Abstract:
A semiconductor device includes a semiconductor substrate, p-type first and n-type second semiconductor regions formed on the substrate so as to be insulated with each other, n-channel and p-channel MOS transistors formed on the first and second semiconductor regions, the n-channel transistor including a first pair of source/drain regions formed on the first semiconductor region, a first gate insulator formed in direct contact with the first semiconductor region and formed as an amorphous insulator containing at least La, and a first gate electrode formed on the first gate insulator, the p-channel MOS transistor including a second pair of source/drain regions formed opposite to each other on the second semiconductor region, a second gate insulator including a silicon oxide film and the amorphous insulating film formed thereon on the second semiconductor region, and a second gate electrode formed on the second gate insulator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-067171, filed Mar. 15, 2007, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a complementary MOS transistor having a strained Si channel. 
     2. Description of the Related Art 
     The advancement of an Si-LSI device has been achieved with the enhancement of the performance of a MOS transistor which is a basic unit of the Si-LSI device. As the performance of the MOS transistor is closely related to the mobility of a carrier (electron, hole) traveling in a channel, attention has been paid to techniques for improving the carrier mobility. One technique for improving the mobility is a strained Si technique. For example, an Si layer is formed on a strain-relaxed SiGe layer to apply tensile strain to Si of a channel in an n-channel MOS transistor, while a gate electrode is coated with a stressor made of a SiN film to improve the electron mobility in a p-channel MOS transistor. 
     However, in the case of, for example, the method in which the Si layer is formed on the strain-relaxed SiGe layer, the dislocation density of the surface of the relaxed SiGe layer is high, leading to problems such as the increase of a leakage current. Further, in the case of the method which coats with the stressor made of the SiN film, the process of manufacturing an FET is naturally complicated, and the amount of strain changes with the change of the FET in size, so that, for example, redesigning is required to change the thickness of the SiN film to adjust the amount of strain, and there arises a problem that the film comes off if the thickness of the SiN film is too large. 
     Furthermore, in JP-A 2004-214386 (KOKAI), a crystalline metal oxide insulating film having lattice spacing different from that of a substrate is formed as a gate insulating film on a channel to modulate the lattice spacing of a channel area, such that the mobility of the carrier is improved. 
     Here, there is concern over the increase of the leakage current when the gate insulating film is polycrystalline. In addition, according to the above-mentioned patent publication, the Si substrate substantially uniformly contains an amount of strain of about 0.7% in an area up to 50 nm from an interface because the gate insulating film is an epitaxial film. When such an amount of strain exists over 50 nm or more, there is concern over the susceptibility to mechanical shocks such that device characteristics might deteriorate due to the relaxation of strain by the occurrence of a dislocation, that is, a crystal defect caused by a small shock. Moreover, the variation between devices increases. 
     Furthermore, for the manufacture of the n- and p-channel MOS transistors, the gate insulating films made of materials of different kinds have to be used to apply tensile and compressive strain to the channels, so that the process of manufacturing a complementary MOS transistor is extremely complicated. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a semiconductor device, which included: 
     a semiconductor substrate; 
     a p-type first semiconductor region formed on the semiconductor substrate; 
     an n-type second semiconductor region formed on the semiconductor substrate so as to be insulated from the first semiconductor region; 
     an n-channel MOS transistor formed on the first semiconductor region; and 
     a p-channel MOS transistor formed on the second semiconductor region, 
     the n-channel MOS transistor including: 
     a first pair of source/drain regions formed opposite to each other on the first semiconductor region; 
     a first gate insulating film formed in direct contact with the first semiconductor region interposed between the first pair of source/drain regions and formed as an amorphous insulating film containing at least La; and 
     a first gate electrode formed on the first gate insulating film, 
     the p-channel MOS transistor including: 
     a second pair of source/drain regions formed opposite to each other on the second semiconductor region; 
