Semiconductor device having multiple source regions

In a region on the left hand of FIG. 1 with respect to the gate electrode (107), a first source region (103a), a body-potential drawing region (105) and a second source region (103b) are formed in this order along the vertical direction of this figure. The first and second source regions (103a, 103b) are of n.sup.+ type, and the body-potential drawing region (105) is of p.sup.+ type. In a thin-film transistor (100), the body-potential drawing region (105) can draw and fix a body potential.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an SOI (Semiconductor On Insulator) type
 thin-film transistor, and more particularly to a technique for fixing a
 potential of its body (referred to as "body potential" hereinafter).
 2. Description of the Background Art
 FIG. 18 is a cross-sectional view illustrating a structure of a general SOI
 type thin-film transistor 900. The thin-film transistor 900 is formed as
 an n-channel MOS transistor in a semiconductor layer 902 provided on an
 insulator 901. The insulator 901 may be formed as a buried layer in a
 not-shown semiconductor substrate.
 In the p.sup.- type semiconductor layer 902, a source region 903 and a
 drain region 904 both of which are n.sup.+ type semiconductor layers are
 provided at a distance from each other. The semiconductor layer 902
 sandwiched by the source region 903 and the drain region 904 is termed
 "body" of the thin-film transistor 900. Above the body, a gate electrode
 907 made of e.g., polysilicon is provided with a gate insulating film 906
 interposed therebetween.
 Since the semiconductor layer 902 is provided on the insulator 901, its
 body potential is in a floating state in the structure of FIG. 18. In this
 state, there are possibilities of generation of leak current and unstable
 operation of the thin-film transistor 900 due to variations in
 power-supply level and ground level and parasitic bipolar effect. The
 parasitic bipolar effect here refers simply to a phenomenon that positive
 holes created by impact ionization are accumulated in the body and the
 body potential thereby rises to increase a leak current in the thin-film
 transistor 900 as an n-channel MOS transistor.
 There may be a case where a cosmic ray such as an .alpha. ray enters the
 body to form a pair of an electron and a positive hole. Since the
 thin-film transistor 900 is used in a state where a channel is formed by
 inverting a surface of the body into n type, the positive hole is
 accumulated, though the electron is drawn out, to raise a possibility of
 inviting a rise of body potential.
 To solve the above problem, a technique for fixing the body potential has
 been proposed. FIG. 19 is a cross-sectional view of a first technique in
 the prior art, illustrating a structure of a thin-film transistor 800 and
 a structure for fixing its body potential. The thin-film transistor 800
 comprises a p.sup.- type semiconductor layer 802 as a body formed on an
 insulator 801 and a source region 803 and a drain region 804 both of which
 are of n.sup.+ type and provided thereabove. Above the body, a gate
 electrode 807 is provided with a gate insulating film 806 interposed
 therebetween.
 Alongside the thin-film transistor 800, an isolation oxide film 809 is
 formed by LOCOS oxidization of the semiconductor layer 802. Below the
 isolation oxide film 809, above the insulator 801, a region 805a is formed
 by enhancing the conductivity of the semiconductor layer 802. On the
 opposite side of the thin-film transistor 800 with respect to the
 isolation oxide film 809, a p type region 805b and a p.sup.+ type region
 805c are layered on the insulator 801 in this order. The regions 805a,
 805b and 805c adjoin the semiconductor layer 802 in this order, and when a
 potential VB is applied to the region 805c, the body potential can be
 fixed at a position away from the thin-film transistor 800 with the
 isolation region 809 interposed.
 Since the first background-art technique, however, uses the isolation oxide
 film 809, it is not suitable for integration. Further, a structure much
 like that of FIG. 19, where the p type semiconductor layer is provided
 between the source region and the insulator to draw the positive hole, is
 disclosed in, for example, Japanese Patent Application Laid Open Gazette
 No. 6-232405.
 On the other hand, the thin-film transistor is often used with the
 potential applied to the source region (referred to simply as "source
 potential") and the body potential being equal, and on the premise of such
 a use, a structure for fixing the body potential can be formed locally in
 the source region. FIG. 20 is a plan view illustrating a structure of a
 thin-film transistor 700 that is advantageous from this viewpoint. The
 second technique in the background art is disclosed in, for example,
 "Silicon-on-insulator technology: materials to VLSI" by J. P. Colinge
 (Kluwer Academic Publishers, 2nd Ed.).
 With the gate electrode 707 centered, on the left hand of this figure
 provided are an n.sup.+ type source region 703 and p.sup.+ type
 body-potential drawing regions 705a and 705b which sandwich the region 703
 vertically in this figure, and on the right hand of this figure provided
 is a drain region 704. A contact structure for supplying the body
 potential and the source potential is formed at a contact region 310
 provided covering part of the body-potential drawing regions 705a and 705b
 across the source region 703. This structure eliminates the necessity of
 the LOCOS oxide film used in the first background-art technique, thereby
 being suitable for integration.
