JPH04177728A - Semiconductor insulating film and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to generate a negative charge in the interface between first and second silicon oxide films by a method wherein the second silicon oxide film is provided on the upper layer of the first silicon oxide film containing Al in its uppermost surface. CONSTITUTION:A silicon thermal oxide film 3 formed by performing a thermal oxidation on the surface of a silicon substrate 1 and an HTO film (a silicon oxide film using a high-temperature CVD method) 5 deposited on the upper layers of the film 3 and a LOCOS isolation oxide film 2 by a CVD method are provided. In such a way, by depositing the second silicon oxide film using the CVD method or the like on the upper layer of the first silicon oxide film containing Al in its uppermost surface, negative charges can be generated in the interfaces between the thermal oxide film and the first and second oxide films deposited by the CVD method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor insulating film used in semiconductor devices such as MO3+- transistors and a method for manufacturing the same.

[Conventional technology]

Usually, a silicon thermal oxide film formed by directly thermally oxidizing silicon has been used as a gate oxide film in a MOS transistor or a capacitor insulating film in a memory.

An example of a semiconductor device having a conventional semiconductor insulating film is shown in FIG. Generally, in a semiconductor device constituting a MOS (MOS) transistor or the like, as shown in FIG. 6, an I, CO8 isolation oxide film 2 is formed as an element isolation insulating film on a silicon substrate 1, A silicon thermal oxide film 3 is formed in the region as a gate oxide film. Further, on the thermal oxide film 3 which is a gate oxide film, an n
+A polysilicon film 6 is formed.

The threshold voltage of the MO3) transistor has been controlled by injecting impurities such as B, P, and As into the silicon substrate 1 below the thermal oxide film 3 using an ion implantation method. 9 is an ion implantation layer for threshold control.

[Invention or problem to be solved]

In conventional semiconductor insulating films made of thermal oxide films such as those mentioned above, when used as oxide films or capacitive insulating films, there is a fixed amount of metal in the thermal oxide film that affects the electrical characteristics of the device. Contains no charge.

Generally, the fixed charge in a thermal oxide film is lXl0”/c
r! Therefore, in order to control the threshold voltage, etc., it was necessary to perform control by implanting impurities using an ion implantation method.

On the other hand, in semiconductor devices, insulating films or silicon oxide films (S
In the case of I02), there was no special manufacturing method that included a certain amount of charge in a partial region of the oxide film.

It is an object of the present invention to provide a semiconductor insulating film containing a certain electric charge, and to provide a method for manufacturing a semiconductor insulating film that can produce a semiconductor insulating film containing a certain electric charge in a simple process. It is.

[Failure to solve the problem]

The semiconductor insulating film according to claim (1) includes a first silicon oxide film containing Al on the outermost surface, and a second silicon oxide film provided on the first silicon oxide film. .

The method for manufacturing a semiconductor insulating film according to claim (2) includes the steps of cleaning a silicon substrate with an alkaline cleaning solution containing Al as an impurity, and oxidizing the cleaned silicon substrate to contain Al1 on the outermost surface. and a step of depositing a second silicon oxide film on top of the first silicon oxide film.

The method for manufacturing a semiconductor insulating film according to claim (3) includes the steps of cleaning a silicon substrate with a cleaning liquid made of a mixed solution of aqueous ammonia and hydrogen peroxide and containing Al as an impurity, and cleaning the silicon substrate after being cleaned. oxidation to form a first silicon oxide film containing Aj2 on the outermost surface; a step of partially etching the upper layer of the first silicon oxide film thinly with diluted HF; and a step of partially etching the upper layer. and depositing a second silicon oxide film on top of the first silicon oxide film.

[For production]

According to this invention, by overlapping the first silicon oxide film containing Al on the outermost surface and the second silicon oxide film, negative charges are generated at the interface between the first and second silicon oxide films. This can be applied to threshold voltage control using charges in an oxide film or to devices using charges in an oxide film.

The negative charge is removed by cleaning the silicon substrate with an alkaline cleaning solution, such as a mixture of aqueous ammonia and hydrogen peroxide, containing Al as an impurity, and then oxidizing it to form a first silicon oxide film. By doing so, the first
It can be formed on the outermost surface of the silicon oxide film, that is, at the interface with the second silicon oxide film. This is because, for example, when a silicon substrate is cleaned with a cleaning solution consisting of a mixture of aqueous ammonia and hydrogen peroxide, Al, which is normally contained as an impurity in the chemical solution, tends to be adsorbed onto the surface of the silicon substrate. This is supported by the property that Al does not diffuse into the silicon substrate even after subsequent oxidation and exists on the outermost surface of the oxide film, and also from the experimental results described later that the location of An and the location of negative charges match. .

