JP2005252052A - Semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device, wherein a concentration of nitrogen in a gate insulating film is arranged to be different according to kinds of transistors, such as conduction type and those which are different in film thickness or the like of the gate insulating films, and improvement in the transistor current drive force and suppression of the deterioration in the transistor performance are both realized. <P>SOLUTION: A device isolating oxide film 104 of about 300 nm in thickness is formed on a p-type semiconductor substrate 101 by using an STI method or the like, after which a thicker first gate insulating film 105a, and a thinner second gate insulating film 105b are formed; and then surfaces of these are brought into contact with nitrogen plasma to nitride. Thereafter, a photoresist 163 is formed on a portion of the p-type semiconductor substrate 101; then the concentration of nitrogen in the film near the surface of the first gate insulating film 105a is reduced, by bringing it into contact with oxygen plasma 162 for 120 seconds, after which a gate electrode, a source/a drain and metal wiring or the like are formed by a known method to complete the semiconductor device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a highly reliable semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device having a nitrogen-containing gate insulating film and a manufacturing method thereof.

  In recent years, semiconductor devices have been miniaturized in order to meet the demands for higher integration, higher functionality and higher speed, and lower power consumption of semiconductor integrated circuit devices. With the miniaturization, two problems have become apparent. One is to see out (or penetrate) boron, and the other is to secure the transistor current driving capability.

  First, boron exudation (or punching) will be described. Since the short channel effect becomes apparent when the gate length is shortened, a surface channel p-type MOS transistor is used after the 0.25 μm generation, and boron is introduced as an impurity in the gate electrode. Boron in the gate electrode diffuses from the gate electrode into the gate insulating film and the silicon substrate during the manufacturing process. Boron diffused into the silicon substrate deteriorates the transistor performance by changing the threshold value of the transistor or lowering the channel mobility. This phenomenon is the oozing out (or punching out) of boron.

  On the other hand, securing the transistor current driving capability is a problem caused by the gate insulating film. Although the gate insulating film has been thinned along with miniaturization, since the leakage current between the gate electrode and the silicon substrate due to direct tunneling becomes obvious when the thickness is 2 nm or less, the thickness of the gate insulating film cannot be further reduced. . On the other hand, unless the gate insulating film is thinned, the transistor current driving capability cannot be improved and the short channel effect cannot be suppressed.

  In order to solve these problems, nitrogen is introduced into the gate insulating film. As the gate insulating film, a silicon oxynitride film containing nitrogen is used instead of a pure silicon oxide film. By introducing the silicon oxynitride film, boron diffusion from the gate electrode into the silicon substrate is reduced, and transistor performance deterioration due to boron oozing can be suppressed. Furthermore, since the silicon oxynitride film has a dielectric constant higher than that of a pure silicon oxide film, a high transistor current driving capability can be obtained when compared with the same film thickness. As a result, the transistor current driving capability can be improved without increasing the leakage current between the gate electrode and the silicon substrate.

A silicon oxynitride film is generally formed by heat-treating a silicon oxide film in a gas phase containing NO, N ₂ O, or NH ₃ , or a silicon substrate is directly heat-treated in NO or N ₂ O and then the substrate is formed. It was formed by oxidation. With such a formation method, it is known that nitrogen in the silicon oxynitride film exists at a high concentration at the interface between the silicon substrate and the silicon oxynitride film, and part of the nitrogen diffuses into the silicon substrate. . Nitrogen diffused to the inside of the silicon substrate deteriorates the transistor performance by changing the threshold value of the transistor or lowering the channel mobility in the same manner as boron exudation. Furthermore, it has been reported that this nitrogen induces a large characteristic deterioration (NBTI: Negative Bias Temperature Instability) in a BT test of a p-type transistor (Non-patent Document 1). Here, NBTI is a change in operating current due to a threshold change.

  Therefore, a technique has been proposed that solves these problems by maintaining a high nitrogen content in the silicon oxynitride film as a whole and reducing the nitrogen concentration at the interface between the silicon substrate and the silicon oxynitride film. .

  Hereinafter, a method for forming a gate insulating film disclosed in Patent Document 1 will be described with reference to FIGS.

