JP2001110807A - Method for forming thin insulation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an extremely thin oxide-nitride film with improved film thickness and composition accuracy and improved TDDB and TZDB characteristics being used for a gate insulation film. SOLUTION: A formed silicon substrate of an element separation film 12 is fitted to a rapid thermal process(RTP) furnace and is heated at 500-800 deg.C within oxidizing/nitriding atmosphere, thus forming an oxide-nitride film 13 on a silicon substrate 11 (c). After that, the substrate is fitted to a resistance heating furnace and is heated at 800-1000 deg.C, thus forming a silicon oxide film 14 by the wet oxidation method or the dry oxidation method (d).

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 ultra-thin insulating film used for a gate insulating film of a MOS transistor, and more particularly to a method of forming a thin-film insulating film including a silicon oxynitride film at least partially. Things.

[0002]

2. Description of the Related Art In a MOS type integrated circuit, a high integration and a high density are being promoted year by year, and accordingly, a transistor size has been miniaturized in a horizontal direction and a vertical direction according to a scaling rule. As a result, the intensity of the electric field applied to the gate oxide film increases, and in addition to the direct tunnel current, Fowler-Nordhei (FN)
m) -type tunnel current flows through the gate oxide film, causing stress to accumulate and reduce the reliability of the gate oxide film.

FIG. 3 is a potential distribution diagram for explaining the situation. Now, assuming that a positive voltage is applied to the gate electrode with respect to the substrate, as shown in FIG. 3A, the electrons 31 undergo direct tunneling and FN tunneling from the substrate to the gate electrode through the gate oxide film. As a result, as shown in FIG. 3B, traps 32 are generated in the gate oxide film. This trap 32
FIG. 3 shows that the FN tunnel current flows.
As shown in (c), the current gradually increases, causing a local increase in the electric field and an increase in the current density. When the trap reaches a certain value, it is destroyed by an avalanche or heat. This is,
This is a fatigue phenomenon called TDDB (Time Dependent Dielectric Breakdown).

Another problem that has become apparent due to the extremely thin gate oxide film is penetration of impurities doped into the gate electrode into the substrate. This is because impurities with a large diffusion coefficient, such as boron, doped in the polysilicon constituting the gate electrode diffuse in the gate oxide film during heat treatment for activating the impurity ions implanted into the source / drain regions. And enter the silicon substrate. Due to the impurity diffusion, problems such as a change in the threshold voltage of the MOS transistor and a decrease in the reliability of the gate oxide film occur. The problem of the penetration of the impurity into the substrate and the problem of the TDDB deterioration caused by the FN tunnel current described above can be solved by forming a part or the whole of the gate insulating film as an oxynitride film (Oxynit).
ride), it is known that, in recent years, all or part of the gate insulating film is oxynitrided in order to solve the above problem and improve the insulating property of the gate insulating film. Techniques for forming a film have been frequently used.

[0005] Such an oxynitride film usually uses a thermal reaction between a silicon substrate and oxygen and nitrogen by supplying nitrous oxide (N ₂ O) gas or nitric oxide (NO) gas into a heating furnace. Formed. As a heating furnace apparatus, a resistance heating furnace and a rapid heating apparatus using a halogen lamp or the like are known, and a film is formed by using any of the apparatuses (Japanese Patent Laid-Open No. 10-209449). No., JP-A-10
223,783).

In recent years, as the transistor size has been reduced, it has recently been required to form the gate insulating film to a thickness of 5 nm or less, for example, about 4 nm. In the case of forming such a thin oxynitride film, it is difficult to control the initial stage of the thermal oxynitridation reaction in a normal resistance heating type furnace, and the amount of nitrogen contained and the position of nitrogen in the insulating film are controlled. It is difficult to do. This is because many resistance heating furnaces adopt a system that introduces a wafer into a high-temperature furnace from a state exposed to the atmosphere, and reacts with oxygen in the atmosphere when introduced into the furnace. This is because some "initial oxide film" formation is unavoidable before entering the thermal reaction process. Further, the resistance heating type furnace has a structure in which a plurality of wafers (usually several tens) are simultaneously processed, but it is extremely difficult to control all the nitrogen positions and the amounts of the wafers having different positions to be equal. Have difficulty.

In terms of controlling the oxynitriding initial reaction, it is advantageous to use a halogen lamp heating device. Because the atmosphere can be controlled from room temperature, the initial oxide film can be considerably suppressed, and since it is of a single-wafer type, there is no disadvantage of the plural-sheet processing as described above. However, experiments by the present inventors have recently revealed that the oxynitride film formed by the halogen lamp heating device has poorer dielectric breakdown (TDDB) characteristics over time than that formed by a resistance heating furnace.

