Method for fabricating semiconductor device

[0002] The present invention relates to a method for fabricating a semiconductor device having a dual gate electrode, more specifically to a method for fabricating a semiconductor device which can prevent boron penetration from a p-type gate electrode without degrading performance of an n-channel MOS transistor.

[0003] With the recent increasing micronization and higher-speed operation of semiconductor devices, the so-called dual gate electrode including a p-type gate electrode which is the gate electrode of a p-channel MOS transistor doped with an acceptor impurity, and an n-type gate electrode which is the gate electrode of an n-channel MOS transistor doped with a donor impurity has been increasingly used. In the p-type gate electrode, boron (B) is widely used as a dopant. However, because of the large diffusion coefficient in the silicon oxynitride film, the thermal diffusion that thermal processing in a later step causes boron in the gate electrode to diffuse through the gate insulation film into the silicon substrate in the channel region is a problem. When the boron penetration is occurred, an impurity concentration in the silicon substrate of the channel region changes to cause characteristic degradation, as of varying a threshold voltage, lowering the impurity concentration in the gate electrode to deplete the gate electrode, or others. It is preferable to reduce the born penetration as much as possible.

[0004] On the other hand, in the processing for opening a contact hole in a narrow region between gate electrodes, the so-called self-aligned contact (SAC) technique is widely used from the viewpoint of ensuring an alignment margin for the lithography. In the SAC technique, the side surface and the upper surface of the gate electrodes are covered with a silicon nitride film having etching selectivity with respect to a silicon oxide film, which is widely used as an inter-layer insulation film, and the inter-layer insulation film is etched with the silicon nitride film as a stopper to thereby open the contact hole arriving at the substrate without exposing the gate electrodes in the contact hole. In the SAC technique, the silicon nitride film is thus formed on the gate electrodes. However, it is reported that thermal processing following the formation of the silicon nitride film on the p-type gate electrodes enhances the born penetration (see, e.g., J. R. Pfiester et al., IEEE Trans. Electron Devices, vol. 37, 1842 (1990)).

[0005] As described above, the boron penetration from the p-type gate electrode is conspicuous in case of forming a silicon nitride film on the gate electrodes especially by the SAC technique. A technique for preventing the boron penetration from the p-type gate electrode is required.

[0006] It is known that the boron penetration from the p-type gate electrode is reduced by introducing nitrogen in the gate insulation film. The gate insulation film is formed by using NO or N₂O, or thermal processing is made in a gas atmosphere of NO, N₂O or NH₃after the gate insulation film has been formed, whereby a gate oxide film of a silicon oxynitride film containing nitrogen by about 10% is formed to prevent the boron penetration. However, in a case that the gate insulation film is formed of a silicon oxynitride film, the incorporated nitrogen is segregated in the interface between the silicon substrate and the gate insulation film, and surface state increase, which is result in lowering driving performance of the n-channel MOS transistors. Furthermore, increased nitrogen concentration increases fixed charges in the film, and an accordingly larger channel dose of the n-channel MOS transistor is necessary, often with results that the performance of the transistor has been degraded, and dopant concentration increase in the substrate has increased junction leakage current.

[0007] The Japanese Patent Application Laid-Open Publication No. 2000-12856, for example, discloses a technique of setting a temperature of thermal processing made after a silicon nitride film has been formed to be below a temperature at which can be prevented from the enhanced diffusion of boron. However, in order to prevent the enhanced diffusion of boron a temperature of thermal processing following the formation of the silicon nitride film must be set to be below about 900° C. The thermal processing at such low temperature is not sufficient to activate the source/drain diffusion, with a result of lower driving performance of the transistor.

[0008] As described above, in the conventional method for fabricating the semiconductor device, the prevention of the boron penetration from the p-type gate electrode degrades driving performance of the n-channel MOS transistor. A technique which can prevent the boron penetration from the p-type gate electrode without degrading performance of the n-channel MOS transistor has been required.

[0009] It is an object of the present invention to provide a method for fabricating the semiconductor device including a dual gate electrode which can prevent the boron penetration from the p-type gate electrode without lowering performance of the n-channel MOS transistor.

[0010] According to one aspect of the present invention, there is provided a method for fabricating the semiconductor device comprising the steps of: forming a gate insulation film on a semiconductor substrate; forming on the gate insulation film a conducting film including a semiconductor film containing boron as an acceptor impurity in at least one region; forming on the conducting film an insulation film including a silicon nitride film having an Si—H bond concentration immediately after deposited, which is below 4.3×10²⁰cm⁻³measured by FT-IR; and patterning the insulation film and the conducting film to form a gate electrode of the conducting film having the upper surface covered by the insulation film.

