JP2008288392A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a two-layer gate insulating film of silicon oxide nitride film/silicon nitride film, with a low interface level density. <P>SOLUTION: A first gate insulating film 10 comprising a silicon oxide film 11 or a silicon oxide nitride film is formed on the surface of a semiconductor substrate 1, and then the first gate insulating film 10 is subjected to a plasma nitriding process. Then, the first gate insulating film 10 is thermally treated in the nitrogen oxide gas or a gas containing nitrogen oxide (first thermal treatment process). Then, the first gate insulating film 10 is subjected to a second thermal treatment process in which it is thermally treated in the inactive gas or under vacuum at a temperature higher than the first thermal treatment temperature. After that, on the first gate insulating film 10, a second gate insulating film 12 comprising a silicon nitride film is deposited by a vapor-phase deposition method. The second thermal treatment process allows the first gate insulating film to be more tight, preventing diffusion of active species generated at deposition of the second gate insulating film 12, not to increase its interface level. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device using a gate insulating film composed of a two-layer film in which a silicon nitride film is laminated on a silicon oxynitride film, and more particularly to forming a gate insulating film having a low interface state density with a silicon substrate. The present invention relates to a method for manufacturing a semiconductor device.

  With the miniaturization of MIS (metal insulator semiconductor) type semiconductor devices, for example, field effect transistors, the gate insulating film along the scaling side is being made thinner.

Conventionally, a silicon oxide film (SiO ₂ film) or a silicon oxynitride film (SiON film) has been used as a gate insulating film. Since these silicon oxide films and silicon oxynitride films have excellent compatibility with silicon crystals, the interface state density with the silicon substrate is low, and they have excellent electrical characteristics as gate insulating films.

  However, when the equivalent oxide film thickness is reduced to about 1 nm, in the gate insulating film made of silicon oxide film or silicon oxynitride film, the tunnel current between the gate electrode and the silicon substrate increases, and the leakage current of the gate electrode increases. As a result, the operating characteristics of the transistor deteriorate.

  Therefore, an attempt has been made to use a silicon nitride film having a high dielectric constant for the gate insulating film instead of the silicon oxide film or the silicon oxynitride film. Since the gate insulating film made of such a high dielectric material has a large actual film thickness even if the equivalent film thickness is small, it is possible to effectively suppress the leakage current caused by the tunnel current.

  However, when the silicon nitride film is formed directly on the semiconductor substrate, interface states and fixed charges are generated at a high density at the interface between the silicon nitride film and the semiconductor substrate. These interface states and fixed charges lower the electron mobility of the semiconductor layer immediately below the interface, thereby degrading the operating characteristics of the semiconductor device, and causing aging fluctuations in characteristics during the stress test. For this reason, it is not preferable to form a silicon nitride film directly on a semiconductor substrate and use it as a gate insulating film.

  Two layers in which a silicon nitride film is laminated on a silicon oxide film or a silicon oxynitride film in order to prevent generation of interface states and fixed charges found in the silicon nitride film and to suppress a leakage current caused by a tunnel current A gate insulating film having a structure is used. In this two-layer gate insulating film, a high dielectric constant silicon nitride film is used as the upper layer, so that the equivalent film thickness is reduced. Therefore, the actual film thickness of the gate insulating film is increased and the leakage current is reduced. As a result, a reduction in leakage current and a low-density interface state of the underlying silicon oxide film are realized at the same time.

  However, if the lower layer of the gate insulating film is composed of a silicon oxide film, the dielectric constant of the silicon oxide film is lower than that of the silicon nitride film. Therefore, to reduce the equivalent film thickness sufficiently, the thickness of the silicon oxide film must be reduced. This must increase the leakage current. For this reason, it is difficult to reduce the leakage current with a gate insulating film having a small equivalent film thickness.

  An increase in leakage current due to the thinning of the silicon oxide film constituting the lower layer can be suppressed by forming the lower layer of the gate insulating film with a silicon oxynitride film having a high dielectric constant. The silicon oxynitride film has a larger dielectric constant than the silicon oxide film. For this reason, even if a thick silicon oxynitride film is used, the equivalent film thickness of the gate insulating film can be reduced, so that the leakage current can be reduced. On the other hand, the interface state and fixed charge generated between the silicon oxynitride film and the silicon substrate are relatively small, and the deterioration of the operating characteristics of the semiconductor device is small.

  In particular, the nitrogen concentration distribution of the silicon oxynitride film is low in the vicinity of the interface with the silicon substrate, and uniformly high in the upper layer other than that, so that there are few interface states and fixed charges, and the equivalent film thickness is thin. It can be a silicon oxynitride film. A conventional method for manufacturing a gate insulating film composed of two layers of silicon oxynitride film / silicon nitride film will be described below. (For example, see unpublished patent application, Japanese Patent Application No. 2006-011603.)

