Abstract:
A body ( 1 ) consisting of a doped semiconductor material with a pn junction ( 10 ) and an area ( 2 ) of reduced mean free path length (λr) for free charge carriers is disclosed. Said area ( 2 ) has sections ( 21, 22 ) which succeed each other in at least one specified direction (x, y, z) and between which there is at least one region ( 23 ), containing a mean free path length (λ 0 ) for the free charge carriers that is larger in relation to the reduced mean free path length (λr).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is a continuation of copending International Application No. PCT/EP01/10751 filed Sep. 17, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a body made of a doped semiconductor material of at least one type of conduction, having a mean free path length for free charge carriers in the semiconductor material and at least one area where the mean free path length for free charge carriers in the semiconductor material is reduced for the free charge carriers relative to a mean free path length of the semiconductor material.  
           [0003]    A body of the aforementioned type is proposed in the older German Patent Application 10030381.1 (2000 P 12486), which was not published previously, the contents of which are part of the disclosure content of the present patent application.  
           [0004]    With this proposed body, the doped semiconductor material has different types of doping and also has:  
           [0005]    a junction between one type of conduction and the opposite type of conduction from this type of conduction,  
           [0006]    a mean free path length for free charge carriers in the semiconductor material for each type of conduction, and  
           [0007]    for one of the two types of conduction, it has a region in which there is a mean free path length for the free charge carriers in the semiconductor material which is reduced relative to the mean free path length for the free charge carriers of the semiconductor material of this type of conduction.  
           [0008]    The area of reduced mean free path length for the free charge carriers in the semiconductor material leads in general to better electrical properties of the body of semiconductor material. Thus, in the case of the body already proposed, a high electric breakdown strength is achieved due to this area.  
         SUMMARY OF THE INVENTION  
         [0009]    The object of this invention is to provide a body of the type defined in the preamble which has even better electric properties.  
           [0010]    This object can be achieved by a body of doped semiconductor material of at least one conduction type, which has a mean free path length for free charge carriers in the semiconductor material and has at least one area in which there is a mean free path length for the free charge carriers in the semiconductor material, this mean free path length being reduced relative to a mean free path length of the semiconductor material for the free charge carriers, whereby the area of reduced mean free path length has sections which follow one another in at least one certain direction and between which there is at least one region in which a greater mean free path length prevails relative to the reduced mean free path length for the free charge carriers in the semiconductor material.  
           [0011]    It is essential with this embodiment that the area of reduced mean free path length has sections which follow one another in at least one certain direction and between which there is at least one region for which free charge carriers are predominant in the semiconductor material.  
           [0012]    Accordingly, with the body according to this invention, the area of reduced mean free path length is not continuous, as is the case with the body proposed in the past, but instead is interrupted by at least one region having a greater mean free path length relative to this path length. Therefore, in the area of reduced mean free path length, production of charge carriers by ionization due to collision is hindered by the reduced free path length of the charge carriers.  
           [0013]    In the region(s) in which the greater mean free path length for the free charge carriers in the semiconductor material is predominant relative to the reduced mean free path length, this is accomplished by the geometry of each region. The charge carriers need a certain path length to be able to absorb enough energy on the basis of this so that they can themselves generate additional charge carriers by ionization due to collision. If this path length is kept small, then these charge carriers cannot take up enough energy.  
           [0014]    In the case of the body according to this invention, measures are taken to ensure to advantage not only that an electric current flows in an area of reduced mean free path length but also that the current flows in at least one region where the mean free path length is greater than the reduced mean free path length.  
           [0015]    Therefore, with the body according to this invention, it is possible to advantage to implement a component with a body made of a semiconductor material in which the free path length of the charge carriers need not be reduced everywhere that a high electric field strength prevails.  
           [0016]    With the body according to this invention, its electric conduction property is improved in comparison with that of the body having the continuous area of reduced mean free path length as was customary in the past.  
           [0017]    An advantageous embodiment of the body according to this invention is designed such that there is a distance between adjacent regions having a greater mean free path length relative to the reduced mean free path length, these regions being separated by a section of the area of reduced mean free path length which determines this distance, which depends on the absolute value of an electric field strength generated by applying a certain electric voltage to the body in the semiconductor material, such that this distance decreases at a location of a lower absolute value and increases at a location of a greater absolute value. For example, this may mean that such regions are arranged in a greater density in areas where the absolute value of the electric field strength is lower, and such regions are arranged in a lower density in areas where the absolute value of the electric field strength is higher.  
