Abstract:
This disclosure concerns a semiconductor memory device comprising a plurality of gate electrodes extending to a first direction; a reinforced insulation film extending to a second direction crossing the first direction, and connected to the adjacent gate electrodes; and an interlayer dielectric film provided between the adjacent gate electrodes, and having a void inside.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2007-168671, filed on Jun. 27, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device and a manufacturing method thereof, and relates to a NAND type memory cell and a manufacturing method thereof, for example. 
         [0004]    2. Related Art 
         [0005]    In NAND memories, there is representatively used an insulation film formed by polysilazane (PSZ), HDP-CVD (High Density Plasma-Chemical Vapor Deposition) or BPSG (Boron-Phosphorous-doped Silicon Glass) as an interlayer dielectric film filling between adjacent gate electrodes. A specific dielectric constant of each of these interlayer dielectric films is relatively low. However, when miniaturization of the semiconductor integrated circuit is progressed and when a gate length becomes 30 nm to 20 nm, there occur (1) a disturbance (threshold variation) due to a parasitic capacitance between adjacent floating gate electrodes, and (2) a disturbance (error writing) of a control electrode of a certain memory cell, inverting a channel of an adjacent memory cell. These problems of disturbances become a malfunction of the memory device. 
       SUMMARY OF THE INVENTION 
       [0006]    A semiconductor memory device according to an embodiment of the present invention comprises a plurality of gate electrodes extending to a first direction; a reinforced insulation film extending to a second direction crossing the first direction, and connected to the adjacent gate electrodes; and an interlayer dielectric film provided between the adjacent gate electrodes, and having a void inside. 
         [0007]    A method of manufacturing a semiconductor memory device according to an embodiment of the present invention comprises forming a plurality of gate electrodes extending to a first direction; forming a reinforced insulation film extending to a second direction crossing the first direction, and connected to the adjacent gate electrodes; and depositing an interlayer dielectric film so as to have a void between the adjacent gate electrodes and beneath the reinforced insulation film. 
         [0008]    A method of manufacturing a semiconductor memory device according to an embodiment of the present invention comprises forming a first gate dielectric film on a semiconductor substrate, a floating gate on the first gate dielectric film, a second gate dielectric film on the floating gate, and a control gate on the second gate dielectric film, the first gate dielectric film, the floating gate, the second gate dielectric film, and the control gate being formed in a stripe shape; depositing a first interlayer dielectric film between the adjacent floating gates and between the adjacent control gates; depositing a reinforced insulation film on the upper surface of the control gate, and on the upper surface of the first interlayer dielectric film, respectively; processing in a stripe shape the reinforced insulation film so as to extend to a direction crossing the extension direction of the control gate; removing the first interlayer dielectric film through a gap of the stripe of the reinforced insulation film; and depositing a second interlayer dielectric film having poorer covering properties than that of the first interlayer dielectric film to block the upper part between the adjacent control gates and the upper part of the gap of the stripe of the reinforced insulation films before a region between the floating gates and a region beneath the reinforced insulation film are filled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  is a top plan view showing a manufacturing method of a NAND type memory according to an embodiment of the present invention; 
           [0010]      FIG. 1B  is a cross-sectional view showing a manufacturing method of a NAND type memory according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a cross-sectional view showing a manufacturing method following  FIG. 1B ; 
           [0012]      FIG. 3A  is a top plan view showing a manufacturing method following  FIG. 2 ; 
           [0013]      FIG. 3B  is a cross-sectional view showing a manufacturing method following  FIG. 2 ; 
           [0014]      FIG. 4A  is a top plan view showing a manufacturing method following  FIG. 3A ; 
           [0015]      FIG. 4B  is a cross-sectional view showing a manufacturing method following  FIG. 3B ; 
           [0016]      FIG. 5  is a cross-sectional view showing a manufacturing method following  FIG. 5 ; and 
           [0017]      FIG. 6  is a cross-sectional view showing an actual aspect ratio of the control gate electrode and the floating gate electrode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. Note that the invention is not limited thereto. 
         [0019]      FIG. 1A  to  FIG. 5  are top plan views and cross-sectional views showing a manufacturing method of a NAND type memory according to an embodiment of the present invention.  FIG. 1A  is a top plan view showing a memory region.  FIG. 1B  is a cross-sectional view along a line B-B in  FIG. 1A . First, as shown in  FIG. 1B , a first gate dielectric film  20  and a floating gate electrode  30  are formed in a line shape (a stripe shape) on a silicon substrate  10 . The first gate dielectric film  20  includes a silicon oxide film, a silicon oxynitride film, or a high dielectric material having a higher specific dielectric constant than that of the silicon oxynitride film, or a lamination film of these films. The floating gate electrode  30  includes doped polysilicon, for example. The floating gate electrode  30  is formed on a channel region of each memory cell, and is in an electrically floating state. 
