JP2563456B2 - MIS type capacitive element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MIS semiconductor capacitor suitable for use in a semiconductor integrated circuit, particularly a symmetrical circuit format used in a linear circuit or the like.

2. Description of the Related Art A MIS type capacitive element is known as one of capacitive elements integrated in a semiconductor integrated circuit.

FIG. 3 is a diagram showing the structure of an MIS type capacitor element built in a bipolar type semiconductor integrated circuit, in which an N type epitaxial layer formed on a P type silicon substrate 1 is formed as a P ⁺ type insulating isolation region 2. In the N-type epitaxial island region 3 formed separately in an island shape, an N-type diffusion region 4 having a higher impurity concentration and an N-type contact diffusion region 5 having a higher impurity concentration than this region are formed, and further, an N-type A metal layer 7 to be one electrode is formed on the silicon dioxide film 6 covering the surface of the diffusion region 4, and a metal layer 8 to be the other electrode is additionally provided to the N-type contact diffusion region 5. . Reference numeral 9 is an N-type buried region having a high impurity concentration. In this MIS type capacitance element, a capacitance having the silicon dioxide film 6 as a dielectric layer is formed.

In the MIS type capacitance element having such a structure, it is provided by the PN junction formed between the P type substrate 5 and the series resistance provided by the N type diffusion region 4 on the electrode 8 side. The added junction capacitance exhibits asymmetry. For this reason, when a conventional MIS type capacitive element is used in a contrasting circuit often used in linear signal processing (for example, a differential amplifier circuit), a parasitic capacitance due to a PN junction is given to one signal line and the other signal is applied. Even if a predetermined frequency characteristic is obtained in the other signal line, the frequency characteristic of one signal line deteriorates and the symmetry of the signal processing circuit is impaired. It was

The present invention is intended to eliminate the above-mentioned problems, and an object thereof is to achieve symmetry of parasitic capacitances applied to both electrodes.

Means for Solving the Problems In the MIS type capacitance element of the present invention, first conductivity type first and second island regions having substantially the same planar area are formed on a semiconductor substrate of opposite conductivity type, and First conductivity type first and second diffusion regions are formed in the second island region, and metal electrodes are formed on the insulating films on the first and second diffusion regions, respectively. Side electrode contacting the diffusion region of
A semiconductor-side electrode that contacts the diffusion region is formed to form a first capacitor and a second capacitor, the metal electrode of the first capacitor and the semiconductor-side electrode of the second capacitor are connected to each other, and
The configuration is such that the metal electrode of the capacitor is connected to the semiconductor-side electrode of the first capacitor.

Operation According to this structure, the parasitic capacitance due to the semiconductor substrate, the island region, and the PN junction is surely given to the semiconductor-side electrode, but since the first capacitance and the second capacitance are reversed and connected in parallel, the MIS-type capacitance element The parasitic capacitance of both electrodes can be made symmetrical,
For example, when connected to a symmetrical circuit, the frequency characteristic of only one of the two signal lines is not deteriorated but is deteriorated equally, so that the phase between the signal lines does not change symmetrically.

Example Hereinafter, the MIS type capacitance element of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view showing the shape of the MIS type capacitance element of the present invention built in a bipolar integrated circuit.
IS type capacitance elements C ₁ and C ₂ are arranged in parallel. The cross-sectional structures of these MIS type capacitance elements C ₁ and C _{2 taken} along the line X-X and the line Y-Y are the same as the structure shown in FIG. by the way,
In the MIS type capacitor of the present invention, the first capacitor C ₁ and the second capacitor C ₂
Although surrounded by the P ⁺ -type insulating isolation region 2 and isolated from each other, the metal layer 12 is located on the capacitance forming regions 10 and 11 and serves as one electrode of the first capacitance and the second capacitance. When
A part of 13 extends to the side of the second capacity and the first capacity,
The metal layer 12 is connected to the semiconductor substrate surface (contact diffusion region surface) in the semiconductor-side electrode window 14 of the second capacitor, while the metal layer 12
A junction structure 13 is connected to the semiconductor substrate surface in the semiconductor-side electrode window 15 of the first capacitor. According to this structure, the metal layers 12 and 13 are used as terminals, and the first capacitance C ₁ and the second capacitance are provided between them.
A composite MIS type capacitive element in which C ₂ is connected in parallel is realized.

FIG. 2 is an equivalent circuit diagram of the MIS type capacitance element shown in FIG. 1, in which the terminal resistance (metal layer) 13 has a series resistance R ₁ and a junction capacitance C _j1 provided by the first capacitance, On the other hand, the terminal (metal layer) 12 has a series resistance R ₂ and a junction capacitance C _j2 added by the second capacitance added thereto. Therefore, the symmetry of the terminals 12 and 13 is significantly improved. In particular, the dimensions of the first and second capacitors are set equal,
If the shapes of both capacitance elements are symmetrical, the symmetry of the terminals 12 and 13 will be almost perfect.

In the above explanation, it was built in the bipolar integrated circuit.
Although the MIS type capacitance element has been illustrated, the same configuration may be used when it is built in a MOS integrated circuit. In this case, the reduction in symmetry due to the series resistance is prevented.

EFFECTS OF THE INVENTION According to the present invention, the first capacitor and the second capacitor are connected in anti-parallel to form the MIS type capacitor element, so that P applied to both electrodes
The parasitic capacitance of the N-junction becomes symmetrical, and for example, the MIS of the present invention
When the capacitive element is connected to a symmetrical circuit, the frequency characteristic of only one of the two signal lines is not deteriorated,
Since they are equally deteriorated, a special effect that the phase between the signal lines does not change relatively is obtained. Further, in order to build this capacitance element, it is not necessary to change the diffusion process of the integrated circuit, and it can be realized by changing the mask corresponding to the process.

[Brief description of drawings]

FIG. 1 is a plan view showing the shape of the MIS type capacitance element of the present invention,
FIG. 2 is an equivalent circuit diagram of the MIS type capacitance element shown in FIG. 1, and FIG. 3 is a conventional MIS built in a bipolar integrated circuit.
It is a section construction drawing of a type capacity element. 1 ... P-type silicon substrate, 2 ... P ⁺ type insulation isolation region, 3
... N-type epitaxial island region, 4 ... N-type diffusion region,
5 ... N-type contact diffusion region, 6 ... silicon dioxide film, 7,8 ... metal layer, 9 ... N ⁺ type buried region, 10,11 ... capacity forming region, 12,13 ... metal layer (Terminal), 14,15 …… Semiconductor side electrode window, R ₁ , R ₂ …… Series resistance, C _j1 , C _j2 …… Junction capacitance.

Continuation of the front page (56) References JP-A-49-104586 (JP, A) JP-A-59-55047 (JP, A) JP-A-61-268057 (JP, A) JP-A-57-207358 (JP , A)

Claims (1)

(57) [Claims] 1. A one-conductivity-type first plate having a substantially equal planar shape area.
The first and second island regions are formed on a semiconductor substrate of opposite conductivity type, and the first and second diffusion regions of one conductivity type are formed in the first and second island regions, respectively. A metal electrode is formed on each insulating film on the second diffusion region, a semiconductor-side electrode that contacts the first diffusion region and a semiconductor-side electrode that contacts the second diffusion region are formed, and Capacity and second
A MIS is characterized in that a capacitance is built in, the metal electrode of the first capacitance is connected to the semiconductor side electrode of the second capacitance, and the metal electrode of the second capacitance is connected to the semiconductor side electrode of the first capacitance. Type capacitive element.