 The second background-art technique, however, has great problems as
 follows. The first problem is due to the position of the body-potential
 drawing region 705a. The body is provided in the back of the gate
 electrode 707 in this figure, though not shown, and a channel is formed
 mainly in a portion surrounded by the source region 703, the drain region
 704 and the gate electrode 707. From this portion, the positive hole
 should be drawn.
 In the structure of FIG. 20, the body-potential drawing regions 705a and
 705b are positioned at an end of the source region 703 along a direction
 where the gate electrode 707 extends (in a vertical direction of this
 figure). Therefore, in order to effectively draw the positive hole from
 the body, a pair of body-potential drawing regions 705a and 705b are
 needed. For example, if the body-potential drawing region 705a is not
 provided, the body-potential drawing region 705b can not effectively draw
 the positive hole from a portion on the upper side of this figure in the
 body. This needs a larger area for the body-potential drawing regions 705a
 and 705b, and a portion which does not function as a channel in a
 direction (gate width) where the gate electrode 707 extends increases in
 width. That inhibits integration of the thin-film transistor.
 The second problem becomes pronounced in a case where the gate electrode
 707 is made of polysilicon and the like. Impurity implantations for
 forming the source region and the drain region are performed, in general,
 by using the gate electrode and the gate insulating film provided between
 the gate electrode and the body as a mask in a self-aligned manner. When
 an impurity to be implanted into the polysilicon to enhance the
 conductivity as the gate electrode is equivalent in conductivity to those
 for the source region and the drain region, the conductivity of the gate
 electrode is obtained by impurity implantation for forming the source
 region and the drain region.
 If a p type impurity is implanted to also form the p.sup.+ type
 body-potential drawing regions 705a and 705b of FIG. 20 in a self-aligned
 manner, however, an effect of the n type impurity which the gate electrode
 707 has is counter-doped. The gate electrode 707 comprises a straight
 portion 707b which is straight in a direction where the gate electrode 707
 extends and a contact portion 707a in which a contact structure is formed
 to apply a predetermined electrical signal to the gate electrode. The
 conductivity is degraded in portions 401a and 401b of the straight portion
 707b near the p.sup.+ type body-potential drawing regions 705a and 705b at
 an end (on the left hand of FIG. 20) in a direction horizontal direction
 of this figure) orthogonal to the direction where the straight portion
 707b extends. This phenomenon becomes especially pronounced in the portion
 401b near the contact portion 707b because transmission of signals to the
 straight portion 707b is degraded.
 Even if a mask is used to selectively implant the p type impurity to form
 the p.sup.+ type body-potential drawing regions 705a and 705b out of the
 self-aligned manner, a margin for alignment of the mask is needed in order
 to surely bring the body-potential drawing regions 705a and 705b into
 contact with the body, and implantation of the p type impurity into the
 gate electrode 707 can not be virtually avoided.
 SUMMARY OF THE INVENTION
 The present invention is directed to a semiconductor device. According to a
 first aspect of the present invention, the semiconductor device comprises:
 an insulator; a first semiconductor layer of a first conductivity type,
 having a first main surface adjacent to the insulator and a second main
 surface on the opposite side to the first main surface; an insulating
 layer provided on the second main surface; a control electrode provided on
 the insulating layer extending in a first direction, immediately below
 which the first semiconductor layer is divided into first and second
 regions along a second direction orthogonal to the first direction; a
 second semiconductor layer of a second conductivity type opposite to the
 first conductivity type provided in the first region; and a third
 semiconductor layer, a fourth semiconductor layer and a fifth
 semiconductor layer of the first conductivity type, the second
 conductivity type and the first conductivity type, respectively, provided
 in the second region extending from the second main surface to the first
 main surface and exposed in this order on the second main surface along a
 side end of the control electrode on a side of the first region.
 Preferably, the third, fourth and fifth semiconductor layers have the same
 length along the second direction.
 Preferably, the length of the fourth semiconductor layer along the second
 direction is shorter than those of the third and fifth semiconductor
 layers along the second direction.
 Preferably, the third semiconductor layer and the fifth semiconductor layer
 are connected farther away from the control electrode than an end portion
 of the fourth semiconductor layer away from the control electrode.
 According to a second aspect of the present invention, in the semiconductor
 device of the first aspect, the control electrode has a straight portion
 extending in the first direction; and a wide portion widened in the second
 direction at a position of the fourth semiconductor layer in the first
 direction.
 Preferably, the length of the fourth semiconductor layer along the second
 direction is shorter than those of the third and fifth semiconductor
 layers in the second direction.
 Preferably, the third semiconductor layer and the fifth semiconductor layer
 are connected farther away from the control electrode than an end portion
 of the fourth semiconductor layer away from the control electrode.
