JPH0563146A - Integrated circuit - Google Patents

Abstract

PURPOSE:To minimize the effect of parasitic capacitance on the resistance between two selected terminals by providing three terminals of which one is an open terminal, or not selected. CONSTITUTION:Three contact holes 2A, 3A and 4A are formed in an insulating SiO2 film 7 on a diffused region 1 in a bulk layer. When the contact hole 3A is selected to connect a conductor 5 to a contact 3 through a wiring pattern, a resistor of a value r1 is obtained. When the contact holes 4A is selected for connection to a contact 4, a resistor of a value r1+r2 is obtained. The other contacts, not in use, are kept open to minimize changes in circuit characteristics without substantial changes in parasitic capacitance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, and more particularly, to improvement in connection of resistance elements formed in the semiconductor integrated circuit.

Generally, a resistance element of a semiconductor integrated circuit constitutes a resistance element by a diffusion resistance or a polysilicon resistance having electric resistance accumulated in the longitudinal direction, and two connections are drawn from these resistance elements at predetermined positions. The ends have a predetermined resistance value. In order to ensure the versatility of the mask pattern when manufacturing a semiconductor integrated circuit, the terminal portion for drawing out the wiring of the resistance element is usually
Three or more are provided, and two of them are selected via the wiring pattern to form a connection end.

[0003]

2. Description of the Related Art A resistance element in a conventional semiconductor integrated circuit will be described with reference to FIGS. This figure shows, as a plan view, a semiconductor integrated circuit portion used as a resistance element of a low-pass filter, for example. The resistance element 1 is formed as a diffusion region on a substrate of a semiconductor integrated circuit, and contact holes 2A to 4A are formed on the resistance element 1 so as to penetrate SiO ₂ forming an insulating material.

As shown in FIG. 1A, when the contact holes 2A and 4A at both ends are selected and the terminal portions (contact portions) 2 and 4 of the resistance element 1 therebelow are connected by the wiring 5, The resistance value of this resistance element is r1 + r2
And the resistance value of the resistance element has r1 when the contact portions 2 and 3 at the left end and the middle portion in the figure are connected by the wiring 5, respectively, as shown in FIG. It will be.

FIG. 6 is a sectional view taken along line VI-VI of FIG. In the figure, the resistance element 1 is ion-implanted on the substrate 10 forming the P− region so as to have a predetermined concentration, and is formed as an n + region having a uniform resistivity. It has a resistance value r1 and a resistance value r2 between the contact portions 3 and 4.

As shown in FIG. 6, generally, when r1 is selected as the resistance value of the resistance element, the contact portion 4 which is not used is also connected to the wiring through the contact hole 4A, and the contact portions 2 to 4 are connected. All of them are connected to the wiring 5 penetrating through the contact holes 2A to 4A to form a connection end.

As described above, the reason for short-circuiting the resistance r2 portion of the resistance element 1 between the contact portion 4 and the contact portion 3 via the wiring 5 is generally to leave the terminal of the circuit element as an open end. It is considered that the electrostatic induction or the like adversely affects the entire circuit including the open end.

[0008]

Parasitic capacitance is formed between the resistance element 1 and the ground. For example, in FIG. 6, the parasitic capacitance is formed between the diffusion region 1 and the p- region of the substrate 10. Since it is formed on the boundary surface 6, it is known that it is substantially proportional to the overall electric resistance of the resistance element 1 which is cumulatively increased in the longitudinal direction which is the horizontal direction in the drawing.

When the parasitic capacitance is so large that it cannot be ignored as compared with the electrostatic capacitance of the capacitive element (capacitor) which constitutes the low-pass filter together with this resistance element, the parasitic capacitance is the static capacitance of the capacitor of the low-pass filter. Since it is added to the capacitance, it will affect its characteristics. However, a simple method of preventing the parasitic capacitance from affecting the characteristics of the low-pass filter and the like has not been known.

Therefore, in view of the problem of the parasitic capacitance of the resistance element of the semiconductor integrated circuit having the above-mentioned conventional resistance element, the present invention suppresses the parasitic capacitance generated in the resistance element used for a low-pass filter or the like, Therefore, it is an object of the present invention to provide a semiconductor integrated circuit having a resistance element with a simple configuration, in which a parasitic capacitance does not easily affect the characteristics of a low-pass filter or the like when used in a low-pass filter or the like.

[0011]

FIG. 1 shows the principle of the present invention. In the figure, 1 is a resistance element, 2 and 3 are connection ends, 4 is an open end, 5 is wiring, and r1 and r2 are resistance elements 1
Is the resistance value of the relevant part.

