Abstract:
The invention provides CCD type solid-state imaging apparatus comprises: photoelectric conversion elements; a plurality of first transfer paths extending in a first direction; and second transfer paths extending in a first direction; the first transfer paths and the second transfer paths respectively including a plurality of discretely formed first layer transfer electrode films and second layer transfer electrode films formed between the first layer transfer electrode films and whose ends are laminated on the ends of the adjacent first layer transfer electrode films via insulating films. The thickness of the insulating film between the first layer transfer electrode film and the second layer transfer electrode film constituting the second transfer path shown is smaller than the thickness of the insulating film between the first layer transfer electrode film and the second layer transfer electrode film constituting the first transfer path shown.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to solid-state imaging apparatus of the CCD (charge coupled device) type, and in particular to a CCD type solid-state imaging apparatus preferable for reducing power consumption and a manufacturing method for the same. 
     2. Description of the Related Art 
     For example, as described in JP-A-02-62170, CCD type solid-state imaging apparatus comprises a vertical transfer path (VCCD) for reading signal charges accumulated in a photoelectric conversion part in accordance with the light receiving quantity and transferring the signal charges in a first direction and a horizontal transfer path (HCCD) for receiving the signal charges transferred by the vertical transfer path, transferring the signal charges in a second direction, and outputting the signal charges from the solid-state imaging apparatus. 
       FIG. 17A  is a partial schematic cross-sectional view of a related art horizontal transfer path (HCCD).  FIG. 17B  is a partial schematic cross-sectional view of a related art vertical transfer path (VCCD). Both the horizontal transfer path and the vertical transfer path include transfer electrodes formed on a semiconductor substrate  1  via a gate insulating film  2 . The illustrated example shows a two-layer transfer electrode. On the horizontal transfer path ( FIG. 17A ), a plurality of first layer transfer electrode films  3  composed of polysilicon are formed apart from each other on the insulating film  2 . An oxidized insulating film  4  is formed on the surface of the first layer transfer electrode film  3  and second layer transfer electrode films  5  composed of polysilicon are formed so as to fill gaps between the first layer transfer electrode films  3 . On the surface of the second layer transfer electrode film  5  is formed an oxidized insulating film  6 . 
     On the vertical transfer path ( FIG. 17B ) also, a plurality of first layer transfer electrode films  8  are formed apart from each other on the gate insulating film  2 . An oxidized insulating film  9  is formed on the surface of the first layer transfer electrode film  8  and second layer transfer electrode films  10  composed of polysilicon are formed so as to fill gaps between the first layer transfer electrode films  8 . On the surface of the second layer transfer electrode film  10  is formed an oxidized insulating film  11 . 
     The horizontal transfer path and the vertical transfer path of related art CCD type solid-state imaging apparatus are manufactured in the same manufacturing process, so that the interlayer insulating film  4  of the horizontal transfer path has the same film thickness as the interlayer insulating film  9  of the vertical transfer path. 
     In case CCD type solid-state imaging apparatus is driven, signal charges in a single row of photoelectric conversion elements arranged in parallel with the horizontal transfer path are transferred to the horizontal transfer path. The horizontal transfer path is driven for transfer so as to output all signals corresponding to the signal charges in the single row from the solid-state imaging apparatus. Signal charges in the next row of photoelectric conversion elements are then transferred to the horizontal transfer path. This sequence is repeated. It is thus necessary to perform transfer driving of the horizontal transfer path at a higher speed than that of the vertical transfer path. 
     The horizontal transfer path that is typically driven at a high frequency of 12 to 36 MHz is one of the most power-consuming components of solid-state imaging apparatus. Power consumption of the horizontal transfer path is proportional to the square of the driving voltage of the horizontal transfer path (typically 0V for a low level and 3.3V for a high level). Reduction of the driving voltage can reduce the power consumption of the CCD type solid-state imaging apparatus. 
     Experiments by the inventor have proven that it is possible to reduce the driving voltage of the horizontal transfer path by providing a thinner interlayer insulating film  4  shown in  FIG. 17A . The problem is that, in the manufacturing process of related art CCD type solid-state imaging apparatus, the interlayer insulating film  4  of the horizontal transfer path has the same film thickness as the interlayer insulating film  9  of the vertical transfer path, so that the withstand voltage across the electrode films  8  and  10  of the vertical transfer path that requires a larger driving voltage (typically −8V for a low level and 0V for a high level) limits the reduction of the thickness of the interlayer insulating film  4 . 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide CCD type solid-state imaging apparatus capable of reducing the driving voltage of a horizontal transfer path to reduce power consumption and its manufacturing method. 
