JP2008041825A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a gate insulation film containing nitrogen where nitrogen concentration near the interface to a gate electrode at the opposite side is increased while suppressing an increase in nitrogen concentration near the interface to the silicon substrate of a gate insulation film. <P>SOLUTION: A step for forming the gate insulation film 12 comprises: a nitride film formation step for forming an island-shaped SiN layer 22a on the silicon substrate 11; an oxide film formation step for forming an SiO<SB>2</SB>layer 21 at the interface at least between the silicon substrate 11 and the island-shaped SiN layer 22a using a wet oxidation method; and a nitride film growth step for growing SiN with the island-shaped SiN layer 22a as a seed, and forming a laminar SiN layer 22 for covering the surface of at least the SiO<SB>2</SB>layer 21. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which a nitrogen-containing gate insulating film is formed on a silicon substrate.

  With the spread of mobile products and the like, there is a demand for lower power consumption of semiconductor devices such as DRAM (Dynamic Random Access Memory). In order to reduce the power consumption of a semiconductor device, a technique is adopted in which the gate insulating film is thinned by introducing nitrogen into the gate insulating film of a MOSFET (Metal Insulator Semiconductor Field Effect Transistor). Nitrogen introduced into the gate insulating film improves the dielectric constant of the gate insulating film, prevents the diffusion of impurities through the film, and improves the characteristics of the MOSFET.

By the way, when introducing nitrogen into the gate insulating film, it is necessary to suppress diffusion of nitrogen to the interface with the silicon substrate. This is because when nitrogen accumulates in the vicinity of the interface with the silicon substrate, the accumulated nitrogen forms an impurity level, which causes various characteristics deterioration of the MOSFET, such as fluctuations and variations in threshold voltage _Vth and reduced carrier mobility. To cause. In order to prevent accumulation of nitrogen in the vicinity of the interface with the silicon substrate, for example, a SiO ₂ layer is formed on the silicon substrate, and a SiN layer is formed on the SiO ₂ layer using a CVD (Chemical Vapor Deposition) method or the like 2 A layered gate insulating film is used.

For example, Patent Document 1 discloses a gate insulating film having a two-layer structure including a SiO ₂ layer and a SiN layer sequentially stacked on a silicon substrate.
JP 2002-203961 A

  By the way, in forming the SiN layer, it is considered to use an atomic layer deposition (ALD) method for the purpose of improving the reliability of the gate insulating film. In forming the SiN layer using the ALD method, a SiN layer having an atomic level is formed by forming a silicon monoatomic layer and nitriding the formed silicon monoatomic layer, and forming the SiN layer. By repeating the film, a SiN layer having a desired thickness is formed. In the ALD method, a layer having a desired film quality can be formed because a layer having a desired thickness is formed by repeating film formation at the atomic level.

However, when the SiN layer is formed on the SiO ₂ layer using the ALD method, the nitrogen concentration in the SiN layer is significantly lower than that in the stoichiometric composition, and the nitrogen concentration is sufficiently increased. There was a problem that could not be. In order to obtain a MOSFET having good characteristics, it is essential to sufficiently increase the nitrogen concentration in the gate insulating film near the interface with the gate electrode.

  In view of the above, the present invention is a method of manufacturing a semiconductor device in which a nitrogen-containing gate insulating film is formed on a silicon substrate, and the reverse is achieved while suppressing an increase in nitrogen concentration in the vicinity of the interface between the gate insulating film and the silicon substrate. An object of the present invention is to provide a method of manufacturing a semiconductor device capable of forming a MOSFET having good characteristics by increasing the nitrogen concentration in the vicinity of the interface with the side gate electrode.

