Abstract:
A semiconductor device comprises a first contact plug, a first structure and a second insulating layer, or comprises a first contact plug, a first structure, a protruding region and a second insulating layer. The first contact plug extends in a predetermined direction and including a step converting a cross section area of the first contact plug perpendicular to the predetermined direction discontinuously via the step in one end side. The second insulating layer is formed on side surface of a part of the first contact plug closer to the first structure than the step, or on side surfaces of the protruding region and a part of the first contact plug closer to the first structure than the step.

Description:
[0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-321036, filed on Dec. 12, 2007, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventionally, the mainstream of semiconductor device configuration has been that a single semiconductor device is equipped with a single semiconductor layer. In recent years, however, there have been proposed such semiconductor device configuration in which a single semiconductor device is equipped with a plurality of semiconductor layers. More specifically, it is possible to enhance the capabilities of a semiconductor device, including the processing speed, while reducing the size and weight of the semiconductor device as a whole by mounting a plurality of semiconductor layers in a multilayered manner within the single semiconductor device. 
         [0006]    When manufacturing this multilayer-structured semiconductor device, it is necessary to laminate and electrically connect the semiconductor layers to one another within the semiconductor device. Hence, this plurality of semiconductor layers are electrically connected to one another through a contact plug. 
         [0007]      FIGS. 15 to 17  illustrate a method for forming a common multilayer structure. First, as shown in  FIG. 15A , semiconductor element  2  is formed on one surface of semiconductor substrate  1 . In  FIG. 15 , an example is shown in which a planar-type MOSFET is formed as semiconductor element  2 . Next, as shown in  FIG. 15B , first interlayer insulating film  3  is formed on the side of semiconductor substrate  1  on which semiconductor element  2  is formed. 
         [0008]    After this, as shown in  FIG. 16A , there is formed mask pattern  4  including openings on first interlayer insulating film  3  in the positions thereof corresponding to the source/drain regions of the planar-type MOSFET. Next, using this mask pattern  4  as a mask, contact holes  5  are formed so as to penetrate through first interlayer insulating film  3  up to the source/drain regions. Next, as shown in  FIG. 16B , mask pattern  4  is removed and then a conductive material is buried in the contact holes, thereby forming contact plugs  6 . 
         [0009]    After this, as shown in  FIG. 17A , second interlayer insulating film  7  is further formed on first interlayer insulating film  3 . Then, there is formed mask pattern  8  including an opening on second interlayer insulating film  7  in the position thereof corresponding to either one of the source/drain regions of the planar-type MOSFET. Next, contact hole  9  is formed so as to penetrate through second interlayer insulating film  7 . Next, as shown in  FIG. 17B , a conductive material is buried in contact hole  9 , thereby forming contact plug  10 . 
         [0010]    In recent years, there has been a progress in the miniaturization of such a multilayer structure as described above and, therefore, it has become increasingly difficult to align a contact plug with a desired region to establish contact when forming the contact plug. Hence, a study has been made of a method capable of aligning a contact plug with high accuracy. 
         [0011]    In the method described in Japanese Patent Laid-Open No. 5-114658, a contact hole for connecting a plurality of conductive layers is formed, and then a film consisting primarily of silicon is buried in the contact hole. After this, the film consisting primarily of silicon is left over so as to cover a contact hole opening, and then a metal film for forming a second conductive layer is formed. The document states that by forming this metal film, it is possible to use the step difference of the film consisting primarily of silicon as an index for alignment in a photolithography step of forming an interconnect and, thereby, increase the alignment accuracy of the interconnect in the second conductive layer. 
         [0012]    In the method described in Japanese Patent Laid-Open No. 10-27845, a silicon dioxide film and a silicon nitride film are formed on a semiconductor substrate including a lower interconnect layer, and then the silicon nitride film in a region in which an interconnect layer is to be formed is selectively etched away, thereby forming a trench. After this, photoresist A is formed in this trench and photoresist B including a hole in a region in which a contact hole is to be formed is further formed. Subsequently, photoresist A in this position is removed to expose the silicon dioxide film. Then, using this photoresist B and the silicon nitride film as masks, the silicon dioxide film in the region in which the contact hole is to be formed is selectively removed to expose the lower interconnect layer, thereby forming a contact hole. Japanese Patent Laid-Open No. 10-27845 states that in the method described therein, high-precision alignment is possible by forming the masks composed of photoresist B and the silicon nitride film in such a stepwise fashion as described above. 
         [0013]    Along with the progress of equipment miniaturization, high integration, and diversification of equipment design in recent years, it has been necessary, in some cases, to include a step of aligning a contact hole from the rear surface side of a semiconductor substrate. I have now discovered that a related method for forming a contact plug, however, had limitations in the accuracy of aligning the contact hole due to, for example, an alignment error arising when forming a mask pattern by photolithography. The recent progress in the miniaturization of a semiconductor device, in particular, has given rise to a demand for high accuracy also in the alignment of a contact plug with a semiconductor element. Failure to carry out such alignment with high accuracy has, in some cases, led to a short-circuit between the contact plug and the semiconductor substrate and between the contact plug and the gate electrode thereof. Furthermore, the methods described in Japanese Patent Laid-Open Nos. 5-114658 and 10-27845 have had limitations in alignment accuracy. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention seeks to solve one or more of the above problems, or to improve upon those problems at least in part. 
         [0015]    In one embodiment, there is provided a semiconductor device, comprising: 
         [0016]    a first contact plug extending in a predetermined direction and including a step converting a cross section area of the first contact plug perpendicular to the predetermined direction discontinuously via the step in one end side; 
         [0017]    a protruding region electrically connected to the first contact plug; 
         [0018]    a first structure electrically connected to the protruding region; and 
         [0019]    a second insulating layer formed on side surfaces of the protruding region and a part of the first contact plug closer to the first structure than the step. 
         [0020]    In another embodiment, there is provided a semiconductor device, comprising: 
         [0021]    a first contact plug extending in a predetermined direction and including a step converting a cross section area of the first contact plug perpendicular to the predetermined direction discontinuously via the step in one end side; 
         [0022]    a first structure electrically connected to the first contact plug; and 
         [0023]    a second insulating layer formed on side surface of a part of the first contact plug closer to the first structure than the step. 
         [0024]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) preparing a semiconductor substrate including a protruding region;
 
(2) forming a second insulating layer on side surface of the protruding region;
 
(3) forming a first structure on top surface of the protruding region;
 
(4) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region, from a rear side opposite to a side on which the first structure is formed, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the protruding region; and
 
(5) forming at least a first contact plug within the second opening.
 
         [0025]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming an interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7) forming a first opening within the interlayer insulating film in a position thereof corresponding to the protruding region, removing the first insulating layer on the protruding region, and further forming a first structure on the protruding region;
 
(8) forming a protective substrate on the first structure;
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region, from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the protruding region;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming at least a first contact plug within the second opening.
 
         [0026]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) forming a first insulating layer over the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, at least one protruding region the portions of which other than a portion below the first mask pattern are exposed;
 
(4) forming a second insulating layer in the exposed portions of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming an interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7) forming a first opening within the interlayer insulating film in a position thereof corresponding to the protruding region, removing the first insulating layer on the protruding region, and further forming a first structure on the protruding region;
 
(8) performing anisotropic etching on the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, so as to leave a portion in the semiconductor substrate corresponding to the first structure, the anisotropic etching being performed so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer; and
 
(9) implanting an impurity into a portion in the semiconductor substrate corresponding to the first structure, to form a first contact plug.
 
         [0027]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) forming a second insulating layer over the entire surface of a semiconductor substrate;
 
(2) forming a first impurity-diffused region in the semiconductor substrate;
 
(3) performing anisotropic etching on the rear surface side of the semiconductor substrate opposite to a side on which the second insulating layer is formed, in a position of the semiconductor substrate corresponding to the first impurity-diffused region, the anisotropic etching being performed so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the first impurity-diffused region; and
 
(4) forming at least a first contact plug within the second opening.
 
         [0028]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) forming a first insulating layer over the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, at least one protruding region the portions of which other than a portion below the first mask pattern are exposed;
 
(4) forming a second insulating layer in the exposed portions of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming an interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7) forming a first opening within the interlayer insulating film in a position thereof corresponding to the protruding region, removing the first insulating layer on the protruding region, and further forming a first structure on the protruding region;
 
(8) performing anisotropic etching on the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, the anisotropic etching being performed in a position corresponding to the protruding region within the semiconductor substrate so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the first impurity-diffused region;
 
(9) forming a third insulating layer on the inner wall of the second opening; and
 
(10) forming at least a first contact plug within the second opening.
 