         [0020]    A second gate dielectric film  40  is formed on the floating gate electrode  30 . A control gate electrode  50  is formed on the second gate dielectric film  40 . The second gate dielectric film  40  includes a silicon oxide film, a silicon oxynitride film, or a high dielectric material having a higher specific dielectric constant than that of the silicon oxynitride film, or a lamination film of these films, for example. The control gate electrode  50  includes doped polysilicon, for example. 
         [0021]    The control gate electrode  50  is formed by performing RIE (Reactive Ion Etching) by using both or either one of an SiN cap  60  and a silicon oxide film (not shown) on the SiN cap  60  as a mask. The control gate electrode  50  is extended to a word line direction (a first direction), as shown in  FIG. 1A . That is, the control gate electrode  50  is formed in a plural-line shape (a stripe shape). The control gate electrode  50  functions not only as a control gate of a memory cell but also as a word line. 
         [0022]    Next, an interlayer dielectric film  70  is deposited. The interlayer dielectric film  70  is ground using CMP (Chemical Mechanical Polishing) until when the upper surface of the SiN cap  60  is exposed. The interlayer dielectric film  70  is etched back to the medium of the SiN cap  60 . In this case, the upper surface of the interlayer dielectric film  70  is higher than the upper surface of the control gate electrode  50 , and is lower than the upper surface of the SiN cap  60 , with the surface of the silicon substrate  10  as a reference. 
         [0023]    Next, the SiN cap  60  is removed with hot-phosphoric solution. Accordingly, the upper surface of the control gate electrode  50  is exposed. Next, a metal film such as nickel, cobalt, or titanium is deposited on the control gate electrode  50 . Next, the deposited result is heat-treated using RTA (Rapid Thermal Anneal), thereby reacting the metal film with the control gate electrode  50 . Accordingly, as shown in  FIG. 2 , a silicide layer  80  is formed as a part of the control gate electrode  50  on the control gate electrode  50 . The silicide layer  80  plays a role of decreasing gate resistance (resistance of a word line). Thereafter, an unreacted metal film is removed by wet etching. 
         [0024]    Next, as shown in  FIG. 3B , a reinforced insulation film material  90  is deposited on the silicide layer  80  and the interlayer dielectric film  70 . Preferably, the reinforced insulation film material  90  has low specific dielectric constant, and has high mechanical strength. For example, the reinforced insulation film material  90  includes a silicon nitride film. The reinforced insulation film material  90  is patterned to extend to a bit line direction (a second direction) by using lithography and RIE. The bit line direction is orthogonal with the word line direction. Accordingly, as shown in  FIG. 3A , the reinforced insulation film  90  is formed in a plural-line shape (a stripe shape) extending to a direction orthogonal with the control gate electrode  50 . The reinforced insulation film material  90  after the RIE process is called the reinforced insulation film  90 .  FIG. 3B  is a cross-sectional view along a line B-B in  FIG. 3A . 
         [0025]    Next, as shown in  FIG. 4A , the interlayer dielectric film  70  is removed by wet treating. Accordingly, the interlayer dielectric film  70  between the adjacent control gate electrodes  50 , the interlayer dielectric film  70  between the adjacent floating gate electrodes  30 , and the interlayer dielectric film  70  beneath the reinforced insulation film  90  are all removed. The reinforced insulation film  90  is connected to the upper surface of the silicide layers  80  adjacent in a bit line direction. The reinforced insulation film  90  physically connects between the control gate electrode  50  and the floating gate electrode  30  adjacent in the bit line direction, and reinforces these electrodes. Accordingly, even when the aspect ratio of the control gate electrode  50  and the floating gate electrode  30  becomes high, the reinforced insulation film  90  physically supports the control gate electrode  50  and the floating gate electrode  30  adjacent in the bit line direction, thereby preventing the control gate electrode  50  and the floating gate electrode  30  from being destructed. 
         [0026]    When the gate length becomes 30 nm to 20 nm based on the miniaturization of the semiconductor memory device, the aspect ratio of the control gate electrode and the floating gate electrode becomes equal to or larger than five. In  FIG. 1A  to  FIG. 5B , to facilitate the understanding, the aspect ratio of the control gate electrode and the floating gate electrode is shown smaller than the actual size. When the aspect ratio of the control gate electrode and the floating gate electrode becomes equal to or larger than five, as shown in  FIG. 6 , the control gate electrode and the floating gate electrode become actually in a very slender shape. The control gate electrode and the floating gate electrode having such a slender shape are actually easily destructed in the manufacturing process. 
         [0027]    In the present embodiment, the reinforced insulation film  90  is connected in a beam shape to the upper surface of the plural control gate electrodes  50  (the silicide layer  80 ) adjacent in the bit line direction, thereby physically supporting the control gate electrode  50  and the floating gate electrode  30 . Accordingly, as shown in  FIG. 4B , even when the interlayer dielectric film  70  is removed, the control gate electrode  50  and the floating gate electrode  30  can be prevented from being destructed. 
         [0028]    In the peripheral circuit region at this stage, the reinforced insulation film  90  covers the whole surface of this region. Therefore, in the peripheral circuit region, the interlayer dielectric film  70  protects the element. 