In order to achieve the above object, a method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device for forming a nitrogen-containing gate insulating film,
Forming the nitrogen-containing gate insulating film comprises:
A nitride film forming step of forming an island-shaped silicon nitride film on the silicon substrate;
An oxide film forming step of forming a silicon oxide film at least at the interface between the silicon substrate and the island-shaped silicon nitride film using a wet oxidation method;
Growing a silicon nitride by using the island-shaped silicon nitride film as a seed, and forming a layered silicon nitride film covering at least the surface of the silicon oxide film; and
Have

  According to the present invention, silicon nitride is grown using the island-shaped silicon nitride film formed on the silicon substrate as a seed. Therefore, unlike the case of growing on the silicon oxide film, a high nitrogen concentration close to the stoichiometric composition is obtained. A silicon nitride film can be formed. In addition, since the silicon oxide film is formed at the interface between the silicon substrate and the island-shaped silicon nitride film by wet oxidation, the reaction is likely to proceed along the interface, silicon oxide is formed between the silicon substrate and the island-shaped silicon nitride film. The film can be reliably interposed with a small thickness.

  In a preferred aspect of the present invention, the nitride film forming step includes sequentially depositing a silicon monoatomic layer and nitriding the silicon monoatomic layer. An island-like silicon nitride film having good film quality can be formed. In this case, preferably, the nitride film forming step repeatedly includes a step of depositing the silicon monoatomic layer and a step of nitriding the silicon monoatomic layer. By adjusting the number of repetitions, the thickness of the island-like silicon nitride film can be controlled.

  In a preferred aspect of the present invention, the step of depositing the silicon monoatomic layer is performed by setting the substrate temperature to less than 500 ° C. or the deposition time to less than 70 seconds. By preventing the deposition of the silicon nitride film on the silicon substrate from being saturated, an island-shaped silicon nitride film can be formed.

  In a preferred aspect of the present invention, the nitride film growth step repeats a step of depositing a silicon monoatomic layer and a step of nitriding the silicon monoatomic layer. A layered silicon nitride film having good film quality can be formed.

  In a preferred aspect of the present invention, the step of forming the nitrogen-containing gate insulating film further includes the step of nitriding the surface of the layered silicon nitride film subsequent to the nitride film growth step. The nitrogen concentration in the vicinity of the interface with the gate electrode in the gate insulating film can be further increased. The nitridation of the surface of the layered silicon nitride film may be performed by, for example, a plasma nitriding method.

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of a semiconductor device manufactured by a method for manufacturing a semiconductor device according to an embodiment of the present invention. The semiconductor device 10 includes a silicon substrate 11, a gate insulating film 12 formed on the silicon substrate 11, and a gate electrode 13 formed on the gate insulating film 12. The gate insulating film 12 is composed of a SiO ₂ layer 21 and a SiN layer 22 which are sequentially stacked, and the gate electrode 13 is composed of polysilicon into which boron is introduced.

  FIG. 2 is a flowchart showing a procedure for forming the gate insulating film 12 of FIG. FIGS. 3A to 3D are cross-sectional views showing cross sections of the semiconductor device 10 in steps S11 to S14 of FIG. Using a known method, an STI (Shallow Trench Isolation) type element isolation structure is formed on the surface portion of the silicon substrate 11 to partition the element formation region, and then the surface of the silicon substrate 11 is cleaned. Subsequently, as shown in FIG. 3A, an island-shaped SiN layer 22a is formed on the silicon substrate 11 in the element formation region by using the ALD method (step S11).

FIG. 4 is a flowchart showing step S11 in detail. When forming the island-shaped SiN layer 22a by the ALD method, first, a silicon monoatomic layer is formed (step S21). When forming a silicon monoatomic layer, for example, dichlorosilane gas is used as a precursor and is thermally decomposed. Next, the purge with N ₂ gas is sufficiently performed, and the precursor in the reaction chamber is completely removed (step S22). Subsequently, the silicon monoatomic layer is nitrided by plasma nitridation using NH ₃ plasma to form an SiN layer having an atomic level thickness (step S23). Further, the purge with N ₂ gas is sufficiently performed to completely remove the NH ₃ plasma in the reaction chamber (step S24). These steps S21 to S24 are repeated.

  By the way, when the silicon monoatomic layer is formed, when the substrate temperature is set to 500 ° C. or higher, for example, 550 ° C. and 70 seconds elapse, the silicon deposition on the silicon substrate 11 is saturated, and the silicon substrate 11 is completely formed. A silicon monoatomic layer having a thickness of about 0.2 nm is formed. When the silicon monoatomic layer that completely covers the silicon substrate 11 is formed, the island-like SiN layer 22 a can no longer be formed on the silicon substrate 11.