[0011] According to another aspect of the present invention, there is provided a method for fabricating the semiconductor device comprising the steps of: forming a gate insulation film on a semiconductor substrate; forming on the gate insulation film a conducting film including a semiconductor film containing boron as an acceptor impurity in at least one region; patterning the conducting film to form a gate electrode of the conducting film; and forming on the side wall of the gate electrode a sidewall insulation film including a silicon nitride film having an Si—H bond concentration immediately after deposited, which is below 4.3×10²⁰cm⁻³measured by FT-IR.

[0012] According to the present invention, the silicon nitride film covering the upper surfaces and/or the side walls of the gate electrodes are deposited under conditions which allow an Si—H bond concentration in the silicon nitride film immediately after deposited to be below a 4.3×10²⁰cm⁻³measured by FT-IR, whereby release of hydrogen in the films in the thermal processing after the silicon nitride films have been formed, and the boron penetration from the p-type gate electrode can be suppressed. Thus, in the p-channel MOS transistor a dopant concentration in the silicon substrate in the channel region is prevented from changing to resultantly deviate a threshold voltage, or a dopant concentration in the gate electrode is prevented from changing to resultantly deplete the gate electrode. Thus, characteristic degradation can be prevented. A nitrogen concentration in the silicon oxynitride film forming the gate insulation film can be lowered, whereby the boron penetration from the p-type gate electrode can be prevented without lower driving performance of the n-channel MOS transistor.

[0013] FIG. 1 is a graph of relationships between film forming temperatures for a silicon nitride film of a sample having the silicon nitride film formed on a gate electrode, and C-V characteristics.

[0014] FIG. 2 is a graph of relationships between thermal processing temperatures after the silicon nitride film has been deposited and release amounts of hydrogen from the silicon nitride film.

[0015] FIGS. 3A-3C, 4A-4C, 5A-5C, and 6A-6C are sectional views of a semiconductor device in the steps of the method for fabricating the same according to a first embodiment of the present invention, which show the method.

[0016] FIGS. 7A-7D are sectional views of a semiconductor device in the steps of the method for fabricating the same according to a second embodiment of the present invention, which show the method.

[0017] FIGS. 8A-8D are sectional views of a semiconductor device in the steps of the method for fabricating the same according to a third embodiment of the present invention, which show the method.

[0018] The method for fabricating the semiconductor device according to the present invention is characterized in that the method comprising the steps of: forming a gate insulation film on a semiconductor substrate; forming on the gate insulation film a conducting film including a semiconductor film containing boron as an acceptor impurity in at least one region; forming on the conducting film an insulation film including a silicon nitride film having an Si−H bond concentration immediately after deposited, which is below 4.3×10²⁰cm⁻³measured by FT-IR; and patterning the insulation film and the conducting film to form a gate electrode of the conducting film having the upper surface covered by the insulation film. The present invention is based on the phenomena found for the first time by the inventors of the present invention that Si—H bonds in the silicon nitride film are a main factor for causing enhanced diffusion of boron in the silicon nitride film.

[0019] The Japanese Patent Application Laid-Open Publication No. 58583/2000 discloses a technique for preventing the boron penetration from the gate electrode by making a hydrogen concentration in the silicon nitride film to be less than 1×10²¹cm⁻³concentration measured by SIMS analysis. However, the inventors of the present application have made earnest studies and made it evident for the first time that the boron penetration is not influenced simply by a hydrogen concentration in the silicon nitride film but is much related with bonding states of hydrogen atoms in the silicon nitride film. Results of the studies of the inventors of the present application will be described below.

[0020] FIG. 1 is a graph of relationships between film forming temperatures of a silicon nitride film on a gate electrode, and C-V characteristics. A gas flow rate ratio of NH₃/SiH₂Cl₂for forming the silicon nitride film in FIG. 1 is 10. As shown, the C-V curves shift to the minus side as the film forming temperatures are higher, and it is seen that the boron penetration is smaller as the film forming temperatures of the silicon nitride film is higher. The C-V characteristics do not substantially change at the film forming temperatures of above 780° C. The silicon nitride film is formed at a film forming temperature of above 780° C., whereby the effect of preventing the boron penetration can be sufficiently exhibited.

[0021] FIG. 2 is a graph of relationships between thermal processing temperatures after the silicon nitride film has been deposited, and release amounts of hydrogen from the silicon nitride film. Three type of silicon nitride films with different deposition temperature are shown in the figure. In FIG. 2, the release amounts of hydrogen from the silicon nitride film were measured by Thermal Desorption Spectroscopy. As shown, as the silicon nitride film is formed at a lower temperature, a temperature for a peak value of the released hydrogen is lower, and also a hydrogen release amount is increased.

