Abstract:
A method for manufacturing a semiconductor device, comprising: defining an active region on the semiconductor substrate; forming an interfacial oxide layer on a surface of the semiconductor substrate; forming a high-K gate dielectric on the interfacial oxide layer; forming a first metal gate layer on the high-K gate dielectric; forming a dummy gate layer on the first metal gate layer; patterning the dummy gate layer, the first metal gate layer, the high-K gate dielectric and the interfacial oxide layer to form a gate stack structure; forming a gate spacer surrounding the gate stack structure; forming S/D regions for NMOS and PMOS respectively; depositing interlayer dielectric and planarization by CMP to expose the surface of dummy gate layer; removing the dummy gate layer so as to form a gate opening; implanting dopant ions into the first metal gate layer; forming a second metal gate layer on the first metal gate layer so as to fill the gate opening; and performing annealing, so that the dopant ions diffuse and accumulate at an upper interface between the high-K gate dielectric and the first metal gate layer and at a lower interface between the high-K gate dielectric and the interfacial oxide layer, and electric dipoles are generated by interfacial reaction at the lower interface between the high-K gate dielectric and the interfacial oxide layer.

Description:
PRIORITY 
     This application is a National Phase application of, and claims priority to, PCT Application No. PCT/CN2012/086126, filed on Dec. 7, 2012, entitled “METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE”, which claimed priority to Chinese Application No. 201210505744.X, filed on Nov. 30, 2012. Both the PCT Application and Chinese Application are incorporated herein by reference in their entireties. 
     TECHNICAL FIELD 
     The present disclosure relates to semiconductor technology, and particularly to a method for manufacturing a semiconductor device comprising a metal gate and a high-K gate di electric. 
     BACKGROUND 
     As the development of semiconductor technology, feature sizes of metal-oxide-semiconductor-field-effect transistors (MOSFETs) decrease continuously. The size decreasing of the MOSFETs causes a severe problem of gate current leakage. The gate leakage current can be reduced by using a high-K gate dielectric, which may have an increased physical thickness with a constant equivalent oxide thickness (EOT). However, conventional Poly-Si gate is incompatible with the high-K gate dielectric. Combination of a metal gate and the high-K gate dielectric not only avoids the exhaustion effect of the Poly-Si gate and decrease gate resistance, but also avoid penetration of boron and enhance device reliability. Therefore, the combination of the metal gate and the high-K gate dielectric is widely used in the MOSFETs. However, integration of the metal gate and the high-K gate dielectric is still confronted with many challenges, such as problems related to thermostability and interface state. Particularly, due to Fermi-Pinning Effect, it is difficult for the MOSEFT using the metal gate and the high-K dielectric to have an appropriately low threshold voltage. 
     In a complementary-metal-oxide-semiconductor (CMOS) device integrating an N-type MOSFET (NMOSFET) and a P-type MOSFET (PMOSFET), to obtain appropriate threshold voltages, the NMOSFET should have an effective work function near the bottom of the conduction band of Si (about 4.1 eV), while the PMOSFET should have an effective work function near the top of the valence band of Si (about 5.2 eV). Different combinations of the metal gate and the high-K dielectric may be selected respectively for the NMOSFET and PMOSFET, so as to realize required threshold voltages. As a result, dual metal gates and dual high-K dielectrics need to be formed in one chip. During manufacture of the CMOS device, usually multi-deposition, photolithography and etching steps for the metal gates and the high-K dielectrics gate stack are performed respectively for the NMOSFET and the PMOSFET. Therefore, the method for manufacturing semiconductor devices comprising the dual metal gates and the dual gate dielectrics is complicated and thus is not suitable for mass production, which further leads to high cost. 
     SUMMARY 
     The present disclosure intends to provide a method for manufacturing a semiconductor device, by which it is possible to adjust an effective work function of the semiconductor device during manufacturing process thereof. 