In FIG. 7A, an element isolation film 2 having an STI structure is formed on a silicon substrate 1, and ion implantation for well, channel stop, and threshold voltage adjustment is performed, and then various cleanings are performed. In FIG. 7B, a silicon oxide film 3 having a thickness of 2.0 to 3.0 nm is formed using an active oxygen species such as O ₃ gas. Next, in FIG. 7C, plasma nitriding is performed to form a silicon oxynitride film 5 (silicon oxynitride film) having a nitrogen concentration peak in the region 4. Thereafter, in FIG. 7 (d), a polycrystalline silicon film 6 having a thickness of 100 nm is formed by the CVD method, the gate electrode 7 is formed by using the photolithography technique and the dry etching technique, and then ion implantation is performed in FIG. 7 (e). Then, activation is performed to form a source / drain, and an interlayer insulating film 8, a contact hole, and a wiring 9 are formed, thereby completing a semiconductor device.

FIG. 8 shows the nitrogen concentration distribution in the silicon oxynitride film measured by SIMS after the silicon oxynitride film 5 is formed. Compared to a conventional silicon oxynitride film formed by thermal nitridation using NO gas, the nitrogen concentration at the silicon oxynitride film surface is high and the nitrogen concentration at the interface with the silicon substrate is kept low. Understand.
JP 2002-222941 A Digest of Technical Papers "2000 Symposium on VLSI Technology", p92.

  However, when the conventional method of Patent Document 1 described above is used, nitrogen is introduced into all the gate insulating films provided on the silicon substrate. This causes the following problems.

  In general, in order to cope with a plurality of operating voltages, at least two kinds of transistors having different gate insulating film thicknesses are mixed in a semiconductor device. For example, when the power supply voltage of the external interface (I / O) circuit is 3 V, the gate insulating film thickness is about 7 to 10 nm, and when 2.5 V, a transistor having a film thickness of about 5 nm is required. . On the other hand, an internal transistor that performs storage, calculation, etc. generally operates at 1 to 1.5 V, but in this case, a transistor having a thickness of about 1.8 to 2.5 nm is required. The above-described NBTI appears remarkably in a transistor having a relatively thick gate insulating film (5 to 10 nm). When the gate insulating film is thick, the number A of charges induced in the channel portion by the gate voltage decreases. Therefore, the ratio B / A between the A and the silicon substrate-silicon oxynitride film interface state number B generated by nitrogen increases as the gate insulating film thickness increases. For this reason, it is considered that NBTI appears remarkably in a transistor having a relatively thick gate insulating film. On the other hand, a transistor with a relatively thick gate insulating film has little effect of improving the dielectric constant due to the high-concentration nitride layer formed on the outermost surface. From the viewpoint of transistor current driving power, nitrogen introduction into the gate insulating film is not I don't need that much.

  In an n-type transistor, since an n-type impurity such as phosphorus is introduced into the gate electrode, the above-described problem caused by boron does not occur, so that nitrogen introduction into the gate insulating film is not so necessary.

  However, in the prior art, the same amount of nitrogen is introduced into all the gate insulating films on the wafer. Therefore, depending on the type of transistor, such as the conductivity type and the thickness of the gate insulating film, into the gate insulating film. The amount of nitrogen introduced cannot be made different. As a result, there is a problem that it is impossible to achieve both improvement in transistor current driving capability and suppression of deterioration in transistor performance.

  In view of the above problems, according to the present invention, the amount of nitrogen introduced into the gate insulating film can be different depending on the type of transistor having different conductivity type (conductivity type) and the thickness of the gate insulating film. An object of the present invention is to provide a semiconductor device and a method for manufacturing the same that can achieve both improvement in driving force and suppression of deterioration in transistor performance.

  In order to achieve the above object, a first semiconductor device of the present invention includes a substrate and one or more first transistors and one or more second transistors each having a gate insulating film formed on the substrate. A semiconductor device is characterized in that a nitrogen concentration in at least one gate insulating film of the first transistor is different from a nitrogen concentration in at least one gate insulating film of the second transistor. .

