JPH03129779A - Semiconductor device having high breakdown strength - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device integrated with Zener diodes having Zener breakdown voltage without sacrifice of overall breakdown strength by setting the impurity concentration at a section in a second region, contacting with a first region, lower than that at a section remote from the first region. CONSTITUTION:An n<-> layer 3 having impurity concentration of about 10<13>-10<16>/cm<2> is laminated on an n<+> substrate 1. A p<-> well 4 is then formed by ion implantation with dosage of about 1X10<13>/cm<2> in the n<-> layer 3, an n<-> cathode layer 51 is formed by ion implantation with dosage of about 1X10<12>-3X10<12>/cm<2> therein, and an n<+> cathode 5 is further formed therein by ion implantation with dosage of about 5X10<15>/cm<2>. Furthermore, a p<+> isolation layer, an electrode 2 contacting with the n<+> substrate 1, anode electrodes 7 contacting respectively with the p<+> isolation layer 6 at the openings of the insulating layer 9, and a cathode electrode 8 contacting with the n<+> cathode layer 5 are provided thus forming a Zener diode comprising a p<-> anode layer 4, an n<-> cathode layer 51 and an n<+> cathode layer 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a semiconductor substrate in which a Zener diode as a protective element is provided on one side of a semiconductor substrate on which a high-voltage semiconductor element having main electrodes on both sides is formed. The present invention relates to integrated high voltage semiconductor devices.

[Conventional technology]

In order to prevent the elements integrated on one side of the semiconductor substrate from being affected by the voltage applied to the main electrode provided on the other side of the substrate C, a PN junction between the substrate area and the element area is used. Semiconductor devices are known as self-isolated devices. 21st! 1 indicates a portion of a Zener diode used in a self-isolated semiconductor device. In the figure, electrode 2 is on the - side.
An n- bulk layer 3 is laminated on an n+ silicon substrate l on which is deposited, and a p- well 4 is selectively formed on the side of the n- layer 3 opposite to the substrate l. Furthermore, this p-well 4
An n layer 5 is selectively formed on the opposite side of the substrate 1.

This n'' layer 5 is the cathode layer of the Zener diode.

The p-well 4 becomes an anode layer. Surrounding the n+ layer 5,
A p+ layer 6 reaching from the surface to the n- layer 3 is provided, and the anode electrode 7 of the Zener diode is in contact with this p+ layer 6, and the cathode electrode 8 is in contact with the n-layer 5 at the opening of the insulating film 9, respectively. There is. By connecting the electrode 7 to an electrode of another integrated element and the electrode 8 to a terminal or another integrated element, the Zener diode can provide protection against overvoltages. The p+ layer 6 serves as a separation layer, and although it is not necessary, it has the effect of suppressing the operation of parasitic elements that occur between adjacent integrated elements.

Figure 3'' shows an example in which a bidirectional Zener diode is formed as a protection element against bidirectional overvoltage, and the p-well 4
Two n'' cathode layers 5 are provided on the wafer, and are connected to other integrated elements or terminals by cathode electrodes 8 in contact with each other. FIG.

The Zener diode consisting of the p-well 4 and the n4 layer 5 in FIG.
They are separated by a PN junction between n-layer 3 and p-layer 4.

[Problem to be solved by the invention]

In order to increase the Zener breakdown voltage of the Zener diode shown in FIG. 2 or 3, the impurity concentration in the p-well 4 of the anode layer must be lowered. However, when the concentration of the p-well 4 is lowered, the direct current amplification factor hF! of a parasitic bipolar transistor with the n+ cathode layer 5 as the emitter, the p-well 4 as the base, and the n- bulk layer 3 and the n'' substrate l as the collector! collector because it gets bigger.

The maximum emitter voltage V CHo decreases. For example, when the Zener breakdown voltage of the Zener diode is 5 V, l:c Vcgo is 90 to 95 V, to V (
7) Sometimes it is 80-85V, and when increased to 25V, V
cio becomes 50V. Since this VCHO determines the voltage that can be applied to the electrode 2, that is, the withstand voltage of the entire semiconductor device, the withstand voltage of the entire semiconductor device is reduced as a result.

