JPH08172091A - Formation of insulating film - Google Patents

Abstract

PURPOSE: To provide a method of forming an insulating film, which has a high reliability to a pressure resistance and consists of an ONO structure, without exerting an effect on a substrate which is used as the base layer of the insulat ing film. CONSTITUTION: A lower oxide film 12 is formed on a substrate 11 and after a nitride film 13 is formed on the film 12, a silicon film 14 consisting of amorphous silicon is formed on the film 13. A thermal oxidation treatment using a high-speed thermal oxidation of the film 14 is performed and an upper oxide film 14a, which is formed by oxidizing the film 14, is formed. Thereby, an insulating film 15, which has the film 14a having little defect density and consists of an ONO structure, is formed on the substrate 11 without exerting the effect of the thermal oxidation treatment on the substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming an insulating film having an ONO structure of oxide film / nitride film / oxide film on a substrate in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art A so-called ONO structure insulating film having a nitride film sandwiched between oxide films is used as a gate insulating film of a MOS transistor or a gate interlayer insulating film between a floating gate and a control gate in a floating gate type memory element. Is being considered.

In the insulating film having the ONO structure, the nitride film having a denser structure than the oxide film secures the breakdown voltage between the upper and lower layers partitioned by the insulating film and prevents the penetration of impurities from the gate electrode. In addition, the oxide film formed on both sides of the nitride film suppresses the interface state between the substrate or each gate and the insulating film.

The insulating film is formed by the following procedure, for example. First, a lower oxide film is formed on the upper surface of a silicon substrate or a floating gate formation layer, and a nitride film is formed on this upper surface. Then, the upper layer of the nitride film is oxidized to form an upper oxide film, or silicon oxide is deposited and deposited on the nitride film by a CVD method to form an upper oxide film.

[0005]

However, the method of forming the insulating film has the following problems. That is,
When the upper oxide film is formed by thermal oxidation of the nitride film, the nitride film is difficult to be oxidized, and therefore, for example, wet oxidation treatment is performed at a high temperature of about 950 ° C. for about 1 hour in the pyrogenic oxidation furnace for a long time. There is a need. Therefore, the thermal oxidation treatment changes the diffusion state of impurities in the substrate, and the oxidation of the substrate and the floating gate forming layer made of silicon, which are more easily oxidized than the nitride film, promotes the oxidation of the lower oxide film. The thickness and the thickness of the floating gate forming layer change. As described above, according to the method of forming the insulating film, the upper oxide film cannot be formed without affecting the underlying layer.

On the other hand, since the upper oxide film formed by the CVD method is a deposited film formed by depositing film forming molecules, it has a higher defect density and a larger leak current than a film obtained by thermal oxidation. It becomes a thing. Therefore, the insulating film forming method cannot form a highly reliable insulating film.

From the above, it is difficult to secure the basic characteristics and reliability of the MOS transistor using the insulating film formed by the above method as the gate insulating film and the memory element using the gate interlayer insulating film. is there.

Therefore, an object of the present invention is to provide a method for forming an insulating film which solves the above problems.

[0009]

In order to achieve the above object, the method of forming an insulating film according to the present invention comprises first forming a lower oxide film on a substrate and then forming a nitride film on the lower oxide film. After that, a silicon film is formed on the nitride film. Next, the silicon film is subjected to thermal oxidation treatment to form an upper oxide film formed by oxidizing the silicon film, and an insulating film formed by sandwiching a nitride film between the lower and upper oxide films is formed on the substrate. The thermal oxidation treatment is performed by rapid thermal oxidation. Also,
The insulating film is formed as a gate insulating film of a MOS transistor or a gate interlayer insulating film of a floating type memory element.

[0010]

In the insulating film forming method, the upper oxide film is formed on the nitride film by thermally oxidizing the silicon film. Therefore, the upper oxide film is formed by oxidizing the nitride film. Is also formed under mild oxidation conditions. Further, since this upper oxide film is a thermal oxide film, it has a lower defect density than the oxide film formed by the CVD method.
Since the thermal oxidation process is performed by rapid thermal oxidation, the silicon film is quickly heated to a predetermined oxidation temperature and oxidized.