     a second gate insulating film including a silicon oxide film and the amorphous insulating film formed thereon, and formed on the second semiconductor region interposed between the second pair of source/drain regions; and a second gate electrode formed on the second gate insulating film. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagram showing an LaAlO 3  film directly deposited on an Si substrate; 
         FIG. 2  is a diagram showing the relation between the depth from the surface of a sample in  FIG. 1  and the atomic density of constituent elements and showing that no interface layer is formed between the LaAlO 3  film and the Si substrate; 
         FIG. 3  is a diagram showing the relation between the irradiation angle of He ions and the RBS yields and showing that the substrate has tensile strain; 
         FIG. 4  is a diagram showing the relation between the depth from the surface of the sample and the atomic density of the constituent elements when a thermal treatment in oxygen is carried out and showing that an interface layer is formed between the LaAlO 3  film and the Si substrate; 
         FIG. 5  is a diagram showing the relation between the irradiation angle of He ions and the RBS yields when the interface layer is formed and showing that there is almost no strain; 
         FIG. 6  is a diagram showing the relation between the depth from the interface and the amount of tensile strain and showing the difference in the amount of tensile strain depending on the presence of the interface layer; 
         FIG. 7  is a sectional view of a semiconductor device according to the first embodiment; 
         FIGS. 8 to 24  are sectional views for the stepwise explanation of the process of manufacturing the semiconductor device in the first embodiment; 
         FIG. 25  is a sectional view of a semiconductor device according to the second embodiment; 
         FIGS. 26 to 29  are sectional views for the stepwise explanation of a method of manufacturing the semiconductor device in the second embodiment; 
         FIG. 30  is a sectional view of a semiconductor device according to the third embodiment; and 
         FIGS. 31 to 33  are sectional views for the stepwise explanation of a method of manufacturing the semiconductor device in the third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before describing embodiments, there is explained on the basis of the knowledge of the present inventors a phenomenon in which an LaAlO 3  film directly deposited on an Si substrate provides tensile strain to the Si substrate.  FIG. 1  is a sectional transmission electron microscopy (TEM) photograph wherein an LaAlO 3  film is deposited, by the pulsed laser deposition method in which an LaAlO 3  single crystal substrate was used as a target material, on a silicon substrate from which native oxide is removed by a diluted HF treatment. It can be recognized from  FIG. 1  that the LaAlO 3  film is amorphous. When an interface layer made of Si oxide such as SiO 2  is present between the LaAlO 3  film and the Si substrate, this layer is observed in white by contrast. However, it is not found in  FIG. 1 , which proves that a direct deposition with no interface layer is achieved. 
     Thus, the LaAlO 3  film in particular is a stable compound at an Si interface and is an insulating film with a high dielectric constant which not only has a nature that makes it difficult for the interface layer to be formed but also has a dielectric constant higher than that of SiO 2 , such that the LaAlO 3  film is a material which can significantly reduce equivalent oxide thickness. This has already been published as a thesis by the present inventors (refer to M. Suzuki et al., Ultra-thin [EOT=3 Å] and Low-leakage Dielectrics of La-Aluminate Directly on Si Substrate Fabricated by High-temperature Deposition. Tech. Dig. IEDM. 2005, pp. 445-448). 
       FIG. 2  shows the in-depth profiles of elements obtained from a Rutherford backscattering spectroscopy (RBS) analysis. The RBS analysis was conducted under a so-called channeling condition in which He +  ions with an energy of 450 keV irradiated along &lt;111&gt; axis direction. It is observed that the composition within the LaAlO 3  film has a stoichiometric ratio, that is, La:Al:O=1:1:3. Moreover, an interface with the Si substrate shows a sharp profile, which means the direct deposition. 
     Here, in order to analyze the strain of the Si substrate, He +  ions with an energy of 450 keV are irradiated to a sample at a step angle of 0.2° within a range of ±2° from an Si&lt;111&gt; axis (54.7° to the normal of the sample surface), and the He +  ions backscattered in the respective irradiation angle conditions are detected by a deflection magnetic field energy analyzer at a position with a scattering angle of 50°.  FIG. 3  shows plots of the yield of backscattering from Si at an interface, and at positions 1, 2, 3 and 5 nm deep from the interface with respect to the irradiation angles of the He +  ions. 