  By adopting such a configuration, in a semiconductor device in which transistors of different types such as conductivity type and gate insulating film thickness are mixed, gate insulation is selected according to the gate insulating film thickness and transistor type. In the gate insulating film with different nitrogen concentration and high nitrogen concentration, diffusion of boron and the like from the gate electrode is suppressed, and the gate insulating film has a high nitrogen concentration with a high relative dielectric constant, improving the transistor current driving capability On the other hand, in a gate insulating film with a low nitrogen concentration, the nitrogen concentration at the interface between the substrate and the gate insulating film can be kept low, and the diffusion of nitrogen into the substrate can be suppressed. As a result, the gate insulating film has a low nitrogen concentration that can suppress the decrease in NBTI and NBTI, and the effect of suppressing deterioration in transistor performance can be obtained. That.

  According to a second semiconductor device of the present invention, in the first semiconductor device, the thickness of the gate insulating film of the second transistor is smaller than the thickness of the gate insulating film of the first transistor.

  With such a configuration, it is possible to have a configuration in which the nitrogen concentration in the gate insulating film differs depending on the thickness of the gate insulating film, and the same effect as the first semiconductor device can be obtained.

  According to a third semiconductor device of the present invention, in the first or second semiconductor device, the nitrogen concentration in at least one gate insulating film in the second transistor is at least one gate insulating in the first transistor. It is characterized by being higher than the nitrogen concentration in the film.

  With such a configuration, the nitrogen concentration in the thin gate insulating film is higher than the nitrogen concentration in the thick gate insulating film. The diffusion of boron, etc. from the substrate can be suppressed, and a high dielectric constant can be realized, and the transistor current driving capability can be improved. On the other hand, in the thick gate insulating film, the nitrogen concentration at the interface between the substrate and the gate insulating film As a result, it is possible to suppress the diffusion of nitrogen to the substrate, suppress the threshold fluctuation of the transistor, the decrease in channel mobility, and NBTI, thereby suppressing the deterioration of the transistor performance. It is done.

  According to a fourth semiconductor device of the present invention, in any one of the first to third semiconductor devices, the thickness of the gate insulating film of the second transistor is in the range of 1.5 nm to 3.0 nm. The thickness of the gate insulating film of the transistor is in the range of 5 nm to 10 nm.

  By adopting such a configuration, the effects of the first to third semiconductor devices can be remarkably obtained.

  According to a fifth semiconductor device of the present invention, in any one of the first to fourth semiconductor devices, the first transistor or the second transistor has one or more n-type transistors and one p-type transistor, respectively. The nitrogen concentration of at least one gate insulating film in the transistor is different from the nitrogen concentration in at least one gate insulating film in the n-type transistor.

  With such a configuration, when only one of the n-type transistor and the p-type transistor has a problem such as weak NBTI resistance, the nitrogen concentration in the gate insulating film having the weaker NBTI resistance is lowered. As a result, the diffusion of nitrogen into the substrate can be suppressed, the above-described threshold fluctuation of the transistor, the decrease in channel mobility and NBTI can be suppressed, and the effect of suppressing deterioration in transistor performance can be obtained. For example, it becomes possible to increase only the nitrogen concentration in the gate insulating film of a p-type transistor having a gate electrode containing a p-type impurity such as boron, and diffusion of p-type impurities such as boron from the gate electrode is suppressed. On the other hand, in an n-type transistor that does not contain p-type impurities such as boron, the nitrogen concentration can be lowered.

  In order to achieve the above object, a first method for manufacturing a semiconductor device of the present invention includes a step of forming a gate insulating film of a first transistor and a gate insulating film of a second transistor on a substrate; Nitriding the gate insulating film of the first transistor and the gate insulating film of the second transistor, and denitrifying at least part of at least one of the gate insulating film of the first transistor and the gate insulating film of the second transistor And a step of performing.