In order to achieve the above object, the semiconductor integrated circuit of the present invention has a resistance element (1) having an electric resistance accumulated in the longitudinal direction and a resistance element (1) arranged at different positions in the longitudinal direction. In a semiconductor integrated circuit including a resistance element composed of two connection ends (2, 3) which are selected from three or more terminal portions and connected by wiring, the semiconductor device is sandwiched between the two connection ends (2, 3). The terminal portion not subjected to the selection is arranged as an open end (4) in a portion other than the resistive element portion.

[0013]

By providing the resistance element portion other than the portion sandwiched by the connection ends 2 and 3 forming the selected two terminal portions with the open end 4 which is not connected to the wiring as the non-selected terminal portion, With respect to the parasitic capacitance formed in the resistance element portion other than the portion sandwiched between the connection ends 2 and 3, the influence of the parasitic capacitance on the circuit including the resistance element can be suppressed to a small level. A description will be given below with reference to the drawings.

FIG. 2 (a) is a conventional diagram shown in FIG.
1B shows an equivalent circuit of the resistance element of FIG. 1B, and FIG. 1B shows an equivalent circuit of the resistance element of FIG. 1 which is a principle diagram of the present invention. In each of these figures, C1 and C2 are respectively
It is a parasitic capacitance formed between the resistors r1 and r2 of the resistance element 1 and the ground.

In FIG. 2A, in the conventional resistance element, of the total parasitic capacitance formed between the contact portion 2 and the contact portion 4 each of which constitutes a connection end, the capacitance formed at the r2 portion. C2 is directly connected to the connection end 3 by short-circuiting the contact part 3 and the contact part 4 forming the connection end. However, in the resistance element according to the present invention shown in FIG. 2B, the capacitance C2 formed in a distributed manner in the resistance r2 portion is not directly connected to the connection end 3 forming the terminal of the resistance element.

The circuit of FIG. 2B is generally the same as that of FIG.
It is equivalent to the circuit. It can be understood from FIG. 7C that the influence of the equivalent parasitic capacitance C2 ′ exerted on the connection end 3 forming one terminal of the resistance element is greater as the equivalent resistance r2 ′ is smaller. In a conventional circuit, this equivalent resistance r2 ′ is substantially equivalent to being short-circuited. Therefore, in the conventional resistance element, the influence of the parasitic capacitance of the resistance element is larger than that of the resistance element of the present invention in FIG. I can understand that.

[0017]

The present invention will be further described with reference to the drawings. Figure 3
FIG. 7 is a sectional view showing a semiconductor integrated circuit portion of an embodiment of the present invention configured as a resistance element of a low-pass filter, similar to FIG. Reference numerals in the figure are shown in correspondence with FIG. 6, respectively. Figure 3
As shown in, the diffusion region 1 forming this resistance element is
Is formed on the substrate 10, and three contact holes 2A to 4A in the bulk layer are Si on the diffusion region 1.
It is formed on the O ₂ insulating film 7.

In this semiconductor integrated circuit, when the contact hole 3A is selected via the wiring pattern and the wiring 5 is connected to the contact portion 3 as shown in the figure, the resistance value of the resistance element becomes r1, and the contact hole is When 4A is selected and the contact portion 4 is connected,
The resistance value of the resistance element is r1 + r2.

FIGS. 4A to 4D are views for explaining the operation when the resistance element of the semiconductor integrated circuit of the above embodiment is used as the resistance element of the primary RC low pass filter. FIG. 1A is a circuit diagram showing a configuration of a general RC low-pass filter including a resistor r and a capacitor C. In this case, the cut-off frequency f _C of the RC low-pass filter is expressed as 1 / 2πrc.

In the RC low pass filter circuit, the cutoff frequencies f _C are 20 kHz and 80 kHz, respectively.
To obtain a low pass filter of Hz, the capacitor C
If a capacitor with a capacitance of 30 pF is adopted as the above, the resistors r are required to have resistance values of 265.3 kΩ and 66.3 kΩ, respectively.

If the above two types of resistance values are to be obtained by the resistance element in the semiconductor integrated circuit of the embodiment, r1 =
A resistance value of 66.3 kΩ and r2 = 199 kΩ will be formed on the resistance element. It is assumed that the parasitic capacitances Ca and Cb formed in the r1 and r2 portions of this resistance element are proportional to the resistance value of the relevant portion of this resistance element and that this is 0.1 pF per resistance value kΩ, respectively. 6.63pF and 1
It will be 9.9 pF.

