Abstract:
The present invention discloses an ESD protection structure in a SOI CMOS circuitry. The ESD protection structure includes a variety of longitudinal (vertical) PN junction structures having significantly enlarged junction areas for current flow. The resulting devices achieve increased heavy current release capability. Processes of fabricating varieties of the ESD protection longitudinal PN junction are also disclosed. Compatibility of the disclosed fabrication processes with current SOI technology reduces implementation cost and improves the integration robustness.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application is the US national stage of PCT/CN2010/079847 filed on Dec. 16, 2010, which claims the priority of the Chinese patent application No. 201010532715.3 filed on Nov. 4, 2010, that application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of semiconductor integrated circuitry, and more particularly to ESD protection for SOI CMOS devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    CMOS devices fabricated on silicon-on-insulator (SOI) substrates provide higher speed and consume less power. Similar to bulk silicon circuits, ESD protection is critical in circuit design and applications in order to achieve device reliability. Diode network structure techniques used in bulk silicon circuits for ESD protection, such as duo-diode, single diode or MVI (Mixed Voltage Interface) composed of diode string networks, are generally adopted for ESD protection in SOI circuits. 
         [0004]    However, the buried oxide layer (BOX) in SOI circuits isolates device from substrate—a mechanism leading to ESD failure mode. Usually, ESD design generally adopts the form of a lateral diode such as the gated diode ESD protection device shown in  FIG. 1 . However, the lateral diode structure presents two major challenges. The first challenge is that the small junction area is vulnerable to defect, because of the heavy current density. These defects prohibit a device from releasing heavy current when needed, and eventually lead to ESD failure. However, attempts to enlarge the ESD diode junction area result in increased device domain area, making scaling difficult. 
         [0005]    Chinese Patent Application No. 200910201331.0 (CN200910201331.0) tries to solve the problem of breaking-down of ESD protection diodes, by fabricating a diode spacer with an epitaxial layer to achieve the ESD protection effect of a traditional longitudinal diode in bulk silicon. Although the CN200910201331.0 design overcomes the junction defect problem, the spacer structure complicates the manufacturing process and reduces the device integration level, resulting in high overall cost. 
         [0006]    Therefore, there is a need for a simpler and low cost ESD protection device for SOI integrated circuitry. 
       SUMMARY OF THE INVENTION 
       [0007]    Consistent with some embodiments of the present invention, an ESD protection structure in SOI is provided. The ESD protection structure comprises: a semiconductor SOI substrate having a top silicon film; a channel having a longitudinal diode formed in the top silicon film, wherein the longitudinal diode includes a PN junction structure having an N-type region and a P-type region; a positive electrode and a negative electrode formed respectively at the two opposite ends of the channel; an ESD protection node; and a gate dielectric layer and a gate electrode successively formed over the channel. 
         [0008]    Preferably, the semiconductor substrate includes a Si substrate; a buried oxide layer (BOX) formed over the Si substrate and a top silicon film formed over the buried oxide layer. 
         [0009]    Preferably, a side-wall spacer is formed surrounding the gate dielectric layer and the gate electrode. 
         [0010]    Preferably, a shallow trench isolation region is formed surrounding the gated diode ESD protection device. 
         [0011]    Preferably, the P-type region of the channel is formed over the N-type region, forming a P-type gated diode ESD protection structure. 
         [0012]    Preferably, the N-type region of the channel is formed over the P-type region, forming an N-type gated diode ESD protection structure. 
         [0013]    Consistent with another embodiment of the present invention, an ESD protection structure comprises: a semiconductor SOI substrate having a top silicon film; a first channel having a longitudinal N-type diode formed in the top silicon film, wherein the longitudinal N-type diode includes a PN junction structure having an N-type region above a P-type region; a positive electrode and a negative electrode formed respectively at the two opposite ends of the first channel; a gate dielectric layer and a gate electrode successively formed over the first channel; a second channel having a longitudinal P-type diode formed in the top silicon film, wherein the longitudinal P-type diode includes a PN junction structure having a P-type region above an N-type region; a positive electrode and a negative electrode formed respectively at the two opposite ends of the second channel; a gate dielectric layer and a gate electrode successively formed over the second channel; and an ESD protection node coupled to the negative electrode of the first channel and the positive electrode of the second channel. 
         [0014]    Consistent with other embodiments of the present invention, a method of manufacturing an ESD protection device in SOI circuit is also provided. The method includes the following steps: providing a SOI substrate having a top silicon film, a buried oxide layer, and a silicon substrate; forming a longitudinal PN junction structure including a P-type region and a N-type region in the top silicon film of the SOI substrate; forming a gate dielectric layer and a gate electrode layer successively over the longitudinal PN junction; forming a spacer and forming a P+ region as the positive electrode and a N+ region as the negative electrode respectively at the two opposite ends of the longitudinal PN junction structure to form a gated diode ESD protection device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross sectional view of a conventional gated-diode ESD protection structure in SOI. 
