JP2001168202A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that the electrical characteristic such as threshold voltage for driving is liable to fluctuate with time in a conventional solid-state image pickup device having gate electrodes to which a relatively high voltage is applied and gate electrodes to which a relatively low voltage is applied. SOLUTION: An ON film or an ONO film is used as gate insulating film for gate electrodes to which a relatively low voltage is applied and an oxide insulating film is used as gate insulating film for gate electrodes to which a relatively high voltage is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having at least two gate electrodes having different applied voltages, the gate electrodes being formed on a semiconductor substrate via an electric insulating film. Related to the device.

[0002]

2. Description of the Related Art A multi-power semiconductor device in which a plurality of circuit elements operating at different drive voltages are formed on a single semiconductor substrate is known. For example, a semiconductor device such as a charge transfer solid-state imaging device has at least two transistors having different voltages applied to the gate electrode.

A semiconductor substrate constituting a semiconductor device is generally a silicon substrate or a substrate such as a sapphire substrate having a silicon layer formed on a surface thereof. Each gate electrode formed on the silicon substrate is electrically insulated from the silicon substrate by a gate insulating film made of a silicon oxide film, an ON film, an ONO film, or the like.

[0004] The ON film referred to in this specification means an electric insulating film having a two-layer structure including an oxide layer formed on a semiconductor substrate and a nitride layer formed on the oxide layer. The ONO film referred to in this specification includes an oxide layer formed over a semiconductor substrate, a nitride layer formed over the oxide layer, and an oxide layer formed over the nitride layer. It means an electrically insulating film having a layer structure.

Each gate electrode formed on a semiconductor substrate is formed of, for example, a polysilicon layer, a metal layer such as aluminum, or the like.

When a part of the plurality of gate electrodes is formed by the first polysilicon layer and the remaining gate electrodes are formed by the second polysilicon layer, silicon is used as a material of a gate insulating film of each gate electrode in advance. Oxide film (hereinafter referred to as
This silicon oxide film may be referred to as “insulating film I”. ) Is provided on a semiconductor substrate, the following two phenomena may occur.

That is, when forming a surface oxide film (insulating film) on the gate electrode made of the first polysilicon layer,
A portion of the insulating film I to be a gate insulating film for the gate electrode made of a polysilicon layer is grown. As a result, the film thickness of the gate insulating film under the gate electrode made of the second polysilicon layer becomes thicker than the film thickness of the gate insulating film under the gate electrode made of the first polysilicon layer (hereinafter, this phenomenon will be referred to as a phenomenon). "Phenomenon A1").

In forming the surface oxide film, the first
An insulating film I grows below the end of the polysilicon layer,
The edge of the first polysilicon layer is turned up (hereinafter, these phenomena are referred to as “phenomenon A2”). Phenomenon A1 and Phenomenon A2
Is hereinafter collectively referred to as “phenomenon A”.

When phenomenon A occurs during the manufacture of a semiconductor device, the threshold voltage for performing a desired operation changes from a design value, and a semiconductor device having desired electrical characteristics may not be obtained. In addition, variations in electrical characteristics between semiconductor devices may increase.

Therefore, when a gate electrode made of the first polysilicon layer and a gate electrode made of the second polysilicon layer are formed on the semiconductor substrate, an ON film or a gate insulating film of each gate electrode is used as a material of the gate insulating film. ONO films are often used.

By using an ON film as a material of the gate insulating film, the above phenomenon A can be suppressed from occurring when a surface oxide film is formed on the first polysilicon layer.

[0012] Even when an ONO film is used as the material of the gate insulating film, it is possible to suppress the above phenomenon A from occurring when a surface oxide film is formed on the first polysilicon layer.

[0013]

In an output circuit such as a charge transfer type solid-state imaging device, a relatively high positive or negative voltage of, for example, tens to tens of volts is applied to at least one gate electrode.

When a relatively high voltage as described above is applied to a semiconductor device provided with a gate insulating film made of an ON film or an ONO film, the semiconductor device is formed in the nitride film constituting the gate insulating film or in the gate insulating film. Carriers may be trapped at the interface between the nitride film and the oxide film constituting the film.

For example, in a circuit element such as an MNOS element that intentionally uses carrier traps, the electron traps are useful.

However, when carriers are trapped in the gate insulating film in a normal circuit element, the electrical characteristics of the circuit element, for example, the threshold voltage and the potential change.

An object of the present invention is to provide a semiconductor device which can easily suppress a change in electrical characteristics.

