JPH10199878A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor device having a thin gate insulation film, having no distribution peak of N at the back surface but having a N concn. sufficiently high to avoid diffusion of B. SOLUTION: By heat-treating in an NO atmosphere a thin nitride oxide film 13 having a high N concn. on the surface of a semiconductor, a substrate 11 is formed. By oxidizing, this film 13 is oxidized and grown at the back surface to form a gate insulating film 13a of the grown film 13. This provides a distribution peak of N at the front surface of the gate insulating film 13a. An MOS transistor having this thin insulation film 13a has a threshold voltage stabilized by blocking B from diffusion, and its current drive power is suppressed from deteriorating, because of the distribution peak of N located at the front surface of the gate insulating film 13a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device in which a thin gate insulating film is formed in a MOS process.

[0002]

2. Description of the Related Art In recent years, power consumption and voltage of semiconductor devices have been reduced, and in MOS transistors, it is required to reduce the thickness of a gate insulating film made of silicon oxide to 4 nm or less. Along with this, CMO
In the S process, it is required to form a PMOS and an NMOS having a low value and a symmetric threshold voltage on the same substrate. For this reason, N-type polysilicon gates have been used for NMOS and P-type polysilicon gates have been used for PMOS.

[0003] However, boron atoms contained in the P-type polysilicon gate diffuse in a gate insulating film made of an oxide film by a heat treatment performed in a later step, easily reach the silicon substrate, and change the threshold voltage. It becomes a factor to make it. This becomes more remarkable when the thickness of the gate insulating film is reduced to 4 nm or less for lowering the voltage. As a countermeasure, an attempt has been made to introduce nitrogen into the gate insulating film. By setting the nitrogen concentration in the gate insulating film made of an oxide film to about 10 ²¹ atoms / cm ³ , the effect of suppressing boron diffusion is improved. Has been confirmed to be obtained.

In order to form a gate insulating film made of a nitrogen-containing oxide film (so-called oxynitride film), a nitriding treatment is performed in an ammonia (NH ₃ ) atmosphere after forming the oxide film, or There is a method of performing an oxidation treatment after performing a nitridation treatment in an NH ₃ atmosphere. Apart from the above method,
There are a method of combining oxynitriding treatment and oxidation treatment in a nitrous oxide (N ₂ O) atmosphere, and a method of performing only oxynitriding treatment in an N ₂ O atmosphere.

[0005]

However, the above-mentioned method of forming a gate insulating film has the following problems. That is, when nitriding is performed in an NH ₃ atmosphere after forming an oxide film, a large amount of hydrogen remains in the formed gate insulating film, which causes a reduction in hot electron resistance and a current leak. . In the case where the oxidation treatment is performed after performing the nitridation treatment in the NH ₃ atmosphere, hydrogen in the film is expelled in the oxidation treatment step. However, since a certain amount of oxidation treatment time is required to sufficiently purge hydrogen, the thickness of the gate insulating film is increased, and a thin gate insulating film having a thickness of 4 nm or less cannot be obtained.

On the other hand, in a method combining oxynitriding treatment and oxidation treatment in an N ₂ O atmosphere, a gate insulating film having a nitrogen concentration sufficient to obtain an effect of suppressing boron diffusion is formed. The oxynitride film formed by the oxynitridation requires a certain thickness. Therefore, similarly to the above method, the thickness of the gate insulating film is increased, and a thin gate insulating film having a thickness of 4 nm or less cannot be obtained.

Further, in the method of forming a gate insulating film only by oxynitriding in an N ₂ O atmosphere, as shown in FIG. 4, the peak of the distribution of nitrogen atoms in the obtained gate insulating film is reduced. It is located on the interface side between the semiconductor substrate and the gate insulating film. This causes a reduction in the current driving capability of the transistor.

Therefore, the present invention provides a thin gate insulating film made of an oxynitride film having a nitrogen concentration sufficient to suppress boron diffusion and having no nitrogen distribution peak at the interface with the semiconductor substrate. It is an object to provide a method capable of forming a film with a thickness.

