JPH0832056A - Field-effect transistor - Google Patents

Abstract

PURPOSE:To provide a field-effect transistor having a reduced total gate capacitance. CONSTITUTION:A protective insulating film 5 comprising fluorine resin (FEP) is formed as if covering a gate electrode 3 on a silicon substrate 1 whereon the gate electrode 3 is formed. The specific conductivity of a gate insulating film 2 comprising silicon oxide is 3.8-3.9 but that of the fluororesin comprising the protective insulating film 5 is 1.9-2.2 that is lower than the former.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field effect semiconductor device having a MOS structure such as MOSFET, and more particularly to a field effect semiconductor device having a reduced total gate capacitance for miniaturization and high speed operation.

[0002]

2. Description of the Related Art A field effect semiconductor device represented by a MOSFET has a structure in which a gate electrode is formed on a silicon substrate with an oxide film interposed therebetween. In such a field effect type semiconductor device, a protective insulating film is formed on the gate electrode so as to cover the gate electrode, for insulation between the gate electrode and an electrode formed thereon and for protection of the gate electrode. Used for.

FIG. 2 is a sectional view showing the structure of a field effect transistor having such a MOS structure. In FIG. 1, 1 is a silicon substrate, 2 is a gate insulating film formed by oxidizing the surface of the silicon substrate 1, 3 is a gate electrode formed on the gate insulating film 2, and 4 is a gate electrode 3 as a mask. The source / drain regions 5a formed in a self-aligned manner by introducing impurities into the surface of the silicon substrate 1 on both sides of the gate electrode 3 are gate electrodes 3
A silicon oxide film formed on the substrate 1 so as to cover the
Is a flattening film for reducing the wiring step due to the gate electrode 3.

By the way, miniaturization of the above-mentioned field effect transistor is currently underway. In order to increase the degree of integration of the integrated circuit in which the field effect transistor is used, it is necessary to reduce the width (gate length) of the gate electrode 3 described above. By reducing the gate length in accordance with the shortening of the channel, it is necessary to increase the film thickness of the gate electrode 3 in order to reduce the resistance thereof. Currently, the gate length w is 0.2 to 1.0 μ
m, the gate thickness h is 0.3 to 0.7 μm, and the thickness t of the gate insulating film 2 is about 9 to 30 nm (FIG. 2).

[0005]

Conventionally, since the gate electrode 3 is configured as described above, the thickness of the gate electrode 3 becomes thicker as the channel becomes shorter, so that the coupling capacitance between the side surface of the gate electrode 3 and the source / drain region 4 is increased. However, there is a problem that the total gate capacitance is increasing more and more. Regarding the gate electrode 3 charged at a constant potential, the gate electrode 3 side surface-the silicon oxide film 5a (protective insulating film) -source together with the parasitic capacitance formed by the gate electrode 3-gate insulating film 2-silicon substrate 1 (semiconductor substrate) -There is a parasitic capacitance composed of the drain region 4.

Electric charges are also generated by electrostatic induction at the joint surface between the side surface of the gate electrode 3 and the silicon oxide film 5a and the joint surface between the silicon oxide film 5a and the source / drain region 4. These increase as the junction area increases, that is, as the gate electrode 3 becomes thicker. As described above, the ratio of the thickness of the gate electrode 3 to the thickness of the gate insulating film 2 is about 30: 1, and the electric field generated from the side surface of the gate electrode 3 toward the source / drain region 4 cannot be ignored.

The present invention has been made to solve the above problems, and an object thereof is to reduce the total gate capacitance of the gate electrode in a field effect semiconductor device.

[0008]

A field effect semiconductor device according to the present invention has a protective insulating film formed so as to cover at least a side surface of a gate electrode, and the protective insulating film is made of a material having a low dielectric constant. It is characterized by being. The protective insulating film is formed so as to cover the gate electrode. Further, in order to obtain a low dielectric constant, the protective insulating film is characterized by being made of a material containing fluorine or its compound. The compound is characterized by being composed of a fluororesin.

[0009]

Function The coupling capacitance between the side surface of the gate electrode and the protective insulating film is reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a MOS according to an embodiment of the present invention.
It is sectional drawing which shows the structure of a type transistor. In the figure, 5 is a fluororesin (FE) formed so as to cover the gate electrode 3 on the silicon substrate 1 on which the gate electrode 3 is formed.
P) is a protective insulating film and is otherwise similar to FIG.

The relative dielectric constant of the gate insulating film 2 made of silicon oxide is 3.8 to 3.9, but the protective insulating film 5
The fluororesin constituting the above has a low relative dielectric constant of 1.9 to 2.2. Therefore, according to this embodiment, the coupling capacitance between the gate electrode 3 and the protective insulating film 5 can be reduced as compared with the case where the silicon oxide film is used as the protective insulating film, and thus the total gate capacitance is reduced. can do.

Although the gate insulating film 2 is made of silicon oxide in the above embodiment, the present invention is not limited to this, and may be silicon nitride, for example. Further, in the above embodiment, the MO formed on the silicon substrate
Although the S-type transistor has been described, the present invention is not limited to this. For example, a junction field effect transistor or a field effect transistor using a Schottky junction may be used, and the same effect can be obtained.

[0013]

As described above, according to the present invention, the dielectric constant of the protective insulating film is made smaller than that of the silicon oxide film used for the gate insulating film or the like by using the fluororesin. Therefore, there is an effect that the gate capacitance due to the increase of the coupling capacitance with each of the source / drain regions due to the electric field from the side surface of the gate electrode can be suppressed, and the total gate capacitance can be suppressed. To do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a MOS transistor which is an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a field effect transistor having a MOS structure.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Gate insulating film, 3 ... Gate electrode, 4 ... Source / drain region, 5 ... Protective insulating film, 6 ...
Planarization film.

Claims (4)

[Claims] 1. A field effect semiconductor device having a gate electrode, comprising a protective insulating film formed so as to cover at least a side surface of the gate electrode, the protective insulating film being made of a material having a low dielectric constant. A field-effect semiconductor device characterized by being provided. 2. The field effect semiconductor device according to claim 1, wherein the protective insulating film is formed so as to cover the gate electrode. 3. The field effect semiconductor device according to claim 1, wherein the material contains fluorine or a compound thereof. 4. The field effect semiconductor device according to claim 3, wherein the compound is composed of a fluororesin.