Abstract:
A method for fabricating a dielectric layer with improved insulating properties is provided, including: providing a dielectric layer having a first resistivity; performing a hydrogen plasma doping process to the dielectric layer; and annealing the dielectric layer, wherein the dielectric layer has a second resistivity greater than that of the first resistivity after annealing thereof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to semiconductor fabrications, and particularly, relates to a method for fabricating a dielectric layer with improved insulating properties and a method for fabricating a semiconductor structure having a dielectric layer with improved insulating properties. 
         [0003]    2. Description of the Related Art 
         [0004]    In semiconductor fabrication, various layers of dielectric insulating materials, semiconductor materials and conducting materials are formed to produce a multi-level semiconductor device. 
         [0005]    One of the limiting factors of the continued evolution toward smaller device sizes and higher densities of semiconductor devices has been insufficient insulation properties of dielectric insulating materials formed in the semiconductor device for isolating metal interconnects and passive or active components therein, since thickness or space of the dielectric insulating materials is also reduced. 
         [0006]    For example, silicon oxide is one of the widely used dielectric insulating materials which function as an insulating layer in applications such as multilevel interconnections, shallow trench isolations (STI), gate spacers, and source or drain contact isolations. A silicon oxide film can be deposited by a thermal chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD) process. However, after a front-end process of the semiconductor device is completed, a sequentially formed silicon oxide film will be formed under a relatively low temperature (e.g. a temperature not greater than 600° C.) to prevent the devices (e.g. CMOS devices) formed in the front-end process from degrading. This relatively low temperature, however, may degrade insulating properties such as bulk resistivity, leakage current, electrical breakdown voltage and mechanical and chemical stability of the formed silicon oxide while the thickness thereof is further reduced. 
         [0007]    Thus, there is a need for a method to fabricate a dielectric layer with improved insulating properties, which allows the thickness of the insulating layer to shrink along with other features such as a metal interconnect line width or a space between adjacent passive/active devices or metal interconnect lines. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A method for fabricating a dielectric layer with improved insulating properties and a method for fabricating a semiconductor structure having a dielectric layer with improved insulating properties are provided. 
         [0009]    An exemplary method for fabricating a dielectric layer with improved insulating properties comprises: providing a dielectric layer having a first resistivity; performing a hydrogen plasma doping process to the dielectric layer; and annealing the dielectric layer, wherein the dielectric layer has a second resistivity greater than that of the first resistivity after annealing thereof. 
         [0010]    An exemplary method for fabricating a semiconductor structure having a dielectric layer with improved insulating properties comprises: providing a semiconductor substrate with a dielectric layer formed thereover, wherein the dielectric layer has a first resistivity; performing a hydrogen plasma doping process to the dielectric layer; and annealing the dielectric layer, wherein the dielectric layer has a second resistivity, after annealing thereof, that is greater than that of the first resistivity. 
         [0011]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a flowchart showing a method for fabricating a semiconductor structure having a dielectric layer with improved insulating properties according to an embodiment of the invention; and 
           [0014]      FIGS. 2A ,  2 B, and  2 C are cross-sections showing a semiconductor structure having a dielectric layer with improved insulating properties according to various embodiments of the invention, respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0016]    In  FIG. 1 , a flowchart showing an exemplary method for fabricating a semiconductor structure having a dielectric layer with improved insulating properties is illustrated. 
         [0017]    In  FIG. 1 , the method begins at step S 1 , in which a semiconductor substrate or a semiconductor structure with a dielectric layer formed thereover is provided. The semiconductor substrate can be, for example, silicon substrate. The dielectric layer may function as an insulating layer and may comprise dielectric insulating materials such as silicon oxide, undoped silicate glass (USG), borosilicate glass (BSG), phosphosilicate glass (PSG) or borophorphosilicate glass (BPSG). Methods for fabricating the dielectric layer can be, for example, spin coating, chemical vapor deposition (CVD), or plasma enhanced chemical vapor deposition (PECVD) methods, or the like. A surface of the dielectric layer is exposed, and original insulating properties such as resistivity (p) and breakdown charge (Q BD ) of the dielectric layer are dependant upon parameters of the method for forming thereof. 