     When the He +  ions are irradiated, the backscattering yield decreases due to channeling effects if the He +  ions are irradiated along the crystal axis of Si. That is, in this measurement, the yield of backscattering from Si is minimized in the &lt;111&gt; axis (i.e., when zero on the horizontal axis) in the case of an Si substrate which is not strained. 
     On the other hand, it is known that the minimum value of the backscattering yield shifts toward the positive angle from the &lt;111&gt; axis when the Si substrate has tensile strain while the minimum value shifts toward the negative angle when the Si substrate has compressive strain. This proves that the tensile strain is applied to the substrate in the case of the current direct deposition because the minimum value has shifted toward the positive angle. It can be seen that the strain increases as the interface becomes closer. 
       FIG. 4  shows in-depth profiles in accordance with the RBS after the film shown in  FIG. 1  is thermally treated in an oxygen atmosphere at 600° C. for 30 minutes. In  FIG. 4 , there is an area of about 1 nm in the vicinity of the interface where Si and oxygen alone exist (this is indicated as an interface layer in  FIG. 4 ). This shows that the Si substrate has been oxidized and the interface layer made of SiO 2  has grown due to the thermal treatment in the oxygen atmosphere. 
     In  FIG. 5 , the yields of backscattering from Si in the sample after the oxygen thermal treatment with respect to the irradiation angle of the He +  ions are plotted for the positions at the respective depths as in  FIG. 3 . It is recognized from the comparison with  FIG. 3  that almost no strain is applied in the case where the interface layer is present because the minimum values of curves substantially correspond to the &lt;111&gt; axis (an irradiation angle of zero). 
     Furthermore, the amount of strain is calculated by the following equation from the extent of deviation of the minimum values of the curves shown in  FIGS. 3 and 5  from the &lt;111&gt; axis.
 
ε=2Δθ/sin 2 θ  (1)
 
where ε indicates the amount of strain, Δθ indicates the amount of the angle of the deviation from the &lt;111&gt; axis, and θ indicates the &lt;111&gt; axis, that is, 54.7° here.
 
       FIG. 6  shows the in-depth profiles of the strain amounts obtained by the above equation. It shows that strain of 0.5% or more is applied in areas up to 3 nm from the interface and that there is almost no strain, on the other hand, in the case where the interface layer is present. As it is known that the strain is not dependent on the thickness of the SiO 2  layer which is the interface layer, it can be said from this result that almost no Si strain is applied as long as the interface is formed by an Si—O—Si bond. 
     Furthermore, it can also be seen that tensile strain of 0.8% or more is contained in an area in the Si substrate within at least 1 nm from the interface with the SiO 2  layer and that tensile strain of less than 0.5% is contained in an area in the Si substrate deeper than at least 3 nm from the interface with the SiO 2  layer. 
     It can be said from what mentioned above that the great strain amount in the case of the direct deposition shown in  FIG. 6  is attributed to the direct deposition of LaAlO 3 . More specifically, this is considered to be attributed to the fact that Si and La that are greatly different in atomic radius form the La—O—Si bond at the deposition interface. As this strain amount is determined by the bonding of atoms, it is a universal strain amount which is not dependent on the size of a transistor as well as the thickness of the LaAlO 3  film, more specifically, not dependent on the area of Si serving as a channel. Thus, the insulating film which is stable at the Si interface and which contains La having an atomic radius greatly different from that of Si is directly deposited on the Si substrate, such that the mobility is improved in an n-channel MOS transistor requiring the tensile strain. 
     Furthermore, the direct deposition is disadvantageous to the improvement of the mobility in a p-channel MOS transistor requiring compressive strain, but this can be solved if one or more atomic layer of SiO 2  is provided at the interface. Further, if a known technique for applying the compressive strain is used, it is possible to provide a structure capable of improving the mobility in both the n- and p-channel MOS transistors. 
     Hereinafter, the embodiments of the present invention will be described with reference to the drawings. It is to be noted that the present invention is not limited to the embodiments described below and various modifications can be made without departing from the spirit of the invention. 