FIG. 4B shows an equivalent circuit of the resistance element of the conventional semiconductor integrated circuit shown in FIG. 5B, in which the parasitic capacitance Cb of the resistor r2 is equal to the contact portion 3 of the resistance element 1, that is, low. It is directly connected to the output terminal of the bandpass filter. This parasitic capacitance Cb has 19.9 pF as described above,
The parasitic capacitance Cb has a large influence on the characteristics of this low-pass filter because it is large enough to reach almost 2/3 of the electrostatic capacitance of the regular capacitor C having 30 pF.

On the other hand, in the case of the semiconductor integrated circuit of the embodiment shown in FIG. 3, its equivalent circuit is that shown in FIG. 4 (c), and the parasitic capacitance Cb is distributed in the resistance r2 portion of the resistance element. Moreover, because of the configuration so connected, unlike the conventional circuit in which the parasitic capacitance Cb is directly connected to the terminal 3 as shown in FIG. 3B, only a part of the parasitic capacitance is the circuit constant of the RC low pass filter. Affect.

The circuit of FIG. 4C is approximately the same as that of FIG.
It is equivalent to the π-type circuit of. According to the π-type circuit in the figure, only Cb / 4 is directly connected to the terminal 3 of the low-pass filter among the parasitic capacitances Cb formed in the r2 portion of the resistance element, and the other 3Cb / 4. Has an effect on the terminal 3 of the low-pass filter only via the resistor r2 / 2 or r2 having a relatively large resistance value, so that the parasitic capacitance Cb has a cut-off frequency f _{C of the} RC low-pass filter as compared with the conventional case. It can be understood that the effect on the can be significantly reduced.

Conventionally, it has been considered that the open end of the circuit element adversely affects the circuit including the open end, so that the open end is not formed by short-circuiting the unused resistance portion of the resistance element as described above. Wiring connection was made to. For this reason, the parasitic capacitance formed in the resistance element greatly changes the circuit characteristics. In the present invention,
Focusing on this, the change in the circuit characteristics is minimized by leaving the unused contact portion as an open end.

It has been confirmed based on the present invention that the open end does not have any adverse effect on the circuit including the resistance element, and particularly when the resistance value of the relevant portion of the resistance element is large. The effect of a large parasitic capacitance formed parasitic on this can be suppressed to a small level. The resistance element of the present invention is particularly preferable when it is used for a low-pass filter as described in the embodiments, because the fluctuation of the cutoff frequency can be suppressed to a small value.

In the above embodiment, the example of the resistance element is shown in which the contact end is formed by selecting from the three contact portions and wiring the two contact portions. However, the contact portion having the contact hole opened to receive the selection. Can be arbitrarily set to 3 or more.

Further, in the above embodiment, the resistance element is described as a diffused resistance for the purpose of illustration, but the resistance element in the present invention can be formed by another type, for example, a polysilicon resistance.

[0029]

As described above, according to the semiconductor integrated circuit of the present invention, the influence of the parasitic capacitance formed parasitic on the resistance element on the circuit characteristics can be suppressed to a small level, despite the simple structure. In particular, when it is used for a low-pass filter or the like, there is a remarkable effect that the cutoff frequency fluctuation can be minimized.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

2A and 2B are diagrams for explaining the operation of the present invention, in which FIG. 2A is an equivalent circuit of a conventional resistance element, FIG. 2B is an equivalent circuit of a resistance element of the present invention, and FIG. ) Are equivalent circuits, respectively.

FIG. 3 is a sectional view of a resistance element portion of a semiconductor integrated circuit according to an exemplary embodiment of the present invention.

4A and 4B are operation explanatory diagrams of the semiconductor integrated circuit of the embodiment of the present invention, FIG. 4A is a general circuit diagram of an RC low pass filter, and FIG. 4B is a circuit diagram of a conventional low pass filter having a resistance element. (C) is a circuit diagram of a low-pass filter having the resistance element of the embodiment, and (d) is a circuit approximately equivalent to (c).

5A and 5B are plan views showing connection of resistance elements in a conventional semiconductor integrated circuit, respectively.

6 is a VI-VI sectional view of FIG. 5 (b).

[Explanation of symbols]

 1: Resistance element 2-4: Contact part 2A-4A: Contact hole 5: Wiring 10: Substrate

Claims (2)

[Claims] 1. A resistance element (1) having an electric resistance accumulated in the longitudinal direction, and a wiring connection selected from three or more terminal portions arranged at mutually different positions in the longitudinal direction of the resistance element. In a semiconductor integrated circuit including a resistance element composed of two connected ends (2, 3), the selection is applied to a part other than the resistance element part sandwiched between the two connected ends (2, 3). A semiconductor integrated circuit, characterized in that a terminal portion which is not received is arranged as an open end (4). 2. The semiconductor integrated circuit according to claim 1, wherein the resistance element constitutes a low pass filter.