         [0029]    In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising: 
         [0000]    (1) forming a first insulating layer over the entire surface of a silicon semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the silicon semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a silicon semiconductor region projecting from a predetermined plane of the silicon semiconductor substrate;
 
(4) forming a second insulating layer in the exposed portions of the silicon semiconductor substrate;
 
(5) forming a first structure including the silicon semiconductor region;
 
(6) polishing the silicon semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the silicon semiconductor substrate;
 
(7) performing anisotropic etching on a position corresponding to the silicon semiconductor region within the silicon semiconductor substrate from the rear surface side thereof, so that the etching rate of the silicon semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the silicon semiconductor region;
 
(8) forming a third insulating layer on the inner wall of the second opening; and (9) forming at least a first contact plug within the second opening.
 
         [0030]    In the above embodiments, “step” means a surface converting a cross section area of the first contact plug perpendicular to the first contact plug extending-direction discontinuously. The cross section area of the first contact plug perpendicular to the first contact plug extending-direction discontinuously converts via the step. For example, the step is illustrated by numerical number  41  in  FIGS. 14 ,  20 ,  24 ,  28  and  48 . 
         [0031]    Consequently, it is possible to manufacture a semiconductor device in which a structure and a contact plug constituting the semiconductor device are precisely aligned with each other. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
           [0033]      FIG. 1  is a schematic view illustrating one step of a method for manufacturing a semiconductor device of the present invention; 
           [0034]      FIG. 2  is another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0035]      FIG. 3  is yet another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0036]      FIG. 4  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0037]      FIG. 5  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0038]      FIG. 6  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0039]      FIG. 7  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0040]      FIG. 8  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0041]      FIG. 9  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0042]      FIG. 10  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0043]      FIG. 11  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0044]      FIG. 12  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0045]      FIG. 13  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0046]      FIG. 14  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0047]      FIG. 15  is a schematic view illustrating one step of a method for manufacturing a related semiconductor device; 
           [0048]      FIG. 16  is another schematic view illustrating one step of the method for manufacturing the related semiconductor device; and 
           [0049]      FIG. 17  is yet another schematic view illustrating one step of the method for manufacturing the related semiconductor device. 
           [0050]      FIG. 18  is a schematic view illustrating an example of a semiconductor device of the present invention; 
           [0051]      FIG. 19  is a schematic view illustrating another example of the semiconductor device of the present invention; 
           [0052]      FIG. 20  is a schematic view illustrating another example of the semiconductor device of the present invention; 
           [0053]      FIG. 21  is a schematic view illustrating another example of the semiconductor device of the present invention; 
           [0054]      FIG. 22  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0055]      FIG. 23  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0056]      FIG. 24  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0057]      FIG. 25  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0058]      FIG. 26  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0059]      FIG. 27  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0060]      FIG. 28  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0061]      FIG. 29  is a schematic view illustrating another example of the semiconductor device of the present invention; 
           [0062]      FIG. 30  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0063]      FIG. 31  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0064]      FIG. 32  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0065]      FIG. 33  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0066]      FIG. 34  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0067]      FIG. 35  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0068]      FIG. 36  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0069]      FIG. 37  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0070]      FIG. 38  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0071]      FIG. 39  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0072]      FIG. 40  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0073]      FIG. 41  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention, 
           [0074]      FIG. 42  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0075]      FIG. 43  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0076]      FIG. 44  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0077]      FIG. 45  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0078]      FIG. 46  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0079]      FIG. 47  is still another schematic view illustrating one step of the method for manufacturing the semiconductor device of the present invention; 
           [0080]      FIG. 48  is a schematic view illustrating another example of the semiconductor device of the present invention; 
           [0081]      FIG. 49  is a schematic view illustrating another example of the semiconductor device of the present invention; 
       
    
    
       [0082]    In the drawings, numerals have the following meanings.  1 : semiconductor substrate,  2 : semiconductor element,  3 ,  7 : interlayer insulating film,  4 ,  8 : mask pattern,  5 ,  9 : contact hole,  6 ,  10 : contact plug,  11 : silicon semiconductor substrate,  12 ,  16 ,  17 ,  24 ,  29 : silicon dioxide film,  13 : silicon nitride film,  14 ,  18 : photoresist,  15 : protruding region A,  19 ,  129 ,  201 : lower impurity-diffused region,  20 ,  20   a : semiconductor region,  21 : gate insulating film,  22 ,  125 : upper impurity-diffused region,  23 : gate electrode,  25 ,  126   a : second contact plug,  26 ,  124 ,  126   b : third contact plug,  27 : protective substrate,  28 : second opening,  30 : protruding region B,  31 : connecting part,  32 ,  110 ,  118 : first contact plug,  33 : transistor portion,  34 ,  127 : interconnect portion,  41 : step,  102 : contact plug,  104 ,  107 : bit line,  105 : capacitor,  106 : semiconductor portion,  108 : word line,  109 : semiconductor part,  111 : gate electrode,  112 : gate sidewall,  113 : source/drain region,  114 : contact plug,  115 : first impurity-diffused region,  116 : isolation region,  117 : gate insulating layer,  119 : interconnect layer,  120 : N-type diffusion region,  121 : P-type diffusion region,  122 : gate electrode material,  123 ,  141 : oxide film,  126 : contact plug material,  130 : resist mask,  140 : insulating layer 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0083]    The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
         [0084]    (Method for Manufacturing Semiconductor Device) 
         [0085]    A method for manufacturing a semiconductor device comprises: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming an interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7) forming a first opening within the interlayer insulating film in a position thereof corresponding to the protruding region, removing the first insulating layer on the protruding region, and further forming a first structure on the protruding region;
 
(8) forming a protective substrate on the first structure;
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region, from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches at least the protruding region;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming at least a first contact plug within the second opening.
 