  With such a structure, in manufacturing a semiconductor device in which transistors of different types such as conductivity type and gate insulating film thickness are mixed, depending on the thickness of the gate insulating film and the type of transistor. Therefore, it is possible to increase or decrease the nitrogen concentration in the gate insulating film. In the gate insulating film with a high nitrogen concentration, diffusion of boron and the like from the gate electrode is suppressed, and a high relative dielectric constant is obtained. A gate insulating film having a high nitrogen concentration can be realized and the transistor current driving capability can be improved. On the other hand, a gate insulating film having a low nitrogen concentration can keep the nitrogen concentration at the interface between the substrate and the gate insulating film low. A low nitrogen concentration that suppresses the diffusion of nitrogen into the substrate and suppresses the above-described transistor threshold fluctuation, channel mobility reduction, and NBTI. Insulating film can be realized, suppressing the deterioration of the transistor performance effect is obtained that attained.

  According to the second method for manufacturing a semiconductor device of the present invention, in the first method for manufacturing a semiconductor device, the thickness of the gate insulating film of the second transistor is smaller than the thickness of the gate insulating film of the first transistor. It is characterized by.

  By adopting such a configuration, it becomes possible to increase or decrease the nitrogen concentration in the gate insulating film according to the film thickness of the gate insulating film, which is the same as the manufacturing method of the first semiconductor device. An effect is obtained.

  A third semiconductor device manufacturing method of the present invention is characterized in that, in the first or second semiconductor device manufacturing method, at least a part of the gate insulating film of the first transistor is selectively denitrified. To do.

  By adopting such a configuration, it becomes possible to make the nitrogen concentration in the thin gate insulating film higher than the nitrogen concentration in the thick gate insulating film. In the thin gate insulating film, While diffusion of boron and the like from the gate electrode is suppressed, a high dielectric constant can be realized, and the transistor current driving capability can be improved. On the other hand, in a thick gate insulating film, at the interface between the substrate and the gate insulating film The nitrogen concentration can be kept low, the diffusion of nitrogen to the substrate can be suppressed, the threshold fluctuation of the transistor, the decrease in channel mobility and NBTI can be suppressed, and the deterioration of transistor performance can be suppressed. Is obtained.

  A fourth method for manufacturing a semiconductor device according to the present invention is characterized in that, in any of the first to third methods for manufacturing a semiconductor device, plasma nitriding is used as the nitriding step.

  By adopting such a configuration, while the nitrogen concentration on the surface of the gate insulating film is increased, the nitrogen concentration at the interface between the substrate and the gate insulating film can be suppressed, and the diffusion of nitrogen to the substrate is suppressed. Thus, it is possible to suppress the above-described threshold fluctuation of the transistor, the decrease in channel mobility, and NBTI, and the effect of suppressing deterioration in transistor performance can be obtained.

  According to a fifth semiconductor device manufacturing method of the present invention, in the third semiconductor device manufacturing method, in the step of selectively denitrifying at least a part of the gate insulating film of the first transistor, the photoresist is masked. It is used as.

  With such a configuration, the photoresist as a mask can be easily removed with an acid or the like, and therefore, the film quality of the gate insulating film of the second transistor covered with the mask is not altered when the mask is removed. Is obtained.

  A sixth method for manufacturing a semiconductor device according to the present invention is characterized in that, in any one of the first to fifth methods for manufacturing a semiconductor device, the denitrification step is an oxidation step.

  With such a configuration, an oxygen atom replaces a nitrogen atom in the gate insulating film, and as a result, an effect is obtained that the gate insulating film can be denitrified relatively easily.

  According to a seventh method for manufacturing a semiconductor device of the present invention, in the sixth method for manufacturing a semiconductor device, at least one of oxygen plasma treatment, phosphoric acid etching, ion implantation, and plasma doping is used in the oxidation process. It is characterized by that.

  With such a configuration, it is possible to obtain an effect that the gate insulating film can be oxidized relatively easily.

  According to the present invention, the amount of nitrogen introduced into the gate insulating film can be made different depending on the types of transistors having different conductivity types and film thicknesses of the gate insulating film, etc. It is possible to achieve both high-performance and high-reliability semiconductor devices that can simultaneously suppress degradation of performance.

  A method for manufacturing a semiconductor device according to an embodiment of the present invention will be described below with reference to FIGS.

  1 to 5 are cross-sectional views of relevant parts for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention.

  FIG. 6 is a nitrogen concentration profile in the gate insulating film for explaining the effect of the semiconductor device manufacturing method according to the embodiment of the present invention.