     The present disclosure provides a method for manufacturing a semiconductor device, comprising: defining an active region on a semiconductor substrate; forming an interfacial oxide layer on a surface of the semiconductor substrate; forming a high-K gate dielectric on the interfacial oxide layer; forming a first metal gate layer on the high-K gate dielectric; forming a dummy gate layer on the first metal gate layer; patterning the dummy gate layer, the first metal gate layer, the high-K gate dielectric and the interfacial oxide layer to form a gate stack structure; forming a gate spacer surrounding the gate stack structure; forming S/D regions for NMOS and PMOS respectively; depositing interlayer dielectric and planarization by CMP to exposure the surface of dummy gate layer; removing the dummy gate layer so as to form a gate opening; implanting the different type of dopant ions into the different type of the areas of the first metal gate layer; forming a second metal gate layer on the first metal gate layer so as to fill the gate opening; and performing annealing, so that the dopant ions diffuse and accumulate at an upper interface between the high-K gate dielectric and the first metal gate layer and at a lower interface between the high-K gate dielectric and the interfacial oxide layer, and electric dipoles are generated by interfacial reaction at the lower interface between the high-K gate dielectric and the interfacial oxide layer. In a preferable embodiment, the semiconductor structure may comprise an NMOSFET and a PMOSFET formed on one semiconductor substrate. Moreover, in the preferable embodiment, a dopant may be implanted in the first metal gate layer of the NMOSFET to decrease an effective work function thereof, and another dopant may be implanted in the first metal gate layer of the PMOSFET to increase an effective work function thereof. 
     In this method, in one aspect, the dopant ions accumulated at the upper interface between the high-K gate dielectric and the first metal gate layer change characteristics of a metal gate, thereby adjusting an effective work function of a corresponding MOSFET advantageously. In a further aspect, the dopant ions accumulated at the lower interface between the high-K gate dielectric and the interfacial oxide layer form the electric dipoles with appropriate polarities by the interfacial reaction, thereby further adjusting the effective work function of the corresponding MOSFET advantageously. The semiconductor device obtained by this method has good stability and the effective work function of the metal gate can be advantageously adjusted. Different dopants may be selected for the two types of MOSFETs to decrease or increase the effective work functions. In CMOS devices, threshold voltages of the two types of MOSFETs can be adjusted respectively simply by changing the dopants, instead of using different combinations of the metal gates and the gate dielectrics. Accordingly, this method can remove corresponding multi-steps of deposition, mask and etching, so as to simplify the process and enable mass production. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to provide a thorough understanding of the present disclosure, the present disclosure will be explained in detail based on the accompanying drawings. 
         FIGS. 1-11  schematically show sectional views of respective semiconductor structures during each stage of manufacturing a semiconductor device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Next, the present disclosure will be explained in detail with references to accompanying drawings. In the following description, similar parts are represented by the same or similar reference signs, regardless of whether they are shown in different embodiments. Respective parts in the drawings are not drawn to scale for the sake of clarity. 
     In the following description, numerous specific details are set forth, such as structures, materials, sizes and treatment processes and technologies of devices, in order to provide a thorough understanding of the present disclosure. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. Each portion of the semiconductor device may consist of materials well known to those of ordinary skill in the art, or materials having similar function developed in future, unless noted otherwise. 
     In the present disclosure, the term “semiconductor structure” refers to a semiconductor substrate and all the layers or regions formed on the semiconductor substrate after corresponding steps of manufacturing a semiconductor device. The term “S/D region” refers to either one of a source region and a drain region of a MOSFET, and both of the source region and the drain region are represented with a same reference sign. The term “N-type dopant” refers to a dopant applied to an NMOSFET and capable of decreasing its effective work function. The term “P-type dopant” refers to a dopant applied to a PMOSFET and capable of increasing its effective work function. 
     A method for manufacturing a semiconductor device will be illustrated with references to  FIGS. 1-11 , according to one embodiment of the present disclosure. The semiconductor device is a CMOS device comprising an NMOSFET and a PMOSFET formed on one semiconductor substrate. 
     The semiconductor structure as shown in  FIG. 1  has gone through part of CMOS process. On a semiconductor substrate  101  (e.g., a Si substrate) there are provided an active region for the NMOSFET and an active region for the PMOSFET, separated by a shallow trench insulation  102 . 
     An interfacial oxide layer  103  (e.g., a silicon oxide layer) is formed on an exposed surface of the semiconductor substrate  101  by chemical oxidation or additional thermal oxidation. In one embodiment, the interfacial oxide layer  103  may be formed by rapid thermal oxidation at a temperature of about 600-900° C. within about 20-120 seconds. In another embodiment, the interfacial oxide layer  103  may be formed by chemical oxidation in water solution containing ozone (O 3 ). 