[0022] In connection with the result shown in FIG. 1, the result will show that when the silicon nitride film on the gate electrode is formed at a lower temperature, a large mount of hydrogen in the silicon nitride film is released by thermal processing after the deposition of the silicon nitride film, with a result that diffusion of boron in the gate electrode and the silicon oxynitride film is enhanced, and the boron penetration is enhanced. Accordingly, it is preferable that a temperature for a peak value of released hydrogen is higher than a heat processing temperature after the deposition of the silicon nitride film, and a release amount is small.

[0023] However, the boron penetration is not only influenced simply by a hydrogen concentration of the silicon nitride film, but also much related with a hydrogen bonding state in the silicon nitride film.

[0024] TABLE 1 shows relationships between hydrogen in the silicon oxynitride film and diffusion coefficients of boron in the silicon nitride film when the silicon nitride film is formed at 780° C. by using a raw material gas of NH₃(ammonia) and SiH₂Cl₂(dichlorosilane). In the Table 1, the Si—H bond and the N—H bond show peak values of FT-IR spectra. A total hydrogen amount in the film can be roughly given by a value of a combination of a peak value of the Si—H bonds and a peak value of the N—H bonds.

[0025] As shown in TABLE 1, when a gas flow rate ratio between NH₃and SiH₂Cl₂(NH₃/SiH₂Cl₂) is changed, values of the Si—H bond and of the N—H bond in the silicon nitride film change. As a gas flow rate ratio becomes higher, the Si—H bond decreases, and the N—H bond increases. As a gas flow rate ratio becomes higher, a total amount of hydrogen in the film increases. In contrast to this, a diffusion coefficient of boron in the silicon oxynitride film decreases as a gas flow rate ratio becomes higher.

[0026] Thus, as a gas flow rate ratio is larger, a total amount of hydrogen in the silicon nitride film increases while a diffusion coefficient of boron in the silicon oxynitride film is smaller, which makes for the boron penetration difficult to occur. That is, the enhanced diffusion of boron will not be determined by a total amount of hydrogen in the silicon nitride film but will be decided by bonding states of hydrogen, more specifically will have correlationships with a total amount of Si—H bonds.

[0027] TABLE 2 shows relationships between film forming temperatures of the silicon nitride film, and concentration of Si—H bonds and N—H bonds in the silicon nitride film. The Si—H bond concentrations and the N—H bond concentrations were measured by FT-IR.

[0028] As shown in TABLE 2, a concentration of the Si—H bond in the silicon nitride film also depends on a film formingtemperature of the silicon nitride film. As a film forming temperature is higher, an Si—H bond concentration in the silicon nitride film decreases. In connection with the result of the C-V characteristics described above, a film forming temperature is set to be above 780° C., i.e., an Si—H bond concentration in the silicon nitride film measured by FT-IR is set to be below 4.3×10²⁰cm⁻³, whereby the boron penetration will be able to be prevented.

[0029] An amount of the Si—H bonds in the silicon nitride film is much related with the boron penetration. It has been made evident for the first time that as described above, an Si—H bond concentration in the silicon nitride film measured by FT-IR is set to be below 4.3×10²⁰cm⁻³, whereby the boron penetration will be able to be prevented.

[0030] Film forming conditions for setting an Si—H bond concentration in the silicon nitride film to be below 4.3×10²⁰cm⁻³measured by FT-IR depend on kinds of raw material gases, fabrication equipments, etc. and cannot be uniformly determined. In the equipment used by the inventors of the present application, when SiH₂Cl₂gas and NH₃gas are used as raw material gases, a gas flow rate ratio (NH₃/SiH₂Cl₂) is set to be above 10, a film forming temperature is set to be above 780° C., and a pressure in the deposition chamber is to be above 40 Pa, whereby a Si—H bond concentration in the silicon nitride film can be controlled to be below 4.3×10²⁰cm⁻³measured by FT-IR.

[0031] A raw material gas having less Si—H bond, e.g., SiHCl₃is used in place of SiH₂Cl₂gas, whereby an amount of the Si—H bonds in the silicon nitride film to be deposited can be further decreased, and the boron penetration can be much effectively prevented. With an Si—H amount in the film set to be the same, a film forming temperature can be lowered.

[0032] It is preferable that film forming conditions for the silicon nitride film are set suitably in accordance with raw material gases to be used and a fabrication equipment so that an Si—H bond concentration in the film immediately after deposited can be 4.3×10²⁰cm⁻³measured by FT-IR.

[0033] Silicon nitride film is formed, in many cases, in a batch of 100 sheets, but because of a determined feed rate it is difficult to make the formed films homogeneous in the film forming, as described above, at above 780° C. using raw materials having a small amount of the Si—H bonds, such as SiHCl₃/NH₃group. In such case, equipments of about 25 sheets-small batch or single-wafer type equipments are used so as to form homogeneous films.

