This application is based upon and claims benefit of priority from the Japanese Application No. 2008-289698, filed on Nov. 12, 2008, the entire contents of which are incorporated herein by reference.
The present invention relates to a semiconductor memory device and a method for manufacturing the same.
In recent years, attention is drawn to ferroelectric memories (or FeRAM: Ferroelectric Random Access Memory) as one type of semiconductor memories. A ferroelectric memory is a nonvolatile memory that includes a ferroelectric film such as a PZT (Pb(ZrxTi1-x)O3) film, a BIT (Bi4Ti3O12) film, or a SBT (SrBi2Ta2O9) film at each capacitor portion, and stores data by virtue of the residual polarization of the ferroelectric film. A capacitor is formed on a semiconductor substrate, and an impurity diffusion layer that is formed on a surface of the semiconductor substrate are connected with a lower electrode film of the capacitor by a contact plug (for example, refer to JP-A 8-335673 (KOKAI)).
In a conventional ferroelectric memory, an interlayer insulating film is formed to cover a transistor formed on a semiconductor substrate, a contact hole is opened to expose a surface of an impurity diffusion layer formed on a surface of the semiconductor substrate, tungsten is used to form a film through a chemical vapor deposition (CVD) method to bury the contact hole, and a chemical mechanical polishing (CMP) process is performed using the interlayer insulating film as a stopper, and a contact plug is formed. If an Ir film that is a lower electrode film of the capacitor is formed on the contact plug formed in this way, a grain (single-crystal lump) is likely to be generated in the Ir film. If the grain is formed in the lower electrode film, oxygen that is contained in a ferroelectric film formed on the lower electrode film is likely to diffuse into the contact plug through a grain interface. If the contact plug is oxidized due to the diffusion of the oxygen, a voltage is not normally applied to the ferroelectric film, operation performance of the ferroelectric memory is deteriorated, and reliability is lowered.
According to one aspect of the present invention, there is provided a semiconductor memory device comprising:
a semiconductor substrate;
an impurity diffusion layer that is formed at a surface portion of the semiconductor substrate;
an interlayer insulating film that is formed on the semiconductor substrate;
a contact plug that penetrates the interlayer insulating film, has a top surface formed higher than a top surface of the interlayer insulating film, a region having a convex shape formed higher than the top surface of the interlayer insulating film, and contacts the impurity diffusion layer;
a lower capacitor electrode film that is formed on the contact plug and a predetermined region of the interlayer insulating film;
a ferroelectric film that is formed on the lower capacitor electrode film; and
an upper capacitor electrode film that is formed on the ferroelectric film.
According to one aspect of the present invention, there is provided a semiconductor memory device comprising:
a semiconductor substrate;
first to third impurity diffusion layers that are formed at a surface portion of the semiconductor substrate at predetermined intervals;
a first interlayer insulating film that is formed on the semiconductor substrate;
a first contact plug that is formed in the first interlayer insulating film and is connected to the first impurity diffusion layer;
a second contact plug that is formed in the first interlayer insulating film and is connected to the second impurity diffusion layer;
a third contact plug that is formed in the first interlayer insulating film and is connected to the third impurity diffusion layer;
a fourth contact plug that is formed on the first contact plug and has first and second convex portions formed on a top surface thereof;
a fifth contact plug that is formed on the second contact plug;
a sixth contact plug that is formed on the third connect plug and has third and fourth convex portions formed on a top surface thereof;
a first capacitor that is formed on the first convex portion and has a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated;
a second capacitor that is formed on the second convex portion and has a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated;
a third capacitor that is formed on the third convex portion and has a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated;
a fourth capacitor that is formed on the fourth convex portion and has a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated;
a second interlayer insulating film that is formed to cover the first to fourth capacitors and the first to third contact plugs;
a seventh contact plug that is formed in the second interlayer insulating film and is connected to the fifth contact plug;
an eight contact plug that is formed in the second interlayer insulating film and is connected to the upper electrode film of the first capacitor;
a ninth contact plug that is formed in the second interlayer insulating film and is connected to the upper electrode film of the third capacitor; and
a wiring layer that is formed on the second interlayer insulating film and is connected to the seventh to ninth contact plugs.
According to one aspect of the present invention, there is provided a method for manufacturing a semiconductor memory device, comprising:
forming an impurity diffusion layer at a surface portion of a semiconductor substrate;
forming an interlayer insulating film on the semiconductor substrate:
forming an opening penetrating the interlayer insulating film and exposing a top surface of the impurity diffusion layer;
burying a metal film in the opening;
removing the interlayer insulating film from a top surface with a predetermined thickness to expose an upper portion of the metal film;
performing a chemical mechanical polishing (CMP) process to remove an upper end of the metal film; and
forming a capacitor having a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated, on the metal film.
