JP3372030B2 - Method of forming thin film insulating film - Google Patents

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 extremely thin insulating film used as a gate insulating film of a MOS transistor, and more particularly to a method for forming a thin film insulating film containing a silicon oxynitride film at least partially. It is a thing.

[0002]

2. Description of the Related Art In MOS type integrated circuits, high integration and high density have been advanced year by year, and therefore transistor sizes have been miniaturized in the horizontal and vertical directions according to the scaling rule. As a result, the electric field strength applied to the gate oxide film is increased, and Fowler-Nordhei (FN; Fowler-Nordhei) is generated in addition to the direct tunnel current.
The flow of m) -type tunnel current through the gate oxide film causes stress to accumulate, leading to a decrease in 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 are subjected to direct tunneling and FN tunneling from the substrate to the gate electrode through the gate oxide film. As a result, traps 32 are generated in the gate oxide film, as shown in FIG. This trap 32
Is caused by the flow of the FN tunnel current.
As shown in (c), it gradually increases, causing local electric field increase and current density increase. When the trap reaches a certain value, it will be destroyed by 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 the 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 forming the gate electrode, diffuse in the gate oxide film during the heat treatment for activating the impurity ions implanted in the source / drain regions. The problem is that it then penetrates into the silicon substrate. This impurity diffusion causes problems such as fluctuations in the threshold voltage of the MOS transistor and deterioration of reliability of the gate oxide film. The problem of the penetration of impurities into the substrate and the problem of TDDB deterioration due to the FN tunnel current described above are due to the oxynitride film (Oxynitride film) formed on a part or the whole of the gate insulating film.
It is known that all of or part of the gate insulating film is oxynitrided in order to solve the above problems and improve the insulating property of the gate insulating film. Membrane technology is becoming widely used.

Such an oxynitride film is normally supplied with nitrous oxide (N ₂ O) gas or nitric oxide (NO) gas into a heating furnace to utilize the thermal reaction between a silicon substrate and oxygen and nitrogen. To form. As a heating furnace device, a resistance heating type furnace and a rapid heating type device using a halogen lamp or the like are known, and a film is formed using any one of the devices (Japanese Patent Laid-Open No. 10-209449). Japanese Laid-Open Patent Publication No.
-2237803 gazette etc.).

Since the transistor size has been reduced, the gate insulating film has recently been required to have a thickness of 5 nm or less, for example, about 4 nm. When 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 contained nitrogen and the nitrogen position in the insulating film are controlled. Is difficult to do. This is because in resistance heating type furnaces, there are many devices that adopt a method of introducing a wafer into a high temperature furnace from the state of being exposed to the atmosphere, and when it is introduced into the furnace, it reacts with oxygen in the atmosphere, This is because the formation of some "initial oxide film" is inevitable before entering the thermal reaction process. Further, the resistance heating type furnace has a structure for simultaneously processing a plurality of wafers (usually several tens of wafers), but it is extremely difficult to control all the nitrogen positions and the amounts of the wafers having different positions uniformly. Have difficulty.

From the viewpoint of controlling the initial reaction of oxynitriding, 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 a single-wafer type, there is no drawback of the above-mentioned plural-sheet processing. However, the results of the present inventors have recently revealed that the oxynitride film formed by the halogen lamp heating device has worse time-dependent dielectric breakdown (TDDB) characteristics than those formed by the 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 a graph which compared d). This is 100 μm x 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 until the dielectric breakdown was measured was measured and calibrated on the horizontal axis. As is clear from the figure, the RTP-NO film has a short dielectric breakdown time of one digit or more. In addition, it is difficult for a lamp heating furnace to flow steam or hydrogen chloride gas due to its device structure, and therefore, a humidified oxide film having excellent TDDB characteristics or a halogen-containing oxide film having excellent time zero dielectric breakdown (TZDB) characteristics should be formed. I can't.

[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 with a precisely controlled nitrogen content in an accurate film thickness. On the other hand, it is difficult to obtain an oxynitride film having excellent TDDB characteristics and TZDB characteristics by the forming method using the rapid heating method. Therefore, the object of the present invention is to
In addition to being able to control the initial reaction process with high accuracy, it is possible to form a gate oxynitride film having excellent TDDB characteristics and TZDB characteristics. This is to make it possible to form the gate insulating film with high reproducibility.

[0010]

In order to solve the above problems, according to the present invention, (1) an oxynitride film is formed on the surface of a silicon substrate in an oxidizing / nitriding atmosphere in a rapid heating furnace. Thin film insulation having the step 1) and (2) the 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 of forming a film is provided.

