JPH05198574A - Formation of insulating film - Google Patents

Abstract

PURPOSE:To form an insulating film on a silicon substrate with film quality more excellent than usual one and with a high destructive strength. CONSTITUTION:A silicon oxide film 12 formed on a silicon substrate 10 is heated at a temperature of 1000 to 1200 deg.C in an N2O gas atmosphere, while it is changed into a silicon oxide-nitrified film (Si0N film) 14 having a film thickness Y which is satisfied with X/Y<=0.9 with respect to a film thickness X of a silicon oxide film. An insulating film is constituted of the silicon oxidenitrified film 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating film, and more particularly to a method for forming an insulating film having a thin film and excellent characteristics.

[0002]

2. Description of the Related Art A VLSI formed by the latest technology,
Especially dynamic random access memory (DR
In AM), an oxide film having an extremely thin film thickness is used for a memory capacitor insulating film and a gate insulating film due to miniaturization. Also, a non-volatile memory such as a Fowler Nordheim thin SiO ₂ film is used.
im) A thin SiO ₂ film is also used in the E ² PROM utilizing the tunnel current to improve the characteristics.

However, these SiO ₂ films are MV / c
A high electric field of the order of m may be applied, and deterioration of the device due to high electric field stress or hot electrons becomes a problem.

Therefore, attempts have been made to improve the film quality of the SiO ₂ film (for example, reference: "Next-generation VLSI process technology-application edition", edited by Masataka Hirose, Realize Co., P .;
75 (1988) "). In the method disclosed in this document, the surface of the SiO ₂ film is converted into a nitride by heating the SiO ₂ film at high temperature in NH ₃ gas, and the thermal oxynitride film (SiO 2) having a denser structure than the Si oxide film is formed. _X N _Y ) (However,
X and Y form a number greater than 0).

If this method of forming a thermal oxynitride film is applied to the formation of a gate insulating film, the stress resistance can be improved.
Further, the diffusion of impurities into the film is suppressed to improve the film quality, and the thermal oxynitride film has a larger dielectric constant than the Si oxide film, so that the thermal oxynitride film can be applied to devices such as VLSI. Is expected.

[0006]

[0007] However, Si when the nitriding by high-temperature heating the SiO ₂ film formed on the substrate in NH ₃ gas, a large amount of hydrogen with a nitrogen (N) (H) is SiO ₂ It penetrates into the film, and as a result, chemical species such as —NH _x group, —CH group and —H group are generated in the SiO ₂ film as reaction by-products. As a result, a MOS field effect transistor (MOSFE) is formed using this thermal oxynitride film.
When T) is constituted, -NH formed as a reaction by-product is produced.
_{The X} group, the -CH group, the -H group, etc. serve as the nucleus of the electron trap, which causes the fluctuation of the threshold voltage of the transistor and the deterioration of the withstand voltage.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for forming an insulating film which is superior in film quality and high in fracture resistance as compared with the prior art.

[0008]

In order to achieve this object, according to the present invention, in a method for forming an insulating film on a silicon underlayer, the silicon oxide film formed on the silicon underlayer is made to contain nitrogen. In the oxidizing gas atmosphere, the silicon oxynitride film is replaced by the silicon oxynitride film to form the insulating film, and the replacement is performed by changing the film thickness of the silicon oxide film to the film thickness of the silicon oxynitride film. However, the film thickness is 0.9 or less.

In carrying out the present invention, preferably, the nitrogen-containing oxidizing gas includes nitrogen monoxide (NO) gas, dinitrogen monoxide (N ₂ O) gas, and nitrogen dioxide (NO ₂ ) gas. It is preferable to use one kind of gas selected from the group or a mixed gas of two or more kinds.

Further, in carrying out the present invention, it is preferable that the above-mentioned heat treatment is carried out at a temperature within the range of 1000 to 1200 ° C.

Here, the term “silicon underlayer” means not only a silicon substrate but also a silicon substrate on which an epitaxial layer is formed, and not limited to these, and an element is formed on the substrate or the epitaxial layer. It widely means a base on which an insulating film should be formed, such as an intermediate.

The method of forming the silicon oxide film formed on the lower surface of silicon is not particularly limited. For example,
A method of oxidizing a silicon underlayer in an oxidizing gas atmosphere in a reaction furnace to form a silicon oxide film on the surface of the silicon underlayer, a known film forming method such as C
Various methods such as a VD method, a method of forming a silicon oxide film by a sputtering method, a method of using polycrystalline silicon as a base of silicon and thermally oxidizing the same can be used. However, considering the continuity with the oxynitriding treatment using an oxidizing gas containing nitrogen, a method of forming a silicon oxide film on the surface of the silicon underlayer by oxidizing the silicon underlayer in an oxidizing gas atmosphere in a reaction furnace is considered. It is suitable.