According to one aspect of the present invention, there is provided a method for manufacturing a semiconductor memory device, comprising:
forming an impurity diffusion layer at a surface portion of a semiconductor substrate;
forming an interlayer insulating film on the semiconductor substrate;
forming an opening penetrating the interlayer insulating film and exposing a top surface of the impurity diffusion layer;
burying a first metal film in the opening;
removing the interlayer insulating film from a top surface with a predetermined thickness to expose an upper portion of the first metal film;
forming a second metal film having a convex shape in an outer circumferential portion of the first metal film on the interlayer insulating film; and
forming a capacitor having a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated, on the first and second metal films.
According to one aspect of the present invention, there is provided a method for manufacturing a semiconductor memory device, comprising:
forming first to third impurity diffusion layers at a surface portion of a semiconductor substrate at predetermined intervals;
forming a first interlayer insulating film on the semiconductor substrate;
forming first to third openings penetrating the first interlayer insulating film and exposing top surfaces of the first to third impurity diffusion layers, respectively;
burying a first metal film in the first to third openings to form first to third contact plugs;
forming a second interlayer insulating film on the first interlayer insulating film and the first to third contact plugs;
forming a fourth opening penetrating the second interlayer insulating film and exposing a top surface of the first contact plug, a fifth opening exposing a top surface of the second contact plug and having a width narrower than that of the fourth opening, and a sixth opening exposing a top surface of the third contact plug and having a width wider than that of the fifth opening;
burying a second metal film in the fourth to sixth openings to form fourth to sixth contact plugs;
forming a resist film in first and second predetermined regions on the fourth contact plug and third and fourth predetermined regions on the sixth contact plug;
removing the second interlayer insulating film and the fourth to sixth contact plugs with a predetermined thickness, using the resist film as a mask;
removing the resist film;
performing a chemical mechanical polishing (CMP) process to remove an upper end of the fourth contact plug of the first and second predetermined regions and an upper end of the sixth contact plug of the third and fourth predetermined regions;
forming first to fourth capacitors having a lower electrode film, a ferroelectric film, and an upper electrode film, which are sequentially laminated, in the first and second predetermined regions on the fourth contact plug and the third and fourth predetermined regions on the sixth contact plug, respectively;
forming a third interlayer insulating film to cover the first to fourth capacitors, the second interlayer insulating film, and the fourth to sixth contact plugs;
forming a seventh opening penetrating the third interlayer insulating film and exposing a top surface of the fifth contact plug;
burying a third metal film in the seventh opening to form a seventh contact plug;
forming eighth and ninth openings penetrating the third interlayer insulating film and exposing a top surface of the upper electrode film of the first capacitor and a top surface of the upper electrode film of the third capacitor, respectively;
burying a fourth metal film in the eighth and ninth openings to form eighth and ninth contact plugs;
forming a fourth interlayer insulating film on the third interlayer insulating film and the seventh to ninth contact plugs;
forming a tenth opening penetrating the fourth interlayer insulating film and exposing top surfaces of the seventh to ninth contact plugs; and
burying a fifth metal film in the tenth opening to form a wiring layer contacting the seventh to ninth contact plugs.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
An interlayer insulating film 107 (silicon oxide film) is formed to surround the MOS transistor.
In the interlayer insulating film 107, a contact plug 111 is formed, which connects the source/drain diffusion layer 102 of the MOS transistor and a lower electrode 114 of a capacitor. The contact plug 111 is, for example, made of tungsten.
As viewed from a top surface of the interlayer insulating film 107, an upper portion of the contact plug 111 has a convex structure. A width of the contact plug 111 in a horizontal direction becomes narrowed when a position of the contact plug in a vertical direction becomes low (becomes close to the semiconductor substrate 101) in the interlayer insulating film 107. In a region of the contact plug 111 that is formed higher than the top surface of the interlayer insulating film 107, the width of the contact plug 111 becomes narrowed when the position of the contact plug in the vertical direction becomes high. That is, a side of the region of the contact plug 111 that is formed higher than the top surface of the interlayer insulating film 107 forms an angle θ (90°<θ<180°) with respect to a top surface of the interlayer insulating film 107 surrounding the contact plug 111.
The capacitor is formed on the interlayer insulating film 107. The capacitor has a lower electrode 114, a ferroelectric film 116, and an upper electrode 117, which are sequentially laminated.
An interlayer insulating film (silicon oxide film) 120 is formed to surround the entire region of the capacitor, and a contact 119 that contacts the upper electrode 117 is formed in the interlayer insulating film 120. The contact 119 is used, for example, to connect the upper electrodes of the adjacent capacitors each other.
