JP2713496B2 - Semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor device used as a power element for an igniter.

2. Description of the Related Art A surge protection diode is a typical semiconductor device used for surge suppression. A conventional semiconductor device will be described below using a surge protection diode as an example.

When a MOSFET is used as an igniter as a switching element, the switch section needs a surge protection diode 23 between the drain and source of the MOSFET 22 as shown in FIG. In the figure, reference numeral 24 denotes a firing point, and reference numeral 25 denotes an ignition coil. Conventionally, such a surge protection diode has been used externally, which is added outside the integrated circuit.

First, the reason why the surge protection diode is required will be described.

FIG. 4 (a) is an operating characteristic diagram when the surge protector diode is not provided in the igniter MOSFET, and FIG. 4 (b) is an operational characteristic diagram when the surge protector diode is attached to the igniter MOSFET. As shown in FIG. 4A, when there is no surge protection diode, the MOSFET 22 is in the operating state.
A positive surge voltage 32 is generated at the moment when the state changes from 26 to the stop state 27. In this case, since there is no surge protection diode, the surge voltage 32 becomes the breakdown voltage 28 between the drain and source of the MOSFET 22.
Higher, MOSFET 22 breaks down between drain and source.

On the other hand, as shown in FIG. 4 (b), when the surge protection diode 23 is attached, a positive surge voltage 33 is generated at the moment when the MOSFET 22 shifts from the operation state 29 to the stop state 30,
The surge voltage 33 does not become higher than the breakdown voltage 31 between the drain and the source due to the function of the surge protection diode.

Next, the state inside the MOSFET 22 when there is no surge protection diode will be described with reference to FIG. As shown in the figure
The MOSFET 22 is in contact with the drain contact region 43 between a source region 42 of the second conductivity type and a drain contact region 43 of the second conductivity type formed in a semiconductor substrate 41 of the first conductivity type. An extended drain region 44 is formed, a surface of the semiconductor substrate 41 between the extended drain region 44 and the source region 42 is used as a channel, and a gate electrode 46 is formed on the channel region via a gate oxide film 45. It is a thing. 47 is a substrate contact region for connecting to the semiconductor substrate 41, 48 is a drain electrode, and 49 is a source electrode. Such a drain contact region 43 of the MOSFET 22
When a breakdown current flows from the semiconductor region to the source region 42,
A potential difference is generated by the resistance component 50 of 41. This potential difference causes the parasitic bipolar transistor 51 to operate, causing an increase in temperature and thermal destruction.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an excellent semiconductor device for surge protection which can be built in the same chip as a MOSFET without adding a process.

Means for Solving the Problems In order to achieve this object, a semiconductor device according to the present invention basically includes a lateral MO formed in a semiconductor substrate of a first conductivity type.
An SFET having a first conductivity type region having a higher impurity concentration than the semiconductor substrate below the semiconductor substrate, a source region connected to the semiconductor substrate, and a source
The structure is such that the thickness of the depletion layer easily reaches the first conductivity type region under the semiconductor substrate when a reverse voltage is applied between the drains.

Operation According to this configuration, a surge protection semiconductor device that has been externally connected between the source and the drain of the MOSFET serving as the igniter switching element can be incorporated in the MOSFET chip without increasing the chip area.

An embodiment 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.

In the lateral MOSFET according to the embodiment of the present invention, the drain contact region 4 is provided between the source region 3 of the second conductivity type and the drain contact region 4 of the second conductivity type formed in the semiconductor substrate 2 of the first conductivity type. An extended drain region 5 of the second conductivity type is formed in contact with the surface of the semiconductor substrate 2 between the extended drain region 5 and the source region 3 as a channel region, and a gate oxide film 6 is interposed on the channel region. A gate electrode 7 is formed, and the semiconductor substrate 2 is
A region 8 of the first conductivity type having a higher impurity concentration than that of the first conductive type is provided. Reference numeral 9 denotes a substrate contact region for connecting to the semiconductor substrate 2, 10 denotes a drain electrode, and 11 denotes a source electrode.

In this embodiment, the impurity concentration of the semiconductor substrate 2 is 3 × 10 ¹⁴
cm ⁻³ , the impurity concentration of the first conductivity type region 8 under the semiconductor substrate 2 was 1 × 10 ¹⁹ cm ⁻³ , and the impurity concentration of the extended drain region 5 was approximately 3 × 10 ¹⁵ cm ⁻³ . Further, the thickness of the semiconductor substrate 2 is set to 15 to make the breakdown voltage between the drain and the semiconductor substrate 400 V.
μm.

FIG. 2 shows the spread of the depletion layer 12 when a reverse voltage is applied between the drain and the source in the semiconductor device configured as described above. When a reverse voltage is applied between the drain electrode 10 and the source electrode 11, the depletion layer 12 spreads between the extended drain region 5 and the semiconductor substrate 2, and finally the first conductivity type region 8 under the semiconductor substrate 2. Reach The downward spread of the depletion layer 12 is suppressed here, and the electric field at the junction at the bottom of the extended drain region 5 increases, and breakdown occurs here.
At this time, the breakdown current flows in the direction of the arrow in FIG. 2, and the operation of the parasitic bipolar transistor does not occur. In the case where there is no region 8 of the first conductivity type under the semiconductor substrate 2,
Has a breakdown voltage of 450 V, and by setting the breakdown voltage between the drain and the semiconductor substrate to 400 V, the breakdown of the MOSFET is prevented.

Effect of the Invention As described above, the present invention provides the first type in which the lateral MOSFET is formed.
A region of the first conductivity type having a higher impurity concentration than the semiconductor substrate is provided below the semiconductor substrate of the conductivity type, the source region is connected to the semiconductor substrate, and a reverse voltage is applied between the source and the drain to the thickness of the semiconductor substrate. The thickness is such that the depletion layer easily reaches the region of the first conductivity type under the semiconductor substrate when it is formed, thereby providing an excellent surge protection that can be built in the same chip as the MOSFET without additional steps. A semiconductor device can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention, FIG. 2 is a diagram showing the expansion of a depletion layer when a reverse voltage is applied between the drain and source of the semiconductor device, and FIG.
Circuit diagram when MOSFET is used for igniter as switching element, Fig. 4 (a) is operating characteristic diagram when igniter does not have surge protection diode, Fig. 4 (b) is surge mitigation diode mounted on igniter FIG. 5 is a diagram showing an 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 ... first conductivity under the semiconductor substrate. 12-shaped depletion layer.

Claims (1)

(57) [Claims] 1. A lateral MOSFET having an extended drain region and a source region of a second conductivity type formed on a surface side of a semiconductor substrate region of a first conductivity type, wherein the extended drain region is formed deeper than the source region. A shallow high-concentration drain contact region of the second conductivity type is provided in a surface region of the extended drain region, and a thickness of the high-concentration region of the first conductivity type provided on the back side of the semiconductor substrate region and the extension drain region are increased. A semiconductor device sandwiching the semiconductor substrate region of the first conductivity type such that a depletion layer that spreads when a reverse voltage between a drain and a source is applied easily reaches a high-concentration region of the first conductivity type.