  First, in FIG. 1A, a plurality of element isolation oxide films 104 having a thickness of about 300 nm are formed on a p-type semiconductor substrate 101 using an STI method or the like. In FIG. 1B, a photoresist 165 is formed on a part of the p-type semiconductor substrate 101, and boron ions 166 are implanted to form p-well regions 103a and 103b in a part of the p-type semiconductor substrate 101. . After removing the photoresist 165, a photoresist 167 is formed on the p-type semiconductor substrate 101 in FIG. 1C, and phosphorus ions 168 are implanted to partially form the n-well region 102a, 102b is formed. If necessary, after performing channel stop for preventing leakage through the element isolation oxide film, impurity control for threshold control, heat treatment for diffusion and activation, etc., the used photoresist is peeled off and p. The mold semiconductor substrate 101 is cleaned with an acid or the like (FIG. 1D).

  Next, in FIG. 2A, a first gate insulating film 105 a having a thickness of about 7.5 nm is formed on the p-type semiconductor substrate 101. In this insulating film forming step, oxidation by an electric furnace or a lamp annealing apparatus is used. An oxygen or water vapor atmosphere is used as the oxidizing atmosphere. However, it is preferable to use water vapor oxidation in a lamp annealing apparatus in order to relieve stress at the STI edge and suppress variations in the thickness of the insulating film. For example, water vapor is generated using a mixed gas of hydrogen and oxygen, and an oxide film having a thickness of about 7.5 nm is formed by applying lamp annealing at 1050 ° C. while bringing the gas containing the water vapor into contact with the p-type semiconductor substrate 101. I do.

  Next, in FIG. 2B, a photoresist 164 is formed on a part of the p-type semiconductor substrate 101, and a portion of the first gate insulating film 105a is formed using a dilute hydrofluoric acid aqueous solution or a buffered hydrofluoric acid aqueous solution. Remove the part. In FIG. 2C, a second gate insulating film 105b is formed on a portion of the p-type semiconductor substrate 101 where the first gate insulating film 105a is not formed. The film thickness of the second gate insulating film 105b is about 2 nm, and is formed by using steam oxidation in a lamp annealing apparatus as before. The temperature is preferably 800 ° C to 900 ° C. At this time, the thickness of the first gate insulating film 105a hardly increases.

  Next, in FIG. 2D, the p-type semiconductor substrate 101 is heated from about 300 ° C. to 500 ° C. and brought into contact with the nitrogen plasma 161 for 40 seconds. The surfaces of the first gate insulating film 105a and the second gate insulating film 105b are nitrided to form oxynitride films having a nitrogen profile indicated by solid lines in FIGS. 6 (a) and 6 (b), respectively. Details of the nitrogen profile will be described later.

Next, in FIG. 3A, a photoresist 163 is formed on a part of the p-type semiconductor substrate 101 (the first film insulating film 105a having a smaller thickness without being formed on the first gate insulating film 105a having a larger film thickness). 2) and is brought into contact with oxygen plasma 162 for 120 seconds. Since the oxygen plasma 162 incinerates the photoresist 163, the thickness of the photoresist 163 gradually decreases (FIG. 3B). On the other hand, the oxygen plasma 162 also diffuses into the first gate insulating film 105a and reacts with nitrogen near the surface of the first gate insulating film 105a to reduce the nitrogen concentration in the film. If necessary, heat treatment at 900 ° C. or lower can be added to promote nitrogen desorption. Further, another gas can be added to the oxygen plasma 162 as necessary. For example, when CF ₄ gas or the like is added, only a portion near the surface of the gate insulating film 105a containing nitrogen at a high concentration can be etched at high speed.

  Further, instead of the treatment with the oxygen plasma 162, a treatment with phosphoric acid etching, ion implantation or plasma doping may be performed. In general, it is known that heated phosphoric acid can selectively etch a silicon nitride film with respect to a silicon oxide film. Therefore, when the p-type semiconductor substrate 101 is placed in heated phosphoric acid and etching is performed, nitrogen present on the surfaces of the first gate insulating film 105a and the second gate insulating film 105b has a high concentration. It is possible to selectively oxidize only the portion in the vicinity of the surface included in the surface. On the other hand, by ion implantation or plasma doping, oxygen ions are introduced into the vicinity of the surface containing nitrogen at a high concentration and heated, so that only the vicinity of the surface containing nitrogen at a high concentration is selectively siliconized as in oxidation. It can be transformed into an oxide film, and substantially the same effect can be obtained.