[0013]

According to the insulating film forming method of the present invention described above,
The silicon oxide film formed on the lower surface of Si is heated to a high temperature in a nitrogen-containing oxidizing gas atmosphere to be replaced with a silicon oxynitride film, and this silicon oxynitride film is used as an insulating film. Since this silicon oxynitride film has a denser structure than a silicon oxide film, it is a high-quality insulating film with a small number of electron traps and high breakdown resistance. As a result, the electrical characteristics of the electronic device are improved, the life is long, and a high-quality insulating film with improved reliability can be obtained.

[0014]

Embodiments of the invention of this application will be described below with reference to the drawings.

It should be noted that the drawings merely schematically show the sizes, shapes and positions of the constituent components to the extent that the present invention can be understood. Further, in the following description, numerical conditions of specific materials and properties are described, but these materials and conditions are merely preferable examples and are not limited thereto.

FIGS. 1A and 1B are process drawings for explaining an embodiment of an insulating film forming method of the present invention, and each drawing is a cross-sectional view of an essential part. 1. Formation of insulating film 1-1. Formation of Silicon Oxide Film First, as a base of silicon, P was formed in a reaction furnace (not shown).
A mold (100) Si substrate 10 is installed. The substrate surface is cleaned as required, and the inside of the reaction furnace is cleaned as required.
Next, the silicon oxide film 12 is formed on the surface of the substrate 10. In this embodiment, the silicon oxide film is formed by heating the substrate 10 in a nitrogen-free oxidizing gas atmosphere. As the nitrogen-free oxidizing gas, oxygen (O ₂ ) gas is used here. When forming a silicon oxide film,
Since the reaction by-products at the time of forming the oxide film are exhausted to the outside of the reaction furnace, the inside of the reaction furnace may be maintained at a low vacuum reduced pressure of, for example, 100 to 10 ^-2 Torr. Was set to atmospheric pressure. Further, it is preferable that the heating temperature for the substrate 10 be 1000 ° C. or higher. The heating of this substrate is preferably an infrared lamp, arc lamp,
It is performed by using a heating means such as a laser beam or a heater.
In this embodiment, an infrared lamp is used, and the surface temperature of the substrate 10 is determined, for example, by an optical pyrometer, and the temperature is preferably raised at an appropriate rate of, for example, 50 ° C./sec to 200 ° C./sec. About 1 at a temperature of about 100 ℃ / sec
The temperature is raised to 100 ° C., and the temperature of 1100 ° C. is maintained for a certain period of time to form a SiO ₂ film 12 having a film thickness of 7 nm ((A) of FIG. 1). The thickness of the Si oxide film can be controlled by, for example, adjusting the oxidation temperature, the oxidation time, the flow rate of the oxidizing gas, and the pressure of the oxidizing gas in the reaction furnace.

1-2. Substitution with silicon oxynitride film Next, the gas supplied into the reaction furnace is switched to a nitrogen-containing oxidizing gas to change the silicon oxide film 12 to a silicon oxynitride film. In this embodiment, N ₂ O gas is used as the nitrogen-containing oxidizing gas, and this N ₂ O gas is introduced into the reaction furnace. In this case, the pressure in the reactor is 100 to 10 ^-2 To
The reduced pressure state of rr may be a low vacuum, but in this embodiment, it is set to about 1 atm. Then, in this N ₂ O gas atmosphere, the substrate temperature is raised to an appropriate temperature within a temperature range of 1000 ° C. to 1200 ° C. at an appropriate rate of, for example, 50 ° C./sec to 200 ° C./sec. The silicon oxynitride film 14 is obtained by oxynitriding the SiO ₂ film 12 while maintaining this temperature for a certain period of time (FIG. 1B). For this sample, the silicon oxide film 12 having a thickness of 7 nm is replaced with a silicon oxynitride film, and the silicon substrate 10 under the silicon oxide film 12 is also oxynitrided to obtain a SiON film 14 having a thickness of 10 nm. As the heating means in this case, the same heating means as that used at the time of forming the silicon oxide film may be used. The thickness of the silicon oxynitride film obtained by replacing the SiO ₂ film is
It can be controlled appropriately by adjusting the temperature, the time and the flow rate of N ₂ O gas. When the heating temperature is lower than 1000 ° C., both the nitriding reaction and the oxidation reaction are suppressed, and the quality of the film particularly near the interface with the silicon underlayer deteriorates.
If the temperature is higher than 1200 ° C, the substrate is damaged, so the heating temperature for oxynitriding is 1000 ° C to 1200 ° C.
Within the range of.