 According to a third aspect of the present invention, the semiconductor
 device comprises: a pair of semiconductor elements each including an
 insulator; a first semiconductor layer of a first conductivity type,
 having a first main surface adjacent to the insulator and a second main
 surface on the opposite side to the first main surface; an insulating
 layer provided on the second main surface; a control electrode provided on
 the insulating layer extending in a first direction, immediately below
 which the first semiconductor layer is divide into first and second
 regions along a second direction orthogonal to the first direction, and
 having a straight portion extending in the first direction and a wide
 portion widened in the second direction at a position of the fourth
 semiconductor layer in the first direction; a second semiconductor layer
 of a second conductivity type opposite to the first conductivity type
 provided in the first region; and a third semiconductor layer, a fourth
 semiconductor layer and a fifth semiconductor layer of the first
 conductivity type, the second conductivity type and the first conductivity
 type, respectively, provided in the second region extending from the
 second main surface to the first main surface and exposed in this order on
 the second main surface along a side end of the control electrode on a
 side of the first region, and a pair of the wide portions being widened in
 opposite directions to each other.
 Preferably, the pair of wide portions are widened in such directions as to
 go away from a boundary between the pair of semiconductor elements.
 Preferably, the third semiconductor layer and the fifth semiconductor layer
 are connected farther away from the control electrode than an end portion
 of the fourth semiconductor layer away from the control electrode.
 The present invention is also directed to a method of manufacturing a
 semiconductor device. According to a fourth aspect of the present
 invention, the method comprises the steps of: (a) forming a first
 semiconductor layer of a first conductivity type on an insulator, which
 has a first main surface adjacent to the insulator and a second main
 surface on the opposite side to the first main surface; (b) forming a
 first insulating layer on the second main surface of the first
 semiconductor layer; (c) forming a first control electrode having a
 straight portion provided on the first insulating layer extending in a
 first direction and a wide portion extending from the straight portion
 along a second direction opposite to the first direction; (d) introducing
 a first impurity of the first conductivity type into the first
 semiconductor layer using at least an end of the wide portion of the first
 control electrode as a mask to form a second semiconductor layer; and (e)
 introducing a second impurity of a second conductivity type opposite to
 the first conductivity type into the first semiconductor layer using the
 first control electrode and a shield covering the second semiconductor
 layer as masks to form a third semiconductor layer and a fourth
 semiconductor layer of the second conductivity type sandwiching the first
 semiconductor layer below the straight portion.
 According to a fifth aspect of the present invention, in the method of the
 fourth aspect, the step (a) has the step of forming a fifth semiconductor
 layer of the second conductivity type, which has a first main surface
 adjacent to the insulator and a second main surface on the opposite side
 to the first main surface thereof and is adjacent to the first
 semiconductor layer with a boundary therebetween, the step (b) has the
 step of forming a second insulating layer on the second main surface of
 the fifth semiconductor layer, the step (c) has the step of forming a
 second control electrode which has a straight portion provided on the
 second insulating layer extending in the first direction and a wide
 portion extending from the straight portion along the second direction,
 the first impurity is introduced in the step (d) using a first shield
 covering a position at a predetermined distance or more from an end of the
 wide portion of the first control electrode, a range from the straight
 portion of the first control electrode to the boundary and a range within
 a predetermined distance from an end of the wide portion of the second
 control electrode, the second impurity is introduced in the step (e) using
 a second shield covering a position at a predetermined distance or more
 from the end of the wide portion of the second control electrode, a range
 from the straight portion of the second control electrode to the boundary
 and a range within a predetermined distance from the end of the wide
 portion of the first control electrode, the method further comprising the
 steps of: (f) introducing a third impurity of the first conductivity type
 using a third shield having the same pattern as the first shield before
 the steps (d) and (e); and (g) introducing a fourth impurity of the second
 conductivity type using a fourth shield having the same pattern as the
 second shield before the steps (d) and (e).
 Preferably, the wide portion of the first control electrode and the wide
 portion of the second control electrode are extended in opposite
 directions.
 Preferably, both the first control electrode and the second control
 electrode are widened in such directions as to go away from the boundary.
 In the semiconductor device of the first aspect of the present invention,
 since the fourth semiconductor layer is provided over the whole thickness
 of the first semiconductor layer, the potential of the first semiconductor
 layer, i.e., the body potential can be fixed by the fourth semiconductor
 layer. Since the fourth semiconductor layer is sandwiched between the
 third and fifth semiconductor layers along the direction where the control
 electrode extends, drawing of carries associated with fixing of the body
 potential can be performed more effectively from the first semiconductor
 layer between the second and third semiconductor layers and from the first
 semiconductor layer between the second and fifth semiconductor layers, as
 compared with a case where the fourth semiconductor layer is positioned at
 an end portion in the direction where the control electrode extends, and
 does not require a large area of the fourth semiconductor layer.
 Furthermore, since the third, fourth and fifth semiconductor layers are
 formed over the whole thickness of the first semiconductor layer, it is
 possible to suppress an effect of a pn junction, e.g., parasite of
 junction capacitance.
 In the semiconductor device of the second aspect of the present invention,
 since the conductivity of the straight portion is hard to deteriorate even
 if the conductivity of the wide portion in the control electrode
 positioned near the fourth semiconductor layer is deteriorated, it is
 possible to avoid deterioration of function of the control electrode.