  In FIG. 3C, the photoresist 163 on the p-type semiconductor substrate 101 is removed with a sulfuric acid / hydrogen peroxide mixed aqueous solution, and a poly-Si (polycrystalline silicon) thin film 155 is deposited to a thickness of 200 nm to 300 nm. If necessary, a silicon oxide film for a hard mask may be formed on the poly-Si thin film 155. Impurities may be introduced into the poly-Si thin film 155 on the p-well regions 103a and 103b in order to prevent depletion when used as a gate electrode. In other words, phosphorus or arsenic ions are implanted to form n-type. Similarly, the poly-Si thin film 155 on the n-well regions 102a and 102b may be made p-type by ion implantation of boron or the like.

In FIG. 4A, the poly-Si thin film 155 is processed using normal lithography and etching, and a first n-type gate electrode 151, a first p-type gate electrode 152, and a second n-type gate electrode 153 are processed. Then, a second p-type gate electrode 154 is formed. Further, an extension layer can be formed in the transistor including the second gate insulating film 105b as needed. For example, ion implantation is performed using the element isolation oxide film 104, the second n-type gate electrode 153, and the second p-type gate electrode 154 as a mask, and an n-type extension layer is formed in a part of the p-well region 103a. A p-type extension layer 172a is formed on a part of the n-well region 102a (see FIG. 4B). The n-type extension layer 171a and the p-type extension layer 172a preferably have an impurity concentration of about 10 ¹⁸ to 10 ¹⁹ cm ⁻³ . Similarly, using the element isolation oxide film 104, the first n-type gate electrode 151, and the first p-type gate electrode 152 as a mask, an n-type extension layer 171b is formed on a part of the p-well region 103b. A p-type extension layer 172b can be formed in a part of the n-well region 102b (see FIG. 4B).

In FIG. 4B, a silicon oxide film or a silicon nitride film is deposited to a thickness of 50 to 70 nm, and anisotropic dry etching is used to form the silicon oxide film or the silicon nitride film into the first n-type gate electrode 151 and the first n-type gate electrode 151. A sidewall insulating film 173 is formed on the sidewalls of the first p-type gate electrode 152, the second n-type gate electrode 153, and the second p-type gate electrode 154. Subsequently, ion implantation is performed using the element isolation oxide film 104, the first n-type gate electrode 151, and the second n-type gate electrode 153 as a mask, so that n is partially formed in the p-well regions 103a and 103b. An n-type diffusion layer 107 to be a source / drain region of the n-type transistor is formed. In the same process, a p-type diffusion layer 108 to be a source / drain region of the p-type transistor is formed in part of the n-well regions 102a and 102b. The impurity concentration of the n-type diffusion layer 107 and the p-type diffusion layer 108 is preferably about 10 ¹⁹ to 10 ²² cm ⁻³ . Next, activation heat treatment of the n-type diffusion layer 107 and the p-type diffusion layer 108 is performed.

  In FIG. 4C, an interlayer insulating film 109 is formed using a high-density silicon oxide film or the like, a contact hole is opened at a desired position by lithography and dry etching, and tungsten or the like is filled therein. Next, the metal wiring layer 121 is formed using a metal such as aluminum or Cu. As a result, the first n-type transistor 111 having the first n-type gate electrode 151, the first p-type transistor 112 having the first p-type gate electrode 152, and the second n-type gate electrode 153 having the second n-type gate electrode 153. A second p-type transistor 114 having two n-type transistors 113 and a second p-type gate electrode 154 is formed. Further, in FIG. 5, a desired number of metal wiring layers 121 and interlayer insulating film 109 are stacked, and finally a surface protective film 181 is formed using a silicon nitride film or the like, thereby completing the semiconductor device.