An object of the present invention is to solve such problems and provide a semiconductor device in which Zener diodes having a high Zener breakdown voltage are integrated without reducing the withstand voltage of the entire semiconductor device.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a first region of a second conductivity type exposed on one main surface side of a semiconductor substrate of a second conductivity type, and a first region of a second conductivity type exposed on the one main surface side. In a high-voltage semiconductor device in which a Zener diode is formed, the portion of the second region in contact with the first region is farther than the first region. shall have a lower impurity concentration.

[Effect]

By reducing the impurity concentration of the portion of the second region in contact with the first region, the second region of the second conductivity type becomes an emitter, the first region of the second conductivity type becomes a base, and the rest of the semiconductor substrate of the second conductivity type The emitter side of the emitter-base junction of the parasitic bipolar transistor whose collector is the region of h
PI' decreases.

As a result, Vci of the parasitic bipolar transistor.

is significantly reduced, but the Zener breakdown voltage of the Zener diode, which is determined by the impurity concentration of the first region, is hardly reduced.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and parts common to those in FIG. 2 are given the same reference numerals. As in the case of Figure 2,
On the n'' substrate 1, there is an impurity concentration of 101@~10''/cd.
About 3 n-layers were laminated. lXl0'' in this n-layer 3
The p-well 4 is formed by ion implantation at a dose of about /cd.
, into which I XlO12~3XIO1'/c
An n- cathode layer 51 was formed by ion implantation at a dose of about rI, and an n+ cathode layer 5 was formed by ion implantation into the layer at a dose of about 5×10''/cd. forming layers, n' electrode 2 in contact with the substrate 1°, p' anode electrode 7 in contact with the separation layer 6 at the opening of the wA membrane 9, n' catho 1 layer 5;
The provision of the contacting cathode electrode 8 was the same as in the prior art.

By forming the Zener diode consisting of the p-"r node F14.n-cathode layer 51 and the n-cathode layer 5 in this way, the n8 layer 5 and n A value of 92V was obtained as Vat of the parasitic bipolar transistor in which the − layer 51 is the emitter, the p− layer d is the base, and the n− layer 3 and the n′ substrate 1 are the collectors.

FIG. 4, like FIG. 3, shows another embodiment of the invention in the case of forming a bidirectional Zener diode.

The cathode layers of the two Zener diodes are separated from the n' layer 5 and the surrounding n' layer 51, respectively.

This made it possible to increase the breakdown voltage of the entire semiconductor device, but if the breakdown voltage required for each Zener diode is different, it is also possible to increase the breakdown voltage of the entire semiconductor device by making one Zener diode double-layered. can.

〔Effect of the invention〕

According to the present invention, the region of the second conductivity type that determines the Zener breakdown voltage of the Zener diode and the region in contact with the junction of the second conductive shadow region that forms the junction are made to have a low impurity concentration, thereby lowering the hPE of the parasitic bipolar transistor. This makes it possible to increase the Zener breakdown voltage without lowering the breakdown voltage of the entire semiconductor device, and to obtain a high breakdown voltage composite semiconductor device protected by Zener diodes with arbitrary breakdown voltages.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a Zener diode portion of a high voltage semiconductor device according to an embodiment of the present invention, FIG. 2 is a sectional view of a Zener diode portion of a conventional high voltage semiconductor device, and FIG. 3 is a sectional view of a Zener diode portion of a conventional high voltage semiconductor device. Cross-sectional view of the Zener diode part of the voltage-resistant semiconductor device, No. 4
The figure is a sectional view of a Zener diode portion of a high voltage semiconductor device according to another embodiment of the present invention. n'' substrate, n-bulk layer, p-well, 5 n+ cathode layers, 1 cathode layer. /, ///// Figure 3 Figure 4

Claims (1)

[Claims] 1) A first region of a second conductivity type exposed on one main surface of the semiconductor substrate of the first conductivity type and a first region provided inside the first region exposed on one main surface of the semiconductor substrate of the first conductivity type and also exposed on the one main surface. A high breakdown voltage semiconductor device in which a Zener diode is formed comprising a conductive type second region, wherein a portion of the second region in contact with the first region has a lower impurity concentration than a portion farther from the first region. .