US20020090792A1 - Method for forming inner-cylindrical capacitor without top electrode mask - Google Patents

Abstract

A method for forming an inner-cylindrical capacitor without top electrode mask is disclosed. The method includes a step of a trench formed on the substrate. The trench structure with a conductive layer as a first lower electrode. The first poly spacer as second lower electrode of inner-cylindrical capacitor formed on sidewall of the trench, and furthermore a dielectric layer is formed by depositing on sidewall of first poly spacer and a floor of the cylindrical trench. Then, the second poly spacer formed on sidewall of dielectric layer. The poly plug is formed by depositing polysilicon layer and polished by chemical mechanical polishing (CMP) process. Thus, an inner-cylindrical capacitor is generated.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0001]
• The present invention generally relates to a method for forming a dynamic random access memory (DRAM), and more particularly to a method for fabricating an inner-cylindrical capacitor in DRAM.[0002]
• 2. Description of the Prior Art[0003]
• Modern semiconductor for fabricating technique in an ultra large scale integration (ULSI) highly increases the circuit density on a chip. The increase of circuit density causes the downsizing of devices and the increase of device packing density.[0004]
• Although commonly referred to as semiconductor devices, the devices are fabricated from various materials, including conductors (e.g., aluminum, tungsten), non-conductors (e.g., silicon dioxide) and semiconductors (e.g., silicon). Silicon is the most commonly used semiconductor, and is used in either its single crystal or polycrystalline form. Polycrystalline silicon is often referred to the silicon is adjusted by adding impurities.[0005]
• The integrated circuit devices with their various conductive layers, semiconductor layers, insulating layers, contacts and interconnects are formed by fabrication processes, including doping processes, deposition processes, photolithorgraphy processes, etching processes and other processes.[0006]
• Demand of dynamic random access memory (DRAM) has rapidly increased owing to widespread use of integrated circuits. Each cell of DRAM includes transistors and a capacitor, which is used for the purpose of charge storage. As DRAM becomes highly integrated, the area occupied by the capacitor of DRAM storage cell shrinks, thus decreasing the capacitance of the capacitor owing to its smaller electrode surface area. In order to reduce the cell dimension and yet obtain a high capacitance, the cylindrical-shaped capacitor, which includes an inner surface in addition to an outer surface, was disclosed to increase the surface area of the capacitor electrode.[0007]
• DRAM is a device broadly used in electronic industry for data storage due to the characteristic of increased circuit density in an integrated circuit (IC). This stored information or message is determined by the charges stored in an internal capacitor of a memory cell. The access of data is performed by operating the read/write circuit and the peripheral memory in a chip. A single DRAM cell comprises a field effect transistor (FET) and a capacitor as a bit for representing a binary data.[0008]
• The basic DRAM cell is usually comprised of a transfer gate transistor and a connected capacitor. Charges are stored in the capacitor section of DRAM, and are accessed via the transfer gate transistor. The ability to densely pack storage cells, while still maintaining sufficient stored charge, is a function of the type and structure of the capacitor section of DRAM. Two iterations of capacitors are presently being manufactured. A trench capacitor, in which charge is stored vertically in a structure fabricated by etching a deep trench in a substrate, has found use where high DRAM densities are desired. This type of capacitor, although eventually needed for the higher density DRAM, is however costly to fabricate, regarding the trench etching, trench filling and planarization processing. The advantage of trench capacitor is that the device surface is much more plane after the capacitors finished. Moreover, the processes for dielectric materials used therein, such as nitride or oxidate nitride, have been well developed. However, it requires deep trenches to provide sufficient capacitance, which increases the difficulties of etching and trench filling. Trench capacitors take another advantage of the vertical space available in a semiconductor substrate material, thus reducing the overall layout size of a semiconductor device on the substrate surface.[0009]
• The disadvantages often associated with such structures are the complexity and number of the process steps required in fabrication. For example, in order to utilize vertical space, trenches for forming capacitors should be fabricated deeper. To form deeper trenches, we need more than one step for forming trench. Furthermore, as the trench is formed deeper the trench also becomes narrower, resulting in manufacturing difficulties during subsequent processing. Another disadvantage with a deep, narrow trench is that the effective capacitance of the cell is required to below a desirable amount.[0010]
• A second type of capacitor used in DRAM technology is stacked capacitor cell. In this design two conductive layers, such as polycrystalline silicon, are placed over a section of the transfer gate transistor, with a dielectric layer sandwiched between the polycrystalline layers. The stacked capacitor iteration has been used extensively in the industry, with emphasis placed on reducing the cost, while still increasing DRAM chip densities.[0011]
• One ongoing goal of semiconductor design and fabrication is to reduce costs. Cost reduction is essential to ongoing success in the field. One manner of reducing costs is to eliminate or optimize steps in the semiconductor fabrication process such as without top electrode mask for forming inner-cylindrical capacitor. In doing so, it is important to maintain or improve device and process efficiency and effectiveness.[0012]
SUMMARY OF THE INVENTION