     First Embodiment 
       FIG. 7  is a sectional view showing the configuration of a complementary MOS (CMOS) transistor according to a first embodiment. A p-type semiconductor layer  3  and an n-type semiconductor layer  5  are formed on an Si substrate  1  via an isolation layer  7  made of SiO 2 . In addition, a substrate having a silicon on insulator (SOI) structure may be used. Moreover, the n-type semiconductor layer  5  may be an SiGe layer. In this case, the SiGe layer has to have an atomic ratio of Ge of 10% or more in order to contain strain that achieves high mobility, and has to have a Ge concentration of 20% or less in order to attain an amount of defects which does not influence transistor characteristics. 
     An n-channel MOS transistor is formed on the p-type semiconductor layer, and a p-channel MOS transistor is formed on the n-type semiconductor layer. In the n-channel MOS transistor, an amorphous LaAlO 3  film having a dielectric constant higher than that of Si is directly deposited as a gate insulating film on the p-type semiconductor layer without having any interface layer, and the Si substrate serving as a channel has a tensile strain of 0.5 to 1% in an area up to at least 3 nm from the interface. At this point, the thickness of the LaAlO 3  film can be freely changed in accordance with the application of the device. 
     A gate electrode made of segregated Al and Ni 2 Si is formed on the LaAlO 3  film. The configuration of the gate electrode is not limited to this, and the composition and material can be freely selected to provide a threshold voltage conforming to the use of the device. 
     Source/drain areas are formed across a channel area immediately under the gate insulating film of the n-channel MOS transistor. Here, tensile strain due to the LaAlO 3  film is applied to the channel portion. A gate sidewall made of SiN is formed around the gate insulating film and the gate electrode. 
     In the p-channel MOS transistor, one atomic layer of SiO 2  is formed as an interface layer on the n-type semiconductor layer, on which the LaAlO 3  film is further formed. At this point, the thickness of the SiO 2  layer and the LaAlO 3  film can be freely changed to conform to various devices. 
     Ni 2 Si is formed as a gate electrode on the LaAlO 3  film, and a gate sidewall insulating film made of SiN is formed around the gate insulating film and the gate electrode that are made of the SiO 2  layer and the LaAlO 3  layer. The configuration of the gate electrode is not limited to this in the p-channel MOS transistor as well, and its material can be freely selected in accordance with the application of the device. 
     Furthermore, an SiN film which is a stressor is formed on the gate sidewall insulating film and the gate electrode to cover these layers. Source/drain areas are formed across a channel area immediately under the SiO 2  interface layer. Here, in the channel area, tensile strain caused by the LaAlO 3  film is relaxed due to SiO 2 , and compressive strain is applied by the deposition of the SiN film which is the stressor. 
     Moreover, the SiO 2  layer at the interface may be eliminated when the effect of the stressor is great and the tensile strain in the case where the LaAlO 3  film is directly deposited can be counteracted. According to the first embodiment, greater improvement of the mobility can be made in both the n- and p-channel MOS transistors owing to the application of the optimum strains than when there is no strain. 
     Next, the process of manufacturing a semiconductor device in the first embodiment will be described. First, as shown in  FIG. 8 , the p-type semiconductor layer  3  and the n-type semiconductor layer  5  are formed on the semiconductor substrate  1  by, for example, an ion implantation method. Then, the isolation layer  7  made of a silicon oxide layer is formed on the surface of the boundary between the p-type semiconductor layer  3  and the n-type semiconductor layer  5 . 
     Subsequently, as shown in  FIG. 9 , for example, SiO 2  and polycrystalline Si are deposited as a dummy gate insulating film  9  and a dummy gate electrode  11  on the p-type semiconductor layer  3  and the n-type semiconductor layer  5 . Then, as shown in  FIG. 10 , the SiO 2  layer  9  and the polycrystalline Si layer  11  are processed using a known etching technique such as RIE to form dummy gate electrodes. 
     Then, n-type impurities and p-type impurities are ion-implanted into an nMOS transistor area and a pMOS transistor area by a known method using the dummy gate electrodes  11  as masks, thereby forming diffusion layers  13 ,  15  serving as the source/drain. It goes without saying that when ions are implanted into the FET on one side, the FET on the other side is masked with a resist (not shown). 