         [0086]    In the manufacturing method, only first insulating layer on the protruding region is removed and second insulating layer present on part of the protruding region is left over in step (7). In addition, in step (10), anisotropic etching is performed on the position corresponding to the protruding region from the rear surface side of the semiconductor substrate, so that the etching rate of the semiconductor substrate is faster than the etching rate of second insulating layer. Then, the second opening is formed until at least the second opening reaches the protruding region. 
         [0087]    In this step (10), there is provided, for example, a mask pattern including an opening on the rear surface side of the semiconductor substrate in a position thereof corresponding to the protruding region. Using this mask pattern as a mask, anisotropic etching is performed on the semiconductor substrate to form the second opening. At this time, anisotropic etching is performed so that the etching rate of the semiconductor substrate is faster than the etching rate of second insulating layer even if, for example, the opening of the mask pattern is not precisely aligned with a position corresponding to the protruding region. Consequently, second insulating layer is left over and only the semiconductor substrate is etched. Accordingly, it is possible to form the second opening with the opening precisely aligned with the protruding region (or with the first structure if the protruding region is removed) in a self-aligned manner. As a result, it is possible to manufacture a semiconductor device in which a first structure and a contact plug are precisely aligned with each other. 
         [0088]    In the present invention, the “first structure” denotes all structure (except a protruding region) formed within an opening (on the protruding region, or if the protruding region is removed, on the part where the protruding region has existed) of an interlayer insulating film formed on the front surface side of a semiconductor substrate. That is, if the protruding region is left, the first structure is formed on the protruding region. If the protruding region is removed, the first structure is formed on the protruding region existing region before removing the protruding region. The first structure is not limited in particular, as long as the first structure is a portion constituting part of the semiconductor device. 
         [0089]    In the present invention, the “first contact plug” denotes a contact plug formed from the rear surface side of the semiconductor substrate. The “second contact plug” denotes a contact plug electrically connected to a vertical MOSFET within the interlayer insulating film formed on the front surface side of the semiconductor substrate. The “third contact plug” denotes a contact plug formed so as to penetrate through the interlayer insulating film provided on the front surface side of the semiconductor substrate across the entire thickness direction of the interlayer insulating film. 
         [0090]    In the present invention, the “connecting part” denotes a conductive portion for electrically connecting the first contact plug and the third contact plug. Examples of the connecting part include an impurity-implanted polysilicon region. 
         [0091]    The first structure may or may not constitute a semiconductor element by itself. Alternatively, the first structure may constitute a single semiconductor element. For example, as the first structure, it is possible to form a semiconductor region the upper portion of which is an upper impurity-diffused region, a gate insulating film, a gate electrode, and a second contact plug. In this case, the semiconductor region comprising the upper impurity diffused region, the gate insulating film, the gate electrode, and the lower impurity-diffused region constitute a vertical MOSFET (metal-oxide semiconductor field-effect transistor). In addition, as the first structure, it is possible to form a third contact plug. In this case, the first structure forms an interconnect structure. Furthermore, with the manufacturing method of the present invention, it is possible to manufacture the vertical MOSFET and the interconnect structure separately or in combination. 
         [0092]    In the method for manufacturing a semiconductor device of the present invention, a semiconductor substrate is first prepared in step (1). Examples of this semiconductor substrate include a silicon semiconductor substrate and an SOI. Next, first insulating layer is formed across the entire surface of this semiconductor substrate. Examples of a method for forming this first insulating layer include forming a silicon dioxide film by performing thermal oxidation if the front surface of the semiconductor substrate is made of silicon. 
         [0093]    Next, in step (2), a first mask pattern is formed on this first insulating layer. Examples of a method for forming this first mask pattern include depositing a silicon nitride film using a CVD method or the like, and then performing patterning on the silicon nitride film using a lithography technique. 
         [0094]    Next, in step (3), first insulating layer and the semiconductor substrate are etched to form at least one protruding region below the first mask pattern using the first mask pattern as a mask. At this time, the portions of the semiconductor substrate other than a portion between the first mask pattern and the lower portion of the semiconductor substrate are exposed. 
         [0095]    Next, in step (4), a second insulating layer is formed on the exposed portions of the semiconductor substrate. Examples of a method for forming this second insulating layer include forming a silicon dioxide film by performing thermal oxidation if the front surface of the semiconductor substrate is made of silicon. 
         [0096]    Next, in step (5), the first mask pattern is removed. Examples of a method for removing this first mask pattern include wet etching. 
         [0097]    Next, in step (6), an interlayer insulating film is formed across the entire surface of the semiconductor device being manufactured. Examples of a method for forming this interlayer insulating film include a plasma CVD method. 
         [0098]    Next, in step (7), a first opening is formed in a position corresponding to the protruding region within the interlayer insulating film. Concurrently, first insulating layer on the protruding region is removed and a first structure is formed so as to have contact with the protruding region. Examples of a method for forming this first opening include forming a mask pattern including an opening in a position corresponding to the protruding region by a lithography technique, and then etching the interlayer insulating film using this mask pattern as a mask. In addition, first insulating layer on the protruding region is removed at the time of this etching. After this, a first structure is formed so as to have contact with the protruding region. After the completion of etching, the mask pattern is removed. 
         [0099]    Next, in step (8), a protective substrate is formed on the first structure, Typically, the first structure exists in the form of being buried within the interlayer insulating film. In addition, there is formed, in some cases, an interlayer insulating film comprising an interconnect layer on the interlayer insulating film within which the first structure is buried. In such a case, the protective substrate may be bonded onto these interlayer insulating films. 
         [0100]    Next, in step (9), the semiconductor substrate is polished from the rear surface side thereof opposite to a side on which the first structure is formed, thereby reducing the thickness of the semiconductor substrate. Examples of a method of this polishing include a CMP (chemical mechanical polish) method. In addition, the thickness of the semiconductor substrate after this polishing is preferably 50 to 150 μm and, more preferably, 50 to 100 μm. By polishing the semiconductor substrate down to such a thickness as described above, second insulating layer is etched to a lesser extent even if a difference in etching rate between the semiconductor substrate and second insulating layer in later step (10) is small. Thus, it is possible to align the second opening with the protruding region in a self-aligned manner and with high accuracy. 
         [0101]    Next, in step (10), anisotropic etching is performed to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of second insulating layer, thereby forming a second opening. Thus, the second opening is formed until the second opening reaches at least the protruding region. 
         [0102]    In performing anisotropic etching, a common ICP type etching apparatus may be used. The anisotropic etching may be performed on electrode cooled down at 10° C. by chiller. HBr, Cl 2  and O 2  may be used as a gas for anisotropic etching. The anisotropic etching conditions include HBr flow rate 100 sccm, Cl 2  flow rate 100 sccm, O 2  flow rate 5 sccm, and pressure 2 Pa. The typical etching rate is 500 nm/min. If a silicon semiconductor substrate is used as the semiconductor substrate, a etching selectivity of the silicon semiconductor substrate to the second insulating film, that is, (silicon semiconductor substrate)/(second insulating film), is 20 or more. 
         [0103]    In step (10), anisotropic etching may be performed until the second opening reaches at least the protruding region. Specifically, this anisotropic etching may be performed until the protruding region is exposed, may be stopped when the protruding region is partially etched, or may be performed until the first structure is exposed. 
         [0104]    The etching rate of this semiconductor substrate is preferably 1.5 or more times and, more preferably, twice or more times the etching rate of second insulating layer. By etching the semiconductor substrate faster than second insulating layer with these differences in etching rate, it is possible to selectively etch the semiconductor substrate alone without deteriorating second insulating layer. As a result, it is possible to align the second opening with the protruding region with even higher accuracy. 
         [0105]    Next, in step (11), a third insulating layer is formed on the inner wall of the second opening. Examples of a method for forming this third insulating layer include forming a silicon dioxide film by performing thermal oxidation if the semiconductor substrate is made of silicon. 
         [0106]    Next, in step (12), at least a first contact plug is formed within the second opening. Typically, the first structure and the first contact plug are electrically connected to each other at this time. In addition, as a method for forming this first contact plug, it is possible to use a publicly-known method for forming a contact plug. 
         [0107]    Hereinafter, a description will be made of specific examples of the manufacturing method of the present invention. 
       First Exemplary Embodiment 
       [0108]    The first exemplary embodiment relates to a method for manufacturing a semiconductor device including a vertical MOSFET. The first exemplary embodiment includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-1) forming a first opening in a position corresponding to the protruding region within the first interlayer insulating film and removing the first insulating layer on the protruding region;
 
(7-2) causing selective epitaxial growth to take place on the protruding region within the first opening to form a semiconductor region on the protruding region;
 
(7-3) removing the first interlayer insulating film to expose the semiconductor region;
 
(7-4) forming a gate insulating film on a side surface of the exposed semiconductor region parallel with a thickness direction of the semiconductor substrate;
 
(7-5) forming a gate electrode on the gate insulating film;
 
(7-6) implanting an impurity into an upper portion of the semiconductor region opposite to the protruding region side, to convert the upper portion of the semiconductor region into an upper impurity-diffused region;
 
(7-7) forming a second interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-8) forming a second contact plug so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region;
 
(8) forming a protective substrate on a first structure (the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the second contact plug);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the semiconductor region is exposed;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming, within the second opening, a lower impurity-diffused region so as to have contact with the semiconductor region and a first contact plug so as to be electrically connected to the lower impurity-diffused region.
 