         [0029]    Next, an interlayer dielectric film  95  having poor covering properties is deposited using PECVD (Plasma Enhanced Chemical Vapor Deposition) or the like. As the interlayer dielectric film  95  having poor covering properties, a PTEOS (Plasma-tetraethoxysilane) film or the like is available. When this interlayer dielectric film  95  is deposited, the upper parts of the control gate electrodes  50  and the upper parts of the adjacent reinforced insulation films  90  are blocked by the interlayer dielectric film  95 , before the region between the adjacent control gate electrodes  50 , the region between the adjacent floating gate electrodes  30 , and the region beneath the reinforced insulation film  90  are filled in. Accordingly, as shown in  FIG. 5 , the interlayer dielectric film  95  having a void  99  in the center is formed both or either one of between the adjacent control gate electrodes  50  and between the adjacent floating gate electrodes  30 . The actual aspect ratio of the control gate electrode  50  and the floating gate electrode  30  is larger than that shown in  FIG. 5 . Therefore, it is easy to deposit the interlayer dielectric film  95  to have the void  99  in the center. The interlayer dielectric film  95  is deposited to a height equal to or higher than the upper surface of the reinforced insulation film  90 . 
         [0030]    Next, the interlayer dielectric film  95  and the reinforced insulation film  90  are flattened using CMP, thereby obtaining a structure as shown in  FIG. 5 . In the peripheral circuit region, the reinforced insulation film  90  covers the whole surface. Therefore, there is fear that the memory region is dished in this CMP process. However, in the present embodiment, because the reinforced insulation film  90  is provided, the reinforced insulation film  90  suppresses the dishing of the memory region. The CMP is performed so that the void  99  does not appear on the upper surface. Therefore, after the CMP process, only the upper surface of the reinforced insulation film  90  and the upper surface of the interlayer dielectric film  95  appear. The upper surface of the reinforced insulation film  90  and the upper surface of the interlayer dielectric film  95  are on the same flat surface. Accordingly, the subsequent process becomes easy. 
         [0031]    Although not shown, thereafter, the reinforced insulation film  90  covering the peripheral circuit region is removed. Then, contacts and wirings (bit lines) are formed using the conventional process, thereby completing the NAND type memory according to the present embodiment. By leaving the reinforced insulation film  90  in the peripheral circuit region, etching conditions for forming the contacts can be changed to etch the reinforced insulation film  90  at the time of forming the contacts. 
         [0032]    In the present embodiment, the NAND type memory includes the plural control gate electrodes  50  extending to the word line direction, the reinforced insulation film  90  extending to the bit line direction orthogonal with the word lines and connected to the adjacent control gate electrodes  50 , and the interlayer dielectric films  95  provided between the adjacent control gate electrodes  50  and between the adjacent floating gate electrodes  30  and having the voids  99  inside. The memory cell includes the control gate electrodes  50  and the floating gate electrodes  30 , and stores a charge tunneling the first gate dielectric film  20  in the floating gate electrode  30 , or discharges the charge from the floating gate electrode  30  via the first gate dielectric film  20 , thereby storing logic data. The memory cell can store data by accumulating a charge having an opposite polarity to that of the charge originally stored in the floating gate electrode  30 . 
         [0033]    Because the void  99  is provided between the control gate electrode  50  and the floating gate electrode  30 , the coupling capacitance between the adjacent control gate electrodes  50  and the coupling capacitance between the adjacent floating gate electrodes  30  decrease. Further, the influence that the control gate electrodes  50  apply to the channel regions of the adjacent cells also decrease. As a result, even when the memory device is miniaturized, the memory device according to the present embodiment can suppress (1) the disturbance due to the parasitic capacitance between the adjacent floating gate electrodes, and (2) the disturbance in which the control gate electrode of a certain memory cell inverts a channel of an adjacent memory cell. 
         [0034]    In the present embodiment, because the reinforced insulation film  90  physically reinforces the control gate electrodes  50  and the floating gate electrodes  30 , the control gate electrodes  50  and the floating gate electrodes  30  can be prevented from being destructed. Further, the reinforced insulation film  90  can suppress the dishing in the process of flattening the interlayer dielectric film  95 . 
         [0035]    The effect of the present embodiment is more advantageously exhibited when the design rule is strict and also when the aspect ratio of the gate electrode is large. For example, when the gate length is equal to or smaller than 30 nm and also when the aspect ratio of the control gate electrode and the floating gate electrode is equal to or larger than five, the effect of the present embodiment can be exhibited effectively. The effect of the present embodiment is not denied even when the gate length is larger than 30 nm and also when the aspect ratio of the control gate electrode and the floating gate electrode is smaller than five. 
         [0036]    While the present embodiment is applied to the floating gate type memory, the present embodiment can be also applied to the MONOS (Metal-Oxide-Nitride-Oxide-Semiconductor) type memory. The MONOS type memory has a floating gate part formed by a silicon nitride film.