• In accordance with the present invention, a method is provided that top electrode mask of inner-cylindrical capacitor can be omitted.[0013]
• It is an object of this invention that substantially can reduce the cost for fabricating inner-cylindrical capacitor.[0014]
• To achieve these objects and advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention that directed toward a method for fabricating a capacitor is proposed. An etch-stop layer and an etch-buffer layer are formed sequentially on the substrate. Then, a first photoresist layer is defined on the etch-buffer layer to form bit line. After the first photoresist layer is removed, a silicon dioxide layer, a first conductive layer, and an insulating layer are formed sequentially on the substrate, wherein the first conductive layer is a first lower electrode of the inner-cylindrical capacitor. Then, a silicon oxide layer, a first conductive layer, and an insulating layer are etched sequentially and then etched stop on etch-buffer layer. Next, etch-buffer layer is etched stop on the etch-stop layer. Therefore, a trench structure is formed on the substrate. Then, first poly spacer, as second lower electrode, formed on the floor and sidewall of the trench. Then, a thin dielectric layer is deposited on the sidewall of first poly spacer. A dielectric layer is consisting of silicon nitride layer and oxide layer. Next, second poly spacer formed on the sidewall of dielectric layer. Then, a polysilicon layer is full filled in the trench structure and excess polysilicon layer is removed by chemical mechanical polishing (CMP). Then, a poly plug as top electrode is formed in the trench.[0015]
BRIEF DESCRIPTION OF THE DRAWINGS
• The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:[0016]
• FIG. 1A is a cross-sectional view of a semiconductor device having a bit structure on substrate and a plug in the substrate;[0017]
• FIG. 1B is a cross-sectional view of a semiconductor device formed on substrate;[0018]
• FIG. 2 shows a cross-sectional view of a semiconductor device having a conductive layer formed on substrate;[0019]
• FIG. 3 shows a cross-sectional view illustrates of the trench structure on the substrate;[0020]
• FIG. 4 shows a cross-sectional view that first poly spacer formed on the sidewall of the trench and a dielectric layer formed in the trench; and[0021]
• FIG. 5 shows a cross-sectional view for an inner-cylindrical capacitor.[0022]
DESCRIPTION OF THE PREFERRED EMBODIMENT
• Some sample embodiments of the invention will now be described in greater detail. Nevertheless, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited except as specified in the accompanying claims.[0023]
• Referring to FIG. 1A and 1B, a[0024]substrate10 with aplug50 is provided. Asilicon nitride layer12 as an etch-stop layer is formed on asemiconductor substrate10 with thickness about 160 angstroms. Asilicon dioxide layer14 is then deposited on etch-stop layer12 to serve as an etch-buffer layer with thickness about 2000 angstroms by using a conventional low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD) method. A first photoresist layer is defined on etch-buffer layer14 to form bit line70 (shown in the FIG. 1A). Thebit line70 is the structure similar to the gate electrode. The first photoresist layer is removed after thebit line70 formed on etch-buffer layer14.
• Referring to FIG. 2, a[0025]silicon dioxide layer16 is deposited on the etch-buffer layer14 by conventional chemical vapor deposition with thickness about 10000 angstroms. Then, apolysilicon layer18 as a first conductive layer is deposited onsilicon dioxide layer16 by conventional chemical vapor deposition method with thickness about 4000 angstroms, wherein anpolysilicon layer18 is first lower electrode for inner-cylindrical capacitor. A tetraethyl orthosilicate layer (TEOS)20 as an insulating layer is deposited cover the surface of the firstconductive layer18 by LPCVD with thickness about 100 angstroms. This is an optional step for this invention.
• Referring to FIG. 3, a second photoresist layer is formed on the insulating[0026]layer20. Next, a pattern is patterned on the insulatinglayer20 using conventional photolithographic techniques. Then, a second photoresist layer is used as a mask. Next, an insulatinglayer20 and firstconductive layer18 are etched subsequently and etched stop on the etch-buffer layer14. Then, etch-buffer layer14 is etched stop onetch stop layer12, thereafter an insulatinglayer20 is removed, thereby atrench24 is formed on thesubstrate10.
• Referring to FIG. 4,[0027]first poly spacer32,34 as second lower electrode of inner-cylindrical capacitor formed on the sidewall of thetrench24 by depositing polysilicon layer over thetrench24 and using anisotropic dry etching to stop etch on the etch-stop layer12. Then,dielectric layer42,44 formed on sidewall offirst poly spacer32,34 by depositing dielectric layer over thetrench24 and using dry etch to stop etch on etch-stop layer12, wherein dielectric layer constructed by silicon oxide/silicon nitride/silicon oxide material and a silicon oxide layer with thickness about 100 angstroms and a silicon nitride layer with thickness about 53 angstroms. In conventional oxide dielectric layer, there are a lot of defects, just like pin hole, by which charge get loose. Generally, the nitride layer which has a dense structure is formed as a barrier layer to prevent the loose of charge.
• Referring to FIG. 5,[0028]second poly spacer52 and54 formed on sidewall ofdielectric layer42 and44 by depositing polysilicon layer and etched back by using anisotropic dry etching process through the etch-stop layer12 extended to theplug50 in thesubstrate10. Then, poly plug60 as top electrode of inner-cylindrical capacitor formed by depositing polysilicon layer into thetrench24 and removing excess the polysilicon layer by means of a conventional planarization process such as chemical mechanical polishing (CMP) process.
• According to the present invention, the top electrode mask for fabricating the inner-cylindrical capacitor in DRAM is omitted. So, the process can be simplified and the cost of fabricating capacitor can be reduced.[0029]
• Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.[0030]

