Abstract:
A semiconductor device manufacturing method includes forming a fin region over a substrate, forming a dummy gate electrode over the fin region, forming a first insulating film over the dummy gate electrode and the fin region, polishing the first insulating film until the dummy gate electrode is exposed, removing part of the exposed dummy gate electrode to form a trench, forming a gate insulator over the surface of the fin region exposed in the trench, and forming a gate electrode over the gate insulator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-331992, filed on Dec. 26, 2008, the entire contents of which is incorporated herein by reference. 
     FIELD 
     The present invention relates to a semiconductor device and a manufacturing method thereof. 
     BACKGROUND 
     A field effect transistor having a fin structure (fin FET) is actively being developed. The fin FET has a fin-like projection perpendicular to a substrate surface, a gate insulator and agate electrode are formed on both side surfaces of the fin-like projection, and source/drain regions are formed on both sides of the gate. 
     In the fin FET, a channel surface is disposed perpendicular to the substrate surface, so that an occupied area may be reduced on the substrate. A cap layer is provided over a silicon layer of a Semiconductor On Insulator (SOI) substrate, and is patterned to form a silicon fin. The cap layer includes an oxide film or a lamination of the oxide film and a nitride film. In the SOI substrate, the silicon layer is disposed over an insulating film. After the gate insulator made of oxide silicon or nitride oxide silicon is formed over a fin surface, a polysilicon layer is deposited and patterned, and a gate electrode is formed. The fin regions on both sides of the gate electrode are doped to form a source/drain region. 
       FIG. 5  illustrates a configuration example of the fin FET. In  FIG. 5 , the silicon layer of the SOI substrate is patterned to form a fin  51  and contact regions  52  and  53 . A cap layer  61  is left over the silicon layer. The oxide film or the nitride film is formed as a gate insulator  62  in the fin sidewall. A gate electrode  71  is formed so as to stride over the fin  51 . A contact region  72  is formed in an end portion of the gate electrode  71 . An impurity is added to the fin  51  by ion implantation to form the source/drain region. After a transistor structure is covered with an interlayer insulator, a contact hole reaching the contact regions  52  and  53  is made, and a conductive plug  80  such as a tungsten plug is made in the contact hole. The gate electrode  71  may be formed by laminating a polysilicon layer and a silicide layer, or may be formed by a metallic layer. 
     A channel of the fin FET is formed in the side surface of the fin. A channel length is determined by a width of the gate electrode. A channel width is determined by a fin height. For example, a fin length is determined by process accuracy. A narrow lead-out portion of the source/drain easily increases resistance of the source/drain. In another proposal, the fin is cut without extending an end portion thereof, and a metallic layer is embedded to form a Schottky contact. 
     When an opposite area between the gate electrode  71  and a semiconductor substrate disposed below the insulating film in the SOI substrate is enlarged, a parasitic capacitance of the gate electrode is increased which interrupts high-speed operation. In order to decrease the parasitic capacitance of the gate electrode, it is desirable to reduce the opposite area between the semiconductor substrate and the gate electrode. 
     There is also proposed a configuration in which the opposite area of the gate electrode is reduced with respect to the semiconductor substrate. In this method, an Si layer of the SOI substrate is etched with a hard mask to form the fin. After an oxide film liner and a nitride film liner are formed over the hard mask and the fin, the oxide film liner and the nitride film liner are covered with an insulating film. Chemical Mechanical Polishing (CMP) is performed to the insulating film until the nitride film liner is exposed, the insulating film is partially etched, and an upper surface of the insulating film is lowered below the nitride film liner. While an opposite portion of the substrate is left, the oxide film liner and the nitride film liner are etched to form a trench, a gate insulator is formed in the exposed Si fin surface, and a polysilicon gate electrode layer is embedded in the trench. The hard mask is exposed by CMP. The polysilicon gate electrode layer is left on the insulating film. A metal gate electrode layer is formed, and a gate etching mask is formed thereon. The metal gate electrode layer and the polysilicon gate electrode layer are etched with the gate etching mask to pattern the gate electrode. The ion implantation of the impurity is performed to the polysilicon gate electrode layer with a space interposed between the fin and the insulating film. The space is formed by the etching. 