           [0018]    Another advantageous embodiment of the body according to this invention is designed so that a distance between adjacent sections of the area of reduced mean free path length, separated by a region with a greater mean free path length relative to the reduced mean free path length, depends on the absolute value of an electric field strength generated by applying a certain electric voltage to the body in the semiconductor material such that this distance is greater at a location of a smaller absolute value and is smaller at a location of a greater absolute value. For example, this may mean that such sections are arranged in a greater density in areas where the absolute value of the electric field strength is greater and they are arranged in a lower density in areas where the absolute value of the electric field strength is lower.  
           [0019]    These two embodiments may be combined.  
           [0020]    In a preferred and advantageous manner, the relative greater mean free path length of a region is equal to the mean free path length of the doped semiconductor material of the one type of conduction outside of the area of reduced mean free path length.  
           [0021]    An especially preferred and advantageous embodiment of the body according to this invention is designed like the body already proposed, so that the doped semiconductor material has different types of doping and  
           [0022]    has at least one junction between one type of conduction and a type of conduction opposite this former type of conduction,  
           [0023]    has a mean free path length for free charge carriers in the semiconductor material for each type of conduction and  
           [0024]    has for at least one of the two types of conduction an area in which there is mean free path length for the free charge carriers in the semiconductor material which is reduced relative to the mean free path length for the free charge carriers of the semiconductor material of this one type of conduction,  
           [0025]    whereby the area of reduced mean free path length has at least two sections which follow one another in the direction perpendicular to a surface in which the junction extends and between which there is a region where a greater mean free path length for the free charge carriers in the semiconductor material prevails relative to the reduced mean free path length, and/or  
           [0026]    whereby the area of reduced mean free path length has as least two sections which follow one another in at least one direction parallel to the surface in which the junction extends and between which there is a region in which a greater mean free path length for the free charge carriers in the semiconductor material prevails relative to the reduced mean free path length.  
           [0027]    On the one hand, a high blocking voltage may be applied at the junction in an advantageous embodiment, while on the other hand, the electric conduction property of the junction is improved.  
           [0028]    In a preferred and advantageous design of the advantageous embodiment, there is a distance between adjacent regions which are separated by a section of the area of reduced mean free path length, this distance depending on the absolute value of an electric field strength generated by applying a certain electric blocking voltage to the junction in the semiconductor material such that this distance is greater at a location of a smaller absolute value and is smaller at a location of a greater absolute value.  
           [0029]    With the body design according to this invention, in particular in its advantage embodiment, a high voltage component can be implemented to advantage with a body of a semiconductor material, which has low forward power losses and switching losses but on the other hand also has a small component volume. It is thus possible to implement both a high voltage component with a small volume as well as a high-voltage IC (HVIC) of extremely high integration.  
           [0030]    High-voltage components are implemented today essentially through the choice of the lowest possible base doping in an n-doped base of its body of semiconductor material. However, there are limits to this measure from the standpoint of the lowest possible total power loss in the component, because reducing the base doping usually also results in an increased component thickness. HVICs are implemented either in junction isolation technology (JI technology) or in dielectric isolation technology (DI technology). Both technologies require a “thick” drift zone to be able to accommodate the required blocking voltage.  
           [0031]    With the body design according to this invention, it is possible to implement, for example, an electric resistor in addition to a thyristor, a transistor or a power MOSFET HVIC.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    This invention is explained in greater detail in the following description on the basis of the drawings as examples; they show:  
         [0033]    [0033]FIG. 1 a cross section through a highly blocking diode formed with a body design according to this invention perpendicular to the surface of a pn junction of the body, and  
         [0034]    [0034]FIG. 2 a cross section through a high-voltage MOS component formed with a body design according to this invention perpendicular to the surface of a pn junction of the body;  
         [0035]    [0035]FIG. 3 a detail of an area of a reduced mean free path length of a body design according to this invention having regions of a relatively greater mean free path length having different distances from one another, and  
         [0036]    [0036]FIG. 4 a detail of an area of reduced mean free path length of a body design according to this invention with sections of this area being different distances from one another. 
     
    
       [0037]    The figures are schematic and are not drawn to scale.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    In FIGS. 1 and 2 the body of doped semiconductor material is labeled as  1  in general and the area of reduced mean free path length is labeled as  2  in general.  
         [0039]    Area  2  is in both cases situated essentially only in the n-doped semiconductor material of body  1 , i.e., in the semiconductor material of conduction type n. This means essentially that in many cases it is expedient to expand area  2  in the semiconductor material of conduction type p of body  1 , which has a high electric field strength, e.g., as indicated in FIGS. 1 and 2.  
         [0040]    A mean free path length λ 0  for free charge carriers prevailed in the n-doped semiconductor material in which area  2  essentially extends.  
         [0041]    In part  20  of area  2 , which is indicated with dotted lines and hatching, the prevailing mean free path length λr for the free charge carriers in the n-doped semiconductor material is reduced relative to the given mean free path length λ 0  of this semiconductor material.  
