JPH0474474A - Semiconductor device - Google Patents

Abstract

PURPOSE:To incorporate a device for surge protection without increasing a chip area, by making the thickness of a semiconductor substrate to thickness so that a depletion layer can easily get to the first conductive-type region under a semiconductor substrate. when the reverse voltage is impressed between a source and a drain. CONSTITUTION:The first conductive-type region 8 with higher concentration of impurities than that of a semiconductor substrate 2 is installed under the semiconductor substrate 2. When the reverse voltage is impressed between a drain substrate 10 and a source electrode 11, a depletion layer 12 spreads between an expanded drain region 5 and a semiconductor substrate 2, and finally gets to the first conductive-type region 8 under the semiconductor substrate 2. Expansion of the depletion layer 12 to the downward direction is restrained here, and the electric field at the junction of the bottom part of the expanded drain region 5 increases, and here the yield generates. The yield electric current flows to the arrow direction, as shown in the Fig. 2, and parasitic bi-polar transistor movement does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor device used as a power element for an igniter.

BACKGROUND OF THE INVENTION A typical semiconductor device used as a surge countermeasure is a surge protection diode, and the conventional semiconductor device will be described below using a surge protection diode as an example.

When using MOSFET as a switching element in an igniter, the switch part is MO8F as shown in Figure 3.
A surge protection diode 23 is required between the drain and source of the ET 22. In the same figure, 24 is the ignition point, 2
5 is an ignition coil. Conventionally, such surge protection diodes have been used as so-called external devices added outside the integrated circuit.

Problems to be Solved by the Invention First, the reason why a surge protection diode is required will be explained.

FIG. 4(a) is an operating characteristic diagram when the igniter MOSFET does not have a surge protection diode, and FIG. 4(b) is an operating characteristic diagram when the igniter MOSFET is equipped with a surge protection diode.

As shown in FIG. 4(a), if there is no surge protection diode, a positive surge voltage 32 is generated at the moment the MO8FET 22 changes from the operating state 26 to the stopped state 27. In this case, there is no surge protection diode, so the surge voltage is 3.
2 becomes higher than the drain-source breakdown voltage 28 of the MO3FET 22, and the MO8FET 22 breaks down between the drain and source.

On the other hand, as shown in FIG. 4(b), when the surge protection diode 23 is installed, a positive surge voltage 33 is generated at the moment the MO3FET 22 changes from the operating state 29 to the stopped state 30.
However, the surge voltage 33 is higher than the breakdown voltage 31 between the train and source due to the function of the surge protection diode (it never becomes higher).

Next, MO8FET when there is no surge protection diode
The inside of 22 will be explained with reference to FIG. As shown in the figure, the MO5FET 22 is connected to a semiconductor substrate 41 of the first conductivity type.
A second conductivity type extended drain region 44 is formed in contact with the drain contact region 43 between a second conductivity type source region 42 and a second conductivity type drain contact region 43 formed therein. The surface of the semiconductor substrate 41 between the drain region 44 and the source region 42 is used as a channel, and a gate electrode 46 is formed on this channel region with a gate oxide film 45 interposed therebetween. In addition, 4
7 is a substrate contact region for connection to the semiconductor substrate 41, 48 is a drain electrode, and 49 is a source electrode. The drain contact region 4 of such MO3FET 22
When a breakdown current flows from the source region 3 to the source region 42, a potential difference is generated due to the resistance component 50 of the semiconductor substrate 41.

This potential difference causes the parasitic bipolar transistor 51 to operate, causing a temperature rise, which may lead to thermal breakdown.

The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide an excellent semiconductor device for surge protection that can be built into the same chip as T without any additional steps.

Means for Solving the Problems To achieve this object, the semiconductor device of the present invention basically consists of a lateral MO formed in a semiconductor substrate of a first conductivity type.
3FET, which has a first conductivity type region with higher impurity concentration than the semiconductor substrate under the semiconductor substrate, the source region is connected to the semiconductor substrate, and the thickness of the semiconductor substrate is reversed between the source and drain. The structure has a thickness such that the depletion layer easily reaches the first conductivity type region under the semiconductor substrate when a voltage is applied.

Effect: With this configuration, a semiconductor device for surge protection, which has conventionally been externally attached between the source and drain of a MOSFET as a switching element for an igniter, can be built into the MOSFET chip without increasing the chip area.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention.