Preferably, the thermal oxynitridation in the first step (1) is performed at a temperature of 500 to 800 ° C., and the thermal oxidation or thermal oxynitridation in the step (2) is 800.
It is carried out at a temperature of ~ 1000 ° C. In addition, the total film thickness of the insulating film formed in the first (1) step and the second (2) step is 5 nm or less.

[0012]

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

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described with reference to the drawings.
The embodiment will be described. FIG. 1 shows the first embodiment of the present invention.
It is sectional drawing in order of a process which shows embodiment. Shown in Figure 1 (a)
So that the LOCOS method or the
Element isolation film 12 is selectively formed by the improved LOCOS method.
To do. For the following description, the element isolation region of FIG.
1 is a partially enlarged view of the active region separated by 12.
It shows in (b). This wafer is a rapid heating furnace, ie RT
It is attached to the P (Rapid Thermal Process) furnace. And
Thermal oxynitriding is performed.
Prior to heat treatment in a reducing atmosphere,
You can This heat treatment reacts with oxygen in the atmosphere
The 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, for example, with H ₂ Supply gas or HF
While heating from 700 ℃ to 1000 ℃
You can

After or without the above heat treatment, 50 in an oxynitriding atmosphere containing nitrogen and oxygen.
The silicon oxynitride film 13 having a film thickness of 1 to 4 nm is formed by heating at a temperature of 0 ° C. to 800 ° C. [FIG. 1 (c)]. At this time, the gas supplied into the furnace is NO gas or N ₂ O gas, mixed gas of NO and O ₂ , mixed gas of N ₂ O and O ₂ , 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 annealer can be advantageously used, but a heating furnace using an argon lamp or a MoSi block heater may be used.

Next, the wafer is mounted in a resistance heating furnace and heated to a temperature of 800 ° C. to 1000 ° C. in an oxidizing atmosphere to form a silicon oxide film 14 having a film thickness of 1 to 4 nm.
Form a thin insulating film with a total thickness of 5 nm or less [Fig. 1
(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. When using the dry method, 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 in these reaction gases.

Also, during the thermal oxidation process, HCl gas or Cl
_The halogen element may be doped in the 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 .

2A to 2D are cross-sectional views in order of the processes, showing a second embodiment of the present invention. First, as shown in FIG. 2A, the element isolation film 22 is selectively formed on the surface of the silicon substrate 21 by using the trench isolation method. For the following description, the active region isolated by the element isolation region 22 of FIG. 2A is partially enlarged and shown in FIG. This wafer is mounted in a rapid heating furnace for thermal oxynitriding. Since the oxynitride film forming process is the same as that of the first embodiment, the description thereof is omitted. As shown in FIG. 2C, the first silicon oxynitride film 23 is formed on the silicon substrate 21.
After forming the wafer, the wafer is mounted in a resistance heating furnace.

Then, the second silicon oxynitride film 24 having a thickness of 1 to 4 nm is formed by heating in an oxynitriding atmosphere to a temperature of 800 ° C. to 1000 ° C., and a thin film insulation having a total film thickness of 5 nm or less. A film is formed [FIG.2 (d)]. 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.
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, as in the case of the first embodiment, during the process of forming the oxynitride film, HCl gas or C
The halogen element may be doped in the silicon oxynitride film formed by supplying a gas containing a halogen element such as l ₂ gas.

[0019]

The preferred embodiments of the present invention will be described below. Example 1 First, after forming an element isolation film on the surface of a silicon substrate 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 surface of the silicon substrate is removed. It was removed by dilute hydrofluoric acid treatment. This wafer is loaded into 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 2 liters of O / min. By this treatment, an oxynitride film having a film thickness of about 1 nm was formed on the surface of the silicon substrate. Then, an oxidation treatment was performed in a resistance heating type diffusion apparatus in a dry oxygen atmosphere at 900 ° C. for 60 minutes (normal pressure) to form a silicon oxide film at the interface between the silicon substrate and the oxynitride film. The total film 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, a dilute hydrofluoric acid treatment was performed on the surface of the silicon substrate. This wafer was mounted in a halogen lamp heating furnace and 10 To was applied while flowing 2 liters of N ₂ O per minute.
Heat treatment was performed at 700 ° C. for 10 seconds under a pressure of rr.
By this treatment, an oxynitride film having a film thickness of about 1 nm was formed on the surface of the silicon substrate. After that, it was mounted in a resistance heating furnace and 850 ° C. while supplying a mixed gas of H ₂ O + O ₂ .
Oxidation treatment was performed for 60 minutes (normal pressure) to form a silicon oxide film on the interface between the silicon substrate and the oxynitride film. The total film 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, a dilute hydrofluoric acid treatment was performed on the surface of the silicon substrate. This wafer was mounted in a halogen lamp heating furnace and heat-treated at 950 ° C. for 20 seconds while flowing H ₂ gas. Then, heat treatment was performed at 700 ° C. for 20 seconds under a pressure of 10 Torr while flowing 2 liters of NO / min. By this treatment, 1.
A first silicon oxynitride film having a film thickness of about 5 nm was formed. After that, it is mounted in a resistance heating furnace and subjected to oxidation treatment at 900 ° C. for 60 minutes (atmospheric pressure) while supplying a mixed gas of NO ₂ + O ₂ , and at the interface between the silicon substrate and the first silicon oxynitride film. A second silicon oxynitride film was formed. The total film thickness of the formed thin film insulating film was about 4 nm.

