Abstract:
An object of the present invention is to provide an ion implantation method for shortening a down time of an ion implantation apparatus after exposure of a chamber and for improving throughput and a method for manufacturing a semiconductor device. Specifically, the object of the invention is to provide an ion implantation method that can improve throughput during an ion implantation step of B and a method for manufacturing a semiconductor device. The ion implantation method comprises the steps of: introducing an impurity imparting p-type conductivity and H 2 O in an ion source; ionizing the impurity imparting p-type conductivity; and implanting into a semiconductor film.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ion implantation method and more specifically to a method for manufacturing a semiconductor device using the ion implantation method. 
   2. Description of the Related Art 
   An ion implantation method is one of doping methods of an impurity. Compared to other doping methods such as a doping method during film formation and a thermal diffusion method, the ion implantation method has an extremely large ion implantation amount and extremely high control accuracy of an implantation depth, and has a merit capable of low concentration control. Dopant used for a semiconductor device can be roughly classified into n-type dopant and p-type dopant. A Group 5 element such as phosphorus (P), arsenic (As), or antimony (Sb), a Group 6 element such as sulfur (S), tellurium (Te), or selenium (Se), or the like that functions as a donor is known as an impurity element imparting n-type conductivity, and P is mainly used in an industry. In addition, a Group 3 element such as boron (B), aluminum (Al), gallium (Ga), or indium (In), a Group 2 element such as zinc (Zn), or the like that functions as an acceptor is known as an impurity element imparting p-type conductivity, and B is mainly used in an industry. 
   Ion implantation is carried out in a chamber by generating an ion from an ion source, extracting an ion by applying an electric field, splitting an ion that is needed with an analyzing magnet, accelerating the ion in electrostatic up to an acceleration energy that is needed, and implanting the ion into a semiconductor film formed over a substrate. 
   Usually, loading and unloading of a substrate to a chamber in an ion implantation apparatus is carried out through a load lock chamber. Therefore, the apparatus can be operated without exposing the chamber to the atmosphere. However, it is necessary to expose the chamber to the atmosphere regularly for, for example, maintenance. In this case, the inside of the chamber is replaced by a doping gas after the chamber is exposed to an atmosphere; however, a constituent such as water adhered to the inside of the chamber by being exposed to the atmosphere is remained for a certain periods after operating the apparatus. Thus, treatment over a substrate has to be refrained until an ion species ratio is stabilized and there is a problem that a long down time ranging from 40 hours to 50 hours is needed for aging. 
   In addition, compared to P, B generally has a low ion species ratio at the time of ion implantation; therefore, B is inferior in respect of throughput. Although it is possible to raise the ion species ratio of B to some extent by increasing a flow or a concentration of a gas that serves as dopant, it is still inadequate to obtain throughput equivalent to P. Moreover, compared to P, B is subject to variation since the ion species ratio is low; therefore, there is a problem that a longer down time is needed to stabilize the ion species ratio after the chamber is exposed to the atmosphere. 
   SUMMARY OF THE INVENTION 
   In view of the above problems, an object of the present invention is to provide an ion implantation method for shortening a down time of an ion implantation apparatus after exposure of a chamber and for improving throughput and a method for manufacturing a semiconductor device. Specifically, the object of the invention is to provide an ion implantation method that can improve throughput during an ion implantation step of B and a method for manufacturing a semiconductor device. 
   The inventors found that an ion species ratio in the chamber and change of moisture concentration over time have close relation with each other.  FIG. 1  shows the ratio of H 2 O and the ion species ratio of B to a time of using a filament of an ion source in an ion implantation apparatus, which are obtained by a mass spectrum. Note that B 2 H 6  is used as dopant, and H 2 O is shown as a ratio to H 3   +  and the ion species of B is shown as a ratio of B 2 H y   +  to the sum of H + , H 2   + , H 3   + , BH x   + , and B 2 H y   + . 
   According to  FIG. 1 , as the time of using a filament gets longer, although there are a few vertical variations, the ratio of H 2 O in the chamber is lowered, and it is infinitely converged to a value close to 0. On the other hand, the ion species ratio of B is lowered while varying vertically as well as the ratio of H 2 O is lowered, and the timing of the vertical variation corresponds to timing in which H 2 O is varied. Accordingly, there is some sort of a correlation between the ratio of H 2 O and the ion species ratio of B, and it is predicted that generation of ion species of B is promoted by the existence of H 2 O. 