As described above, by depositing the second silicon oxide film by CVD or the like on top of the first silicon oxide film containing Al on the outermost surface, the thermal oxide film and the first and CVD deposited silicon oxide films are deposited. Negative charges can be generated at the interface of the oxide film No. 2.

〔Example〕

FIG. 1 is a sectional view of a semiconductor device having a semiconductor insulating film according to a first embodiment of the present invention. In Figure 1, 1 is a silicon substrate, 2 is an LOG for separating each element.
OS isolation oxide film, 3 is a silicon thermal oxide film formed by thermally oxidizing the surface of the silicon substrate 1, 4 is △l present on the outermost surface of the silicon thermal oxide film 3, 5 is a silicon thermal oxide film 3 and LOGO 3 CV on the upper layer of isolation oxide film 2
The HTO film (silicon oxide film formed by high-temperature CVD method) is deposited by method D, and 6 is an n+ polysilicon film as a gate electrode.

By adopting the above structure, negative charges are generated at the interface between the silicon thermal oxide film 3 and the HTO film 5, and the electrical characteristics of the device can be changed by this negative charge. That is, by changing the amount of /l on the outermost surface of the silicon thermal oxide film 3, the thickness of the silicon thermal oxide film 3, and the thickness of the HTO film 5, the threshold value of the element formed on the semiconductor substrate 1 can be adjusted. It is possible to control voltage or flatband voltage.

2(a) to 2(e) are step-by-step cross-sectional views showing a method for manufacturing the semiconductor insulating film shown in FIG. 1.

The method for manufacturing the above semiconductor insulating film will be described below with reference to FIG.

First, as shown in FIG. 2(a), an oxide film 2 with a thickness of 11 fft for 3 LOCO is formed on a predetermined region of the surface of the silicon substrate 1. Then, as shown in FIG. Note that FIG. 2(a) shows the state before the formation of the oxide film.

Next, as shown in Figure 2(b), Al
Cleaning is performed using an alkaline cleaning solution containing, for example, a mixed solution of aqueous ammonia and aqueous hydrogen peroxide (hereinafter referred to as aqueous ammonia and hydrogen peroxide).

Cleaning with ammonia hydrogen peroxide solution is NH4OH・H
At a mixing ratio of 2C,:H20=115, at a liquid temperature of 80°C,
The test was carried out for about 10 minutes. The ammonia-hydrogen peroxide cleaning solution has the effect of strongly removing particles on the surface of the silicon substrate 1, and at the same time, the cleaning solution has the effect of strongly removing particles on the surface of the silicon substrate 1. It has the characteristic of being easily incorporated into Therefore, by cleaning with ammonia hydrogen peroxide solution,
As shown in FIG. 2(b), A1 is applied to the surface of the silicon substrate l.
Adsorb 4.

Thereafter, as shown in FIG. 2C, a silicon thermal oxide film 3 is formed on the surface of the silicon substrate 1 on which Al4 has been adsorbed by pyrogenic oxidation (900° C., 15 minutes). As will be described later, Ajl'4 adsorbed onto the surface of the silicon substrate 1 by aqueous ammonia and hydrogen peroxide does not diffuse into the silicon substrate 1 even after oxidation, but is distributed on the outermost surface of the silicon thermal oxide film 3. .

Thereafter, as shown in FIG. 2 (dl), an HTO film (silicon oxide film) 5 is deposited at a temperature of 840° C. using a high temperature CVD method.

Then, as shown in FIG. 2(e), an n+ polysilicon film 6 is deposited using the CVD method.

By the above manufacturing method, silicon thermal oxide film 3 and H
It becomes possible to generate negative charges near the interface with the TO film 5.

The semiconductor insulating film manufactured in this way can be applied to threshold voltage control using the charges in the oxide film or to devices (for example, ROM (read only memory)) using the charges in the oxide film.

FIG. 3 (al to (it) are step-by-step cross-sectional views showing a method for manufacturing a semiconductor insulating film according to a second embodiment of the present invention.

Below, using FIG. 3, we will explain a method for manufacturing two series of semiconductor insulating films.Similar to the embodiment shown in FIG. 2, first, as shown in FIG. A LOCO8 isolation oxide film 2 is formed in a predetermined region.

Thereafter, as shown in FIG. 3(b), the silicon substrate 1 is cleaned with aqueous ammonia and hydrogen peroxide, and Al4 is adsorbed onto the surface of the silicon substrate 1.

Thereafter, as shown in FIG. 3(C), the surface of the silicon substrate 1 is thermally oxidized to form a silicon thermal oxide film 3.