     For example, Japanese Laid-Open Patent Publication Nos. 2002-289871 and 2005-150742 disclose a technique concerning the fin FET. 
     SUMMARY 
     According to an aspect of the invention, a semiconductor device manufacturing method includes forming a fin region over a substrate, forming a dummy gate electrode over the fin region, 
     forming a first insulating film over the dummy gate electrode and the fin region, polishing the first insulating film until the dummy gate electrode is exposed, removing part of the exposed dummy gate electrode to form a trench, forming a gate insulator on the surface of the fin region exposed in the trench, and forming a gate electrode over the gate insulator. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       FIGS.  1 AP to  1 HP are plan views illustrating a fin FET producing method according to a first embodiment of the invention, FIGS.  1 AX to  1 HX are sectional views of a fin FET taken on a line X-X of FIG.  1 AP, and FIGS.  1 AY to  1 HY are sectional views of the fin FET taken on a line Y-Y of FIG.  1 AP; 
         FIGS. 2A to 2D  are perspective views illustrating a semiconductor device in the producing method of the first embodiment; 
       FIGS.  3 AP to  3 HP are plan views illustrating a fin FET producing method according to a second embodiment of the invention, FIGS.  3 AX to  3 HX are sectional views of a fin FET taken on a line X-X of FIG.  3 AP, and FIGS.  3 AY to  3 HY are sectional views of the fin FET taken on a line Y-Y of FIG.  3 AP; 
         FIG. 4A  is a perspective view illustrating a semiconductor device having a CMOS configuration, and  FIG. 4B  is an equivalent circuit diagram; and 
         FIG. 5  is a perspective view illustrating a fin FET in the related art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     FIGS.  1 AP to  1 HP are plan views illustrating a fin FET producing method according to a first embodiment of the invention, FIGS.  1 AX to  1 HX are sectional views of a fin FET taken on a line X-X of FIG.  1 AP, and FIGS.  1 AY to  1 HY are sectional views of the fin FET taken on a line Y-Y of FIG.  1 AP. 
     The case in which an n-type MOSFET is formed using an SOI substrate will be described by way of example. In the SOI substrate, an oxide silicon layer  12  is disposed over a support semiconductor substrate  11  having a flat surface, and a p-type silicon layer  13  is disposed over the oxide silicon layer  12 . The case in which a thickness of the silicon layer  13  is matched with a fin height of 40 nm to 60 nm will be described as an example. 
     As illustrated in FIGS.  1 AP,  1 AX, and  1 AY, an oxide silicon film  14  having a thickness of about 20 nm to about 50 nm is formed over the p-type silicon layer  13  by thermal oxidation or thermal CVD. The oxide silicon layer  14  acts as a hard mask in etching and then acts as a cap layer of a fin region. A resist pattern RP 1  that defines a planar shape of a fin region is formed over the cap layer  14  by photolithography or electron beam lithography. For example, the resist pattern RP 1  defines a width of 20 nm to 30 nm and a length of several hundred nanometers in the fin region. The dimensions of the fin region are not limited to the embodiment. 
     For the SOI-type MOSFET having the planar structure, although the optimum fin width depends slightly on an impurity concentration, MOSFET exhibits a full depletion operation when a channel thickness is equal to or lower than one-third of a gate length, and MOSFET exhibits a partially depletion operation when the channel thickness is more than one-third of the gate length. Suitably the full depletion operation suppresses short channel effect and decreases an off-leakage current of a transistor to reduce power consumption. For the full depletion operation, preferably the channel thickness is equal to or thinner than 10 nm when the channel length is 30 nm. In the fin FET, because the channels are formed on both the side surfaces of the fin region, the width of the fin region becomes double the channel thickness. That is, MOSFET exhibits the partially depletion operation when the width of the fin region is more than two-thirds of the gate length. For the gate length of 45 nm, the full depletion operation is performed when the width of the fin region is equal to or narrower than 30 nm. For the gate length of 30 nm, the full depletion operation is performed when the width of the fin region is equal to or narrower than 20 nm. 