  In the present embodiment, a metal silicide layer is not formed on the gate electrodes 151 to 154 or the diffusion layers 107 to 108, but the metal is self-aligned by a normal method using a metal such as Ti, Co, or Ni. A silicide layer may be formed.

  When the method for manufacturing a semiconductor device according to the present invention is used, NBTI of a p-type transistor can be significantly suppressed. This will be described with reference to FIG. 6A and 6B show nitrogen profiles in the first gate insulating film 105a and the second gate insulating film 105b, respectively. As described above, the solid line is immediately after plasma nitriding, and very high concentration of nitrogen exists near the surface. On the other hand, since various heat treatments are subsequently applied to the p-type semiconductor substrate 101, nitrogen also partially diffuses, and when the conventional method is used, a nitrogen profile indicated by a broken line is obtained after the completion of the semiconductor device. In the first gate insulating film 105a made of a thick insulating film, the interface nitrogen concentration with the silicon substrate is significantly increased. On the other hand, when the semiconductor device manufacturing method according to the present invention is used, the nitrogen concentration in the insulating film is reduced by plasma oxidation immediately after nitriding. Therefore, as shown by the one-dot chain line in FIG. As a result, the nitrogen concentration in the insulating film is reduced, and in particular, the interface nitrogen concentration with the silicon substrate can be suppressed to a concentration that is hardly different from that immediately after nitriding. Thereby, the nitrogen concentration at the silicon substrate-silicon oxynitride film interface can be suppressed to 5 at% or less, preferably 1 at% or less, and NBTI of the p-type transistor can be significantly suppressed. On the other hand, the second gate insulating film 105b having a smaller thickness has no difference in nitrogen profile when using the method of manufacturing a semiconductor device according to the present invention and when using the conventional method. As shown in FIG. 6B, the interface nitrogen concentration with the silicon substrate is considerably higher than that of the first gate insulating film 105a, but the number of charges induced in the channel portion by the gate voltage is overwhelmingly large as described above. Therefore, NBTI degradation does not become a big problem.

  Therefore, according to the present embodiment, in the gate insulating film 105b having a high nitrogen concentration, diffusion of boron or the like from the gate electrode 154 can be suppressed, and a gate insulating film having a high relative permittivity and a high nitrogen concentration can be realized. The driving force can be improved. On the other hand, in the gate insulating film 105a with a low nitrogen concentration, the nitrogen concentration at the interface between the substrate and the gate insulating film can be suppressed low, and the diffusion of nitrogen into the substrate can be suppressed. A gate insulating film having a low nitrogen concentration that can suppress the decrease in the degree of NBTI and NBTI can be realized, and the effect of suppressing deterioration in transistor performance can be obtained.

  In the present embodiment, the thicker gate insulating film 105a has a thickness of about 7.5 nm and the thinner gate insulating film 105b has a thickness of about 2 nm. However, the thicker gate insulating film 105a has a thickness of 5 to 10 nm. When the thinner gate insulating film 105b is in the range of 1.5 nm to 3.0 nm, the above-described effect is remarkably obtained.

  In this embodiment, the nitrogen concentration of the first gate insulating film 105a having a thick gate insulating film is lowered. However, even if the nitrogen concentration is partially lowered in the same gate insulating film, Good. For example, the nitrogen concentration in the first gate insulating film 105a is reduced in both the n-type transistor and the p-type transistor having the first gate insulating film 105a, but only one of the n-type transistor or the p-type transistor is NBTI resistant. If there is a problem such as weakness, only the nitrogen concentration in the gate insulating film 105a of either the n-type transistor or the p-type transistor is reduced only by changing the formation region of the photoresist 163 (FIG. 3). be able to.

  In this embodiment, a p-type Si substrate can be used as the p-type semiconductor substrate 101. Further, the conduction type is not limited to the p-type, and may be an n-type or an insulating type. Moreover, as a semiconductor, it is good also as semiconductors other than Si, such as SiC and GaAs. Further, instead of the semiconductor substrate, a substrate made of an insulator such as glass may be used. In the case of using a substrate made of an insulator, it is desirable to form a semiconductor layer on the insulator.

