Abstract:
A method for making a semiconductor device includes providing a substrate of a first conductivity type and having a surface region, forming a well region of a second conductivity type and having a first depth in the substrate, adding a gate dielectric layer overlying the surface region, adding a gate layer overlying the gate dielectric layer, forming a first LDD region of the first conductivity type and having a second depth within the well region, forming an emitter region of the second conductivity type within the first LDD region, and forming a second LDD region of the first conductivity type with the well region, a channel region separates the first and second LDD regions. The method further includes forming a source region being of the first conductivity type within the second LDD region and adding an output pad coupled to both the drain and emitter regions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 12/483,195, filed Jun. 11, 2009, entitled “Integrated Electrostatic Discharge (ESD) Device,” the entire content of which is incorporated herein by reference for all purposes. The U.S. application Ser. No. 12/483,195 claims the benefit and priority under 35 U.S.C. 119 of Chinese Patent Application No. 200810040570.8, filed Jul. 15, 2008, entitled “Integrated Electrostatic Discharged Device,” by inventors Chi Kang Liu, Ta Lee Yu, and Quan Li, commonly assigned. Both of these applications are commonly owned and incorporated by reference herein for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method and device for an ESD device incorporating a high voltage LDD structure for the manufacture of integrated circuits. The invention provides techniques for an ESD device which has a lower trigger voltage and offers more effective protection to the integrated circuit than conventional devices. Merely by way of example, the invention has been applied to ESD protection of high voltage I/O circuit for the manufacture of integrated circuits. But it would be recognized that the invention has a much broader range of applicability. 
     Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across. 
     Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. An example of such a limit is electrostatic discharge (ESD) protection devices used for the manufacture of integrated circuits in a cost effective and efficient way. 
     Fabrication of custom integrated circuits using chip foundry services has evolved over the years. Fabless chip companies often design the custom integrated circuits. Such custom integrated circuits require a set of custom masks commonly called “reticles” to be manufactured. A chip foundry company called Semiconductor Manufacturing International Company (SMIC) of Shanghai, China is an example of a chip company that performs foundry services. Although many ESD protection circuits and methods are provided by fabless chip companies and foundry services, inherent limitations still exist. For example, in a high voltage process, it is difficult to fabricate efficient electrostatic discharge (ESD) bipolar junction transistor (BJT) devices. Because in a high voltage process deep N-type and P-type wells are used. Conventional ESD bipolar devices built in these deep wells cannot be easily triggered by high voltage pulses caused by ESD events. Conventional high voltage ESD devices which include simple N+/P-well or P+/N-well diodes suffer from large areas and poor ESD performance. 
       FIG. 1  is a cross-sectional view diagram of a conventional bipolar ESD clamp device. As shown ESD clamp device  100  includes a bipolar transistor  140  formed with P-type double diffused drain (DDD)  130 , high-voltage N-well  120 , and P-type substrate  110 . To provide device protection, an ESD bipolar transistor needs to trigger at a moderate voltage, for example 10-15 volts for some applications. Then a large current is allowed to flow through the bipolar transistor at a substantially reduced voltage, thus avoiding damages to other devices in the integrated circuit. In the conventional ESD clamp device shown in  FIG. 1 , the base width of bipolar transistor  140 , which is determined by a depth of the HV N-well region  120  in  FIG. 1 , can be as large as 3 um. Therefore it would take a very high voltage for the bipolar transistor to trigger. As a result ESD protection is only provided by a diode junction breakdown in bipolar transistor  140 . When operation voltage is higher than the junction breakdown voltage, for example, 30V, the energy of junction break down during the ESD pulse, which can be expressed as a product of voltage and current (V*I), can be very large.  FIG. 2  is a simplified drawing of a current-voltage curve during a junction breakdown of a conventional bipolar ESD clamp device. Large devices are therefore needed to increase ESD junction area to avoid junction burnout. These and other limitations are described throughout the present specification and more particularly below. 