   In the ion implantation method and the method for manufacturing a semiconductor device of the invention, H 2 O, as well as a gas used as dopant, is supplied continuously and successively to the chamber, and the ratio of the H 2 O in the chamber is kept constant by taking advantage of the above phenomenon reversely. As a specific supplying method, an inert gas containing H 2 O may be supplied to the chamber, or H 2 O itself can be supplied directly to the chamber. 
   Note that a semiconductor device included in a category of the invention has every possible semiconductor device, for example, an integrated circuit such as a microprocessor or an image processing circuit, a semiconductor display device, or the like. The semiconductor display device includes in the category a liquid crystal display device, a light-emitting device provided with a light-emitting element typified by an organic light-emitting element (OLED) for each pixel, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), a FED (Field Emission Display), and the like, and other display devices having a circuit element using a semiconductor film in a driver circuit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph showing a component ratio of H 2 O and an ion species ratio of B to a time of using a filament; 
       FIG. 2  is a view showing a structure of an ion implantation apparatus used in the present invention; 
       FIG. 3  is a view showing a structure of an H 2 O supplying means; 
       FIG. 4  is a view showing a structure of a high-frequency discharge type ion source; 
       FIG. 5  is a view showing a structure of a DC arc discharge type ion source; 
       FIGS. 6A to 6C  are views showing a method for manufacturing a semiconductor device of the invention; 
       FIGS. 7A to 7C  are views showing a method for manufacturing a semiconductor device of the invention; 
       FIGS. 8A to 8C  are views showing a method for manufacturing a semiconductor device of the invention; 
       FIG. 9  is a graph showing concentration distribution of boron by SIMS measurement; 
       FIG. 10  is a graph showing concentration distribution of boron by SIMS measurement; 
       FIG. 11  is a graph showing concentration distribution of boron by SIMS measurement; 
       FIGS. 12A to 12E  are views showing a method for manufacturing a sample used for measurement of source/drain resistance in Embodiment 2; and 
       FIG. 13  is a measured value of source/drain resistance in every aging time. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   [Best Mode for Carrying Out the Invention] 
   Hereinafter, embodiment mode of the present invention will be described below with reference to the accompanying drawings. However, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, the invention is not interpreted with limiting to the description in this embodiment mode. 
     FIG. 2  shows a structure of an ion implantation apparatus used in an ion implantation method and a method for manufacturing a semiconductor device of the invention. In  FIG. 2 , reference numeral  101  denotes an ion source;  102 , a chamber,  103 , a stage on which a substrate  104  is placed;  105 , a valve between the chamber  102  and a vacuum pumping system;  106 , a Faraday cup; and  107 , a current integrator. In addition, a load lock chamber  108  is provided adjacent to the chamber  102 , and a transport means  109  to transport the substrate  104  to the chamber  102  is supplied to the load lock chamber  108 . 
   A gas used as dopant can be supplied to the chamber  102  from dopant supplying means  110  and  111 . In addition, an inert gas can be supplied to the chamber  102  from an inert gas supplying means  112 . Flow of dopant supplied from the dopant supplying means  110  and  111  to the chamber  102  can be controlled by flow controlling means  113  and  114 . Moreover, flow of the inert gas supplied from the inert gas supplying means  112  to the chamber  102  can be controlled by a flow controlling means  115 . 
   Note that mode using two dopant supplying means  110  and  111  is shown in  FIG. 2 ; however, the number of a dopant supplying means is not limited thereto and a practitioner can determine the number appropriately. An impurity element imparting p-type conductivity can be used for dopant and, for example, B, Al, Ga, In, Zn, or the like can be used. Herein, B is assumed to be used as dopant. 
   In addition, reference numeral  116  denotes a means for adding H 2 O (H 2 O supplying means) into the inert gas supplied from the inert gas supplying means  112  to the chamber  102 .  FIG. 2  shows mode in which the inert gas added with H 2 O is supplied to the chamber  102 ; however, the supply of H 2 O to the chamber  102  is not limited thereto. Alternatively, H 2 O may be supplied directly to the chamber  102 . For example, nitrogen, argon, or the like can be used for an inert gas used to supply H 2 O. 
     FIG. 2  shows a situation in which a dopant gas and an inert gas added with H 2 O are introduced into the chamber  102  from a gas inlet provided for the ion source  101 ; however, the gas inlet is not limited to the mode shown in  FIG. 2 . In addition, the ion source  101  is classified into a high-frequency discharge type and a DC arc discharge type, according to a plasma generating method; however, either ion source is applicable to the invention. A structure of a high-frequency discharge type ion source  101  is shown in  FIG. 4  and a DC arc discharge type ion source  101  is shown in  FIG. 5 . 