     The invention provides CCD type solid-state imaging apparatus comprising: a semiconductor substrate; a plurality of photoelectric conversion elements two-dimensionally arranged and formed on the surface of the semiconductor substrate so as to form a plurality of rows, each comprising a set of photoelectric conversion elements arranged in a first direction, being formed in a second direction orthogonal to the first direction; first transfer paths each of which is formed along each of the rows of the photoelectric conversion elements and comprises (i) first layer transfer electrode films separated in the first direction and (ii) second layer transfer electrode films formed between the first layer transfer electrode films and whose ends are laminated on ends of the first layer transfer electrode films of the first transfer paths via insulating films; and a second transfer path that receives light-receiving charges of the photoelectric conversion elements transferred by the first layer transfer paths and transfers the light-receiving charges in the second direction, the second transfer path comprising (iii) first layer transfer electrode films separated in the second direction and (iv) second layer transfer electrode films formed between the first layer transfer electrode films and whose ends are laminated on ends of the first layer transfer electrode films of the second transfer path via insulating films, wherein thickness of the insulating films between the first layer transfer electrode films and the second layer transfer electrode films constituting the second transfer path is smaller than that of the insulating films between the first layer transfer electrode films and the second layer transfer electrode films constituting the first transfer paths. 
     The invention provides a method for manufacturing CCD type solid-state imaging apparatus, the method comprising: forming a first insulating film on a semiconductor substrate; forming, on the first insulating film, a plurality of separated first layer transfer electrode films constituting the first transfer paths and the second transfer path; forming first oxidized films on surfaces of the first layer transfer electrode films by way of a first oxidization process; forming a second insulating film covering the first transfer paths and the second transfer path; removing the second insulating film on the first transfer path by way of a photolithography process; growing the first oxidized films on the surfaces of the first layer transfer electrode films on the first transfer path; removing the second insulating film on the second transfer path; and forming a plurality of second layer transfer electrode films filling gaps between the first layer transfer electrode films and whose ends are laminated on ends of the first layer transfer electrode films adjacent thereto. 
     The invention provides a method for manufacturing CCD type solid-state imaging apparatus, the method comprising: forming a first insulating film on a semiconductor substrate; forming, on the first insulating film, a plurality of separated first layer transfer electrode films constituting the first transfer paths and the second transfer path; forming first oxidized films on a surface of the first layer transfer electrode films by way of a first oxidization process; removing the first oxidized films on surfaces of the first layer transfer electrode films on the first transfer paths by way of a photolithography process; growing an oxidized film on each of surfaces of the first layer transfer electrode films on the first transfer paths and surfaces of the first layer transfer electrode films on the second transfer path by way of a second oxidization process; and forming a plurality of second layer transfer electrode films filling gaps between the first layer transfer electrode films and whose ends are laminated on ends of the first layer transfer electrode films adjacent thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a surface schematic view of CCD type solid-state imaging apparatus according to the first embodiment of the invention; 
         FIG. 2A  is a partial schematic cross-sectional view of the horizontal transfer path of the CCD type solid-state imaging apparatus shown in  FIG. 1 ; 
         FIG. 2B  is a partial schematic cross-sectional view of the vertical transfer path of the CCD type solid-state imaging apparatus shown in  FIG. 1 ; 
         FIG. 3  is a process chart showing the procedure for manufacturing CCD type solid-state imaging apparatus according to the first embodiment of the invention; 
         FIG. 4  is a process chart subsequent to  FIG. 3  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 5  is a process chart subsequent to  FIG. 4  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 6  is a process chart subsequent to  FIG. 5  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 7  is a process chart subsequent to  FIG. 6  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 8  is a process chart subsequent to  FIG. 7  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 9  is a process chart subsequent to  FIG. 8  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 10  is a process chart showing the procedure for manufacturing CCD type solid-state imaging apparatus according to the second embodiment of the invention; 
         FIG. 11  is a process chart subsequent to  FIG. 10  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 12  is a process chart subsequent to  FIG. 11  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 13  is a process chart subsequent to  FIG. 12  showing the procedure for manufacturing CCD type solid-state imaging apparatus; 
         FIG. 14  is a process chart subsequent to  FIG. 13  showing the procedure for manufacturing CCD type solid-state imaging apparatus according to the second embodiment of the invention; 
         FIG. 15  is a process chart subsequent to  FIG. 14  showing the procedure for manufacturing CCD type solid-state imaging apparatus according to the second embodiment of the invention; 
         FIG. 16A  is a partial schematic cross-sectional view of a horizontal transfer path of the CCD type solid-state imaging apparatus according to the third embodiment of the invention; 
         FIG. 16B  is a partial schematic cross-sectional view of a vertical transfer path of the CCD type solid-state imaging apparatus according to the third embodiment of the invention; 
         FIG. 17A  is a partial schematic cross-sectional view of a horizontal transfer path of the related art CCD type solid-state imaging apparatus; and 
         FIG. 17B  is a partial schematic cross-sectional view of a horizontal transfer path of the related art CCD type solid-state imaging apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention will be described referring to drawings. 