           [0016]      FIG. 2  is a cross sectional view of an ESD protection structure in SOI, according to the first embodiment of the present invention. 
           [0017]      FIG. 3  is a cross sectional view of an ESD protection structure, according to the second embodiment of the present invention. 
           [0018]      FIG. 4   a  is a cross sectional view of an ESD protection structure, according to the third embodiment of the present invention. 
           [0019]      FIG. 4   b  is a diagram of the duo-diode ESD protection circuit, according to the third embodiment of the present invention. 
           [0020]      FIGS. 5   a - 5   d  describe the manufacturing process of the ESD protection structure, according to some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0021]    The present invention is further explained in detail according to the accompanying drawings. 
       First Embodiment 
       [0022]      FIG. 2  illustrates the cross sectional view of a P-type gate-diode ESD protection structure in a SOI circuit, according to the first embodiment of the present disclosure. The P-type gated-diode ESD protection structure in a SOI circuit includes a semiconductor substrate  4  and a P-type gated diode ESD protection device  10  (enclosed in the dashed lined box) formed on the semiconductor substrate  4 . 
         [0023]    The semiconductor substrate  4  includes a Si substrate  3 ; a buried oxide layer (BOX)  2  formed on the Si substrate  3  and a top silicon film  1  formed on the buried oxide layer  2 . There are a number of PMOS transistors and NMOS transistors in the vicinity, generally isolated from each other by shallow trench isolation region (STI)  18  fabricated in the semiconductor substrate  4 . For reference, only one PMOS transistor  5  and one NMOS transistor  6  are shown in  FIG. 2   
         [0024]    The P-type gated diode ESD protection device  10  includes a channel  19 , a positive electrode (P+ region)  11 , a negative electrode (N+ region)  12  formed respectively at the two opposite ends of channel  19 , a gate dielectric layer  13  and a gate electrode layer  14  successively formed on channel  19 . Channel  19  consists of a bottom N-type region  16  and a top P-type region  15  located on top of the N-type region  16 . The top P-type and bottom N-type regions form a longitudinal (vertical) PN junction structure in channel  19 . 
         [0025]    The P-type gated-diode ESD protection device  10  further includes a side-wall spacer  17  formed surrounding gate dielectric layer  13  and gate electrode  14 . A shallow trench isolation region  18  is formed enclosing gated-diode ESD protection device  10 . 
         [0026]    Contrary to a conventional P-type channel gated-diode where the diodes are laterally positioned with limited channel layer thickness to form the PN junction area, P-type gated diode ESD protection device  10  has a vertical PN junction structure, significantly increased the gated-diode PN junction area without changing the device size. With a much larger PN junction, the current releasing capability at time of a heavy current surge is increased and the integration level of the ESD protection circuit in SOI is enhanced. 
         [0027]    Connector  8   a  ties negative electrode  12  of the P-type gated diode protection device  10  to the ESD protection node  8  in the SOI circuit. Connector  7   a  ties positive electrode  11  to Vss  7  (negative power supply or ground) and connector  7   b  ties gate electrode  14  to Vss  7 . ESD protection node  8  and Vss are external electrical contacts for a gated single-diode ESD protection circuit, as shown in  FIG. 4   b.    
       Second Embodiment 
       [0028]      FIG. 3  is the cross sectional view of an N-type gated single diode ESD protection structure, according to the second embodiment of the present invention. The N-type gated single diode ESD protection structure includes a semiconductor substrate  34 , and a N-type gated diode ESD protection device  20  formed on the semiconductor substrate  34 ; the semiconductor substrate  34  includes a Si substrate  33 ; a buried oxide layer (BOX)  32  formed on the Si substrate  33 , and a top silicon film  31  formed on the buried oxide layer  32 . There are a number of PMOS transistors and NMOS transistors in the vicinity, isolated by shallow trench isolation region (STI)  38  fabricated on the semiconductor substrate  34 . For reference, only one PMOS transistor  35  and one NMOS transistor  36  are shown in  FIG. 3 . 
         [0029]    The N-type gated diode ESD protection device  20  includes a channel  29 , a positive electrode (P+ region)  21 , a negative electrode (N+ region)  22  formed respectively at the two opposite ends of the channel  29 , a gate dielectric layer  23  and a gate electrode  24  successively formed over the channel  29 . The channel  29  consists of a P-type region  25  and an N-type region  26  which is formed on the P-type region  25 . The P-type and N-type regions form a longitudinal (vertical) PN junction structure. 
         [0030]    The N-type gated diode ESD protection device  20  further includes a side-wall spacer  27  formed surrounding the gate dielectric layer  23  and the gate electrode  24 , and a shallow trench isolation region  28  is formed enclosing gated-diode ESD protection device  20 . 