   The high-frequency discharge type ion source  101  shown in  FIG. 4  includes a plasma source  130  in which plasma is generated, an extraction/acceleration electrode system  131  having a plurality of electrodes for extracting and accelerating a generated ion, a power supply system for acceleration voltage  132  having a plurality of power supplies for applying an acceleration voltage to the extraction/acceleration electrode system, a high frequency power supply  133  for controlling generation of plasma, and a matching box  134 . 
   The DC arc discharge type ion source  101  shown in  FIG. 5  includes a plasma source  140  in which plasma is generated, an extraction/acceleration electrode system  141  having a plurality of electrodes for extracting and accelerating a generated ion, a power supply system for accelerating voltage  142  having a plurality of power supplies for applying an acceleration voltage to the extraction/acceleration electrode system, a DC power supply  143  for preventing generation of plasma, a filament  144  and an anode ring  145  to generate plasma, and a filament power supply  146  to control the potential of the filament  144 . 
   As shown in  FIGS. 4 and 5 , dopant, added with H 2 O, introduced from the gas inlets of the ion source is ionized in the plasma sources  130  and  140 . Note that the ion sources of two-stage acceleration type is shown in  FIGS. 4 and 5 ; however, the ion source that can be used in the invention is not limited thereto and one-stage acceleration type may be also employed. 
   Note that the amount of H 2 O supplied for the chamber  102  can be controlled by a flow rate of an inert gas, a vapor pressure of H 2 O supplied from the H 2 O supplying means  116 , or the like. In addition, the concentration of H 2 O in the chamber  102  can be actually grasped by mass spectroscopy such as QMS. 
   One mode of the H 2 O supplying means  116  is shown in  FIG. 3 . The H 2 O supplying means shown in  FIG. 3  includes a tank  120  in which H 2 O is contained, a conduit  121  to supply an inert gas for the tank  120 , and a conduit  123  to exhaust the inert gas from the tank  120 . The inert gas with which the tank  120  is supplied from the conduit  121  is exhausted through the conduit  123  after staying under H 2 O contained in the tank  120 ; therefore, H 2 O is added into the inert gas exhausted through the conduit  123 . 
   In addition, reference numeral  124  denotes a means for regulating a temperature in the tank  120  (temperature regulating means). A vapor pressure of water in the tank  120  can be controlled by regulating a temperature in the tank  120  by the temperature regulating means  124 . The amount of the H 2 O in the inert gas exhausted from the conduit  123  depends on the flow rate of the inert gas and a vapor pressure of water in the tank  120 . 
   According to the above embodiment of the invention, the concentration of H 2 O in the chamber can be kept constant regardless of exposure to the atmosphere. Thus, an ion species ratio of B can be stabilized. Therefore, a down time of the ion implantation apparatus after exposing the chamber to the atmosphere can be shorten and throughput can be improved. In addition, H 2 O is supplied to the chamber, so that the ion species ratio of B can be raised much more and throughput during the ion implantation step of B can be improved as compared to the case when the concentration of H 2 O is infinitely converged to 0. 
   EMBODIMENT 1 
   Next, a specific method for manufacturing a semiconductor device of the present invention is described. Note that this embodiment is described by giving the case where an n-channel type TFT and a p-channel type TFT are manufactured over one substrate as an example. 
   First, as shown in  FIG. 6A , a base film  502  is formed on an insulating surface of a substrate  501 . For example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, a ceramic substrate, or the like can be used for the substrate  501 . In addition, a metal substrate including a stainless steel substrate or a surface of a substrate on which an insulating film is formed may be used. A substrate made of a synthetic resin having flexibility such as plastic generally tends to have a lower heat resistant temperature than that of the above substrates. However, it can be used as long as it can withstand a processing temperature in a manufacturing step. 
   The base film  502  is provided to prevent alkali metal such as Na or alkaline earth metal contained in the substrate  501  from diffusing into a semiconductor film and giving an adverse effect to properties of a semiconductor element. Thus, the base film  502  is formed by using an insulating film such as silicon oxide, silicon nitride, or silicon nitride oxide which can control diffusion of alkali metal or alkaline earth metal into a semiconductor film. In this embodiment, a silicon nitride oxide film is formed by using a plasma CVD method to have a film thickness ranging from 10 nm to 400 nm (preferably, from 50 nm to 300 nm). 
   Note that silicon oxynitride is an insulating film expressed by SiOxNy (x&gt;y) in this specification, which is distinguished from silicon nitride oxide expressed by SiNxOy (x&gt;y). 