 In the semiconductor device of the third aspect and the method of
 manufacturing semiconductor device of the sixth aspect of the present
 invention, wiring of a power-supply line can be easily performed when an
 inverter is constituted of a pair of semiconductor devices.
 In the method of manufacturing a semiconductor device of the fourth aspect
 of the present invention, since the first impurity is introduced into the
 fist semiconductor layer by using the wide portion as a mask in the step
 (d), it is possible to avoid introduction of the first impurity into the
 straight portion when the second semiconductor layer which is adopted as a
 region for drawing the body potential is formed. Therefore, the
 conductivity of the straight portion is not deteriorated. Further, since
 introduction of the second impurity into the second semiconductor layer is
 suppressed in the step (e), the conductivity of a region for drawing the
 body potential is not deteriorated.
 In the method of manufacturing a semiconductor device of the fifth aspect
 of the present invention, since the first and third shields have the same
 pattern and the second and fourth shields have the same pattern, the LDD
 structure can be obtained while the photomask is diverted.
 An object of the present invention is to provide a new structure for
 drawing the body potential of the SOI type thin-film transistor and a
 method of manufacturing the same.
 These and other objects, features, aspects and advantages of the present
 invention will become more apparent from the following detailed
 description of the present invention when taken in conjunction with the
 accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The First Preferred Embodiment
 FIG. 1 is a plan view showing a structure of a thin-film transistor 100 in
 accordance with the first preferred embodiment of the present invention,
 and FIGS. 2 and 3 are cross-sectional views showing sections taken along
 the positions Q1--Q1 and Q2--Q2 of FIG. 1, respectively.
 The thin-film transistor 100 is formed on an insulator 101 which may be
 formed as a buried layer in a not-shown semiconductor substrate.
 Specifically, a lower surface of a p.sup.- type semiconductor layer 102
 adjoins the insulator 101 and on an upper surface thereof, a straight
 portion 107a of a gate electrode 107 is formed with a gate insulating film
 106 interposed therebetween. The gate electrode 107 has a contact portion
 107b in which a contact structure is formed to apply a predetermined
 electrode signal to the gate electrode at both ends of the straight
 portion 107a. Instead of paired contact portions 107b, only one of them
 may be provided.
 The straight portion 107a of the gate electrode 107 extends in a first
 direction which is vertical in FIG. 1, immediately below which the
 semiconductor layer 102 is divided along a second direction which is
 horizontal of FIGS. 1 to 3. In the semiconductor layer 102 on the right
 hand of FIGS. 1 to 3, an n.sup.+ type drain region 104 is provided
 extending from the upper surface to the lower surface of the semiconductor
 layer 102.
 On the other hand, in the semiconductor layer 102 on the left hand of FIGS.
 1 to 3, a first source region 103a, a body-potential drawing region 105
 and a second source region 103b are formed in this order in the first
 direction. The first and second source regions 103a and 103b are of
 n.sup.+ type and the body-potential drawing region 105 is of p.sup.+ type.
 These are formed extending from the upper surface to the lower surface of
 the semiconductor layer 102. The positions Q1--Q1 and Q2--Q2 are found at
 positions in the first direction where the first source region 103a exists
 and the body-potential drawing region 105 exists, respectively.
 In the thin-film transistor 100, since the body-potential drawing region
 105 is provided over the whole thickness of the semiconductor layer 102, a
 potential of the semiconductor layer 102, i.e., the body potential, can be
 fixed by the body-potential drawing region 105. For example, as shown in
 FIG. 1, when a contact structure is formed in a contact region 301
 covering part of the first source region 103a and part of the second
 source region 103b across the body-potential drawing region 105, the
 source potential can be used also as the body potential.
 Since the body-potential drawing region 105 is disposed between the first
 and second source regions 103a and 103b along a direction where the
 straight portion 107a of the gate electrode 107 extends, drawing of a
 positive hole by the body-potential drawing region 105 can be more
 effectively performed from the semiconductor layer 102 between the first
 source region 103a and the drain region 104 and the semiconductor layer
 102 between the second source region 103b and the drain region 104, as
 compared with the case where the body-potential drawing regions 705a and
 705b are disposed at ends of the first direction where the straight
 portion 707b extends in the thin-film transistor 700 having the structure
 of FIG. 20, to thereby solve the first problem. In other words, an area of
 the body-potential drawing region 105 relative to the length of the gate
 electrode 107 along the first direction can be reduced.
 Further, since the first source region 103a, the body-potential drawing
 region 105 and the second source region 103b are formed over the whole
 thickness of the semiconductor layer 102, unlike the thin-film transistor
 800 having the structure of FIG. 19 where the semiconductor layer 802
 exists between the source region 803 and the insulator 801, it is possible
 to suppress an effect of a pn junction, e.g., parasite of junction
 capacitance.
