# Patent

## Title
Fabricating method of DRAM cylindrical capacitor

## Abstract

A method of manufacturing dynamic random access memory (DRAM) cylindrical capacitor is provided. A substrate having a polysilicon plug formed therein is provided. A dielectric layer having an opening is disposed on the substrate, wherein the opening exposes the polysilicon plug. Thereafter, an amorphous silicon spacer is formed on the sidewall of the opening to expose a portion of the polysilicon plug. Next, a top portion of the exposed polysilicon plug is removed and a seeding method is used to grow a hemispherical silicon grain (HSG) layer on a surface of the amorphous silicon spacer. A capacitor dielectric layer is formed on the surface of the HSG layer and a conductive layer is then formed on the capacitor dielectric layer. As no HSG is formed on the polysilicon plug, and therefore the contact area of the capacitor is not decreased.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application Ser. No. 94143538, filed on Dec. 9, 2005. All disclosure of the Taiwan application is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DRAM cylindrical capacitor and a method of fabricating the same. More particularly, the present invention relates to a DRAM cylindrical capacitor and a method of fabricating the same, reduction of yield caused by difficulty in growing a capacitor dielectric layer may be effectively reduced.
2. Description of Related Art
A semiconductor memory mainly comprises a transistor and a capacitor. In a high depth-to-width ratio semiconductor process, the size of the capacitor must be reduced so that it occupies comparatively smaller space in the device. As the memory space required for storage of software grows rapidly, the demand for corresponding increase in the number of capacitors also grows. Accordingly, it highly desired to develop the semiconductor process technology to meet this demand.
At present, larger capacitance may be achieved by increasing the surface area of the bottom electrode of the capacitor. For example, in a conventional cylindrical capacitor, the bottom electrode of the capacitor is made into a cylindrical form, and a Hemispherical Silicon Grain (HSG) structure is formed on the surface of the bottom electrode for increasing the area of the capacitor.
However, as the dimensions of the device proceeds towards further miniaturization, the bottom width of the cylindrical capacitor must be smaller. However, when a HSG structure is formed on the small width cylindrical capacitor, the bottom electrodes may be undesirably connected to each other, and thus the area of the capacitor is reduced.
SUMMARY OF THE INVENTION
One object of the invention is to provide a method for manufacturing a DRAM cylindrical capacitor, wherein the difficulty of forming a capacitor dielectric layer due to the presence of a HSG structure at the bottom of the capacitor may be reduced such that the possibility of undesirable connection between the upper and bottom electrodes can be reduced.
Another object of the invention is to provide a DRAM cylindrical capacitor having a bottom electrode with a larger surface area.
Yet another object of the invention is to provide a DRAM cylindrical capacitor, wherein HSG structure is not formed at the bottom of the bottom electrode.
The present invention provides a method for manufacturing a DRAM cylindrical capacitor. A substrate having a polysilicon plug formed thereon is provided. A dielectric layer is formed on the substrate. Next, a portion of the dielectric layer is removed such that the opening exposes the polysilicon plug. Next, amorphous Silicon spacer is formed on the sidewall of the opening. Thereafter, a portion of the polysilicon plug is removed and then a seeding method is used to grow a HSG layer on a surface of the amorphous silicon spacer. Next, a capacitor dielectric layer and a conductive layer are sequentially formed on the surface of the HSG layer.
According to an embodiment of the present invention, a metal layer may be further formed on the surface of the HSG layer to serve as a bottom electrode before forming a capacitor dielectric layer on the surface of the HSG layer. According to an embodiment of the present invention, a portion of the metal layer disposed outside the opening may be removed.
According to an embodiment of the present invention, the dielectric layer is removed after the portion of the polysilicon plug is removed but before the HSG layer is formed on the surface of the amorphous silicon spacer. Furthermore, a metal layer may be formed on the surface of the HSG layer to serve as a bottom electrode before the capacitor dielectric layer is formed.
