JPH05136345A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a high resistance by using conventional impurity diffusion regions without newly forming a low-concentration-impurity diffusion resistance in a semiconductor device. CONSTITUTION:An insulating film 4 situated directly above the part of a P-type impurity diffusion resistance region 12 is oxidized to be deeper than another insulating film 3; it is formed to be thick. Consequently, since the insulating film situated directly above the part of the P-type impurity diffusion resistance region 12 oxidizes a high-concentration part on the surface of the P-type impurity diffusion resistance region 12, the resistivity of the P-type impurity diffusion resistance region is made high and its thickness is made apparently thin. A high resistance can be obtained without changing the concentration of the P-type impurity diffusion resistance region. In addition, when the insulating film 4 on the P-type impurity diffusion resistance region 12 is made thick, an effect that a threshold voltage at which a parasitic MOS transistor is operated is made higher than that in conventional techniques is obtained simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a structure of impurity diffusion resistance.

[0002]

2. Description of the Related Art An example of a conventional semiconductor device is shown in FIG. FIG. 2 is a cross-sectional structure of an impurity diffusion resistor, in which an insulating film 3 having a uniform thickness is provided immediately above a P-type impurity diffusion region 2 formed in an N-type epitaxial layer 1 on a P-type semiconductor substrate 6. There are a plurality of metal electrodes 4 formed as described above.

By electrically connecting these metal electrodes to both ends of the impurity diffusion region 2, the impurity diffusion region 2 between the metal electrodes operates as a resistor.

The resistance value R of the resistor having such a structure can be expressed by the following equation (1).

[0005]

However, L: length between metal electrodes (resistance length),
W: width of impurity diffusion region (resistance width), t: depth of impurity diffusion region (thickness of resistor), ρ: resistivity.

Here, since the resistivity is determined by the impurity concentration of the impurity diffusion region and the depth of the impurity diffusion region is determined by the manufacturing process of the semiconductor integrated circuit, it can be expressed by the following two equations.

[0008]

Here, if R (sheet) is called sheet resistance and R (sheet) is a constant, equation (1) can be expressed as equation (3) below, and the resistance value is the resistance length. ,
It is determined only by the ratio of the resistance width.

[0010]

[0011]

In the conventional semiconductor device described above, when high resistance is required, (A) the sheet resistance is increased, (B) the length of the P-type impurity diffusion region is increased,
(C) The width of the P-type impurity region is reduced.

However, in order to increase the sheet resistance, the impurity concentration must be changed, and a new impurity region is required. On the other hand, increasing the resistance length increases the area of the diffusion region. In addition, since the diffusion region has a certain amount of lateral diffusion when performing thermal diffusion and the resistance width is corrected, if the width is narrowed, the effect of the correction width becomes large and the absolute accuracy deteriorates. It was

An object of the present invention is to provide a semiconductor device in which a high resistance can be obtained by providing the same resistance length and resistance width without providing a new impurity region.

[0014]

The present invention is characterized by an impurity diffusion resistance region of one conductivity type formed in an epitaxial layer of opposite conductivity type on a surface of a semiconductor substrate of one conductivity type, and the impurity diffusion resistance region. An insulating film by oxidation formed on the surface of the epitaxial layer including the above, a pair of contact holes formed in the insulating film, and both ends of the impurity diffusion resistance region from the surface of the epitaxial layer in the contact hole. A pair of extracted impurity regions of one conductivity type reaching
In a semiconductor device having a pair of metal electrodes connected to the surface of the extraction impurity region in each of the contact holes and extending on the insulating film, a first insulating film formed on the impurity diffusion resistance region by the oxidation. Part is formed deeper inward from the surface of the epitaxial layer than the second part of the insulating film in the periphery thereof, whereby each of the contact holes is formed in the first part and the second part of the insulating film. The semiconductor device has a structure in which it is formed so as to straddle the portion.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view of an embodiment of the present invention. A P-type impurity diffusion region 12 and a P-type extraction impurity region 13 are continuously formed in the N-type epitaxial layer 1 on the P-type semiconductor substrate 6 by using a thermal diffusion method or an ion implantation method. Then, the entire surface of the N-type epitaxial layer 1 is oxidized to form the insulating film 3. After that, the P-type impurity diffusion region 12 that operates as a resistor is extracted by using the photolithography technique, and is oxidized deeper than the insulating film (second portion of the insulating film) 3 to make a thick insulating film 4 (first insulating film). Part) is formed.

With such a structure, the thick insulating film (first portion of the insulating film) 4 is formed by oxidizing a part of the P-type impurity diffusion resistance region 12, so that the P-type impurity diffusion resistance region 12 is formed. 12 appears to be thinner. The surface of the P-type impurity diffusion resistance region 12 has a high concentration before oxidation, and the deeper it is within the N-type epitaxial layer 1, the thinner it becomes. This is the same as forming a diffusion region having a low concentration.

Therefore, the sheet resistance R (sheet) can be increased. By changing the thickness of the insulating film 4 formed right above the P-type impurity diffusion resistance region 12, the sheet resistance R (sheet) can be increased from several times to ten and several times.

Then, a contact hole 14 is formed so as to extend over the first portion 4 and the second portion 3 of the insulating film, and the metal electrode 5 extending over the insulating film is connected to the extraction impurity region 13.

[0019]

As described above, according to the present invention, the insulating film formed on the P-type impurity diffusion resistor and thicker than the other insulating films is formed by oxidizing the high concentration portion of the P-type diffusion layer surface. Therefore, the thickness of the P-type diffusion layer is apparently thin and the resistivity is high. Therefore, it is possible to obtain a high sheet resistance without providing a new impurity region.

Further, since the thickness of the oxide film on the diffusion layer is thick, it also has an effect that the threshold voltage at which the parasitic MOS transistor operates becomes higher than that of the conventional one.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional diffused resistor.

[Explanation of symbols]

 1 N-type epitaxial region 2, 12 P-type impurity diffusion resistance region 3 Insulating film (oxide film) 4 Insulating film (oxide film) thickly formed 5 Metal layer electrode connected to diffusion resistance 6 P-type semiconductor substrate 13 Extraction impurity region 14 contact holes

Claims (1)

[Claims] 1. An impurity diffusion resistance region of one conductivity type formed in an epitaxial layer of opposite conductivity type on the surface of a semiconductor substrate of one conductivity type, and on the surface of the epitaxial layer including on the impurity diffusion resistance region. An insulating film formed by oxidation, and a pair of contact holes formed in the insulating film;
A pair of one conductivity type extraction impurity regions reaching both ends of the impurity diffusion resistance region from the surface of the epitaxial layer in the contact hole, and the insulating film connected to the surface of the extraction impurity region in each of the contact holes. In a semiconductor device having a pair of metal electrodes extending above, the first portion of the insulating film formed by the oxidation on the impurity diffusion resistance region is formed on the epitaxial layer more than the second portion of the insulating film on the periphery thereof. Is deeply formed from the surface of the insulating film to the inside thereof, whereby each of the contact holes is formed so as to extend over the first portion and the second portion of the insulating film. apparatus.