   The base film  502  may be formed in either a single layer or a laminated layer of a plurality of insulating films. In addition, when a substrate containing some sort of alkali metal or alkaline earth metal, for example, a glass substrate, a stainless steel substrate, or a plastic substrate is used, it is effective to provide a base film in respect of preventing diffusion of an impurity. However, it is not necessarily needed to provide a base film when diffusion of an impurity is less problematic as the case of a quartz substrate. 
   Then, island-shape semiconductor films  503  and  504  used as active layers are formed on the base film  502 . The film thicknesses of the island-shape semiconductor films  503  and  504  are set to range from 25 nm to 100 nm (preferably, from 30 nm to 60 nm). Note that the island-shape semiconductor films  503  and  504  may be an amorphous semiconductor, a semi-amorphous semiconductor (microcrystal semiconductor), or a polycrystalline semiconductor. In addition, not only silicon but also silicon germanium can be used as a semiconductor. When silicon germanium is used, the concentration of germanium preferably ranges from 0.01 atomic % to 4.5 atomic %. 
   When a polycrystalline semiconductor is used, first, an amorphous semiconductor film is formed, and the amorphous semiconductor film may be crystallized by using a known crystallization method. A method for carrying out crystallization with heating by a heater, a method for carrying out crystallization with irradiation of laser light, a method for carrying out crystallization by using catalyst metal, a method for carrying out crystallization by using infrared light, or the like is given as an example of the known crystallization method. 
   For example, when crystallization is carried out by using laser light, an pulsed or continuous wave excimer laser, YAG laser, YVO 4  laser, or the like is used. When a YAG laser is used for example, a wavelength of a second harmonic that is easily absorbed in a semiconductor film is used. An oscillating frequency is set to range from 30 kHz to 300 kHz; and an energy density, from 300 mJ/cm 2  to 600 mJ/cm 2  (typically, from 350 mJ/cm 2  to 500 mJ/cm 2 ), and a scanning speed may be determined so that an optional point can be irradiated by several shots. 
   Next, as shown in  FIG. 6B , a gate insulating film  506  is formed to cover the island-shape semiconductor films  503  and  504 . In subsequent dry etching which is carried out to form a gate electrode, the film thickness of the gate insulating film  506  decreases ranging approximately from 10 nm to 20 nm; therefore, it is preferable that the film thickness is set by taking the decrease into consideration. Specifically, the gate insulating film is formed to have a film thickness ranging approximately from 40 nm to 150 nm (more preferably, from 60 nm to 120 nm). 
   For example, silicon oxide, silicon nitride or silicon nitride oxide can be used for the gate insulating film  506 . A plasma CVD method, a sputtering method, or the like can be used for a deposition method. For example, when a gate insulating film using silicon oxide is formed with a plasma CVD method, it is formed by using a mixed gas of TEOS (Tetraethyl Orthosilicate) and O 2 , setting a reaction pressure at 40 Pa; a substrate temperature, ranging from 300° C. to 400° C.; and a high-frequency (13.56 MHz) power density, ranging from 0.5 W/cm 2  to 0.8 W/cm 2 . 
   In addition, aluminum nitride can be used for the gate insulating film  506 . Aluminum nitride has comparatively high thermal conductivity and can diffuse heat generated in a TFT efficiently. After silicon oxide, silicon oxynitride, or the like in which aluminum is not contained is formed, aluminum nitride is laminated thereover, which may be used as the gate insulating film. 
   Then, as shown in  FIG. 6C , a conductive film  507  is formed on the gate insulating film  506 . The conductive film  507  may be formed in a single layer, or, if necessary, in a laminated structure composed of a plurality of layers such as a double layer or a triple layer. In this embodiment, the conductive film  507  is formed to have a film thickness of 300 nm by using W. 
   Each conductive film can be formed of an element of Ta, W, Ti, Mo, Al, and Cu or an alloy or a compound mainly containing the elements. For example, the combination that a first layer is Ta and a second layer is W, the combination that the first layer is TaN and the second layer is Al, and the combination that the first layer is TaN and the second layer is Cu can be considered. An AgPdCu alloy may be used for either the first layer or the second layer. A triple layer structure in which W, an alloy of Al and Si (Al—Si), and TiN are sequentially laminated may be also used. Tungsten nitrogen may be used instead of W, an alloy film of Al and Ti (Al—Ti) may be used instead of the alloy of Al and Si (Al—Si), or Ti may be used instead of TiN. However, when a plurality of conductive films is formed, a material each of which can take a selection ratio of the etching is used to give a difference in width in a channel length direction of a conductive film in each layer after etching. 