The lower electrode 114 includes a TiAlN film 114a and an Ir film (noble metal film) 114b that is a barrier layer. A bottom surface of the Ir film 114b is formed in a higher position than the top surface of the contact plug 111. For example, the ferroelectric film 116 is composed of a PZT film and the upper electrode 117 is composed of an IrO2 film.
Meanwhile, in this embodiment, the grain is rarely formed in the Ir film 114b of the lower electrode 114, and the oxygen that is contained in the ferroelectric film 116 is prevented from diffusing into the contact plug 111. Since oxidization of the contact plug is suppressed, a voltage can be normally applied to the ferroelectric film, and operation performance of a ferroelectric memory can be improved. Accordingly, a semiconductor memory device having high reliability can be realized.
A method of manufacturing the semiconductor memory device will be described using
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In this way, a semiconductor memory device where the upper portion of the contact plug 111 has a convex structure below the lower electrode 114 is obtained. A grain is rarely formed in the Ir film 114b of the lower electrode 114, and oxygen that is contained in the ferroelectric film 116 is prevented from diffusing into the contact plug 111.
Since oxidization of the contact plug is suppressed, a voltage can be normally applied to the ferroelectric film, and operation performance of a ferroelectric memory can be improved. Accordingly, a semiconductor memory device having high reliability can be manufactured.
Further, even though the noble metal film of the lower electrode is thinner, oxidation resistance can be maintained. Therefore, a capacitor size can be reduced, and it is preferable that a capacity of the ferroelectric memory can be increased.
In the first embodiment, when the tungsten film 111 shown in
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Thereafter, if the same processes as the processes according to the first embodiment shown in
A method of manufacturing a semiconductor memory device according to a second modification will be described.
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In the semiconductor memory device according to this embodiment, a conductive material film 201 is provided in an outer circumferential portion of an upper portion (a portion that is formed higher than a top surface of an interlayer insulating film 107) of a contact plug 111. A shape of when the upper portion of the contact plug 111 and the conductive material film 201 are combined has a convex structure where a side has a taper angle as viewed from the top surface of the interlayer insulating film 107, similar to the upper portion of the contact plug 111 in the semiconductor memory device according to the first embodiment. Accordingly, in the shape of when the upper portion of the contact plug 111 and the conductive material film 201 are combined, a width of the contact plug 111 in a horizontal direction becomes narrowed when a position of the contact plug in a vertical direction becomes high, in a region of the contact plug that is formed higher than the top surface of the interlayer insulating film 107.
For this reason, similar to the first embodiment, a grain is prevented from being generated in a noble metal film (Ir film) 114b of a lower electrode 114, and oxidization of the contact plug 111 is suppressed, which results in obtaining a semiconductor memory device having high reliability.
A method of manufacturing the semiconductor memory device will be described using
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In this way, a semiconductor memory device where the upper portion of the contact plug 111 has a convex structure below the lower electrode 114 is obtained. A grain is rarely formed in the Ir film 114b of the lower electrode 114, and oxygen that is contained in the ferroelectric film 116 is prevented from diffusing into the contact plug 111.
Since oxidization of the contact plug is suppressed, a voltage can be normally applied to the ferroelectric film, and operation performance of a ferroelectric memory can be improved. Accordingly, a semiconductor memory device having high reliability can be manufactured.
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In the second embodiment, when the tungsten film 111 is buried in the contact hole 110, as shown in
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Thereafter, if the same processes as the processes shown in
A method of manufacturing a semiconductor memory device according to a third embodiment of the present invention will be described using
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In the opening pattern, wide openings and narrow openings are alternately formed. That is, in the contact plug 307, wide portions and narrow portions are alternately formed.
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Similar to the first embodiment, since the upper portion of the contact plug 307 has a convex structure as viewed from the top surface of the interlayer insulating film 306, a grain is rarely formed in the Ir film 308b.
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In the opening pattern, the contact plug 313 and openings used to expose the top surfaces of the two contact plugs 312 at both sides of the contact plug 313 are continuously formed. By the wiring layer 315, the contact plug 313 and the contact plugs 312 at both sides thereof are connected to each other. In this way, a chain structure where memory cells, each of which includes one transistor and one capacitor connected in parallel, are connected in series is obtained.
As such, even in the ferroelectric memory that has the chain structure, a grain is rarely formed in the Ir film 308b of the lower electrode of the capacitor, and oxygen that is contained in the ferroelectric film 309 is prevented from diffusing into the contact plug 307.
Since oxidization of the contact plug is suppressed, a voltage can be normally applied to the ferroelectric film, and operation performance of the ferroelectric memory can be improved. Accordingly, a semiconductor memory device having high reliability can be realized.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2008-289698 | Nov 2008 | JP | national |