 The Second Preferred Embodiment
 FIG. 4 is a plan view showing a structure of a thin-film transistor 110 in
 accordance with the second preferred embodiment of the present invention,
 and FIGS. 5 and 6 are cross-sectional views showing sections taken along
 the positions Q3--Q3 and Q4--Q4 of FIG. 4, respectively.
 The thin-film transistor 110 is different from the thin-film transistor 100
 of the first preferred embodiment only in structure where the source
 region and the body-potential drawing region are formed in the
 semiconductor layer on the left hand with a portion immediately below the
 straight portion 107a of the gate electrode 107 as a boundary. While the
 first and second source regions 103a and 103b are separated from each
 other by the body-potential drawing region 105 in the thin-film transistor
 100, a source region 103 is connected on a side of the body-potential
 drawing region 105 opposite to the gate electrode 107 in the thin-film
 transistor 110 as shown in FIG. 4. The source region 103 and the
 body-potential region 105 are formed extending from the upper surface to
 the lower surface of the semiconductor layer 102, like in the first
 preferred embodiment.
 The positions Q3--Q3 and Q4--Q4 are found at positions in the first
 direction along the gate electrode 107 where the first source region 103
 exists and the body-potential drawing region 105 exists, respectively. As
 shown in FIG. 6, since a right end of the body-potential drawing region
 105 in this figure comes into contact with the semiconductor layer 102,
 this preferred embodiment can produce the same effect as the first
 preferred embodiment.
 Further, in this case, a contact structure for applying the source
 potential as the body potential may not include a left end of the
 body-potential drawing region 105 in this figure like a contact region
 302, and may include the left end of the body-potential drawing region 105
 in this figure like a contact region 303.
 The Third Preferred Embodiment
 FIG. 7 is a plan view showing a structure of a thin-film transistor 120 in
 accordance with the third preferred embodiment of the present invention,
 and FIGS. 8 and 9 are cross-sectional views showing sections taken along
 the positions Q5--Q5 and Q6--Q6 of FIG. 7, respectively.
 The thin-film transistor 120 is different from the thin-film transistor 110
 of the second preferred embodiment in that a wide portion 107c is attached
 to the straight portion 107a of the gate electrode 107. The wide portion
 107b is widened from the straight portion 107a leftward in this figure at
 the position of the body-potential drawing region 105 in the first
 direction. Because of existence of the wide portion 107c, the right end of
 the body-potential drawing region 105 in this figure moves leftward. In
 other words, the body-potential drawing region 105 is surrounded by the
 source region 103 and the semiconductor layer 102 below the wide portion
 107b.
 In this structure, even if the p type impurity implantation for forming the
 body-potential drawing region 105 is performed also to the wide portion
 107c of the gate electrode 107, the conductivity of the straight portion
 107a is kept. Therefore, the second problem can be also solved. It is
 natural that the left end of the body-potential drawing region 105 reaches
 a left end of the source region 103 in this figure. A specific method of
 forming the body-potential drawing region 105 will be discussed in the
 fourth preferred embodiment.
 In the first to third preferred embodiments, there may be a case where a
 first n type impurity implantation is performed by using the gate
 electrode 107 as a mask, side walls are formed on the gate electrode 107
 and a second n type impurity implantation in which the impurity
 concentration is higher than that of the first n type impurity
 implantation is performed by using the side walls and the gate electrode
 107 as masks, to form an LDD (Light Doped Drain) structure. Further, these
 preferred embodiments can be naturally applied to a p channel MOS
 transistor.
 The Fourth Preferred Embodiment
 FIG. 10 is a plan view showing a structure of a CMOS transistor in
 accordance with the fourth preferred embodiment of the present invention,
 and FIGS. 17A and 17B are cross-sectional views showing sections taken
 along the positions Q7--Q7 and Q8--Q8 of FIG. 10, respectively. A PMOS
 transistor having an LDD structure is formed in a region A1 and an NMOS
 transistor having an LDD structure is formed in a region A2. The regions
 A1 and A2 adjoin each other, forming a boundary S. The PMOS transistor
 comprises a p.sup.+ type source region 34, a p.sup.+ type drain region 44
 and a p.sup.+ type gate electrode 71, and the NMOS transistor comprises an
 n.sup.+ type source region 33, an n.sup.+ type drain region 43 and an
 n.sup.+ type gate electrode 74. The source region 34 and the drain region
 44 are provided to sandwich a semiconductor layer 21 below the gate
 electrode 71, and the source region 33 and the drain region 43 are
 provided to sandwich a semiconductor layer 22 below the gate electrode 74.
 The gate electrode 71 comprises a straight portion 72 and a wide portion
 73, corresponding to the straight portion 107a and the wide portion 107c
 of the thin-film transistor 120, respectively. Similarly, the gate
 electrode 74 comprises a straight portion 75 and a wide portion 76. In
 FIG. 10, for simple illustration, the side walls 77 and 78 adjacent to the
 gate electrode 71 and 74, respectively, are included in the gate
 electrodes 71 and 74.