         [0109]    In the first exemplary embodiment, steps (1) to (6), (8), (9), (11) and (13) are the same as steps (1) to (6), (8), (9), (11) and (13) described in the section “(Method for manufacturing semiconductor device).” Accordingly, no further explanation will be made of these steps. Hereinafter, only steps (7), (10) and (12) will be explained. 
         [0110]    In step (7-1) of the first exemplary embodiment, the first opening is provided within the first interlayer insulating film in a position corresponding to the protruding region, and the first insulating layer on the protruding region is removed. 
         [0111]    Next, in step (7-2), selective epitaxial growth is caused to take place on the protruding region within the first opening, thereby forming a semiconductor region on the protruding region. The conditions for selective epitaxial growth can be set as appropriate, according to the desired characteristics of the semiconductor region. 
         [0112]    Next, in step (7-3), the first interlayer insulating film is removed to expose the semiconductor region. Examples of a method for removing this first interlayer insulating film include dry etching and wet etching. 
         [0113]    Next, in step (7-4), a gate insulating film is formed on a side surface of the exposed semiconductor region parallel with the thickness direction of the semiconductor substrate. Here, the “side surface of the exposed semiconductor region parallel with the thickness direction of the semiconductor substrate” denotes a surface vertical to the front surface of the semiconductor substrate. Examples of a method for forming this gate insulating film include thermally oxidizing a side surface of the semiconductor region parallel with the thickness direction of the semiconductor substrate, or depositing a gate insulating film material on the entire surface of the semiconductor device being manufactured by a CVD method or the like and then etching back the gate insulating film material, thereby leaving over the gate insulating film on the side surface parallel with the thickness direction of the semiconductor substrate. 
         [0114]    Next, in step (7-5), a gate electrode is formed on the gate insulating film. Examples of a method for forming this gate electrode include a DOPOS (doped polycrystalline silicon) method. 
         [0115]    Next, in step (7-6), an impurity is implanted into the upper portion of the semiconductor region opposite to the protruding region side, thereby converting the upper portion of the semiconductor region as an upper impurity-diffused region. The type of impurity to be implanted for the upper impurity-diffused region and the conditions of implanting the impurity can be set as appropriate, according to a desired vertical MOSFET. 
         [0116]    Next, in step (7-7), a second interlayer insulating film is formed across the entire surface of the semiconductor device being manufactured. Examples of a method for forming this second interlayer insulating film include the same method as that for forming the first interlayer insulating film. 
         [0117]    Next, in step (7-8), a second contact plug is formed so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region. Examples of a method for forming this second contact plug include the same method as that for forming the first contact plug. 
         [0118]    In step (10), anisotropic etching is performed to remove the protruding region and form the second opening until the semiconductor region is exposed. 
         [0119]    In addition, in step (12), a lower impurity-diffused region is formed so as to be electrically connected to the semiconductor region. Likewise, a first contact plug is formed so as to be electrically connected to the lower impurity-diffused region. Examples of a method for forming this lower impurity-diffused region include a DOPOS method and a method for forming a polysilicon layer and then implanting an impurity into this polysilicon layer after. The lower impurity-diffused region and the first contact plug are formed in separate steps. 
         [0120]    In the first exemplary embodiment, a semiconductor region the upper portion of which is an upper impurity-diffused region, a gate insulating film, a gate electrode, and a second contact plug are formed as the first structure. In some cases, the other structure may be formed as the first structure. In addition, the semiconductor region comprising the upper impurity-diffused region, the gate insulating film, the gate electrode, and the lower impurity-diffused region constitute a vertical MOSFET. 
         [0121]    The vertical MOSFET formed in the first exemplary embodiment may be either an N-type MOSFET or a P-type MOSFET. When forming an N-type MOSFET, an N-type impurity is implanted into the upper impurity-diffused region and the lower impurity-diffused region. In addition, a P-type impurity is implanted into the semiconductor region. When forming a P-type MOSFET, a P-type impurity is implanted into the upper impurity-diffused region and the lower impurity-diffused region. In addition, an N-type impurity is implanted into the semiconductor region. 
         [0122]    In a modified example of the present exemplary embodiment, an impurity is implanted into the protruding region in step (7), thereby converting the protruding region as the lower impurity-diffused region. In addition, in step (10), anisotropic etching is performed to form the second opening until the second opening reaches the protruding region which is the lower impurity-diffused region, and leave over the protruding region. After this, in step (12), a first contact plug is formed so as to be electrically connected to the lower impurity-diffused region. Specifically, this modified example includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-1) forming a first opening in a position corresponding to the protruding region within the first interlayer insulating film and removing the first insulating layer on the protruding region;
 
(7-2) implanting an impurity into the protruding region to convert the protruding region into a lower impurity-diffused region;
 
(7-3) causing selective epitaxial growth to take place on the protruding region, which is the lower impurity-diffused region within the first opening, to form a semiconductor region on the protruding region;
 
(7-4) removing the first interlayer insulating film to expose the semiconductor region;
 
(7-5) forming a gate insulating film on a side surface of the exposed semiconductor region parallel with a thickness direction of the semiconductor substrate;
 
(7-6) forming a gate electrode on the gate insulating film;
 
(7-7) implanting an impurity into an upper portion of the semiconductor region opposite to the protruding region side, to convert the upper portion of the semiconductor region into an upper impurity-diffused region;
 
(7-8) forming a second interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-9) forming a second contact plug so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region;
 
(8) forming a protective substrate on a first structure (the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the second contact plug);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches the protruding region which is the lower impurity-diffused region;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming a first contact plug within the second opening so as to be electrically connected to the lower impurity-diffused region.
 
         [0123]    In step (10) of the above-described modified example, anisotropic etching may be performed until the lower impurity-diffused region is exposed or may be performed so that the lower impurity-diffused region is partially etched. When performing anisotropic etching so that this lower impurity-diffused region is partially etched, the anisotropic etching is performed so that the etching rate of the semiconductor substrate and the lower impurity-diffused region is faster than the etching rate of second insulating layer. 
       Second Exemplary Embodiment 
       [0124]    The second exemplary embodiment relates to a method for manufacturing a semiconductor device including a vertical MOSFET and an interconnect structure. The second exemplary embodiment includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a plurality of protruding regions composed of protruding regions A and B the portions of which other than portions below the first mask pattern are exposed;
 
(4) forming a second insulating layer in the exposed portions of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-1) forming a first opening in a position corresponding to the protruding region A within the first interlayer insulating film and removing the first insulating layer on the protruding region A;
 
(7-2) causing selective epitaxial growth to take place on the protruding region A within the first opening, to form a semiconductor region on the protruding region A;
 
(7-3) removing the first interlayer insulating film to expose the semiconductor region;
 
(7-4) forming a gate insulating film on a side surface of the exposed semiconductor region parallel with a thickness direction of the semiconductor substrate;
 
(7-5) forming a gate electrode on the gate insulating film;
 
(7-6) implanting an impurity into an upper portion of the semiconductor region opposite to the protruding region A side, to convert the upper portion of the semiconductor region into an upper impurity-diffused region;
 
(7-7) forming a second interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-8) forming a second contact plug so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region, forming a first opening in a position corresponding to the protruding region B within the second interlayer insulating film, removing the first insulating layer on the protruding region B, and forming a third contact plug so as to be electrically connected to the protruding region B;
 
(8) forming a protective substrate on a first structure (the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the second and third contact plugs);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in positions corresponding to the protruding regions A and B from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the semiconductor region and the third contact plug are exposed;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming a lower impurity-diffused region so as to have contact with the semiconductor region within the second opening, forming a first contact plug so as to be electrically connected to the lower impurity-diffused region, forming a connecting part so as to be electrically connected to the third contact plug, and forming a first contact plug so as to be electrically connected to the connecting part.
 
         [0125]    In the second exemplary embodiment, steps (1), (2), (4) to (6), (8), (9) and (11) are the same as steps (1), (2), (4) to (6), (8), (9) and (11) described in the first exemplary embodiment. Accordingly, no further explanation will be made of these steps and only steps (3), (7), (10) and (12) will be explained. 
         [0126]    In the second exemplary embodiment, a plurality of protruding regions are formed in step (3). Among these protruding regions, a region in which a vertical MOSFET is to be formed is referred to as protruding region A, whereas a region in which a third contact plug is to be formed is referred to as protruding region B. In steps (7-1) and (7-2), a semiconductor region is formed only on protruding region A. In these steps, it is possible to use the same methods as used in steps (7-1) and (7-2) of the first exemplary embodiment. At this time, it is possible to prevent the first opening and the semiconductor region from being formed on protruding region B by forming a mask in a portion corresponding to protruding region B on the first interlayer insulating film. 
         [0127]    In steps (7-3) to (7-7), the gate insulating film and the gate electrode are formed in the same way as in steps (7-3) to (7-7) of the first exemplary embodiment only on the side surface of the semiconductor region formed on protruding region A parallel with the thickness direction of the semiconductor substrate. In addition, the upper portion of the semiconductor region is converted into the upper impurity-diffused region. After this, the second interlayer insulating film is formed across the entire surface of the semiconductor device being manufactured. 
         [0128]    Next, in step (7-8), the second contact plug is formed so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region. In addition, the first opening is formed in a position corresponding to protruding region B, concurrently with forming an opening for the second contact plug in a position within this second interlayer insulating film corresponding to the upper impurity-diffused region. Furthermore, first insulating layer on protruding region B is removed. In addition, the third contact plug is formed so as to be electrically connected to protruding region B, concurrently with forming the second contact plug in a position within the opening corresponding to the upper impurity-diffused region. As described above, in step (7-8), the first opening is also formed on protruding region B when forming the opening for the second contact plug. Thus, it is possible to simultaneously form the second contact plug and the third contact plug. 
         [0129]    In the second exemplary embodiment, the formation of the first opening in step (7) described in the above-discussed section “(Method for manufacturing semiconductor device)” is performed in two separate steps. That is, the steps of forming first openings on protruding regions A and B are respectively carried out as separate steps. 
         [0130]    In step (10), the second opening is formed in the same way as in the first exemplary embodiment by performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side of the semiconductor substrate. This formation of the second opening is performed until the semiconductor region and the third contact plug are exposed. 
         [0131]    In step (12), the lower impurity-diffused region is formed within the second opening, in the same way as in the first exemplary embodiment, so as to be electrically connected to the semiconductor region. Likewise, the first contact plug is formed so as to be electrically connected to the lower impurity-diffused region. In addition, the connecting part is formed so as to be electrically connected to the third contact plug, and the first contact plug is formed so as to be electrically connected to the connecting part. 
         [0132]    In the second exemplary embodiment, (a) the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the second contact plug, and (b) the third contact plug are formed, as the first structure. Thus, the vertical MOSFET is composed of (a) the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the lower impurity-diffused region constituting this first structure. In addition, (b) the third contact plug and the connecting part constitute the interconnect structure. In some cases, the other structure may be formed as the first structure. 
         [0133]    In the modified example of the present exemplary embodiment, anisotropic etching is performed in step (10) to form the second openings until the second openings reach the lower impurity-diffused region and the connecting part, which are protruding regions A and B, respectively. In addition, protruding regions A and B are left over. After this, the first contact plugs are formed so as to be electrically connected to the lower impurity-diffused regions and the connecting part. Specifically, this modified example includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a plurality of protruding regions composed of protruding regions A and B the portions of which other than portions below the first mask pattern are exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-1) forming a first opening in a position corresponding to the protruding region A within the first interlayer insulating film and removing the first insulating layer on the protruding region A;
 
