Abstract:
Disclosed are an LDMOS device and a method for manufacturing the same capable of decreasing the concentration of a drift region between a source finger tip and a drain, thereby increasing a breakdown voltage. An LDMOS device includes a gate which is formed on a substrate, a source and a drain which are separately arranged on both sides of the substrate with the gate interposed therebetween, a field oxide film which is formed to have a step between the gate and the drain, a drift region which is formed of first condition type impurity ions between the gate and the drain on the substrate, and at least one internal field ring which is formed inside the drift region and formed by selectively ion-implanting second conduction type impurity ions in accordance with the step of the field oxide film.

Description:
[0001]    The present application claims priority to Korean Patent Application No. 10-2011-0096334 (filed on Sep. 23, 2011), which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    An LDMOS transistor which is used in a high-voltage power device has advantages of fast switching speed, high input impedance, low power consumption, and compatibility with a CMOS process, and is widely used in various power devices including a display driving IC, a power converter, a motor controller, and a power supply for a vehicle. In the case of a power device, since on-resistance and breakdown voltage are important factors which significantly affects the device performance, various techniques have been suggested so as to increase the breakdown voltage while maintaining on-resistance Rsp. 
         [0003]    For example, a structure has been suggested in which an internal field ring made of a dopant of a type opposite to a drift region is formed below the gate end portion in the drift region of the LDMOS transistor. 
         [0004]    On the other hand, the breakdown voltage characteristic of the semiconductor device is closely related to the radius of curvature of a source region or a drain region. In particular, the radius of curvature of the relatively small source region is one of the main factors which may cause a decrease in the breakdown voltage of the device, due to an electric field concentration phenomenon occurring in a junction area having a small radius of curvature. 
         [0005]      FIG. 1  is a layout view of a power semiconductor device of the related art, for example, an LDMOS transistor.  FIG. 2  is a sectional view taken along the line of  FIG. 1 . In  FIGS. 1 and 2 , the same reference numerals represent the same regions or layers. 
         [0006]    As illustrated in  FIGS. 1 and 2 , the LDMOS transistor of the related art includes a source  10 , a drain  20 , a source-side protrusion  10 ′, a drain-side protrusion  20 ′, a gate  30 , and an N drift region  40 . The drain  20  is separated from the source  10  at a predetermined interval. 
         [0007]    The source  10  includes a source electrode on the surface of a p-type semiconductor substrate  1  and is a highly doped n+ type source region formed in the semiconductor substrate  1  below the source electrode. 
         [0008]    The drain  20  includes a drain electrode on the surface of the semiconductor substrate  1  and an N drift region  40  formed in the semiconductor substrate  1  below the drain electrode. The N drift region  40  is an n-well region formed by an n-type impurity ion implantation process. 
         [0009]    As illustrated in  FIG. 2 , the drain  20  is an n+ type drain region formed inside the N drift region  40 . A p-type top region  25  is formed inside the N drift region  40 . 
         [0010]    The gate  30  is formed so as to be insulated from an underlying channel region by a gate insulating film  50 , and the source electrode, the drain electrode, and a gate electrode are insulated from each other by an insulating interlayer. 
         [0011]    The LDMOS transistor also includes a field oxide film  42  having a LOCOS structure. 
         [0012]    The semiconductor having the LDMOS transistor of the related art analyzes the ratio of the number of electric charges in the layout corresponding to the N drift region  40  and the P-type top region  25  to obtain the optimum conditions of the breakdown voltage and the on-resistance. 
         [0013]    In the case of an LDMOS which is used in a high-voltage application, from the viewpoint of design layout, there is a phenomenon that the charge balance is lost depending on the boundary condition. That is, in a source finger structure in which a round is formed on the basis of the source  10  or a drain finger structure in which a round is formed on the basis of the drain  20 , there is a phenomenon that the optimum breakdown voltage characteristic decreases. In particular, in the case of an n-type LDMOS, it is more difficult to ensure the breakdown voltage characteristic, having a limit to ensure the breakdown voltage due to the corner effect. In general, in order to correct the phenomenon that the breakdown voltage of the n-type LDMOS is limited, a method is used in which the n-type LDMOS of the corner region is not taken into consideration, or a method is used in which the n-type LDMOS characteristic is taken into consideration but limitedly used. 
         [0014]    According to these methods, there is a phenomenon that the device characteristic per cross-sectional area of the LDMOS is not ensured. Accordingly, there is demand for a method capable of ensuring the optimum LDMOS characteristic per given size. 