According to an embodiment of the present invention, the step of forming an amorphous silicon spacer on the sidewall of the opening comprises forming an amorphous silicon layer on the substrate to cover the surface of the dielectric layer and the opening and etching the amorphous silicon layer anisotropically to remove a portion of the amorphous silicon layer disposed outside the opening and a portion of the amorphous silicon layer at the bottom of the opening.
According to an embodiment of the present invention, the step of forming the dielectric layer and forming an opening therein comprises sequentially forming an etching stop layer, an inter-layer dielectric layer and a hard mask layer on the substrate; patterning the hard mask to expose a portion of the inter-layer dielectric layer; anisotropically etching the exposed inter-layer dielectric layer using the patterned hard mask as an etching mask until a portion of the etching stop layer is exposed; and removing the exposed etching stop layer to form the opening.
According to an embodiment of the present invention, the capacitor dielectric layer may be formed using an atomic layer deposition (ALD) process.
The invention further provides a structure of a DRAM cylindrical capacitor comprising a substrate, a dielectric layer, an amorphous silicon spacer, a polysilicon plug, a HSG layer, a conductive layer and a capacitor dielectric layer. The dielectric layer is disposed on the substrate, wherein the dielectric layer comprises an opening. The amorphous silicon spacer is disposed on the sidewall of the opening, wherein the polysilicon plug is exposed by the opening. The polysilicon plug comprises a notch, and the internal surface of the notch is at the same plane as the internal surface of the amorphous silicon spacer. The HSG layer is disposed on the surface of the amorphous silicon spacer. Furthermore, the conductive layer is disposed on the HSG layer and the capacitor dielectric layer is disposed between the HSG layer and the conductive layer.
According to an embodiment of the present invention, a metal layer may be further disposed between the HSG layer and the capacitor dielectric layer to serve as a bottom electrode of a metal-insulator-metal (MIM) capacitor, wherein the bottom electrode may be comprised of, for example, TiN, Ru, Pt or TaN.
According to an embodiment of the present invention, the dielectric layer comprises an inter-layer dielectric layer and an etching stop layer disposed between the inter-layer dielectric layer and the substrate.
According to an embodiment of the present invention, the polysilicon plug may be a dual damascene structure.
According to an embodiment of the invention, the conductive layer may comprise, for example, TiN, Ru, Pt or TaN.
The invention further provides a DRAM cylindrical capacitor, comprising a substrate, a polysilicon plug, an amorphous silicon cylinder, a HSG layer, a conductive layer and a capacitor dielectric layer. The polysilicon plug is disposed in the substrate, wherein the polysilicon plug comprises a notch on a top surface thereof. The amorphous silicon cylinder is disposed on the polysilicon plug, and the inside surface of the amorphous silicon cylinder is at the same plane of the inside surface of the notch. Furthermore, the HSG layer is disposed on the surface of the amorphous silicon cylinder, the conductive layer is disposed on the HSG layer, and the capacitor dielectric layer is disposed between the HSG layer and the conductive layer.
According to another embodiment of the present invention, a metal layer is further disposed between the HSG layer and the capacitor dielectric layer, wherein the metal layer may be comprised of, for example, TiN, Ru Pt, or TaN.
According to an embodiment of the present invention, an etching stop layer may be further disposed on the substrate.
According to an embodiment of the present invention, the polysilicon plug may be, for example, a dual damascene structure.
According to an embodiment of the invention, the conductive layer may be comprised of, for example, TiN, Ru, Pt or TaN.
It should be noted that the HSG structure is only grown at the upper surface of the cylindrical capacitor, therefore the difficulty of growing a capacitor dielectric layer on the bottom of the capacitor may be avoided. Thus, the yield can be effectively increased, and also the surface area of the capacitor can be increased.
In order to the make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1H are schematic sectional views of the manufacturing process of a DRAM cylindrical capacitor according to an embodiment of the invention.
FIG. 2 is a sectional view of the DRAM cylindrical capacitor according to an embodiment of the invention.
FIG. 3 is a sectional view of the DRAM cylindrical capacitor according to another embodiment of the invention.
FIG. 4 is a sectional view of the DRAM cylindrical capacitor according to yet another embodiment of the invention.