[0034] [A First Embodiment]

[0035] The method for fabricating the semiconductor device according to a first embodiment of the present invention will be explained with reference to FIGS. 3A-3C, 4A-4C, 5A-5C, and 6A-6C.

[0036] FIGS. 3A-3C, 4A-4C, 5A-5C, and 6A-6C are sectional views of a semiconductor device in the steps of the method for fabricating the same according to the present embodiment, which show the method.

[0037] First, a device isolation film 12 of a silicon oxide film is formed in a silicon substrate 10 by, e.g., shallow trench isolation technique (FIG. 3A). In FIG. 3A, the region on the left side of the device isolation film 12 is a region for a p-channel MOS transistor to be formed in, and the region on the right side of the device isolation film 12 is a region for an n-channel MOS transistor to be formed in.

[0038] Next, a p-well (not shown) is formed as required in the region for an n-channel MOS transistor to be formed in, and an n-well (not shown) is formed as required in the region for a p-channel MOS transistor to be formed in. Ion implantation for controlling threshold voltages is performed in the respective regions for the transistors to be formed in.

[0039] Then, a silicon oxide film as a base film is formed in, e.g., an oxidizing atmosphere, and then thermal processing is performed at 900° C. in an NO atmosphere to form on the silicon substrate 10 defined by the device isolation film 12 a 4.5 nm-thick gate insulation film 14 of a silicon oxynitride film having a 3% nitrogen concentration.

[0040] Next, a 70 nm-thick amorphous silicon film 16, for example, is formed on the gate insulation film 14 by, e.g., CVD method (FIG. 3B). The amorphous silicon film is formed at a 540° C. film forming temperature by, e.g., pyrolysis method using SiH₄as a raw material gas.

[0041] Next, a photoresist film 18 for covering the region for an n-channel MOS transistor to be formed in is formed by the photolithography technique.

[0042] Then, with the photoresist film 18 as a mask, a p-type dopant ion is implanted into the amorphous silicon film 16 in the region for a p-channel MOS transistor to be formed in. For example, boron ions are implanted at 5 keV acceleration energy and a 1.5×10¹⁵cm⁻²dose (FIG. 3C).

[0043] Next, the photoresist film 18 is removed, and then a photoresist film 20 for covering the region for a p-channel MOS transistor to be formed in is formed by the photolithography technique.

[0044] Then, with the photoresist film 20 as a mask, an n-type dopant ion is implanted into the amorphous silicon film 16 in the region for an n-channel MOS transistor to be formed in. For example, phosphorus (P) ions are implanted at 10 keV acceleration energy and a 5×10¹⁵cm⁻²dose (FIG. 4A).

[0045] Then, the photoresist film 20 is removed, and then thermal processing is performed, for example, for 30 minutes at 800° C. in a nitrogen atmosphere to crystallize the amorphous silicon film into a polycrystalline silicon film while activating the implanted boron and phosphorus, so as to transform the amorphous silicon film 16 in the region for a p-channel MOS transistor to be formed in to a p-type polycrystalline silicon film 22pand the amorphous silicon film 16 in the region for an n-channel MOS transistor to be formed in to an n-type polycrystalline silicon film 22n.

[0046] Then, a 5 nm-thick tungsten nitride (WN) film 24 and a 40 nm-thick tungsten (W) film 26 are sequentially deposited on the polycrystalline silicon films 22p, 22nby, e.g., sputtering method. The tungsten nitride film 24 is a barrier metal for preventing the reaction between the polycrystalline silicon film 22 and the tungsten film 26.

[0047] Next, a 100 nm-thick silicon nitride film 28 is formed on the tungsten film 26 by, e.g., CVD method (FIG. 4B). At this time, conditions for forming the film are set so that an Si—H bond concentration in the silicon nitride film 28 is below 4.3×10²⁰cm⁻³measured by FT-IR. An Si—H bond concentration in the film can be below 4.3×10²⁰cm⁻³measured by FT-IR by forming the film, e.g., at a 100 sccm SiH₂Cl₂gas flow rate, a 1000 sccm NH₃gas flow rate, a 780° C. film forming temperature and a 40 Pa pressure.

[0048] Then, the silicon nitride film 28, the tungsten film 26, the tungsten nitride film 24 and the polycrystalline silicon film 22p, 22nare patterned by the photolithography and etching to form in the region for a p-channel MOS transistor to be formed in a p-type gate electrode 30pof the so-called polymetal structure having the upper surface covered by the silicon nitride film 28 and formed of the layer structure of the polycrystalline silicon film 22p, the tungsten nitride film 24 and the tungsten film 26 and form in the region for an n-channel MOS transistor to be formed in an n-type gate electrode 30nof the polymetal structure having the upper surface covered by the silicon nitride film 28 and formed of the layer structure of the polycrystalline silicon film 22nthe tungsten nitride film 24 and the tungsten film 26 (FIG. 4C).