Next, as shown in FIG. 3(d), a pattern is formed using resist l-7 and diluted T-IP (for example, I(20
・T (F=30021) (Thus, the outermost surface of the silicon thermal oxide film 3 in the area where the resist 7 is not attached is removed by etching to a thickness of about IO.

Thereafter, as shown in FIG. 3(e), by removing the resist 1-7, Affi is formed on the outermost surface of the silicon thermal oxide film 3.
A region containing Al (an oxide film with negative charges) and a region without Al (an oxide film with no negative charges) are formed.

Next, as shown in Figure 3), an HTO film (silicon oxide film) 5 is deposited by high temperature CVD.

Then, as shown in FIG. 3(g), an n+ polysilicon film 6 is deposited.

Thereafter, as shown in FIG. 3(h), patterning is performed using the resist 8.

Finally, as shown in FIG. 3(1), the n+ polysilicon film 6 is partially etched away using the resist 8 as a mask, and then the resist 8 is removed to form a desired element.

By the manufacturing method described above, when the regions A and B shown in FIG. 3(i) are used as transistor regions, for example, the threshold voltages of the transistors in each region A and B can be controlled. As a result, for example, enhancement (E) type transistors and depletion (D) type I
・It is possible to manufacture transistors and form elements such as E/D inverters.

Next, the characteristics of the semiconductor insulating film in the above embodiment will be explained using FIGS. 4 and 5.

FIG. 4 shows the structure of a film obtained by cleaning a silicon substrate with an ammonia-hydrogen peroxide solution and then oxidizing the film, and the analysis results of Al of the film by 31MS (secondary ion mass spectrometry).

Figure 4(a) shows the configuration of a sample for SIMS analysis, in which a 19 nm thick silicon oxide film (
th-8i○2) 12, and then about 50
A polysilicon film 13 with a thickness of nm is deposited, and the outermost surface of the silicon oxide film 12 contains A1.

Reference numeral 14 denotes the outermost surface etching layer to be etched away for analysis.

FIG. 4 (1) shows the SIMS analysis results, curve A shows the analysis results of a sample in which the polysilicon film 13 was deposited without etching the outermost surface of the silicon oxide film 12, and curve B
This shows the analysis results of a sample in which a polysilicon film 13 was deposited after the outermost surface of the silicon oxide film 12 was etched away by about 30 people (the thickness of the remaining silicon oxide film 12 was, for example, about 15.3 nm). . From this SIMS analysis result, Al was detected in the deposited polysilicon film 13 after oxidation, and after removing the outermost surface of the silicon oxide film 12 after thermal oxidation by etching about 30 degrees,
In the sample deposited with No. 3, Al was below the detection limit.

From the above experimental results, the Al adsorbed on the surface of the silicon substrate 1 is distributed on the outermost surface of the silicon oxide film 12 after the silicon oxide film 12 is formed on the surface by thermal oxidation of the silicon substrate 1. I was able to confirm that.

FIG. 5 shows the measurement results of the flat band voltage of a MOS diode as an example of the electrical characteristics of the semiconductor insulating film in the example.

FIG. 5(a) shows the process flow of the sample whose electrical characteristics were evaluated. There are four types of measurement samples to be evaluated, and cleaning before oxidation is cleaning with ammonia hydrogen peroxide solution (
There are two conditions: washing with diluted HF (D HF ) and washing with diluted HF (APM). In addition, samples were also prepared in which the outermost surface of each oxide film was removed by etching with DHF.

A cross-sectional view of the measurement sample is shown in FIG. 5(b). In the figure, 21 is a P-type silicon substrate, 22 is a silicon oxide film (
th 5iO2), 23 is an etching layer made of DI(F), 24 is an HTO film, and 25 is a polysilicon film.

Figure 5 (C1 shows C of MOS diodes of four types of samples.
An example of (capacitance)-V (voltage) measurement is shown, and FIG. 5(d) shows the measurement results of flat band voltage.

In sample 1, the silicon substrate 21 was cleaned with DHF, and 9
A silicon oxide film (gate oxide film) 22 with a thickness of about 15 nm is formed by thermal oxidation at 00°C, an HTO film 24 with a thickness of about 98 nm is formed by high temperature CVD, and finally a HTO film 24 with a thickness of about 330 nm is formed. A polysilicon film 25 was formed, which was used as the final sample (2).

Sample 2 was prepared by cleaning the silicon substrate 21 with APM and
A silicon oxide film (gate oxide film) 22 with a thickness of about 15 nm is formed by thermal oxidation at 00°C, an HTO film 24 with a thickness of about 98 nm is formed by high temperature CVD, and finally a HTO film 24 with a thickness of about 330 nm is formed. A polysilicon film 25 was formed, which was used as the final sample (2).