[0022]

As described above, according to the method of forming a thin film insulating film of the present invention, an oxynitride film is first 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, it is possible to form an oxynitride film having a highly accurate film thickness and composition in the initial stage of forming an insulating film, and to form a thin insulating film having excellent TDDB characteristics and TZDB characteristics. Therefore, it is possible to provide an insulating film having high reproducibility and high reliability even if it is an extremely thin insulating film having a thickness of 4 nm or less.

[Brief description of drawings]

1A to 1C are cross-sectional views in order of the steps, showing a first embodiment of the present invention.

2A to 2D are cross-sectional views in order of the steps, showing a second embodiment of the present invention.

FIG. 3 is a potential distribution diagram for explaining the problems of the conventional technique.

FIG. 4 is a graph showing TDDB characteristics for explaining the problems of the conventional technique.

[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 electronic 32 traps

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/312 H01L 21/314 H01L 21/316 H01L 21/318 H01L 29/78

Claims (14)

(57) [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, the method for forming a thin film insulating film. 2. The method for forming a thin film insulating film according to claim 1, wherein heat treatment in a reducing atmosphere is performed in the rapid heating furnace prior to the step (1). 3. The method for forming a thin film insulating film according to claim 2, wherein the heat treatment is performed at a temperature of 700 to 1000 ° C. in an atmosphere of H ₂ gas or NH ₃ gas. 4. The method for forming a thin film insulating film according to claim 1, wherein the rapid heating furnace used in the step (1) is a halogen lamp heating furnace. 5. The oxidizing and nitriding atmosphere in the step (1) comprises NO or N ₂ O, a mixed gas of NO and O ₂ or a mixed gas of N ₂ O and O ₂ or NO in the furnace. N ₂
Mixed gas or N of a mixed gas or N ₂ O and N ₂ and
The method for forming a thin film insulating film according to claim 1, wherein the method is formed by supplying a mixed gas of O and a rare gas or a mixed gas of N ₂ O and a rare gas. 6. The oxynitridation in the first step is 500.
The method for forming a thin film insulating film according to claim 1, wherein the method is performed at a temperature of ˜800 ° C. 7. 7. The method of forming a thin film insulating film according to claim 1, wherein the thermal oxidation in the second step (2) is performed by a wet oxidation method or a dry oxidation method. . 8. The dry oxidation method is applied to the resistance heating furnace in an O ₂ gas, O ₃ gas, or O ₂ and O ₃ gas.
The method for forming a thin film insulating film according to claim 7, which is performed by supplying a mixed gas of 9. The oxidizing and nitriding atmosphere in the second step (2) contains NO gas, N ₂ O gas, NO ₂ gas, a mixed gas of NO and O ₂ or N ₂ O and O _{2 in the} furnace. A mixed gas of NO ₂ and O ₂ , a mixed gas of NO and N ₂ , a mixed gas of N ₂ O and N ₂ , a mixed gas of NO ₂ and N ₂ , or a mixed gas of NO and a rare gas Mixed gas or mixed gas of N ₂ O and rare gas or NO ₂
7. 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 a rare gas and the gas. 10. The thin film insulating film according to claim 1, wherein the thermal oxidation or thermal oxynitridation in the second 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 thermal oxidation or thermal oxynitridation in the second step (2) is performed in an atmosphere containing HCl gas or Cl ₂ gas. Method of forming thin insulating film. 13. HCl gas is used as CCl ₄ , C ₂ HCl.
13. The method for forming a thin film insulating film according to claim 12, wherein it is generated by using ₃ , CH ₂ Cl ₂ or C ₂ H ₃ Cl ₃ . 14. The total film thickness of the insulating film formed in the step (1) and the step (2) is not more than 5 nm. Method for forming thin film insulating film of.