     The cap layer is patterned by Reactive Ion Etching (RIE) with the resist pattern RP 1  as an etching mask and a mixed gas of C 4 F 6 /CO/Ar/O 2  as an etchant, and the silicon layer is patterned by RIE with a mixed gas of HBr/O 2  as an etchant, thereby forming the fin region  13 . The resist pattern RP 1  may be removed after the hard mask is formed, may be eliminated during the etching, or may be removed after the etching.  FIG. 2A  illustrates the patterned fin region  13 . An upper surface of the fin region  13  is covered with the cap layer  14 . 
     As illustrated in FIGS.  1 BP,  1 BX, and  1 BY, a dummy gate electrode layer is deposited over the substrate while the fin region  13  is covered therewith, and the dummy gate electrode layer is patterned with a resist pattern. The dummy gate electrode layer is made of an insulating material having an etching characteristic different from that of the cap layer. For example, a nitride silicon film  16  having a thickness of about 20 nm to about 50 nm is isotropically deposited by thermal CVD with dichlorosilane and ammonia as a source gas. A resist pattern RP 2  is formed over the nitride silicon film  16  so as to traverse the fin region  13 . The planar shape of the resist pattern RP 2  defines the planar shape of the dummy gate electrode. The width of the resist pattern RP 2  defines the channel length. For example, the width of the resist pattern RP 2  ranges from 30 nm to 45 nm. There is no particular limitation as long as the length of the resist pattern RP 2  is more than the width of the fin region. 
     The nitride silicon film  16  is patterned to form the dummy gate electrode  16  by RIE with the resist pattern RP 2  as the mask and the mixed gas of CH 2 F 2 /Ar/O 2  as the etchant. The etchant gas may be changed and the cap layer  14  made of oxide silicon is patterned. Then the resist pattern RP 2  is removed.  FIG. 2B  illustrates the state in which the resist pattern RP 2  is removed. The dummy gate electrode  16  is formed so as to traverse the side surface of the fin region  13  and the side surface and upper surface of the cap layer  14 . 
     As illustrated in FIGS.  1 CP,  1 CX, and  1 CY, ion implantation is performed to the fin region  13  to form an extension region Ext. For the n-type MOSFET, for example, As, an n-type impurity, is implanted with acceleration energy of 4 keV, a dose amount of 1×10 15 /cm 2 , and from plural directions of 10 degrees to 20 degrees relative to an implantation angle line normal to the substrate. Because the upper surface of the fin region  13  is covered with the cap layer  14  made of oxide silicon, the impurity is implanted into the side surface of the fin region  13 . For the p-type MOSFET, B that is a p-type impurity is implanted with the acceleration energy of 0.6 keV and the dose amount of 1×10 15 /cm 2 . It is not always necessary to form the extension region. 
     As illustrated in FIGS.  1 DP,  1 DX, and  1 DY, the sidewall spacer  18  is formed. For example, an oxide silicon film having the thickness of about 5 nm to about 20 nm is deposited by the thermal CVD with silane and oxygen as a source gas, and anisotropic etching is performed by RIE with the mixed gas of C 4 F 6 /CO/Ar/O 2  as the etchant. A sidewall spacer  18  is formed on the side surface of the dummy gate electrode  16  of FIG.  1 DP and the side surface of the fin region  13 . The formation of the sidewall spacer is omitted when the formation of the extension region is omitted. 
     Ion implantation is performed to a low-resistance diffusion region Dif of the source/drain region. For the n-type MOSFET, for example, As, an n-type impurity is implanted with the acceleration energy of 25 keV, the dose amount of 5×10 15 /cm 2 , and from the implantation angles of 10 degrees to 20 degrees. For the p-type MOSFET, BF 2 , a p-type impurity, is implanted with the acceleration energy of 15 keV, the dose amount of 3×10 15 /cm 2  to 5×10 15 /cm 2 , and from implantation angles of 10 degrees to 20 degrees. After the ion implantation, spike annealing is performed at a temperature range of 1000° C. to 1100° C., for example, at 1050° C. to activate the impurity. 