Then, the upper oxide film forming the gate insulating film of the MOS transistor and the gate interlayer insulating film in the floating gate type memory element is formed under a mild oxidizing condition with a low defect density.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. Here, a case will be described as an example where an insulating film to be the gate insulating film 15a of the MOS transistor 2 shown in FIG. 2C is formed. First, as shown in FIG. 1A, a rapid thermal oxidation (hereinafter, referred to as R) is formed on the upper surface of a substrate 11 made of, for example, p-type silicon.
The lower oxide film 12 is formed by (hereinafter referred to as TO). Here, the substrate 11 is heated to 800 ° C.
Oxygen is supplied to the surface at a flow rate of 2 slm to thermally oxidize the upper layer of the substrate 11. Thereby, the lower oxide film 12 having a film thickness of 2 nm is formed.

Next, on the lower oxide film 12, for example, LP
(Low Presser) -CVD (Chemical Vapore Depositio
The nitride film 13 is formed by the n) method. Here, for example, 5 sccm of dichlorosilane (SiH ₂ Cl ₂ ) and 200 sccm of ammonia (NH ₃ ) are supplied to the reduced pressure atmosphere while maintaining the substrate 11 at 760 ° C. in the reduced pressure atmosphere of 10 Pa. As a result, the lower oxide film 1
A nitride film 13 having a film thickness of 4 nm is formed on the upper surface of 2.

Thereafter, for example, LP-C is formed on the nitride film 13.
A silicon film 14 made of amorphous silicon or polysilicon is formed by the VD method. Here, for example, while maintaining the substrate 11 at 580 ° C. in a reduced pressure atmosphere of 10 Pa, 10 sccm of dichlorosilane is supplied into the reduced pressure atmosphere. As a result, a silicon film 14 made of amorphous silicon and having a film thickness of 1.5 nm is formed on the upper surface of the nitride film 13.

Then, as shown in FIG. 1B, the silicon film 14 is thermally oxidized into silicon oxide by, for example, RTO, and an upper oxide film 14a made of silicon oxide is formed on the nitride film 13. Here, for example, oxygen is supplied to the surface of the silicon film 14 heated to 1100 ° C. at a flow rate of 2 slm to thermally oxidize the silicon film 14. This thermal oxidation is performed for 30 seconds, and the upper oxide film 14a having a film thickness of 2 nm is formed.
To form a film.

As described above, the lower oxide film 12 and the nitride film 1
ONO (Oxide, Nitrid) composed of 3 and the upper oxide film 14a.
An insulating film 15 having an (e, Oxide) structure is formed on the substrate 11.
In the method of forming the insulating film 15, the upper oxide film 14a is formed with a thermal history of 1100 ° C. for 30 seconds. On the other hand, when the upper layer oxide film is formed by thermally oxidizing the nitride film, heat treatment at 950 ° C. for 60 minutes at a high temperature is required. From this, it is understood that the method of forming the insulating film reduces the influence of heating on the underlying layer when forming the upper oxide film. Further, since the upper oxide film 14a is a thermal oxide film, it has a low defect density and an excellent film quality.

In the case of forming a MOS transistor using the insulating film 15, the following is done. First, FIG.
As shown in (1), for example, the gate electrode formation layer 21 is formed on the insulating film 15 formed as described above. The gate electrode formation layer 21 is a film having a polycide structure composed of, for example, lower polysilicon and upper tungsten silicide. Next, as shown in FIG. 2B, after the gate electrode formation layer 21 is etched to form the gate electrode 21a, the gate electrode 21a is used as a mask to diffuse impurities into the substrate 11 on both sides of the gate electrode 21a. To form the diffusion layer 11a. Then, the insulating film 1 is formed using the gate electrode 21a as a mask.
5 is etched to form a gate insulating film 15a under the gate electrode 21a.

After that, as shown in FIG. 2C, the substrate 1 is covered with the gate electrode 21a and the gate insulating film 15a.
An inter-layer insulating film 22 is formed on the surface 1. Next, a contact hole 23 is formed in the interlayer insulating film 22, and an electrode 24 made of aluminum is formed so as to fill the contact hole 23. Thereby, the MOS transistor 2 is formed.