         [0042]    According to this invention, area  2  of reduced mean free path length λr has sections which follow one another in at least one certain direction and between which there is at least one region in which a greater mean free path length for the free charge carriers in the semiconductor material prevails relative to the reduced mean free path length λr.  
         [0043]    For example, in FIGS. 1 and 2, several sections  21  of area  2  follow one another in direction x, the reduced mean free path length λr prevailing in these sections, and regions  23  being provided between them, where the prevailing mean free path length for the free charge carriers in the semiconductor material, e.g., the given greater path length λ 0 , is greater than the reduced mean free path length  
         [0044]    In the direction y perpendicular to direction x, there also follow, for example, sections  22  of area  2  in which the reduced mean free path length λr is predominant and between which there are regions  23  in which the prevailing mean free path length for the free charge carriers in the semiconductor material, e.g., the given greater path length λ 0 , is greater than the reduced mean free path length λr.  
         [0045]    A similar condition may also prevail in direction z which is perpendicular to directions x and y and to the plane of the drawings in the figures.  
         [0046]    In particular, FIGS. 1 and 2, for example, show each region  23  completely surrounded by sections  21  and  22  of area  2 , and moreover, regions  22  in particular are arranged in rows and columns in the form of a matrix in directions x and y. Each section  21  extends in direction y through the entire area  2 , each section  22  extends in direction x through the entire area  2  and sections  21  and  22  intersect and enclose regions  23  between them.  
         [0047]    In the example of body  1  according to FIGS. 1 and 2, the doped semiconductor material is doped by the opposite type of conduction p and n, i.e., it is p-doped and n-doped, and has a pn junction  10  which extends in an area  100  perpendicular to the plane of the drawing in these figures.  
         [0048]    For each type of conduction p and/or n, the semiconductor material has a given mean free path length λ 0  for free charge carriers in the semiconductor material.  
         [0049]    Area  2  of the reduced mean free path length λr extends essentially only in the n-doped semiconductor material and is adjacent at least to the pn junction  10  of body  1 .  
         [0050]    Direction x in which sections  21  follow one another and between which regions  23  are present stands for example perpendicular to area  100  in which the pn junction  10  extends.  
         [0051]    In addition, the direction y in which sections  22  follow one another and between which regions  23  are present is, for example, parallel to the surface  100  in which the pn junction  10  extends. A similar situation may also apply to the direction z which also runs parallel to surface  100  where the pn junction extends.  
         [0052]    Body  1  according to FIG. 1 is that of a highly blocking diode. This body  1 , whose semiconductor material is silicone, for example, has a p+-doped area  13 , which is adjacent to a surface section  11  of this body and is contacted by a terminal electrode (not shown) of the diode which is arranged on this surface section  11 ; it also has on the side of area  13  facing away from surface section  11  an n-doped area  14  adjacent to this area  13  and on the side of area  14  facing away from surface section  11  it has an n+-doped area  15  which is adjacent to this area  14  and is also adjacent to a surface section  12  of body  1  which faces away from surface section  11  and is contacted by a terminal electrode (not shown) of the diode arranged on the surface section  12 .  
         [0053]    The interface between the p+-doped area  13  and the n-doped area  14  is surface  100  in which the pn junction  10  of the diode extends.  
         [0054]    Area  2  which has sections  21  and  22  as well as regions  23  and is an area of reduced mean free path lengths extends essentially only over the n-doped area  14 , i.e., it generally projects only slightly into the p+-doped area  13  and/or into the n+-doped area  15 . With respect to this extend and the other provisions of area  2 , see also the discussion in this regard in the older German Patent Application 10030381.1, which is also applicable here.  
         [0055]    Body  1  according to FIG. 2 is that of a high voltage MOS component. This body  1 , which may also be made of silicon, for example is arranged on the surface  31  of a substrate  3  of electrically insulating material, e.g., SiO2. The pn junction  10  of this body  1  extends in the surface  100 , which is perpendicular to the surface  31  of substrate  3  and separates a left p+-doped area  13 ′ of body  1  from a right n-doped area  14 ′ of body  1 . Both the p+-doped area  13 ′ and n-doped area  14 ′ are adjacent to a surface section  11 ′ of body  1 , which faces away from substrate  3 .  
         [0056]    In the n-doped area  14 ′ there is arranged at a distance from the pn junction  10  an n+doped area  15 ′ which is adjacent to the surface section  11 ′ of body  1  and is contacted by a drain electrode  14  of the component situated on the surface section  11 ′.  
         [0057]    An n+-doped area  16 , which is adjacent to surface section  11 ′ of body  1 , is arranged at a distance from the pn junction  10  in the p+-doped area  13 ′.  