[0009]

SUMMARY OF THE INVENTION The present invention is a method of manufacturing a semiconductor device to achieve the above object. That is, in the first method, after an oxynitride film is formed on the surface of a semiconductor substrate by a heat treatment in a nitrogen monoxide (NO) atmosphere, the oxynitride film is oxidized and grown by performing an oxidation process. Thus, an insulating film made of an oxynitride film is formed on the surface layer of the semiconductor substrate. This insulating film is formed as a gate insulating film.

In the first method, the surface of the semiconductor substrate is oxynitrided in an NO atmosphere. Compared with an oxynitride film formed by oxynitridation in an N ₂ O atmosphere, an oxynitride film formed by oxynitridation in a NO atmosphere has a higher nitrogen concentration in the film with respect to the film thickness. Become. Therefore, the film thickness for obtaining the required amount of nitrogen capable of suppressing the diffusion of boron is set to be smaller than that in the case of performing oxynitriding in an N ₂ O atmosphere. Then, since the oxidation treatment is performed after the oxynitridation treatment,
In this oxidation treatment, the oxidation of the semiconductor substrate proceeds on the back side of the oxynitride film formed by the oxynitridation treatment, and the oxynitride film grows. Therefore, the nitrogen-containing portion in the grown oxynitride film is pushed up to the surface side. Therefore,
In the insulating film made of the oxynitride film, the distribution peak of nitrogen atoms is not arranged on the interface side with the semiconductor substrate.

In a second method, after cleaning the surface of the semiconductor substrate, a nitride film is formed on the surface of the semiconductor substrate by a heat treatment in a nitrogen gas (N ₂ ) atmosphere. Next, the nitride film is oxidized and grown by performing an oxidation process. Thus, a gate insulating film made of an oxynitride film is formed on the surface layer of the semiconductor substrate.

In the second method, the clean surface of the semiconductor substrate is nitrided in an N ₂ atmosphere. Compared with the oxynitride film formed by oxynitriding under N ₂ O atmosphere or oxynitridation under NO atmosphere, the nitride film formed by nitriding under N ₂ atmosphere The nitrogen concentration in the film is higher. Therefore, the film thickness for obtaining the required amount of nitrogen capable of suppressing the diffusion of boron is set to be smaller than in the first method. Since the oxidation treatment is performed after the nitridation treatment, in the oxidation treatment, the oxidation of the semiconductor substrate and the nitride film proceeds on the back surface side of the nitride film formed by the nitridation treatment. For this reason, the nitride film grows as an oxynitride film, and a distribution peak of nitrogen atoms is arranged on the interface side with the semiconductor substrate in the gate insulating film made of the oxynitride film as in the first method. Never.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, first and second embodiments in which a method of manufacturing a semiconductor device according to the present invention is applied to a method of manufacturing a MOS transistor will be described with reference to FIGS. 1 (1) to 1 (4). This will be described with reference to process drawings.

(First Embodiment) As shown in FIG. 1A, an element isolation 12 is formed on a surface side of a semiconductor substrate 11 made of, for example, silicon. This element isolation 12 is formed by a usual trench method or LOCOS method.

Next, as shown in FIG. 1 (2), rapid heat treatment (RTP) in a nitrogen monoxide (NO) atmosphere is performed.
The surface layer of the semiconductor substrate 11 is oxynitrided by a thermal process, and a silicon oxynitride film 13 having a thickness of, for example, about 1 nm is formed on the surface of the semiconductor substrate 11. An example of the oxynitriding conditions under the above NO atmosphere is shown below. NO gas flow rate: 2 slm (standard litter / mimutes), substrate heating temperature: 1000 ° C., processing time: 20 seconds,

Thereafter, as shown in FIG. 1C, a wet oxidation treatment is performed in a diffusion furnace to oxidize and grow the silicon oxynitride film 13 to a thickness of, for example, 4 nm.
The following is an example of the above oxidation conditions. Supply gas and flow rate: hydrogen gas (H ₂ ) / oxygen gas (O ₂ ) =
5slm / 5slm, substrate heating temperature: 850 ° C, processing time: 3 minutes,

The silicon oxynitride film 13 having a thickness of 4 nm formed as described above is used as the gate insulating film 13a. Then, the following steps shown in FIG.
This is performed similarly to the OS process. That is, the gate insulating film 1
The gate electrode 14 is patterned on 3a. The gate electrode 14 is formed of boron-containing P-type polysilicon in a region where a PMOS transistor is formed,
The region where the MOS transistor is formed is made of N-type polysilicon containing phosphorus or arsenic.