         [0018]    Next, at step S 2 , a hydrogen plasma doping (PLAD) process is performed on the exposed surface of the dielectric layer to improve insulating properties such as resistivity (ρ) and breakdown charge (Q BD ) thereof. The hydrogen PLAD process can be performed by a plasma doping (PLAD) ion implanter rather than the conventional beam-line ion implanter. PLAD ion implanters used herein can be, for example, Varian&#39;s VIISta® PLAD and Applied Material&#39;s P3i implanters, which are commercially available. In the hydrogen PLAD process, pure hydrogen gas is used as a source gas to dope the dielectric layer with hydrogen atoms at a fixed dosage and at varying implant energies. The dielectric layer may have a thickness, for example, of about 2-500 nm, and the hydrogen plasma doping process can be performed under an implant energy, for example, of about 20-50000 eV and an implant dosage, for example, of about 1e16-1e17/cm 2 . In one embodiment, the implant energy of the hydrogen PLAD process may linearly ramp up in a predetermined interval, for example 2000 eV to 5000 eV, for the hydrogen PLAD process. However, implant dosages, implant times, and implant energies used in the hydrogen PLAD process depend on a thickness of the dielectric layer. For example, in one embodiment, the implant dosage is about 4e16-8e16/cm 2 , the implant time is about 53-98 seconds, and the implant energy is about 2000 eV to 5000 eV while a thickness of the dielectric layer is about 50 nm. In another embodiment, the implant dosage is about, 2e16-4e16/cm 2 , the implant time is about 30-53 seconds, and the implant energy is about 1000 eV to 3000 eV while a thickness of the dielectric layer is about 30 nm. In yet another embodiment, the implant dosage is about 5e16-1e17/cm 2 , the implant time is about 60-100 seconds, and the implant energy is about 2000 eV to 10000 eV while a thickness of the dielectric layer is about 100 nm. 
         [0019]    Next, at step S 3 , an annealing process is performed after the hydrogen PLAD process is completed to uniformly drive the hydrogen atom within the dielectric layer. In one embodiment, the annealing process is performed at a temperature of between 300-600° C. for 30-60 minutes, under an atmosphere of pure N 2 . The annealing temperature and the process time of the annealing process depend on the implant dosages, implant times and implant energies of the hydrogen PLAD process. After the annealing process, insulating properties such as resistivity (ρ) and breakdown charge (Q BD ) of the dielectric layer formed over the semiconductor structure processed by the hydrogen PLAD process are now higher in quantity than when compared with the original insulating properties prior to processing of the hydrogen PLAD process. For example, a resistivity (ρ) of the dielectric being processed by the hydrogen PLAD process and the annealing can be increased by at least 2.2 times to that of the dielectric layer which is not processed by the hydrogen PLAD process and annealed, and a breakdown charge (Q BD ) of the dielectric being processed by the hydrogen PLAD process and the annealing can be increased by at least 50 times to that of the dielectric layer which is not processed by the hydrogen PLAD process and annealed. Therefore, insulating properties of the dielectric layer processed by the hydrogen PLAD process and the annealing are improved. 
         [0020]    Next, at step S 4 , other processes can be sequentially performed to pattern the dielectric layer or to form other elements or features in or over the dielectric layer, thereby forming a semiconductor structure with the dielectric layer having improved insulating properties capable of a predetermined functionality. 
         [0021]      FIGS. 2A ,  2 B, and  2 C are cross-sections showing various semiconductor structures with the dielectric layer having improved insulating properties capable of a predetermined functionality. The various semiconductor structures shown in  FIGS. 2A ,  2 B, and  2 C can be fabricated by the method illustrated in  FIG. 1 , and the various semiconductor structures may comprise a dielectric layer with improved insulating properties formed by the method described in the steps S 2 -S 3  shown in  FIG. 1 . 
         [0022]    As shown in  FIG. 2A , an exemplary semiconductor structure comprising a semiconductor substrate  100  having a trench  104  formed therein and a dielectric layer  102  formed thereover is illustrated. The dielectric layer  102  is formed over the semiconductor substrate  100  and fills the trench  104 , functioning as an isolation element such as a shallow trench isolation (STI) element. Since the dielectric layer  102  is now formed with improved insulating properties according to the fabrication steps S 2 -S 3  shown in  FIG. 1 , it is capable of providing sufficient insulation despite the continuing evolution toward smaller device sizes and higher densities, wherein a thickness or an isolation space of the dielectric layer  102  is reduced. 
         [0023]    In addition, as shown in  FIG. 2B , another exemplary semiconductor structure comprising a semiconductor  200  having source/drain regions  202  formed therein, a gate dielectric layer  204 , a gate electrode  206 , insulating spacers  208 , and a dielectric layer  210  with a conductive contact  212  therein is illustrated. In this embodiment, the insulating spacers  208  functioning as gate spacers and/or the insulating layer  210  functioning as source/drain contact isolations, is formed with improved insulating properties according to the fabrications steps S 2 -S 3  shown in  FIG. 1 . Thus, the insulating spacers  208  and/or the dielectric layer  210  is capable of providing sufficient insulation despite the continuing evolution toward smaller device sizes and higher densities, wherein a thickness or an isolation space of the insulating spacers  208  and/or the dielectric layer  210  is reduced. 
         [0024]    Moreover, as shown in  FIG. 2C , yet another exemplary semiconductor structure comprising stacked dielectric layers  300 ,  304 , and  306  formed over a semiconductor substrate (not shown), a conductive element  302  formed in the dielectric layer  300 , and an interconnecting element  310  formed in the dielectric layers  304  and  306  is illustrated. In this embodiment, at least one of the dielectric layers  300 ,  304 , and  306  is now formed with improved insulating properties according to the fabrication steps S 2 -S 3  shown in  FIG. 1 . Thus, the at least one of the dielectric layers  300 ,  304 , and  306  is capable of providing sufficient insulation despite the continuing evolution toward smaller device sizes and higher densities, wherein a thickness or an isolation space of the at least one of the dielectric layers  300 ,  304 , and  306  is reduced. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Measurement results of insulating properties of a silicon oxide layer formed over a silicon substrate 
               