     Subsequently, an SiN layer is deposited on the entire surface by a known method, and etched by RIE, thereby forming gate sidewalls  17 , as shown in  FIG. 12 . Then, n-type impurities and p-type impurities are ion-implanted into the n-channel MOS transistor area and the p-channel MOS transistor area using the dummy gate electrodes  11  and the gate sidewalls  17  as masks, and a thermal treatment is performed for activation, thereby forming source/drain areas  19 ,  21  including the shallow extension source/drain portions  13 ,  15 , as shown in  FIG. 13 . 
     A selective epitaxial growth method may be used for the formation of the extension portions  13 ,  15 , and an elevated source/drain structure may be used which can suppress a short channel effect in terms of the device characteristics. Moreover, impurities may be introduced simultaneously with the formation of the elevated source/drain structure. 
     Next, the tops of the gate electrodes  11  are masked with resists  23  by a photo engraving process (PEP). Then, an Ni layer  25  is deposited at about 10 nm on the entire surface by a known method such as a sputtering method. Then, Ni is made to react with Si by a thermal treatment at about 400° C., and then unreacted Ni and the resists  23  on the gate electrodes  11  are removed by, for example, a chemical solution, thereby forming NiSi layers  27  as contacts on the surfaces of the source/drain areas  19 ,  21 , as shown in  FIG. 15 . The surfaces of the source/drain areas have only to be metal silicide formed by the thermal treatment in a self-aligning manner, such as CoSi. Moreover, conditions of the thermal treatment in the above-mentioned silicidation can be suitably changed. 
     Then, after forming an interlayer insulating film  29  made of SiO 2 , its surface is planarized by, for example, a chemical mechanical polishing (CMP) method, thereby exposing the surfaces of the gate electrodes  11 , as shown in  FIG. 16 . Then, the gate electrodes  11  are selectively removed by, for example, chemical dry etching (CDE) using CF 4  etching gas, and then the dummy gate insulating films  9  are dissolved and removed by hydrofluoric acid, thereby forming gate embedding trenches  31 , as shown in  FIG. 17 . 
     Next, amorphous LaAlO 3  films are formed as gate insulating films  33  with a thickness of about 3 nm at the bottoms of the gate embedding trenches  31  as shown in  FIG. 17  without forming any interface layer, by a sputtering method using an LaAlO 3  single crystal as a target at the substrate temperature of 600° C. in a vacuum (1×10 −6  Pa). 
     It is to be noted that the film formation method is not limited to the sputtering method, and a chemical vapor deposition (CVD) method, a molecular beam epitaxy (MBE) method, the laser ablation method, etc. may be used. Moreover, the ratio of La, Al can be suitably changed with regard to the constitution of the gate insulating film  33 . In addition, an insulating film containing La such as La 2 O 3 , LaSiO or LaHfO may be used as the gate insulating film  33 . 
     Then, Si having a thickness of, for example, 50 nm is formed on the entire surface by, for example, the CVD method, and Si thus formed is then patterned by the PEP, thereby forming a mask material  35  made of Si on the n-channel MOS transistor area, as shown in  FIG. 19 . Here, a thermal treatment is performed at 600° C. in the atmospheric oxygen, such that a SiO 2  layer  37  serving as an interface layer is formed at a thickness of 0.2 to 2 nm (about one to ten atomic layers) between the substrate and LaAlO 3  in the p-channel MOS transistor area alone, as shown in  FIG. 20 . The conditions of the thermal treatment and the thickness of the interface layer here can be freely set in accordance with the application of the device. 
     Next, the mask material  35  formed on the n-type MOS transistor area is removed. The combination of the mask material  35  and a material for removing this mask material are not limited as long as similar effects can be provided. Then, polycrystalline Si and Ni are deposited on the LaAlO 3  films  33  in the gate embedding trenches and thermally treated, thereby forming Ni 2 Si layers  39 , as shown in  FIG. 21 . 