         [0031]    Contrary to a conventional N-type channel gated-diode where the diodes are laterally formed and the channel layer thickness limits the PN junction area size, N-type gated diode ESD protection device  20  has a longitudinal PN junction structure; therefore the gated-diode PN junction area is greatly increased without changing the device size. With a larger PN junction, the current releasing capability is increased and the integration level of the ESD protection circuit in SOI is enhanced. 
         [0032]    Connector  38   a  ties negative electrode  22  of the N-type gated diode protection device  20  to the ESD protection node  38  in the SOI circuit. Connector  37   a  ties positive electrode  21  to Vss  37  (negative power supply or ground) and connector  37   b  ties gate electrode  24  to Vdd  39  (positive supply). ESD protection node  38 , Vdd  39 , and Vss  37  are external electrical contacts for a gated single-diode ESD protection circuit, as shown in  FIG. 4   b.    
       Third Embodiment 
       [0033]      FIG. 4   a  is the cross sectional view of a gated duo-diode ESD protection structure in a SOI CMOS circuit. The gated duo-diode ESD protection structure includes a semiconductor substrate  44 , a P-type gated diode ESD protection device  410  and an N-type gated diode ESD protection device  420  formed in the semiconductor substrate  44 . The semiconductor substrate  44  includes a Si substrate  43 ; a buried oxide layer (BOX)  42  formed on the Si substrate  43  and a top silicon film  41  formed on the buried oxide layer  42 . A number of PMOS transistors and NMOS transistors in SOI CMOS circuits are isolated from each other by shallow trench isolation region (STI)  48 , which are fabricated in the semiconductor substrate  44 . A PMOS transistor  5  and a NMOS transistor  6  are shown in  FIG. 4   a.    
         [0034]    The N-type gated diode ESD protection device  420  and the P-type gated diode ESD protection device  410  are serially connected. The negative electrode  423  and the gate electrode  424  of the N-type gated diode ESD protection device  420  are connected with V DD    490  (positive power supply). The positive electrode  421  and the gate electrode  414  of the P-type gated diode ESD protection device  410  are connected with Vss  470  (negative power supply or ground). The positive electrode  451  of the N-type gated diode ESD protection device  420  and the negative electrode  453  of the P-type gated diode ESD protection device  410  are both connected with the ESD protection node  480  of the SOI CMOS circuit. 
         [0035]      FIG. 4   b  is the circuit diagram of the gated duo-diode ESD protection structure. 
         [0036]    It should be noted that ESD protection structures disclosed in the above embodiments may include other components, such as more gated duo-diode ESD protection devices or other varieties of ESD protection circuits. 
         [0037]      FIGS. 5   a - 5   d  illustrate process steps in fabricating an ESD protection structure of a SOI CMOS integrated circuit. 
         [0038]    (A) provide a shallow trench isolation region (STI) on a SOI substrate, which has a top silicon film, a buried oxide layer, and a silicon substrate, as shown in  FIG. 5   a,    
         [0039]    (B) coat the SOI substrate with photo resist, perform a lithography process, pattern an open window in a given position for an ESD protection device; fabricate a longitudinal PN junction structure consisting of a P-type region and a N-type region in the top silicon film of the SOI substrate. The PN junction may be formed by a number of techniques, for example, including ion implantation process or diffusion. The longitudinal PN junction structure may have the N-type region located above the P-type region to form a N-type gated diode ESD protection device; or the P-type region located above the N-type region to form a P-type gated diode ESD protection device, as shown in  FIG. 5   b  and  FIG. 5   c.    
         [0040]    (C) deposit a gate dielectric layer and a gate electrode layer successively over the longitudinal PN junction; form a spacer and then form a P+ region as the positive electrode and a N+ region as the negative electrode respectively at the two opposite ends of the longitudinal PN junction structure, which has the N-type region located above the P-type region to form a N-type gated diode ESD protection device. 
         [0041]    Similarly, a P-type gated diode ESD protection device is fabricated by forming a longitudinal PN junction structure with the P-type region located above the N-type region, followed by depositing a gate dielectric layer and a gate electrode layer successively over the longitudinal PN junction. 
         [0042]    (D) complete the ESD protection structure by forming interconnecting structures. 
         [0043]    Varieties of ESD protection circuits similar to the ESD protection structure described in the above embodiments could be fabricated by variations of the above process. 
         [0044]    An ESD protection device having a longitudinal PN junction structure significantly enlarges the junction area, therefore increases current releasing capability during heavy current surges. The disclosed process of fabricating the ESD protection device is compatible with the current manufacturing process of SOI integrated circuit. Therefore, implementation of the disclosed ESD devices is practical and cost effective. 
         [0045]    The above description of the detailed embodiments are only to illustrate the preferred implementation according to the present invention, and it is not to limit the scope of the present invention, Accordingly, all modifications and variations completed by those with ordinary skill in the art should fall within the scope of present invention defined by the appended claims.