  As described above, the present invention can achieve both ensuring of transistor current driving capability and high reliability, and is useful for a fine semiconductor device, a manufacturing method thereof, and the like.

Sectional drawing which shows the principal part which shows each process of the manufacturing method of the semiconductor device which concerns on embodiment of this invention Sectional drawing which shows the principal part which shows each process of the manufacturing method of the semiconductor device which concerns on embodiment of this invention Sectional drawing which shows the principal part which shows each process of the manufacturing method of the semiconductor device which concerns on embodiment of this invention Sectional drawing which shows the principal part which shows each process of the manufacturing method of the semiconductor device which concerns on embodiment of this invention Sectional drawing which shows the principal part which shows each process of the manufacturing method of the semiconductor device which concerns on embodiment of this invention Nitrogen profile diagram in gate insulating film in manufacturing method of semiconductor device according to embodiment of present invention Partial expanded sectional view which shows the manufacturing method of the conventional semiconductor device Nitrogen profile in gate insulating film by conventional semiconductor device manufacturing method

Explanation of symbols

101 p-type semiconductor substrate 102a, 102b n-well region 103a, 103b p-well region 104 element isolation oxide film 105a first gate insulating film 105b second gate insulating film 109 interlayer insulating film 111 first n-type transistor 112 first P-type transistor 113 second n-type transistor 114 second p-type transistor 121 metal wiring layer 151 first n-type gate electrode 152 first p-type gate electrode 153 second n-type gate electrode 154 second p-type gate electrode 155 poly-Si thin film 161 nitrogen plasma 162 oxygen plasma 163 photoresist 164 photoresist 165 photoresist 166 boron ion 167 photoresist 168 phosphorus ion 171a, 171b n-type extension layers 172a, 172b p-type Extension layer 173 Side wall insulating film 181 Surface protective film

Claims (12)

A semiconductor device comprising a substrate, and one or more first transistors and one or more second transistors each having a gate insulating film formed on the substrate,
A semiconductor device, wherein a nitrogen concentration in at least one gate insulating film of the first transistor is different from a nitrogen concentration in at least one gate insulating film of the second transistor.   2. The semiconductor device according to claim 1, wherein a thickness of the gate insulating film of the second transistor is smaller than a thickness of the gate insulating film of the first transistor.   3. The nitrogen concentration in at least one gate insulating film in the second transistor is higher than the nitrogen concentration in at least one gate insulating film in the first transistor. The semiconductor device described.   The thickness of the gate insulating film of the second transistor is in the range of 1.5 nm to 3.0 nm, and the thickness of the gate insulating film of the first transistor is in the range of 5 nm to 10 nm. The semiconductor device according to claim 1.   The first transistor or the second transistor has at least one n-type transistor and one p-type transistor, and the nitrogen concentration of at least one gate insulating film in the p-type transistor is within the n-type transistor. 5. The semiconductor device according to claim 1, wherein the semiconductor device has a nitrogen concentration different from that of at least one gate insulating film. Forming a gate insulating film of a first transistor and a gate insulating film of a second transistor on a substrate;
Nitriding the gate insulating film of the first transistor and the gate insulating film of the second transistor;
Denitrifying at least part of at least one of the nitrided gate insulating film of the first transistor and the gate insulating film of the second transistor;
A method for manufacturing a semiconductor device, comprising:   The method for manufacturing a semiconductor device according to claim 6, wherein a film thickness of the gate insulating film of the second transistor is thinner than a film thickness of the gate insulating film of the first transistor.   8. The method of manufacturing a semiconductor device according to claim 6, wherein at least a part of the gate insulating film of the first transistor is selectively denitrified.   9. The method of manufacturing a semiconductor device according to claim 6, wherein plasma nitriding is used as the nitriding step.   9. The method for manufacturing a semiconductor device according to claim 8, wherein a photoresist is used as a mask in the step of selectively removing at least part of the gate insulating film of the first transistor.   The method for manufacturing a semiconductor device according to claim 6, wherein the denitrifying process is an oxidizing process.   12. The method of manufacturing a semiconductor device according to claim 11, wherein in the oxidation process, at least one of oxygen plasma treatment, phosphoric acid etching, ion implantation, and plasma doping is used.

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