 Like the body-potential drawing region 105, an n.sup.+ type body-potential
 drawing region 53 is surrounded by the source region 34 and the
 semiconductor layer 21 below the wide portion 73. A p.sup.+ type
 body-potential drawing region 54 is surrounded by the source region 33 and
 the semiconductor layer 22 below the wide portion 76.
 Since the wide portions 73 and 76 protrude to opposite sides with respect
 to the boundary S, a connecting line L1 connected to both the source
 region 34 and the body-potential drawing region 53 of the PMOS transistor
 at a contact 305 (neither the line L1 nor the contact 305 is shown in FIG.
 17B) and a connecting line L2 connected to both the source region 33 and
 the body-potential drawing region 54 of the NMOS transistor at a contact
 306 (neither the line L2 nor the contact 306 is shown in FIG. 17B) are
 extended towards opposite directions to each other (leftward and rightward
 in this figure) with respect to the boundary S.
 Further, the gate electrodes 71 and 74 are connected in common with a
 connecting line L4, and the drain regions 43 and 44 are connected to a
 connecting line L3 with a contact 307 across the boundary S (neither the
 line L3 nor the contact 307 is shown in FIG. 17A). The connecting lines L3
 and L4 are extended towards opposite directions (upward and downward in
 this figure) with respect to the respective CMOS transistors.
 Even when the connecting lines L1 and L2 are connected to a high potential
 and a low potential, respectively, a CMOS inverter can be obtained where
 power-supply lines for supplying these potentials are easily placed
 without crossing the gate electrodes 71 and 74 and the connecting line L3.
 FIGS. 11A to 16B are cross-sectional views sequentially showing the steps
 of manufacturing the structure of FIGS. 10 and 17A and 17B. FIGS. 11A,
 12A, 13A, 14A, 15A and 16A are cross-sectional views taken along the
 position Q7--Q7 of FIG. 10, and FIGS. 11B, 12B, 13B, 14B, 15B and 16B are
 cross-sectional views taken along the position Q8--Q8 of FIG. 10.
 In FIGS. 11A and 11B, the n.sup.- type semiconductor layer 21 and the
 p.sup.- type semiconductor layer 22 are formed adjacently to each other at
 the boundary S on an insulator 1 which may be formed as a buried layer in
 a not-shown semiconductor substrate. On the semiconductor layers 21 and
 22, the gate electrodes 71 and 74 are formed, respectively, with the gate
 insulating films 6 interposed. As a material of the insulator 1, for
 example, a silicon oxide is used. As a material of the semiconductor
 layers 21 and 22, for example, a silicon is used. As a material of the
 gate electrodes 71 and 74, for example, a polysilicon is used.
 In FIG. 11A, only the straight portions 72 and 75 appear as the gate
 electrodes 71 and 74, respectively, while in FIG. 11B, the wide portions
 73 and 76 as well as the straight portions 72 and 75 appear as the gate
 electrodes 71 and 74, respectively. The straight portions 72 and 75 are
 extended almost in parallel to the boundary S.
 Next performed is an impurity implantation for forming a low-concentration
 impurity region in the LDD structure of the NMOS transistor. For example,
 arsenic implantation is performed (see FIGS. 12A and 12B). In this case, a
 resist 81 is so formed as to entirely cover the structure formed on the
 region A1 at the position Q7--Q7 as shown in FIG. 12A and cover also a
 portion where the body-potential drawing region 54 of the NMOS transistor
 is to be formed later at the position Q8--Q8 as shown in FIG. 12B. In the
 region A2, arsenic is introduced into a surface of the semiconductor layer
 22 ranging from the boundary S to the straight portion 75, to form an
 n.sup.- type semiconductor region 41.
 As shown in FIG. 12B in more detail, the resist 81 covers a range from an
 end 76E of the wide portion 76 farther away from the boundary S to a
 portion at a certain distance from the boundary S. With the shape of the
 resist 81, arsenic is implanted into a surface of the semiconductor layer
 22 at a certain distance from the end 76E of the wide portion 76, to form
 an n.sup.- type semiconductor region 31. In FIG. 12A, the semiconductor
 region 31 extends to an end 75E of the straight portion 75 farther away
 from the boundary S.
 At the portion Q8--Q8, the resist 81 is partially opened in the region A1
 in consideration of use of a photomask as discussed later. As shown in
 FIG. 12B in more detail, the resist 81 is opened in a range from an end
 73E of the wide portion 73 farther away from the boundary S to a portion
 at a certain distance from the boundary S. With this opening, arsenic is
 introduced into a surface of the semiconductor layer 21, to form an
 n.sup.- semiconductor region 51.
 In an impurity implantation, usually, an impurity is diffused also below
 the masked position. Therefore, the semiconductor region 51 is slightly
 extended to a position closer to the boundary S than the end 73E of the
 wide portion 73, the semiconductor region 41 is slightly extended to a
 position farther away from the boundary S than an end 75S of the wide
 portion 75, and the semiconductor region 31 is slightly extended to a
 position closer to the boundary S than the end 75E of the wide portion 75.
