Abstract:
The present disclosure provides an example of a semiconductor device. In addition, a method for fabricating a semiconductor device is outlined. The semiconductor device may be fabricated by providing a semiconductor substrate, forming a gate over the substrate, forming diffusion barrier ion regions, forming halo regions, forming a source, and forming a drain.

Description:
TECHNICAL FIELD  
       [0001]     The present disclosure relates to semiconductor devices and, in particular, to semiconductor devices and methods for fabricating the same.  
       BACKGROUND  
       [0002]     As the minimum feature size in semiconductor integrated circuits shrinks, the distance between the source and drain regions becomes smaller. The reduced spacing between the source and drain regions for the field-effect transistors results in short channel effects.  
         [0003]     To relieve the short channel effects, the semiconductor industry is constantly optimizing the fabrication processes for metal oxide semiconductor field effect transistor (MOSFET) devices. Current trends in very large scale integration (VLSI) fabrication of complimentary metal oxide semiconductor (CMOS) devices seem to focus on reducing the junction depth of the source/drain regions because shallow junctions reduce the encroachment of the source/drain depletion regions into the channel.  
         [0004]     As CMOS technology becomes smaller, e.g., less than 50 nanometers (nm) in gate length, it becomes more and more difficult to improve the short channel device performance and at the same time maintain acceptable values for off-state leakage current.  
         [0005]     One technique for trying to achieve this is a halo implant having extra dopant implant regions positioned next to the source and drain extension regions. The halo implant, also called a “pocket implant,” can limit the lateral diffusion of the source and drain impurities. The halo implant implants impurities having a conductivity type opposite to that of the source and drain. Usually, the halo implant comes after defining the gate and before the source/drain diffusion. However, the halo impurities also diffuse into the source/drain or the channel region during an annealing for the source/drain diffusion. This diffusion of the halo impurities may cause a threshold voltage of the transistor to fall outside of a pre-determined range, and the leakage currents may also be increased. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIGS. 1A  to  1 E show cross sectional views illustrating various stages of fabrication of a semiconductor device according to the present disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0007]     With reference to  FIG. 1E , a gate  104  is formed over a semiconductor substrate  101 . A gate insulating layer  103  is formed below the gate  104 . The gate  104  defines a channel  200  thereunder in the substrate  101  having a source side and a drain side.  
         [0008]     Two halo regions  106  are formed in the source side and the drain side of the channel  200 , contacting the channel  200 . Halo regions  106  contain halo impurity ions  160  of a first conductivity, which are injected by performing a tilted ion implantation.  
         [0009]     In the halo regions  106 , diffusion barrier ions  150  are also injected. The diffusion barrier ion  150  is smaller than an atom of the substrate  101  and has corresponding size to the halo impurity ion  160 . Therefore, the diffusion barrier ion  150  occupies an interstitial site in a crystal lattice of the substrate  101  and acts as a diffusion barrier of the halo impurity ion  160 .  
         [0010]     The diffusion barrier ions  150  can be injected by performing a tilted ion implantation.  
         [0011]     For example, the diffusion barrier ion  150  can be a carbon ion and the halo impurity ion  160  can be a boron ion.  
         [0012]     A source  107  is formed in the substrate  101  adjacent to the source side of the channel  200 . In the same way, a drain  108  is formed in the substrate  101  adjacent to the drain side of the channel  200 .  
         [0013]     One of the halo regions  106  is located between the source  107  and the channel  200 , and the other halo region  106  is located between the drain  108  and the channel  200 .  
         [0014]     The source  107  and drain  108  contain impurity ions of a second conductivity different from the conductivity of the halo ions. For example, the first conductivity can be p-type and the second conductivity can be n-type.  
         [0015]     The method for fabricating the semiconductor device as described above is explained in detail as follows.  
         [0016]     First, an isolation process, for example, shallow trench isolation (STI), is performed to define an active area in a semiconductor substrate  101 . As shown in  FIG. 1A , a trench  102  is formed in a field area of the substrate  101  as a result of the STI process.  
         [0017]     A single crystalline silicon wafer of a first conductivity, for example, p-type, can be used as the substrate  101 .  
         [0018]     A gate insulating layer  103  is formed on the active area of the substrate  101 . The gate insulating layer  103  may be a silicon oxide formed by thermal oxidation.  
         [0019]     After forming the gate insulating layer  103 , BF 2  ions can be implanted into the surface of the substrate  101  for controlling a threshold voltage.  
         [0020]     A conducting layer for a gate  104  is formed on the gate insulating layer  103 . For example, a highly doped-polycrystalline silicon layer or a silicide layer thereon may be used as the conducting layer.  
         [0021]     A photoresist pattern having a gate pattern is formed on the conducting layer. The photoresist pattern is used to etch the conducting layer and the gate insulating layer  103  to form gate  104  and the gate insulating layer  103  on portions of the active area.  
         [0022]     Gate  104  may define an upper border of channel  200  in the substrate  101  during the operation of the device.  
         [0023]     Before halo ion implantation, diffusion barrier ions  150  are injected into the substrate  101  to form diffusion barrier ion regions  105 , which correspond to halo regions  106  and are in contact with the channel  200 , as shown in  FIG. 1C .  
         [0024]     For example, carbon ions can be tilt implanted with a tilt angle of 5° to 30° from an axis orthogonal to the surface of the substrate  101 . The carbon ions can be implanted with an energy of 10 to 50 kilo electron-volts (keV) and a concentration of 10 13  to 10 15  ions/cm 2 .  
         [0025]     Next, halo impurity ions  160  of a first conductivity are injected into the portions of the substrate  101  corresponding to the diffusion barrier ion regions  105  to form halo regions  106 , as shown in  FIG. 1D .  
