JPS6412103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device including a resistor network.

In recent years, the field of application of semiconductor devices has been expanding at a remarkable rate, and they are rapidly penetrating into fields that require sufficient precision using conventional individual components or adjustment techniques.

One such example is a voltage divider circuit using a resistor network and a reference voltage source. This voltage divider circuit is often used in parallel analog-to-digital converters. A parallel analog-to-digital converter is composed of a voltage dividing circuit and a plurality of comparator groups. It has the function of comparing the voltage of the input analog signal and the voltage of the voltage divider circuit using a group of comparators and obtaining a digital output signal. Therefore, the accuracy of the voltage divider circuit determines the accuracy of the parallel analog-to-digital converter.

As a method for realizing a resistor network constituting a voltage dividing circuit with high precision, a resistor network formed by cascading a group of unit resistors is commonly used. An example is shown in FIG. 1 (plan view). A large number of unit resistors (e.g. diffused resistors or polysilicon resistors) on a semiconductor substrate
11 are provided side by side, which interconnect conductors 1
2 and a contact portion 13 having a constant area, and are connected in series. Although the resistor network shown in FIG. 1 is an excellent method in terms of accuracy, it is necessary to separate each of the unit resistor groups, so the problem of a reduction in the degree of integration cannot be avoided.

An example of an improved resistor network shown in FIG. 1 for the purpose of increasing the degree of integration is shown in FIG. 2 (plan view). As shown in FIG. 2, the interconnection conductors in FIG. 1 are omitted as much as possible and the contact portions are overlapped to improve the degree of integration. That is, long resistors 21, each of which is directly connected to the unit resistors shown in FIG. A divided voltage extraction conductor 24 is led out from the contact portion 23 .

Although the resistor network of FIG. 2 is intended to improve the degree of integration, it has a drawback in terms of accuracy due to variations in contact resistance. In other words, in a resistor network as shown in Fig. 1, even if variations in resistance value of unit resistors and variations in contact resistance occur independently, each unit resistor has the same two contacts, so the resistance circuit The accuracy of the net is not affected. On the other hand, in the configuration of a resistor network as shown in Figure 2, if variations in resistance value of the resistor and variations in contact resistance occur independently, two contacts are provided only at the folded portion of the resistor. , it is clear that the accuracy deteriorates in that part.

An equivalent circuit diagram of the resistor network shown in FIG. 2 is shown in FIG. In Figure 3, 31 is the resistance (unit resistance) from one contact to the next, and 32
indicates the resistance of the interconnection conductor, 33 indicates the contact resistance, and 34 indicates the lead-out conductor terminal. As can be seen from FIG. 3, there is usually one contact resistor 3 between one unit resistor 31 and the next unit resistor 31.
However, two contact resistors 33 are present at the folded portion (connection portion between long resistors). Therefore, when variations in the resistance value of the unit resistor and variations in the resistance value of the contact resistor occur independently, the variation in the contact resistance in this folded portion determines the limit of accuracy of the resistor network.

If the resistance value of the unit resistor is made larger than the resistance value of the contact resistor, accuracy will be improved, but a decrease in the degree of integration cannot be avoided.

The present invention improves the above-mentioned drawbacks and provides a semiconductor device equipped with a highly accurate resistor network without reducing the degree of integration.

Hereinafter, the present invention will be explained in detail based on Examples.

FIGS. 4a and 4b are a plan view and a sectional view for explaining the first embodiment of the present invention. In the figure, 46 is a semiconductor substrate, 41 is a diffused resistor (long resistor) formed on the semiconductor substrate, 47 is an insulating film (usually a silicon oxide film) coated on the surface, 4
2 is a conductor for connecting the diffused resistors to each other; 45 is a contact portion between the diffused resistor and the connecting conductor;
Reference numeral 44 denotes a divided voltage extraction conductor, and 43 a contact portion between the extraction conductor and the diffused resistor.

This embodiment is characterized in that the area of the contact section 45 between the resistor and the connecting conductor is approximately twice the area of the contact section 43 between the resistor and the lead-out conductor. The contact area is approximately 2
By doubling the amount, the disadvantages of the conventional method are eliminated.

Generally, the contact resistance Rcon of the contact part is
It is expressed as a function of the surface conductivity σc between the unit resistor 1 and the interconnection conductor 2 and the area S of the contact portion.

Rcon=K1/σcS...(1) (K: constant) From formula (1), if the surface conductivity σc is constant, doubling the area of the contact area will increase the contact resistance.
Rcon can be reduced to 1/2. In other words, the sum of the contact resistances of the folded connection parts of the resistor can be the same as the contact resistance of the parts other than the folded parts, and even if the variation in contact resistance and the variation in the resistance value of the resistor occur independently. , without degrading the accuracy of the resistor network.

FIG. 5 is a plan view showing a second embodiment of the invention. In this embodiment as well, the area of the contact portion 55 between the resistor 51 and the connecting conductor 52 is approximately twice the area of the contact portion 53 between the resistor 51 and the divided voltage take-out conductor 54. Since the portions of the resistor other than the contact portions are formed thin, the resistance value of the unit resistor can be increased compared to the embodiment shown in FIG. 4.

In the embodiment shown in FIG. 4, the case of a diffused resistor has been described, but the present invention can be sufficiently applied to other resistors such as polysilicon resistors and other thin film resistors.

As described above in detail with reference to the drawings, by using the present invention, it is possible to realize a semiconductor device with a high degree of integration and a resistor network with excellent accuracy, which is effective in expanding the field of application of semiconductor devices. .

[Brief explanation of the drawing]

1 and 2 are plan views of a conventional resistor network, FIG. 3 is an equivalent circuit diagram of FIG. 2, and FIGS. 4a and 4b are plan views and A- A sectional view and FIG. 5 are plan views of a second embodiment of the present invention. 11... Unit resistor, 12, 22, 42, 52...
Connection conductor, 13, 23, 43, 53... Interconnection conductor, 21, 51... Resistor, 24, 44, 54... Takeout conductor, 31... Unit resistance, 32... Resistance of connection conductor, 33... Contact resistance, 34... Output terminal, 45, 55... Contact portion between resistor and connection conductor, 46... Semiconductor substrate, 47... Insulating film.

Claims (1)

[Claims] 1. In a semiconductor device in which a resistor network is formed on a semiconductor substrate in which a plurality of unit resistors each having one or more lead-out conductors led out from an intermediate portion are connected in series by a connecting conductor, the connection between the connecting conductor and the unit resistor is A semiconductor device characterized in that a contact portion of each connection portion has a contact resistance approximately half that of a circuit connection portion between the lead-out conductor and the unit resistor.