   For example, the conductive film  507  may be formed by laminating a conductive film made of TaN having a film thickness ranging from 20 nm to 100 nm and a conductive film made of W having a film thickness ranging from 100 nm to 400 nm. In this case, TaN can be formed under a deposition rate of approximately 40 nm/min by using Ta of which purity is 99.99% for a target, setting a temperature in a chamber at a room temperature; a flow rate of Ar, 50 ml/min; a flow rate of N 2 , 10 ml/min; a pressure in the chamber, 0.6 Pa; and a deposition power, 1 kW. In addition, W can be formed under a deposition rate of approximately 390 nm/min by using W of which purity is 99.99% for a target, setting a temperature in a chamber at 230° C.; a flow rate of Ar, 100 ml/min; a pressure in the chamber, 1.5 Pa; and a deposition power, 6 kW. 
   Note that it is important to select the most suitable etching gas according to a material of the conductive film. In addition, a material of each conductive layer is not limited to the one shown in this embodiment. 
   Next, as shown in  FIG. 7A , gate electrodes  508  and  509  are formed by patterning the conductive film  507 . In this embodiment, an ICP (Inductively Coupled Plasma) etching method is employed. Etching is carried out by using a mixed gas of Cl 2  and CF 4  as an etching gas and by supplying RF (13.56 MHz) power of 3.2 W/cm 2  under a pressure of 1 Pa to generate plasma. RF (13.56 MHz) power of 224 mW/cm 2  is also supplied to a substrate side (sample stage), whereby a negative self-bias is substantially applied thereto. Under this condition, an etching rate of the W film is approximately 100 nm/min. Through the above etching, the edges of the gate electrodes  508  and  509  slightly have taper shapes. In addition, when etching is carried out not to leave a residue of the conductive film, the surface of the gate insulating film  506  not covered with the gate electrodes  508  and  509  is sometimes etched to range from 5 nm to 10 nm or more. 
   Then, as shown in  FIG. 7B , an impurity (dopant) imparting n-type conductivity is added into the island-shape semiconductor films  503  and  504  by using the gate electrodes  508  and  509  as masks (a first doping treatment). Doping is carried out by an ion implantation method. Doping is carried out under a dose amount ranging from 1×10 13  ions/cm 2  to 1×10 15  ions/cm 2  and an acceleration voltage ranging from 30 kV to 90 kV. A Group 5 atom such as P, As, or Sb or a Group 6 atom such as S, Te, or Se that functions as donor is used for an impurity element imparting n-type conductivity; however, P is used in this embodiment. Through the first doping treatment, first impurity regions  510  to  513  are formed in a self-aligned manner. An impurity element imparting n-type conductivity is added into the first impurity regions  510  to  513  to have a concentration range of from 1×10 18  atoms/cm 3  to 1×10 20  atoms/cm 3 . 
   Next, as shown in  FIG. 7C , a resist mask  520  is formed so that the semiconductor film  504  is entirely covered to carry out a second doping treatment. The second doping treatment uses the n-type impurity element the same as that of the first doping treatment as dopant, and an acceleration voltage is set to range from 50 kV to 150 kV; and a dose amount, from 1×10 15  ions/cm 2  to 1×10 17  ions/cm 2 . 
   Through the second doping treatment, second impurity regions  521  and  522  are formed in a region overlapped with the resist mask  520 , and third impurity regions  523  and  524  are formed by further adding an impurity into the first impurity regions  510  and  511  in the island-shape semiconductor film  503 . An impurity element imparting n-type conductivity is added into the second impurity regions  521  and  522  to have a concentration range of from 5×10 17  atoms/cm 3  to 5×10 19  atoms/cm 3 . An impurity element imparting n-type conductivity is added into the third impurity regions  523  and  524  to have a concentration range of from 1×10 19  atoms/cm 3  to 5×10 21  atoms/cm 3 . The second impurity regions  521  and  522  correspond to Loff regions and the third impurity regions  523  and  524  correspond to a source/drain region. 
   Note that it is not necessary to dope an n-type impurity into the island-shape semiconductor film  504  in which a p-channel type TFT is formed according to the first doping treatment shown in  FIG. 7B ; therefore, the semiconductor film  504  may be covered with the resist mask in case of the first doping. In addition, a resist mask is dare not to be provided to reduce the number of a resist mask and a polarity of the island-shape semiconductor film may be reversed to p-type conductivity by increasing the concentration of an impurity imparting p-type conductivity. In this embodiment, the case that the polarity of the island-shape semiconductor film is reversed to p-type conductivity is described. 