     First Embodiment 
       FIG. 1  is a surface schematic view of CCD type solid-state imaging apparatus according to the first embodiment of the invention. The CCD type solid-state imaging apparatus  20  comprises numerous photoelectric conversion elements  21  arranged and formed in the shape of a matrix, a single horizontal transfer path  22  provided at a bottom side, and a plurality of vertical transfer paths  23  arranged adjacent to the right side of the photoelectric conversion elements  21  arranged in vertical direction. 
       FIG. 2A  is a partial schematic cross-sectional view of the horizontal transfer path  22 .  FIG. 2B  is a partial schematic cross-sectional view of the vertical transfer path  23 . Both the horizontal transfer path  22  and the vertical transfer path  23  include transfer electrodes formed on a semiconductor substrate  30  via a gate insulating film  31 . The illustrated example shows a two-layer transfer electrode. On the horizontal transfer path  22 , a plurality of first layer transfer electrode films  32  composed of polysilicon are formed apart from each other on the insulating film  31 . A thin oxidized insulating film  34  is formed on the surface of the first layer transfer electrode film  32  and a plurality of second layer transfer electrode films  35  composed of polysilicon are formed so as to fill gaps between the first layer transfer electrode films  32 . On the surface of the second layer transfer electrode film  35  is formed an oxidized insulating film  36 . 
     On the vertical transfer path  23  also, a plurality of first layer transfer electrode films  32  are formed apart from each other on the gate insulating film  31  formed on the surface of the semiconductor substrate  30 . An oxidized insulating film  37  whose thickness is larger than that of the oxidized insulating film  34  is formed. Second layer transfer electrode films  35  composed of polysilicon are formed so as to fill gaps between the first layer transfer electrode films  32 . On the surface of the second layer transfer electrode film  35  is formed an oxidized insulating film  36 . 
     In this way, the film thickness b of the interlayer insulating film  34  between the electrode films  32 ,  35  of the horizontal transfer path  22  is reduced with respect to the film thickness a of the interlayer insulating film  37  between the electrode films  32 ,  35  of the vertical transfer path  23  in this embodiment. It is thus possible to reduce the driving voltage used to control transfer in the horizontal transfer path  22  thereby reducing the power consumption of the CCD type solid-state imaging apparatus  20 . The following describes a method for manufacturing the horizontal transfer path and the vertical transfer path shown in  FIGS. 2A and 2B . 
       FIGS. 3 through 9  are process charts showing the procedure for manufacturing a horizontal transfer path and a vertical transfer path. The illustrated transfer path range corresponds to the cross section along the line III-III shown in  FIG. 1 . While the vertical transfer path  23  and the horizontal transfer path  22  are shown to be coupled in communication in  FIGS. 3 through 9  (also  FIGS. 10 through 15  described later), this is to illustrate the manufacturing process where film thickness differs between the interlayer insulating films  34 ,  37 . In reality, the structure of the junction between the vertical transfer path  23  and the horizontal transfer path  22  is more complicated than illustrated although the details thereof are omitted. 
     As shown in  FIG. 3 , a gate insulating film  31  of the ONO (oxidized film-silicon nitride film-oxidized film) structure is formed on the semiconductor substrate  30 . On the gate insulating film  31  is formed first layer transfer electrode films  32  composed of polysilicon are formed apart from each other, and a thin thermally oxidized film  34  is formed on its surface. Then, an Si 3 N 4  film  45  is formed on the entire substrate. 
     Next, as shown in  FIG. 4 , a photoresist  46  is applied to the horizontal transfer path  22 . As shown in  FIG. 5 , a photolithography process is executed to remove the Si 3 N 4  film  45  on the vertical transfer path  23 . Then, as shown in  FIG. 6 , the photoresist  46  is removed. 