       SUMMARY 
       [0015]    Embodiments relate to a semiconductor and manufacturing a semiconductor device, and in particular, to an LDMOS device and a method for manufacturing the same capable of increasing a breakdown voltage and optimizing an on-resistance characteristic without causing an increase in the radius of curvature in a corner region. 
         [0016]    In accordance with embodiments, there is provided an LDMOS device and a method for manufacturing the same capable of performing separate ion implantation processes in a strip region and a corner region of a drift region, and forming an internal field ring in the corner region by n-type impurity and p-type impurity implantation processes, thereby optimizing on-resistance and breakdown voltage characteristics. 
         [0017]    Embodiments are not limited to those mentioned herein, and other embodiments will be apparently understood by those skilled in the art through the following description. 
         [0018]    In accordance with embodiments, there is provided an LDMOS device. The LDMOS device may include a gate which is formed on a substrate, a source and a drain which are separately arranged on sides of the substrate with the gate interposed therebetween, a field oxide film which is formed between the gate and the drain, a drift region which is formed between the gate and the drain using first condition type impurity ions with respect to a strip region, and a plurality of internal field rings which are formed of first and second condition type impurity ions inside a corner region having the fingertip of the source and the fingertip of the drain, and are coupled to each other. Each of the internal field rings includes a region formed of the second condition type impurity ions inside a region formed of the first condition type impurity ions. 
         [0019]    The LDMOS device may further include a top region which is formed of the second condition type impurity ions below the field oxide film, and the internal field rings may be formed below the top region. 
         [0020]    The concentration of the corner region may be determined by the number of internal field rings. 
         [0021]    The concentration of the corner region may be determined by the ion implantation amount or implantation energy of the second conduction type impurity ions for forming the internal field rings. 
         [0022]    The internal field rings may have a plurality of first internal rings which are formed of the first condition type impurity ions and are coupled to each other in a polygonal shape, and a plurality of second internal rings which are respectively formed inside the first internal rings and are formed of the second condition type impurity ions to have a polygonal shape. 
         [0023]    The first internal rings may be formed to have a hexagonal shape and coupled to each other in a honeycomb structure. 
         [0024]    In accordance with embodiments, there is provided a method for manufacturing an LDMOS device which has a source and a drain separately arranged on sides of a substrate with a gate interposed therebetween. The method may include implanting first condition type impurity ions on the substrate corresponding to a strip region excluding a corner region having the fingertip of the source and the fingertip of the drain to form a drift region, forming a field oxide film on the substrate corresponding to the corner region, and implanting the first and second condition type impurity ions in the corner region to form a plurality of internal field rings coupled to each other. Each of the internal field rings may include a region formed of the second conduction type impurity ions inside a region formed of the first conduction type impurity ions. 
         [0025]    The method may further include, prior to forming the internal field rings, implanting the second condition type impurity ions below the field oxide film to form a top region. The internal field rings may be formed below the top region. 
         [0026]    In the method, the forming the internal field rings may include performing a process for implanting the first condition type impurity ions using an ion implantation mask, in which a portion of the corner region is exposed, to form a plurality of first internal rings coupled to each other in a polygonal shape, and performing a process for implanting the second condition type impurity ions using an ion implantation mask, in which another portion of the corner region exposed is exposed, to form a plurality of second internal rings in a polygonal shape inside the first internal rings. 
         [0027]    In the method, in the forming the first internal rings, the first internal rings may be formed to have a hexagonal shape and coupled to each other in a honeycomb structure. 
         [0028]    In accordance with embodiments, it is possible to perform separate ion implantation processes in the strip region and the corner region of the drift region and to form the internal field rings in the corner region by the n-type and p-type impurity ion implantation processes, thereby increasing the breakdown voltage without causing an increase in the radius of curvature of the corner region, and optimizing the on-resistance characteristic. 
     
    
     
       DRAWINGS 
         [0029]    The objects and features of the present invention will become apparent from the following description of embodiments given in conjunction with the accompanying drawings, in which: 
           [0030]      FIG. 1  is a layout view illustrating an LDMOS transistor as a power semiconductor device of the related art. 
           [0031]      FIG. 2  is a sectional view taken along the line II-II′ of  FIG. 1 . 
           [0032]    Example  FIG. 3  is a layout view illustrating an LDMOS device in accordance with embodiments. 