  FIG. 7 is a cross-sectional view of a conventional gate insulating film manufacturing process, showing a cross section of a gate insulating film portion of a field effect transistor.

  Referring to FIG. 7A, in a conventional gate insulating film manufacturing process, first, a semiconductor substrate 1 made of silicon is thermally oxidized to form a silicon oxide film 11 as a first gate insulating film 10 on the semiconductor substrate 1. To do. Next, the surface is exposed to the nitrogen plasma 20 or downstream thereof to nitride the surface of the silicon oxide film 11, thereby forming a nitride layer 11 a on the surface of the silicon oxide film 11.

  Next, referring to FIG. 7B, a silicon nitride film 103 (second gate insulating film) is deposited on the first gate insulating film 10 by using a CVD method (chemical vapor deposition method).

  Next, referring to FIG. 7C, heat treatment in a reduced pressure oxygen atmosphere and heat treatment in nitrogen gas are performed to form a gate insulating film composed of two layers of silicon oxynitride film / silicon nitride film.

  In the above-described conventional gate insulating film manufacturing process, the silicon oxide film 11 is plasma-nitrided, and then a silicon nitride film is deposited. The silicon nitride film is usually deposited by a CVD method using a source gas containing ammonia. At that time, an active species in which a nitrogen atom and a hydrogen atom are bonded or an active species containing a hydrogen atom is generated. These active species easily pass through the silicon oxide film 11 and reach the interface with the semiconductor substrate, and form high-density interface states and fixed charges at the interface between the silicon oxide film 11 and the semiconductor substrate. As a result, the operating characteristics of the transistor deteriorate.

  As a high dielectric constant material constituting the upper layer of the gate insulating film, instead of a silicon nitride film, a high dielectric constant metal oxide film (oxide film of Al, Hf, Zr or the like) or an oxide silicate film of these metals is used. Methods for depositing are known. (For example, refer to Patent Document 1). In this gate insulating film, the problem that active species generated during the deposition of the silicon nitride film pass through the silicon oxide film or the silicon oxynitride film to form interface states and fixed charges is avoided.

  FIG. 8 is a sectional view of another conventional gate insulating film manufacturing process, showing a gate insulating film having a two-layer structure in which a high dielectric film made of a metal oxide or a metal silicate is deposited on a silicon oxynitride film. Yes.

  Referring to FIG. 8A, first, a silicon oxide film 11 is formed on a semiconductor substrate 1 made of silicon by thermal oxidation.

  Then, referring to FIG. 8B, the surface nitride layer 11a is formed on the surface of the silicon oxide film 11 by being exposed to the nitrogen plasma 20 (plasma nitriding treatment).

  Next, referring to FIG. 8C, heat treatment is performed in NO gas. By this treatment, nitridation proceeds to a deep layer of the silicon oxide film 11, and a deep nitride layer 11b is formed at a deeper position than the surface nitride layer 11a previously formed on the surface of the silicon oxide film 11. As a result, the silicon oxide film 11 becomes a silicon oxynitride film having a nitrogen concentration distribution in which the nitrogen concentrations of the surface nitride layer 11a and the deep nitride layer 11b are superimposed. The deepest portion of the silicon oxide film 11, that is, the silicon oxide film 11 near the semiconductor substrate 1 located under the deep nitride film 11b is a low-concentration nitride layer 11c having a low nitrogen concentration.

  Next, referring to FIG. 8D, heat treatment is performed in nitrogen gas to form a first gate insulating film 10 including the heat-treated shallow nitride layer 11a, deep nitride layer 11b, and low-concentration nitride layer 11c.

  8E, a high dielectric film 101 made of a metal oxide film or a metal silicate film is deposited on the first gate insulating film 10, and the first gate insulating film 10 and the high dielectric A gate insulating film 102 composed of two layers with the body film 101 is manufactured.

  In the manufacture of the gate insulating film including the metal oxide film described above, the silicon oxide film 11 is subjected to nitridation twice of plasma nitriding and heat treatment in NO gas, and nitrided to a deep position of the silicon oxide film 11 at a high concentration. To do. For this reason, a large portion of the first gate insulating film 10 is uniformly nitrogen-doped silicon oxynitride film having a high nitrogen concentration, and the first gate insulating film 10 having a large equivalent film thickness is obtained. Such a silicon oxynitride film having a high nitrogen concentration suppresses permeation of boron into the first gate insulating film 10.