     Preferably, the surface of the semiconductor substrate  101  may be cleansed before the interfacial oxide layer  103  is formed. Cleansing the semiconductor substrate  101  may comprise cleansing the semiconductor substrate  101  normally and then immersing the semiconductor substrate  101  in mixed solution including hydrofluoric acid, isopropanol and water. After that, the semiconductor substrate  101  may be washed with deionized water, and then spin-dried. In one embodiment, the hydrofluoric acid, isopropanol and water in the mixed solution may have a volume ratio of about 0.2-1.5%:0.01-0.10%:1, and the time duration for immersing the semiconductor substrate  101  in the mixed solution may be about 1-10 minutes. Cleansing the semiconductor substrate  101  can obtain a clean surface of the semiconductor substrate  101 , thereby inhibiting particle pollution and generation of natural oxidation on the surface of silicon, and thus help to form the interfacial oxide layer  103  with high quality. 
     Then, by deposition processes, for example, ALD (atomic layer deposition), CVD (chemical vapor deposition), MOCVD (metal organic chemical vapor deposition), PVD (physical vapor deposition), sputtering and so on, a high-K gate dielectric  104 , a first metal gate layer  105 , a barrier layer  106  and a dummy gate layer  107  is formed on the surface of the semiconductor structure in sequence, as shown in  FIG. 2 . 
     The high-K gate dielectric  104  may comprise any appropriate material with a dielectric constant greater than that of SiO 2 , such as any one selected from ZrO 2 , ZrON, ZrSiON, HffrO, HfZrON, HfON, HfO 2 , HfAlO, HfAlON, HfSiO, HfSiON, HfLaO, HfLaON, and any combination thereof. The first metal gate layer  105  may comprise any appropriate material capable of forming a metal gate, such as any one selected from TiN, TaN, MoN, WN, TaC, and TaCN. The barrier layer  106  may comprise any material capable of blocking reaction and inter-diffusion between the dummy gate layer  107  and the first metal gate layer  105 , such as any one selected from TaN, MN and TiN. The dummy gate layer  107  may comprise a Poly-Si layer or a a-Si layer. It is to be noted that the barrier layer  106  is optional. The barrier layer  106  is not necessary if there is no reaction and inter-diffusion between the dummy gate layer  107  and the first metal gate layer  105 . In one embodiment, the high-K gate dielectric  104  may be a HfO 2  layer having a thickness of about 1.5-5 nm, the first metal gate layer  105  may be a TiN layer having a thickness of about 2-30 nm, the barrier layer  106  may be a TaN layer having a thickness of about 3-8 nm, and the dummy gate layer  107  may be a Poly-Si layer having a thickness of 30-120 nm, for example. 
     Preferably, post-deposition-annealing of the high-K gate dielectric may be performed between forming the high-K gate dielectric  104  and forming the first metal gate layer  105 , so as to improve quality of the high-K dielectric layer, which benefits to obtain a uniform thickness of the first metal gate layer  105  formed subsequently. In one embodiment, rapid thermal annealing at a temperature of about 500-1000° C. within about 5-100 seconds may be performed as the post-deposition-annealing. 
     Then, a plurality of gate stack structures are formed by patterning using a photoresist mask (not shown) or a hard mask (not shown). During the patterning, exposure portions of the dummy gate layer  107 , the barrier layer  106 , the first metal gate layer  105 , the high-K gate dielectric  104  and the interfacial oxide layer  103  are selectively removed by dry etching, such as ion-milling etching, plasma etching, reactive ion etching, or laser ablation, or by wet etching using etchant solution, so as to form the gate stack structures of the NMOSFET and the PMOSFET respectively, as shown in  FIG. 3 . The gate stack structure of the NMOSFET as shown in  FIG. 3  comprises a dummy gate layer  107   a , a barrier layer  106   a , a first metal gate layer  105   a , a high-K gate dielectric  104   a  and an interfacial oxide layer  103   a . The gate stack structure of the PMOSFET comprises a dummy gate layer  107   b , a barrier layer  106   b , a first metal gate  105   b , a high-K gate dielectric  104   b  and an interfacial oxide layer  103   b.    
     During the patterning for forming the gate stack structures, different etchants may be applied to different layers. In one embodiment, etchant gas based on F, etchant gas based on Cl or etchant gas based on HBr/Cl 2  may be applied in dry etching of the dummy gate layer  107 . Etchant gas based on BCl 3 /Cl 2  may be applied in dry etching of the first metal gate layer  105  and/or the high-K gate dielectric  104 . Preferably, Ar and/or O 2  may be added into the aforementioned etchant gases to improve etching effect. It is desirable that the gate stack structures have steep and continuous etching profiles, high anisotropy, and high etching selectivity with respect to the silicon substrate in order to avoid any damage to the silicon substrate. 