Further, the silicon oxynitride film 14 (having a thickness of 10 n) is formed by the same procedure as described above except that the thickness of the silicon oxide film 12 formed on the silicon substrate 10 is 8 nm.
m), and the silicon oxide film 12 having a thickness of 9
Samples each having the silicon oxynitride film 14 (film thickness 10 nm) are prepared by the same procedure as described above except that the thickness is set to nm.

2. Insulating Film Characteristic Test Next, using the lithography and etching techniques, each of the above-mentioned samples (the film thickness of the silicon oxide film before oxynitridation was 7,
4) on the silicon oxynitride film 14 of each sample of 8 and 9 nm)
A gate electrode 16 of polycrystalline Si doped with phosphorus at a concentration of × 10 ²⁰ cm ^-3 (minus cube) was formed to fabricate a MOS capacitor having a structure shown in the cross-sectional view of the main part in FIG.

Electrons are injected into the silicon oxynitride film 14 from the gate electrode of this capacitor at a constant current density, and the potential difference (V _gs ) between the substrate 10 and the gate electrode 16 before and after the injection.
And the fluctuation amount of the flat band voltage (V _FB ) were measured at room temperature.

The constant current electron injection was performed by grounding the substrate 10 and connecting a constant current source in series between the gate electrode 16 and the ground.

FIG. 3 shows a negative variation amount -ΔV _gs of the potential difference V _gs between the substrate 10 and the gate electrode 16 before and after injecting electrons having a total charge amount of 3 C / cm ² into a capacitor having an area of 0.020 mm ² . It is the figure which showed the measurement result of (unit V). The vertical axis represents the negative fluctuation amount of the potential difference V _gs , and the horizontal axis represents the thickness of the silicon oxynitride film 14 formed by oxynitriding the silicon oxide film 12 (see FIG. 1B) to the silicon before oxynitriding. Oxide film 1
A value Z defined by subtracting the film thickness X of 2 (see FIG. 1A)
(Z = Y−X).

The circles in FIG. 3 indicate the samples of the examples, that is, Z.
= 3 nm, 2 nm, 1 nm measurement data of each sample. In addition, ● mark is the measurement data of the sample of the comparative example. In the sample of this comparative example, a SiO ₂ film having a film thickness of 9 nm was used as NH ₃
This is a sample formed by heating the substrate surface temperature to 1100 ° C. in a gas and performing heat treatment at 1100 ° C. during the time period until the film thickness of the thermal oxynitride film is formed to 10 nm.
The thermal oxynitride film of the sample of the comparative example was formed by first oxidizing the silicon substrate to obtain a silicon oxide film in the same manner as in the example, and then purging oxygen gas from the inside of the reaction furnace and then NH _{3 in the} reaction furnace.
It is carried out by heating the substrate so that the surface of the silicon substrate becomes 1100 ° C. in a state where the gas is introduced and the inside of the reaction furnace is maintained at 300 to 400 Torr.

[0024] The negative variation of the potential difference (V _gs) (-ΔV _gs)
Is related to the amount of electron traps generated in the SiON film. It is known that the larger the value of −ΔV _gs, the larger the amount of electron traps generated, the larger the characteristic variation of the film, and the poor film quality.

Considering this point, referring to FIG. 3, the silicon oxynitride film formed by heating the silicon oxide film in the N ₂ O gas atmosphere has at least Z = 1 nm or more, that is, the silicon oxide film. When the film thickness X of 12 is 0.9 or less (X / Y ≦ 0.9) with respect to the film thickness Y of the silicon oxynitride film 14, the potential difference is smaller than that of the conventional nitriding in the NH ₃ gas atmosphere. It can be seen that the variation amount (-ΔV _gs ) is small and the film quality is excellent.

Next, the value of the flat band voltage (V _FB ) was determined by measuring the capacitance of the MOS capacitor at high frequency (1 MHz).

[0027] FIG. 4 is a negative variation amount of the area 0.0264Mm ² flat band voltage before and after the injection of electrons total charge 2C / cm ² to the capacitor _{(V FB) (- △ V} FB)
The measurement result of (unit V) is shown. The vertical axis of FIG. 4 represents the negative fluctuation amount of the flat band voltage of the MOS capacitor (−ΔV _FB ).
(Unit is Volt (V)). Horizontal axis is Z as in Fig. 3
(Z = Y−X). Further, the circles and the circles are the same as in the case of FIG. 3, and the circles are the example data and the circles are the comparative data.