   Then, as shown in  FIG. 8A , an impurity imparting p-type conductivity is doped into the island-shape semiconductor film  504  by covering the n-channel type island-shape semiconductor film  503  with a resist mask  530  made of a resist (a third doping treatment). In the third doping treatment, a gate electrode  509  functions as a mask and a fourth impurity region  531  into which an impurity imparting p-type conductivity to the island-shape semiconductor film  504  used for the p-channel type TFT is added is formed. The fourth impurity region  531  is formed by an ion implantation method using diborane (B 2 H 6 ) in this embodiment. 
   Note that B is used as an impurity element imparting p-type conductivity in this embodiment. However, the invention is not limited thereto and other impurity element can be used as long as it is an impurity element imparting the above p-type conductivity. In addition, diborane is used as a n impurity containing B in this embodiment; however, the invention is not limited thereto and other impurity containing B, for example, BF 3  or the like may be used. 
   In this embodiment, a gas diluted with hydrogen so that the concentration of diborane ranges approximately from 3% to 30% and an inert gas added with H 2 O are flown into the chamber of the ion implantation apparatus, and thus ion implantation of B is carried out. In this embodiment, a gas diluted with hydrogen so that the concentration of diborane is 5% is flown into the chamber to have a flow rate of 90 sccm. In addition, nitrogen is used as an inert gas, and nitrogen added with H 2 O is flown into the chamber at a flow rate of, for example, 5 sccm. The amount of added H 2 O is that the component ratio of H 2 O to H 3   +  in the chamber, for example, ranges approximately from 0.1 to 1. Note that the amount of the added H 2 O is not limited thereto and a practitioner may determine the amount of the H 2 O appropriately so that the amount of the H 2 O in the chamber is constant regardless of opening and closing of the chamber. 
   In the fourth impurity region  531 , doping treatment is carried out so that an impurity element imparting p-type conductivity has the concentration ranging from 2×10 20  atoms/cm 3  to 2×10 21  atoms/cm 3 . Thus, p-type conductivity is predominant, so that the fourth impurity region  531  functions as source/drain regions of the p-channel type TFT. 
   Through the above steps, the impurity region is formed in the island-shape semiconductor films  503  and  504 . 
   Next, as shown in  FIG. 8B , a first interlayer insulating film  532  is formed by covering the island-shape semiconductor films  503  and  504 , the gate insulating film  506 , and the gate electrodes  508  and  509 . An insulating film such as silicon oxide, silicon nitride, or silicon oxynitride containing silicon can be used for the first interlayer insulating film  532  and the film thickness ranges approximately from 100 nm to 200 nm. 
   Next, heat treatment is carried out to activate an impurity element added into the island-shape semiconductor films  503  and  504 . A thermal annealing method using an annealing furnace, a laser annealing method, or rapid thermal annealing (RTA) method can be used in this step. For example, in activating with a thermal annealing method, it is carried out in a nitrogen atmosphere with the oxygen concentration of 1 ppm or less, preferably 0.1 ppm or less, at temperatures ranging from 400° C. to 700° C. (preferably from 500° C. to 600° C.). Furthermore, heat treatment is carried out at temperatures ranging from 300° C. to 450° C. for an hour to 12 hours in an atmosphere containing hydrogen ranging from 3% to 100%, and a step of hydrogenating the island-shape semiconductor films is carried out. This step is carried out for terminating dangling bonds by thermally excited hydrogen. As an alternative method for hydrogenating, plasma hydrogenation (using hydrogen excited by plasma) may be carried out. In addition, activation treatment may be carried out before forming the first interlayer insulating film  532 . 
   Through the above-mentioned series of steps, an n-channel type TFT  533  and a p-channel type TFT  534  can be formed over one substrate. 
   Then, as shown in  FIG. 8C , a second interlayer insulating film  537  and a third interlayer insulating film  538  are formed so that the first interlayer insulating film  532  is covered. An organic resin film, an inorganic insulating film, an organopolysiloxane, or the like can be used for the second interlayer insulating film  537 . In this embodiment, the second interlayer insulating film  537  is formed by using non-photosensitive acryl, which is one of an organic resin film. 
   Next, the gate insulating film  506 , the first interlayer insulating film  532 , the second interlayer insulating film  537 , and the third interlayer insulating film  538  are etched to form a contact hole. Then, a wiring  539  that forms a contact with the island-shape semiconductor films  503  and  504  is formed. 
   After the step shown in  FIG. 8C , a step of manufacturing an element capable of displaying a gradation according to an electrical signal (a display element) such as a liquid crystal cell and a light-emitting element used for a semiconductor display device is carried out. 