(7-2) implanting an impurity into the protruding region A to convert the protruding region A into a lower impurity-diffused region;
 
(7-3) causing selective epitaxial growth to take place on the protruding region A which is the lower impurity-diffused region within the first opening, to form a semiconductor region on the protruding region A;
 
(7-4) removing the first interlayer insulating film to expose the semiconductor region;
 
(7-5) forming a gate insulating film on a side surface of the exposed semiconductor region parallel with a thickness direction of the semiconductor substrate;
 
(7-6) forming a gate electrode on the gate insulating film;
 
(7-7) implanting an impurity into an upper portion of the semiconductor region opposite to the protruding region A side, to convert the upper portion of the semiconductor region into an upper impurity-diffused region;
 
(7-8) forming a second interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-9) forming a second contact plug so as to penetrate through the second interlayer insulating film and be electrically connected to the upper impurity-diffused region, forming a first opening in a position corresponding to the protruding region B within the second interlayer insulating film, removing the first insulating layer on the protruding region B, and implanting an impurity into the protruding region B to form a connecting part, and forming a third contact plug so as to be electrically connected to the connecting part;
 
(8) forming a protective substrate on a first structure (the semiconductor region the upper portion of which is the upper impurity-diffused region, the gate insulating film, the gate electrode, and the second and third contact plugs);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in positions corresponding to the protruding regions A and B from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches the protruding region A which is the lower impurity-diffused region and the protruding region B which is the connecting part;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming a first contact plug so as to be electrically connected to the lower impurity-diffused region and the connecting part within the second opening.
 
         [0134]    In step (10) of the above-described modified example, anisotropic etching may be performed until the lower impurity-diffused region and the connecting part are exposed, or may be performed so that the lower impurity-diffused region and the connecting part are partially etched. When performing anisotropic etching so that the lower impurity-diffused region and the connecting part are partially etched, the anisotropic etching is performed so that the etching rate of the semiconductor substrate, the lower impurity-diffused region and the connecting part is faster than the etching rate of the second insulating layer. 
         [0135]    In the above-described modified example, the formation of the first opening in step (7) described in the above-discussed section “(Method for manufacturing semiconductor device)” is performed in two separate steps. That is, the steps of forming the first openings on protruding regions A and B are respectively carried out as separate steps. 
       Third Exemplary Embodiment 
       [0136]    The third exemplary embodiment relates to a method for manufacturing a semiconductor device including an interconnect structure. The third exemplary embodiment includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate,
 
(7-1) forming a first opening in a position corresponding to the protruding region within the first interlayer insulating film and removing the first insulating layer on the protruding region;
 
(7-2) forming a third contact plug so as to penetrate through the first interlayer insulating film and have contact with the protruding region;
 
(8) forming a protective substrate on a first structure (the third contact plug);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the third contact plug is exposed;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming a connecting part so as to be electrically connected to the third contact plug within the second opening and forming a first contact plug so as to be electrically connected to the connecting part.
 
         [0137]    In the third exemplary embodiment, steps (1) to (6), (8), (9), (11) and (13) are the same as steps (1) to (6), (8), (9), (11) and (13) described in the first exemplary embodiment. Accordingly, no further explanation will be made of these steps and only steps (7), (10) and (12) will be explained. 
         [0138]    In step (7-1) of the third exemplary embodiment, the first opening is formed within the first interlayer insulating film in a position corresponding to the protruding region, and first insulating layer on the protruding region is removed, in the same way as in step (7-1) of the first exemplary embodiment. 
         [0139]    Next, in step (7-2), the third contact plug is formed so as to penetrate through the first interlayer insulating film and be electrically connected to the protruding region. 
         [0140]    In step (10), anisotropic etching is performed, in the same way as in the first exemplary embodiment, in a position corresponding to the protruding region within the semiconductor substrate from the rear surface side thereof, thereby forming the second opening. This formation of the second opening is performed until the third contact plug is exposed. 
         [0141]    In addition, in step (12), the connecting part is formed so as to have contact with the third contact plug within the second opening, and the first contact plug is formed so as to have contact with the connecting part, as in the first exemplary embodiment. In this third exemplary embodiment, the third contact plug is formed as a first structure. In some cases, the other structure may be formed as the first structure. 
         [0142]    In the modified example of the present exemplary embodiment, anisotropic etching is performed in step (10) to form the second opening until the second opening reaches the protruding region which is the connecting part, and the protruding region is left over. After this, the first contact plug is formed so as to be electrically connected to the connecting part. Specifically, this modified example includes: 
         [0000]    (1) forming a first insulating layer across the entire surface of a semiconductor substrate;
 
(2) forming a first mask pattern on the first insulating layer;
 
(3) etching the first insulating layer and the semiconductor substrate using the first mask pattern as a mask to form, below the first mask pattern, a protruding region a portion of which other than a portion below the first mask pattern is exposed;
 
(4) forming a second insulating layer in the exposed portion of the semiconductor substrate;
 
(5) removing the first mask pattern;
 
(6) forming a first interlayer insulating film over the entire surface of the semiconductor substrate;
 
(7-1) forming a first opening in a position corresponding to the protruding region within the first interlayer insulating film and removing the first insulating layer on the protruding region;
 
(7-2) implanting an impurity into the protruding region to convert the protruding region into a connecting part;
 
(7-3) forming a third contact plug so as to penetrate through the first interlayer insulating film and be electrically connected to the protruding region which is the connecting part;
 
(8) forming a protective substrate on a first structure (the third contact plug);
 
(9) polishing the semiconductor substrate from the rear surface side thereof opposite to a side on which the first structure is formed, to reduce a thickness of the semiconductor substrate;
 
(10) performing anisotropic etching to the semiconductor substrate in a position corresponding to the protruding region from the rear surface side thereof, so that the etching rate of the semiconductor substrate is faster than the etching rate of the second insulating layer, to form a second opening until the second opening reaches the protruding region which is the connecting part;
 
(11) forming a third insulating layer on the inner wall of the second opening; and
 
(12) forming a first contact plug so as to be electrically connected to the connecting part within the second opening.
 