     Then, the p-channel MOS transistor area is masked with a resist  41 , and Al is ion-implanted from above the gate electrode  39  of the n-channel MOS transistor as shown in  FIG. 22 , and then Al is segregated at the interface between the gate electrode  39  and the gate insulating film  33  by the subsequent thermal treatment, thereby forming a segregation layer  43 . This Al segregation layer  43  is formed to adjust the work function of the gate electrode in the n-type MOS transistor. Although the combination of the conditions of the ion implantation and the conditions of the subsequent thermal treatment can be arbitrarily set to enable the segregation of Al, at least the LaAlO 3  film has to be amorphous in order to segregate Al at the interface without the diffusion of Al in the LaAlO 3  film. Moreover, the Al film may be deposited on the Ni 2 Si layer  39  instead of the ion implantation. 
     Next, the interlayer insulating film  29  in the p-channel MOS transistor area is removed using the known PEP technique as shown in  FIG. 23 , thereby forming a resist mask  45  on the n-channel MOS transistor area. Further, an SiN layer  47  of 100 nm is formed on the entire surface by, for example, the CVD method as a stressor for the compressive strain in the p-channel MOS transistor area. The stressor is not limited in the material and thickness as long as it provides compressive strain to the substrate. Then, the resist  45  is lifted off to remove the SiN layer  47  on the n-channel MOS transistor area. Thus, a CMOS transistor as shown in  FIG. 24  is formed. 
     According to the first embodiment described above, the gate insulating film  33  with a high dielectric constant is directly deposited onto the p-type semiconductor layer  3  without forming the interface layer in the n-channel MOS transistor, such that the tensile strain can be introduced into Si in the p-type semiconductor layer  3 . Moreover, in the p-channel MOS transistor, an Si channel having compressive strain can be easily formed using a known technique, such that it is possible to provide a complementary MOS transistor having good mobility. 
     Second Embodiment 
     In a second embodiment, a MOS transistor having Schottky source/drain made of silicide and the process of manufacturing this MOS transistor will be described. To make it easy to understand, the same reference signs are assigned to the same parts as those in the first embodiment, and redundant explanations are omitted. 
       FIG. 25  is a sectional view showing the configuration of a semiconductor device (CMOS transistor) according to the second embodiment. A p-type semiconductor layer  3  and an n-type semiconductor layer  5  are formed on an Si substrate  1  via an isolation layer  7  made of SiO 2 . In addition, a substrate having a silicon on insulator (SOI) structure may be used. An n-channel MOS transistor is formed on the p-type semiconductor layer, and a p-channel MOS transistor is formed on the n-type semiconductor layer. 
     The second embodiment is different from the first embodiment in that source/drain layers have Schottky sources/drains  28 ,  29  made of CoSi. The second embodiment is similar to the first embodiment in other respects, so that the explanation of the structure is omitted and a manufacturing method will be described. 
     First, as in  FIG. 8  in the first embodiment, the isolation layer  7  made of a silicon oxide layer is formed on the boundary between the p-type semiconductor layer  3  and the n-type semiconductor layer  5 , and then an amorphous LaAlO 3  film  9  is deposited at a thickness of about 3 nm as a gate insulating film using a known method such as the CVD method or the sputtering method without forming any interface layer, as shown in  FIG. 26 . Then, a polycrystalline Si layer  11  is formed on the LaAlO 3  film  9  by, for example, the CVD method. 
     Subsequently, as shown in  FIG. 27 , the LaAlO 3  film  9  and the polycrystalline Si layer  11  are processed using a known etching technique such as the RIE to form dummy gate electrodes. Then, gate sidewall insulating films  18  made of SiN are formed by, for example, the CVD method, and etched by, for example, the known RIE method to reduce its thickness. Then, the dummy gate electrodes are masked with resists (not shown), and Co is deposited at about 15 nm on the entire surface by, for example, the sputtering method. 
     Then, CoSi layers  28  are formed in the source/drain areas by a thermal treatment process at 600° C. as shown in  FIG. 28 , and then unreacted Co and the resist are removed by, for example, a drug solution, thereby silicidating the source/drain areas. At this point, a metal such as Ni may be used for the silicidation instead of Co. 