  Accordingly, in step S21, the substrate temperature is set to less than 500 ° C. or the deposition time is set to less than 70 seconds so that the silicon deposition on the silicon substrate 11 is not saturated. When the substrate temperature is lowered or the deposition time is shortened, decomposition of the precursor and adsorption of silicon onto the silicon substrate 11 can be suppressed. In this embodiment, for example, the substrate temperature is set to 550 ° C., and the deposition time is set to 50 seconds. In step S23, for example, the substrate temperature is set to 550 ° C., and the deposition time is set to 140 seconds.

Returning to FIG. 2, following step S11, wet oxidation of the surface of the silicon substrate 11 is performed. In the wet oxidation, since the reaction easily proceeds along the interface, the surface of the silicon substrate 11 exposed from the island-shaped SiN layer 22a is oxidized and the silicon substrate 11 is aligned along the interface between the silicon substrate 11 and the SiN layer 22a. The surface of is oxidized to form the SiO ₂ layer 21 shown in FIG. 3B (step S12). By such wet oxidation, the SiO ₂ layer 21 can be formed thinner than when the SiO ₂ layer 21 is formed directly on the silicon substrate 11.

Subsequently, by using the ALD method, SiN is grown using the island-shaped SiN layer 22a as a seed, and a layered SiN layer 22 covering the entire surface of the SiO ₂ layer 21 is formed as shown in FIG. S13). The SiO ₂ layer 21 and the SiN layer 22 constitute the gate insulating film 12.

  Step S13 is performed according to the procedure of FIG. 4, but the conditions of the substrate temperature and the deposition time are different from those of step S11. In step S21, the substrate temperature is set to 500 ° C. or higher and the deposition time is set to 70 seconds or longer so that silicon deposition on the silicon substrate 11 is saturated. In this embodiment, for example, the substrate temperature is set to 550 ° C., and the deposition time is set to 70 seconds. In step S23, for example, the substrate temperature is set to 550 ° C., and the processing time is set to 140 seconds.

In step S13, SiN is grown using the island-shaped SiN layer 22a formed on the silicon substrate 11 as a seed. Therefore, unlike the case where SiN is grown on the SiO ₂ layer, the nitrogen concentration in the SiN layer 22 is increased. , Close to the stoichiometric composition. Further, since SiN is grown using the island-like SiN layer 22a as a seed, the SiN layer 22 having small variations in film thickness and the like can be formed as compared with the case where SiN is grown on the SiO ₂ layer.

  Further, as shown in FIG. 3D, plasma nitridation is performed on the gate insulating film 12, and nitrogen is introduced into the surface portion of the gate insulating film 12 (step S14). Thereby, the nitrogen concentration in the surface portion of the gate insulating film 12 can be further increased.

According to the manufacturing method of the present embodiment, SiN is grown using the island-shaped SiN layer 22a formed on the silicon substrate 11 as a seed. Therefore, compared with the conventional manufacturing method in which SiN is grown on the SiO ₂ layer, The nitrogen concentration in the SiN layer 22 can be increased to approach the nitrogen concentration at the stoichiometric composition. Further, by performing plasma nitridation after the formation of the SiN layer 22, the nitrogen concentration in the surface portion of the gate insulating film 12 can be further increased.

The reaction proceeds easily wet oxidation along the interface, so to form a SiO ₂ layer 21 along the interface between the silicon substrate 11 and the island-like SiN layer 22a, SiO ₂ between the silicon substrate 11 and the SiN layer 22a The layer 21 can be reliably interposed. As a result, the nitrogen concentration and the impurity level in the vicinity of the interface between the gate insulating film 12 and the silicon substrate 11 can be sufficiently suppressed.

The reaction proceeds easily wet oxidation along the interface, so along the interface between the silicon substrate 11 and the island-like SiN layer 22a to form the SiO ₂ layer 21, directly to form a SiO ₂ layer on a silicon substrate 11 Compared to the conventional manufacturing method, the thickness of the SiO ₂ layer 21 can be reduced. Thereby, the dielectric constant of the gate insulating film 12 can be effectively increased.