In the MOS transistor 2 described above, the insulating film 15 having the ONO structure formed as described above is used as the gate insulating film 15a. Therefore, the gate insulating film 1
By the thermal oxidation process for forming 5a, the diffusion state of the p-type impurities in the substrate 11 and the film thickness of the lower oxide film 12 are maintained in the initial state without being changed, and the MOS transistor 2
The basic characteristics of are secured. Further, the insulating film 15a having the upper oxide film 14a of good film quality formed by the heat treatment prevents the generation of the leak current and secures the reliability of the MOS transistor 2.

Next, a method of forming the insulating film of the second embodiment will be described with reference to FIG. The insulating film forming method of the second embodiment is a method of oxynitriding the silicon film 14 formed on the nitride film 13 in the film forming method of the first embodiment.
In this case, first, the silicon film 1 similar to that of the first embodiment is used.
4 is thermally oxidized into silicon oxide as in the first embodiment, and then the silicon oxide is oxynitrided by, for example, RTO. At this time, for example, nitrous oxide or nitric oxide is supplied at a flow rate of 2 slm to the surface of the silicon oxide heated to 1100 ° C. to thermally oxynitride the silicon oxide. This thermal oxynitriding treatment is performed for 30 seconds to form an upper oxide film 14a made of silicon oxynitride with a film thickness of 2 nm.

As described above, the insulating film 15 having the ONO structure is formed on the substrate 11. According to the method of forming the insulating film 15, the upper oxide film 14a having a small defect density and excellent film quality as in the first embodiment can be formed on the underlying layer without being affected by heating. In addition, the insulating film 1
The MOS transistor having 5 has the same characteristics as those of the first embodiment.

The second embodiment does not limit the method of oxynitriding the silicon film 14 to the above. The upper oxide film 14a may be formed by thermally oxynitriding the silicon film 14 using nitrous oxide or nitrous oxide. In addition to the above, after the silicon film 14 is oxidized into silicon oxide, it is nitrided using ammonia, and then is nitrided using oxygen, dinitrogen monoxide, mononitrogen monoxide, or the like. Hydrogen may be released to give silicon oxynitride.

Next, a method of forming an insulating film according to the third embodiment will be described with reference to FIG. Here, a case will be described as an example where an insulating film to be the gate interlayer insulating film 35a between the floating gate and the control gate in the floating gate type storage element 4 shown in FIG. 4C is formed. As shown in FIG. 3A, the substrate 31 on which the insulating film is formed is formed by stacking a silicon substrate 311, a gate insulating film forming layer 312, and a floating gate forming layer 313 made of polysilicon in this order from the lower layer. .

When the insulating film is formed on the substrate 31 having the above structure, first, the lower oxide film 32 is formed on the upper surface of the substrate 31 by RTO. Here, oxygen is supplied to the surface of the floating gate forming layer 313 at a flow rate of 2 slm while heating the floating gate forming layer 313 in the upper layer portion of the substrate 31 to 900 ° C. to heat the surface layer of the floating gate forming layer 313. Oxidize. Thus, the lower oxide film 32 made of silicon oxide having a film thickness of 3 nm is formed.

Next, a nitride film 33 similar to the nitride film (13) of the first embodiment is formed on the lower oxide film 32.
Here, the nitride film 33 having a film thickness of 7 nm is formed by extending the film formation time under the same conditions as the method for forming the nitride film (13) of the first embodiment.

Then, a silicon film 34 similar to the silicon film (14) of the first embodiment is formed on the nitride film 33. Here, the film formation time is lengthened under the same conditions as the film formation method of the silicon film (14) of the first embodiment, and the film thickness is 2 nm.
A silicon film 34 made of amorphous silicon is formed. The silicon film 34 may be made of polysilicon.

Then, as shown in FIG. 3B, the silicon film 34 is thermally oxidized into silicon oxide in the same manner as in the first embodiment, and the silicon oxide film having a thickness of 3 nm is formed on the nitride film 33. The upper oxide film 34a is formed. Thus, the insulating film 35 including the lower oxide film 32, the nitride film 33, and the upper oxide film 34a is formed.

The insulating film 35 having the ONO structure as described above.
Are formed on the substrate 31. In the method of forming the insulating film 35, as in the first and second embodiments, it is possible to form the upper oxide film 34a having a small defect density and an excellent film quality on the underlying layer without the influence of heating. Become.