Thereafter, an impurity for forming the LDD diffusion layer 15 is introduced into the surface layer of the semiconductor substrate 11 by ion implantation using the gate electrode 14 as a mask, and then a side wall is formed on the side walls of the gate electrode 14 and the gate insulating film 13a. A wall 16 is formed. Next, an impurity for forming the source / drain 17 is introduced into the surface layer of the semiconductor substrate 11 by ion implantation using the gate electrode 14 and the sidewall 16 as a mask, and then the gate electrode 14 and the sidewall 16 are covered. Then, an interlayer insulating film 18 is formed. Next, after a contact hole 19 is formed in the interlayer insulating film 18, wirings 20 respectively connected to the source / drain 17 and the gate electrode 14 are formed to complete the semiconductor device 1.

In the manufacturing method of the first embodiment, since the silicon oxynitride film 13 is formed on the surface of the semiconductor substrate 11 by the oxynitriding process in the NO atmosphere, the film is formed in the N ₂ O atmosphere. The nitrogen concentration in the film with respect to the film thickness becomes higher than that of the silicon oxynitride film. For example, the silicon oxynitride film 13 formed by the oxynitridation process of the first embodiment has a higher nitrogen concentration than the oxynitride film formed by using N ₂ O under the same conditions as the oxynitridation process. Is 5 to 6 times and the film thickness is about 50 to 70%. Therefore, a required nitrogen amount capable of suppressing the diffusion of boron can be obtained with a film thickness of about 1 nm.

Since the oxidizing process is performed after the oxynitriding process, the oxidizing process oxidizes the semiconductor substrate 11 and the silicon oxynitride film 13 on the back side of the silicon oxynitride film 13 formed by the oxynitriding. Advances. Therefore, the nitrogen-containing portion in the silicon oxynitride film 13 is pushed up to the surface side. Therefore, as shown in the concentration profile of oxygen (O) and nitrogen (N) in the gate insulating film 13a in FIG. 2, the distribution of nitrogen atoms in the silicon oxynitride film 13 grown by oxidation (that is, the gate insulating film 13a). The peak is on the surface side of the gate insulating film 13a. The nitrogen concentration in the gate insulating film 13a is
The concentration is about 10 ²¹ atoms / cm ³ , that is, a concentration that can prevent the diffusion of boron.

As described above, since the gate insulating film 13a has such a nitrogen concentration that the effect of suppressing the diffusion of boron can be obtained, the semiconductor device 1 having the gate insulating film 13a is free from the gate electrode 14 of the PMOS transistor. Boron diffusion is suppressed, and a stable threshold voltage is obtained. Further, since the distribution peak of nitrogen is not located on the interface side with the semiconductor substrate 11 in the gate insulating film 13a,
In the semiconductor device 1 having the gate insulating film 13a, the current driving capability of the transistor is secured. In addition, since the gate insulating film 13a has a thin film thickness of 4 nm, the semiconductor device 1 having the gate insulating film 13a has a low threshold voltage and is further miniaturized.

(Second Embodiment) The difference between the manufacturing method of the second embodiment described here and the first embodiment lies in the step of the oxidation treatment shown in FIG. That is, here, dry oxidation is performed instead of wet oxidation in the first embodiment.

Therefore, after performing the steps described with reference to FIGS. 1A and 1B in the same manner as in the first embodiment, in the step shown in FIG. The silicon oxynitride film 13 is oxidized and grown to a thickness of, for example, 4 nm by dry oxidation. The following shows an example of the oxidation conditions. Supply gas and flow rate: oxygen gas (O ₂ ) = ₂ slm, substrate heating temperature: 1000 ° C., processing time: 3 minutes,

The silicon oxynitride film 13 having a thickness of 4 nm formed as described above is used as the gate insulating film 13a. Then, the semiconductor device 1 is completed by performing the step shown in FIG. 1D in the same manner as in the first embodiment.