         [0143]    In step (10) of the above-described modified example, anisotropic etching may be performed until the connecting part is exposed or may be performed so that the connecting part is partially etched. When performing anisotropic etching so that the connecting part is partially etched, the anisotropic etching is performed so that the etching rate of the semiconductor substrate and the connecting part is faster than the etching rate of the second insulating layer. 
       Variations of the First to Third Exemplary Embodiments 
       [0144]    Furthermore, the portions of the semiconductor device according to the first to third exemplary embodiments can be varied as described below. 
         [0145]    Gate Electrode 
         [0146]    The gate electrode may be formed of polysilicon. Alternatively, the gate electrode may be formed of a metal material as a metal gate electrode. In this case, the metal gate electrode may be composed an alloy of one or more metal materials, or the like. 
         [0147]    Moreover, the metal gate electrode may be formed of silicide. The silicide is not particularly limited provided that the silicide is composed of a metal which can be silicidized by being allowed to react with silicon. The silicide may be, for example, NiSi, Ni 2 Si, Ni 3 Si, NiSi 2 , WSi 2 , TiSi 2 , WSi 2 , CrSi 2 , ZrSi 2 , NbSi 2 , MoSi 2 , TaSi 2 , CoSi, CoSi 2 , PtSi, Pt 2 Si, or Pd 2 Si. 
         [0148]    Gate Insulating Film 
         [0149]    The gate insulating film may be formed of an oxide film. Alternatively, the gate insulating film may be formed of a high-dielectric-constant insulating film containing Hf and offering a high dielectric constant. Alternatively, the gate insulating film may be formed of a high-dielectric-constant insulating film containing no Hf and offering a high dielectric constant. The “high-dielectric-constant insulating film” refers to an insulating film offering a larger relative dielectric constant than SiO 2  (SiO 2  offers a relative dielectric constant of about 3.6), which is commonly utilized as a gate insulating film in the semiconductor device. Typically, the relative dielectric constant of the high-dielectric-constant insulating film may be several tens to several thousands. The high-dielectric-constant insulating film may be, for example, HfSiO, HfSiON, HfZrSiO, HfZrSiON, ZrSiO, ZrSiON, HfAlO, HfAlON, HfZrAlO, HfZrAlON, ZrAlO, or ZrAlON. 
         [0150]    Other Materials 
         [0151]    The interconnect material may be silicide or metal, or any other conductive substance. 
         [0152]    The insulating material is not limited to an oxide film but may be a nitride film. Alternatively, SiON, SiOC, or the like may be used as the insulating material. 
         [0153]    Application of the Vertical MOSFET 
         [0154]    The vertical MOSFET may be utilized as a flash memory by forming a floating portion in the gate electrode. Furthermore, the transistor may be utilized as an ordinary transistor, or holes may be stored in the body of the transistor so that the transistor can be utilized as a floating body cell (FBC) that operates as a memory. 
       Example 
       [0155]    A semiconductor device including a vertical MOSFET and an interconnect structure was manufactured in the manner described below. This method for manufacturing a semiconductor device corresponds to the manufacturing method of the above-described second exemplary embodiment. 
         [0156]    First, silicon semiconductor substrate  11  was prepared and then the front surface of this silicon semiconductor substrate  11  was oxidized to form silicon dioxide film (first insulating layer)  12  (step (1)). Dry oxidization was performed as a method of this oxidization, thereby forming a 10 nm-thick silicon dioxide film. 
         [0157]    After this, a nitride film was grown to a thickness of 100 nm. Then, line-and-space formation was performed using a lithography technique and photoresist  14  was subjected to patterning. At this time, the width of a line was set to 70 nm and the width of a space was set to 70 nm. Next, using the pattern of this photoresist  14  as a mask, the nitride film was subjected to patterning to form the first mask pattern (reference numeral  13 ) ( FIG. 1 : step (2)). 
         [0158]    After this, the photoresist used for the lithography technique was separated. Then, using the first mask pattern (reference numeral  13 ) made of the nitride film as a hard mask, silicon dioxide film  12  and silicon semiconductor substrate  11  were dry-etched to a depth of 50 nm, thereby forming protruding region A (reference numeral  15 ) and protruding region B (reference numeral  30 ) below the first mask pattern. At this time, the portions of silicon semiconductor substrate  11  other than a portion below the first mask pattern were exposed (step (3)). 
         [0159]    After this, thermal oxidation was performed on the exposed portions of the silicon semiconductor substrate to form 10 nm-thick silicon dioxide film (second insulating layer)  16  ( FIG. 2 : step (4)). 
         [0160]    After this, the first mask pattern (reference numeral  13 ) made of the nitride film was removed by wet etching (step (5)). Then, 500 nm-thick silicon dioxide film (first interlayer insulating film)  17  was formed by means of oxide film growth across the entire surface of the semiconductor device being manufactured (step (6)). After this, an improvement was made to the planarity of the silicon dioxide film by means of CMP. Then, photoresist mask pattern  18  was formed using a lithography technique so as to include an opening in a position corresponding to protruding region A ( FIG. 3 ). 
         [0161]    After this, silicon dioxide film  17  was dry-etched using this mask pattern  18  as a mask, thereby forming the first opening in a position corresponding to protruding region A (reference numeral  15 ). Concurrently, silicon dioxide film (first insulating layer)  12  on protruding region A (reference numeral  15 ) was removed (step (7-1)). After this, the resist mask was separated. Then, arsenic was implanted into protruding region A (reference numeral  15 ) under the condition of 10 KeV and 1×10 15 /cm 2  to form lower impurity-diffused region  19  (step (7-2)). 
         [0162]    After this, selective epitaxial growth was caused to take place on lower impurity-diffused region  19  within the first opening, thereby forming semiconductor region  20  made of silicon crystal on lower impurity-diffused region  19  ( FIG. 4 : step (7-3)). 
         [0163]    After this, silicon dioxide film (first interlayer insulating film)  17  was set back to the front surface of the silicon semiconductor substrate by dry etching or by wet etching, thereby exposing semiconductor region  20  (step (7-4)). Then, a side surface of the exposed semiconductor region parallel with the thickness direction of the semiconductor substrate was oxidized to form gate insulating film  21  made of a 10 nm-thick silicon dioxide film (step (7-5)). 
         [0164]    After this, 30 nm-thick DOPOS (doped polycrystalline silicon) was grown on gate insulating film  21 , and then etched back by dry etching to form 30 nm-thick gate electrode  23  ( FIG. 5 : step (7-6)). 
         [0165]    After this, arsenic was implanted into the upper portion of semiconductor region  20  under the condition of 10 KeV and 11×10 15 /cm 2  to convert the upper portion of semiconductor region  20  into upper impurity-diffused region  22  (step (7-7)). Then, silicon dioxide film (second interlayer insulating film)  24  was deposited using a CVD method, and then planarized by means of CMP ( FIG. 6 : step (7-8)). 
         [0166]    After this, second and third contact plugs  25  and  26  were formed. That is, a mask pattern (not illustrated) aligned with the semiconductor region and protruding region B was formed on silicon dioxide film (second interlayer insulating film)  24 . Then, using this mask pattern as a mask, an opening was formed within silicon dioxide film  24  in a position corresponding to semiconductor region  20  and the first opening formed within silicon dioxide film  24  in a position corresponding to protruding region B (reference numeral  30 ). Next, after removing silicon dioxide film  12  (second insulating film) on this protruding region B (reference numeral  30 ), an impurity was implanted into protruding region B to convert the protruding region B into connecting part  31 . After this, polysilicon was buried in the opening in a position corresponding to the semiconductor region and in the first opening in a position corresponding to connecting part  31 . Then, boron was implanted into this polysilicon under the condition of 10 keV and 1×10 15 /cm 2  ( FIG. 7 : step (7-9)). Consequently, second contact plug  25  was formed so as to be electrically connected to upper impurity-diffused region  22  of the semiconductor region and third contact plug  26  was formed so as to be electrically connected to connecting part  31 . 
         [0167]    After this, an upper interconnect layer and a contact were formed on silicon dioxide film (second interlayer insulating film)  24  using a publicly-known method ( FIG. 8 ). Then, 1 mm-thick supporting substrate  27 , for example, was bonded on top of this semiconductor device being manufactured ( FIG. 9 : step (8)). 
         [0168]    After this, an assembly of the silicon semiconductor substrate and the supporting substrate thus integrated was turned upside down ( FIG. 10 ). Then, the assembly was polished from the rear surface side of silicon semiconductor substrate  11  by means of CMP to thin down the silicon semiconductor substrate ( FIG. 11 : step (9)). 
