erasing.
Although only types were mainly used, recently, many types use a plurality of high voltages.

The reason therefor is to make the operation time of writing and erasing uniform, or to shorten the inspection time by rewriting at a voltage higher than the normal operating voltage in the inspection stage. .

In order to generate such a plurality of high voltages, various measures have been conventionally made to the voltage clamp circuit.

The first of such measures is to connect a plurality of Zener diodes having different breakdown voltages in parallel and switch them by a control signal to obtain a plurality of clamp voltages.

This method has a drawback in that the manufacturing process is complicated because it is necessary to form a plurality of Zener diodes having different breakdown voltages. What was devised in order to eliminate this drawback is to connect another circuit element that can be formed by a normal manufacturing process in series with the Zener diode, and to apply the voltage across the circuit element to the breakdown of the Zener diode. Whether or not the voltage is added is selected by a control signal. For example, the following patents have been published.

Japanese Unexamined Patent Publication No. 62-275395 “Semiconductor integrated circuit device” Kazutoshi Ujiie 1982 Hitachi Cho-LS Engineering Co., Ltd.

The structure of a conventional voltage clamp circuit will be described below with reference to the drawings. FIG. 5 is a transcription of FIG. 1 described in the above-mentioned published patent publication. However,
A high voltage generation circuit that is a part other than the voltage clamp circuit,
The oscillator circuit for generating the clock for operating the high voltage generating circuit is not necessary for the description of the present invention, and therefore is omitted in the block diagram and its detailed description is omitted.

As shown in the circuit diagram of FIG. 5, a Zener diode D1 and a plurality of MOSFET QCs in diode form provided in series with the Zener diode D1.
1, QC2, QC3, QC4 and a constant voltage circuit form a voltage clamp circuit, and these diode-connected MOSFETs QC1, QC2, Q are connected in series.
Change the number of C3 and QC4 to the switch MOSFETs QC5 and Q
A plurality of types of clamp voltage operations are realized by selectively short-circuiting with C6 and QC7.

[0012]

The conventional voltage clamp circuit shown in FIG. 5 is excellent in that the manufacturing process is not complicated.

However, a diode type MOSFET is used in the constant voltage circuit. Because of this, M
There is a problem in that the voltage of the constant voltage circuit fluctuates due to the manufacturing variation of the threshold voltage of the OSFET, and the variation of the clamp voltage increases due to the multi-stage connection of the voltage. is there.

An object of the present invention is to provide a semiconductor integrated circuit device such as an EEPROM having a voltage clamp circuit capable of obtaining a stable clamp voltage with little manufacturing variation while maintaining the simplicity of the manufacturing process at the level of the prior art. It is to be.

[0015]

The typical ones of the inventions disclosed in this application will be briefly described as follows.

The semiconductor integrated circuit device of the present invention comprises a Zener diode electrically used in the reverse direction and a plurality of pn junction diodes connected in series to the Zener diode and electrically used in the forward direction. A voltage clamp circuit is configured by connecting the
By selectively short-circuiting the number of junction diodes by a switch MOSFET, a plurality of types of clamp voltage operation are realized. Furthermore, a pn junction diode that is electrically used in the forward direction is provided on the insulating film. It is formed on a crystalline silicon film.

[0017]

According to such means, the manufacturing variation is caused by one zener diode and the constant voltage circuit in which the pn junction diode of the polycrystalline silicon film which is easily obtained by the common manufacturing process with other circuits is combined. It is possible to obtain a plurality of stable clamp voltages with less.

In the present invention, the reason why the clamp voltage with less manufacturing variation can be realized is that the forward characteristic of the pn junction diode is used for the constant voltage circuit. p
It is known that the forward characteristics of the n-junction diode are extremely stable, independent of the impurity concentration, etc., except for the series resistance component, and the present invention utilizes the characteristics of such a pn-junction diode. It is a thing.

In the case of a pn junction diode formed in a semiconductor substrate by a general manufacturing process of a semiconductor integrated circuit, the present inventor never knows that the semiconductor substrate acts as a collector and causes a bipolar transistor operation. It has been found that it cannot be used in the forward direction. Therefore, in the present invention, p used in the forward direction is used.
The n-junction diode is formed on the insulating film.

