SEMICONDUCTOR DEVICE
A semiconductor device having a clamp diode has a breakdown voltage adjusting first conductivity type low concentration region provided on a semiconductor substrate. A second conductivity type high concentration region of circular shape is provided within the breakdown voltage adjusting first conductivity type low concentration region so as to be surrounded by the first conductivity type low concentration region but not surrounded by any other low concentration region. A first conductivity type high concentration region is provided within the first conductivity type low concentration region, without being held in contact with the second conductivity type high concentration region.
1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a clamp diode used in a semiconductor device.
2. Description of the Related Art
A clamp diode is a device which uses a junction breakdown voltage between the p-type semiconductor and the n-type semiconductor to maintain (clamp) a voltage supplied to a circuit constant in a semiconductor device. Since a clamp diode is a device capable of limiting a voltage easily, there is a high demand and a wide usage in electronic devices.
When manufacturing a clamp diode, which limits a voltage to be constant, it is extremely important for the clamp diode to have small fluctuations in breakdown voltage within a wafer, among wafers, and among lots, and to have little change over time. In addition, it is also important for the clamp diode to have a small leakage current until breakdown occurs. Even though the structure of the clamp diode is simple, it is not easy to produce a clamp diode which satisfies all of the above-mentioned characteristics.
Japanese Published Patent Application No.11-307787 discloses the invention for improving the above-mentioned change over time.
Though the change over time can be improved by the invention disclosed in the Japanese Published Patent Application, there is no description, however, on the degree of fluctuations within a wafer, between wafers, and among lots, and the presence or absence of leakage before breakdown occurs. Indeed, in the invention disclosed in the Japanese Published Patent Application the fluctuations within a wafer, between wafers, and among lots are not reduced because of the following reasons.
Since an electric field corresponding to a voltage applied to the electrode 8 is applied to a p-n junction through the oxide film 9 in the structure illustrated in
Further, due to the presence of a first conductivity type region 7 below the element isolation insulating film 2 of FIGS. and 8, impurities in the first conductivity type region 7 affect impurity distribution near the p-n junction, and the breakdown voltage of the p-n junction changes. Also in this regard, ideally, when the first conductivity type regions 7 are produced in the same condition, the breakdown voltages of the p-n junctions are the same. Actually the concentrations of impurities in the first conductivity type regions 7, however, are not the same within a wafer, between wafers, and among lots, and the p-n junction breakdown voltages are affected to various degrees. As a result, the p-n junction breakdown voltages fluctuate.
According to the Japanese Published Patent Application No. 11-307787, a planar shape of the second conductivity type high concentration region 1 of
As described above, there are many factors that cause the breakdown voltages of the p-n junctions to fluctuate, and, in order to suppress such fluctuations, the clamp diode needs to have a structure as simple as possible, and the factors that cause fluctuations need to be eliminated as much as possible.
SUMMARY OF THE INVENTIONThe present invention has been made in view of the above-mentioned problems, and the present invention provides a clamp diode which suppresses deterioration with time, fluctuations within a wafer surface, among wafers, and among lots, and leakage before breakdown.
In order to solve the above-mentioned problems, according to an exemplary embodiment of the present invention, a semiconductor device including a clamp diode includes: a breakdown voltage adjusting first conductivity type low concentration region provided on a semiconductor substrate; a second conductivity type high concentration region provided within the breakdown voltage adjusting first conductivity type low concentration region, the second conductivity type high concentration region being circular; an element isolation insulating film provided within the breakdown voltage adjusting first conductivity type low concentration region, the element isolation insulating film being provided in a ring shape and surrounding the second conductivity type high concentration region without being held in contact therewith; and a first conductivity type high concentration region provided outside the ring of the element isolation insulating film within the breakdown voltage adjusting first conductivity type low concentration region.
By the foregoing arrangement, the present invention provides a clamp diode having little deterioration with time, small fluctuations within a wafer surface, among wafers, and among lots, and little leakage before breakdown.
In the accompanying drawings:
A mode for carrying out the present invention is described below with reference to the attached drawings.
A breakdown voltage adjusting first conductivity type low concentration region 5 is provided on a surface of a semiconductor substrate 6, and a second conductivity type high concentration region 1, which has a conductivity type opposite to that of the breakdown voltage adjusting first conductivity type low concentration region 5, is provided on a part of a surface of the breakdown voltage adjusting first conductivity type low concentration region 5 so as to be circular in a plan view. On the surface of the breakdown voltage adjusting first conductivity type low concentration region 5, an element isolation insulating film 2 having a ring shape is provided in such a way that the element isolation insulating film 2 surrounds the second conductivity type high concentration region 1 without being held in contact therewith The ring shape as used herein does not necessarily mean an annular shape or a doughnut shape, and an inner part of the ring shape of the element isolation insulating film 2 is circular, but an outer shape thereof is rectangular in this embodiment. Further, on the breakdown voltage adjusting first conductivity type low concentration region 5, a rectangular first conductivity type high concentration region 3 is provided so as to surround the element isolation insulating film 2. The second conductivity type high concentration region 1 and the first conductivity type high concentration region 3 have surfaces covered with insulating films, and are respectively connected to different wirings via contacts 4.
When a voltage is applied between the first conductivity type high concentration region 3 and the second conductivity type high concentration region 1, due to breakdown of a p-n junction of the second conductivity type high concentration region 1 and the breakdown voltage adjusting first conductivity type low concentration region 5, the voltage is clamped to be a constant voltage. Depending on the purposes, the semiconductor device may include only a clamp diode, or may include a circuit having components other than the clamp diode, such as a transistor.
Effect 1As illustrated in
Accordingly, in
In
In
In
In
In order to clamp a voltage in any current band at the same voltage, the clamp diode is required to have steep breakdown characteristics. In order to obtain the steep breakdown characteristics, a parasitic resistance may be reduced. In the present invention, the distance between the second conductivity type high concentration region 1 and the first conductivity type high concentration region 3 is short, and a parasitic resistance of the breakdown voltage adjusting first conductivity type low concentration region 5 is reduced, thereby obtaining the steep breakdown characteristics.
As illustrated in
In all of the above-mentioned exemplary embodiments of the present invention, the element isolation insulating film 2 is assumed to be formed by LOCOS. However, even when the element isolation insulating film 2 is formed by shallow trench isolation (STI), the same effect can be obtained. In this manner, the present invention is not limited to the above-mentioned embodiments, and can be modified within the scope of the present invention without departing from the gist thereof.
Claims
1. A semiconductor device, comprising:
- a semiconductor substrate;
- a breakdown voltage adjusting first conductivity type low concentration region provided on the semiconductor substrate;
- a second conductivity type high concentration region provided near a surface within the breakdown voltage adjusting first conductivity type low concentration region so as to be surrounded by the first conductivity type low concentration region but not surrounded by any low concentration region other than the first conductivity type low concentration region, the second conductivity type high concentration region being circular; and
- a first conductivity type high concentration region provided on the surface within the breakdown voltage adjusting first conductivity type low concentration region without being held in contact with the second conductivity type high concentration region.
2. A semiconductor device according to claim 1, wherein the first conductivity type high concentration region has a ring shape and is provided so as to surround the second conductivity type high concentration region.
3. A semiconductor device according to claim 2, wherein at least an inner part of the ring shape of the first conductivity type high concentration region is circular.
Type: Application
Filed: Jun 22, 2015
Publication Date: Oct 8, 2015
Inventor: Tomomitsu RISAKI (Chiba-shi)
Application Number: 14/746,018