         [0169]    After this, a photoresist mask pattern (not illustrated) including openings in positions corresponding to protruding regions A and B was formed on the rear surface side of silicon semiconductor substrate  11  using a lithography technique. Next, using this photoresist mask pattern as a mask, anisotropic dry etching was performed on the rear surface side of silicon semiconductor substrate  11 . At this time, the condition of anisotropic dry etching was set so that the etching rate of silicon semiconductor substrate  11 , connecting part  31  and lower impurity-diffused region  19  was faster than the etching rate of second insulating layer (reference numeral  16 ) and that a selection ratio between the silicon semiconductor substrate and the silicon dioxide film was large. By setting the anisotropic dry etching to these conditions, it was possible to etch silicon semiconductor substrate  11  and the like so as to leave over silicon dioxide film  16 . In addition, it was possible to form the second opening (reference numeral  28 ) until the second opening reached lower impurity-diffused region  19  and connecting part  31 , with the opening precisely aligned in a self-aligned manner. In the present exemplary embodiment, not only silicon semiconductor substrate  11  but also connecting part  31  and lower impurity-diffused region  19  were partially removed by anisotropic dry etching ( FIG. 12 : step (10)). Subsequently, the photoresist mask pattern was separated. 
         [0170]    After this, thermal oxidation was performed on the silicon semiconductor substrate under the condition of, for example, 850° C., thereby forming 20 nm-thick silicon dioxide film (third insulating layer)  29  on the inner wall of the second opening (reference numeral  28 ) (step (11)). 
         [0171]    Subsequently, a polysilicon layer was buried in the second opening (reference numeral  28 ), and then an impurity was implanted into the polysilicon layer. Thus, first contact plug  32  was formed so as to be electrically connected to lower impurity-diffused region  19 , and another first contact plug  32  was formed so as to be electrically connected to connecting part  31  ( FIG. 13 : step (12)). In the manner described above, it was possible to obtain the semiconductor device ( FIG. 14 ). 
         [0172]    It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.  FIG. 18  is a schematic view illustrating a finally formed semiconductor device. 
         [0173]    In the present embodiment, the vertical MOSFET includes a channel portion formed by performing a selective epitaxial growth as a crystal nucleus of a silicon semiconductor substrate. The channel portion formed by a selective epitaxial growth has a better crystallinity than a channel portion formed by CVD. Since the vertical MOSFET is connected with the second contact plug and interconnect and the semiconductor device of the present embodiment does not need a space for the interconnect, the semiconductor device has advantage for miniaturization of device. In the present embodiment, the first contact plug can be formed in the self-aligned manner, even misalignment of mask is large during forming the first contact plug from the rear side of the semiconductor substrate. As a result, the device can be easily formed. The structure formed by the present embodiment has a feature of an enlarged margin of misalignment during forming a contact hole. 
       Variation of Exemplary Embodiment 1 
       [0174]    The portions of Exemplary Embodiment 1 can be varied as described below. 
         [0175]    As shown in  FIG. 19 , contact plug  102  may be formed which connects interconnect  101  formed on the front surface side of the semiconductor substrate making up the vertical MOSFET to interconnect  103  formed on the rear surface side thereof. 
         [0176]    As shown in  FIG. 20 , bit line  104  connected to the upper impurity-diffused region of the vertical MOSFET may be formed on the front surface side of the semiconductor substrate. Capacitor  105  connected to the lower impurity-diffused region of the vertical MOSFET may be formed on the rear surface side of the semiconductor substrate. In this case, the vertical MOSFET and the capacitor make up a DRAM. The first structure includes the vertical MOSFET, the second contact plug, the bit line, and the like. The semiconductor device as a whole may be utilized as a phase change memory by replacing capacitor  105  with a phase change substance. 
         [0177]    As shown in  FIG. 21 , capacitor  105  connected to the upper impurity-diffused region of the vertical MOSFET may be formed on the front surface side of the semiconductor substrate. Bit line  104  connected to the lower impurity-diffused region of the vertical MOSFET may be formed on the rear surface side of the semiconductor substrate. In this case, the semiconductor device may be utilized as a DRAM. The first structure includes the vertical MOSFET, the second contact plug, the capacitor, and the like. The semiconductor device as a whole may be utilized as a phase change memory by replacing capacitor  105  with a phase change substance. 
         [0178]    If a minimum process dimension is defined as “F”, interconnect layer opposite to the capacitor sandwiching the MOSFET can be formed in 2F pitch. If interconnect layer is formed in 2F pitch only over front surface side of the semiconductor substrate, process flow becomes very complicated. In contrast, in the present embodiment, 2F pitch interconnect layer can be easily formed. For example, formation of 2F pitch bit line improves an integration level per unit area of DRAM, and the like. 
       Exemplary Embodiment 2 
       [0179]    In the present exemplary embodiment, the first contact is formed from the rear surface side of the semiconductor substrate by a forming method different from that used in Exemplary Embodiment 1. First, the manufacturing process is carried out as is the case with Exemplary Embodiment 1 until the step shown in  FIG. 11 . However, the present exemplary embodiment differs from Exemplary Embodiment 1 in that the present exemplary embodiment omits the step of implanting the impurity into protruding region  15  to form the lower impurity-diffused region. Instead, after formation of semiconductor region  20 , the impurity is implanted into the lower portion of semiconductor region  20 , which contacts protruding region  15 , to form lower impurity-diffused region  19 . 
         [0180]      FIGS. 22 to 24  show subsequent steps. First, the rear surface side of semiconductor substrate  11  is polished by CMP ( FIG. 22 ). Thereafter, the lithography technique is used to pattern semiconductor substrate  11  from the rear surface side thereof to form a plurality of semiconductor portions  109  in association with respective semiconductor regions  20  and respective third contact plugs  26  ( FIG. 23 ). Then, the impurity is implanted into respective semiconductor portions  109  to form first contact plugs  110  ( FIG. 24 ). 
         [0181]    In the method for forming the first contact plug according to the present exemplary embodiment, when semiconductor substrate  11  is patterned from the rear surface side thereof, anisotropic etching is performed so that the etching rate of semiconductor substrate  11  is faster than that of second insulating layer (reference numeral  16 ), thereby providing openings. Thus, first contact plugs  110  can be formed in a self-aligned manner. 
         [0182]    There is no semiconductor such as silicon between such a formed contact plug  110  and the other contact plug  110 . The above feature of the present embodiment is definitely different from the first embodiment. In present embodiment, forming of such structure reduces a short circuit of interconnect layer and improves a yield of a semiconductor device. 
       Exemplary Embodiment 3 
       [0183]    In the example illustrated in Exemplary Embodiments 1 and 2, the vertical MOSFET is formed on the front surface side of the semiconductor substrate. However, the vertical MOSFET may or may not be used as a part of the transistor formed on the front surface of the semiconductor substrate. Alternatively, an ordinary planar transistor alone may be formed on the front surface side of the semiconductor substrate. 
         [0184]      FIGS. 25 to 28  show a method for manufacturing a semiconductor device using only a planar transistor as the transistor. First, a well-known method is used to form gate insulating film  117  on the front surface side of semiconductor substrate  11 . Thereafter, isolation region (STI)  116  and a planar transistor are formed on the front surface side of semiconductor substrate  11 . At the same time or in a different step, first impurity-diffused region  115  is formed on the front surface side of semiconductor substrate  11  so as to be isolated from the planar transistor by isolation region  116 . Then, an interlayer insulating film is formed across the entire front surface side of semiconductor substrate  11 . An opening is then provided at a position in the interlayer insulating film which corresponds to first impurity-diffused region  115 . Contact plug  114  is formed in the opening. Thereafter, protective substrate  27  is bonded to the upper part of the interlayer insulating film ( FIG. 25 ). 
         [0185]    Thereafter, semiconductor substrate  11  is turned upside down, and a CMP process is carried out on semiconductor substrate  11  from the rear surface side thereof. Then, the lithography technique is used to pattern semiconductor substrate  11 . Anisotropic etching is performed on a position corresponding to first impurity-diffused region  115 , to form a third opening such that the third opening reaches at least the first impurity-diffused region. At this time, a contact hole can be formed in a self-aligned manner by performing anisotropic etching under the condition that the etching rate of semiconductor substrate  11  is faster than that of gate insulating film  117  ( FIG. 26 ). 
         [0186]    Then, a portion of semiconductor substrate  11  exposed in the third opening is oxidized to form insulating film layer  140 . Then, a conductive material is buried in the contact hole to form first contact plug  118  ( FIG. 27 ). Thereafter, interconnect layer  119  is formed by a well-known method so that interconnect layer  119  is connected to first contact plug  118  ( FIG. 28 ). 
         [0187]    As described above, even if the device including the planar transistor is formed on the front surface side of the semiconductor substrate, the interconnect layer can be formed from the rear surface side of the semiconductor substrate. 
       Exemplary Embodiment 4 
       [0188]    In the example illustrated in Exemplary Embodiments 1 to 3, the transistor is formed on the front surface side of the semiconductor substrate. However, the device formed on the front surface side of the semiconductor substrate is not limited to the transistor but may be a diode.  FIG. 29  is a diagram showing such a semiconductor device. The diode in  FIG. 29  is formed of N-type diffusion layer  120  and P-type diffusion layer  121 . Alternatively, the diffusion layers denoted by reference numerals  120  and  121  may be of the P type and the N type, respectively, depending on the configuration of the semiconductor device. In this case, the diode, the second and third contact plugs, and the like make up the first structure. 