         [0026]     For example, boron ions or hydrogen ions can be tilt implanted with a tilt angle of 5° to 30° from an axis orthogonal to the surface of the substrate  101 . The boron ions can be implanted with an energy of 10 to 50 keV and a concentration of 5×10 13  to 5×10 14  ions/cm 2 .  
         [0027]     The diffusion barrier ion  150  is smaller than an atom of the substrate  101  and has corresponding size to the halo impurity ion  160 . Therefore, the implanted diffusion barrier ion  150  occupies an interstitial site in a crystal lattice of the substrate  101  and acts as a diffusion barrier of the halo impurity ions  160 .  
         [0028]     The interstitial site in a silicon crystal lattice has a smaller space than the size of the silicon atom. When a smaller atom than the silicon atom is injected in the silicon matrix, the small atom diffuses along the interstitial site.  
         [0029]     Therefore, a diffusion barrier ion having a size similar to that of the halo impurity ion and occupying the interstitial site, blocks the diffusion of the halo impurity ion into the source/drain or the channel.  
         [0030]     Next, as shown in  FIG. 1E , a source  107 , and a drain  108  are formed by injecting impurity ions of a second conductivity. The source  107  is formed in the substrate  101  adjacent to the source side of the channel  200 , and the drain  108  is formed in the substrate  101  adjacent to the drain side of the channel  200 .  
         [0031]     Arsenic ions or phosphorus ions can be used as the impurity ions of a second conductivity. For example, arsenic ions can be implanted with an energy of 10 to 30 keV and a concentration of 1×10 14  to 1×10 15  ions/cm 2  and phosphorus ions can be implanted with an energy of 5 to 25 keV and a concentration of 1×10 14  to 1×10 15  ions/cm 2 .  
         [0032]     Finally, the substrate  101  is annealed at about 900° C. to 1050° C. for a time period of about 10 to about 20 seconds to activate the implanted ions. That is, during the annealing, the diffusion barrier ions and halo impurity ions are activated, and the formation of the source and drain is completed by activating the impurity ions of the second conductivity.  
         [0033]     As described above, the diffusion of the halo impurity ions into the source, drain, and/or the channel is prevented due to the diffusion barrier ions which occupy the interstitial site in the crystal lattice of the substrate.  
         [0034]     Therefore, the profile of the halo regions can be controlled in detail.  
         [0035]     The subject matter disclosed in this application was disclosed in a corresponding Korean patent application. Accordingly, this application claims priority to and the benefit of Korean Patent Application No. 10-2003-0064912, filed on Sep. 18, 2003 in the Korean Intellectual Property Office. The entire contents of Korean Patent Application No. 10-2003-0064912 are incorporated herein by reference.  
         [0036]     As disclosed herein in detail, a semiconductor device and a fabrication method thereof prevent the diffusion of the halo impurities.  
         [0037]     In one example, a semiconductor device may include a semiconductor substrate and a gate formed over the substrate. The gate may define a channel in the substrate having a source side and a drain side. Halo regions may be formed in the source side and the drain side of the channel. The halo regions may contact the channel and contain halo impurity ions of a first conductivity. A source formed in the substrate may contain impurity ions of a second conductivity. A drain formed in the substrate may contain impurity ions of a second conductivity. Diffusion barrier ions may be injected in the halo regions in some configurations.  
         [0038]     According to one example, the diffusion barrier ion may occupy an interstitial site in a crystal lattice of the substrate. The diffusion barrier ion may be smaller than an atom of the substrate and have corresponding size to the halo impurity ion. In one example, the diffusion barrier ion may be a carbon ion and the halo impurity ion may be a boron ion.  
         [0039]     The first conductivity may be p-type and the second conductivity may be n-type.  
         [0040]     Also disclosed herein is a method of fabricating a semiconductor device by providing a semiconductor substrate and forming a gate over the substrate. The gate defines a channel in the substrate having a source side and a drain side. Diffusion barrier ion regions may be formed by injecting diffusion barrier ions into the source side and the drain side of the channel. The diffusion barrier ion regions may be in contact with the channel. Halo regions may be formed by injecting halo impurity ions of a first conductivity into the portions corresponding to the diffusion barrier ion regions. A source may be formed by injecting impurity ions of a second conductivity into the substrate adjacent to the source side of the channel. A drain may be formed by injecting impurity ions of a second conductivity into the substrate adjacent to the drain side of the channel.  
         [0041]     The diffusion barrier ion regions may be formed by performing a tilted ion implantation with a tilt angle of 5° to 30° from an axis orthogonal to the surface of the substrate.  
         [0042]     The halo impurity ion regions may be formed by performing a tilted ion implantation with a tilt angle of 5° to 30° from an axis orthogonal to the surface of the substrate.  
         [0043]     The diffusion barrier ions may be injected with an energy of 10 to 50 keV and a concentration of 10 13  to 10 15  ions/cm 2 .  
         [0044]     The halo impurity ions may be injected with an energy of 10 to 50 keV and a concentration of 5×10 13  to 5×10 14  ions/cm 2 .  
         [0045]     As the impurity ions of the second conductivity, arsenic ions may be injected with an energy of 10 to 30 keV and a concentration of 1×10 14  to 1×10 15  ions/cm 2  to form the source and drain.  
         [0046]     As the impurity ions of the second conductivity, phosphorus ions may be injected with an energy of 5 to 25 keV and a concentration of 1×10 14  to 1×10 15  ions/cm 2  to form the source and drain.  
         [0047]     Additionally, the method further includes annealing the substrate at a temperature of about 900° C. to 1050° C. for a time period of about 10 to about 20 seconds.  
         [0048]     Although certain apparatus constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers every apparatus, method and article of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.