     As necessary, a metallic layer such as Ni and Co that may generate the silicide reaction is deposited over the substrate, and an annealing treatment is performed to form a silicide layer SL on a silicon surface. For NiSi, an annealing temperature is about 450° C. The silicide layer SL is formed on the upper surface of the source/drain region in the fin region. The silicide layer SL is not formed on the side surface of the source/drain region covered with the sidewall spacer  18 . 
     As illustrated in FIGS.  1 EP,  1 EX, and  1 EY, an insulating film  20  such as an oxide silicon film is deposited over the entire substrate, the surface of the insulating film  20  is planarized by CMP, and a top portion of the dummy gate electrode  16  is exposed.  FIG. 2C  illustrates the state after CMP. The dummy gate electrode  16  surrounded by the sidewall spacer  18  is exposed in the surface of the insulating film  20 . 
     As illustrated in FIGS.  1 FP,  1 FX, and  1 FY, the dummy gate electrode  16  made of nitride silicon is etched using hot phosphoric acid. The etching is ended such that the bottom portion of the dummy gate electrode  16  is left. A trench T is formed so as to be extended in a depth direction from the surface of the insulating film  20 . The fin region covered with the dummy gate electrode  16  is exposed in the trench T. The side surfaces of the trench T are surrounded by the sidewall spacer  18  and the fin region  13 . 
     As illustrated in FIGS.  1 GP,  1 GX, and  1 GY, an oxide silicon film having a thickness of about 0.5 nm to about 0.7 nm is formed on the exposed surface of the fin region  13  at a substrate temperature of about 270° C. by an oxidation treatment using ozone (O 3 ). Then an insulating film is deposited. For example, a mixed gas of tetra tert-butoxy hafnium (HTB, Hf (t-OC 4 H 9 ) 4 ) and Si 2 H 6  is caused to flow at a substrate temperature of about 270° C. to deposit a HfSiO film having a thickness of about 1.5 nm to about 2.0 nm. A HfSiON film may be formed by performing nitriding in nitrogen gas plasma. A gate insulator  21  is formed by laminating the oxide silicon film and the insulating film. A HfO 2  film, a HfAlO film, a HfAlON film, a LaO 2  film, a LaSiO film, or a LaAlO film may be formed as the insulating film instead of the HfSiO film and the HfSiON film. 
     A TiN film and a W film are deposited over the gate insulator  21  by sputtering to form a gate electrode  22 . The TiN film is formed by the sputtering with a Ti target in an atmosphere of a mixed gas of Ar and N 2  so as to have the thickness of about 5 nm to about 30 nm. The W film having the thickness of about 10 nm to about 50 nm is formed by the sputtering with a W target in an Ar atmosphere so as to fill the trench T therewith. The gate electrode may be formed using one of the TiN film and the W film. The unnecessary metallic layer over the insulating film  20  is removed by CMP. Therefore, a gate electrode structure G is formed by laminating the gate insulator  21  and the gate electrode  22 .  FIG. 2C  illustrates the state in which the gate electrode structure G is formed. 
     As illustrated in FIGS.  1 HP,  1 HX, and  1 HY, an interlayer insulator  24  such as oxide silicon film is deposited over the substrate, a contact hole is etched to expose the gate electrode  22  and the surface of the source/drain region S/D, and a conductive plug  26  is embedded. For example, the conductive plug is formed by laminating the TiN film and the W film.  FIG. 2D  illustrates the state in which the conductive plug  26  is formed. 
     In the first embodiment, the dummy gate electrode having the same shape as the gate electrode structure is formed in the fin surface to form the source/drain region. After the interlayer insulator with which the dummy gate electrode is covered is formed, the dummy gate electrode is removed, and the trench T is embedded to form the gate electrode structure, so that the gate electrode structure may be obtained with high accuracy. 
     FIGS.  3 AP to  3 HP are plan views of an SOI substrate illustrating a fin FET producing method according to a second embodiment of the invention, FIGS.  3 AX to  3 HX are sectional views of a fin FET taken on a line X-X of FIG.  3 AP, and FIGS.  3 AY to  3 HY are sectional views of the fin FET taken on a line Y-Y of FIG.  3 AP. 
