This application is based upon and claims the benefit of priority from Japanese Patent Application No.2017-059927, filed on Mar. 24, 2017; the entire contents of which are incorporated herein by reference.
Embodiments relate to a semiconductor memory device and a method for manufacturing the same.
In recent years, there has been proposed a stacked-type semiconductor memory device in which memory cells are integrated three-dimensionally. Such a stacked-type semiconductor memory device is provided with a stacked body in which electrode films and insulating films are alternately stacked on a semiconductor substrate. Semiconductor pillars are provided through the stacked body. A memory cell transistor is formed for each crossing portion of the electrode film and the semiconductor pillar. A challenge for the stacked-type semiconductor memory device is to ensure reliability.
In general, according to one embodiment, a semiconductor memory device includes a stacked body in which electrode films and insulating films are stacked alternately along a first direction, a semiconductor member extending in the first direction, and a charge storage member provided between the semiconductor member and the electrode film. The electrode film includes a first conductive layer and a second conductive layer. The first conductive layer is provided on an upper surface of the insulating film and on a lower surface of the insulating film. The second conductive layer is provided between the first conductive layer in a first portion of the electrode film. The second conductive layer is formed from a material different from that of the first conductive layer. Thickness of the first conductive layer in the first portion is thinner than thickness of the first conductive layer in a second portion of the electrode film. The second portion is placed between the first portion and the semiconductor member.
In general, according to other embodiment, a method for manufacturing a semiconductor memory device includes forming a slit in a stacked body. The stacked body has insulating films and first films stacked alternately along a first direction, a semiconductor member extending in the first direction, and a charge storage member provided between the semiconductor member and the first film. The slit extends in a second direction crossing the first direction. The method includes forming a space between the insulating films by removing the first film through the slit. The method includes forming a third conductive layer on an inner surface of the space through the slit. The method includes removing a portion of the third conductive layer through the slit. The portion is placed in a first portion of the space on the slit side. The method includes forming a fourth conductive layer thinner than the third conductive layer through the slit on the inner surface of the space in the first portion. The method includes forming a second conductive layer in the first portion.
A first embodiment is now described.
The drawings are schematic, and are emphasized and omitted as appropriate.
As shown in
In the following, in this specification, an XYZ orthogonal coordinate system is adopted for convenience of description. Two directions parallel to the upper surface 10a of the silicon substrate 10 and orthogonal to each other are referred to as “X-direction” and “Y-direction”. The direction perpendicular to the upper surface 10a of the silicon substrate 10 is referred to as “Z-direction”. In the Z-direction, the direction from the silicon substrate 10 toward the source electrode film 82 is also referred to as “upper”, and the opposite direction is also referred to as “lower”. However, these expressions are also used for convenience, and irrelevant to the direction of gravity.
In this specification, the “silicon substrate” refers to a substrate composed primarily of silicon (Si). The same also applies to the other components. That is, the component with the designation including a material name is composed primarily of that material. Furthermore, silicon is generally a semiconductor material. Thus, unless otherwise specified, the silicon substrate is a semiconductor substrate. The same also applies to the other components. That is, unless otherwise specified, the characteristics of the component reflect the characteristics of its main ingredient.
A cell underside circuit 90 is formed in an upper portion of the silicon substrate 10 and the interlayer insulating film 81. The cell underside circuit 90 is part of a driving circuit for performing writing, reading, and erasing of data on the memory cell transistor MC described later. The cell underside circuit 90 includes e.g. a sense amplifier. For instance, the upper portion of the silicon substrate 10 is partitioned into a plurality of active areas by STI (shallow trench isolation) 84. An n-type MOSFET (metal-oxide-semiconductor field-effect transistor) 85 is formed in one active area. A p-type MOSFET 86 is formed in another active area.