Another object of the present invention is to provide a method of manufacturing a semiconductor device in which it is easy to obtain a semiconductor device in which a change in electrical characteristics is easily suppressed.

[0019]

According to one aspect of the present invention, there is provided a semiconductor substrate and a plurality of gate electrodes formed on the semiconductor substrate, wherein at least applied voltages are different from each other. A plurality of gate electrodes including two gate electrodes, and a gate electrode between the plurality of gate electrodes except for the gate electrode to which a relatively large voltage is applied and the semiconductor substrate; ON film or ON
A gate insulating film made of an O film, and an electric insulating film made of an electric insulating oxide interposed between the gate electrode and the semiconductor substrate to which a relatively large voltage is applied among the plurality of gate electrodes. Is provided.

According to another aspect of the present invention, a laminated film forming step of forming an ON film or an ONO film on one surface of a semiconductor substrate, at least a nitride layer in the ON film or a nitride layer in the ONO film Forming a first recess above the plurality of readout gate regions by locally removing an oxide layer on the nitride layer; and depositing an oxide film in the first recess. Or an oxide insulating film forming step of forming an oxide insulating film by growing an oxide layer at the bottom of the first recess, and a relatively large voltage is applied on the oxide insulating film. Forming a gate electrode to form a gate electrode to which a relatively small voltage is applied on the ON film or the ONO film.

In the above semiconductor device, the gate insulating film at the gate to which a relatively large voltage is applied is formed of an oxide insulating film. Therefore, a change in electrical characteristics of the semiconductor device due to trapping of carriers in the gate insulating film is prevented.

The gate insulating film of the gate electrode to which the applied voltage is relatively small is formed on the ON film or ONO film. Therefore, even if a semiconductor substrate made of a silicon substrate is used and each gate electrode is formed of two-layered polysilicon, at least the phenomenon A2 described above can be suppressed. By forming the gate electrode to which a relatively large voltage is applied from the first polysilicon layer, it is possible to suppress the phenomena A1 and A2, that is, the phenomenon A from occurring.

For these reasons, in the above-described semiconductor device, it is easy to suppress the electrical characteristics from fluctuating with time.
In addition, it is easy to reduce variations in electrical characteristics between semiconductor devices.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a semiconductor device 3 according to the first embodiment.
It is a conceptual diagram of 0. As shown in FIG.
Are two transistors 1 formed on the semiconductor substrate 1
0 and 20 are provided.

Here, the voltage applied to the gate electrode of the transistor 10 is, for example, 10 to 30 V. The voltage applied to the gate electrode of the transistor 20 is, for example, 3 to 7V.

The semiconductor substrate 1 is made of, for example, p-type silicon. An n-type region 2 is formed on one surface side of the semiconductor substrate 1 made of the p-type silicon.

Transistor 10 has a source region 11 composed of ap ⁺ -type region formed at a predetermined location in n-type region 2.
And a drain region 12 formed of ap ⁺ -type region formed close to the source region 11.

The source electrode 13 is connected to the surface of the source region 11, and the drain electrode 14 is connected to the surface of the drain region 12. The source electrode 13 is electrically insulated from the semiconductor substrate 1 by an electric insulating film 15 except for a region on the source region 11. The same applies to the drain electrode 14.

A gate electrode 18 made of a polysilicon layer is connected to a surface of an n-type region (channel region) 16 between the source region 11 and the drain region 12 via a gate insulating film 17 made of a silicon oxide film. Have been.

Transistor 20 has a source region 21 composed of ap ⁺ -type region formed at a predetermined location in n-type region 2.
And a drain region 22 formed of ap ⁺ -type region formed close to the source region 21. The source electrode 23 is connected to the surface of the source region 21, and the drain electrode 24 is connected to the surface of the drain region 22. The source electrode 23 is electrically insulated from the semiconductor substrate 1 by the electric insulating film 15 except for a region on the source region 21. The same applies to the drain electrode 24.

A gate electrode 28 made of a polysilicon layer is formed on the surface of an n-type region (channel region) 26 between the source region 21 and the drain region 22 via a gate insulating film 27 made of an ON film or an ONO film. It is connected.

In the illustrated semiconductor device 30, the gate insulating film 1 of the gate electrode 18 to which a relatively high voltage is applied
7 is made of a silicon oxide film as described above.

Therefore, even if a relatively high voltage is applied to the gate electrode 18, it is difficult for carriers to be trapped in the gate insulating film 18.