Further, since the pn junction diode in the voltage clamp circuit as described above is not electrically used in the reverse direction, the inventor of the present invention has p-type diode having a poor reverse direction characteristic.
It has been found that even an n-junction diode can be used without any problem. Therefore, a pn junction diode made of a polycrystalline silicon film, which has never been used in a semiconductor integrated circuit device until now, is used because of its poor reverse direction characteristics, thereby keeping the manufacturing process simple. .

By thus forming the pn junction diode in the polycrystalline silicon film, the pn junction diode used in the forward direction can be mounted on the semiconductor integrated circuit device without complicating the manufacturing process. It is possible.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a voltage clamp circuit according to the present invention. However, the high voltage generating circuit is not an essential part of the present invention, and therefore is shown in a block diagram and detailed description thereof is omitted.

As shown in FIG. 1, two pn junction diodes 3 are connected in series, and three pn junction diodes 3 connected in series with a switch MOSFET 5 are connected in series. Furthermore, the Zener diode 1 is connected in series at one end of the three series connections, and pn
The junction diode 3 is connected in the opposite direction. The voltage clamp circuit is configured in this way, and the terminal on the side of the Zener diode 1 of this voltage clamp circuit is connected to the output of the high voltage generation circuit, and the terminal on the opposite side is connected to the ground potential.

The gates of the three switch MOSFETs 5 are respectively connected to different control signals, and the signals control the number of the switch MOSFETs 5 in the ON state, thereby selecting the clamp voltage.

In the example of FIG. 1, switch MOSFE
Two pn junction diodes 3 are connected in parallel with T5, but the number is not limited and may be arbitrarily set according to the voltage interval of the clamp voltage to be selected.

In the example of FIG. 1, the pn junction diode 3 and the switch MOSFET 5 are connected in parallel in three sets, but this may be set arbitrarily according to the number of clamp voltages selected.

No matter how many numbers are set, FIG.
As described above, by using the pn junction diode 3 in the forward direction, it is possible to obtain a stable clamp voltage with little manufacturing variation.

Next, the configuration of the pn junction diode 3 which is used electrically in the forward direction as shown in FIG. 1 will be described in detail. FIG. 2 shows an embodiment of the pn junction diode 3 according to the present invention, and is shown in a sectional view without a protective film.

In FIG. 2, a polycrystalline silicon film 11 is provided on a portion of the insulating film 9 covering the surface of the semiconductor substrate 7, and a portion of the polycrystalline silicon film 11 is diffused with impurities such as boron. A p-type region and an n-type region in which impurities such as phosphorus are diffused are provided in the other part of the polycrystalline silicon film 11 to form a p-type region.
It is an n-junction diode. And these p-type regions and n
A metal wiring film 15 of aluminum or the like is connected to the mold region through the opening of the intermediate insulating film 13 to form an electrode.

In FIG. 2, there are two important points for achieving the object of the present invention.

First, the first point is that the pn junction diode is formed on the insulating film 9. As a result, this pn junction diode is connected to other circuit elements in the semiconductor integrated circuit only through the metal wiring film 15, which causes a bipolar transistor operation even if it is used in the forward direction. Since there is no part corresponding to the collector, no problem occurs.

The second point is that the pn junction diode is formed in the polycrystalline silicon film 11.
As described above, since the pn junction diode is used in the forward direction, the reverse characteristic is irrelevant. Therefore, the pn of the polycrystalline silicon film, which is inferior to the single crystal silicon in the reverse characteristic, is used. It can also be used as a junction diode, and can easily be formed by pn without the need for a complicated manufacturing process of forming a single crystal silicon film on the insulating film 9.
It is possible to obtain a junction diode.

Next, another embodiment using the pn junction diode shown in FIG. 2 will be described in detail. FIG. 3 is a circuit diagram showing another embodiment of the voltage clamp circuit according to the present invention. However, the high voltage generating circuit is not an essential part of the present invention, and therefore is shown in a block diagram and detailed description thereof is omitted.