FIG. 4 shows TDDB characteristics (Qb) of an oxynitride film (RTP-NO) formed in a halogen lamp heating furnace and an oxynitride film (Furnace-NO) formed in a resistance heating furnace.
It is the graph which compared d). This is 100 μm × 1
A current of 0.1 A / cm ² was passed through the gate oxynitride film of the accumulation-type pMOS having a size of 00 μm, and the time required for dielectric breakdown was measured. As is clear from the figure, the RTP-NO film has a short breakdown time by one or more digits. Further, it is difficult for the lamp heating furnace to flow steam or hydrogen chloride gas due to the structure of the lamp heating furnace. Therefore, it is necessary to form a humidified oxide film having excellent TDDB characteristics and a halogen-containing oxide film having excellent time zero dielectric breakdown (TZDB) characteristics. Can not.

[0009]

As described above,
In the method of forming an oxynitride film using a resistance heating furnace, it is difficult to control the oxynitridation reaction in the initial stage, and it is difficult to form an oxynitride film having a precisely controlled nitrogen content to an accurate thickness. On the other hand, in the formation method using the rapid heating method, it was difficult to obtain an oxynitride film having excellent TDDB characteristics and TZDB characteristics. Therefore, the object of the present invention is to
In addition to being able to accurately control the initial reaction process, it is also possible to form a gate oxynitride film having excellent TDDB characteristics and TZDB characteristics. The purpose is to form a gate insulating film with high reproducibility.

[0010]

According to the present invention, there is provided a method for forming an oxynitride film on a surface of a silicon substrate in an oxidizing / nitriding atmosphere in a rapid heating furnace. (1) a second step of forming a silicon oxide film or a silicon oxynitride film on the surface of a silicon substrate in an oxidizing or oxidizing / nitriding atmosphere in a resistance heating furnace; A method for forming a film is provided.

Preferably, the thermal oxynitriding in the first step (1) is performed at a temperature of 500 to 800 ° C., and the thermal oxidation or thermal oxynitriding in the second step (800) is performed at 800 ° C.
It is performed at a temperature of 〜1000 ° C. The total thickness of the insulating films formed in the first and second steps is 5 nm or less.

[0012]

In the present invention, a nitrogen-containing layer having high oxidation resistance is first formed by a rapid heating furnace. By doing so, an initial oxide film,
It is easy to suppress the entrapment oxide film, and it is possible to maintain high film thickness controllability and nitrogen distribution controllability when a thin film is formed. Further, in general, an oxide film and an oxynitride film formed in a rapid heating furnace have lower film quality and lower reliability than an oxide film formed in a resistance heating furnace, but in the present invention, a part of the gate insulating film is used. The film quality can be improved by forming in a resistance heating furnace. Furthermore, in a rapid heating furnace in which the use of a metal jig is basically unavoidable, it is difficult to flow a halogen-based gas. However, according to the method of the present invention, a gate insulating film containing nitrogen and containing a halogen element is formed. It is also possible to create.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment will be described. FIG. 1 shows a first embodiment of the present invention.
It is sectional drawing of a process order which shows embodiment. As shown in FIG.
LOCOS method or silicon substrate 11
Forming element isolation film 12 selectively by improved LOCOS method
I do. For the following description, the element isolation region of FIG.
12 is a partially enlarged view of the active region separated by
(B). The wafer is placed in a rapid heating furnace, ie, RT
Install in a P (Rapid Thermal Process) furnace. And
Thermal oxynitridation is performed.
Prior to heat treatment in a reducing atmosphere,
Can be. By this heat treatment, it reacts with oxygen in the atmosphere
Thin film formed on the surface of the silicon substrate
The initial oxide film (natural oxide film) can be removed.
This heat treatment is performed by, for example, H _Two Supply gas or HF
While heating to a temperature of 700 ° C to 1000 ° C
Can be.

After or without the heat treatment described above, under an oxynitriding atmosphere containing nitrogen and oxygen,
The silicon oxynitride film 13 having a thickness of 1 to 4 nm is formed by heating to a temperature of 0 ° C. to 800 ° C. (FIG. 1C). At this time, the gas supplied into the furnace is NO gas, N ₂ O gas, a mixed gas of NO and O ₂ , a mixed gas of N ₂ O and O ₂ , a mixed gas of NO and N ₂ , or N ₂ O
Either a mixed gas of N ₂ and N ₂ , a mixed gas of NO and a rare gas, or a mixed gas of N ₂ O and a rare gas can be used. As the rapid heating furnace, a halogen lamp anneal can be advantageously used, but a heating furnace using an argon lamp or a MoSi block heater may be used.