Therefore, in the semiconductor device 30, it is easy to suppress the electrical characteristics from changing over time.

Further, a phenomenon that the thickness of the gate insulating film under the gate electrode made of the second polysilicon layer is larger than the film thickness of the gate insulating film under the gate electrode made of the first polysilicon layer is a semiconductor device. 30 is prevented from occurring in the manufacturing process. Further, the phenomenon that the edge of the gate electrode made of the first polysilicon layer is turned up is suppressed from occurring in the manufacturing process of the semiconductor device 30.

For these reasons, in the semiconductor device 30,
It is easy to realize desired electrical characteristics. In addition, the semiconductor device 3
When a plurality of semiconductor devices 30 are manufactured, variations in electrical characteristics between the individual semiconductor devices 30 can be easily reduced.

Next, an example of a method for manufacturing the above-described semiconductor device 30 will be described with reference to FIGS. 2 (a) to 2 (d).

FIGS. 2A to 2D show the semiconductor device 3.
FIG. 10 is a conceptual diagram for describing an example of a manufacturing process of No. 0.

First, as a preparation step, a semiconductor substrate on which regions such as a source, a drain, and a channel required for forming a desired number of circuit elements are prepared (preparation step). This semiconductor substrate is hereinafter referred to as a semiconductor substrate 1a. In the semiconductor substrate 1a, a field oxide film and a channel stop are previously formed in the element isolation region as necessary.

As shown in FIG. 2A, the semiconductor substrate 1a
In the entire surface on the side where the above-mentioned regions (not shown in FIGS. 2A to 2D) are formed, O
An N film 15 is formed (laminated film forming step).

In forming the ON film 15, first, a silicon oxide layer having a thickness of about 100 to 500 angstroms is formed by a method such as thermal oxidation. The silicon oxide layer is formed, for example, in a dry oxidation atmosphere at 8
It is performed under a temperature condition of 50 to 1000 ° C.

Next, a silicon nitride layer having a thickness of about 200 to 700 angstroms is formed on the silicon oxide layer by a method such as a vapor phase growth method. The silicon nitride layer is, for example, by chemically reacting the monosilane (SiH ₄₎ and ammonia (NH ₃₎ at 700 to 1000 ° C., can be formed.

As shown in FIG. 2B, the first film 15a is formed above the channel region 16 (see FIG. 1) by locally removing the ON film 15 (recess forming process).

The first concave portion 15 a may penetrate the ON film 15 or may not penetrate the ON film 15.
However, when the ON film 15 is not penetrated, at least the nitride layer is removed to expose the oxide layer thereunder. FIG. 2B shows the first concave portion 15 penetrating the ON film 15.
a.

When there are a plurality of locations where a gate insulating film made of an oxide insulating film is to be formed (hereinafter, this location is referred to as "location I"), the first recess 15a is formed by one or more predetermined number of openings. Be composed. One opening, in plan view,
One or a plurality of points I.

The first concave portion 15a consisting of a through hole is formed by the ON film 1
For example, after forming a resist pattern of a predetermined shape on the ON film 15 by a method such as photolithography, the nitride layer constituting the ON film is dry-etched using the resist pattern mask. Patterning. Etching at this time,
For example, it can be performed using a mixed gas of CF ₄ and O ₂ .

Next, the oxide layer (the oxide layer forming the ON film) exposed by removing the nitride layer is patterned by, for example, wet etching. The etching at this time can be performed using, for example, a dilute hydrogen fluoride solution. Thereafter, the unnecessary resist pattern is removed.

In the case where the first concave portion 15a is formed by a concave portion that does not penetrate the ON film 15, for example, after removing the nitride layer and removing the unnecessary resist pattern as described above, The process can proceed to an oxide insulating film forming step described below. At this time, the oxide layer may be etched or may not be etched.

As shown in FIG. 2C, the first recess 15a
A silicon oxide film 7 on the surface of the semiconductor substrate 1a or the oxide layer (the oxide layer constituting the ON film) exposed at the bottom of the silicon oxide film 7
1 (oxide insulating film forming step). FIG. 2 (c)
Illustrates a case where the surface of the semiconductor substrate 1a is exposed from the bottom of the first recess 15a.

The silicon oxide film 71 can be formed by, for example, dry oxidation at a temperature condition of about 900 to 1100 ° C. or wet oxidation at a temperature condition of about 850 to 1000 ° C.