     From the above, it is seen that an improved technique for processing semiconductor devices is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention techniques are provided for integrated circuits and their processing. More particularly, the invention provides a method and device for an ESD device incorporating a high voltage LDD structure for the manufacture of integrated circuits. The invention provides techniques for an ESD device which has a lower trigger voltage and offers more effective protection to the integrated circuit than conventional devices. Merely by way of example, the invention has been applied to ESD protection of high voltage I/O circuit for the manufacture of integrated circuits. But it would be recognized that the invention has a much broader range of applicability. 
     In a specific embodiment, the invention provides semiconductor device including a semiconductor substrate comprising a surface region and a well region within the semiconductor substrate. The semiconductor substrate is characterized by a first conductivity type, and the well region is characterized by a second conductivity type. The well region is also characterized by a first depth. The device includes a first lightly-doped-drain (LDD) region within the well region. The first LDD region is of the first conductivity type and is characterized by a second depth. The device also includes an emitter region within the first LDD region. The emitter region is characterized by the second conductivity type. The device includes a drain region of the first conductivity type within the first LDD region, and a second lightly-doped-drain (LDD) region of the first conductivity type within the well region. The second LDD region is separated from the first LDD region by a channel region. The device further includes a source region of the first conductivity type within the second LDD region. The device also includes gate dielectric overlying the surface region, and a gate layer overlying the gate dielectric layer. The device also includes an output terminal coupled to both the drain region and the emitter region. The first LDD region, the well region, and the substrate are associated with a first bipolar transistor, which is characterized by a first trigger voltage. The emitter region, the first LDD region, and the well region are associated with a second bipolar transistor, which is characterized by a second trigger voltage. In an embodiment, the semiconductor substrate is a silicon based semiconductor substrate. In an embodiment, the first lightly-doped-drain (LDD) region is a high-voltage LDD region (HV-LDD). In a specific embodiment, the first conductivity type is P-type and the second conductivity type is N-type. In another embodiment, the first conductivity type is N-type and the second conductivity type is P-type. In an embodiment, the first depth and second depth are selected such that the first trigger voltage and the second trigger voltage are less than a predetermined voltage. In an embodiment, the first depth is approximately 3 um, whereas the second depth is approximately 0.5-1.5 um. In another embodiment, the second depth is approximately one half of the first depth. In some embodiment, the first trigger voltage is less than 30 volts, whereas in other embodiment, the first trigger voltage is approximately 10 volts. In an embodiment, the second trigger voltage is less than 30 volts. In another embodiment, the second trigger voltage can be approximately 10 volts. In a specific embodiment, the second LDD region is characterized by a third depth, and the third depth is less than the second depth. 
     In another embodiment, the invention provides a semiconductor device for ESD protection that includes a semiconductor substrate of a first conductivity type and a well region of a second conductivity type formed within the substrate. The well region is characterized by a first depth. An MOS transistor includes a first lightly doped drain (LDD) region of a second depth within the well region, and a drain region and an emitter region within in the first LDD region. The emitter region is characterized by a second conductivity type. A first bipolar transistor is associated with the emitter region, the first LDD region, and the well region, and is characterized by a first trigger voltage. A second bipolar transistor is associated with the first LDD region, the well region, and the substrate, and is characterized by a second trigger voltage. The first depth and second depth are selected such that the first trigger voltage and the second trigger voltage are less than a predetermined voltage. In an embodiment, the first lightly-doped-drain (LDD) region is a high-voltage LDD region (HV-LDD). 
     In another embodiment the invention provides a bipolar ESD clamp apparatus for the manufacture of integrated circuits. The apparatus includes a p-type silicon substrate which includes a surface region. The apparatus also includes an N-well region within the substrate, the N-well region being characterized by a first depth. The apparatus includes a p-type high-voltage lightly-doped-drain (LDD) within the N-well region, an N+ region within the high voltage LDD region, and a P+ region within the high voltage LDD region. The N+ region and the P+ region are connected to a pad structure. In an embodiment, the high voltage LDD region, the N-well region, and the substrate are associated with a first bipolar transistor characterized by a first trigger voltage, and the N+ region, the high voltage LDD region, and the N-well region are associated with a second bipolar transistor characterized by a second trigger voltage. In an embodiment, the first depth and second depth are selected such that the first trigger voltage and the second trigger voltage are less than a predetermined voltage. In a specific embodiment, the first trigger voltage is less than about 30 volts and the second trigger voltage is less than about 30 volts. In another embodiment, the first trigger voltage is approximately 10 volts and the second trigger voltage is approximately 10 volts. In an embodiment, the high voltage LDD region is characterized by a first depth that is approximately one half of a depth of the N-well region. 