The negative fluctuation amount (V _FB ) of the flat band voltage (V _FB ) is related to the generation amount of positive charges in the silicon oxynitride film. It is known that the larger the value of _{−ΔV FB,} the larger the amount of positive charges generated, the lower the dielectric breakdown resistance, and the lower the film quality.

Considering this point, the measurement result of FIG. 3 shows that the silicon oxynitride film formed by heating the silicon oxide film in the N ₂ O gas atmosphere has at least Z = 1 nm.
That is, the film thickness X of the silicon oxide film 12 is 0.9 or less (X / Y ≦) with respect to the film thickness Y of the silicon oxynitride film 14.
In the range of 0.9), the value of the negative fluctuation amount of the flat band voltage (-ΔV _FB ) is smaller than that of the conventional nitriding in the NH ₃ gas atmosphere, and the insulation resistance is excellent.

As described above, the silicon oxide film having the film thickness X is N ₂ O, judging comprehensively from the measurement results of −ΔV _gs and −ΔV _FB.
In the silicon oxynitride film formed by heat treatment in a gas atmosphere, the thickness X of the silicon oxide film is 0.9 or less (X / Y ≦ 0.9) with respect to the thickness Y of the silicon oxynitride film. Then
It can be seen that the film quality is superior to the thermal oxynitride film obtained by the conventional nitriding in the NH ₃ gas atmosphere.

3. Modifications and Modifications It is obvious that the present invention is not limited to the above-described embodiments.

Since a normal SiO ₂ film has many unpaired bonds and weak bonds of Si atoms and O atoms in the film, these bonds are broken by the stress of electron injection, or a positive bond generated by electron injection is generated. The insulation film is broken due to the trapping of the holes. However, this SiO ₂
By nitriding the film, the number of unpaired bonds or weak bonds is reduced by bonding or substituting nitrogen atoms to these unstable bonding portions. These are all chemical processes performed after forming the SiO ₂ film. Therefore, the Si substrate 10 of FIG.
Conductivity type and plane orientation, SiO ₂ film 12 formed at regardless on the thickness of the heating temperature and oxygen partial pressure and the SiO ₂ film in the FIG. 1 (A), the it is apparent that the present invention can be applied. Further, the same improvement effect can be obtained by forming the SiO ₂ film 12 by a chemical deposition method such as CVD or by oxidizing polycrystalline Si.

Further, in the above embodiment, the second nitrogen-containing second
Although the example of N ₂ O gas is used as the oxidizing gas in the description,
A simple substance gas of nitric oxide (NO) gas or nitrogen dioxide (NO ₂ ) gas, or a mixed gas of two or more kinds selected from the group of NO gas, N ₂ O gas and NO ₂ gas may be used. Further, in the above-described embodiment, the film thickness of the silicon oxynitride film is set to 10 nm (100 angstrom), but a film thickness different from this, particularly a film thickness smaller than this, can obtain the same improvement effect as the embodiment. 4. Application Example Since the present invention improves the breakdown resistance of the insulating film, it can be applied to all types of semiconductor elements having an insulating film and has the effect of extending the breakdown life.

Nonvolatile MOSFETs are shown in FIGS.
An example in which the present invention is applied to a memory element will be shown. FIG. 5 shows MNOS (Metal Nitride Oxi).
2 shows a cross-sectional structure of a main part of a deSemiconductor type memory device. This memory device comprises a diffusion layer 22 for source / drain regions on a Si substrate 20, and a silicon oxynitride film 24 formed according to the insulating film forming method of the present invention on the upper surface of the substrate 20 and, for example, Si ₃ N 2. The insulating film 26 is made of ₄ or Al ₂ O ₃ , and the gate electrode 28 is provided on the insulating film 26. A fouling occurs mainly from the substrate side in the interface state existing in the vicinity of the interface between the two insulating films 24 and 26 of the gate insulating film 30 composed of the silicon oxynitride film (tunnel oxide film) 24 and the insulating film 26. -The memory operation is performed by injecting and trapping carriers by passing a Noordheim tunnel current or a direct tunnel current.

Since data rewriting is performed by applying a high electric field to the insulating film (tunnel oxide film) 24, the reliability of this memory element largely depends on the breakdown resistance of the insulating film 24. Conventionally, a SiO ₂ film is used as the insulating film 24. However, by using the silicon oxynitride film obtained by the present invention for the insulating film 24, the breakdown resistance of the insulating film is improved and the characteristic fluctuation and deterioration are suppressed. Therefore, it is expected that a long-life memory device having a large number of data rewritings and excellent data retention characteristics can be realized.