When a floating gate type storage element is formed using the insulating film 35, the following is performed. First, as shown in FIG. 4A, a control gate forming layer 41 made of polysilicon is formed on the insulating film 35 formed as described above. Next, as shown in FIG. 4B, the control gate forming layer 41, the insulating film 35, and the floating gate forming layer 313 are etched to form the control gate 41a, the gate interlayer insulating film 35a, and the floating gate 313a. Then, using the control gate 41a as a mask, impurities are injected into the silicon substrate 311 on both sides of the mask to diffuse the diffusion layer 3 into the silicon substrate 311.
11a is formed. Then, the control gate 41a
The gate insulating film formation layer 312 is etched by using as a mask to form a gate insulating film 312a.

Thereafter, as shown in FIG. 4C, an interlayer insulating film 42 is formed on the silicon substrate 311 so as to cover the control gate 41a, the gate interlayer insulating film 35a, the floating gate 313a and the gate insulating film 312a. . Then, similarly to the first embodiment, the contact hole 43 and the electrode 44 filling the inside thereof are formed. Thereby, the memory element 4 is formed.

In the memory element 4 described above, the insulating film 35 having the ONO structure formed as described above is used as the gate interlayer insulating film 35.
It is used as a. Therefore, the gate interlayer insulating film 35
The silicon substrate 3 is formed by the thermal oxidation treatment when forming a.
The p-type impurity in 11 is kept in the initial state without changing the diffusion state and the film thicknesses of the lower oxide film 32 and the gate insulating film forming layer 312, and the basic characteristics of the memory element 4 are secured.
In addition, the upper oxide film 3 of good film quality formed by heat treatment
The gate interlayer insulating film 35a having 4a prevents the generation of leak current, and ensures the reliability of the memory element 4.

Similar to the second embodiment, the insulating film 35 of the third embodiment can obtain the same effect as above by forming the upper oxide film 34a as silicon oxynitride.

The silicon film 1 shown in each of the above embodiments
The thermal oxidation methods of Nos. 4,34 and the reaction gas used in these methods are not limited to those in the above-mentioned examples, but include oxygen or an oxidizing gas composed of oxygen and nitrogen, or these gases and an inert gas. You may use the mixed gas etc. with hydrogen gas. Further, the processing temperature, processing time, and other processing conditions at the time of thermal oxidation are not limited to the above.

[0034]

As described above, according to the method for forming an insulating film of the present invention, the upper oxide film of the insulating film having the ONO structure is formed by thermally oxidizing the silicon film, so that the defect density is small. A good quality upper oxide film can be formed with a gentle thermal history. Therefore, it becomes possible to form an insulating film having an ONO structure with high reliability against voltage resistance without affecting the underlying substrate. Further, by performing the thermal oxidation of the silicon by the rapid thermal oxidation, it is possible to quickly heat the silicon film to the oxidation temperature, shorten the oxidation treatment time, and minimize the influence on the substrate. Become. Further, by using the insulating film as a gate insulating film of a MOS transistor or a gate interlayer insulating film of a floating gate type storage element, basic characteristics and reliability of the MOS transistor and the storage element can be secured.

[Brief description of drawings]

FIG. 1 is a first diagram illustrating first and second embodiments.

FIG. 2 is a second diagram illustrating the first and second embodiments.

FIG. 3 is a first diagram illustrating a third embodiment.

FIG. 4 is a second diagram illustrating the third embodiment.

[Explanation of symbols]

 2 MOS transistor 4 Storage element 11, 31 Substrate 12, 32 Lower oxide film 13, 33 Nitride film 14, 34 Silicon film 14a, 34a Upper oxide film 15, 35 Insulating film 15a Gate insulating film 35a Gate interlayer insulating film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 29/788 29/792

Claims (3)

[Claims] 1. A method for forming on a substrate an insulating film having a nitride film sandwiched between a lower oxide film and an upper oxide film, the method comprising forming the lower oxide film on the substrate, A step of forming a silicon film on the nitride film after forming the nitride film on the oxide film, and performing a thermal oxidation treatment of the silicon film to oxidize the silicon film to form the upper oxide film. And a step of forming the insulating film. 2. The method for forming an insulating film according to claim 1, wherein the thermal oxidation treatment of the silicon film is performed by rapid thermal oxidation. 3. The method for forming an insulating film according to claim 1, wherein the insulating film is formed as a gate insulating film of a MOS transistor or a gate interlayer insulating film of a floating gate type storage element. Method for forming insulating film.