     Then, by the aforementioned deposition processes, a silicon nitride layer having a thickness of about 10-50 nm may be formed on the surface of the semiconductor structure. Then, anisotropy etching may be performed to the silicon nitride layer, so that a spacer  108   a  surrounding the gate stack structure is formed in the active region of the NMOSFET, and a spacer  108   b  surrounding the gate stack structure is formed in the active region of the PMOSFET, as shown in  FIG. 4 . 
     Then, the gate stack structures and the spacers thereof are used as hard masks to perform S/D ion implantation, and then activation annealing is performed. Therefore, S/D regions  109   a  of the NMOSFET and S/D regions  109   b  of the PMOSFET are formed in the semiconductor substrate  101 , as shown in  FIG. 5 . The S/D regions  109   a  of the NMOSFET locate at both sides of the gate stack structure thereof, and may comprise extension regions at least partly extending to under the high-K gate dielectric  104   a . The S/D regions  109   b  of the PMOSFET locate at both sides of the gate stack structure thereof, and may comprise extension regions at least partly extending to under the high-K gate dielectric  104   b . Due to protection of the dummy gate layers  107   a  and  107   b , dopant ions implanted during the S/D ion implantation will not enter the first metal gate layers  105   a  and  105   b , which helps to adjust the effective work functions during subsequent implantation in metal gates. 
     Rapid thermal annealing (RTA), spike annealing, laser annealing, and microwave annealing may be performed for the activation annealing of the S/D regions. The temperature for the annealing may be about 950-1100° C., and the time duration for the annealing may be about 2 ms-30 s. 
     Then, silicide regions  110   a  (e.g., nickel silicide, nickel platinum silicide) may be formed at the surface of the S/D regions  109   a , and silicide regions  110   b  (e.g., nickel silicide, nickel platinum silicide) may be formed at the surface of the S/D regions  109   b , as shown in  FIG. 6 . The silicide regions can decrease series resistance and contact resistance of the S/D regions. 
     Then, by the aforementioned deposition processes, an interlayer dielectric layer  111  (e.g., a silicon nitride layer or a silicon oxide layer) covering the active regions may be formed on the surface of the semiconductor structure. By chemical-mechanical polishing (CMP), the surface of the interlayer dielectric layer  111  is planarized, and top surfaces of the dummy gate layers  107   a  and  107   b  is exposed, as shown in  FIG. 7 . 
     Then, the dummy gate layers  107   a  and  107   b  are selectively removed with respect to the interlayer dielectric layer  111 , by dry etching, such as ion-milling etching, plasma etching, reactive ion etching, or laser ablation, or by wet etching using etchant solution, so as to form a plurality of gate openings, as shown in  FIG. 8 . 
     Then, by photolithography process including exposure and development, a patterned photoresist mask PR 1  is formed, so as to cover the active region of the PMOSFET and expose the active region of the NMOSFET. Ion implantation is performed using the photoresist mask PR 1  through the corresponding gate opening to implant N-type dopant in the first metal gate layer  105   a  in the active region of the NMOSFET, as shown in  FIG. 8 . The N-type dopant for the metal gate may be one selected from a group consisting of P, As, Sb, La, Er, Dy, Gd, Sc, Yb, Er and Tb. By controlling energy and dosage of the ion implantation, the implanted dopant ions only distribute in the first metal gate layer  105   a  without entering the high-K gate dielectric  104   a . Moreover, by controlling the energy and the dosage of the ion implantation, the first metal gate layer  105   a  can have an appropriate dopant depth and an appropriate dopant concentration, so that a desired threshold voltage can be obtained. In one embodiment, the energy of the ion implantation is about 0.2 KeV-30 KeV, the dosage of the ion implantation is about 1E13-1E15 cm 2 . The photoresist mask PR 1  is removed by ashing or dissolution after the aforementioned ion implantation. 