FIG. 6 shows FLOTOX (Floating
1 shows a gate tunnel oxide type memory device.

This memory device also has a diffusion layer 22 for the source / drain regions on the Si substrate 20. And
On the upper surface of the substrate 20, the silicon oxynitride film 34 formed according to the insulating film forming method of the present invention and the floating gate 3 are formed.
6, the interlayer insulating film 38, and the gate electrode 40 in this order.

In this memory element, a part of the silicon oxynitride film 34 (tunnel oxide film) which is an insulating film below the floating gate 36 is extremely thin. This thin film part 3
4a.

A Fowler-Nordheim tunnel current is caused to flow through the thin film portion 34a of the tunnel oxide film to inject carriers into the floating gate 36 to perform a memory operation. Conventionally, a SiO ₂ film is used for the insulating film 34, but by using the silicon oxynitride film of the present invention for the insulating film 34, the breakdown resistance of the insulating film is improved, the characteristic fluctuation and deterioration are suppressed, and It can be expected to realize a long-life memory device that has a large number of rewrites and has excellent data retention characteristics.

[0040]

As is apparent from the above description, according to the insulating film forming method of the present invention, the silicon oxide film formed on the silicon underlayer is subjected to the heat treatment in the nitrogen-containing oxidizing gas atmosphere. X for the film thickness X of the silicon oxide film
Since the silicon oxynitride film instead of the silicon oxynitride film with a thickness Y satisfying the /Y≦0.9 and the insulating film, compared with a thermal oxynitride film formed by nitriding with conventional NH ₃ gas Negative fluctuation of flat band voltage-value of ΔV _FB ,
Negative fluctuation of the potential difference between the substrate and the gate electrode-both the value of ΔV _gs becomes small. Therefore, since the amount of positive charges generated is small, a high-quality insulating film having a high dielectric breakdown resistance can be obtained, and the amount of generated electron traps is small, so that an insulating film with less characteristic fluctuation can be obtained.

Therefore, when an electronic device such as a non-volatile MOSFET memory element or a MNOS type memory element is manufactured by using the insulating film formed according to the present invention, the life and reliability of these electronic devices can be improved as compared with the conventional ones. ..

[Brief description of drawings]

FIG. 1A and FIG. 1B are process drawings for explaining an embodiment of an insulating film forming method of the present invention.

FIG. 2 is an MO used for evaluation of an insulating film forming method of the present invention.
FIG. 4 is a cross-sectional view of an essential part for explaining an S capacitor.

FIG. 3 is a characteristic showing a relationship between a film thickness of a silicon oxynitride film and a negative variation amount (−ΔV _gs ) of a potential difference between a substrate and a gate electrode, which is used for explaining an embodiment of an insulating film forming method of the present invention. It is a figure.

FIG. 4 is a characteristic diagram showing the relationship between the film thickness of the silicon oxynitride film and the negative variation amount (−ΔV _FB ) of the flat band voltage, which is used for explaining an embodiment of the insulating film forming method of the present invention. is there.

FIG. 5 is a cross-sectional view of an essential part of a MNOS type memory element using a silicon oxynitride film formed by the insulating film forming method of the present invention.

FIG. 6 is a cross-sectional view of an essential part of a FLOTOX type memory device using a silicon oxynitride film formed by the insulating film forming method of the present invention.

[Explanation of symbols]

 10, 20: Si substrate 12: Silicon oxide film 14, 24, 34: Silicon oxynitride film 16, 28, 40: Gate electrode 22: Diffusion layer 26: Insulating film 34a: Thin film portion of silicon oxynitride film 36: Floating gate 38: Interlayer insulating film

Claims (2)

[Claims] 1. A method of forming an insulating film on a silicon underlayer, wherein the silicon oxide film formed on the silicon underlayer is heat-treated in a nitrogen-containing oxidizing gas atmosphere to replace the silicon oxynitride film. The silicon oxynitride film is used as the insulating film, and the substitution is performed so that the film thickness of the silicon oxide film is 0.9 or less with respect to the film thickness of the silicon oxynitride film. Insulating film forming method. 2. The insulating film forming method according to claim 1, wherein the nitrogen-containing oxidizing gas is nitric oxide (NO) gas,
Nitrous oxide (N ₂ O) gas and nitrogen dioxide (NO ₂ )
A method for forming an insulating film, which comprises using one kind of gas selected from a group of gases or a mixed gas of two or more kinds.