             
          
           
               
                   
                   
                   
                   
                 Anneal 
                 Anneal 
                   
                   
                   
               
               
                   
                 Implant 
                 Energy 
                 Dosage 
                 temperature 
                 time 
                 Thickness 
                 ρ 
                 Q BD   
               
               
                 Sample 
                 Type 
                 (eV) 
                 (atoms/cm 2 ) 
                 (° C.) 
                 (min) 
                 (nm) 
                 (Ω-cm) 
                 (C/cm 2 ) 
               
               
                   
               
               
                 1 
                 None 
                 None 
                 None 
                 None 
                 None 
                 55.02 
                 8.50 × l0 14   
                 3.9 × 10 −2   
               
               
                 2 
                 Hydrogen 
                 2000- 
                 4E16 
                 None 
                 None 
                 55.27 
                 6.84 × l0 14   
                 1.1 × 10 −2   
               
               
                   
                 PLAD 
                 5000 
               
               
                 3 
                 Hydrogen 
                 2000- 
                 4E16 
                 300° C. 
                 30 
                 53.72 
                 1.27 × l0 15   
                 None 
               
               
                   
                 PLAD 
                 5000 
               
               
                 4 
                 Hydrogen 
                 2000- 
                 4E16 
                 400° C. 
                 30 
                 53.58 
                 1.91 × 10 15   
                 1.9 
               
               
                   
                 PLAD 
                 5000 
               
               
                 5 
                 Hydrogen 
                 2000- 
                 4E16 
                 500° C. 
                 30 
                 53.66 
                 2.12 × 10 15   
                 2.6 × 10 −5   
               
               
                   
                 PLAD 
                 5000 
               
               
                 6 
                 Hydrogen 
                 2000- 
                 8E16 
                 N/A 
                 None 
                 54.24 
                 4.18 × 10 14   
                 2.3 × 10 −3   
               
               
                   
                 PLAD 
                 5000 
               
               
                 7 
                 Hydrogen 
                 2000- 
                 8E16 
                 300° C. 
                 30 
                 53.27 
                 6.82 × 10 14   
                 None 
               
               
                   
                 PLAD 
                 5000 
               
               
                 8 
                 Hydrogen 
                 2000- 
                 8E16 
                 400° C. 
                 30 
                 51.49 
                 1.05 × 10 15   
                 1.7 
               
               
                   
                 PLAD 
                 5000 
               
               
                 9 
                 Hydrogen 
                 2000- 
                 8E16 
                 500° C. 
                 30 
                 51.30 
                 1.59 × 10 15   
                 7.0 × 10 −5   
               
               
                   
                 PLAD 
                 5000 
               
               
                   
               
             
          
         
       
     
         [0025]    As shown in Table 1, measurement results of insulating properties of nine samples comprising a silicon oxide layer formed on a 300 mm p-type single crystal silicon substrate are disclosed. The silicon oxide layer in these samples are formed by the PECVD method at a temperature of about 400° C. and a pressure of about 1.8 Ton, using tetraethyl orthosilicate (TEOS) and oxygen as source gases. Physical properties such as film thicknesses, resistivities (ρ), and breakdown charges (Q BE ) of the silicon oxide layer formed over the silicon substrate with or without the hydrogen PLAD processing are measured. In Sample 1, the silicon oxide layer formed over the silicon substrate is not processed by the hydrogen PLAD process. In Samples 2-5, the silicon oxide layer formed over the silicon substrate is processed by the hydrogen PLAD process, wherein implant energy is ramped from 2000-5000 eV at a fixed implant dosage of about 4E16 atoms/cm 2 , and the silicon oxide layer is then annealed at different temperatures or not annealed. In Samples 6-9, the silicon oxide layer formed over the silicon substrate is processed by the hydrogen PLAD process, wherein implant energy is ramped from 2000-5000 eV at a fixed implant dosage of about 8E16 atoms/cm 2 , and the silicon oxide layer is then annealed at different temperatures or not annealed. 
         [0026]    According to the measurement results of the insulating properties of the silicon oxide layer in the various embodiments disclosed in Table 1, a resistivity of the silicon oxide layer in Sample 4 which was processed by the hydrogen PLAD process under an implant dosage of about 4E16 atoms/cm 2  and annealed under a temperature of about 400° C. for 30 minutes, increased by 2.2 times to that of the silicon oxide layer in Sample 1 which was not processed by the hydrogen PLAD process and annealed. In addition, a breakdown charge of the silicon oxide layer in Sample 4 which was processed by the hydrogen PLAD process under an implant dosage of about 4E16 atoms/cm 2  and annealed under a temperature of about 400° C. for 30 minutes, increased by about 50 times to that of the silicon oxide layer in Sample 1 which was not processed by the hydrogen PLAD process and annealed. Therefore, leakage current of the silicon oxide layer in Sample 4 was reduced and the electrical isolation property of the silicon oxide layer in Sample 4 was significantly improved by the hydrogen PLAD process and sequential annealing process. 
         [0027]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.