JPS61229367A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To set the desired electric characteristics by making the impurity concentration of the channel region set in the conductive region differ from that of other conduction regions than the channel region. CONSTITUTION:On the surface of the semiconductor substrate 20 the resist film 40 is formed to cover the surface, and the aperture 42 to diffuse impurity is formed on the film 40. From the aperture 42 the impurity like boron, etc. is diffused. As to the condition of impurity diffusion, the impurity concentration decreases in accordance with the distance from the aperture 42. After the P well 22 is formed in this way by locally controlling the impurity concentration, the source region 26 and the drain region 28 are installed in the P well 22 in the manner wherein the region where the specified impurity concentration is obtained becomes the drain region 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device such as an MO3 field effect transistor, and a method for manufacturing the same.

[Conventional technology]

Generally, as shown in FIGS. 7 and 8, a field effect transistor includes a semiconductor substrate 2 of one conductivity type, such as N-type silicon, and a p-well (well) as a conductive region of the opposite conductivity type.
l) 4 is formed, and in this p-well 4, a source region 6 and a drain region 8 of the opposite conductivity type to that of the p-well 4 are formed at regular intervals, and between these source region 6 and drain region 8, A channel region pattern 0 is formed in the area.

The surfaces of the semiconductor substrate 2, p-well 4, source region 6, and drain region 8 are covered with an oxide film 12, and a source electrode 14 and a drain electrode 16 are formed on the surfaces of the source region 6 and drain region 8. , the oxide film 13 covering the channel region 10 is set thinner than other parts,
A gate electrode 18 is formed on the surface of this thin oxide J[13 by vapor deposition of aluminum or the like.

[Problem that the invention seeks to solve]

Conventionally, in such a field effect transistor, impurities are diffused or ion-implanted indiscriminately into the surface of the semiconductor substrate 2 without considering the portions where the source region 6, drain region 8, and channel region 10 are to be formed. Tep
Since the well 4 is formed, the center of the p-well 4 and its surface layer have the highest impurity concentration, and a concentration gradient is exhibited in the plane direction and the depth direction. That is, the impurity concentration of the channel region 10 and the impurity concentrations near the source region 6 and drain region 8 have a uniform profile.

For this reason, this type of field effect transistor has frequency characteristics, breakdown voltage, and threshold voltage V? Electrical characteristics such as H are fixed, making it difficult to arbitrarily set these characteristics, and it has been impossible to arbitrarily form devices with different characteristics on the same semiconductor substrate.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor device in which electrical characteristics such as frequency characteristics, withstand voltage, and dark voltage can be arbitrarily set, and a method for manufacturing the same.

[Means for solving problems]

This invention will be explained with reference to the embodiments shown in FIGS. 1 to 6.

In the semiconductor device of the present invention, a source region 26 and a drain region 28 are provided in a conductive region (p well 22) of an opposite conductivity type provided in a semiconductor substrate 20 of one conductivity type. In a semiconductor device in which a gate faces a channel region 24 formed in between, the impurity concentration of the channel region 24 set in the conductive region (p well 22) is compared with the impurity concentration of other conductive regions other than the channel region. They are different.

Further, in the method of manufacturing a semiconductor device of the present invention, a conductive region having a conductivity type opposite to that of the semiconductor substrate is formed by shielding a portion of the semiconductor substrate 20 that will become the channel region 24 by diffusion of impurities or ion implantation, and Control the impurity concentration low.

[For production]

In the semiconductor device of the present invention, the impurity concentration of the channel region 24 is made lower than that of the conductive region excluding the channel region 24 to make the impurity concentration distribution different, and the frequency characteristics are determined by the electric field effect of the diffusion profile in the peripheral portion of the conductive region. , electrical characteristics such as withstand voltage and dark value voltage are arbitrarily set.

Further, the method for manufacturing a semiconductor device of the present invention includes diffusing impurities from a portion other than a portion where a channel region is to be formed;
Alternatively, ion implantation is performed to reduce the impurity concentration of the conductive region set in the channel region.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 and 2 show an embodiment of the semiconductor device of the present invention, with FIG. 1 showing its planar structure, and FIG. 2 showing its cross section along the line ■-■.

1 and 2, a p-well 22 as a conductive region of the opposite conductivity type is formed in a semiconductor substrate 20 of one conductivity type such as N-type silicon.

In this embodiment, approximately in the central region of this p-well 22,
A source region 26 and a drain region 28 of a conductivity type opposite to that of the p-well 22 are formed using a portion with a low impurity concentration as a channel region 24 .

The surfaces of the semiconductor substrate 20, the p-well 22, the source region 26, and the drain region 28 are covered with an oxide film 30, and a source electrode 32 and a drain electrode 34 are formed on the surfaces of the source region 26 and drain region 28. has been done.

The oxide film 36 covering the channel region 24 is set thinner than other parts, and a gate electrode 38 is formed on its surface by vapor deposition of aluminum or the like.