   Note that a step of adding an impurity imparting conductivity into a channel formation region to control a threshold voltage (channel dope) may be provided. For example, when an impurity imparting p-type conductivity is channel-doped, as well as the third doping treatment, a gas diluted with hydrogen so that the concentration of diborane ranges approximately from 1% to 30% and an inert gas added with H 2 O are flown into the chamber of the ion implantation apparatus, and thus ion implantation of B is carried out. Then, a gas diluted with hydrogen so that the concentration of diborane is 1% is flown into the chamber to have a flow rate ranging from 30 sccm to 60 sccm. In addition, when nitrogen is used as an inert gas, nitrogen added with H 2 O is flown into the chamber at a flow rate of, for example, 5 sccm. The amount of added H 2 O is that a component ratio of H 2 O to H 3   +  in the chamber, for example, ranges approximately from 0.1 to 1. Note that the amount of the added H 2 O is not limited thereto and a practitioner may determine the amount of the H 2 O appropriately so that the amount of the H 2 O in the chamber is constant regardless of opening and closing of the chamber. 
   Note that the method for manufacturing the semiconductor device using a top gate type TFT is shown in this embodiment; however, the invention is not limited thereto. It is possible to apply the invention also to a method for manufacturing a semiconductor device using a bottom gate type TFT. 
   The invention is not necessarily limited to the manufacturing method shown in this embodiment. The above manufacturing method just described one embodiment mode of the invention. Therefore, the invention is not limited to the above embodiment mode, and various changes based on a technical idea of the invention are possible. 
   EMBODIMENT 2 
   In this embodiment, after exposing a chamber to the atmosphere, a relation between an aging time to remove an impurity in the chamber and a concentration of boron, oxygen, and hydrogen in a semiconductor film into which doping of boron is carried out after aging is described. 
     FIG. 9  shows a concentration (atoms/cm 3 ) of boron to a depth (nm) of a sample measured by a secondary ion mass spectrometry (SIMS) by each aging time of after 6 hours, 36 hours, and 70 hours. A semiconductor film into which boron is directly doped is used for the sample used for SIMS measurement. When a TFT actually manufactured is assumed to be doped after a gate insulating film having a film thickness of approximately 80 nm is formed over a semiconductor film having a film thickness of approximately 50 nm, it is predicted that concentration distribution in a source/drain region corresponds to concentration distribution in a depth ranging from 80 nm to 130 nm shown in  FIG. 9 . 
   In addition, when a semiconductor film is doped so as to transmit through a gate electrode formed over a gate insulating film in a TFT actually manufactured, an impurity region (Lov region) overlapping with the gate electrode through the gate insulating film is formed. The gate electrode is unlikely to transmit ion than the semiconductor film at the time of ion implantation; therefore, it is assumed that double of the film thickness of the gate electrode corresponds to the film thickness of the semiconductor film. Thus, in this case, when the film thickness of the gate insulating film is assumed to be approximately 80 nm; that of the semiconductor film, approximately 50 nm; and that of the gate electrode, approximately 25 nm, it is predicted that concentration distribution in the Lov region corresponds to concentration distribution in a depth ranging from 160 nm to 210 nm shown in  FIG. 9 . 
   It is understood from the concentration distribution of boron shown in  FIG. 9  that the shorter an aging time is, the higher a concentration of boron in a semiconductor film is; and the longer an aging time is, the lower a concentration of boron in a semiconductor film is. 
   Then,  FIG. 10  shows a concentration (atoms/cm 3 ) of oxygen to a depth (nm) of a sample measured by a secondary ion mass spectrometry (SIMS) by each aging time of after 6 hours, 20 hours, 36 hours, and 70 hours. A sample used for SIMS measurement is the same as the case of  FIG. 9 . It is understood from the concentration of oxygen shown in  FIG. 10  that the shorter an aging time is, the higher a concentration of oxygen in a semiconductor film is; and the longer an aging time is, the lower a concentration of oxygen in a semiconductor film is. 
   Next,  FIG. 11  shows a concentration (atoms/cm 3 ) of oxygen to a depth (nm) of a sample measured by a SIMS by each aging time of after 6 hours, 20 hours, 36 hours, and 70 hours. A sample used for SIMS measurement is the same as the case of  FIG. 9 . It is understood from the concentration of hydrogen shown in  FIG. 11  that, the shorter an aging times is, the higher a concentration of hydrogen in a semiconductor film is; and the longer an aging time is, the lower a concentration of hydrogen in a semiconductor film is. On the other hand, in a deep region where the depth is more than 100 nm, it is understood that the shorter an aging times is, the lower a concentration of hydrogen in a semiconductor film is; and the longer an aging time is, the higher a concentration of hydrogen in a semiconductor film is. 