     Next, as shown in  FIG. 7 , when the oxidization process is executed, the oxidized film on the surface of the first layer transfer electrode film  32  of the first vertical transfer path  23  grows thick to form an oxidized film  37  shown in  FIG. 2B . Then, as shown in  FIG. 8 , the Si 3 N 4  film  45  on the horizontal transfer path  22  is removed using the same method as that used to remove the Si 3 N 4  film  45  in the vertical transfer path  23  in  FIGS. 3 and 4 . As shown in  FIG. 9 , second layer transfer electrode films  35  are formed between the first layer transfer electrode films  32  and its surface is thermally oxidized to form an oxidized film  36 . 
     With this manufacturing method, it is possible to increase the thickness of the interlayer insulating film  37  between the first and second layer transfer electrode films  32 ,  35  on the vertical transfer path  23  to withstand the high driving voltage of the vertical transfer path  23  as well as to reduce the thickness of the interlayer insulating film  34  between the first and second layer transfer electrode films  32 ,  35  on the horizontal transfer path to reduce the driving voltage of the horizontal transfer path  22  thereby saving the driving power of the horizontal transfer path  22 . 
     Second Embodiment 
       FIGS. 10 through 15  are process charts showing the procedure for manufacturing a horizontal transfer path and a vertical transfer path according to the second embodiment of the invention. As shown in  FIG. 10 , a gate insulating film  31  of the ONO (oxidized film-silicon nitride film-oxidized film) structure is formed on the semiconductor substrate  30 . On the gate insulating film  31  is formed first layer transfer electrode films  32  composed of polysilicon are formed apart from each other, and a thermally oxidized film  40  is formed on its surface. Then, a thermally oxidized film  40  is formed thereon. 
     Next, as shown in  FIG. 11 , a photoresist  46  is applied to the vertical transfer path  23 . As shown in  FIG. 12 , a photolithography process is executed to remove the thermally oxidized film  40  on the horizontal transfer path  22 . Then, as shown in  FIG. 13 , the photoresist  46  is removed. 
     Next, as shown in  FIG. 14 , when the oxidization process is executed, a thin oxidized film  34  grows anew on the surface of the first layer transfer electrode film  32  on the horizontal transfer path  22 . A new oxidized film grows on the oxidized film  40  on the vertical transfer path  23  shown in  FIG. 13  to form a thick oxidized film  37 . 
     Then, as shown in  FIG. 15 , second layer transfer electrode films  35  are formed between the first layer transfer electrode films  32  and their surfaces are thermally oxidized to form oxidized films  36 . 
     With this manufacturing method also, it is possible to increase the thickness of the interlayer insulating film  37  between the first and second layer transfer electrode films  32 ,  35  on the vertical transfer path  23  to withstand the high driving voltage of the vertical transfer path  23  as well as to reduce the thickness of the interlayer insulating film  34  between the first and second layer transfer electrode films  32 ,  35  on the horizontal transfer path to reduce the driving voltage of the horizontal transfer path  22  thereby saving the driving power of the horizontal transfer path  22 . 
     Third Embodiment 
       FIG. 16  is a partial schematic cross-sectional view of a horizontal transfer path ( FIG. 16A ) and a vertical transfer path ( FIG. 16B ) having a single-layer structure according to the third embodiment of the invention. In this embodiment, a gate insulating film  51  of the ONO structure is formed on the surface of the semiconductor substrate  50 . On the gate insulating film  51  are formed a plurality of transfer electrode films  52  adjacently to each other with minute gaps arranged therebetween. Each transfer electrode film  52  is covered with an insulating film  53  thus filling each gap between the transfer electrode films  52  with the insulating film  53 . 
     Talking of the gap between the transfer electrode films  52 , the gap a on the vertical transfer path ( FIG. 16B ) is wide enough to have a withstand voltage against a high driving voltage while the gap b on the horizontal transfer path ( FIG. 16A ) is narrow so as to reduce the driving voltage to provide lower power consumption. 
     The CCD type solid-state imaging apparatus having transfer paths of such a single-layer structure also saves the driving power of the horizontal transfer path of the CCD type solid-state imaging apparatus. 
     The CCD type solid-state imaging apparatus according to the invention has a thin insulating film between the transfer electrode films on the second transfer paths. This reduces the transfer driving voltage of the second transfer path thus reducing power consumption. 
     The CCD type solid-state imaging apparatus according to the invention can save the driving power of the horizontal transfer path and is thus useful as CCD type solid-state imaging apparatus mounted on electronic equipment having a small battery alone such as a digital still camera and a cell phone. 
     The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.