Interconnects 87 are provided in a plurality of stages in the interlayer insulating film 81. A contact 88 for connecting the interconnect 87 to the silicon substrate 10, and a via 89 for connecting the interconnects 87 to each other are also provided. In
A silicon oxide film 11 is provided on the source electrode film 82. Silicon oxide films 12 and electrode films 13 are stacked alternately along the Z-direction on the silicon oxide film 11. A stacked body 15 is formed from a plurality of silicon oxide films 12 and a plurality of electrode films 13 stacked alternately.
A slit 43 extending in the X-direction is formed in the stacked body 15. The slit 43 divides the stacked body 15 in the Y-direction. In the stacked body 15 divided by the slit 43, each electrode film 13 extends in the X-direction. That is, the X-direction length of the electrode film 13 is longer than the Z-direction length (thickness) of the electrode film 13 and the Y-direction length (width) of the electrode film 13. A silicon oxide plate 18 is provided in the slit 43. A silicon oxide member 19 extending in the X-direction is provided in an upper part of the Y-direction central portion of the stacked body 15 divided by the slit 43.
A silicon pillar 30 extending in the Z-direction and penetrating through the stacked body 15 is provided in the stacked body 15. The silicon pillar 30 is made of polysilicon. The silicon pillar 30 is shaped like e.g. a circular cylinder occluded at the lower end. The lower end of the silicon pillar 30 is connected to the source electrode film 82. The upper end of the silicon pillar 30 is exposed at the upper surface of the stacked body 15. The silicon pillars 30 are arranged periodically along a plurality of rows, such as eight rows, extending in the X-direction. The eight rows of silicon pillars 30 are placed on both Y-direction sides of the silicon oxide member 19, four rows on each side. As viewed in the Z-direction, the silicon pillars 30 are arranged in a staggered arrangement. The placement of the silicon pillars 30 are not limited to eight rows, but may be e.g. four rows.
A plurality of bit lines 22 extending in the Y-direction are provided on the stacked body 15. The bit line 22 is connected to the upper end of the silicon pillar 30 through a plug 23. Thus, the silicon pillar 30 is connected between the bit line 22 and the source electrode film 82.
In the stacked body 15, one or more stages of electrode films 13 from the top function as upper select gate lines SGD. An upper select gate transistor STD is configured for each crossing portion of the upper select gate line SGD and the silicon pillar 30. The silicon oxide member 19 is placed between the upper select gate lines SGD. One or more stages of electrode films 13 from the bottom function as lower select gate lines SGS. A lower select gate transistor STS is configured for each crossing portion of the lower select gate line SGS and the silicon pillar 30.
The electrode films 13 other than the lower select gate lines SGS and the upper select gate lines SGD function as word lines WL. A memory cell transistor MC is configured for each crossing portion of the word line WL and the silicon pillar 30. Thus, a plurality of memory cell transistors MC are connected in series along each silicon pillar 30. The lower select gate transistor STS and the upper select gate transistor STD are connected to both ends of the silicon pillar 30. Accordingly, a NAND string is formed.
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The tunnel insulating film 31 is a film that is normally insulating, but passes a tunnel current under application of a prescribed voltage within the range of the driving voltage of the semiconductor memory device 1. For instance, the tunnel insulating film 31 is formed from silicon oxide (SiO). The charge storage film 32 is a film capable of storing charge. For instance, the charge storage film 32 is formed from silicon nitride (SiN). The block insulating film 33 is a film passing substantially no current even under application of voltage within the range of the driving voltage of the semiconductor memory device 1. For instance, the block insulating film 33 is a stacked film of a silicon oxide layer and a high-dielectric layer.
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The electrode film 13 is provided with a barrier metal layer 27, an insulating layer 28, and a metal layer 29. The barrier metal layer 27 is formed from e.g. metal nitride such as titanium nitride (TiN) and tungsten nitride (WN). The barrier metal layer 27 is provided on the upper surface and the lower surface of the silicon oxide film 12 and on the side surface of the block insulating film 33. The insulating layer 28 is made of e.g. silicon oxide. The insulating layer 28 is placed between the barrier metal layers 27 in the central portion 25 of the electrode film 13. The metal layer 29 is made of e.g. metal such as tungsten (W). The metal layer 29 is placed between the barrier metal layers 27 in the end portion 26 of the electrode film 13. For instance, the resistivity of the metal layer 29 is lower than the resistivity of the barrier metal layer 27. The barrier metal layer 27 is placed also between the insulating layer 28 and the metal layer 29.