         [0058]    A layer  5  of electrically insulating material is arranged over the pn junction  10  on the surface section  11 ′ of the body  1 , extending from the n-doped area  14 ′ over the p+-doped area  13 ′ into the n+-doped area  16  and covering only a portion of area  13 ′ and area  16 .  
         [0059]    A gate electrode  6  of the component is arranged on layer  5  made of an electrically insulating material, over the pn junction  10 , also extending from the n-doped area  14 ′ over the p+-doped area  13 ′ into the n+-doped area  16 .  
         [0060]    The uncovered portions of area  13 ′ and area  16  are contacted jointly by a source electrode  7  of the component arranged on the surface section  11 ′ of body  1 .  
         [0061]    The interface between the p+-doped area and the n-doped area  14  forms the surface  100  in which the pn junction  10  of the diode extends.  
         [0062]    The area  2  of a reduced mean free path length λr having sections  21  and  22  of a reduced mean free path length λr as well as regions  23  with a greater mean free path length relative to the reduced mean free path length λr extends essentially only over the n-doped area  14 ′, i.e., in general it projects only slightly into the p+-doped area  13 ′ and/or into the n+-doped area  15 ′. With regard to this extent and the other provisions of area  2 , see also the discussion in the older German Patent Application 10030381.1, which is also applicable here.  
         [0063]    [0063]FIG. 3 shows a detail from an area  2  of a reduced mean free path length of a body  1  according to this invention, as illustrated in the sectional diagram according to FIGS. 1 and 2.  
         [0064]    In this area  2 , sections  21  of area  2 , in which the reduced mean free path length λr prevails, follow one another in direction x, and between these sections  21  there are regions  23  in which a mean free path length which is greater than the reduced mean free path length λr prevails for the free charge carriers in the n-doped semiconductor material, e.g., the given greater path length λ 0 . In this area  2 , there is a distance between adjacent regions  23  having a greater mean free path length relative to the reduced mean free path length λr, these regions being separated by a section  21  of the area  2  of a reduced mean free path length λr, and which section  21  determines this distance by its extent d in direction x, this distance depending on the absolute value |E| of an electric field strength E generated by applying a certain electric voltage to the body  1  in the semiconductor material, such that this distance d is smaller at a location of a smaller absolute value |E| and is greater at a location of a greater absolute value |E|.  
         [0065]    For example, let us assume that the value |E|1 prevails at the left location S 1  in FIG. 3, and the value |E|2 of the absolute value |E| of the electric field strength E prevails at the right location S 2 , where |E|1 is smaller than |E|2. Accordingly, at the left location S 1 , the distance d has a value d1 which is smaller than the value d2 of the distance d at the right location S 2 .  
         [0066]    For example, this may mean that such regions  23  are arranged in a greater density in locations where the absolute value |E| of the electric field strength E is smaller, and these regions are arranged in a lower density in areas where the absolute value |E| of the electric field strength E is greater.  
         [0067]    The extent b of each region  23  in direction x may be the same or different for several or all of regions  23 .  
         [0068]    [0068]FIG. 4 shows a detail of an area  2  of a reduced mean free path length of a body  1  according to this invention in a sectional diagram according to FIGS. 1 and 2. In this area, sections  21  of area  2 , in which the reduced mean free path length λr prevails, follow one another in direction x, and between these sections  21  there are regions  23  in which a greater mean free path length relative to the reduced mean free path length λr prevails for the free charge carriers in the n-doped semiconductor material, e.g., the given greater path length λ 0 .  
         [0069]    In FIG. 4 there is a distance between adjacent sections  21  of area  2  of a reduced mean free path length λr, which are separated by a region  23  having a greater mean free path length relative to the reduced mean free path length λr, and which region  23  determines this distance by its extent b in direction x, this distance depending on the absolute value |E| of an electric field strength E generated by applying a certain electric voltage to the body in the semiconductor material such that this distance b is greater at a location of a smaller absolute value |E| and is smaller at a location of a greater absolute value |E|.  
         [0070]    For example, let us assume that the value |E|1 prevails at the left location S 1  in FIG. 4 and the value |E|2 of the absolute value |E| of the electric field strength E at the right location S 2 , where |E|1 is again considered as being less than |E|1 [sic; |E|2]. Accordingly, the distance b at the left location S 1  has a value b1, which is greater than value b2 of the distance b at the right location S 2 .  
         [0071]    For example, this can mean that such sections  21  are arranged in greater density where the absolute value |E| of the electric field strength E is greater, and they are arranged in a lower density in areas where the absolute value |E| of the electric field strength E is smaller.  
         [0072]    The extent d of each section  21  in direction x may be the same or different for several sections or for all sections  21 .