For sample 3, the silicon substrate 21 was cleaned by DHP and 9
A silicon oxide film (gate oxide film) 22 with a thickness of approximately 15 nm is formed by thermal oxidation at 00°C, and a thickness of approximately 4 nm from the silicon oxide film 22 is removed by etching with DHF. 98nm thick HT
A film 24 is formed, and finally a polysilicon film 25 with a thickness of about 330 nm is formed to form a final sample (2). Sample 4
In step 9, the silicon substrate 21 is cleaned with A and PM.
A silicon oxide film (gate oxide film) 22 with a thickness of 15 nm is formed by thermal oxidation at 00°C, and about 4 nm of the silicon oxide film 22 is removed by etching with DHF, and then a 98 nm thick film is formed by high-temperature CVD. HTO of thickness
A film 24 was formed, and finally a polysilicon film 25 with a thickness of 330 nm was formed to obtain a final sample (2).

In addition, Fig. 5(a), (C1, (dl sample number ■ ~
■ corresponds to each.

From FIG. 5(C), only the sample (2) in which the silicon substrate 21 was oxidized after being cleaned with ammonia/hydrogen peroxide (APM cleaning) and the HTO film 24 was deposited immediately after that, the flat band voltage was in the positive direction, that is, the oxidation It can be seen that there is a negative charge in the film. This is ammonia hydrogen peroxide cleaning (A
This shows that only when oxidation is performed after PM cleaning), negative charges exist on the outermost surface of the silicon oxide film 22, and that the negative charges can be removed by etching the outermost surface.

〔Effect of the invention〕

According to the semiconductor insulating film according to claim (1), A is provided on the outermost surface.
Since the second silicon oxide film is provided on top of the first silicon oxide film containing l, negative charges can be generated at the interface between the first and second silicon oxide films, which increases the threshold of the MO3 structure. It can be applied to devices that control the value voltage or utilize charges in oxide films.

According to the method for manufacturing a semiconductor insulating film according to claim (2), after cleaning the silicon substrate with an alkaline cleaning liquid containing Aff as an impurity, the silicon substrate is oxidized and the first
By forming a silicon oxide film and depositing a second silicon oxide film on top of the silicon oxide film, negative charges can be formed at the interface between the first and second silicon oxide films, and the manufacturing process is extremely simple.

According to the method for manufacturing a semiconductor insulating film according to claim (3),
A silicon oxide film region containing a negative charge and an oxide film region not containing a negative charge can be mixed on a silicon substrate, and for example, two types of semiconductor elements with different threshold voltages can be provided side by side. .

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view of a semiconductor device having a semiconductor insulating film according to a first embodiment of the present invention, and FIGS. 2(a) to (e) are a first embodiment of the present invention. 3(a) to (1) are step-by-step sectional views showing a method for manufacturing a semiconductor insulating film according to a second embodiment of the present invention; FIG. (Al is a cross-sectional view of a sample containing Al in the semiconductor insulating film, Figure 4 (b) is a diagram showing the SIMS analysis results of the sample in Figure (a), and Figure 5 (a) is a diagram showing the evaluation of electrical characteristics. Figure 5(b) is a cross-sectional view of the sample, and Figure 5(c) is the C-■ of the MOS diode.
Characteristic diagram, Figure 5 (dj is the electrical characteristic of the MOS diode (
FIG. 6, which is a diagram showing the flat band measurement results, is a cross-sectional view of a conventional semiconductor device. ■...Silicon substrate, 2...r, ocos isolation oxide film, 3 silicon thermal oxide film (first silicon oxide film), 4...Al, 5...T (TO film ( second silicon oxide film), 6. n+ polysilicon film, 7, 8
...Resist, 9...Ion-implanted layer for threshold control Patent applicant Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 1...Silicon substrate 0

Claims (3)

[Claims] (1) a first silicon oxide film containing Al on the outermost surface;
A semiconductor insulating film comprising a second silicon oxide film provided on the first silicon oxide film. (2) A step of cleaning the silicon substrate with an alkaline cleaning solution containing AE as an impurity, and a step of oxidizing the cleaned silicon substrate to form a first silicon oxide film containing Al on the outermost surface. and depositing a second silicon oxide film on top of the first silicon oxide film. (3) A step of cleaning the silicon substrate with a cleaning solution made of a mixed solution of ammonia water and hydrogen peroxide solution and containing Al as an impurity, and oxidizing the silicon substrate after cleaning to contain Al on the outermost surface. a step of forming a first silicon oxide film; a step of partially etching the upper layer of the first silicon oxide film thinly with diluted HF; 2nd on top
and depositing a silicon oxide film.