     In an alternative embodiment, a method is provided for making a semiconductor device. The method includes providing a semiconductor substrate comprising a surface region. The semiconductor substrate is characterized by a first conductivity type. The method includes forming a well region of a second conductivity type within the semiconductor substrate. The well region is also characterized by a first depth. The method also includes adding a gate dielectric layer overlying the surface region, and adding a gate layer overlying the gate dielectric layer. The method further includes forming a first lightly-doped-drain (LDD) region within the well region, the first LDD region being of the first conductivity type and characterized by a second depth. The method includes forming an emitter region of the second conductivity type within the first LDD region. The method also forms a drain region of the first conductivity type within the first LDD region. The method also forms a second lightly-doped-drain (LDD) region of the first conductivity type within the well region. The second LDD region is separated from the first LDD region by a channel region. The method includes forming a source region of the first conductivity type within the second LDD region. The method then adds an output pad coupled to both the drain region and the emitter region. In an embodiment, the first LDD region, the well region, and the substrate are associated with a first bipolar transistor characterized by a first trigger voltage. The emitter region, the first LDD region, and the well region are associated with a second bipolar transistor characterized by a second trigger voltage. In an embodiment the first conductivity type is P-type and the second conductivity type is N-type. In an embodiment the first depth and second depth are selected such that the first trigger voltage and the second trigger voltage are less than a predetermined voltage. 
     Many benefits are achieved by way of the present invention over conventional techniques. For example, the present technique provides an easy to use process that relies upon conventional technology. In some embodiments, the invention provides a method for achieving low trigger voltage and effective device protection against high voltage ESD events. Additionally, the method provides a process that is compatible with conventional process technology without substantial modifications to conventional equipment and processes. 
     Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout the present specification and more particularly below. 
     Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view diagram of a conventional bipolar ESD clamp device; 
         FIG. 2  is a simplified drawing of a current-voltage curve showing a junction breakdown of a conventional bipolar ESD clamp device; 
         FIG. 3  is a simplified cross-sectional view diagram of an ESD clamp device according to an embodiment of the present invention; 
         FIG. 4  is a simplified drawing of a current-voltage curve showing a snapback of bipolar ESD device according to an embodiment of the present invention; 
         FIG. 5  is a simplified cross-sectional view diagram of an ESD clamp device according to another embodiment of the present invention; 
         FIG. 6  is a simplified cross-sectional view diagram of a transistor integrated with a bipolar ESD clamp device according to an embodiment of the present invention; 
         FIG. 7  is a simplified cross-sectional view diagram of a transistor integrated with a bipolar ESD clamp device according to an alternative embodiment of the present invention; 
         FIG. 8  is a simplified flow chart of a method for making a transistor device with integrated ESD clamp device according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to embodiments of the present invention techniques are provided for integrated circuits and their processing. More particularly, the invention provides a method and device for an ESD device incorporating a high voltage LDD structure for the manufacture of integrated circuits. The invention provides techniques for an ESD device which has a lower trigger voltage and offers more effective protection to the integrated circuit than conventional techniques. Merely by way of example, the invention has been applied to ESD protection of high voltage I/O circuit for the manufacture of integrated circuits. But it would be recognized that the invention has a much broader range of applicability. 
     Depending upon the embodiment, the present invention includes various features, which may be used. These features include the following: 
     1. An ESD protection device having low trigger voltage and offering more effective protection of the integrated circuit than conventional devices. 
