Abstract:
A semiconductor device and method of manufacturing the same are provided. A device can include an LDMOS region and a high side region on a semiconductor substrate. The device can further include an insulating region separating the LDMOS region from the high side region and the insulating region can include a plurality of second conductive type wells, a plurality of second conductive type buried layer patterns, or both.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2013-0026151, filed Mar. 12, 2013, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Power semiconductors are commonly used in various application fields. A device having a power semiconductor is controlled by a low-power circuit operated with several tens of volts or below. This low-voltage circuit may control a high-voltage-driven circuit that is operated with several hundreds of volts and provides high-voltage power to another electronic device. Therefore, such a circuit has a low side region and a high side region. 
     The high side region of an integration circuit is electrically insulated from the low side region by insulation junction. A low-voltage signal is level-shifted to higher voltage by a level shift transistor so that a low-voltage control signal is suitable for a high-voltage element. 
     That is, a high voltage integration circuit according to the related art is divided into a high side region and a level shifter. The high side region represents a region floated to high voltage, and the level shifter serves to transmit a signal of a low side region to the high side region. 
       FIG. 1  is a schematic planar view illustrating a general high-voltage semiconductor device. 
     Referring to  FIG. 1 , in a high-voltage integration circuit  1 , a laterally-diffused metal oxide semiconductor (LDMOS; also known as a lateral double diffused metal oxide semiconductor) device  4  can be surrounded by a high side region  12   b , and the LDMOS device  4  can be separated from the high side region  12   b  by a certain distance by an insulating region  1   a.    
       FIG. 2  is a cross-sectional view illustrating the related art semiconductor device taken along line A-A′ of  FIG. 1 , wherein the semiconductor device has a high voltage withstanding Double Reduced Surface Field (RESURF) structure and a level shift function. 
     Referring to  FIG. 2 , the semiconductor device includes an N channel RESURF LDMOS field effect transistor (LDMOSFET) (LDMOS region) on the left side and a RESURF separation island region (high side region). The semiconductor device also includes a semiconductor substrate  1  doped with P−, N− epitaxial layers  12   a  and  12   b , a P diffusion region  3  contacted to the P− substrate  1 , an N+ buried diffusion region  4 , an N diffusion region  5 , a P diffusion region  6 , an oxide film  7 , an aluminum wiring  8 , a polysilicon gate  9 , an aluminum electrode  10 , and polysilicon  11 . 
     The aluminum electrode  10  contacts the N diffusion region  5  and the P diffusion region  6  and is formed at the same location as the RESURF separation island region. The polysilicon  11 , to which the same potential as the P diffusion region  3  is applied, serves as a field plate. The N diffusion region  5  and the N+ buried diffusion region  4  form RESURF structures surrounded by the P diffusion regions  3 . 
     In the related art semiconductor device configured as described above, the N channel LDMOSFET is turned on by biasing the gate electrode  9  to positive potential, and current that flows in the P diffusion region  6  induces a potential difference between the electrode  10  and the aluminum wiring  8 . By outputting this potential difference, a logic signal applied to the gate  9  may be level-shifted to a high-potential side. 
     In order to reduce leakage current that flows from a level shift transistor to the high side region  12   b , a P− epitaxial layer having low concentration is used for insulation. However, the reduction of the leakage current is limited. In the case of increasing a distance W of the insulating region  1   a , an amount of charges for forming a RESURF structure is unbalanced, and thus a breakdown voltage rapidly decreases. 
     That is, when a P type well is formed to insulate the N channel LDMOSFET from the RESURF separation island region, as the length of the P type well increases, the leakage current is reduced more efficiently, but the breakdown voltage rapidly decreases. 
     BRIEF SUMMARY 
     Embodiments of the subject invention provide a semiconductor device, and a method for manufacturing the same, that can maintain high breakdown voltage without increasing a distance between a region of a level shift transistor and a high side region. 
     Embodiments also provide a method for forming a region of ion injection through a mask on an insulating region located between a laterally-diffused metal oxide semiconductor (LDMOS; also referred to as a lateral double-diffused metal oxide semiconductor) transistor serving as a level shifter and a high side region in order to give a semiconductor device that can maintain high breakdown voltage. 
