JPH04107876A - Semiconductor device and ignitor using it - Google Patents

Abstract

PURPOSE:To protect a MOSFET from damage by breakdown by permitting the depth of a drain contact area to be deeper than an extended drain area, permitting the surface of a first conductivity type semiconductor substrate between the extended drain area and a source area to be a channel area, forming a gate electrode on the channel area and forming a bottom layer high- density area of first conductivity type below the semiconductor substrate. CONSTITUTION:A bottom layer high-density area 11 of first conductivity type which is denser than a substrate 10 is provided below a semiconductor substrate 10. When a reverse voltage is applied between a drain area 6 and a second conductivity type source area 8 provided on the substrate 10, since a depletion layer spreads from both the area between the drain area 6 and the substrate 10 and the area between the first conductivity type area 7 and the drain area 6, the density of the extended drain area 6 is permitted to be denser to attain high pressure resistance than a structure which does not have the first conductivity type area. Therefore, the on-resistance between the drain 6 and the source 8 is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor device that can be used as a power element for an igniter, and an igniter device using the same.

2. Description of the Related Art Conventionally, when a MOSFET is used as a switching element in an igniter, it is necessary to provide a surge protection diode 14 between the drain and source of the MOSFET 13 in the switching section as shown in FIG. Furthermore, the second
During rotation, 12 is a transformer, and 15 is a light emitting point.

Problems to be Solved by the Invention The reason why this surge protection diode is necessary will be explained below. Figure 3 shows MOSFET 13 in Figure 2 operating 1.
6.17. It shows the drain voltage when stopped at 18 and 19. 3A shows the case with the external diode 14, and FIG. 3A shows the case without the external diode 14.

- Point #l [#22.26 is the drain-source breakdown voltage of MOSFET 13. Since the load is an inductance load, a positive voltage surge 20.21 occurs the moment the MOSFET stops. External surge protection diode 1
4, the surge voltage will be higher than the drain-source breakdown voltage of MOSFET13, so MOSFET1
3 breaks down between the drain and source, and as shown in FIG. 4, when a breakdown current flows from the drain contact region 28 to the source 31, a voltage difference occurs due to the resistance component 34 of the semiconductor substrate 35, and the parasitic bipolar transistor 33 operates. This causes a temperature rise, leading to thermal damage. Therefore, MOSFE
Diode 14 with a breakdown voltage lower than that of T13
must be inserted between the drain and source of the MOSFET. In FIG. 4, 24 is a drain electrode, 25 is a source electrode, 30 is an extended drain region, 29 is a first conductivity type region, 26 is a silicon oxide film, 27 is a gate electrode, and 32 is a substrate contact region.

In this way, in the conventional structure, the drain of MOSFET
A surge protection diode had to be installed between the sources.

Means for Solving the Problems In order to solve the above problems, the present invention uses the horizontal M shown below.
It has an OSFET structure. In other words, an extended drain region of the second conductivity type that is in contact with the drain contact region is formed between the source region of the second conductivity type and the drain contact region formed in the semiconductor substrate of the first conductivity type, and the drain region is formed on the surface of the extended drain region. forming a first conductivity type region that is reverse biased, the depth of the drain contact region is deeper than the extended drain region, and the surface of the first conductivity type semiconductor substrate between the extended drain region and the source region is used as a channel region. , a gate electrode is formed on this channel region via a gate oxide film, a lower high concentration region of the first conductivity type is formed under the semiconductor substrate, and a reverse voltage is applied between the drain and the source. This structure is such that breakdown occurs between the drain contact region and the semiconductor substrate when this happens.

Function: According to the structure of the present invention, a diode having a breakdown voltage lower than that of the MOSFET can be inserted between the drain and source of the MOSFET, and the MOSFET can be protected from destruction due to breakdown.

Embodiment FIG. 1 shows a cross section of a semiconductor device according to an embodiment of the present invention. A semiconductor substrate 10 of a first conductivity type (for example, P type) is provided with an extended drain region 6 of a second conductivity type (for example, N type), and a surface inside the drain region 6 is reverse biased with respect to this drain region 6. A first conductivity type region 7 is formed. A lower high concentration region 11 of a first conductivity type, which has a higher concentration than the substrate 10, is provided below the semiconductor substrate 10.

When a reverse voltage is applied between the drain region 6 and the second conductivity type source region 8 provided on the substrate 10, the drain region 6
and the substrate 10, and between the first conductivity type region 7 and the drain region 6.
Since the depletion layer spreads between both regions, the concentration of the extended drain region 6 is more concentrated (
Moreover, high breakdown voltage can be achieved, so drain 6 - source 8
The on-resistance between the two can be significantly lowered. In order to make the characteristics of the element suitable for an igniter, the concentration of the semiconductor substrate 10 is set to 3×101.
40Il-3. A contact region 9 of the substrate 10 was formed in contact with the source region 8, and at the same time, contact was made with the source electrode 2. The gate electrode 4 is made of polycrystalline silicon, and the substrate surface has a silicon oxide film 3 of 2 microns or more.
was formed. The lower part of the gate electrode 4 of this silicon oxide film 3 becomes a gate oxide film. The drain electrode 1 was made to have the same width as the source electrode. By setting the depth of the extended drain region 6 to 5 microns and the depth of the drain contact region 5 to 10 microns, the breakdown voltage of the diode is 360V, MO
The breakdown voltage of S is 400v.

Effects of the Invention As described above, according to the present invention, a diode having a breakdown voltage lower than that of the MOSFET can be formed between the drain and source of the MOSFET, and can be built into one chip.

[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 circuit diagram of a general igniter device, and FIG. 3 is a waveform showing changes in drain voltage during switching of the MOSFET shown in FIG. Figure 4 shows breakdown between the drain and source of the MOSFET. ...Gate electrode, 5...Drain contact region, 6
...Extended drain region, 7...First conductivity type region, 8...Source region, 9...
Substrate contact region, 10...Semiconductor substrate, 1
1... First conductivity type region with higher concentration than the substrate. Name of agent Patent attorney Akira Kokaji et al. 22 Figure 1 M closed? 4----・2'5...-? 6-...? 7 °°- Drain the source electrode #i-based silicon gate electrode] 30- Back drain sword 0 32- Inner plate contact 0^

Claims (2)

[Claims] (1) An extended drain region of a second conductivity type that is in contact with the drain contact region is provided between a source region of a second conductivity type and a drain contact region formed in a semiconductor substrate of a first conductivity type, and the extended drain region of the second conductivity type is provided in contact with the drain contact region. An extended drain region and a reverse biased first conductivity type region are provided on the surface of the region, a drain contact region deeper than the extended drain region is provided, and a first conductivity type region having a higher concentration than the semiconductor substrate is provided below the first conductivity type substrate. A conductivity type lower layer high concentration region is provided, the surface of the first conductivity type semiconductor substrate located between the extended drain region and the source region is used as a channel region, and a gate electrode is provided on the channel region via a gate oxide film, A semiconductor device in which a source region is electrically connected to the semiconductor substrate, and breakdown occurs between the drain contact region and the semiconductor substrate when a reverse voltage is applied between the drain and the source. (2) An igniter device using the semiconductor device according to claim 1.