     2. A method for forming a high voltage I/O transistor having an integrated ESD protection device. 
     3. A method for forming high voltage NMOS and PMOS I/O transistors having embedded ESD protection devices. 
     As shown, the above features may be in one or more of the embodiments to follow. These features are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
       FIG. 3  is a simplified cross-sectional view diagram of an ESD clamp device  300  according to an embodiment of the present invention. This diagrams is merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown, ESD clamp device  300  includes P-type substrate  310  having a surface region  315 , and an N-type well region  320  formed within the P-type substrate  310 . In an embodiment, N-type well region  320  has a depth of about 2-3 um. ESD clamp device  300  also includes a high voltage PLDD region (HV-PLDD)  330  formed within N-well region  320 . In an embodiment, HV-PLDD region  330  has a depth of, e.g., approximately 0.5-1.5 um and is doped with P-type impurities such as boron or boron-containing impurities to a concentration of e.g., approximately 1E16 to 1E17/cm 3 . These depth and concentration values are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. ESD clamp device  300  further includes N+ region  340  and P+ region  350  formed within the HV-PLDD region  330 . The N+ regions  340  is heavily doped with N-type impurities such as arsenic or phosphorus to a concentration of e.g. approximately 1E18 to 1E19/cm 3 , depending on specific applications. P+ regions  350  is heavily doped with P-type impurities such as boron or boron-containing impurities to a concentration of e.g. approximately 1E18 to 1E19/cm 3 , depending on specific applications. As shown in  FIG. 3 , ESD clamp device  300  includes a pad region  360  which is schematically shown to be electrically connected to N+ region  340  and P+ region  350 . A contact in N-well is also provided to be electrically connected to a ground  370 . Depending upon the embodiment, one of ordinary skill in the art would recognize other variations, modifications, and alternatives. 
     Referring to  FIG. 3 , two bipolar transistor structures are formed in ESD clamp device  300 . As shown schematically, PNP bipolar transistor  380  includes an emitter (P+ region  350  and HV-PLDD region  330 ), a base (N-well  380 ), and a collector (P-sub  310 ). Compared with the conventional ESD device in  FIG. 1 , PNP transistor  380  has a shorter base width in N-well region  320 , because the HV-PLDD region  330  extends the emitter region and shortens the base region. Base width of bipolar transistor can be selected by adjusting a depth of N-well region  320  and a depth of HV-PLDD region  330 . PNP transistor  380  can therefore be triggered by a lower voltage of, for example, 10-15 volts, whereas a conventional device may have a trigger voltage higher than 30 volts. Therefore PNP transistor  380  can provide better protection against ESD events which raise a negative high voltage at PAD  360 . 
     Also shown schematically in  FIG. 3  is an NPN bipolar transistor  390  which includes an emitter (N+ region  340 ), a base (HV-PLDD  330 ), and a collector (N-well  320 ). NPN bipolar transistor  390  can be triggered at a predetermined trigger voltage and offer protection against ESD events which present a positive high voltage at PAD  360 . The base width of NPN bipolar transistor  390  is determined by a depth of the HV_PLDD region. According to embodiments of the invention, the depth of HV-PLDD region  330  is chosen to be more than that of conventional P-type LDD region for logic transistors. As mentioned earlier, the depth of HV-PLDD region  330  also affects the base width of PNP transistor  380 . The doping concentration and depth of the HV-PLDD region are chosen to provide appropriate width and doping concentration of bipolar transistor base regions, which are design parameters selected to optimize trigger voltages for both PNP transistor  380  and NPN transistor  390 . In a specific embodiment, HV-PLDD region  330  has a depth of approximately 0.5-1.5 um and is doped with P-type impurities such as boron or boron-containing impurities to a concentration of approximately 1E16 to 1E17/cm 3 . These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
       FIG. 4  is a simplified drawing of a current-voltage curve showing a snapback of a bipolar ESD device, such as device  300  in  FIG. 3 , according to an embodiment of the present invention. As shown, when an external ESD high voltage reaches a trigger voltage Vtr, for example, 10-15 volts, a bipolar transistor in the ESD clamp device  300  is triggered, allowing current to flow at a safe voltage level Von, for example, 1-2 volts. Depending on the polarity of the ESD voltage, either PNP transistor  380  or NPN transistor  390  can be triggered. These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
       FIG. 5  is a simplified cross-sectional view diagram of an ESD clamp device according to another embodiment of the present invention.  FIG. 5  shows an ESD clamp device similar to device  300  in  FIG. 3 , but having reversed polarities, i.e., with N-type and P-type conductivities interchanged. Specifically, a high voltage NLDD (HV-NLDD) region  530  is used instead of HV-PLDD region  330  in  FIG. 3 . Various other components in  FIG. 5  have their counterparts in  FIG. 3 . For example, NPN transistor  580  is triggered by a negative high voltage at PAD  560 , and PNP transistor  590  is triggered by a negative high voltage at PAD  560 . According to embodiments of the invention, the doping concentration and depth of the HV-NLDD region  530  are chosen to provide appropriate width and doping concentration of the base regions, which are design parameters selected to optimize the trigger voltages for both PNP transistor  590  and NPN transistor  580 . In a specific embodiment, HV-NLDD region  530  has a depth of approximately 0.5-1.5 um and is doped with P-type impurities such as boron or boron-containing impurities to a concentration of approximately 1E16 to 1E17/cm 3 . In a specific embodiment, the P-well region is about 2-3 um thick. These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skills in the art would recognize many variations and modifications according to specific applications. 