     As illustrated in FIGS.  3 AP,  3 AX, and  3 AY, the fin region  13  having the cap layer  14  is formed using the resist pattern RP 1 . The description of the process similar to that of the first embodiment is appropriately omitted. 
     As illustrated in FIGS.  3 BP,  3 BX, and  3 BY, the dummy gate electrode  16  is formed on the fin region  13 . 
     As illustrated in FIGS.  3 CP,  3 CX, and  3 CY, a dummy insulating film  28  such as an oxide silicon film is deposited over the entire substrate, the surface of the dummy insulating film  28  is planarized by CMP, and the top portion of the dummy gate electrode  16  is exposed. 
     As illustrated in FIGS.  3 DP,  3 DX, and  3 DY, the dummy gate electrode  16  is etched. A trench T is formed in the dummy insulating film  28 . 
     As illustrated in FIGS.  3 EP,  3 EX, and  3 EY, the gate electrode structure G including the gate insulator  21  and gate electrode  22  is formed in the trench T surrounded by the dummy insulating film  28 . 
     As illustrated in FIGS.  3 FP,  3 FX, and  3 FY, the dummy insulating film  28  is removed. The dummy insulating film  28  is etched using dilute hydrofluoric acid when the dummy insulating film is made of oxide silicon. The fin region  13  in which the gate electrode structure is formed is exposed. Ion implantation for the extension region is performed to the fin regions  13  on both sides of the gate electrode structure G. 
     As illustrated in FIGS.  3 GP,  3 GX, and  3 GY, the sidewall spacer  18  is formed. Then ion implantation is performed to the low-resistance diffusion region Dif of the source/drain. After the ion implantation, spike annealing is performed at a temperature range of 1000° C. to 1100° C., for example, at 1050° C. to activate the impurity. The silicide layer SL may be formed. 
     As illustrated in FIGS.  3 HP,  3 HX, and  3 HY, the insulating film  20  is deposited, and the insulating film  20  is planarized by CMP to expose the top portion of the gate electrode  22 . Then, as illustrated in FIGS.  1 HP,  1 HX, and  1 HY, the interlayer insulator forming process and the conductive plug forming process are performed to draw each electrode to the surface of the interlayer insulator. 
     In the second embodiment, the impurity implantation region and the silicide layer are not formed when the gate electrode is formed, thereby relaxing a temperature limitation of the subsequent heating process. For example, after the gate insulator is formed, the annealing may be performed at about 1000° C. for about five seconds to enhance quality of the gate insulator. 
       FIG. 4A  illustrates a configuration example of the fin FET. An n-channel MOS transistor nMOS and a p-channel MOS transistor pMOS basically have the structure of the first or second embodiment, and the transistor nMOS differs from the transistor pMOS in the conductivity type. The gate electrodes of the transistor nMOS and transistor pMOS are connected, and an input signal Vin is applied to the gate electrodes. The source of the transistor nMOS is grounded, and the source of the transistor pMOS is connected to a power supply voltage. The drains of the transistor nMOS and transistor pMOS are connected to supply an output voltage Vout. 
       FIG. 4B  is an equivalent circuit diagram illustrating the fin FET of  FIG. 4A . The nMOS transistor and the pMOS transistor are series-connected, and the gates of the nMOS transistor and pMOS transistor are connected to each other. The input signal Vin is fed into the gates, and the output is supplied from a mutual connecting point. 
     The embodiments of the invention have been described above, but the invention is not limited to the embodiments. For example, the gate electrode may be formed by laminating TaN, TaC, TaCN, TaCNO, TaSi, TaSiN, TaAlN, TiSi, TiAlN, MoN, or MoAlN and W or Si. The transistor nMOS may differ from the transistor pMOS in the material for the gate electrode. Instead of oxide silicon, a low-dielectric-constant insulating film having a dielectric constant lower than that of oxide silicon such as porous silica may be used as the insulating film. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.