       Exemplary Embodiment 5 
       [0189]    In recent years, techniques have been developed which enable wafers to be conveyed even with the reduced thickness of the semiconductor substrate. Thus, a thicker interconnect layer enables the semiconductor device to be processed without the need to bond the protective substrate to the semiconductor substrate.  FIG. 46  shows a semiconductor device with no protective substrate bonded to the semiconductor substrate. With this semiconductor device, the reduced thickness of the semiconductor substrate allows omission of the step of performing the CMP process on the semiconductor substrate from the rear surface side thereof. 
       Exemplary Embodiment 6 
       [0190]    If the vertical MOSFET is formed on the front surface side of the semiconductor substrate, the impurity for the lower impurity-diffused region may be implanted into the semiconductor substrate from the rear surface side thereof. In this case, the impurity may be implanted exclusively into a part of the lower portion of the semiconductor region of the vertical MOSFET. 
         [0191]    In this manufacturing method, first, the manufacturing process is carried out as is the case with Exemplary Embodiment 1 until the step shown in  FIG. 11 . However, the present exemplary embodiment differs from Exemplary Embodiment 1 in that the present exemplary embodiment omits the step of implanting the impurity into protruding region  15  to form the lower impurity-diffused region. Then, as shown in  FIG. 47 , resist mask  130  is formed on the rear surface side of semiconductor substrate  11 ; resist mask  130  has opening only in a portion thereof corresponding to a part of semiconductor region  20  of the vertical MOSFET. Thereafter, the impurity is implanted into semiconductor substrate  11  from the rear surface side thereof using resist mask  130  as a mask, to form lower impurity-diffused region  129  in the part of the lower part of semiconductor region  20 . 
         [0192]    Then, resist mask  130  is removed. First contact plug  32  is thereafter formed so as to be connected to third contact plug  24  and lower impurity-diffused region  129 . An interconnect layer is then formed so as to be connected to first contact plug  32  ( FIG. 48 ). The present exemplary embodiment reduces the potential of carriers in the vertical MOSFET. This in turn reduces the floating body effect of the vertical MOSFET to facilitate designing. 
       Exemplary Embodiment 7 
       [0193]    When the vertical MOSFET and vertical diode according to the above-described exemplary embodiments are formed, the semiconductor region may be formed by utilizing a silicon semiconductor substrate instead of utilizing the selective epitaxial growth. The present exemplary embodiment relates to a manufacturing method for forming the vertical MOSFET utilizing the silicon semiconductor substrate. 
         [0194]    First, silicon oxide film  12  is formed on silicon semiconductor substrate  11 . The film thickness of the silicon oxide film is 10 nm. Then, nitride film  13  is grown to a thickness of 100 nm as a mask material. The lithography technique is then used to pattern resist  14  so as to form a pattern covering a portion of the substrate in which the vertical MOSFET is to be formed and a portion of the substrate in which the third contact plug is to be formed. 
         [0195]    Then, nitride film  13  is etched using resist mask  14  as a mask ( FIG. 30 ). Silicon semiconductor substrate  11  is thereafter dry etched to a depth of 120 nm using nitride film  13  patterned as a mask. At this time, the semiconductor substrate is etched to a depth that is larger than the channel length of the MOSFET, to form, below nitride film  13 , semiconductor region  20   a  protruding from a predetermined plane of silicon semiconductor substrate  11  ( FIG. 31 ). 
         [0196]    Then, thermal oxidation is performed to cover the exposed surface of semiconductor region  20   a  with oxide film  16  ( FIG. 32 ). The film thickness of oxide film  16  is 5 nm. Then, HDP oxide film growth is caused to take place on oxide film  16  to deposit oxide film  141  ( FIG. 33 ). The film thickness of oxide film  141  is 30 nm. 
         [0197]    Then, gate electrode material  122  is deposited on oxide film  141  by CVD. Gate electrode material  122  is, for example, DOPOS, and is deposited to a thickness of 20 nm. Thereafter, gate electrode material  122  is etched back ( FIG. 34 ). Gate electrode material  122  is further etched to form a structure shown in  FIG. 35 . 
         [0198]    Then, an interlayer insulating film made up of oxide film  123  is formed on the structure in  FIG. 35 . The CMP process is thereafter carried out to flatten oxide film  123  ( FIG. 36 ). Wet etching is then performed using thermal phosphoric acid, to remove nitride film  13 . 
         [0199]    Then, the lithography technique is used to form a resist mask (not shown in the drawings) that is open in a portion thereof corresponding to the portion of the substrate in which the vertical MOSFET is to be formed. The impurity is implanted into the silicon portion using the resist mask as a mask, to form upper impurity-diffused region  125  of the vertical MOSFET. The impurity implantation is performed using As as the impurity under conditions of 20 KeV and 1×10 15  atoms/cm 2 . 
         [0200]    Then, the resist mask is removed. Furthermore, the lithography technique is used to form a resist mask (not shown in the drawings) that is open in a portion thereof corresponding to the portion of the substrate in which the third contact plug is to be formed. The impurity is implanted into the silicon portion using the resist mask as a mask, to form contact plug portion  124 . The impurity implantation is performed three times using As at 1×10 15  atoms/cm 2  under conditions of 20 KeV, 80 KeV, and 150 KeV ( FIG. 37 ). 
         [0201]    Then, the resist mask is removed. Oxide film  12  is thereafter dry etched to expose silicon from a top surface of the semiconductor region ( FIG. 38 ). A contact plug material is then deposited across the entire surface of the semiconductor device being manufactured. The CMP process is then carried out to flatten and strike the contact plug material. Second and third contact plugs  126   a  and  126   b  are thus formed ( FIG. 39 ). 
         [0202]    Then, an interconnect layer and a contact layer are formed so as to be connected to second and third contact plugs  126   a  and  126   b . An interlayer insulating film is thereafter formed across the entire surface of the semiconductor device being manufactured ( FIG. 40 ). 
         [0203]    Thereafter, protective substrate  27  is bonded over the interlayer insulating film ( FIG. 41 ). The silicon semiconductor substrate and protective substrate in  FIG. 41  are turned upside down ( FIG. 42 ). The CMP process is then carried out on silicon semiconductor substrate  11  from the rear surface side thereof to thin silicon semiconductor substrate  11 . The lithography technique is then used to perform patterning to form a resist mask (not shown in the drawings) that is open in portions thereof corresponding to the semiconductor region of the vertical MOSFET and the third contact plug. 
         [0204]    Then, silicon semiconductor substrate  11  is dry etched using the resist mask as a mask so that the etching rate of silicon semiconductor substrate  11  is faster than that of oxide film  16  ( FIG. 43 ). Thermal oxidation is then performed to oxidize the rear surface side of silicon semiconductor substrate  11 . A portion of the substrate corresponding to the semiconductor region of the vertical MOSFET is opened by the lithography technique. 
         [0205]    Thereafter, the impurity is implanted into the semiconductor region of the vertical MOSFET from the rear surface side thereof to form lower impurity-diffused region  201 . The impurity implantation is performed using As as the impurity under conditions of 20 KeV and 1×10 15  atoms/cm 2 . 
         [0206]    Then, the resist mask is removed, and the insulating film is etched back ( FIG. 44 ). A material for the first contact plug is then deposited in the opening. The material for the first contact plug is then flattened by the CMP process to form first contact plug  32  ( FIG. 45 ). A contact layer and an interconnect layer are thereafter formed. 
         [0207]    In the present embodiment, the vertical MOSFET includes a channel portion formed by performing a selective epitaxial growth as a crystal nucleus of a silicon semiconductor substrate. The channel portion formed by a selective epitaxial growth has a better crystallinity than a channel portion formed by CVD. Since the vertical MOSFET is connected with the second contact plug and interconnect and the semiconductor device of the present embodiment does not need a space for the interconnect, the semiconductor device has advantage for miniaturization of device. In the present embodiment, the first contact plug can be formed in a self-aligned manner, even misalignment of mask is large during forming the first contact plug from the rear side of the semiconductor substrate. As a result, the device can be easily formed. The structure formed by the present embodiment has a feature of an enlarged margin of misalignment during forming a contact hole. 
         [0208]    (Feature of the Structure of the Present Invention) 
         [0209]    The various examples of the present invention have been described as the exemplary embodiments. The present invention is not limited to the above-described exemplary embodiments. The essential elements of the present invention are as follows. 
         [0210]    (1) The silicon substrate is patterned to form the portion in which the insulating film is buried and the silicon portion. 
         [0211]    (2) The contact is formed in the silicon substrate from the rear surface side thereof in a self-aligned manner. 
         [0212]      FIG. 49  shows only the essential components of the present invention. Optional components are denoted by  128 .