As shown in FIG. 3, four pn junction diodes 3 are connected in series, and the Zener diode 1 is connected in series to one end of the pn junction diodes 3 connected in series.
And it is connected in the opposite direction to the pn junction diode 3. Then, the other end of this series connection, the connection point of the second and third pn junction diodes 3 and the Zener diode 1 and p
The switch MOSFET 5 is connected to each connection point with the n-junction diode 3. These three switches MO
The source side terminal of the SFET 5 is connected to the ground potential, and the Zener diode 1 is connected to the output of the high voltage generating circuit.

The gates of the three switch MOSFETs 5 are respectively connected to different control signals, and the signals are controlled so that any one of the three switch MOSFETs 5 is turned on, thereby selecting the clamp voltage. Is going.

Next, another embodiment will be described in detail with reference to the drawings. FIG. 4 is a circuit diagram showing another embodiment of the voltage clamp circuit according to the present invention. However, regarding the high voltage generation circuit,
Since it is not an essential part of the present invention, it is shown in a block diagram and detailed description thereof is omitted.

As shown in FIG. 4, the Zener diode 1 is connected to the output of the high voltage generating circuit, and the switch MOSFET 5 is connected between the Zener diode 1 and the ground potential. The two pn junction diodes 3 and another switch MOSFET 5 are connected in series, and the four pn junction diodes 3 and another switch MOSFET 5 are connected in parallel to the first switch MOSFET 5, respectively. There is.

The gates of the three switch MOSFETs 5 are respectively connected to different control signals, and the signals are controlled so that any one of the three switch MOSFETs 5 is turned on, thereby selecting the clamp voltage. Is going.

Zener diode 1 is in the opposite direction, and p
The connection of the n-junction diodes 3 in the forward direction is the same as in FIG. 1 or 3.

The present invention has been specifically described based on the embodiments as described above, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, FIG. 1, FIG. 3, or FIG.
In the above, the position where the voltage clamp circuit is inserted is between the positive high voltage and the ground potential, but substantially the same clamp voltage is obtained between the negative high voltage and the positive power supply voltage. It may be the one that has been done.

Also in this case, if the Zener diode is used in the reverse direction and the pn junction diode is used in the forward direction, a stable clamp voltage with less manufacturing variation can be obtained.

[0043]

As described above, by using the pn junction diode formed in the polycrystalline silicon film on the insulating film in the voltage clamp circuit so as to be electrically forward, the manufacturing process is simplified. It is possible to provide a semiconductor integrated circuit device having a plurality of stable clamp voltages with little manufacturing variation while maintaining the above, and the effect is very large. Especially, when it is applied to a semiconductor integrated circuit device such as an EEPROM, the effect is great.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing the structure of a pn junction diode according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a voltage clamp circuit according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a voltage clamp circuit according to an embodiment of the present invention.

FIG. 5 is a circuit diagram showing a voltage clamp circuit in a conventional example.

[Explanation of symbols]

 1 Zener diode 3 pn junction diode 5 switch MOSFET 7 semiconductor substrate 9 insulating film 11 polycrystalline silicon film 13 intermediate insulating film 15 metal wiring film

Claims (3)

[Claims] 1. A voltage clamp circuit for clamping an output voltage of a high voltage generation circuit, a zener diode electrically used in a reverse direction, and a zener diode connected in series to the zener diode, and electrically connected in a forward direction. Used are a series connection of a plurality of pn junction diodes formed in a polycrystalline silicon film on an insulating film, and a MOSFET which receives a control signal and electrically short-circuits both ends of these pn junction diodes or their interconnection points. A semiconductor integrated circuit device comprising. 2. A voltage clamp circuit for clamping an output voltage of an internal high voltage generating circuit for generating a high voltage for electrically writing or erasing a memory cell composed of a nonvolatile memory element of an EEPROM. As
Series connection of a Zener diode used electrically in the reverse direction and a plurality of pn junction diodes formed in a polycrystalline silicon film on an insulating film, which are connected in series to this Zener diode and used in the forward direction electrically And a MOSFET which receives a control signal and electrically short-circuits both ends of these pn junction diodes or their interconnection points. 3. The semiconductor integrated circuit device according to claim 1, wherein a pn junction diode formed in a polycrystalline silicon film on an insulating film is used as the diode to be electrically used in the forward direction.