Next, the wafer is set in a resistance heating furnace and heated in an oxidizing atmosphere to a temperature of 800 ° C. to 1000 ° C. to form a silicon oxide film 14 having a thickness of 1 to 4 nm.
A thin insulating film having a total thickness of 5 nm or less is formed [FIG.
(D)]. This thermal oxidation is performed by a wet oxidation method or a dry oxidation method. When the wet method is used, H ₂ O gas or a mixed gas of H ₂ O and O ₂ can be used. O ₂ ,
O ₃ or a mixed gas thereof can be supplied.
Further, at this time, an inert gas such as Ar or N ₂ can be mixed into these reaction gases.

During the thermal oxidation step, HCl gas or Cl gas is used.
_A halogen element may be doped into a silicon oxide film formed by supplying a gas containing a halogen element such as _two gases. When supplying HCl gas, CCl ₄ , C ₂ HCl ₃ , CH ₂ Cl ₂ or C ₂
HCl gas may be generated using H ₃ Cl ₃ .

FIG. 2 is a sectional view showing a second embodiment of the present invention in the order of steps. First, as shown in FIG. 2A, an element isolation film 22 is selectively formed on the surface of a silicon substrate 21 by using a trench isolation method. For the following description, FIG. 2B is a partially enlarged view of the active region separated by the element isolation region 22 in FIG. This wafer is mounted in a rapid heating furnace to perform thermal oxynitriding. The process of forming this oxynitride film is the same as that of the first embodiment, and a description thereof will be omitted. As shown in FIG. 2C, a first silicon oxynitride film 23 is formed on a silicon substrate 21.
Is formed, the wafer is mounted in a resistance heating furnace.

In a oxynitriding atmosphere, a second silicon oxynitride film 24 having a thickness of 1 to 4 nm is formed by heating to a temperature of 800 ° C. to 1000 ° C. A film is formed (FIG. 2D). At this time, the gas supplied into the furnace is NO gas, N ₂ O gas, NO ₂ gas, a mixed gas of NO and O ₂ , or N ₂ O gas.
Mixed gas of NO and O ₂ , mixed gas of NO ₂ and O ₂ , mixed gas of NO and N ₂ , mixed gas of N ₂ O and N ₂ , mixed gas of NO ₂ and N ₂ , or NO Either a mixed gas of a rare gas, a mixed gas of N ₂ O and a rare gas, or a mixed gas of NO ₂ and a rare gas can be used. Then, the concentration of N (nitrogen) in the second silicon oxynitride film 24 can be made lower than that of the first silicon oxynitride film 23. Further, similarly to the first embodiment, during the process of forming the oxynitride film, HCl gas or C
A halogen element may be doped into a silicon oxynitride film formed by supplying a gas containing a halogen element such as l ₂ gas.

[0019]

Next, a preferred embodiment of the present invention will be described. [Example 1] First, after forming an element isolation film on the silicon substrate surface by the LOCOS method, the silicon nitride film used in the LOCOS method is removed with phosphoric acid, and the silicon oxide film on the silicon substrate surface is further removed. It was removed by dilute hydrofluoric acid treatment. This wafer is set in a halogen lamp heating furnace and N
Heat treatment was performed at 700 ° C. for 10 seconds under a pressure of 10 Torr while flowing O at 2 liters per minute. By this processing, an oxynitride film having a thickness of about 1 nm was formed on the surface of the silicon substrate. Thereafter, an oxidation treatment was performed in a dry oxygen atmosphere at 900 ° C. for 60 minutes (normal pressure) in a resistance heating type diffusion device to form a silicon oxide film at the interface between the silicon substrate and the oxynitride film. The total thickness of the formed thin film insulating film was about 4 nm.

Example 2 After forming a trench type element isolation film on the surface of a silicon substrate, dilute hydrofluoric acid treatment was performed on the surface of the silicon substrate. 10To while flowing 2 liters per minute of N ₂ O to the wafer by mounting a halogen lamp heating furnace
Heat treatment was performed at 700 ° C. for 10 seconds under a pressure of rr.
By this processing, an oxynitride film having a thickness of about 1 nm was formed on the surface of the silicon substrate. After that, it is mounted in a resistance heating furnace and supplied with a mixed gas of H ₂ O + O ₂ at 850 ° C.
Oxidation treatment was performed for 60 minutes (at normal pressure) to form a silicon oxide film on the interface between the silicon substrate and the oxynitride film. The total thickness of the formed thin film insulating film was about 4 nm.

Example 3 After forming a trench type element isolation film on the surface of a silicon substrate, dilute hydrofluoric acid treatment was performed on the surface of the silicon substrate. This wafer was mounted on a halogen lamp heating furnace and heat-treated at 950 ° C. for 20 seconds while flowing H ₂ gas. Thereafter, heat treatment was performed at 700 ° C. for 20 seconds under a pressure of 10 Torr while flowing 2 liters of NO per minute. By this processing, 1.
A first silicon oxynitride film having a thickness of about 5 nm was formed. Thereafter, the substrate is mounted in a resistance heating furnace and oxidized at 900 ° C. for 60 minutes (normal pressure) while supplying a mixed gas of NO ₂ + O ₂ , so that the interface between the silicon substrate and the first silicon oxynitride film is formed. A second silicon oxynitride film was formed. The total thickness of the formed thin film insulating film was about 4 nm.