[0049] Next, thermal processing is performed in an atmosphere containing, e.g., hydrogen and steam for 60 minutes at 800° C. to oxidize selectively only the side walls of the polycrystalline silicon films 22n, 22pwithout oxidizing the tungsten film 26 and the tungsten nitride film 24 to form a silicon oxide film 32.

[0050] Then, a photoresist film 34 for covering the region for an n-channel MOS transistor to be formed in is formed by the photolithography technique.

[0051] Then, with the photoresist film 34 and the gate electrode 30pas a mask, BF₂ions are implanted at 15 keV acceleration energy and a 3×10¹⁴cm⁻²dose to form in the silicon substrate 10 on both sides of the gate electrode 30pimpurity diffused regions 36pwhich are to be lower-concentration regions of the LDD structure or shallow diffused regions of the extension source/drain structure (FIG. 5A).

[0052] Then, the photoresist film 34 is removed, and then a photoresist film 38 for covering the region for a p-channel MOS transistor to be formed in is formed by the photolithography technique.

[0053] Next, with the photoresist film 38 and the gate electrode 30nas a mask, arsenic (As) ions are implanted at 20 keV acceleration energy and a 5×10¹⁴cm⁻²dose to form in the silicon substrate 10 on both sides of the gate electrode 30nimpurity diffused regions 36nwhich are to be lower-concentration regions of the LDD structure or shallow diffused regions of the extension source/drain structure (FIG. 5B).

[0054] Then, after the photoresist film 38 has been removed, rapid thermal processing is performed for 10 seconds at 900° C. in a nitrogen atmosphere to activate the implanted dopant ions.

[0055] Then, a 20 nm-thick silicon nitride film is deposited on the entire surface by, e.g., CVD method and is etched back to form a sidewall insulation film 40 of the silicon nitride film on the side walls of the gate electrodes 30p, 30nand of the silicon nitride film 28 (FIG. 5C). At this time, film forming conditions for the silicon nitride film to be the sidewall insulation film 40 are set so that an Si—H bond concentration in the silicon nitride film immediately after deposited is below 4.3×10²⁰cm⁻³measured by FT-IR. For example, the silicon nitride film can be formed at a 100 sccm SiH₂Cl₂gas flow rate and a 1000 sccm NH₃gas flow rate, a 780° C. -film forming temperature and at a 40 Pa pressure, whereby an Si—H bond concentration in the silicon nitride film can be below 4.3×10¹⁰cm⁻³measured by FT-IR.

[0056] Next, a photoresist film 42 for covering the region for an n-channel MOS transistor to be formed in is formed by the photolithography technique.

[0057] Then, with the photoresist film 42, the gate electrode 30pand the sidewall insulation film 40 as a mask, boron ions are implanted at 7 keV acceleration energy and a 3×10¹⁵cm⁻²dose to form impurity diffused regions 44pwhich are to be higher-concentration regions of the deep diffused regions of the source/drain structure (FIG. 6A).

[0058] Then, after the photoresist film 42 is removed, a photoresist film 46 for covering the region for a p-channel MOS transistor to be formed in is formed by the photolithography technique.

[0059] Next, with the photoresist film 46, the gate electrode 30nand the sidewall insulation film 40 as a mask, arsenic ions are implanted at 50 keV acceleration energy and at a 3×10¹⁵cm⁻²dose to form impurity diffused regions 44nwhich are to be higher-concentration regions of the deep diffused regions of the source/drain structure (FIG. 6B).

[0060] Then, after the photoresist film 46 is removed, thermal processing is performed in a nitrogen atmosphere, e.g., for 10 seconds at 950° C. to activate the implanted dopant ions to form a p-type source/drain diffused layer 48pof the dopant diffused regions 36p, 44p, and an n-type source/drain diffused layer 48nof the dopant diffused regions 36n, 44n(FIG. 6C).

[0061] Thus, a semiconductor device having dual gate electrodes 30p, 30nof the polymetal structure is fabricated.

[0062] A MOS transistor was fabricated by the above-described process in which the gate insulation film was provided by a silicon oxynitride film having an above 3% peak value of the nitrogen concentration in the film, and rapid thermal processing at above 950° C. was performed as the thermal processing for activating the source/drain diffused layer. In the MOS transistor, an Si—H bond concentration in the silicon nitride film immediately after deposited was set to be below 4.3×10²⁰cm⁻³measured by FT-IR, whereby the boron penetration could be suppressed to a negligible level.