  As described above, in the manufacture of the gate insulating film 102 including the metal oxide film or the like, the first gate insulating film 10 constituting the lower layer is nitrided after the silicon oxide film 11 and before the high dielectric film 101 is deposited. Heat treatment in nitrogen gas. This heat treatment in nitrogen gas improves the transconductance of the semiconductor device.

  Furthermore, in manufacturing the gate insulating film including the metal oxide film described above, a metal oxide film or a metal silicate film is deposited on the first gate insulating film. The metal oxide film or the metal silicate film is deposited by a CVD method or a plasma CVD method using a source gas containing C and N. Nevertheless, in the deposition of the metal oxide film or the like, since the source gas contains only a small amount of ammonia, active species that can easily pass through the silicon oxide film 11, for example, active species in which nitrogen and hydrogen are combined. Very little occurs. Therefore, the interface state between the silicon oxide film and the semiconductor substrate and the density of fixed charges are kept sufficiently low. For this reason, an excellent gate insulating film is formed.

  On the other hand, the source gas for depositing the metal oxide film or the like is not preferable because it contains a substance unsuitable for the manufacturing process of the semiconductor device. For this reason, it is desired to use a silicon nitride film that does not contain such a substance and has a relatively high dielectric constant as the high dielectric film. However, the silicon nitride film is often deposited by a CVD method using a source gas containing ammonia, and active species that easily pass through the silicon oxide film or the silicon nitride film during the deposition, for example, nitrogen and hydrogen are combined. A large amount of active species is produced. As a result, high-density interface states and high-density fixed charges are formed, and the operating characteristics of the semiconductor device are deteriorated. This situation is the same in the PCVD method (plasma vapor deposition method) using a source gas containing nitrogen.

  In order to prevent the transmission of these active species, the silicon oxide film (or silicon nitride film) having a small dielectric constant must be thickened. As a result, the equivalent film thickness cannot be reduced in the gate insulating film having a two-layer structure of silicon oxide film / silicon nitride film.

For this reason, manufacturing a gate insulating film with a reduced equivalent film thickness by a conventional gate insulating film manufacturing method in which a silicon nitride film is deposited on a silicon oxide film or silicon oxynitride film is effective in reducing leakage current and reducing the interface. It was difficult from the viewpoint of suppressing the level and fixed charge.
International Publication WO2004 / 097925 Pamphlet

  As described above, in the conventional method for manufacturing a gate insulating film having a two-layer structure, a silicon oxynitride film formed by nitriding a silicon oxide film by plasma nitriding and heat treatment in a nitrogen oxide gas is used as a lower layer, and the lower layer is formed on the lower layer. A silicon nitride film was deposited using chemical vapor deposition or plasma vapor deposition.

  However, in this manufacturing method, the active species generated during the deposition of the silicon nitride film permeate the lower silicon oxide film or silicon oxynitride film and reach the interface between the silicon oxide film and the semiconductor substrate, so And high density of fixed charges. For this reason, it is difficult to realize excellent operating characteristics in a semiconductor device using such a gate insulating film.

  A two-layer structure in which a silicon oxide film is nitrided by plasma nitriding and nitrogen oxide gas heat treatment to form a silicon oxynitride film, followed by further nitrogen heat treatment, and depositing metal oxide or metal silicate thereon. A method of forming the gate insulating film is disclosed. In the deposition of these metal oxides and metal silicates, the generation of active species that pass through the silicon oxynitride film and form interface states or fixed charges during the deposition is small, and the operating characteristics of the semiconductor device are rarely degraded.

  However, it is not disclosed to deposit a silicon nitride film on such a silicon oxynitride film. Since the deposition of silicon nitride film generates a large amount of active species that form interface states and fixed charges, unlike the deposition of metal oxide films or metal silicate films, high density interface states and fixed charges may be formed. There is.

  The present invention relates to a method for manufacturing a gate insulating film in which a silicon nitride film is stacked on a silicon oxynitride film, and forms a gate insulating film having a low interface state and a fixed charge density at the interface between the silicon substrate and the gate insulating film. An object of the present invention is to provide a method for manufacturing a semiconductor device.

In order to solve the above-described problems, a method of manufacturing a semiconductor device according to the present invention includes a step of forming a first gate insulating film made of a silicon oxide film or a silicon oxynitride film on a surface of a semiconductor substrate, and plasma forming the first gate insulating film. A step of nitriding, a first heat treatment step of heat-treating the first gate insulating film in a nitrogen oxide gas or a gas containing nitrogen oxide, and then the first gate insulating film in an inert gas or vacuum A second heat treatment step in which heat treatment is performed at a temperature higher than the first heat treatment temperature, and then a step in which a second gate insulating film made of a silicon nitride film is deposited on the first gate insulating film using a vapor deposition method. In the present invention, first, a silicon oxide film (or silicon oxynitride film) is subjected to a plasma nitridation process and a heat treatment (first heat treatment) in a nitrided oxide gas, and silicon acid doped with nitrogen at a high concentration deeply. A nitride film is formed. This silicon oxynitride film is nitrided deeply to a high concentration and has a low equivalent film thickness because of its high dielectric constant.