In the Z-direction, the thickness to of the barrier metal layer 27 in the end portion 26 is thinner than the thickness tb of the barrier metal layer 27 in the central portion 25, i.e., ta<tb. The thickness ta is e.g. half or less of the thickness tb. On the other hand, the thickness of the electrode film 13 is generally uniform. That is, in the Z-direction, the thickness of the central portion 25 and the thickness of the end portion 26 are generally equal. Thus, the metal layer 29 is thicker than the insulating layer 28.
Next, a method for manufacturing the semiconductor memory device according to the embodiment is described.
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Next, the silicon nitride films 41 are removed by e.g. wet etching through the slit 43. Thus, a space 44 is formed after the removal of the silicon nitride films 41. In the Z-direction, the space 44 is located between the silicon oxide films 12. At this time, the block insulating film 33 is not removed. Thus, the block insulating film 33, and the charge storage film 32, the tunnel insulating film 31, the silicon pillar 30, and the core member 35 surrounded with the block insulating film 33 remain and serve as a strut for supporting the stacked body 15.
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Next, the effect of the embodiment is described.
In the semiconductor memory device 1 according to the embodiment, as shown in
The block insulating film 33 is spaced from the metal layer 29 by the barrier metal layer 27 and the insulating layer 28. Thus, when depositing tungsten in the step shown in
Furthermore, in the embodiment, as shown in
Next, a second embodiment is described.
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Next, a method for manufacturing the semiconductor memory device according to the embodiment is described.
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Next, the effect of the embodiment is described.
In the embodiment, in the step shown in
The configuration, manufacturing method, and effect of the embodiment other than the foregoing are similar to those of the above first embodiment.
The embodiments described above can realize a semiconductor memory device having high reliability and a manufacturing method thereof.
In the example shown in the above first and second embodiments, the barrier metal layer 27 is formed from metal nitride such as titanium nitride, and the metal layer 29 is formed from metal such as tungsten. However, the embodiments are not limited thereto, but an arbitrary conductive material can be used.
In the example shown in the above first and second embodiments, the insulating layer 28 is formed from silicon oxide. However, the embodiments are not limited thereto, but an arbitrary insulating material can be used. A conductive layer may be provided instead of the insulating layer 28 as long as there is no trouble such as shape failure due to stress and quality degradation due to process gas. Furthermore, an air gap may be formed instead of providing the insulating layer 28.
Furthermore, in the example shown in the above first and second embodiments, the cell underside circuit 90 and the source electrode film 82 are provided between the silicon substrate 10 and the stacked body 15, and the lower end of the silicon pillar 30 is connected to the source electrode film 82. However, the embodiments are not limited thereto. For instance, the cell underside circuit 90 and the source electrode film 82 may not be provided, and the lower end of the silicon pillar 30 may be connected to the silicon substrate 10. In this case, for instance, a conductive member for applying a source potential from the upper interconnect to the silicon substrate 10 may be provided in the silicon oxide plate 18.
Moreover, in the example shown in the above first and second embodiments, the insulating layer 28 is necessarily placed between the block insulating film 33 and the silicon oxide plate 18. However, the embodiments are not limited thereto. For instance, depending on the process condition, the diameter of the memory hole 42 may become larger and the width of the slit 43 may become wider toward the upper part of the stacked body 15. In this case, in the upper part of the stacked body 15, the distance between the memory hole 42 nearest to the slit 43 and the slit 43 becomes shorter. Thus, in the step shown in
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2017-059927 | Mar 2017 | JP | national |