[0063] As described above, according to the present embodiment, the silicon nitride film forming the silicon nitride film 28 covering the upper surfaces of the gate electrodes 30p, 30n, and the silicon nitride film forming the sidewall insulation film 40 covering the side walls of the gate electrodes 30p, 30nare deposited under conditions which makes an Si—H bond concentration in the silicon nitride films immediately after deposited can be below 4.3×10²⁰cm⁻³measured by FT-IR, whereby the release of hydrogen in the film in the thermal processing step following the formation of the silicon nitride films can be decreased, and the boron penetration from the p-type gate electrode 30pcan be suppressed. Thus, a nitrogen concentration in the silicon oxynitride film forming the gate insulation film can be made low, whereby the boron penetration from the p-type gate electrode can be prevented without lowering driving performance of the n-channel MOS transistor.

[0064] [A Second Embodiment]

[0065] The method for fabricating the semiconductor device according to a second embodiment of the present invention will be explained with reference to FIGS. 7A-7D. The same members of the present embodiment as those of the method for fabricating the semiconductor device according to the first embodiment shown in FIGS. 3A-3D, 4A-4C, 5A-5C, and 6A-6C are represented by the same reference numbers not to repeat or to simplify their explanation.

[0066] FIGS. 7A-7D are sectional views of a semiconductor device in the steps of the method for fabricating the same according to the present embodiment, which show the method.

[0067] In the method for fabricating the semiconductor device according to the first embodiment, the present invention is applied to the fabrication of a semiconductor device having the so-called polymetal gate electrodes. However, the present invention is not limited to the semiconductor devices having the polymetal gate electrodes. In the present embodiment, the present invention is applied to a gate electrode formed of a single layer of polycrystalline silicon film.

[0068] First, a device isolation film 12 is formed of a silicon oxide film in a silicon substrate 10 by, e.g., shallow trench isolation technique.

[0069] Next, a p-well (not shown) is formed as required in a region for an n-channel MOS transistor to be formed in, and an n-well (not shown) is formed as required in a region for a p-channel MOS transistor to be formed in. Ion implantation for the control of a threshold voltage is performed in the regions for the respective transistors to be formed in.

[0070] Next, for example, a silicon oxide film as a base film is formed in an oxidizing atmosphere, and thermal processing of 900° C. is performed in an NO atmosphere to form a 4.5 nm-thick gate insulation film 14 of a silicon oxynitride film of a 3% nitrogen concentration on the silicon substrate 10 defined by the device isolation film 12.

[0071] Then, a 200 nm-thick polycrystalline silicon film 22, for example, is formed on the gate insulation film 14 by, e.g., CVD method (FIG. 7A). For example, a polycrystalline silicon film is formed at a 620° C. film forming temperature by pyrolysis method using SiH₄as a raw material gas.

[0072] Then, in the same way as, e.g., in the method for fabricating the semiconductor device according to the first embodiment shown in FIGS. 3C and 4A, p-type dopant ions are implanted into the polycrystalline silicon film 22 in the region for a p-channel MOS transistor to be formed in and n-type dopant ions are implanted into the polycrystalline silicon film 22 in the region for an n-channel MOS transistor to be formed in. In the region for a p-channel MOS transistor to be formed in, for example, boron ions are implanted at 5 keV acceleration energy and at a 3×10¹⁵cm⁻²dose. In the region for an n-channel MOS transistor to be formed in, for example, phosphorus ions are implanted at 10 keV acceleration energy and a 6×10¹⁵cm⁻²dose.

[0073] Next, thermal processing is performed, e.g., in a nitrogen atmosphere at 800° C. for 30 minutes to activate the boron and phosphorus implanted in the polycrystalline silicon film 22 to transform the polycrystalline silicon film 22 in the region for a p-channel MOS transistor to be formed in to a p-type polycrystalline silicon film 22pand the polycrystalline silicon film 22 in the region for an n-channel MOS transistor to be formed in to an n-type polycrystalline silicon film 22n.

[0074] Next, a 100 nm-thick silicon nitride film 28 is formed on the polycrystalline silicon film 22p, 22nby, e.g., CVD method (FIG. 7B). At this time, film forming conditions are set so that an Si—H bond concentration in the silicon nitride film immediately after deposited is below 4.3×10²⁰cm⁻³measured by FT-IR. The film is formed under conditions of, e.g., a 100 sccm SiH₂Cl₂gas flow rate, a 1000 sccm NH₃gas flow rate, a 780° C. film forming temperature and a 40 Pa pressure, whereby an Si—H bond concentration in the film can be below 4.3×10²⁰cm⁻³measured by FT-IR.