     Next, after forming an interlayer insulating film  29  by a known method, the polycrystalline Si layer  11  which is the dummy gate electrode is removed, as shown in  FIG. 29 . The subsequent steps are similar to those after  FIG. 18  in the first embodiment. 
     According to the second embodiment, as in the first embodiment, a gate insulating film  33  with a high dielectric constant is directly deposited on the p-type semiconductor layer  3  without forming the interface layer in the n-channel MOS transistor, such that the tensile strain can be introduced into Si in the p-type semiconductor layer  3 . Moreover, owing to the Schottky source/drain structure, it is possible to provide a complementary MOS transistor with suppressed parasitic resistance and with good performance. 
     In addition, as in the first embodiment, the semiconductor areas  3 ,  5  can be made of SiGe (the composition ratio of Ge is 10% or more and 20% or less) in the second embodiment. 
     Third Embodiment 
     In a third embodiment, there will be described a semiconductor device having as stressors SiGe layers epitaxially grown in source/drain areas of a p-type MOS transistor, and the process of manufacturing this semiconductor device. To make it easy to understand, the same reference signs are assigned to the same parts as those in the first embodiment, and redundant explanations are omitted. 
       FIG. 30  is a sectional view showing the configuration of a semiconductor device (CMOS transistor) according to the third embodiment. A p-type semiconductor layer  3  and an n-type semiconductor layer  5  are formed on an Si substrate  1  via an isolation layer  7  made of SiO 2 . In addition, a substrate having an SOI structure may be used. An n-channel MOS transistor is formed on the p-type semiconductor layer, and a p-channel MOS transistor is formed on the n-type semiconductor layer. 
     The third embodiment is different from the first embodiment in that the epitaxially grown SiGe layers are provided as stressors in the source/drain of the p-channel MOS transistor. The third embodiment is similar to the first embodiment in other respects, so that the explanation of the structure is omitted and a manufacturing method will be described. 
     First, after the processing of a dummy gate electrode  11  and a gate insulating film  9  as in  FIGS. 9 and 10  in the first embodiment, the p-channel MOS transistor area is masked with a resist (not shown) as in  FIG. 11 , and then n-type impurities are ion-implanted into the n-channel MOS transistor area using the dummy gate electrode  11  as a mask, thereby forming source/drain diffusion layers  13  which are extension areas. 
     Then, after the resist in the p-channel MOS transistor area is removed, the n-channel MOS transistor is masked with a resist  14  as shown in  FIG. 31 , so that the source/drain areas of the p-channel MOS transistor are etched. The depth of this etching should desirably be equal to or more than the distribution of impurities provided by the subsequent ion implantation. 
     Next, as shown in  FIG. 32 , SiGe containing Ge at an atomic ratio of 10% is epitaxially grown on the etched areas. At this point, Ge has to be at an atomic ratio of 10% or more in order to apply compressive strain to Si serving as a channel, and the amount of Ge has to be 20% or less in order to attain an amount of defects which does not influence transistor characteristics. 
     Next, ions are implanted into the p-channel MOS transistor area, so that extension areas  15  of the p-channel MOS transistor are formed, as shown in  FIG. 33 . Then, the resist  14  on the nMOS transistor is removed. The subsequent steps conform to the steps after  FIG. 12  in the first embodiment, but the SiN film which is a stressor for the compressive strain in the first embodiment may be omitted. If this is used together, stronger strain can be provided to the channel areas of the p-channel MOS transistor. 
     According to the third embodiment, as in the first embodiment, the gate insulating film  33  with a high dielectric constant is directly deposited onto the p-type semiconductor layer  3  without forming the interface layer in the n-channel MOS transistor, such that the tensile strain can be introduced into Si in the p-type semiconductor layer  3 . Moreover, in the p-channel MOS transistor area, SiGe layers  22  are provided as the stressor, the compressive strain can be provided to the Si channel as in the first embodiment. 
     As described above, according to the present invention, it is possible to provide a complementary MOS transistor capable of applying to the channel of the n-channel MOS transistor tensile strain which is not dependent on the size of the transistor. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.