     Then, by photolithography process including exposure and development, a patterned photoresist mask PR 2  is formed, so as to cover the active region of the NMOSFET and expose the active region of the PMOSFET. Ion implantation is performed using the photoresist mask PR 2  through the corresponding gate opening to implant P-type dopant in the first metal gate layer  105   b  in the active region of the PMOSFET, as shown in  FIG. 10 . The P-type dopant for the metal gate can be one selected from a group consisting of In, B, BF 2 , Ru, W, Mo, Al, Ga and Pt. By controlling energy and dosage of the ion implantation, the implanted dopant ions only distribute in the first metal gate layer  105   b  without entering the high-K gate dielectric  104   b , and the first metal gate layer  105   b  can have an appropriate dopant depth and an appropriate dopant concentration, so that a desired threshold voltage can be obtained. In one embodiment, the energy of the ion implantation is about 0.2 KeV-30 KeV, and the dosage of the ion implantation is about 1E13-1E15 cm −2 . The photoresist mask PR 2  is removed by ashing or dissolution after the aforementioned ion implantation. 
     Then, by the aforementioned deposition processes, a second metal gate layer is formed on the surface of the semiconductor structure. CMP is performed using the interlayer dielectric layer  111  as a polishing stop layer, so as to remove part of the second metal gate layer locating outside the gate openings while reserve part of the second metal gate layer locating inside the gate openings, as shown in  FIG. 11 . The second metal gate layer may comprise a material identical or non-identical to the material comprised in the first metal gate layer, such as one selected from a group consisting of W, Ti, TiAl, Al, Mo, Ta, TiN, TaN, WN, and any combination thereof. In one embodiment, the second metal gate layer may be a W layer having a thickness of about 30-80 nm, for example. The gate stack structure of the NMOSFET as shown comprises the second metal gate layer  112   a , the barrier layer  106   a , the first metal gate layer  105   a , the high-K dielectric  104   a , and the interfacial oxide layer  103   a . The gate stack structure of the PMOSFET as shown comprises the second metal gate layer  112   b , the barrier layer  106   b , the first metal gate layer  105   b , the high-K gate dielectric  104   b , and the interfacial oxide layer  103   b . Although the gate stack structures of the NMOSFET and the PMOSFET are formed by the same layers, the metal gates of the NMOSFET and the PMOSFET comprise opposite types of dopant ions, which perform opposite adjusting functions to the respective effective work functions. 
     After contact formation and metallization are performed, annealing of the aforementioned semiconductor structure is performed within inert atmosphere (e.g., N 2 ) or weakly reducing atmosphere (e.g., combination of N 2  and H 2 ). In one embodiment, the annealing is performed in a furnace at a temperature of about 350-450° C. for about 20-90 minutes. The annealing force the dopant ions implanted to diffuse and accumulate at upper interfaces and lower interfaces of the high-K gate dielectrics  104   a  and  104   b , and further form electric dipoles by interfacial reaction at the lower interfaces of the high-K dielectrics  104   a  and  104   b . The upper interfaces of the high-K dielectrics  104   a  and  104   b  herein refer to interfaces between the high-K dielectrics  104   a  and  104   b  and the first metal gate layers  105   a  and  105   b  thereon. The lower interfaces of the high-K dielectrics  104   a  and  104   b  herein refer to interfaces between the high-K dielectrics  104   a  and  104   b  and the interfacial oxide layers  103   a  and  103   b  thereunder. 
     The annealing changes distribution of the dopant ions. In one aspect, the dopant ions accumulated at the upper interfaces of the high-K gate dielectrics  104   a  and  104   b  change characteristics of the metal gates, thereby adjusting the effective work functions of the corresponding MOSFETs advantageously. In a further aspect, the dopant ions accumulated at the lower interfaces of the high-K gate dielectric layers  104   a  and  104   b  form the electric dipoles with appropriate polarities by the interfacial reaction, thereby further adjusting the effective work functions of the corresponding MOSFETs advantageously. 
     Not every detail of the MOSFETs, such as formation of S/D contact, formation of additional interlayer dielectric layer and formation of conductive path, has been disclosed in the foregoing disclosure. Standard CMOS processes for forming the aforementioned portions are well known to those of ordinary skill in the art, and thus description thereof is omitted. 
     It should be noted that the foregoing only illustrates examples and describes the present disclosure, but not intends to exhaust and limit the present disclosure. Therefore, the present disclosure is not limited to the aforementioned embodiments. Any alternatives or modification obvious to those of ordinary skill in the art will fall within the scope of the present disclosure without departing from the spirit and principle thereof.