  Further, a second heat treatment is performed on the silicon oxynitride film in an inert gas or vacuum. By this second heat treatment, damage caused in the silicon oxynitride film during plasma nitriding is recovered, and the silicon oxynitride film becomes dense and the density increases.

  In the present invention, the silicon oxynitride film thus densified is used as a first gate insulating film, and a silicon nitride film is deposited thereon as a second gate insulating film. Then, a gate insulating film is formed by laminating a second gate insulating film made of a silicon nitride film on the first gate insulating film made of a silicon oxynitride film.

  That is, the silicon oxynitride film of the present invention is densified by a second heat treatment performed in an inert gas atmosphere or an atmosphere containing an inert gas prior to the deposition of the silicon nitride film (second gate insulating film). ing. The inventor of the present invention has clarified through experiments that the silicon oxynitride film densified by the second heat treatment suppresses diffusion in the active silicon oxynitride film generated during the deposition of the silicon nitride film. did. According to this experiment, even when a silicon nitride film is deposited on the silicon oxynitride film that has undergone the second heat treatment, the interface state at the interface between the silicon oxynitride film and the semiconductor substrate and the density increase of the fixed charges are slight. Does not affect the operating characteristics of the semiconductor device.

  Therefore, the semiconductor device using the gate insulating film manufactured by the method of the present invention has the same operating characteristics as the semiconductor device using the gate insulating film made of a silicon oxide film or a silicon oxynitride film. Further, since the equivalent film thickness of the gate insulating film is smaller than that of the conventional silicon oxide film or silicon oxynitride film, the leakage current is smaller than that of the conventional semiconductor device using these as the gate insulating film.

  In the present invention, the silicon nitride film can be deposited using a chemical vapor deposition method (CVD method), for example, a CVD method in which ammonia is contained in a source gas. Thereby, a silicon nitride film with few defects can be deposited. Alternatively, high-speed deposition can be performed using a plasma enhanced chemical vapor deposition method (PCVD method) using a source gas containing nitrogen.

  In the second heat treatment of the present invention, the silicon oxide film is formed to such an extent that the active species generated during the deposition of the silicon nitride film does not form a high density of interface states or the like that is allowed by diffusing in the silicon oxynitride film. The nitride film must be densified and densified.

  The second heat treatment is performed in an inert gas (for example, nitrogen gas) or in a vacuum. In this atmosphere, active species that easily pass through the silicon oxynitride film are not generated, and a new interface state is not formed. In addition, new nitridation of the silicon oxynitride film is negligibly small. On the other hand, interface states and fixed charges are reduced.

  Further, the second heat treatment is performed at a high temperature at which the silicon oxynitride film can be sufficiently densified (that is, densified). Therefore, it must be at least higher than the processing temperature of the first heat treatment for promoting nitrogen doping, for example, 900 ° C. or higher, more preferably 1000 ° C. or higher. The silicon oxynitride film increases in density at 900 ° C. or higher, and is increased by pulse heat treatment of about 10 seconds at 1000 ° C. or higher, so that it can be easily matched with the manufacturing process of a semiconductor device using lamp annealing or the like. Can do. On the other hand, in order to prevent an increase in the thickness of the silicon oxynitride film due to the progress of oxidation, the second heat treatment temperature should be low, for example, preferably 1100 ° C. or lower.

  The first gate insulating film of the present invention is preferably a silicon oxide film formed by thermally oxidizing a silicon semiconductor substrate in terms of excellent bond matching at the semiconductor substrate interface. In addition, an insulating film having a low interface state density, for example, a silicon oxynitride film deposited by a CVD method or a silicon oxynitride film formed by oxidizing a silicon nitride film formed on the surface of a silicon semiconductor substrate is used. You can also.

  The first gate insulating film is doped with nitrogen by a plasma nitridation process and a first heat treatment performed prior to the second heat treatment.

  In the plasma nitriding treatment, the first gate insulating film is exposed to a plasma containing nitrogen to nitride the surface layer of the first gate insulating film, and the surface layer of the first gate insulating film is formed from a silicon nitride film or a high-concentration silicon oxynitride film. Into a nitride layer (hereinafter referred to as “surface nitride layer”).