   Then, a TFT is formed by using an aging time to remove an impurity in the chamber and the semiconductor film that is doped after aging, and a result of measurement of source/drain resistance of the TFT is shown in  FIG. 13 . First, a method for manufacturing a TFT used as a sample is described with reference to  FIGS. 12A to 12E . 
   First, as shown in  FIG. 12A , semiconductor films  08  and  09  are formed over an insulating surface of a substrate  07 . In this embodiment, a polycrystalline semiconductor is used for the semiconductor films  08  and  09 . A film thickness of the semiconductor films  08  and  09  is set to be 50 nm. Then, a gate insulating film  06  with a film thickness of 115 nm; TaN, 30 nm; and W, 370 nm are sequentially formed over the semiconductor films  08  and  09  by using silicon oxide. Then, the TaN and the W are etched by using a mask  10  to form double-layered conductive films  11  (a lower layer  11   a  and an upper layer  11   b ) and  12  (a lower layer  12   a  and an upper layer  12   b ). 
   Next, as shown in  FIG. 12B , the double-layered conductive films  11  and  12  are etched to form gate electrodes  13  (a lower layer  13   a  and an upper layer  13   b ) and  14  (a lower layer  14   a  and an upper layer  14   b ) by using the mask  10  of which width gets narrow by being etched in the above etching treatment. Note that the gate electrode  13  is etched so that a width of a channel length direction of the lower layer  13   a  is longer than that of the upper layer  13   b . The gate electrode  14  is etched so that a width of a channel length direction of the lower layer  14   a  is longer than that of the upper layer  14   b . Through the above etching treatment carried out twice, the gate insulating film  06 , which is an exposed portion without being overlapped with the gate electrodes  13  and  14  is etched to have a film thickness of 80 nm. 
   Then, as shown in  FIG. 12B , phosphorus is added into the semiconductor films  08  and  09  (a first doping treatment) by using the gate electrodes  13  and  14  as masks. Doping is carried out by an ion implantation method. Doping is carried out under a dose amount of 7×10 13  ions/cm 2  and an acceleration voltage of 50 kV. Through the first doping treatment, first impurity regions  15  and  16  are formed in a self-aligned manner. 
   Next, as shown in  FIG. 12C , only the upper layers  13   b  and  14   b  are used as masks between the gate electrodes  13  and  14  to carry out second doping treatment. In the second doping treatment, doping is carried out under an acceleration voltage of 65 kV and a dose amount of 3×10 15  ions/cm 2  so that an impurity passes through the lower layers  13   a  and  14   a . Through the second doping treatment, second impurity regions  18  and  20  are formed in a region exposed without being overlapped with the gate electrodes  13  and  14 . In addition, third impurity regions  17  and  19  are formed in a region overlapped only with the lower layers  13   a  and  14   a  between the gate electrodes  13  and  14 . 
   Subsequently, as shown in  FIG. 12D , a third doping treatment is carried out. In the third doping treatment, diborane (B 2 H 6 ) is used as dopant and it is carried out by covering the semiconductor film  08  with a mask  21 . It is carried out under an acceleration voltage of 80 kV and a dose amount of 2×10 16  ions/cm . Through the third doping treatment, fourth impurity regions  22  and  23  are formed in a region exposed without being overlapped with the upper layer  14   b  of the gate electrode  14 . Note that only the fourth impurity region  22  between the fourth impurity regions  22  and  23  is overlapping with the lower layer  14   a  of the gate electrode  14 . 
   Next, as shown in  FIG. 12E , a passivation film  24  is formed. Then, heat treatment is carried out in an atmosphere containing hydrogen to activate the impurity element added into the semiconductor films  08  and  09 . 
   Source/drain resistance of a p-type TFT  25  manufactured by the above-mentioned series of steps is shown in  FIG. 13 . Note that,  FIG. 13  shows source/drain resistance in the third doping treatment by each aging time of after 6 hours, 20 hours, 36 hours, and 70 hours. It is understood from  FIG. 13  that the shorter an aging time is, the lower source/drain resistance is. 
   According to the above embodiment of the invention, the ion species ratio of B in the chamber can be kept constant regardless of exposure to the atmosphere. Thus, a down time of the ion implantation apparatus after exposing the chamber to the atmosphere can be shorten and throughput can be improved. In addition, H 2 O is supplied to the chamber, so that the ion species ratio of B can be raised much more and throughput during the ion implantation step of B can be improved as compared to the case when the concentration of H 2 O is infinitely converged to 0. 
   This application is based on Japanese Patent Application serial No. 2003-307236 filed in Japanese Patent Office on Aug. 29 in 2003, the contents of which are hereby incorporated by reference.