           [0033]    Example  FIG. 4  is a sectional view taken along the line IV-IV′ of example  FIG. 3 . 
           [0034]    Example  FIGS. 5A to 5C  are process sectional views illustrating a process of forming internal field rings in the LDMOS device in accordance with embodiments. 
           [0035]    Example  FIG. 6  is a layout view illustrating an LDMOS device in accordance with embodiments. 
           [0036]    Example  FIG. 7  is a sectional view taken along the line VII-VII′ of  FIG. 6 . 
           [0037]    Example  FIGS. 8A to 8D  are process sectional views illustrating a process of forming internal field rings in the LDMOS device in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0038]    Advantages and features of the invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of embodiments and the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be more readily understood by those skilled in the art, and the invention will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification. 
         [0039]    Hereinafter, an n-channel LDMOS transistor according to embodiments which has a small radius of curvature in a source and can increase a breakdown voltage will be described with reference to the accompanying drawings. 
         [0040]    Example  FIG. 3  is a layout view illustrating an LDMOS device according to embodiments. Example  FIG. 4  is a sectional view taken along the line IV-IV′ of example  FIG. 3 . In Example  FIGS. 3 and 4 , the same reference numerals represent the same regions or layers. 
         [0041]    Referring to example  FIGS. 3 and 4 , the LDMOS device according to embodiments includes a p-type substrate or a p-type SOI substrate  300 , a source  310 , a drain  320 , a source-side protrusion  310 ′, a drain-side protrusion  320 ′, a gate  330 , and an N drift region  340  which is formed in the p-type substrate or the p-type SOI substrate  300  and used as a drift region of the LDMOS device. Here, the drain  320  is separated from the source  310  at a predetermined interval. 
         [0042]    The source  310  may include a source electrode on the surface of the substrate  300  and may be a highly doped n+ type source region formed in the substrate  300  below the source electrode. 
         [0043]    The drain  320  may include a drain electrode on the surface of the substrate  300  and may be an n+ type drain region formed in the substrate  300  below the drain electrode. 
         [0044]    The gate  330  may be formed to be insulated from an underlying channel region by a gate insulating film  332 , and a gate electrode may be formed at the upper part of the gate  330  to apply a voltage to the gate  330 . 
         [0045]    The LDMOS device may also include a field oxide film  350  having a LOCOS structure. In embodiments, the field oxide film  350  may be generated by an oxidation process. For example, a LOCOS (LOCal Oxidation of Silicon) oxide film may be exemplified. 
         [0046]    In embodiments, a source  310  and a drain  320  may respectively include source and drain fingertips  310   t  and  320   t  having a protrusion shape at the center thereof. 
         [0047]    In the LDMOS device having the above-described structure, there is an electric field concentration phenomenon in the N drift region  340  between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 , that is, in the corner regions, causing a breakdown current. In order to prevent the breakdown current, in embodiments, internal field rings  380  are formed in a first corner region  360  between the source fingertip  310   t  and the drain  320  and a second corner region  370  between the drain fingertip  320   t  and the source  310  to control the doping concentration. 
         [0048]    The internal field rings  380  may be formed of a p-type impurity and an n-type impurity in the first and second corner regions  360  and  370 . The internal field rings  380  may have a plurality of first internal rings  382  which may be formed of the n-type impurity to have a polygonal shape, and a plurality of second internal rings  384  which may be formed of the p-type impurity to have a polygonal shape. 
         [0049]    The first internal rings  382  of the internal field rings  380  may be coupled to each other and formed in an octagonal shape. 
         [0050]    In the LDMOS device in accordance with embodiments, the N drift region  340  is formed only in a portion excluding portions where the internal field rings  380  will be formed, that is, a portion excluding the first and second corner regions  360  and  370 . That is, the N drift region  340  may be formed in the portion (strip region) excluding the first and second corner regions  360  and  370 , in which the internal field rings  380  will be formed, through a high-concentration n-type impurity ion implantation process, and the internal field rings  380  may then be formed in the first and second corner regions  360  and  370  through an n-type impurity ion implantation process and a p-type impurity ion implantation process. 
         [0051]    In embodiments, the internal field rings  380  may be coupled to each other in a honeycomb structure and formed below the field oxide film  350 . 
         [0052]    As described above, the internal field rings  380  may be formed between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 . Therefore, it is possible to increase the breakdown voltage without causing an increase in the radius of curvature between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 , and to optimize the on-resistance characteristic. 