The same effect as in the first embodiment can be obtained by the above manufacturing method.

FIGS. 3A to 3D are manufacturing process diagrams of a third embodiment and a fourth embodiment to which the present invention is applied. Hereinafter, the third embodiment and the fourth embodiment will be described with reference to these drawings. The first embodiment and the second embodiment
The same components as those of the embodiment are denoted by the same reference numerals, and overlapping description will be omitted.

(Third Embodiment) First, as shown in FIG. 3A, after an element isolation 12 is formed on a surface layer of a semiconductor substrate 11 made of, for example, silicon, the surface of the semiconductor substrate 11 is cleaned here. Become Here, the term “cleaning” refers to removing a natural oxide film on the surface of the semiconductor substrate 11 and exposing the bare surface of the semiconductor substrate 11. Here, the cleaning is performed by heat treatment in a high vacuum. less than,
An example of the above cleaning conditions will be described. Processing atmosphere pressure: 1.33 × 10 ⁻⁸ Pa, substrate heating temperature: 1100 ° C., processing time: 2 seconds,

Next, as shown in FIG. 3B, the surface of the cleaned semiconductor substrate 11 is nitrided by a heat treatment in a nitrogen gas (N ₂ ) atmosphere. Here, heat treatment is performed in a reduced pressure atmosphere, and a silicon nitride film 31 having a thickness of about 1 nm is formed on the surface of the semiconductor substrate 11. An example of the above nitriding conditions is shown below. N ₂ gas flow rate: 100 sccm (standard cubic ce
ntimeter / mimutes), pressure in processing atmosphere: 1.33 × 10 ⁻³ Pa, substrate heating temperature: 750 ° C., processing time: 1.5 hours,

Thereafter, as shown in FIG. 3C, the silicon nitride film 31 is oxidized and grown to a silicon oxynitride film 32 having a thickness of 4 nm by performing a wet oxidation treatment in a diffusion furnace. An example of the oxidation conditions is shown below. Supply gas and flow rate: H ₂ / O ₂ = 5 slm / 5 slm, substrate heating temperature: 850 ° C., processing time: 3 minutes,

The 4 nm-thick silicon oxynitride film 32 formed as described above is used as the gate insulating film 32a. Then, the semiconductor device 3 using the gate insulating film 32a is formed by performing the step shown in FIG. 3D in the same manner as described in the first and second embodiments with reference to FIG. To complete.

In the manufacturing method of the third embodiment, the clean surface of the semiconductor substrate 11 is nitrided in an N ₂ atmosphere.
On the surface layer of the semiconductor substrate 11, a silicon nitride film 31 is formed. Therefore, the nitrogen concentration in the film with respect to the film thickness becomes higher than in the case of forming the silicon oxynitride film, and the film thickness for obtaining the required nitrogen amount capable of suppressing the diffusion of boron is equal to the first film thickness. It is set to be thinner than in the embodiment and the second embodiment. Therefore, with a film thickness of about 1 nm, a sufficient amount of nitrogen necessary to suppress the diffusion of boron can be obtained.

Since the oxidation treatment is performed after the nitridation treatment, the oxidation of the semiconductor substrate 11 and the silicon nitride film 31 proceeds on the back surface side of the silicon nitride film 31 in this oxidation treatment. Therefore, the silicon nitride film 31 is oxidized and grown as the silicon oxynitride film 32, and the nitrogen-containing portion in the silicon oxynitride film 32 is pushed up to the surface side. Therefore, as shown in the concentration profiles of oxygen and nitrogen in the gate insulating film 32a in FIG. 2, the distribution peak of the nitrogen atoms in the silicon oxynitride film (gate insulating film) 32a is on the surface side of the gate insulating film 32a. The nitrogen concentration in the gate insulating film 32a made of the silicon oxynitride film 32 grown to 4 nm is higher by about one digit than in the first and second embodiments, and the diffusion of boron is sufficiently prevented. You.