       FIG. 6  is a simplified cross-sectional view diagram of a transistor device  600  integrated with a bipolar ESD clamp device according to an embodiment of the present invention. This diagrams is merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown, transistor device  600  includes P-type substrate  610  having a surface region  615 , and an N-type well region  620  formed within the P-type substrate  610 . In an embodiment, the N-well region has a depth of about 3 um. Transistor device  600  also includes a high voltage PLDD region (HV-PLDD)  630  formed within N-well region  620 . HV-PLDD region  630  has a depth of, for example, approximately 0.5-1.5 um and is doped with P-type impurities such as boron or boron-containing impurities to a concentration of, for example, approximately 1E16 to 1E17/cm 3 . These depth and concentration values are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skills in the art would recognize many variations and modifications according to specific applications. Transistor device  600  also includes P-type region  635 , which has substantially the same depth and doping concentration as HV-PLDD region  630  according to an embodiment of the invention. In other embodiments, P-type region  635  can have different depths and doping concentrations, depending upon specific applications. Transistor device  600  further includes N+ region  640  and P+ region  650  formed within the HV-PLDD region  630 , and P+ region  655  formed in P− region  635 . The N+ regions  640  is heavily doped with N-type impurities such as arsenic or phosphorus to a concentration of approximately 1E18 to 1E19/cm 3 , depending on specific applications. P+ regions  650  and  655  are heavily doped with P-type impurities such as boron or boron-containing impurities to a concentration of approximately 1E18 to 1E19/cm 3 , depending on specific applications. These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
     Referring to  FIG. 6 , transistor device  600  includes an ESD clamp structure similar to device  300  in  FIG. 3 . For example, PNP transistor  680  includes an emitter (P+ region  650  and HV-PLDD region  630 ), a base (N-well  620 ), and a collector (P-sub  610 ). NPN bipolar transistor  690  includes an emitter (N+ region  640 ), a base (HV-PLDD  630 ), and a collector (N-well  620 ). PAD  660  is electrically connected to the emitter regions of PNP transistor  680  and NPN transistor  690 . Together PNP bipolar transistor  680  and NPN bipolar transistor  690  are triggered by high voltages caused by ESD events and provide a current path to protect devices in the integrated circuit. An example of such device is a PMOS transistor  605  included in transistor device  600 . 
     As shown in  FIG. 6 , transistor device  600  further includes gate oxide layer  625  overlying a surface region  615  of N-well region  620 , a polysilicon gate  665  overlying gate oxide layer  625 , and spacer regions  667  and  668 . As shown, PMOS transistor  605  includes a drain region (P+ regions  650 ), source region (P+ region  655 ), and a substrate (N-well region  620 ), in addition to gate  665 , gate oxide  625 , and channel region  615 . Depending on applications, drain region (P+ regions  650 ) and source region (P+ region  655 ) can be interchanged, such that P+ regions  650  is operated as a source region and P+ region  655  is operated as a drain region. PMOS transistor  605  also includes spacers  667  and  668 , and LDD regions  635  and  630 . Transistor  605  can be used as a high voltage I/O device, embedded with ESD clamp devices  680  and  690 . A high voltage at PAD  660  caused by an ESD event will be diverted by ESD clamp devices  680  and  690 , thus protecting PMOS transistor  605  from ESD damages. Depending upon the embodiment, one of ordinary skill in the art would recognize other variations, modifications, and alternatives. 