[0075] Then, the silicon nitride film 28 and the polycrystalline silicon film 22p, 22nare patterned by the photolithography and etching to form a p-type gate electrode 30pformed of the polycrystalline silicon film 22phaving the upper surface covered by the silicon nitride film 28 in the region for a p-channel MOS transistor to be formed in, and an n-type gate electrode 30nformed of the polycrystalline silicon film 22nhaving the upper surface covered by the silicon nitride film 28 is formed in the region for an n-channel MOS transistor to be formed in (FIG. 7C).

[0076] Next, in the same way as, e.g., in the method for fabricating the semiconductor device according to the first embodiment shown in FIGS. 5A to 6C, a sidewall insulation film 40 is formed on the side walls of the gate electrodes 30p, 30nof a silicon nitride film having an Si—H bond concentration of below 4.3×10²⁰cm⁻³immediately after deposited, a p-type source/drain diffused layer 48pis formed in the silicon substrate 10 on both sides of the gate electrode 30p, and an n-type source/drain diffused layer 48nis formed in the silicon substrate 10 on both sides of the gate electrode 30n(FIG. 7D).

[0077] Thus, the semiconductor device having the dual gate electrodes 30p, 30nof the single polycrystalline silicon gate structure is fabricated.

[0078] As described above, according to the present embodiment, the silicon nitride film 28 covering the upper surfaces of the gate electrodes 30p, 30n, and the silicon nitride film forming the sidewall insulation film 40 covering the side walls of the gate electrodes 30p, 30nare deposited under conditions which allow an Si—H bond concentration in the silicon nitride films immediately after deposited is below 4.3×10²⁰cm⁻³, whereby release of hydrogen in the film in the thermal processing after the silicon nitride films have been formed can be decreased, and boron penetration from the p-type gate electrode 30pcan be suppressed. Thus, a nitrogen concentration in the silicon oxynitride film forming the gate insulation film can be low, whereby the boron penetration from the p-type gate electrode can be prevented without lowering driving performance of the n-channel MOS transistor.

[0079] [A Third Embodiment]

[0080] The method for fabricating the semiconductor device according to a third embodiment of the present invention will be explained with reference to FIGS. 8A-8D. The same members of the present embodiment as those of the method for fabricating the semiconductor device according to the second and the third embodiments shown in FIGS. 3A-3D, 4A-4C, 5A-5C, 6A-6C, and 7A-7C are represented by the same reference numbers not to repeat or to simplify their explanation.

[0081] FIGS. 8A-8D are sectional views of the semiconductor device in the steps of the method for fabricating the same according to the present embodiment, which show the method.

[0082] In the above-described embodiments, the present invention is applied to a semiconductor device having the polymetal gate electrodes or the polycrystalline silicon gate electrodes. However, the present invention is not limited to a semiconductor devices having polymetal gate electrodes or polycrystalline silicon gate electrodes. In the present embodiment, the present invention is applied to polycide gate electrodes.

[0083] A device isolation film 12 is formed of a silicon oxide film in a silicon substrate 10 by, e.g., shallow trench isolation technique.

[0084] Next, a p-well (not shown) is formed as required in a region for an n-channel MOS transistor to be formed in, and an n-well (not shown) is formed as required in a region for a p-channel MOS transistor to be formed in. Ion implantation for controlling threshold voltages is performed in the respective regions for the transistors to be formed in.

[0085] Then, for example, a silicon oxide film as a base film is formed in an oxidizing atmosphere and, then thermal processing of 900° C. is performed in an NO atmosphere to form a gate insulation film 14 of a 4.5 nm-thick silicon oxynitride film having a 3% nitrogen concentration formed on the silicon substrate 10 defined by the device isolation film 12.

[0086] Next, a 700 nm-thick amorphous silicon film 16, for example, is formed on the gate insulation film 14 by, e.g., CVD method (FIG. 8A). For example, the amorphous silicon film 16 is formed at 540° C. by pyrolysis method using SiH₄as a raw material gas.

[0087] Then, in the same way as, e.g., in the method for fabricating the semiconductor device according to the first embodiment shown in FIGS. 3C and 4C, p-type dopant ions are implanted into the amorphous silicon film 16 in the region for a p-channel MOS transistor to be formed in, and an n-type dopant ions are implanted in the amorphous silicon film 16 in the region for an n-channel MOS transistor to be formed in. In the region for a p-channel MOS transistor to be formed in, boron ions are implanted at 5 keV acceleration energy and at a 1.5×10¹⁵cm⁻²dose, and phosphorus ions are implanted at 10 keV acceleration energy and at a 5×10¹⁵cm⁻²dose in the region for an n-channel MOS transistor to be formed in.

[0088] Then, thermal processing is performed, e.g., in a nitrogen atmosphere at 800° C. for 30 minutes to crystallize the amorphous silicon film to a polycrystalline silicon film while activating the implanted boron and phosphorus ions to transform the amorphous silicon film 16 in the region for a p-channel MOS transistor to be formed in to a p-type polycrystalline silicon film 22pand the amorphous silicon film 16 in the region for an n-channel MOS transistor to be formed in to an n-type polycrystalline silicon film 22n.