DESCRIPTION OF EMBODIMENTS
FIGS. 1A to 1H are schematic sectional views of the manufacturing process of the DRAM cylindrical capacitor according to one preferred embodiment of the invention.
Referring to FIG. 1A, first a substrate 10 having a polysilicon plug 106 formed thereon is provided, wherein the substrate 10 may be comprised of a silicon wafer 100 with semiconductor devices formed thereon. A source/drain region 102 may be disposed in the silicon wafer 100 and the polysilicon plug 106 is disposed in an inter-layer dielectric layer (ILD) 104 on the silicon wafer 100, wherein the polysilicon plug 106 is connected to the source/drain region 102. The polysilicon plug 106 may be a dual damascene structure.
Next, referring to FIG. 1B, a dielectric layer with an opening is formed over the substrate 10. For example, an etching stop layer 108, another ILD 110 and a hard mask 112 may be sequentially formed over the substrate 10.
Referring to FIG. 1C, the hard mask 112 is patterned (referring to FIG. 1B) to expose a part of the dielectric layer 110. Next, the exposed ILD 110 is anisotropically etched using the patterned hard mask 112a as an etching mask until a portion of the etching stop layer 108 is exposed. Next, the exposed etching stop layer 108 is removed to form an opening 114 exposing the polysilicon plug 106. Thus, the dielectric layer 116 with the opening 114 is formed. Next, an amorphous silicon layer 118 is formed on the substrate 10 covering the dielectric layer 116 and filling the opening 114.
Next, referring to FIG. 1D, the amorphous silicon layer 118 (referring to FIG. 1C) is anisotropically etched to remove a portion of the amorphous silicon layer 118 disposed outside the opening 114 and a portion of amorphous silicon layer 118 the bottom of the opening 114 to form an amorphous Silicon spacer 118a on the sidewall of the opening 114, wherein a portion of the polysilicon plug 106 by the opening 114.
Next, referring to FIG. 1E, a portion of the exposed polysilicon plug 106, for example a thickness d, is partially removed. During the process of removing a portion of the polysilicon plug 106, a portion of the amorphous silicon spacer 118a (referring to FIG. 1D) is also removed and the remaining portion forms the silicon spacer 118b. Therefore, a notch 120 is formed in the top surface of the polysilicon plug 106, wherein the inside surface of the notch 120 is at the same plane as the amorphous silicon spacer 118b. 
Still referring to FIG. 1F, a seeding method is used to grow an HSG layer 122 only on the surface of the amorphous Silicon spacer 118b. 
Next, referring to FIG. 1G, a capacitor dielectric layer 124 is formed on the surface of the HSG layer 122 using, for example, an atomic layer deposition film process. The capacitor dielectric layer 124 is formed on the surface of the HSG layer 122 and also covers the surfaces of the patterned hard mask 112a and the polysilicon plug 106.
Next, referring to FIG. 1H, the patterned hard mask 112a (referring to FIG. 1G) may be selectively removed first, and portions of the capacitor dielectric layer 124 disposed outside the opening 114 are removed, or vice versa. Next, a conductive layer 126 is formed on the capacitor dielectric layer 124 to serve as an upper electrode, wherein the conductive layer 126 may comprise, for example, TiN, Ru, Pt or TaN. Thus, a metal-insulator-silicon (MIS) capacitor comprising the substrate 10, the dielectric layer 116, the amorphous Silicon spacer 118b, the polysilicon plug 106, the HSG layer 122, the conductive layer 126 and the capacitor dielectric layer 124 is formed. The polysilicon plug 106 is disposed in the substrate 10 below the opening 114. The inside surface of the notch 120 disposed on the top surface of the polysilicon plug 106 is at the same plane as the inside surface of the amorphous silicon spacer 118b. 
As described above, the HSG structure is formed only on the top surface of the bottom electrode and the HSG structure is not formed at the inside surface of the bottom electrode, and therefore the possibility of the bottom electrodes undesirably connecting to each other may be effectively avoided. Furthermore, the surface area of the capacitor is increased.
Furthermore, a method of fabricating a MIM capacitor according to another embodiment of the present invention is provided with reference to FIG. 2, wherein identical or similar elements are represented by the same element symbols as in the above embodiment.
Referring to FIG. 2, a metal layer 200 may be formed on the HSG layer 122 to serve as a bottom electrode before the capacitor dielectric layer 124 is formed (as shown in FIG. 1G). The step of forming the metal layer 200 may include, for example, depositing a metal layer on the substrate 10 and removing portions of the metal layer disposed outside the opening 114, wherein the bottom electrode comprises, for example, a conductive material such as TiN, Ru, Pt or TaN. Next, the capacitor dielectric layer 124 is formed, wherein the capacitor dielectric layer 124 comprises, for example, a material with high dielectric constant such as HfO2, Al2O3, Ta2O5 or BaTiO3. Furthermore, the metal layer 200 disposed between the HSG layer 122 and the capacitor dielectric layer 124 can be used as the bottom electrode of the MIM capacitor.
Furthermore, a method of fabricating a DRAM cylindrical capacitor according to another embodiment of the present invention is provided with reference to FIG. 3, wherein identical or similar elements are represented by the same element symbols as in the above embodiment.
Referring to FIG. 3, the dielectric layer 116 may be removed after the portion of the exposed polysilicon plug 106 is removed (as shown in FIG. 1E) but before the HSG layer 122 is formed on the surface of the amorphous silicon spacer 118b (as shown in FIG. 1F). The remaining portion of the amorphous silicon spacer serves an amorphous silicon cylinder 300. Thus, a DRAM cylindrical capacitor is formed comprising the substrate 10, the polysilicon plug 106, the amorphous Silicon cylinder 300, the HSG layer 122, the conductive layer 126 and the capacitor dielectric layer 124. The inside surface of the notch 120 formed on the top surface of the polysilicon plug 106 is at the same plane as the inside surface of the amorphous silicon cylinder 300. Moreover, the HSG layer 122 is disposed on the surface of the amorphous silicon cylinder 300 so that the contact area of the bottom electrode of the capacitor can be significantly increased.
The present invention further provides a structure of a DRAM cylindrical capacitor according to another embodiment as shown in FIG. 4, wherein identical or similar elements are represented by the same element symbols as in FIG. 3.
Referring to FIG. 4, a metal layer 400 may be formed on the surface of the HSG layer 122 to serve as a bottom electrode of the MIM capacitor before the capacitor dielectric layer 124 is formed. The metal layer 400 may be formed by, for example, depositing a metal layer on the substrate 10, removing portions of the metal layer disposed outside the surface of the HSG layer 122 and forming the capacitor dielectric layer 124.
In view of the above, according to the invention, a notch is formed at the top surface of the polysilicon plug, wherein the inside surface of the notch is at the same plane as the inside surface of the amorphous silicon spacer, and then the HSG layer is grown on the surface of the amorphous silicon spacer. Thus, no HSG structure is formed at the inside surface of the bottom electrode of the formed DRAM cylindrical capacitor. Therefore, the problem of yield reduction caused due shorting of the upper and the bottom electrodes may be effectively avoided. Furthermore, it should be noted that the present invention may also be applied to a MIM capacitor.
Though the present invention has been disclosed above by the preferred embodiments, it is not intended to limit the invention. Anybody skilled in the art can make some modifications and variations without departing from the spirit and scope of the invention. Therefore, the protecting range of the invention falls in the appended claims.