         [0053]    A process of forming the internal field rings will be described with reference to example  FIGS. 5A to 5C . 
         [0054]    Example  FIGS. 5A to 5C  are process sectional views illustrating a process of forming internal field rings according to embodiments. 
         [0055]    As illustrated in example  FIG. 5A , first, a high-concentration n-type impurity ion implantation process is performed to form the N drift region  340  of the LDMOS device in the p-type substrate or the p-type SOI substrate  300 . Specifically, an ion implantation mask in which a portion of the N drift region  340  corresponding to the strip region is exposed is formed on the substrate  300 , and the high-concentration n-type impurity ion implantation process is performed to form the N drift region  340  in the substrate  300 . The strip region may mean the portion excluding the portion where the field oxide film  350  will be formed, that is, the portion excluding the first and second corner regions  360  and  370 . 
         [0056]    Next, as illustrated in example  FIG. 5B , a first ion implantation mask  342  in which a portion excluding the N drift region  340 , that is, a portion of the first and second corner regions  360  and  376  is exposed is formed, and a high-concentration n-type impurity ion implantation process is then performed using the first ion implantation mask  342  to form the n-type first internal rings  382 . The first internal rings  382  are formed in the first and second corner regions  360  and  370  and are coupled to each other in an octagonal shape. 
         [0057]    Next, after the first ion implantation mask  342  is removed, a second ion implantation mask in which another portion of the first and second corner regions  360  and  370  is exposed is formed, and a high-concentration p-type impurity ion implantation process is performed using the second ion implantation mask to form the p-type second internal rings  384 . Next, the second ion implantation mask is removed. The second internal rings  384  are formed inside the first internal rings  382  to have an octagonal shape, similarly to the first internal rings  382 . 
         [0058]    The breakdown voltage of the LDMOS device in accordance with embodiments can be controlled by adjusting the depth and width of the second internal rings  384  inside the internal field rings  380 . The depth and width of the second internal rings  384  can be adjusted by adjusting the ion implantation amount and ion implantation energy in the p-type impurity ion implantation process. 
         [0059]    Example  FIG. 6  is a layout view illustrating an LDMOS device according to embodiments. Example  FIG. 7  is a sectional view taken along the line VII-VII′ of  FIG. 6 . In example  FIGS. 6 and 7 , the same reference numerals represent the same regions or layers. 
         [0060]    Referring to example  FIGS. 6 and 7 , the LDMOS device according to embodiments includes a p-type substrate or a p-type SOI substrate  300 , a source  310 , a drain  320 , a source-side protrusion  310 ′, a drain-side protrusion  320 ′, a gate  330 , an N drift region  340  which is formed in the p-type substrate or the p-type SOI substrate  300  and used as a drift region of the LDMOS device, and a P top region  400 . Here, the drain  320  is separated from the source  310  at a predetermined interval. 
         [0061]    The source  310  may include a source electrode on the surface of the substrate  300  and may be a highly doped n+ type source region formed in the substrate  300  below the source electrode. 
         [0062]    The drain  320  may include a drain electrode on the surface of the substrate  300  and may be an n+ type drain region formed in the substrate  300  below the drain electrode. 
         [0063]    The gate  330  may be formed to be insulated from an underlying channel region by a gate insulating film  332 , and a gate electrode may be formed at the upper part of the gate  330  to apply a voltage to the gate  330 . 
         [0064]    The LDMOS device may also include a field oxide film  350  having a LOCOS structure. In embodiments, the field oxide film  350  may be generated by an oxidation process. For example, a LOCOS (LOCal Oxidation of Silicon) oxide film may be exemplified. The P top region  400  may be formed through a p-type impurity ion implantation process and formed below the field oxide film  350 . 
         [0065]    In embodiments, a source  310  and a drain  320  may respectively include source and drain fingertips  310   t  and  320   t  having a protrusion shape at the center thereof. 
         [0066]    In the LDMOS device having the above-described structure, there is an electric field concentration phenomenon in the N drift region  340  between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 , causing a breakdown current. In order to prevent the breakdown current, in embodiments, internal field rings  380  are formed in a first corner region  360  between the source fingertip  310   t  and the drain  320  and a second corner region  370  between the drain fingertip  320   t  and the source  310  to control the doping concentration. The internal field rings  380  may be formed of a p-type impurity and an n-type impurity after the P top region  400  is formed. The internal field rings  380  may have a plurality of first internal rings  382  which may be formed of the n-type impurity to have a polygonal shape, and a plurality of second internal rings  384  which may be formed of the p-type impurity to have a polygonal shape. 
