Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-10-31
2004-10-12
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S309000, C257S751000
Reexamination Certificate
active
06803621
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to computer memory devices and, more specifically, to capacitor cell containers formed in such semiconductor memory devices.
2. State of the Art
Computer memory devices, such as DRAM (dynamic random access memory) semiconductor device modules, utilize a series or an array of capacitors to store charge in retaining digital data for subsequent recall. Each capacitor is coupled to a transistor and includes a cell which holds a charge representative of a bit of data (i.e., a “1” or a “0”) depending on the charge of the cell. An array of capacitors, with a plurality of them holding a charge, allows for digital information to be stored in a compact and efficient manner which may be recalled by examining the charge on each capacitor. However, DRAM type memory requires constant refreshing at a rapid rate due to leakage from the capacitors. Thus, one of the inherent inefficiencies of DRAM type semiconductor device memory is the time and power utilized in the continual refreshing of the array of capacitors.
With the rapid advance in computer technology, DRAM semiconductor device memory modules have been designed with a higher density of memory cells. While such density of memory cells has led to expanded capacity in a smaller package, it has also produced new design challenges. For example, regardless of how small or how dense a storage cell array is packaged, each cell must hold a minimum amount of charge. Thus, in a high-density memory cell array, the ability to retain the minimum level of charge in a smaller volume memory needs to be addressed. One method of addressing such an issue has been to increase the effective surface area of the memory cell, and thus the electrode associated with the memory cell.
An example of increasing the surface area of a capacitor memory cell container may be seen in drawing
FIG. 1
, which shows a prior art partially fabricated memory cell within an integrated circuit such as a DRAM semiconductor memory device or chip. A conductive plug
10
located between neighboring word lines
12
, usually comprising polysilicon, forms electrical contact with an active area
14
of a semiconductor substrate
16
. A planarized insulating layer
18
, such as borophosphosilicate glass (BPSG), surrounds the word lines
12
. The conductive plug
10
is formed within an opening through the insulating layer
18
. A structural layer
20
overlies the insulating layer
18
and may also be composed of BPSG or similar material. A container
22
is formed in the structural layer, generally by anisotropically etching the structural layer
20
through a mask. The container
22
is generally a cylindrical cavity formed contiguous with the conductive plug
10
and includes sidewalls
24
which extend to an opening in the structural layer
20
. A layer
26
of hemispherical grained (HSG) polysilicon covers the interior surface of the container
22
. The HSG layer
26
increases the surface area of the cell container
22
due to the hemispherical arrangement and patterning of the silicon. By increasing the surface area of the memory cell container, and thus an associated electrode, capacitance charge may be increased for a generally smaller cell container.
A thin layer of nitride
28
is deposited over the HSG layer
26
as well as the surface of the structural layer
20
. It is noted that the layer of nitride
28
grows much thinner over the surface of the BPSG structural layer
20
than on the HSG layer
26
due to the large nucleation incubation time of silicon nitride on BPSG. The slower growth of cell nitride on the BPSG layer
20
results in various problems. One problem is that the thin layer of nitride
28
on the structural layer
20
fails to effectively block oxygen during processes such as oxidation or followed oxidation (reox). The inefficiency of the thin cell layer of nitride
28
allows oxygen to pass through the structural layer
20
, resulting in the oxidation of the HSG layer
26
. Of course, the amount of oxidation depends on the actual thickness of the layer of nitride
28
above the structural layer
20
. Additionally, the thin layer of nitride
28
allows for current leakage at the edge of the container
22
, thus creating an additional inefficiency with regard to the operation of the capacitor cell structure.
In view of the shortcomings in the art, it would be advantageous to provide a memory cell structure and a method for forming such a structure that assists in preventing oxidation of the cell plate. Further, it would be advantageous to provide a structure which is simple to manufacture and a method which does not significantly interfere with existing manufacturing processes. It would also be advantageous to provide a memory cell structure and method for manufacturing the structure with reduced current leakage at the edge of the cell container, thus improving the overall efficiency of the memory cell.
BRIEF SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, a method of forming a cell container for the capacitor of a memory device, such as a DRAM semiconductor memory device or chip or module, is provided. The method includes forming a structural layer above a conductive plug. A cavity is formed in the structural layer, such as by etching. The cavity includes at least one sidewall, such as a continual sidewall in a cylinder, a bottom surface which is contiguous with the conductive plug, and an opening at the upper surface of the structural layer. A layer of polysilicon is deposited over the bottom and sidewall of the cavity. A dielectric, such as a nitride layer, is formed over the polysilicon layer and at least a portion of the upper surface of the structural layer including the area surrounding the opening of the cavity at the opening thereof. A barrier layer is deposited over at least a portion of the dielectric layer including the area surrounding the opening of the cavity and a portion of the sidewall adjacent the opening. The barrier layer is deposited such that the majority of the sidewall as well as the bottom surface are not covered with the barrier layer. The container may then be subjected to an oxidation process wherein the barrier layer is oxidized and acts as an oxygen barrier for the structural layer.
The structural layer may be formed of BPSG with the polysilicon layer being formed of a hemispherical grained polysilicon to improve the surface area of the cell container. The dielectric layer may be formed of silicon nitride. Aluminum is a suitable material for the barrier layer and may be deposited by sputtering the aluminum on to help keep the aluminum layer from substantially covering the interior cell surface. Other metallic materials are also suitable, such as tantalum, zirconium, hafnium, tungsten, titanium or aluminum nitride. The formation of the metallic layer provides an oxygen barrier for the cell structure during oxidation processes as well as leakage protection for the cell at the opening edge.
In accordance with another aspect of the invention, a memory cell container is provided. The memory cell includes a cavity formed in a structural layer such as BPSG. The cavity is formed to have a bottom, which is contiguous with a conductive plug, and a sidewall extending from the bottom of the cavity to an opening at the upper surface of the structural layer. A polysilicon layer, such as HSG polysilicon, is deposited in the cavity on the bottom and along the sidewall. A nitride layer, such as silicon nitride, is formed over the polysilicon layer and at least a portion of the upper surface of the structural layer. A barrier layer, such as aluminum, covers at least a portion of the nitride above the structural layer and a small portion of the nitride along the sidewall of the cavity adjacent the opening. The barrier layer forms an oxygen barrier for the cell container and also protects against edge leakage during operation. As with the method, various materials may be utilized to form the cell container, including various mater
Yang Sam
Zheng Lingyi A.
Prenty Mark V.
TraskBritt
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