  The first heat treatment performed next is performed in a nitrogen oxide gas or a gas containing nitrogen oxide, nitrides a layer below the surface nitride layer, and nitrides below the surface nitride layer (hereinafter referred to as “deep nitride layer”). .). This heat treatment is performed so that the deep nitride layer and the surface nitride layer overlap with each other, and a low-concentration nitride layer with a small nitrogen dose is formed between the deep nitride layer and the semiconductor substrate. It is preferable to select conditions. By overlapping the nitride layers in this manner, a uniform and high concentration nitrogen concentration distribution can be formed from the surface of the first gate insulating film to a deep position. For this reason, the equivalent film thickness of the first gate insulating film can be reduced. Further, by providing the low concentration nitride layer in the vicinity of the semiconductor substrate, the interface state or fixed charge density caused by nitrogen can be kept low.

  According to the present invention, a gate insulating film having a low interface state density and a fixed charge density with a semiconductor substrate and a reduced equivalent film thickness can be formed. A semiconductor device with low current can be manufactured.

  In the first embodiment of the present invention, a silicon oxide film formed by thermal oxidation is nitrided to form a silicon oxynitride film, and then a heat treatment is performed to form a gate insulating film having a densified silicon oxynitride film as a lower layer. The present invention relates to a method for manufacturing a semiconductor device.

  FIG. 1 is a manufacturing process sectional view of a first embodiment of the present invention, and shows a section of a MIS transistor.

  In the first embodiment, first, referring to FIG. 1A, an element isolation band 2 for insulatingly isolating a transistor formation region is formed on the upper surface of a semiconductor substrate 1 made of silicon. The element isolation band 2 is formed by filling a trench with an insulator such as silicon oxide, silicon nitride or polysilicon, or a combination thereof. Alternatively, it is formed by a LOCOS oxide film formed on the surface.

  Next, referring to FIG. 1B, a two-layer gate insulating film 3 is formed on the upper surface of the semiconductor substrate 1. Hereinafter, the manufacturing process of the gate insulating film 3 will be described.

  FIG. 2 is a cross-sectional view of a gate insulating film manufacturing process according to the first embodiment of the present invention, showing a manufacturing process of a gate insulating film having a two-layer structure.

  Referring to FIG. 3A, the upper surface of the semiconductor substrate 1 is thermally oxidized to form a silicon oxide film 11 having a thickness of, for example, 0.8 nm as the first gate insulating film 10 on the transistor formation region. Thermal oxidation is normal thermal oxidation of silicon, and can be formed by heat treatment in dry oxygen or water vapor or a mixed atmosphere of these and an inert gas. During the thermal oxidation of silicon, a gas containing nitrogen (N) is simultaneously supplied to form a silicon oxynitride film, and this silicon oxynitride film can be used in place of the silicon oxide film 11.

  Next, referring to FIG. 3B, the semiconductor substrate 1 is placed on a substrate holder (not shown) in the plasma nitriding apparatus, and the upper surface of the silicon oxide film 11 is exposed to the nitrogen plasma 20 for 10 seconds. . As a result, the surface of the silicon oxide film 11 is nitrided, and the surface of the silicon oxide film 11 is converted into a surface nitride layer 11a having a high nitrogen concentration. This plasma nitriding treatment was performed at room temperature and was performed without intentionally cooling or heating the semiconductor substrate 1.

  Next, referring to FIG. 3C, the semiconductor substrate 1 is heat-treated (first heat treatment) in an atmosphere containing nitrogen oxide, and a portion deeper than the surface nitride layer 11a of the silicon oxide film 11 is nitrided and deepened. The nitride layer 11b is converted. The heat treatment conditions of the deep nitrided layer 11b are controlled so that the maximum nitrogen concentration is deeper than the surface nitrided layer 11a.

The first heat treatment is performed in an atmosphere composed of nitrogen oxides such as NO, N ₂ O or N _x O _y or a mixed gas of these with an inert gas such as N ₂ or Ar, for example, a heat treatment temperature of 800 ° C. to 900 ° C. This is done for 10 seconds. Under this heat treatment condition, a low-concentration nitride layer 11c having a low nitrogen concentration is formed at the bottom of the deep nitride layer 11b. Since the nitrogen concentration of the low-concentration nitride layer 11 c is low, only a few interface states and fixed charges are formed at the interface with the semiconductor substrate 1.

Next, referring to FIG. 3D, the semiconductor substrate 1 is heat-treated in nitrogen gas (N ₂ gas) (second heat treatment). The second heat treatment was performed at a temperature of 1000 ° C. for 10 seconds. By this second heat treatment, the first gate insulating film 10 having a multilayer structure of the surface nitrided layer 11a, the deep nitrided layer 11b, and the low-concentration nitrided layer 11c becomes dense, and the density of the first gate insulating film 10 increases. Even when the second heat treatment was performed in a vacuum or in an Ar atmosphere, the increase in density was the same. In the second heat treatment, which is a heat treatment in nitrogen, the nitrogen concentration distribution in the first gate insulating film 10 is not substantially changed.