 Through the above impurity implantation, arsenic is introduced into at
 least the straight portion 75 in the gate electrode 74, to enhance the
 conductivity thereof. In some cases, the arsenic is not necessarily
 introduced into a portion in the vicinity of the end 76E of the wide
 portion 76. That is because the resist 81 also covers the end 76E in order
 to avoid extension of the semiconductor region 31 to a portion below the
 end 76E of the wide portion 76. Since the wide portion 76 serves as a mask
 for disposing the body-potential drawing region 54 so as to be away from
 the straight portion 75 rather than as a gate electrode, the conductivity
 of the wide portion 76 is not needed to be high.
 Next, the resist 81 is removed, and then an impurity implantation is
 performed to form a low-concentration impurity region in the LDD structure
 of the PMOS transistor. For example, an ion implantation using boron
 fluoride (BF.sub.2) is performed (see FIGS. 13A and 13B). At this time, a
 resist 82 is formed, which covers the whole structure formed on the region
 A2 at the position Q7--Q7 as shown in FIG. 13A and covers a position where
 the body-potential drawing region 53 of the PMOS transistor is to be
 formed later at the position Q8--Q8 as shown in FIG. 13B. The resist 82
 can adopt a pattern complementary to that of the resist 81. In the region
 A1, boron is introduced into the surface of the semiconductor layer 21
 ranging from the boundary S to the straight portion 72, to form a p.sup.-
 type semiconductor region 42.
 As shown in FIG. 13B in more detail, the resist 82 covers the end 73E of
 the wide portion and the semiconductor region 51. An end of the
 semiconductor region 51 farther away from the boundary S may be exposed.
 With the shape of the resist 82, boron is implanted into the surface of
 the semiconductor layer 21 at a certain distance from the end 73E of the
 wide portion 73 or further a surface of the end of the semiconductor
 region 51 farther away from the boundary S, to form a p.sup.- type
 semiconductor region 32. In FIG. 13A, the semiconductor region 32 extends
 to an end 72E of the straight portion 72 farther away from the boundary S.
 At the portion Q8--Q8, the resist 82 is partially opened in the region A2
 in consideration of use of a photomask as discussed later. As shown in
 FIG. 13B in more detail, the resist 82 is opened in a range from the end
 76E of the wide portion 76 to an end of the semiconductor region 31 closer
 to the boundary S. With this opening, boron is introduced into the surface
 of the semiconductor layer 22 or further the end of the semiconductor
 region 31 closer to the boundary S, to form a p.sup.- semiconductor region
 52.
 In an impurity implantation, usually, an impurity is diffused also below
 the masked position. Therefore, the semiconductor region 52 is slightly
 extended to a position closer to the boundary S than the end 76E of the
 wide portion 76, the semiconductor region 42 is slightly extended to a
 position farther away from the boundary S than an end 72S of the straight
 portion 72, and the semiconductor region 32 is slightly extended to a
 position closer to the boundary S than the end 72E of the straight portion
 72.
 Through the above impurity implantation, boron is introduced into at least
 the straight portion 72 in the gate electrode 71, to enhance the
 conductivity thereof. In some cases, the boron is not necessarily
 introduced into a portion in the vicinity of the end 73E of the wide
 portion 73. That is because the resist 82 also covers the end 73E in order
 to avoid extension of the semiconductor region 32 to a portion below the
 end 73E of the wide portion 73. Since the wide portion 73 serves as a mask
 for disposing the body-potential drawing region 53 so as to be away from
 the straight portion 72 rather than as a gate electrode, the conductivity
 of the wide portion 73 is not needed to be high. Further, boron may be
 introduced into the end 76E of the wide portion 76. That is because the
 conductivity at this position is not needed to be high as mentioned
 earlier.
 Next, the resist 82 is removed, and then the side walls 77 and 78 are
 formed by a well-known method (FIGS. 14A and 14B). In FIG. 14A, the side
 walls 77 appear on both ends 72S and 72E of the straight portion 72 and
 the side walls 78 appear on both ends 75S and 75E of the straight portion
 75. In FIG. 14B, the side walls 77 appear on the end 72S of the straight
 portion 72 and the end 73E of the wide portion 73 and the side walls 78
 appear on end 75S of the straight portion 75 and the end 76E of the wide
 portion 76.
 Next, an impurity implantation is performed to form a high-concentration
 impurity region in the LDD structure of the NMOS transistor. For example,
 an ion implantation using arsenic is performed (see FIGS. 15A and 15B). A
 resist 83 adopts the same pattern as that of the resist 81 shown in FIGS.
 12A and 12B. At the position Q7--Q7 as shown in FIG. 15A, the n.sup.+ type
 source region 33 and the n.sup.+ type drain region 43 which have slight
 wraparounds below the side walls 78 are formed in the semiconductor layer
 22 while the n.sup.- type semiconductor regions 31 and 41 are left below
 the straight portion 75 and the side walls 78. At the position Q8--Q8 as
 shown in FIG. 15B, the n.sup.+ type body-potential drawing region 53 is so
 formed as to be surrounded by the semiconductor layer 21.