  In the manufacturing method of the present embodiment, the gate insulating film 12 having an equivalent oxide thickness (EOT) of 2 nm, for example, can be formed while suppressing diffusion of impurities through the film and leakage current.

By the way, as a method for forming the gate insulating film 12 that increases the nitrogen concentration in the vicinity of the interface with the gate electrode 13 while suppressing the increase in the nitrogen concentration in the vicinity of the interface with the silicon substrate 11, a thermal oxidation method or the like has been conventionally used. A method is known in which a SiO ₂ layer is formed on a silicon substrate 11 and then a SiN layer is formed on the SiO ₂ layer using a CVD method or the like. As a method for suppressing the impurity level in the vicinity of the interface with the silicon substrate 11, after forming a SiN layer on the silicon substrate 11, oxidation treatment is performed, and oxidized species are introduced from the surface of the SiN layer to form the silicon substrate. There is a method in which the impurity level is extinguished by diffusing it at the interface with H.

By the way, in order to realize the EOT of about 2 nm required in recent DRAMs, it is necessary to suppress the film thickness of the SiO ₂ layer to about 1 nm. However, with the former method, it is not easy to suppress the thickness of the SiO ₂ layer to about 1 nm. Further, in the latter method, since the oxidized species react in the SiN layer or on the surface side thereof, it is not easy to diffuse efficiently to the interface with the silicon substrate.

  On the other hand, in the manufacturing method of the embodiment, the nitrogen concentration near the interface with the gate electrode 13 can be effectively increased while suppressing the nitrogen concentration and impurity level near the interface with the silicon substrate 11. I can do it. Accordingly, the manufacturing method of the embodiment is adopted.

  As described above, the present invention has been described based on the preferred embodiments. However, the method for manufacturing a semiconductor device according to the present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made from the configuration of the above-described embodiment. Semiconductor device manufacturing methods that have been modified and changed are also included in the scope of the present invention.

It is sectional drawing which shows the structure of the semiconductor device formed with the manufacturing method of the semiconductor device which concerns on one Embodiment of this invention. 3 is a flowchart sequentially illustrating a procedure for forming the gate insulating film of FIG. 1. FIGS. 3A to 3D are cross-sectional views showing cross sections of the semiconductor device in steps S11 to S14 of FIG. It is a flowchart which shows the procedure of step S11, S13 of FIG. 2 in detail.

Explanation of symbols

10: Semiconductor device 11: Silicon substrate 12: Gate insulating film 13: Gate electrode 21: SiO ₂ layer 22: SiN layer 22a: Island-like SiN layer

Claims (6)

A method of manufacturing a semiconductor device for forming a nitrogen-containing gate insulating film,
Forming the nitrogen-containing gate insulating film comprises:
A nitride film forming step of forming an island-shaped silicon nitride film on the silicon substrate;
An oxide film forming step of forming a silicon oxide film at least at the interface between the silicon substrate and the island-shaped silicon nitride film using a wet oxidation method;
Growing a silicon nitride by using the island-shaped silicon nitride film as a seed, and forming a layered silicon nitride film covering at least the surface of the silicon oxide film; and
A method for manufacturing a semiconductor device, comprising:   The method for manufacturing a semiconductor device according to claim 1, wherein the nitride film forming step includes a step of depositing a silicon monoatomic layer and a step of nitriding the silicon monoatomic layer.   The method of manufacturing a semiconductor device according to claim 2, wherein the nitride film forming step includes a step of depositing the silicon monoatomic layer and a step of nitriding the silicon monoatomic layer.   4. The method of manufacturing a semiconductor device according to claim 2, wherein the step of depositing the silicon monoatomic layer is performed by setting a substrate temperature to less than 500 ° C. or a deposition time to less than 70 seconds.   5. The method of manufacturing a semiconductor device according to claim 1, wherein the nitride film growth step repeatedly includes a step of depositing a silicon monoatomic layer and a step of nitriding the silicon monoatomic layer.   6. The semiconductor according to claim 1, wherein the step of forming the nitrogen-containing gate insulating film further includes a step of nitriding the surface of the layered silicon nitride film subsequent to the nitride film growth step. Device manufacturing method.

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