Claims (22)

What is claimed is:

1. A method for forming a capacitor, said method comprising:

providing a substrate;

forming a cylindrical trench in said substrate;

forming first poly spacer on sidewall of said trench;

forming a conformal dielectric layer on sidewall of said first poly spacer;

forming second poly spacer on said wall of said dielectric layer; and

forming a poly plug in said trench;

2. The method according toclaim 1, wherein a material of said first poly spacer is polysilicon.

3. The method according toclaim 1, wherein said dielectric layer comprises a silicon oxide/silicon nitride/silicon oxide layer.

4. The method according toclaim 1, wherein a material of said second poly spacer is polysilicon.

5. The method according toclaim 1, wherein said a poly plug is formed by depositing into said trench and removing excess said polysilicon layer.

6. A method for fabricating inner-cylindrical capacitor in dynamic random access memory, said method comprising:

providing a semiconductor structure having a substrate, a plug in said substrate, an etch-stop layer is formed on said substrate and said plug, an etch-buffer layer is formed on said etch-stop layer, a bit line structure is formed on said etch-buffer layer, a planarized silicon dioxide layer is formed on said etch-buffer layer and said bit line structure, and a first conductive layer formed on said silicon dioxide layer;

forming a cylindrical trench in said first conductive layer, said silicon dioxide layer, said etch-buffer layer over said etch-stop layer;

depositing a first poly spacer on sidewall of said trench;

depositing a conformal dielectric layer on said first poly spacer;

depositing a second poly spacer on sidewall of dielectric layer; and

forming a poly plug in said trench.

7. The method according toclaim 6, wherein a material of said etch-stop layer is silicon nitride.

8. The method according toclaim 6, wherein a material of said etch-buffer layer is silicon dioxide.

9. The method according toclaim 6, wherein a material of said first conductive layer is polysilicon.

10. The method according toclaim 6, wherein a material of said first poly spacer is polysilicon.

11. The method according toclaim 6, wherein a material of said second poly spacer is polysilicon.

12. The method according toclaim 6, wherein a material of said poly plug is polysilicon.

13. The method according toclaim 6, wherein said poly plug is formed by depositing a polysilicon layer into said trench and removing excess said polysilicon layer.

14. A method for fabricating a inner-cylindrical capacitor in dynamic random access memory, said method comprising:

providing a semiconductor structure having a substrate, a plug in said substrate, an etch-stop layer is deposited on said substrate and said plug, an etch-buffer layer is deposited on said etch-stop layer, a bit line structure is formed on said etch-buffer layer, a planarized silicon dioxide layer is formed on said an etch-buffer layer and said bit line structure, an insulating layer is deposited on said silicon dioxide layer, and a first conductive layer formed on said silicon dioxide layer;

forming an inner-cylindrical trench in said insulating layer, said first conductive layer, said silicon dioxide layer, said etch-buffer layer over said etch-stop layer;

depositing first poly spacer on sidewall of said trench;

depositing a dielectric layer over said first poly spacer and a bottom of said trench;

depositing second poly spacer on sidewall of said dielectric layer; and

forming a plug in said trench.

15. The method according toclaim 14, wherein a material of said etch-stop layer is a silicon nitride.

16. The method according toclaim 14, wherein a material of said etch-buffer layer is a silicon dioxide.

17. The method according toclaim 14, wherein a material of said first conductive layer is polysilicon;

18. The method according toclaim 14, wherein a material of said insulating layer is tetraethyl orthosilicate.

19. The method according toclaim 14, wherein said dielectric layer comprises a silicon dioxide/silicon nitride/silicon dioxide layer;

20. The method according toclaim 14, wherein a material of said poly plug is polysilicon.

21. The method according toclaim 14, wherein a material of said poly plug is formed by depositing a polysilicon layer into said trench and removing excess said polysilicon layer.

22. The method according toclaim 14, wherein a material of said excess polysilicon removed is by chemical mechanical polishing.

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