     In an embodiment, a semiconductor device can include a lateral double diffused metal oxide semiconductor (LDMOS) region and a high side region formed on a semiconductor substrate and an insulating region separating the LDMOS region from the high side region. The insulating region can include a plurality of second conductive type wells on the semiconductor substrate, a plurality of second conductive type buried layers on the semiconductor substrate, or both. For example, the insulating region can include a plurality of second conductive type wells and no second conductive type buried layers, a plurality of second conductive type wells and one second conductive type buried layer, no second conductive type wells and a plurality of second conductive type buried layers, one second conductive type well and a plurality of second conductive type buried layers, or a plurality of second conductive type wells and a plurality of second conductive type buried layers. 
     In another embodiment, a method of fabricating a semiconductor device can include: forming a lateral double diffused metal oxide semiconductor (LDMOS) region and a high side region on a semiconductor substrate; and forming an insulating region separating the LDMOS region from the high side region. Forming the insulating region can include forming a plurality of second conductive type wells on the semiconductor substrate, forming a plurality of second conductive type buried layers on the semiconductor substrate, or both. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic planar view illustrating a general high-voltage semiconductor. 
         FIG. 2  is a cross-sectional view of a related art semiconductor device taken along line A-A′ of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a semiconductor device according to an embodiment of the subject invention, as taken along line A-A′ of  FIG. 1 . 
         FIG. 4  is a schematic planar view of a high-voltage integration circuit according to an embodiment of the subject invention. 
         FIG. 5  is a cross-sectional view of a layout of a high-voltage semiconductor device according to an embodiment of the subject invention. 
         FIG. 6  is a cross-sectional view of a layout of a high-voltage semiconductor device according to an embodiment of the subject invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. 
     When the terms “on” or “over” are used herein, when referring to layers, regions, patterns, or structures, it is understood that the layer, region, pattern, or structure can be directly on another layer or structure, or intervening layers, regions, patterns, or structures may also be present. When the terms “under” or “below” are used herein, when referring to layers, regions, patterns, or structures, it is understood that the layer, region, pattern, or structure can be directly under the other layer or structure, or intervening layers, regions, patterns, or structures may also be present. 
     Referring again to  FIG. 2 , a high-voltage semiconductor device can be divided into a laterally-diffused metal oxide semiconductor (LDMOS; also known as a lateral double diffused metal oxide semiconductor) region  12   a  in which an LDMOS transistor serving as a level shifter is formed, a high side region  12   b  floated to high voltage, and an insulating region for blocking current that flows from the LDMOS region  12   a  to the high side region  12   b . In an embodiment of the subject invention, the layout of the insulating region can be modified compared to that in  FIG. 2  in order to provide a structure of a semiconductor device for maximizing the insulating effect while maintaining high breakdown voltage. 
       FIG. 3  is a cross-sectional view of a semiconductor device according to an embodiment of the subject invention, taken along line A-A′ of  FIG. 1 . 
     Referring to  FIG. 3 , a semiconductor device can include an N channel Double Reduced Surface Field (RESURF) LDMOS field effect transistor (LDMOSFET) (LDMOS region) on the left side and a RESURF separation island region (high side region). The semiconductor device can also include a semiconductor substrate  1  (e.g., doped with P−, N− epitaxial layers  12   a  and  12   b ), a P diffusion region  3  contacted to the P− substrate  1 , an N+ buried diffusion region  4 , an N diffusion region  5 , a P diffusion region  6 , an insulating film  7 , a wiring  8 , a gate  9 , an electrode  10 , and polysilicon  11 . The insulating film  7  can be, for example, an oxide film, though embodiments are not limited thereto. The wiring  8  can be, for example, an aluminum wiring, though embodiments are not limited thereto. The gate  9  can be, for example, a polysilicon gate, though embodiments are not limited thereto. The electrode  10  can be, for example, an aluminum electrode, though embodiments are not limited thereto. 
     The electrode  10  can contact the N diffusion region  5  and the P diffusion region  6  and can be formed at the same location as the RESURF separation island region. The polysilicon  11 , to which the same potential as the P diffusion region  3  is applied, serves as a field plate (polysilicon). The N diffusion region  5  and the N+ buried diffusion region  4  form RESURF structures surrounded by the P diffusion regions  3 . 
     A P-type well having a low concentration can be formed to insulate the LDMOS region from the high side region. 
     Hereinafter, a method for forming an insulating region according to an embodiment will be described. 