 The resist 81 of FIGS. 12A and 12B adopts the same pattern as that of the
 resist 83 in order to divert the photomask for forming the body-potential
 drawing region 53. The existence of the semiconductor layer 51 does not
 inhibit formation of the body-potential drawing region 53 having the same
 conductivity and higher concentration. It is natural that the pattern of
 the resist 81 may cover the whole region A1 at the position Q8--Q8 like at
 the position Q7--Q7 if the above advantage in terms of photomask is not
 required.
 On the other hand, the resist 83 inhibits formation of the source region 33
 in a range within a certain distance from the wide portion 76, in order
 not to inhibit formation of the p.sup.+ type body-potential drawing region
 54 in the subsequent step by arsenic implantation in the step of FIGS. 15A
 and 15B. As mentioned earlier, arsenic may not be introduced into the end
 76E of the wide portion 76 and arsenic may be introduced into the end 73E
 of the wide portion 73. On the other hand, the conductivity of the
 straight portion 75 is further enhanced.
 Next, the resist 83 is removed, and then an impurity implantation is
 performed to form a high-concentration impurity region in the LDD
 structure of the PMOS transistor. For example, an ion implantation using
 boron fluoride (BF) is performed (see FIGS. 16A and 16B). A resist 84
 adopts the same pattern as that of the resist 82 shown in FIGS. 13A and
 13B. At the position Q7--Q7 as shown in FIG. 16A, the p.sup.+ type source
 region 34 and the p.sup.+ type drain region 44 which have slight
 wraparounds below the side walls 77 are formed in the semiconductor layer
 21 while the p.sup.- type semiconductor regions 32 and 42 are left below
 the straight portion 72 and the side walls 77. At the position Q8--Q8 as
 shown in FIG. 16B, the p.sup.+ type body-potential drawing region 54 is so
 formed as to be surrounded by the semiconductor layer 22 and the source
 region 33. The resist 82 of FIGS. 13A and 13B adopts the same pattern as
 that of the resist 84 in order to divert the photomask for forming the
 body-potential drawing region 54. It is natural that the pattern of the
 resist 82 may cover the whole region A2 at the position Q8--Q8 like at the
 position Q7--Q7 if the above advantage in terms of photomask is not
 required.
 On the other hand, the resist 84 inhibits formation of the source region 34
 in a range within a certain distance from the wide portion 73, in order
 not to counter-dope the n.sup.+ type body-potential drawing region 53
 formed in the preceding step by boron fluoride implantation in the step of
 FIGS. 16A and 16B. As mentioned earlier, boron may not be introduced into
 the end 73E of the wide portion 73 and boron may be introduced into the
 end 76E of the wide portion 76. On the other hand, the conductivity of the
 straight portion 72 is further enhanced.
 Then, removing the resist 84 from the structure of FIGS. 16A and 16B, the
 structure of FIGS. 17A and 17B can be obtained.
 Thus, in this preferred embodiment, since the impurities for forming the
 body-potential drawing regions 53 and 54 are introduced into the
 semiconductor layers 21 and 22 by using the wide portions 73 and 75 and
 the side walls 77 and 78 as masks, it is possible to dispose the
 body-potential drawing regions 53 and 54 so as to be away from the
 straight portions 72 and 75 of the gate electrodes 71 and 74. Formations
 of the body-potential drawing regions 53 and 54 do not invite count doping
 of the straight portions 72 and 75 and the conductivities of the gate
 electrodes 71 and 74 are not deteriorated. It is clearly advantageous that
 the conductivities of the gate electrodes 71 and 74 should not be
 deteriorated wherever the wide portions 73 and 75 are disposed along the
 directions where the straight portions 72 and 75 extend in the PMOS
 transistor and the NMOS transistor.
 In this preferred embodiment, though the semiconductor regions 51 and 52
 which are not needed in terms of electrical function are also formed in
 consideration of use of photomask, these semiconductor regions may not be
 formed as mentioned earlier. Further, the semiconductor regions 31, 32, 41
 or 42 may not be formed, not to adopt the LDD structure. In this case, the
 steps of introducing impurities by using the resists 81 and 82 as
 discussed with reference to FIGS. 12A and 12B and FIGS. 13A and 13B,
 respectively, are not needed. In this case, clearly, the body-potential
 drawing region 53 of the PMOS transistor can be formed in the same step as
 the source region 33 and the drain region 43 of the NMOS transistor are
 formed, and the body-potential drawing region 54 of the NMOS transistor
 can be formed in the same step as the source region 34 and the drain
 region 44 of the PMOS transistor are formed, to thereby produce an effect
 of avoiding deterioration in conductivity of the gate electrodes 71 and
 74.
 While the invention has been shown and described in detail, the foregoing
 description is in all aspects illustrative and not restrictive. It is
 therefore understood that numerous modifications and variations can be
 devised without departing from the scope of the invention.