  Next, referring to FIG. 3E, a silicon nitride film (second gate insulating film) is formed on the first gate insulating film 10 by a CVD method (chemical vapor deposition method) using a source gas containing ammonia. Deposited. Instead of the CVD method, an ALD method or a PCVD method using a source gas containing ammonia, or a PCVD method using a nitrogen-containing source gas can be used.

  In these deposition methods, a large amount of active species that pass through the silicon oxide film or the silicon oxynitride film that has not been subjected to the second heat treatment and forms interface states or fixed charges on the surface of the semiconductor substrate are generated. Nevertheless, in the first embodiment, the interface state or fixed charge formed at the interface between the first gate insulating film 10 and the semiconductor substrate is negligible. Through this process, the gate insulating film 3 having a two-layer structure in which a second gate insulating film made of a silicon nitride film is stacked on the first gate insulating film 10 made of a silicon oxynitride film is formed.

  Returning to FIG. 1 again, referring to FIG. 1C, a polysilicon film is deposited on the gate insulating film 3 and patterned to form the gate electrode 4. Thereafter, if necessary, a low concentration impurity region (lightly doped region of LDD structure) is formed by ion implantation using the gate electrode 4 as a mask.

  Next, referring to FIG. 1D, a silicon oxide film, a silicon nitride film, or a laminated film thereof is deposited on the entire surface of the semiconductor substrate 1 and etched back, whereby the sides made of an insulating film are formed on both sides of the gate electrode 4. Wall 5 was formed. At this time, the gate insulating film 3 extending to the outside of the sidewall 5 was also etched back to expose the surface of the semiconductor substrate outside the sidewall 5.

  Next, referring to FIG. 1E, ions are implanted using the gate electrode 4 and the sidewalls 5 as a mask to form source / drain regions 5. Thereafter, activation heat treatment is performed to manufacture a MIS type semiconductor device (MIS transistor).

  FIG. 3 is a distribution diagram of nitrogen concentration in the first gate insulating film of the first embodiment of the present invention. Nitrogen in the depth direction from the surface of the first gate insulating film measured by SIMS (secondary ion mass spectrometer). Represents the concentration distribution. Note that the horizontal axis of FIG. 3 represents the depth from the surface of the first gate insulating film.

  Referring to FIG. 3, there is a layer having a high nitrogen concentration (position indicated by a in FIG. 3) near the surface of the first gate insulating film, and the nitrogen concentration decreases as the depth increases from there. The layer having a high nitrogen concentration near the surface is generated by the surface nitrided layer 11a formed mainly by plasma nitriding.

  A small peak of nitrogen concentration is observed near the depth of about 0.6 nm from the surface (position indicated by b in FIG. 3), where the decrease in nitrogen concentration is gentle, that is, close to a uniform nitrogen concentration distribution. Yes. This peak is formed by the deep nitride layer 11b formed by the first heat treatment performed in the nitrogen oxide. This reveals that this peak causes high concentration of nitriding to the deep layer of the first gate insulating film.

  The first gate insulating film layer located deeper than the deep nitride layer 11b and in the vicinity of the substrate interface has a low nitrogen concentration. Therefore, the nitrogen concentration in the vicinity of the surface of the semiconductor substrate 1 is also kept low. Therefore, there are few bonds between nitrogen and nitrogen and hydrogen.

  Thus, the first gate insulating film of the first embodiment has a high dielectric constant because it is nitrided to a high concentration deeply, and has a thin equivalent film thickness. On the other hand, since the nitrogen concentration is kept low in the vicinity of the semiconductor substrate 1, the operating characteristics of the semiconductor device do not deteriorate.

  FIG. 4 is a diagram showing the film thickness dependence of the leakage current according to the first embodiment of the present invention. The leakage current when the gate insulating film of the present invention is used is the same as the leakage current when the conventional gate insulating film is used. Comparing. The vertical axis in FIG. 4 represents the logarithm of the leak current normalized by an arbitrary leak current value. Further, the horizontal axis of FIG. 4 indicates the converted film thickness of the gate insulating film converted to the silicon oxide film.