     Referring to  FIG. 6 , HV-PLDD region  630  extends the emitter region of PNP transistor  680  and shortens its base region. PNP transistor  680  can therefore be triggered by a lower voltage such as 10-15 volts, and offers better protection against ESD events which presents a negative high voltage at the pad  660 . NPN bipolar transistor  690  has a base width determined by the depth of HV-PLDD region  630 . NPN bipolar transistor  690  can be triggered by a positive ESD high voltage at the pad  660  and offers protection against such ESD events. According to embodiments of the invention, the doping concentration and depth of the HV-PLDD region  630  are chosen to provide appropriate width and doping concentration of the base regions of bipolar transistors  680  and  690 . These design parameters are selected to optimize the trigger voltages for both PNP transistor  680  and NPN transistor  690 . In a specific embodiment, HV-PLDD region  630  has a depth of approximately 0.5-1.5 um and is doped with P-type impurities such as boron or boron-containing impurities to a concentration of approximately 1E16 to 1E17/cm 3 . These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
       FIG. 7  is a simplified cross-sectional view diagram of a transistor incorporated with a bipolar ESD clamp device according to an alternative embodiment of the present invention. In  FIG. 7 , device  700  includes NMOS transistor  705  with an embedded ESD clamp device, similar to device  600  in  FIG. 6 , but having reversed polarities, i.e., with N-type and P-type conductivities interchanged. For example, a high voltage NLDD (HV-NLDD) region  730  is used instead of HV-PLDD region  630  in  FIG. 6 . N-well region  710  is formed within P-type substrate  709 . Alternatively, N-well region can be replaced by an N-type substrate. Various other components in  FIG. 7  have their counterparts in  FIG. 6 . For example, NPN transistor  780  is triggered by a positive high voltage at PAD  760 , and PNP transistor  790  is triggered by a negative high voltage at PAD  760 . According to embodiments of the invention, the doping concentration and depth of the HV-NLDD region  730  are chosen to provide appropriate width and doping concentration of the base regions, which are design parameters selected to optimize the trigger voltages for both PNP transistor  790  and NPN transistor  780 . In a specific embodiment, P-well region  720  has a depth of approximately 2-3 um. HV-NLDD region  730  has a depth of approximately 0.5-1.5 um and is doped with N-type impurities with a concentration of approximately 1E16 to 1E17/cm 3 . These design parameters are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
     A method for fabricating an integrated circuit device according to an embodiment of the present invention may be outlined as follows: 
     1. Provide a substrate, e.g., silicon wafer; 
     2. Form well regions including at least an N-well region; 
     3. Form gate oxide region; 
     4. Form polysilicon layer for transistors; 
     5. Form lightly doped drain regions; 
     6. Form spacer region on sides of the polysilicon gates; 
     7. Form the source and drain of the logic transistors. 
     8. Form an emitter region for the ESD clamp device; 
     9. Perform backend processing including interlayer dielectrics, metal, and contacts. 
     The above sequence of steps provides a method according to an embodiment of the present invention. As shown, the method uses a combination of steps including a way of forming a high voltage LDD region for an ESD protection device according to embodiments of the present invention. Other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein. Further details of the present method can be found throughout the present specification and more particularly below. 