The lateral MO3FETI of the embodiment of the present invention has a drain contact region 4 between a second conductivity type source region 3 formed in a first conductivity type semiconductor substrate 2 and a second conductivity type train contact region 4. An extended drain region 5 of the second conductivity type is formed in contact with the extended drain region 5. The surface of the semiconductor substrate 2 between the extended drain region 5 and the source region 3 is used as a channel region, and a gate oxide film 6 is formed on the channel region. A gate electrode 7 is formed therein, and a first conductivity type region 8 having a higher impurity concentration than the semiconductor substrate 2 is provided below the semiconductor substrate 2. Note that 9 is a substrate contact region for connection to the semiconductor substrate 2, 10 is a drain electrode, and 11 is a source electrode.

In this embodiment, the impurity concentration of the semiconductor substrate 2 is 3×101
4 cm''3, the impurity concentration of the first conductivity type region 8 under the semiconductor substrate 2 was set to IX1019 side -3, and the impurity concentration of the extended drain region 5 was set to approximately 3×10151015c.The thickness of the semiconductor substrate 2 was In order to set the breakdown voltage between the drain and the semiconductor substrate to 400V, the thickness was set to 15 μm.

In the semiconductor device configured in this way, the drain
FIG. 2 shows the expansion of the depletion layer 12 when a reverse voltage is applied between the sources. Drain electrode 10 and source electrode 1
1, the depletion layer 12 spreads between the extended drain region 5 and the semiconductor substrate 2, and finally reaches the region 8 of the first conductivity type below the semiconductor substrate 2. depletion layer 1
The downward spread of 2 is now suppressed and the electric field at the junction at the bottom of the extended train region 5 becomes high, where breakdown occurs. At this time, the breakdown current flows in the direction of the arrow in FIG. 2, and no parasitic bipolar transistor operation occurs. Note that the breakdown voltage of the MOSFET when there is no region 8 of the first conductivity type under the semiconductor substrate 2 is 450V, and by setting the breakdown voltage between the train and the semiconductor substrate to 400V, the MOSFET
Destruction of SFET is prevented.

Effects of the Invention As described above, the present invention provides a region of the first conductivity type with a higher impurity concentration than the semiconductor substrate under the semiconductor substrate of the first conductivity type on which the lateral MO8FET is formed, and a source region is formed on the semiconductor substrate. By connecting and making the thickness of the semiconductor substrate such that the depletion layer easily reaches the region of the first conductivity type under the semiconductor substrate when a reverse voltage is applied between the source and drain, it can be made the same as a MOSFET. It is possible to realize an excellent semiconductor device for surge protection that can be built into a chip without adding any additional steps.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device according to an embodiment of the present invention, FIG. 2 is a diagram showing the spread of the depletion layer when a reverse voltage is applied between the train and source of the semiconductor device, and FIG.
Figure 4 (a) is a circuit diagram when an OSFET is used as a switching element in an igniter, and Figure 4 (b) is an operating characteristic diagram when the igniter does not have a surge protection diode.
) is an operating characteristic diagram when a surge protection diode is attached to the igniter, and FIG. 5 is a diagram showing the internal state of the MOSFET when a breakdown current flows when there is no surge protection diode. 2...Semiconductor substrate, 3...Source region, 4...Drain contact region, 5...
... Extended drain region, 6... Gate oxide film,
7...Gate electrode, 8...Region of the first conductivity type under the semiconductor substrate, 12...Depletion layer. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 4, 1, 2g, 1000th 51Y]

Claims (1)

[Claims] a second conductivity type source region and a second conductivity type drain contact region formed in a first conductivity type semiconductor substrate; a second conductivity type extended drain region in contact with the drain contact region; , a semiconductor device having a channel in the surface of the semiconductor substrate between the extended drain region and the source region, and having a gate electrode on the channel region via a gate oxide film, the semiconductor device having the semiconductor of the first conductivity type; A region of a first conductivity type having an impurity concentration higher than that of the semiconductor substrate is provided under the substrate, a source region is connected to the semiconductor substrate, and a reverse voltage is applied between the drain and the source to reduce the thickness of the semiconductor substrate. 1. A semiconductor device characterized in that the thickness of the depletion layer is such that when the depletion layer expands, it easily reaches a region of the first conductivity type below the semiconductor substrate.