  In FIG. 4, a straight line A represents a leakage current of a gate insulating film having a two-layer structure of silicon oxynitride film / silicon nitride film formed by the same process as in the first embodiment. A straight line B represents a leakage current of a conventional gate insulating film having a two-layer structure of silicon oxide film / silicon nitride film. The straight line C represents the leakage current of the gate insulating film of the conventional silicon oxynitride film manufactured by the process shown in FIG. Note that the gate insulating film indicated by the straight line B is manufactured by using a manufacturing process conventionally used for manufacturing a conventional gate insulating film made of a thick silicon oxide film / silicon nitride film. In addition, the thickness of the silicon nitride film is constant, and a gate insulating film is manufactured in which the thicknesses of the silicon oxynitride film (straight line a), the silicon oxide film (straight line) and the silicon oxynitride film (straight line c) are changed, Gate insulating films with different equivalent film thicknesses were manufactured.

  Referring to FIG. 4, the logarithm of the leakage current decreases linearly with the increase of the equivalent film thickness. With the same equivalent film thickness, the leakage current is the largest in the one-layer gate insulating film made of the silicon oxynitride film shown by the straight line c, and then made of the silicon oxide film / silicon oxynitride film shown by the straight line b. The gate insulating film having the two-layer structure is small, and the gate insulating film made of the silicon oxynitride film / silicon nitride film manufactured by the first embodiment of the present invention shown in the straight line C is the smallest.

  The equivalent film thickness of the gate insulating film in which the leakage current is I shown in FIG. 4 is t0 in the gate insulating film of the present invention consisting of the silicon oxynitride film / silicon nitride film shown in the straight line A, and the silicon oxide film shown in the straight line B The conventional gate insulating film made of a silicon oxynitride film has a thickness t1 that is 0.18 nm thicker than t0, and the conventional gate insulating film that has a silicon oxynitride film shown by a straight line c has a thickness t2 that is 0.36 nm thicker than t0.

  Thus, compared to the silicon oxynitride film indicated by the straight line C, the equivalent film thickness that gives the same leakage current is thinner by 0.36 nm in the gate insulating film of the present invention. For this reason, the effective film thickness of the gate current can be reduced without increasing the leakage current. In contrast, a conventional gate insulating film made of a silicon oxide film / silicon nitride film can only be made thinner by 0.18 nm than a silicon oxynitride film. Thus, the gate insulating film of the present invention has a small leakage current even when the equivalent film thickness is reduced.

  FIG. 5 is a diagram showing the film thickness dependence of the interface state density according to the first embodiment of the present invention. In FIG. 5, the straight line A, the straight line B, and the straight line C correspond to the gate insulating films indicated by the straight line A, the straight line B, and the straight line C in FIG.

  Referring to FIG. 5, the interface state density increases as the converted film thickness decreases. A conventional gate insulating film having a two-layer structure of silicon oxide film / silicon nitride film indicated by a straight line B has the lowest interface state density. On the other hand, the interface order density of the silicon oxynitride film / silicon nitride film of the present invention indicated by a straight line A is not significantly different from a gate insulating film made of a silicon oxynitride film indicated by a straight line c.

  FIG. 6 is a diagram illustrating the characteristics of the gate insulating film according to the first embodiment of the present invention, and compares the characteristics of the gate insulating film according to the first embodiment of the present invention with various conventional gate insulating films. In FIG. 6, Comparative Examples 1 and 2 are gate insulating films manufactured by a conventional manufacturing method. The first embodiment (A) represents the gate insulating film manufactured according to the first embodiment of the present invention described above.

Referring to FIG. 6, Comparative Example 1 (C) is a conventional gate insulating film made of a silicon oxynitride film (SiON) indicated by a straight line C in FIGS. 4 and 5, and Comparative Example 2 (B) is FIG. And a conventional gate insulating film having a two-layer structure of silicon oxide film (SiO ₂ ) / silicon nitride film (Si ₃ N ₄ ) indicated by straight lines in FIG.

  In Comparative Example 1 made of SiON, the equivalent film thickness is slightly reduced, but the leakage current is still large. Although the interface state density is slightly inferior to that of a normal gate insulating film made of a silicon oxide film, the interface state density is sufficiently low in practical use.

Referring to Comparative Example 2 (C), the gate insulating film made of SiO ₂ / Si ₃ N ₄ has a leakage current smaller than that of Comparative Example 1, but is still insufficient for practical use. This is because it is difficult to reduce the equivalent film thickness because it includes a low dielectric constant SiO ₂ film. Note that the interface state density of Comparative Example 2 in this film thickness range is low. However, if the SiO ₂ film is thinned until the equivalent film thickness becomes 1 nm or less, the interface order density increases. Therefore, it is not preferable to use a gate insulating film having this structure with an equivalent film thickness of 1 nm or less.

  On the other hand, the gate insulating film of the first embodiment (A) of the present invention has the interface state density of the same level as that of Comparative Example 1 (C) in which SiON is used as the gate insulating film, which is practically sufficient. Can be used. Moreover, the equivalent film thickness is sufficiently thin. Therefore, the gate insulating film of the first embodiment of the present invention has excellent leakage current characteristics and a sufficiently low interface state density for practical use.