From the above, this gate insulating film 32a
The semiconductor device 3 having the same effects as those of the first embodiment and the second embodiment, and having a finer and lower voltage than those of the first and second embodiments. can do.

(Fourth Embodiment) The difference between the fourth embodiment and the third embodiment lies in the oxidation treatment step shown in FIG. That is, here, dry oxidation is performed instead of wet oxidation in the third embodiment.

Therefore, after performing the steps described with reference to FIGS. 3A and 3B in the same manner as in the third embodiment, in the step shown in FIG. The silicon oxynitride film 32 is oxidized to a thickness of, for example, 4 nm. An example of the oxidation conditions is shown below. Supply gas and flow rate: oxygen gas (O ₂ ) = ₂ slm Substrate heating temperature: 1000 ° C., processing time: 3 minutes,

The 4-nm-thick silicon oxynitride film 32 formed as described above is used as the gate insulating film 32a. Then, the step shown in FIG. 3D is performed in the same manner as in the first embodiment, thereby completing the semiconductor device 3.

According to the manufacturing method of the fourth embodiment,
The same effects as in the third embodiment can be obtained.

Incidentally, in the nitriding treatment performed in the third and fourth embodiments, if the required amount of nitrogen capable of suppressing the diffusion of boron is obtained, the film thickness of the nitride film and the nitriding conditions are set as described above. It is not limited.

The oxidation treatment described in each of the above embodiments may be performed by RTO (rapid thermal oxidation), and the final thickness of the gate insulating film obtained by this oxidation treatment is as follows:
It is set according to the transistor characteristics, and is not limited to 4 nm shown in the above embodiments. Further, the film thickness formed by the oxynitriding or nitriding treatment is set according to the required nitrogen concentration in the gate insulating film, and is not limited to 1 nm shown in each of the above embodiments.

[0040]

As described above, according to the method of manufacturing a semiconductor device of the present invention, the oxidizing treatment is performed after the oxynitridation of the surface of the semiconductor substrate is performed in a nitrogen monoxide atmosphere, or the cleaned semiconductor substrate is cleaned. By oxidizing after nitriding the surface in a nitrogen gas atmosphere, it is made of an oxynitride film containing nitrogen enough to prevent diffusion of boron without forming a nitrogen distribution peak on the interface side with the semiconductor substrate. The insulating film can be formed with a small thickness. Therefore, it is possible to obtain a semiconductor device having a stable threshold voltage without lowering the current driving capability of the transistor even though it has a thin gate insulating film.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a first embodiment and a second embodiment.

FIG. 2 is a concentration profile of oxygen and nitrogen in a gate insulating film according to the present invention.

FIG. 3 is a manufacturing process diagram of a third embodiment and a fourth embodiment.

FIG. 4 is a concentration profile of oxygen and nitrogen in a gate insulating film according to a conventional method.

[Explanation of symbols]

1,3 Semiconductor device 11 Semiconductor substrate 11a
Surface 13, 32 Silicon oxynitride film (oxynitride film) 13a, 32a Gate insulating film 31 Silicon nitride film (nitride film)

Claims (4)

[Claims] A step of forming an oxynitride film on a surface of the semiconductor substrate by heat treatment in a nitrogen monoxide atmosphere; and performing an oxidation treatment to oxidize and grow the oxynitride film, thereby forming a surface of the semiconductor substrate. Forming an insulating film made of an oxynitride film on the layer. 2. The method for manufacturing a semiconductor device according to claim 1, wherein said insulating film is formed as a gate insulating film. 3. A step of cleaning the surface of the semiconductor substrate, a step of forming a nitride film on the surface of the semiconductor substrate which has been cleaned by a heat treatment in a nitrogen gas atmosphere, and Forming an insulating film made of an oxynitride film on a surface layer of the semiconductor substrate by oxidizing and growing a nitride film. 4. The method for manufacturing a semiconductor device according to claim 3, wherein said insulating film is formed as a gate insulating film.