When the first recess 15a is formed by a recess that does not penetrate the ON film 15, the first recess 15a
By growing the oxide layer forming the bottom surface of 5a (the oxide layer forming the ON film), the target silicon oxide film 71 can also be formed.

As shown in FIG. 2D, a gate electrode 18 is formed on the ON film 15, and a gate insulating film 28 is formed on the surface of the ON film 7 above the channel region 26 (see FIG. 1) (see FIG. 2D). Gate electrode forming step).

Hereinafter, a case where the gate electrode 18 is formed of the first polysilicon layer and the gate electrode 28 is formed of the second polysilicon layer will be described as an example.

Gate electrode 1 made of first polysilicon layer
In forming 8, first, a polysilicon layer covering one surface of the semiconductor substrate 1 a is formed. The polysilicon layer can be formed by a normal pressure CVD method, a low pressure CVD method, or the like. The polysilicon layer can be formed, for example, by thermally decomposing monosilane (SiH ₄ ) at 500 to 800 ° C.

Next, a resist pattern having a predetermined shape is formed on the polysilicon layer by a method such as photolithography.

Next, using the resist pattern as a mask, the polysilicon layer is subjected to reactive ion etching to pattern the gate electrode 18 into a desired shape. The etching at this time can be performed using, for example, a chlorine-based gas. Thereafter, the unnecessary resist pattern is removed.

Next, the surface of the gate electrode 18 made of the first polysilicon layer is oxidized to form a silicon oxide film on the surface. The upper layer of the ON film is formed of a nitride layer having an oxidation preventing function. Therefore, the gate electrode 18
When the surface is oxidized, oxygen hardly penetrates into the semiconductor substrate 1a and the oxide layer below the nitride layer.

Thereafter, a gate electrode 28 having a desired shape is formed of the second polysilicon layer in the same manner as the formation of the gate electrode 18.

The semiconductor device 30 can be obtained by performing the above steps.

When an ONO film is used in place of the ON film 15, the ONO film is formed by, for example, stacking a silicon oxide film, a silicon nitride film, and a silicon oxide film in this order from the semiconductor substrate 1a side. can get.

At this time, the thickness of the silicon oxide film on the lower side (semiconductor substrate 1a side) can be appropriately selected within a range of approximately 100 to 500 angstroms. The thickness of the silicon nitride film can be appropriately selected within a range of approximately 200 to 700 Å. The thickness of the upper silicon oxide film can be appropriately selected within a range of approximately 30 to 100 Å. The thickness of the ONO film is approximately 300
In the range of １０００1000 Å.

The ONO film is formed, for example, by forming a silicon oxide film and a silicon nitride film in the same manner as the ON film, and then forming a silicon oxide film on the silicon nitride film by a thermal oxidation method or the like. can get. The upper silicon oxide film can be formed, for example, in a dry oxidation atmosphere at 900 to 1100 ° C.

Although the solid-state imaging device of the present invention has been described with reference to the embodiments, the present invention is not limited to the above-described embodiments. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0065]

As described above, according to the present invention, it is possible to provide a semiconductor device in which a change in electrical characteristics is easily suppressed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a semiconductor device according to a first embodiment.

FIG. 2 is a conceptual diagram illustrating an example of a manufacturing process of the semiconductor device according to the first embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 10, 20 ... Transistor, 1
7, 27: gate insulating film, 18, 28: gate electrode,
30 ... Semiconductor device

Claims (2)

[Claims] A semiconductor substrate; and a plurality of gate electrodes formed on the semiconductor substrate, the plurality of gate electrodes including at least two gate electrodes having different applied voltages. A gate insulating film made of an ON film or an ONO film interposed between the remaining gate electrode and the semiconductor substrate except for the gate electrode to which a relatively large voltage is applied among the plurality of gate electrodes; A semiconductor device comprising: a gate electrode to which a relatively large voltage is applied among the plurality of gate electrodes; and an electric insulating film made of an electric insulating oxide interposed between the semiconductor substrate. 2. An ON film or an O film on one surface of a semiconductor substrate.
A stacked film forming step of forming a NO film; and at least a nitride layer or the ON layer in the ON film.
Forming a first recess above the plurality of read gate regions by locally removing the nitride layer and the oxide layer on the nitride layer in the O film; and oxidizing the first recess. An oxide insulating film forming step of forming an oxide insulating film by depositing an object film or growing an oxide layer at the bottom of the first concave portion; Forming a gate electrode to which a large voltage is applied, and forming a gate electrode to which a relatively small voltage is applied on the ON film or the ONO film.