## Claims

1. A method for manufacturing a dynamic random access memory (DRAM) cylindrical capacitor, comprising:
providing a substrate having a polysilicon plug formed therein;
forming a dielectric layer having an opening formed therein, wherein the opening exposes the polysilicon plug;
forming an amorphous silicon layer over the substrate to cover the surface of the dielectric layer and fill the opening;
anisotropically etching the amorphous silicon layer to remove portions of the amorphous silicon layer disposed outside the opening and a bottom of the opening in order to form an amorphous silicon spacer on the sidewall of the opening and expose a portion of the polysilicon plug;
partially removing a top portion of the exposed polysilicon plug;
using a seeding method to grow a hemispherical silicon grain (HSG) layer on a surface of the amorphous silicon spacer;
forming a capacitor dielectric layer on a surface of the HSG layer; and
forming a conductive layer on the capacitor dielectric layer.

2. The method for manufacturing a DRAM cylindrical capacitor as claimed in claim 1, further comprising a step of forming a metal layer on the surface of the HSG layer to serve as a bottom electrode before the step of forming the capacitor dielectric layer on the surface of the HSG layer.

3. The method for manufacturing DRAM cylindrical capacitor as claimed in claim 1, further comprising a step of removing the dielectric layer and a remaining portion of the amorphous silicon spacer before the step of growing the HSG layer on the surface of the amorphous silicon spacer.

4. The method for manufacturing DRAM cylindrical capacitor as claimed in claim 3, further comprising a step of forming a metal layer on the surface of the HSG layer to serve as a bottom electrode before the step of forming the capacitor dielectric layer on the surface of the HSG layer.

5. The method for manufacturing DRAM cylindrical capacitor as claimed in claim 1, wherein the step of forming the dielectric layer having the opening therein comprises:
sequentially forming an etching stop layer, an inter-layer dielectric layer (ILD) and a hard mask over the substrate;
patterning the hard mask to expose a portion of the ILD;
anisotropically etching the exposed ILD using the patterned hard mask as an etching mask until the etching stop layer is exposed; and
removing the exposed etching stop layer to form the opening.

6. The method for manufacturing DRAM cylindrical capacitor as claimed in claim 1, wherein the capacitor dielectric layer is formed using an atomic layer deposition process.