         [0067]    The first internal rings  382  of the internal field rings  380  may be coupled to each other and formed in an octagonal shape. 
         [0068]    In the LDMOS device in accordance with embodiments, the N drift region  340  is formed only in a portion excluding the portions where the internal field rings  380  will be formed, that is, a portion excluding the first and second corner regions  360  and  370 , for example, the strip region. That is, the N drift region  340  may be formed in the portion excluding the first and second corner regions  360  and  370 , in which the internal field rings  380  will be formed, through a high-concentration n-type impurity ion implantation process. Subsequently, the P top region  400  may be formed in the first and second corner regions  360  and  370  through a p-type impurity ion implantation process. Thereafter, the internal field rings  380  may be formed in the first and second corner regions  360  and  370  through an n-type impurity ion implantation process and a p-type impurity ion implantation process. 
         [0069]    In embodiments, the internal field rings  380  may be coupled to each other in a honeycomb structure and formed below the field oxide film  350 . 
         [0070]    As described above, the internal field rings  380  may be formed between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 . Therefore, it is possible to increase the breakdown voltage without causing an increase in the radius of curvature between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310 . 
         [0071]    A process of forming the internal field rings will be described with reference to example  FIGS. 8A to 8D . 
         [0072]    Example  FIGS. 8A to 8D  are process sectional views illustrating a process of forming internal field rings according to embodiments. 
         [0073]    As illustrated in example  FIG. 8A , first, a high-concentration n-type impurity ion implantation process is performed to form the N drift region  340  of the LDMOS device in the p-type substrate or the p-type SOI substrate  300 . Specifically, an ion implantation mask in which the portion where the N drift region  340  will be formed, that is, where the strip portion is exposed, is formed on the substrate  300 , and a high-concentration n-type impurity ion implantation process is performed to form the N drift region  340  in the substrate  300 . The strip region may mean the portion excluding the portion where the field oxide film  350  will be formed, that is, the portion excluding the first and second corner regions  360  and  370 . 
         [0074]    Next, as illustrated in example  FIG. 8B , a first ion implantation mask  402  in which the portions excluding the N drift region  340 , that is, the first and second corner regions  360  and  370  are exposed is formed, and a p-type impurity ion implantation process is performed using the first ion implantation mask  402  to form the P top region  400 . 
         [0075]    Next, as illustrated in example  FIG. 8C , after the first ion implantation mask  402  is removed, a second ion implantation mask  404  in which a portion excluding the N drift region  340 , that is, a portion of the first and second corner regions  360  and  370  is exposed is formed, and a high-concentration n-type impurity ion implantation process is then performed using the second ion implantation mask  404  to form the n-type first internal rings  382 . The first internal rings  382  are formed in the first and second corner regions  360  and  370  and are coupled to each other in an octagonal shape. 
         [0076]    Next, as illustrated in example  FIG. 8D , after the second ion implantation mask  404  is removed, a third ion implantation mask in which another portion of the first and second corner regions  360  and  370  is exposed is formed, and a high-concentration p-type impurity ion implantation process is then performed using the third ion implantation mask to form the p-type second internal rings  384 . Thereafter, the third ion implantation mask is removed. The second internal rings  384  are formed inside the first internal rings  382  to have an octagonal shape, similarly to the first internal rings  382 . 
         [0077]    The breakdown voltage of the LDMOS device according with embodiments can be controlled by adjusting the depth and width of the second internal rings  384  inside the internal field rings  380 . The depth and width of the second internal rings  384  can be adjusted by adjusting the ion implantation amount and ion implantation energy in the p-type impurity ion implantation process. 
         [0078]    In accordance with embodiments, the n-type and p-type ion implantation processes are performed in the corner regions  360  and  370  between the source fingertip  310   t  and the drain  320  and between the drain fingertip  320   t  and the source  310  to form n type and p-type first and second internal rings  382  and  384 , such that the electric field is arranged in the current direction and the width direction, thereby increasing on-resistance and breakdown voltage. 
         [0079]    Although in embodiments, examples have been described where the internal field rings  380  have the octagonal shape, the internal field rings may be formed to have various shapes, such as circle, rectangle, and/or triangle. 
         [0080]    While the invention has been shown and described with respect to embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.