     A P type buried layer can be formed on a semiconductor substrate between a region where the LDMOS transistor is formed and the high side region. During the formation of the P type buried layer, a photoresist pattern (not illustrated) can be formed on the semiconductor substrate  1  (e.g., a P-type semiconductor substrate), and then P type buried layer patterns  30   a ,  30   b ,  30   c ,  30   d  having certain line widths can be formed. In an embodiment, the P type buried layer patterns  30   a  to  30   d  can be formed by performing development and exposure processes. Although the drawings show that four P type buried layer patterns can be formed, embodiments are not limited thereto. In various embodiments, two or more P type buried layer patterns can be formed according to a size of the insulating region. For example, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, or more P type buried layer patterns can be formed. 
     Thereafter, the photoresist pattern can be removed, and epitaxial layers  12   a  and  12   b  doped with N− can be formed over the semiconductor substrate. In an embodiment, an ion injection process can be performed to form P wells doped with P-type impurities at a location or locations corresponding to the P type buried layer patterns on the N− epitaxial layers. The photoresist pattern for forming the P type buried layer patterns can be used, and P wells  20   a ,  20   b ,  20   c ,  20   d  can be formed on the P buried layer patterns  30   a  to  30   d.    
     A thermal process can be performed on the semiconductor substrate so that the P type buried layer patterns  30   a  to  30   d  and the P wells  20   a  to  20   d , respectively, diffuse and contact each other. 
     Therefore, between the LDMOS region and the high side region, an insulating region in which P wells and N− layers alternate with each other can be formed. Since a depletion region can be formed due to a PN junction, the insulating layer can block a drain current that flows from the LDMOS region to the high side region. 
     That is, according to embodiments of the subject invention, the effect of blocking a leakage current can be improved, and a high breakdown voltage can be maintained without increasing a line width of a P type layer of an insulating layer. 
       FIG. 4  is a schematic planar view illustrating a high-voltage semiconductor device according to an embodiment of the subject invention. 
     Referring to  FIG. 4 , the layout of the insulating region between the LDMOS region  4  and the high side region  12   b  can have a structure in which the P wells  20   a  to  20   d  surround three sides of the LDMOS region  4  and alternate with N layers. 
       FIG. 5  is a cross-sectional view illustrating a layout of a high-voltage semiconductor device according to an embodiment of the subject invention. 
     Referring to  FIG. 5 , a P type buried layer  30  can be formed on a semiconductor substrate. N epitaxial layers  12   a  and  12   b  can be stacked, and a photoresist pattern for sections for forming P wells can be formed on the N type epitaxial layers  12   a  and  12   b . P type impurities can be injected to regions opened by the photoresist so as to form P wells  20   a  to  20   d . Thereafter, a thermal process can be performed on the semiconductor substrate so that the P wells  20   a  to  20   d  and the P type buried layer  30  diffuse and adhere to each other. As described above, a depletion region can be formed due to a PN junction, and thus a drain current that flows from the LDMOS region to the high side region can be blocked. Each of the P wells  20   a  to  20   d  can have a certain line width, and at least two P wells can be formed. More specifically, each of the P wells  20   a  to  20   d  can have a line width such that the P wells diffuse and contact the P type buried layer  30  when the thermal process is performed. 
       FIG. 6  is a cross-sectional view illustrating a layout of a high-voltage semiconductor device according to an embodiment of the subject invention. 
     Referring to  FIG. 6 , a photoresist pattern can be formed on a region where an insulating region is to be formed on a semiconductor substrate, and P type buried layer patterns  30   a  to  30   d  can also be formed on that region. An N type epitaxial layer can be stacked, and a single P well  20  can be formed on the insulating region. Thereafter, a thermal process can be performed so that the P well  20  and the P type buried layer patterns  30   a  to  30   d  diffuse and join each other. Each of the P type buried layer patterns  30   a  to  30   d  can form a depletion region due to a PN junction and can thus serve as an insulating region for blocking a drain current that flows from the LDMOS region to the high side region. 
     According to embodiments of the subject invention, a structure of an insulating region between an LDMOS transistor serving as a level shifter and a high side region can be modified, and thus a leakage current that flows from a level shift transistor to a high side region can be efficiently inhibited without increasing the length of the insulating region. 
     Further, even though the length of the insulating region is not increased, a breakdown voltage of a semiconductor device does not decrease. 
     Moreover, according to the embodiments, a high breakdown voltage can be obtained without performing additional masking or additional processes, and thus manufacturing costs can be reduced. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.