       FIG. 8  is a simplified flow chart of a method for making a transistor device with an integrated ESD clamp device according to an embodiment of the present invention. This flowchart is merely an example, which should not unduly limit the scope of the claims herein. Referring to the flowchart in  FIG. 8 , the method includes step  810  for providing a substrate (e.g., silicon wafer) comprising a surface region. In step  820 , the method includes forming adequate well structures within the substrate. The well structures include an N-well region for a PMOS device. In a specific embodiment, the N-well region has a depth of approximately 2-3 um. In other embodiments, the depth can be adjusted for different applications. Alternatively, a P-well can be formed for an NMOS device. A P-well region includes boron based impurities or the like, and an N-well region includes N-type dopants such as phosphorus or arsenic based impurities. In step  830 , the method includes forming a gate dielectric layer (e.g., gate oxide, nitride, silicon oxynitride) overlying the surface region, which extends over the well region as shown. The gate dielectric is often formed using a thermal oxidation process to form high quality gate oxide, which is substantially free from voids. Proper gate dielectric layer depths are often required for devices to operate at different voltages. Depending upon the embodiment, there can be other variations, modifications, and alternatives. 
     Referring to  FIG. 8 , the method in step  840  includes forming a polysilicon film overlying the gate dielectric layer. The polysilicon film is often doped using impurities to provide conductive characteristics. The film can be doped using diffusion and/or in-situ doping techniques of phosphorus bearing impurities, e.g., phosphine. For PMOS devices, boron-containing impurities, such as diborine can be used. The film can be a single layer or multiple layers of different materials, depending upon the embodiment. The polysilicon film is then patterned to form gate electrodes for MOS transistors. 
     In step  850 , the method includes forming high voltage lightly doped drain (“HV-LDD”) structures for each of the transistors. Photoresist masks are used to allow implanting N-type impurities into NMOS regions and implanting P-type impurities into PMOS regions. In preferred embodiments, HV-LDD regions are provided to withstand high operating voltages. As a result, they are often deeper than conventional LDD implants used in logic devices. In a specific embodiment, HV-LDD region has a depth of approximately 0.5-1.5 um and is doped with impurities to a concentration of approximately 1E16 to 1E17/cm 3 . Also in step  850 , low voltage lightly doped drain (LV-LDD) regions may also be formed with the well region. The LV-LDD regions are provided to reduce the short-channel effect. These design parameters are merely examples, which should not unduly limit the scope of the claims herein. In some embodiments, the polysilicon gates are used as a mask during the HV-LDD implant steps. In other embodiments, HV-LDD implant can be performed before polysilicon gate formation. Here, a photoresist mask can be used to define HV-LDD regions, and then polysilicon gates can be patterned and aligned to the HV-LDD regions. 
     In some embodiments, the HV-LDD is formed on both sides of the channel, i.e., on both the drain side and the source side. In other embodiments, the HV-LDD is formed on the drain side of the device, and a source side LDD region can be formed using similar masking and implant steps. The source side LDD is similar to conventional LDD region in logic MOS or CMOS device, having shallower junction and may be implanted with a lower dose and lower energy than the HV-LDD. One of ordinary skill in the art would recognize many variations and modifications according to specific applications. 
     After the HV-LDD implant, a dielectric layer (e.g., oxide) is deposited and etched back to form spacers (step  860 ). After spacer formation, transistor source/drain (S/D) formation processes are performed (step  870 ). Here photoresist masks are used to allow N-type impurities to be implanted into NMOS regions and P-type impurities into PMOS regions. The S/D implant uses a dose of impurities ranging from about 3E15 atoms/centimeter 2  to about 5E15 atoms/centimeter 2  according to preferred embodiments. According to embodiments of the invention, an emitter region for an ESD clamp device is then formed in step  880 . Here, a photoresist mask is used to define an emitter region in HV-LDD region, and ion implantation is then performed to dope the emitter region with impurities of a conductivity type opposite to that of a source or drain region of the transistor. For example, an N+ emitter region is formed in a PMOS transistor, and a P+ emitter is formed in an NMOS transistor. As discussed earlier, the emitter region will become part of a bipolar transistor ESD clamp device. 
     In step  890 , typical backend processes are performed. Here, the method includes forming interlayer dielectrics, conductor layers, and contact structures. In an embodiment, contacts are provided to pad regions of the integrated circuit. Examples of resulting device structures of a transistor having an integrated ESD clamp device are shown in  FIGS. 6 and 7  and discussed earlier. Of course, one of ordinary skill in the art would recognize other variations, modifications, and alternatives. 
     It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.