[0022]

As described above, according to the method for forming a thin film insulating film of the present invention, first, an oxynitride film is formed in a rapid heating furnace, and then an oxide film or an oxynitride film is formed in a resistance heating furnace. Since it is formed, an oxynitride film having a high-precision film thickness and composition can be formed in an initial stage of forming the insulating film, and a thin insulating film having excellent TDDB characteristics and TZDB characteristics can be formed. This makes it possible to provide an insulating film with high reproducibility and high reliability even with an extremely thin insulating film of 4 nm or less.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention in the order of steps.

FIG. 2 is a sectional view showing a second embodiment of the present invention in the order of steps.

FIG. 3 is a potential distribution diagram for explaining a problem of the related art.

FIG. 4 is a graph showing TDDB characteristics for explaining a problem of the related art.

[Explanation of symbols]

 11, 21 Silicon substrate 12, 22 Element isolation film 13 Silicon oxynitride film 14 Silicon oxide film 23 First silicon oxynitride film 24 Second silicon oxynitride film 31 Electron 32 trap

Claims (14)

[Claims] (1) a first step of forming an oxynitride film on a surface of a silicon substrate in an oxidizing / nitriding atmosphere in a rapid heating furnace; and (2) oxidizing or oxidizing in a resistance heating furnace. A second step of forming a silicon oxide film or a silicon oxynitride film on the surface of the silicon substrate in a nitriding atmosphere, a method of forming a thin film insulating film. 2. The method according to claim 1, wherein a heat treatment is performed in a reducing atmosphere in the rapid heating furnace prior to the step (1). 3. The method according to claim _2, wherein the heat treatment is performed in an H ₂ gas or NH ₃ gas atmosphere at a temperature of 700 to 1000 ° C. 4. The method for forming a thin film insulating film according to claim 1, wherein the rapid heating furnace used in the first step is a halogen lamp heating furnace. 5. The oxidizing / nitriding atmosphere in the step (1) contains NO, N ₂ O, a mixed gas of NO and O ₂ , a mixed gas of N ₂ O and O ₂ , or a mixed gas of NO and N ₂ O in a furnace. N ₂
Mixed gas of N ₂ O and N ₂ or N ₂ O and N ₂
Method of forming a thin film insulating film according to any one of claims 1 to 4, characterized in that it is formed by supplying O and mixed gas of the mixed gas or N ₂ O and rare gas and a rare gas. 6. The oxynitridation in the step (1) is 500
The method according to claim 1, wherein the method is performed at a temperature of from about 800 ° C. to about 800 ° C. 6. 7. The method according to claim 1, wherein the thermal oxidation in the step (2) is performed by a wet oxidation method or a dry oxidation method. . 8. The method according to claim 8, wherein the dry oxidation method is performed by adding O ₂ gas or O ₃ gas or O ₂ and O ₃ gas into the resistance heating furnace.
8. The method for forming a thin film insulating film according to claim 7, wherein the method is performed by supplying a mixed gas with 9. The oxidizing / nitriding atmosphere in the step (2) contains NO gas, N ₂ O gas, NO ₂ gas, a mixed gas of NO and O ₂ , N ₂ O and O _{2 in a} furnace. Mixed gas of NO ₂ and O ₂ , mixed gas of NO and N ₂ , mixed gas of N ₂ O and N ₂ , mixed gas of NO ₂ and N ₂ , or mixed gas of NO and rare gas Mixed gas or mixed gas of N ₂ O and rare gas or NO ₂
The method for forming a thin-film insulating film according to claim 1, wherein the thin-film insulating film is formed by supplying a mixed gas of hydrogen and a rare gas. 10. The thin film insulating film according to claim 1, wherein the thermal oxidation or thermal oxynitridation in the step (2) is performed at a temperature of 800 to 1000 ° C. Forming method. 11. The thin film insulating film according to claim 1, wherein the thermal oxidation or thermal oxynitridation in the step (2) is performed in an atmosphere containing a halogen element. Forming method. 12. The method according to claim 1, wherein the thermal oxidation or thermal oxynitridation in the step (2) is performed in an atmosphere containing HCl gas or Cl ₂ gas. A method for forming a thin insulating film. 13. HCl gas is CCl ₄ , C ₂ HCl
_3, CH ₂ Cl ₂ or C ₂ H ₃ forming a thin film insulator according to claim 12, wherein the generating using Cl _3. 14. The method according to claim 1, wherein the total thickness of the insulating films formed in the first and second steps is 5 nm or less. Method of forming a thin film insulating film.