[0089] Then, a 5 nm-thick tungsten nitride (WN) film 24 and a 100 nm-thick tungsten silicide (WSi₂) film 50 is formed sequentially on the polycrystalline silicon film 22p, 22nby, e.g., CVD method.

[0090] Then, a 100 nm-thick silicon nitride film 28 is formed on the tungsten silicide film 50 by, e.g., CVD method (FIG. 8B). At this time, film forming conditions are set so that an Si—H bond concentration in the silicon nitride film 28 is below 4.3×10²⁰cm⁻³measured by FT-IR. The film is formed under conditions of, e.g., a 100 sccm SiH₂Cl₂gas flow rate, a 1000 sccm NH₃gas flow rate, a 780° C. film forming temperature and a 40 Pa pressure, whereby an Si—H bond concentration in the film can be below 4.3×10²⁰cm⁻³measured by FT-IR.

[0091] Next, the silicon nitride film 28, the tungsten silicide film 50, the tungsten nitride film 24 and the polycrystalline silicon film 22p, 22nare patterned by the photolithography and etching to form in the region for a p-channel MOS transistor to be formed in a p-type gate electrode 30phaving the upper surface covered by the silicon nitride film 28 and formed of the layer film of the polycrystalline silicon film 22p, the tungsten nitride film 24 and the tungsten silicide film 50 and form in the region for an n-channel MOS transistor to be formed in an n-type gate electrode 30nhaving the upper surface covered by the silicon nitride film 28 and formed of the layer structure of the polycrystalline silicon film 22n, the tungsten nitride film 24 and the tungsten silicide film 50 (FIG. 8C).

[0092] Then, in the same way as, e.g., in the method for fabricating the semiconductor device according to the first embodiment shown in FIGS. 5A to 6C, a sidewall insulation film 40 is formed on the side walls of the gate electrodes 30p, 30nof a silicon nitride film having a below 4.3×10²⁰cm⁻³Si—H concentration immediately after deposited, a p-type source/drain diffused layer 48pformed in the silicon substrate 10 on both sides of the gate electrode 30p, and an n-type source/drain diffused layer 48nformed in the silicon substrate on both sides of the gate electrode 30n(FIG. 8D).

[0093] Thus, the semiconductor device having the dual gate electrodes 30p, 30nof the polycide structure is fabricated.

[0094] As described above, according to the present embodiment, the silicon nitride film 28 covering the upper surfaces of the gate electrodes 30p, 30n, and the silicon nitride film forming the sidewall insulation film 40 covering the side walls of the gate electrodes 30p, 30nare deposited under conditions which allow the films to have Si—H bond concentrations to be below 4.3×10²⁰cm⁻³measured by FT-IR immediately after deposited, whereby the release of hydrogen in the films in the thermal processing after the silicon nitride films have been formed can be decreased, and the boron penetration from the p-type gate electrode 30pcan be suppressed. Thus, a nitrogen concentration in the silicon oxynitride film forming the gate insulation film can be low, and the boron penetration from the p-type gate electrode can be prevented without lowering driving performance of the n-channel MOS transistor.

[0095] [Modifications]

[0096] The present invention is not limited to the above-described embodiments and covers other various modifications.

[0097] For example, in the above-described embodiments, SiH₂Cl₂and NH₃are used as raw materials to form the silicon nitride film covering the upper surfaces and the side walls of the gate electrodes, but the raw material gases for forming the silicon nitride film are not limited to such raw materials. For example, SiHCl₃and NH₃, or SiCl₄and NH₃can be used as raw material gases.

[0098] In the first embodiment the present invention is applied to the dual gate electrodes of the polymetal structure, and in the third embodiment the present invention is applied to the dual gate electrodes of the polycide structure. The metal film and the silicide film forming the gate electrodes are not limited to tungsten film and tungsten silicide film described in the first and the third embodiments.

[0099] In the first to the third embodiments the insulation film covering the upper surfaces of the gate electrodes, and the sidewall insulation film are the single layer structure of silicon nitride film. However, the present invention is applied to a case in which the insulation film covering the upper surfaces of the gate electrodes, and the sidewall insulation film are formed of a layer film including silicon nitride film, whereby the boron penetration can be suppressed. The present invention can produce the effect even in a case that the insulation film covering the upper surfaces of the gate electrodes, and the sidewall insulation film have silicon oxide film on the lower side and silicon nitride film on the upper side.

[0100] The present invention is applied also to a case in which one of the insulation film on the gate electrodes, and the sidewall insulation film includes silicon nitride film.