The invention described above includes the invention described in the following supplementary notes.
(Appendix 1) A step of forming a first gate insulating film made of a silicon oxide film or a silicon oxynitride film on a semiconductor substrate surface;
Plasma nitriding the first gate insulating film;
Next, a first heat treatment step of heat-treating the first gate insulating film in a nitrogen oxide gas or a gas containing nitrogen oxide;
A second heat treatment step of heat-treating the first gate insulating film at a temperature higher than a heat treatment temperature of the first heat treatment step in an inert gas or vacuum;
And a step of depositing a second gate insulating film made of a silicon nitride film on the first gate insulating film using a vapor deposition method.
(Supplementary note 2) The method for manufacturing a semiconductor device according to supplementary note 1, wherein the gas containing nitrogen oxide is a mixed gas of nitrogen oxide and inert gas.
(Additional remark 3) The said nitrogen oxide is nitric oxide or dinitrogen monoxide, The manufacturing method of the semiconductor device of Additional remark 1 or 2 characterized by the above-mentioned.
(Supplementary note 4) In the semiconductor device according to Supplementary note 1, 2, or 3, wherein the first gate insulating film is a silicon oxide film or a silicon oxynitride film formed by thermally oxidizing the surface of the semiconductor substrate. Production method.
(Supplementary note 5) The method of manufacturing a semiconductor device according to any one of supplementary notes 1 to 4, wherein the silicon nitride film is deposited by a chemical vapor deposition method using a source gas containing ammonia.
(Additional remark 6) The said silicon nitride film is deposited by the plasma chemical vapor deposition method using the plasma containing nitrogen, The manufacturing method of the semiconductor device in any one of Additional remark 1-4 characterized by the above-mentioned.
(Supplementary note 7) The method of manufacturing a semiconductor device according to any one of supplementary notes 1 to 6, wherein a heat treatment temperature of the first heat treatment is set to 800 ° C. or more and 900 ° C. or less.
(Additional remark 8) The said 2nd heat processing temperature shall be 900 degreeC or more and 1100 degrees C or less, The manufacturing method of the semiconductor device in any one of Additional remarks 1-7 characterized by the above-mentioned.

  By applying the present invention to the manufacture of a MIS transistor, a gate insulating film having a small equivalent film thickness and a low interface state density can be formed. Therefore, a semiconductor device having a small gate leakage and a small deterioration in operating characteristics. Can be provided.

First embodiment of the present invention manufacturing process sectional view Sectional view of manufacturing process of gate insulating film of first embodiment of the present invention First Embodiment of the Present Invention Nitrogen concentration distribution diagram in gate insulating film The figure showing film thickness dependence of the leakage current of the first embodiment of the present invention The figure showing the film thickness dependence of interface state density of 1st Embodiment of this invention The figure showing the gate insulating film characteristic of 1st Embodiment of this invention Cross-sectional view of conventional gate insulating film manufacturing process Cross-sectional view of another conventional gate insulating film manufacturing process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Element isolation zone 3 Gate insulating film 4 Gate electrode 5 Side wall 6 Source / drain region 10 1st gate insulating film 11 Silicon oxide film 11a Surface nitrided layer 11b Deep nitrided layer 11c Low concentration nitrided layer 12 2nd gate insulation Film 20 Nitrogen plasma 101 High dielectric film 102 Gate insulating film 103 Silicon nitride film

Claims (5)

Forming a first gate insulating film made of a silicon oxide film or a silicon oxynitride film on the surface of the semiconductor substrate;
Plasma nitriding the first gate insulating film;
Next, a first heat treatment step of heat-treating the first gate insulating film in a nitrogen oxide gas or a gas containing nitrogen oxide;
A second heat treatment step of heat-treating the first gate insulating film at a temperature higher than the first heat treatment temperature in an inert gas or vacuum;
And a step of depositing a second gate insulating film made of a silicon nitride film on the first gate insulating film using a vapor deposition method.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the nitrogen oxide is nitrogen monoxide or dinitrogen monoxide.   3. The method of manufacturing a semiconductor device according to claim 1, wherein the first gate insulating film is a silicon oxide film or a silicon oxynitride film formed by thermally oxidizing the surface of the semiconductor substrate.   4. The method of manufacturing a semiconductor device according to claim 1, wherein the silicon nitride film is deposited by a chemical vapor deposition method using a source gas containing ammonia.   4. The method of manufacturing a semiconductor device according to claim 1, wherein the silicon nitride film is deposited by a plasma chemical vapor deposition method using a plasma containing nitrogen.

Images