In this way, the impurity concentration gradient of the conductive region constituting the p-well 22 is made different between the channel region 24 and other regions,
For example, by reducing the impurity concentration of the channel region 24, electrical characteristics such as frequency characteristics, dynamic breakdown voltage, static breakdown voltage, and threshold voltage vT□ can be obtained.

Furthermore, as shown in FIG. 3, the p-well 22 may have its peripheral edge located in the center of the channel region 24. In this way, a portion of the p-well 22 with a low impurity concentration can be set as the channel region 24, and electrical characteristics such as the dark voltage VTH can be changed.

4 to 6 show an embodiment of the method for manufacturing a semiconductor device according to the present invention.

This embodiment shows the case where the p-well 22 is formed by diffusion of impurities, and as shown in FIG. 4, a resist film 40 is formed on the surface of the semiconductor substrate 20 to cover the surface, and the resist film An opening 42 for impurity diffusion is selectively formed in 40 . In this case, the channel area 24
The portion to be formed is covered with a resist film 40, an opening 42 is formed around the resist film 40, and an impurity such as boron is diffused.

Regarding the diffusion state of impurities, as shown in FIG. 5, the impurity concentration decreases as the distance from the opening 42 increases. in this case,
The impurities diffused from the openings 42 on both sides overlap the peripheral edge of the p-well 22, but the impurity concentration decreases as the distance from the opening 42 increases, so the impurity concentration of the portion that will become the channel region 24 is directly below the opening 42. In addition to further reducing the impurity concentration, the impurity concentration in the portion that will become the channel region can be controlled by the amount of impurity diffusion and the position of the opening 42.

For example, as shown in FIG. 6, a peripheral portion where the impurity concentration of the p-well 22 is lowest can be set in a portion that will become a channel region.

After forming the p-well 22 by controlling the impurity concentration locally in this way, a source region 26 and a drain region are formed in the p-well 22 so that the region where a specific impurity concentration is obtained becomes the channel region 24. Install 28.

Then, a semiconductor substrate 20, a p-well 22, a source region 2
6 and the oxide film 3 formed on the surface of the drain region 28
A source electrode 32 and a drain electrode 34 are formed in the source region 26 and drain region 28 of 0, respectively, and a gate electrode 38 is formed on the surface of the oxide film 36 covering the channel region 24.

Therefore, according to such a manufacturing method, the p-well 2
The impurity concentration of the portion set in the channel region 24 of 2 can be controlled, and such control can be performed partially at a desired position on the same semiconductor substrate, and the diffusion profile of the peripheral portion of the p well 22 can be controlled. A semiconductor device with improved electrical characteristics can be obtained by utilizing the field effect and impurity concentration.

Although the p-well 22 is formed by impurity diffusion in this embodiment, it may also be formed by ion implantation.

Furthermore, in the embodiment, a case has been described in which a p-well is formed in an N-type semiconductor substrate, but the present invention can be similarly provided in a case in which an n-well is formed in a P-type semiconductor substrate.

Further, the gate electrode 38 may be made of metal as in the embodiment, or may be made of polysilicon.

〔Effect of the invention〕

° As explained above, according to the semiconductor device of the present invention, desired electrical characteristics such as frequency characteristics, dark voltage, dynamic breakdown voltage, and static breakdown voltage can be set by controlling the impurity concentration of the channel region, and moreover, Different properties can be set on the substrate.

Further, according to the method of manufacturing a semiconductor device of the present invention, the impurity concentration of the channel region can be arbitrarily controlled.
A semiconductor device having desired characteristics can be easily manufactured.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a planar structure of an embodiment of the semiconductor device of the present invention, FIG. 2 is a sectional view taken along line nn in FIG. 1, and FIG. 3 is another embodiment of the semiconductor device of the present invention. 4 is a plan view showing a resist film installed on a semiconductor substrate and its opening, FIG. 5 is a sectional view showing the state of impurity diffusion, and FIG. 6 is another example of impurity diffusion. A cross-sectional view showing,
FIG. 7 is a plan view showing the electrode arrangement of a general field effect transistor, and FIG. 8 is a cross-sectional view taken along the line ■--■ in FIG. 20...Semiconductor substrate, 22...P as a conductive region
Well, 24... Channel region, 26... Source region, 28... Drain region. Figure 3 Figure 4 Figure 5 Figure 7 Figure 8

Claims (2)

[Claims] (1) A source region and a drain region are provided in a conductive region of the opposite conductivity type provided on a semiconductor substrate of one conductivity type, and a gate is made to face a channel region formed between the source region and the drain region. 1. A semiconductor device, wherein the impurity concentration of the channel region set in the conductive region is made different from the impurity concentration of the conductive region other than the channel region. (2) A semiconductor characterized by controlling the impurity concentration of the channel region by shielding a portion of the semiconductor substrate that will become the channel region and forming a conductive region of the opposite conductivity type to that of the semiconductor substrate by impurity diffusion or ion implantation. Method of manufacturing the device.